@農자료창고

번역하기 참 까다로운 문장이었다. 용어도 낯설고, 문장도 어려운 편이었기 때문.

핵심만 요약하자면, 제초제를 쓰지 않고 밭에서 풀을 관리하는 최고의 방법은 '부지런함'이 첫째요, '풀씨를 받지 않음'이 둘째요, '풀이 자라는 초기에 잡음'이 셋째라는 말이다.

작물을 심기 직전에 풀을 한 번 싹 잡아주고 심으면 작물이 자라는 초기에 자라는 놈들은 그다지 풀들과 경쟁관계에 놓이지 않기에 상관이 없다. 그 풀들을 4~6주쯤 되었을 때 다시 한 번 싹 잡아주면 나중에 수확할 때까지 그다지 걱정하지 않아도 된다는 말이렸다.

또한 풀씨를 자꾸 받는 건 다음 농사에 지장을 불러오는 일이니 피해야 할 일이다. 풀들이 아직 잘잘하여 씨를 맺을 생각을 하고 있지 않을 때 부지런히 갈거나 베어서 씨를 받지 말라고 충고한다.

그리고 너무 풀이 만연하여 잡기 힘들면, 덮개작물을 활용하는 등의 방법으로 풀을 어느 정도 억제해 놓고서 농사를 짓는 것이 좋다고 권한다.

그 내용은 엉터리 번역이지만 아래의 글을 보면 그래도 좀 이해가 되실 듯하다.

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들어가며

유기적 풀 관리의 “통제” 부분은 노동력, 연료, 기계에 대한 비용과 토양에 대한 해로움을 최소로 하면서 현재 또는 미래의 생산을 위협하는 풀을 제거하는 것을 목표로 한다. 농장의 모든 풀을 제거하려고 하는 것은 손실로 이어질 것이며, 건강한 토양을 만들려고 하는 노력도 허사가 될 수 있다. 따라서 농부는 지속적으로 고려해야 한다. 지금 이 작물에 있는 풀을 죽여야 하는가? 농사짓는 동안 풀을 통제하기 위해 중요한 순간은 언제인가? 

한 가지 기준이 있을 수 있다: “풀은 언제나 작물의 성장과 수확량을 억제시킨다.” 텃밭 농부들은 큰 풀을 뽑거나 잘라서 공짜로 덮개나 퇴비 재료를 얻어서 어느 정도 성공을 거두며 이 지침을 활용한다. 그러나 농장 규모에서는 이렇게 하면 작물을 구출하는 데 필요한 노력이 수익을 떨어뜨리거나 토양의 비옥함을 감소시키기에 너무 늦다, 유기농 농부에게 '풀을 통제하기 위한 중요한 기간'은 풀의 악영향에서 현재와 미래의 작물을 가장 효과적으로 보호할 수 있는 시점이다. 중요한 시점은 다음과 같다. 

• 작물을 심을 때
• 풀의 싹이 막 나올 때
• 작물의 최소 풀이 없는 기간 동안
• 여러해살이 풀의 양이 최소에 이르렀을 때
• 풀이 씨앗이나 번식체를 맺기 전

깨끗한 모판에서 시작하라

작물을 심기 전이나 함께 나오는 풀들은 나중에 나오는 풀보다 작물의 수확량에 더 큰 영향을 미친다. 깨끗하고 풀이 없는 농지에 심는 일은 필수적이다. 작물을 심기 며칠 전에 겉보기에 깨끗한 모판을 준비해도 아직 눈에 띄지 않는 풀의 싹이 1200평당 수백만 개가 있을 수 있다(그림 1). 가능하면 땅을 준비하는 마지막 단계 직후에 곧바로 심어라.

그림 1. 이 모판은 사진을 찍기 며칠 전에 준비한 상태이다(왼쪽). 겉으로는 깨끗해 보이지만, 가볍게 표면을 긁은 다음 다시 보라!(오른쪽). 심기 전 곧바로 매우 얕이갈이하여 이 모판에서 새롭게 발아한 풀의 대부분을 잡을 수 있다.   사진: Mark Schonbeck, Virginia Association for Biological Farming.

대부분의 작물은 이렇게 초기에 풀의 싹을 제거하면 작물이 다 자랄 때까지 모판을 깨끗하게 사용할 수 있다. 더 큰 모판의 채소는 유리하게 시작하기 위해 로터리를 칠 수 있다. 당근처럼 늦게 발아하는 작물을 이기는 풀의 싹은 불태워서 제거할 수 있다. 일부 농민들은 유리판으로 두둑을 덮고 이 작업을 한다. 작물이 유리 밑에서 처음 나올 때, 밭은 불태워 김을 맨다. 작물의 나머지는 하루 이틀 뒤 깨끗한 밭에서 나온다. 

풀이 작을 때 처리하라

풀이 작아야 더 쉽게 잡을 수 있다. 대규모 풀의 제거가 일어나곤 하는 농사철 초기, 많은 농민들이 밭에서 풀이 눈에 띌 때까지 기다리기보다 풀이 "흰 선"으로 보이는 초기 단계 또는 막 나타났을 때 얕이갈이를 한다(풀이 작물과 경쟁을 시작하기 오래 전). 얕이갈이는 다음과 같은 이유 때문에 한다. 

• 토양 구조와 토양 생물의 손상을 최소화
• 햇빛에 자극되어 발아하는 풀들이 추가되는 걸 최소화
• 더 적은 연료와 노동력이 필요함
• 새로 나타나고 있는 수백만의 풀을 잡을 수 있음

이 방법은 특히 작물이 뿌리내리고 성장하는 초기 단계에 유용할 수 있다(그림 2). 풀이 더 자라기 전에 갈이를 한다. 일부 풀은 이 단계를 지나서 갈이 이후 다시 뿌리를 내리는 놀라운 능력을 개발했을 수도 있다. 풀이 5~8cm 정도 자라면 더 격렬하게 갈이해야 해서 더 많은 연료를 소비하고, 토양 구조를 해치며, 추가로 풀 씨앗이 발아되도록 자극하게 된다. 

그림 2. 이 바구니 제초기(basket weeder)는 어린 모종의 줄 사이에 있는 작은 풀을 제거하기 위해 3cm 정도 깊이에서 작동한다.   사진: Mark Schonbeck, Virginia Association for Biological Farming.

적기 갈이를 위한 이러한 "사전적" 방식의 한 가지 단점일 수 있는 건 작물이 뿌리내리기 전까지 작은 풀들을 제거하기 위해서 여러 번 작업할 수 있다는 것이다. 갈이의 깊이보다 빈도를 최소화하기 위해 노력하는 대안적인 전략은 특정 상황에 적합할 수 있다(상자를 참조).

많은 좋은 도구와 방법이 작물의 여러 성장 단계와 줄 간격 등에 맞춰 개발되어 왔다. 

최소로 풀이 없는 기간 동안 작물을 깨끗하게 유지하라

풀을 초기에 제거한 뒤, 작물이 최소로 풀이 없는 기간을 지날 때까지는 계속해서 나중에 나타나는 풀을 관찰하고 통제한다. 이 기간에 활발한 채소는 보통 작물 재배철의 첫 1/3 또는 4~6주에 해당하는데, 토마토와 호박, 오이, 강낭콩, 옮겨심은 십자화과 같은 작물이 그렇고, 아마 가지와 고추는 약간 더 길다. 양파나 당근처럼 덜 활발한 작물은 적어도 생애주기의 적어도 처음 절반 동안은 풀 없는 조건이 필요할 수 있다. 아마 8주나 그 이상이다.

어떻게 이 기간 동안 충분히 깨끗하도록 하는가? 작물들도 최소로 풀이 없는 기간 동안 풀에 대한 고유한 내성에 차이가 있다. 파슬리처럼 천천히 자라고, 풀에 민감한 채소, 직파하는 양파나 당근은 풀이 갈이 전 잎이 2개인 단계에 이르도록 놔두면 힘들어 할 수 있다. 따라서 "초기에 자주 갈이"하여, 작물이 잘 자리잡을 때까지 풀이 흰 선인 단계에 잡아야 한다. 콩과 단옥수수 또는 감자와 같은 활발한 작물은 풀의 잎이 2장 나오는 단계 또는 심지어 좀 더 커서 갈이를 해도 충분하다. 

작물이 아직 작은데, 풀이 작물에 가깝게 크면 가장 심각하게 경쟁한다. 따라서 작물의 줄 안만이 아니라 줄 사이의 풀도 효과적으로 제거해야 한다. 풀이 작고 작물이 충분히 클 때에만 작물의 줄 안에서 기계로 작업이 가능하다. 최소로 풀이 없는 기간 이후에 작물이 자라면서 줄 안에 자라는 풀에 그늘을 드리우기 시작하는데, 줄 사이의 풀은 여전히 방해받지 않고 자라 위협이 될 수 있다. 이 시점에서 일부 채소는 사이갈이를 하며 북을 주어 줄 안에 자라는 작은 풀들을 흙에 묻어 잡을 수 있다. 이 작업은 감자, 옥수수, 토마토, 브로콜리와 기타 북을 줄 수 있는 키가 큰 채소를 대상으로 할 수 있지만, 상추와 시금치 기타 땅에 가까이 먹는 부분이 자라는 채소에는 알맞지 않다.

그 양이 적을 때 여러해살이 풀을 쳐라

뿌리줄기, 뿌리, 기는 줄기, 덩이줄기나 알뿌리로 복제하는 개밀, 향부자, 캐나다 엉겅퀴 같은 외래종과 방황성 여러해살이는 가장 관리하기 어려운 풀이다. 이러한 구조를 잘게 자를 정도로 깊이 초기 경운을 하면 각 조각은 곧 새로운 식물을 다시 생성함으로써 풀이 효과적으로 퍼질 것이다. 그러나 이러한 식물들은 방해받지 않는 땅속의 구조에서 자라는 식물보다는 더 약하다. 분할된 뒤 처음 3~4주 동안, 뿌리나 뿌리줄기의 조각은 다시 재생하고자 자신의 땅속의 양을 늘린다. 그 각각은 여러 잎을 내면서 광합성을 통해 그 양을 다시 구축한다. 그 이후 곧바로 그들은 새로운 뿌리줄기, 알뿌리, 덩이줄기 또는 기타 식물의 번식을 시작할 수 있다.

추가 경운 또는 그저 윗부분만 제거하여, 풀의 잎이 3~4장에 이를 때마다 매우 효과적으로 외래종 여러해살이 풀을 훨씬 약화시킬 수 있다(그림 3). 농부는 심하게 퍼진 풀을 잡으려면 3~4주 간격으로 이렇게 몇 번 해야 할 수 있다. 경운 이후 곧바로 빽빽한 비율로 메밀이나 기타 덮개작물을 심어 풀이 만연하는 걸 막고, 더 적은 갈이로 더 빨리 작업을 마칠 수 있다.

그림 3. 이 두둑은 브로콜리를 심기 바로 전 지역화하여 만연한 캐나다 엉겅퀴의 뿌리를 조각내면서 갈이를 했다. 잘린 뿌리와 조각은 현재 그 양을 재구축하기 충분할 만한 크기로 새로 재생되고 있다. 이 외래종 여러해살이 풀을 약화시키는 과정으로 즉각적인 갈이나 괭이질을 계속해야 한다.   사진: Mark Schonbeck, Virginia Association for Biological Farming.

방황성 여러해살이 풀이 채소 작물에 나타나면, 이 풀의 잎이 3~4장이 될 때마다 풀의 윗부분을 자르는 갈이를 한다. 딸깍이나 칼로 토양의 표면 바로 아래 부분을 자른다. 

풀이 퍼지는 걸 막아라

작물이 일단 최소로 풀이 없는 기간을 지나면, 풀 통제는 너무 엄격히 할 필요가 없다. 그러나 풀이 씨앗을 맺는 걸 최대로 방지하는 것이 유기농업에서는 매우 중요하다. 4년 연속으로 모든 풀의 씨앗이 맺히는 걸 막으면 실질적으로 봄과 초여름에 나타나는 풀의 개체밀도를 줄일 수 있다. 농장 규모에서 이를 달성하기란 어려울 수 있지만, 풀씨가 맺히는 걸 최소화하려는 노력이 오랫동안 풀의 밀도를 낮추는 보상으로 돌아온다. 

나중에 나타나는 풀들은 이러한 풀들이 꽃을 피우기 전에 수확하는 빨리 성숙하는 채소로 쉽게 관리할 수 있다. 수확한 다음 풀이 씨를 맺기 전에 간단히 갈거나 신속히 벤다. 연달아 몇몇 재배기간이 짧은 채소를 심는 것도 풀이 전파되는 걸 제한하는 하나의 방법이고, 토양(풀의 종자은행)에 풀씨의 수를 줄일 수 있다.

재배기간이 긴 채소에서는, 이러한 늦게 자라는 풀들이 씨를 맺는 걸 막기 위해 줄 사이의 풀을 베거나 갈이 또는 손으로 뽑거나 자르는 것과 같은 추가 조치가 필요하다. 수확이 완료되자마자, 베거나 갈이로 풀이 더 퍼지는 걸 근절시킨다. 작물의 잎과 줄기에 의해 그늘이 지게 된 풀들은 상대적으로 적은 씨앗을 형성하는 반면, 대량의 긴급 "탈출"이 토양의 풀씨 종자은행에 많이 저축되어 앞으로 농사지을 때 주요한 풀 문제를 일으킬 수도 있다. 그건 각각에서 수천 개의 씨앗이 빠져나가기 전에 큰 풀들을 "밭에 걸어다니면서" 뽑아내는 게 좋다(그림 4). 뿌리째 뽑히거나 잘린 풀은 종종 덜 익은 씨앗이 숙성될 수 있으니, 수분이 일어나기 전에 밭에서 그 풀을 제거해야 함을 기억하다. 

그림 4. 이 명아주는 충분히 늦게 나오고 멀어서 여름 호박을 수확할 때 크기나 품질에 어떤 영향도 주지 못한다. 그러나 이들이 밭의 풀 종자은행에 대규모로 "저금"을 하여 몇 배로 받기 전에 뽑거나 잘라낸다.   사진: Mark Schonbeck, Virginia Association for Biological Farming.

외래종이나 방황성 여러해살이에 주의를 기울여, 그들이 적극적으로 "씨앗"을 형성하기 전에 발목 높이일 때 처리하라. 그것이 그들의 전파를 방지하기에 실용적이지 않은 경우라도 수확 이후 곧바로 밭 전체를 활발히 갈이하거나 작물의 줄 사이에 있는 풀을 베는 것이 뿌리줄기와 덩이줄기가 형성되는 걸 제한할 것이다. 

풀이 통제를 벗어나는 것 같을 때

만약 풀이 특정 밭을 "접수"하는 것 같다면, 그건 보통 일정 기간 동안 풀 관리에 대한 관심이 부족했다는 걸 뜻한다. 특정 기간 동안 풀 통제를 위한 하나 이상의 중요한 시기를 빠뜨리면 풀이 작물보다 우위를 차지하는 결과가 나올 수 있다. 풀이 퍼지게 하면 풀의 개체밀도가 더 높아져 다음 농사철에 통제하기 더 어려워진다는 걸 뜻한다. 부지런함과 적시 갈이에도 풀이 "접수"하려고 한다면, 풀을 막기 위한 관리법에 더 많은 관심이 필요하다. 이는 풀의 생애주기를 방해하도록 작물의 돌려짓기를 조정하고, 덮개작물의 활용도를 높이며, 작물이 풀의 성장을 이기도록 토양의 영양 관리를 개선하거나 심지어 몇 년 동안 여러해살이 토끼풀이 밭에 번지도록 하는 방법을 포함한다.   

외래종 영양번식 여러해살이 풀은 관리하기 특히 어렵고, 부지런히 통합적 풀 관리 프로그램을 활용해도 걷잡을 수 없을 때가 있다. 너무 지나치게 무성해지면, 땅속의 양이 최소에 이를 때까지(3~4장의 잎이 나왔을 때) 반복적으로 풀을 쳐라. 2~3번의 경운 이후 곧바로 메밀과 동부 또는 호밀+완두 같이 빨리 자라고, 매우 경쟁적인 덮개작물을 심어 여러해살이 풀의 재생을 훨씬 지연시킬 수 있을 뿐만 아니라, 반복된 경운을 통해 손실된 토양 유기물과 토질을 되살리는 데에도 도움이 된다.

http://www.extension.org/pages/18882/knock-weeds-out-at-critical-times

소농에게 닭은 참으로 유용한 동물이다.

소나 돼지처럼 먹을 걸 많이 들이지 않아도 되고, 그만큼 노동력이 훨씬 덜 들면서 소중한 단백질 공급원인 달걀과 고기를 제공한다.

또한 닭은 왕성한 식욕으로 풀과 해충을 먹어치우는가 하면, 질소질이 풍부한 똥거름을 제공하기도 한다.

농부에게 닭은 하나도 버릴 것이 없는 어여쁜 존재이다.

최근 미국에서는 '뒤뜰 양계(Backyard Chicken)'라는 형태의 양계법이 확산되고 있다. 그 사람들이 닭과 함께 텃밭 농사를 잘 짓는 법까지 고민하며 실천하고 있는가 보다.

어릴 때 시골에 가면 닭들이 자유로이 돌아다니며 먹이를 먹는 모습을 보곤 했다. 어미를 좇아다니는 귀여운 병아리들 하며, 발로 흙을 팍팍 걷어찰 때의 당당한 위용이란 지금 생각해도 놀랍다. 지렁이나 개구리를 던져주면 부리나케 달려와서 어찌나 잘 먹던지...

우리도 이런 방법을 실천하는 사람들이 많아지면 좋겠다. 그들의 경험이 쌓이고 쌓여 다른 사람들에게 널리 퍼지면 참 좋겠다.

---------

닭을 키우는 거의 모든 텃밭농부들이 하는 무서운 이야기가 있다. 날카로운 부리와 강인한 발로 텃밭을 망쳐 놓을 수 있다. 그러나 조금만 신경 쓰면 훨씬 쉽게 달과 함께 농사를 지을 수 있다. 

시애틀 지역의 경관 설계자이자 닭을 방사하는 텃밭(Free-Range Chicken Gardens)의 저자 Jessi Bloom 씨는 행복한 공존을 위해 텃밭에 준비할 것들에 관해 이야기한다. 

첫 번째 고려사항은 공간에 알맞은 적절한 닭의 마릿수이다. "사람들은 공간에 비해 너무 많은 닭을 키웁니다”라고 Bloom 씨는 말한다. 그녀는 작은 도시의 마당이면 3~5마리 이상은 키우지 말고, 좀 더 큰 교외의 부지라도 5~8마리 이상은 사육하지 말기를 권한다. 

Bloom 씨는 “300평의 부지에 30마리의 닭이 있으면 풀어놓지 마세요”라며, “닭들이 다 망쳐 놓을 겁니다” 한다.

필라델피아에서는 불법인 닭 사육을 하는 Linette 씨는 지난해 뒷마당에 6마리의 닭을 들여왔다. 그녀의 부지는 480평으로 충분히 커서, 닭들이 Linette 씨가 보호하길 바라는 식물은 건드리지 않고도 다닐 만큼 공간이 많다. 그럼에도 Linette 씨는 채소 텃밭에는 울타리를 쳐서 재배하는 동안에는 닭들이 들어가지 못하도록 한다. 

울타리가 작물을 보호하기에 알맞지 않으면 간단한 방법으로 수정할 수 있다.

1. 철조망은 친구이다

작은 식물에 둘러친 철조망의 색깔이 식물이 먹을 만큼 자랄 때까지 닭들이 덤비지 못하게 한다.

철조망 구조를 만들기 위해 지주 몇 개를 사용한다. Bloom 씨는 자신의 텃밭이 봄에 환상적이라고 한다. 식물이 어려서 민감할 때 닭들을 쫓으려고 여러 철조망과 장치들이 즐비하기 때문이라고. Linette 씨는 발 높이를 넘지 않는 낮은 철조망 울타리를 사용하여 딸기에 닭들이 덤비지 못하게 한다.

이 정도만 되어도 닭들이 활동할 공간이 넓고 먹을 것이 많기 때문에 울타리를 넘어 작물을 건드리지 않는다. 

2. 무엇이 더 필요한가? 도금 철망도 좋다

철조망보다 더 튼튼한, 이 철망은 새로 심은 씨앗을 보호하는 데 쓸 수도 있다.

사각형으로 자르고, 네 귀퉁이를 또 조금씩 자른다. 그걸 땅에 세울 수 있게 구부리고, 돌멩이 같은 걸로 눌러 놓는다. 사진이 새로 심은 양파의 두둑을 보호하고 있는 모습이다. 닭들이 양파는 잘 안 먹지만, 흙을 파헤치다 새로 심은 모종을 해칠 수 있다.

3. 벽돌과 돌을 활용하라

적극적인 닭은 작은 돌멩이는 날려버릴 수 있지만, 벽돌이나 큰 돌을 식물 주변에 둘러놓으면 그걸 막을 수 있다.

이 방법은 특히 새로 심은 화분에 좋다. 

4. 풀을 활용하라

그렇다, 풀도 작물을 보호하는 데 도움이 될 수 있다.

풀을 뽑아 흙이 노출되면 자석에 끌리듯 닭들이 몰려온다. 닭들은 지렁이와 벌레 등을 잡아먹은 다음, 흙에 눕고 흙목욕을 즐긴다. 마늘 같은 튼튼한 작물도 여기에는 못 견디는데, 두둑에 풀을 덮어주는 간단한 방법으로 닭들이 작물을 해치지 않도록 할 수 있다. 

5. 전략적인 파종

Bloom 씨는 닭들이 건드릴 수 없는 좁은 틈에 꽃씨를 심으라고 제안한다. 아래 철조망 사이에 심은 금련화처럼 말이다.

닭이 파헤치거나 쪼을 수 없어 식물이 싹을 틔울 수 있다. 싹이 나면 닭들이 맛을 보려고 몇 번 건드리지만, 마당의 다른 부분처럼 쉽게 건드리지 못한다. 

6. 닭을 위한 식물을 마련하라

덤불과 떨기나무는 닭들이 천적을 피하는 대피처가 될 수 있다.

Linette 씨의 마당에는 닭들이 돌아다니다 위협을 당할 경우 도망갈 덤불이 늘 마련되어 있다. 무더운 날에는 덤불의 그늘에서 오랫동안 휴식을 취하기도 한다. 닭들이 즐길 수 있게 겨울에도 푸르른 나무를 심으면 좋다. 또한 Bloom 씨는 마당에 닭에게 먹일 다양한 딸기를 재배하여 닭을 키우는 데 들어가는 사료값을 줄인다. 그녀는 특정 식물을 추천하지는 않는데, 그게 침입종이 될 수도 있기 때문이다. 그러나 딱총나무 같은 것은 먹이도 되고 대피처도 되기에 좋다고 한다. 블루베리도 닭의 좋은 먹이라고 한다.

닭과 함께 농사짓는 것은 끊임없이 진화하고 있는 중이다. 어떤 체계도 완벽하지 않지만, 몇몇 저렴한 전략이 농사를 더 쉽게 할 수 있다. 

http://modernfarmer.com/2013/06/how-to-chicken-proof-your-garden/

Superweeds.pdf

나는 풀이 싫다. 아무리 뽑아도 풀은 계속 난다. 제초제 없이 풀을 없애는 최선의 방법은 무엇인가?  

http://modernfarmer.com/2013/06/dear-modern-farmer-the-know-your-hoes-edition/

글리포세이트 계통 제초제에 저항성을 가진 풀들이 널리 퍼졌을 뿐만 아니라, 그 문제가 여러 종으로 번지고 있다. 

미국 농민은 농경지의 약 75억 평에 글리포세이트 저항성 풀이 만연해 있다고 답했는데, 이는 2010년의 2배 수준이다. 

Stratus는 지난 3년에 걸쳐 31개 주에서 수많은 농민들에게 저항성에 관해 물었다. 그 추세는 엄청나다:

• 조사한 미국 농민의 약 절반(49%)이 2012년 자신의 농장에 글리포세이트 저항성 풀이 있다고 답하여, 이는 2011년 34%에서 증가한 수치이다. 
• 저항성은 여전히 남부에서 최악이다. 예를 들어, 조지아주 농민의 92%가 글리포세이트 저항성 풀이 있다고 답했다.
• 그러나 중남부와 중서부의 주가 따라잡고 있다. 2011~2012년 네브라스카, 아이오와, 인디애나주에서 저항성 풀의 면적이 거의 2배가 되었다.
• 해마다 더 빠르게 퍼지고 있다: 전체 저항성 풀의 면적이 2011년 25%에서 2012년 51%로 증가했다. 
• 그리고 그 문제는 더욱 복잡해지고 있다. 더욱더 많은 농장에서 적어도 2가지 종 이상의 저항성 풀이 생겼다. 2010년 그런 농장은 12%뿐이었지만, 2년도 지나지 않아 27%로 늘어났다. 
• 망초는 명아주 다음으로 글리포세이트 저항성이 있다고 보고되는 풀이다. 연구에서는 또 다른 6가지 종을 추적했다. 

저항성의 폭발은 확실히 우려를 고조시켰지만, 미국의 농민들은 항상 농업의 과제에 대응해 왔다. Stratus는 미국 농민들이 어떻게 그 문제를 처리할지에 대해 연구를 진행하고 있다. 
Stratus는 캐나다의 저항성에 대해서도 추적하고 있다. 
더 많은 정보는 다음을 참조하라.

U.S. Resistance Tracking Study 

Canada Resistance Tracking Study  

Resistance Management Study

Abstract

Mulches contribute to weed management in organic crops by reducing weed seed germination, blocking weed growth, and favoring the crop by conserving soil moisture and sometimes by moderating soil temperature. Opaque synthetic mulches like black plastic provide an effective barrier to most weeds and are amenable to mechanized application, but they must be removed at the end of the season. Organic mulches like straw suppress annual weed seedlings, conserve moisture, and add organic matter as they break down, but they are more labor-intensive to apply. This article examines uses, advantages, and limitations of different mulching systems for weed control in organic vegetable production. Two companion articles provide additional information onorganic mulches and synthetic mulches.

Introduction

Mulching can reduce weed competition against vegetable crops, and save fuel and labor costs for weed control. Covering the soil surface with a suitable mulch can:

• Reduce weed seed germination.
• Shade and physically hinder emerging weeds.
• Enhance crop growth and competitiveness by conserving soil moisture and sometimes by modifying soil temperature.

Synthetic mulches like black polyethylene film (the most widely used plastic mulch) or landscape fabric are laid on a prepared seedbed just before transplanting or seeding a vegetable crop through holes or slits cut into the mulch. In-row drip irrigation lines under the mulch provide water and liquid fertilizers to the crop. Mechanization, with equipment such as tractor-drawn bed shapers, mulch layers, and planters, allows the farmer to mulch and plant a multi-acre field within a single day (Fig. 1). Black plastic, other opaque materials, and infrared-transmitting (IRT) mulch effectively block weed emergence, and promote soil warming and early crop growth. Weeds emerging through planting holes may require manual removal, and alleys between mulched beds generally need cultivation or other weed control measures.

The National Organic Program (NOP) final rule (United States Department of Agriculture [USDA], 2000) requires removal of plastic mulches from the field at the end of the growing season, and tractor-drawn mulch lifters are now commercially available to facilitate this chore. Despite the costs of capital equipment, the plastic itself, application, and removal, many organic vegetable farmers consider black plastic their most economical weed management option (John Britton, Appalachian Harvest, 35-member marketing co-op in Abingdon, VA, pers. comm.; Ellen Polishuk, Potomac Vegetable Farms, Purcellville, VA, pers. comm.).

Figure 1. Black polyethylene film mulch gives these tomato transplants a head start by blocking weeds, retaining moisture, and warming the soil. Figure credit: Becky Crouse, Marketing Manager, Potomac Vegetable Farms in Purcellville, VA.

Organic mulches such as hay (Fig. 2a), straw (Fig. 2b), leaves, and chipped brush, are usually applied when the vegetable crop is well established and the soil has warmed to near-optimum temperatures. They are most effective on weeds emerging from seed, and least effective on aggressive perennial weeds emerging from rootstocks, rhizomes, or tubers. Organic mulch applied immediately after a final cultivation often suppresses later-emerging weeds until the crop has passed through its minimum weed-free period. Organic mulches generally lower soil temperatures and conserve soil moisture by slowing evaporation while allowing rainfall to penetrate. Normally, organic mulch is left in the field after harvest and, as it breaks down, it helps build soil organic matter.

Figure 2. Organic mulches. (a) About 3 inches of hay mulch have suppressed emergence from a large weed seed bank of galinsoga (Galinsoga spp.) and other annual broadleaf weeds in broccoli, onion, and garlic in the Appalachian region of Virginia. (b) Pepper thrives in a straw mulch in the Tidewater region of Virginia. At both sites, a few grasses and perennial weeds are beginning to break through, but the vegetables have benefited from soil moisture conservation as well as weed suppression by the mulch. Figure credit: Mark Schonbeck, Virginia Association for Biological Farming.

Manual application of hay and other organic mulches is labor intensive, and is practical only on a small scale. A few growers use bale choppers to mechanize application of hay or straw from small rectangular bales.

Many vegetable farmers apply straw or other organic mulches in alleys between plastic-mulched beds, either at planting or after cultivation (Fig. 3). In addition to suppressing alley weeds, this system adds organic matter, helps conserve soil moisture and soil quality, and prevents excessive soil heating during summer, thereby realizing many of the benefits of both organic and synthetic mulches. The organic mulch can also improve fruit quality in pumpkin and other vine crops by preventing fruit-soil contact in alleys.

Figure 3. Alleys between plastic mulched beds are covered with a thick layer of hay to suppress alley weeds in this pepper crop at Wheatland Vegetable Farms in Purcelle, VA. The organic mulch adds organic matter, conserves soil moisture, and prevents soil erosion in alleys. When hot summer weather arrives, the hay is pulled over the black film to prevent excessive soil heating, as shown here. Figure credit: Mark Schonbeck, Virginia Association for Biological Farming.

Mulches and Weed Seed Germination and Emergence

Light promotes seed germination in many agricultural weeds (Egley, 1996), including common lambsquarters (Chenopodium album), hairy galinsoga (Galinsoga ciliata), common chickweed (Stellaria media), common ragweed (Ambrosia artemesiifolia), common purslane (Portulaca oleracea), some pigweeds (Amaranthus spp.), black nightshade (Solanum nigrum), and annual bluegrass (Poa annua) (Mohler and DiTommaso, unpublished). Any opaque mulch, such as black plastic or several inches of hay, straw, or leaves, blocks the light stimulus, thereby reducing seed germination in these weeds after mulch application.

Seeds of an even wider range of common weeds respond to wide daily soil temperature fluctuations, including some that do not respond to light, such as horsenettle (Solanum carolinense), common cocklebur (Xanthium strumarium), and foxtails (Setaria spp.). Many summer annuals, including pigweeds, galinsoga, and purslane, germinate in response to high soil temperatures (85–100°F). Organic mulches and white or reflective plastic films lower soil temperature and dampen daily fluctuations, thereby deterring weed seed germination.

Even with light and temperature stimuli blocked, a percentage of the weed seed population will germinate. However, the mulch intercepts light essential for photosynthesis and physically hinders seedling emergence. Dicot (broadleaf) seedlings are fairly delicate and easily suppressed by this mulch effect. Hay, straw, or cover crop residues at 3–5 tons per acre (2–4 inches, loosely packed) can prevent emergence of small-seeded broadleaf weed seedlings for at least several weeks, whereas a heavier mulch (7–10 tons per acre) may be required to block larger seeded species like common cocklebur or velvetleaf (Abutilon theophrasti), and some grasses, whose shoots are protected by a pointed sheath (coleoptile). Perennial weed shoots emerging from rootstocks, tubers, rhizomes, or bulbs can penetrate most organic mulches, and a few weeds, such as nutsedges, can puncture plastic film.

Dark colored synthetic mulches and IRT mulches increase soil temperatures and daily temperature fluctuations, which may stimulate weed germination. Since these mulches also block seedling growth, the net result is to draw down the weed seed bank.

Mulch Effects on Crop and Weed Growth

In addition to reducing weed seed germination and emergence, mulch can improve the growth and competitiveness of established crops by conserving soil moisture and modifying soil temperatures (Schonbeck and Evanylo, 1998; Swaider et al., 1992) (Fig. 4). Soil warming under black or IRT plastic can enhance early season growth and maturation in heat-loving crops, while the soil cooling effect of organic and reflective film mulches benefits cool-weather vegetables like potato, and can help most crops thrive during hot summer weather.

Some organic mulches, such as hay, provide slow-release nutrients, or reduce certain pests by harboring their natural enemies. Reflective or colored synthetic mulches have been found to enhance the yields of certain crops by repelling pests or modifying the light environment around the crop (Orzolek and Lamont, 2000).

It is important to note that, once a weed manages to emerge through the mulch, or emerges through a planting hole in plastic film, it enjoys the same soil moisture conservation and other mulch benefits as does the established crop. Conversely, any crop seedlings emerging beneath a mulch will be suppressed. Thus, it is common practice to spread straw or other organic mulches only after the crop is well established, and immediately after cultivation or manual removal of existing weeds.

Figure 4. Tomato grown in a non-irrigated field in the Tidewater region of Virginia thrived in hay mulch (right), and grew poorly without mulch (left). In addition to reducing weed emergence, the organic mulch conserved soil moisture and moderated soil temperatures. Figure credit: Mark Schonbeck, Virginia Association for Biological Farming.

Mulching Limitations and Pitfalls

In some circumstances, mulching can aggravate weed problems. Organic mulches, especially hay from off-farm sources, may carry seeds of new weed species into the field (Fig. 5). An organic mulch that is too thin to suppress weeds (e.g., 1–2 tons per acre, or an inch or so of material) may allow weed emergence, then enhance weed growth by conserving soil moisture (Mohler and Teasdale, 1993). Legume residues have also been reported to release enough nitrate-N to trigger germination of nitrate-responsive weeds such as redroot pigweed (Amaranthus retroflexus) (Teasdale and Mohler, 2000). Aggressive perennial weeds can emerge through a heavy (6 inch) organic mulch, thrive, and steal moisture and nutrients intended for the crop. Weeds growing through mulch are more difficult to control mechanically, and may require special high-residue cultivators.

Figure 5. Wild buckwheat (Polygonum convolvulus), a new weed in this garden, arrived in the mulch hay. Figure credit: Mark Schonbeck, Virginia Association for Biological Farming.

Untimely mulching, or using the wrong mulch for a particular crop, can slow its growth and leave it more vulnerable to weed competition. For example, fresh (“bright”) grain straw can lower soil temperatures by as much as 10°F. Spreading straw or other soil-cooling mulches around newly-transplanted tomato or melon can set the crop back several weeks and give the weeds a head start.

Mulch materials with a high ratio of carbon to nitrogen (C:N ratio) have the potential to slow crop growth by immobilizing soil N. This is most likely to occur with finely divided materials (e.g., sawdust) or materials rich in soluble carbohydrates that can leach into the soil (e.g., sorghum–sudan greenchop). Coarse, dry materials like grain straw or chipped brush rarely tie up soil N unless they are incorporated into the soil.

Applying organic mulch around small, succulent lettuce, brassica, or other vegetable seedlings can result in defoliation by slugs or insects, leading to poor stands or delayed establishment. However, these organisms have been observed to attack weed seedlings as well, and can reduce weed populations without seriously impacting well-established crops (Mohler, 1996; Mohler and Teasdale, 1993). In addition, many organic mulch materials, especially freshly cut immature cereal grains, hay, or forage crops, may release substances that inhibit germination and seedling growth in both weeds and crops (allelopathy). Mulches applied when crops are well established will minimize these risks to crop production, and can provide mid- and late-season weed suppression.

Generally, organic mulches enhance moisture infiltration and reduce runoff. However, in situations where moisture is limiting, applying a thick, organic mulch on dry soil can prevent light rainfalls from reaching the soil and crop roots. In this situation, farmers can irrigate the soil thoroughly (to near field capacity), or install in-row drip irrigation lines prior to mulching.

Non-porous plastic mulches can hinder infiltration of rainfall or overhead irrigation into the crop root zone. Some water runs into planting holes, but much of it runs off the mulch into alleys and may not reach crop roots. Thus, almost all growers who use plastic install drip irrigation under the mulch to deliver water to the crop.

Other disadvantages of synthetic mulches include the labor of end-of-season removal, the petroleum embodied in the mulch, generation of non-biodegradable waste, and the fact that synthetic mulches do not add organic matter or nutrients to the soil. Compost or other solid organic fertilizers and amendments must be applied to crop rows prior to laying the mulch, and sidedressing the crop is limited to liquid fertilizers via the drip line and foliar feeding.

Even black plastic mulch will not give 100% weed control. Weeds, especially fast-growing viny species like morning glories (Ipomoea spp.) can emerge through crop planting holes, and require manual removal. A few aggressive perennial weeds like nutsedges (Cyperus spp.) can pierce synthetic mulches (Webster, 2005), compete with the crop, and complicate mulch removal.

Integrating Mulch with Other Weed Management Practices

Mulching cannot alone provide sufficient weed control, and works most effectively in conjunction with other practices. For example, market gardeners often spread hay or straw after cultivating one or more times during crop establishment (Fig. 6). Because organic mulches rarely block 100% of weed emergence, they give best results when used in conjunction with good crop rotation and measures to prevent or limit weed propagation. Similarly, measures to reduce populations of nutsedge, morning glory, and other aggressive weeds may be needed before synthetic mulches can be used successfully.

Figure 6. Weeds were successfully managed in carrot in this Floyd, VA garden through a combination of cultivation and mulching. Sown at the end of June, 2009, hoed twice during establishment, then mulched in early August (a), the crop remained mostly weed-free and closed canopy by early September (b). Figure credit: Mark Schonbeck, Virginia Association for Biological Farming.

References Cited

• Egley, G. H. 1996. Stimulation of weed seed germination in soil. Reviews of Weed Science 2: 67–89.
• Mohler, C. L. 1996. Ecological bases for the cultural control of annual weeds. Journal of Production Agriculture 9: 468–474.
• Mohler, C. L., and A. DiTommaso. Unpublished. Manage weeds on your farm: A guide to ecological strategies; version 5.1 (Cornell University, Dec. 4, 2008).
• Mohler, C. L., and J. R. Teasdale. 1993. Response of weed emergence to rate of Vicia villosa Roth and Secale cereale L. residue. Weed Research 33: 487–499. (Available online at: http://dx.doi.org/10.1111/j.1365-3180.1993.tb01965.x) (verified 20 Dec 2011).
• Orzolek, M. D., and W. J. Lamont, Jr. 2000. Summary and recommendations for the use of mulch color in vegetable production. (Available online at:http://extension.psu.edu/plasticulture/technologies/plastic-mulches/summary-and-recommendations-for-the-use-of-mulch-color-in-vegetable-production) (verified 20 Dec 2011).
• Schonbeck, M. W., and G. E. Evalylo. 1998. Effects of mulches on soil properties and tomato production. I. Soil temperature, soil moisture, and marketable yield. Journal of Sustainable Agriculture 13: 55–81. (Available online at:http://dx.doi.org/10.1300/J064v13n01_06) (verified 20 Dec 2011).
• Swaider, J. M., G. W. Ware, and J. P. McCollum. 1992. Producing Vegetable Crops, 4th ed. Interstate Publishers, Inc., Danville, IL. 626 pp.
• Teasdale, J. R., and C. L. Mohler. 2000. The quantitative relationship between weed emergence and the physical properties of mulches. Weed Science 48: 385–392. (Available online at: http://dx.doi.org/10.1614/0043-1745(2000)048%5B0385:TQRBWE%5D2.0.CO;2) (verified 20 Dec 2011).
• United States Department of Agriculture. 2000. National organic program: Final rule. Codified at 7 C.F.R., part 205. (Available online at:http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?c=ecfr&rgn=div5&view=text&node=7:3.1.1.9.32&idno=7) (verified 18 March 2010).
• Webster, T. M. 2005. Patch expansion of purple nutsedge (Cyperus rotundus) and yellow nutsedge (Cyperus esculentus) with and without polyethylene mulch. Weed Science 53: 839–845. (Available online at: http://dx.doi.org/10.1614/WS-05-045R.1) (verified 20 Dec 2011).

Introduction

Weed prevention begins at the planning stage of any cropping system. Plan the crop rotation and cropping system to keep the soil fully occupied by desired living vegetation, or at least covered by organic residues, as much of the year as possible.

An idle soil is the weed devil’s playground! For example, growing continuous corn each summer with winter fallow leaves the entire field available for weeds from harvest in early fall until crop emergence late the following spring. Between-row spaces remain open for weed growth until crop canopy closure—which may take two months or more for corn. This is why continuous corn is economically feasible only for conventional producers who use synthetic herbicides—and many of them now strive to save soil, money, and chemicals by planting a winter rye cover crop after corn harvest.

Any plant or other organism requires a suitable habitat or niche in order to grow and reproduce. A niche is a site within which certain conditions exist, allowing the organism to thrive and complete its life cycle. For most weeds of vegetables and other annual cropping systems, any space or time in which the soil has been recently disturbed or is open and uncovered by other vegetation constitutes a suitable niche. Thus, a key step in ecological weed management is to reduce the number and size of these weed niches in the cropping system.

Most organic vegetable farms grow a diversity of crops throughout the season, and the nonuse of herbicides opens options for crop rotation, multicropping, and cover cropping to limit niches for weeds. However, open niches typically occur during early stages of crop growth (Fig. 1). Those vegetable crops that do not form a solid canopy or root mass pose the greatest challenge, in that they do not fully occupy the niche and are thus most likely to become weedy.

Figure 1. Morning glories and other weeds are just beginning to emerge in the wide expanses of bare soil between these rows of young winter squash. Figure credit: Mark Schonbeck, Virginia Association for Biological Farming.

A few basic tips for minimizing weed niches include:

• Design tight crop rotations, including production and cover crops that keep fields covered by vegetation as much as possible throughout the calendar year. In regions with cold winters, provide winter cover in the form of dormant hardy cover crops, winter-killed high-biomass covers, or other mulch or crop residues.
• For each field, bed, or section, schedule crop planting to take place promptly after harvesting or terminating the previous crop.
• Schedule a cover crop whenever a field or bed is expected to come out of production for longer than 30 days during the growing season, or for the remainder of the fall and winter (Fig. 2).
• Choose planting patterns—row spacing and within-row spacing—that promote early canopy closure (foliage covers the ground so you can’t see soil surface when viewed from above), without compromising crop yield by crowding.
• When practical, plan to mulch bare soil between crop rows or beds (open niches in space). While mulch does not close off the weed niche as thoroughly as a closed canopy of living crops, it hinders most annual weeds, and conserves moisture and nutrients for the crop.

Figure 2. In the left side of this field, a cover crop of winter rye–hairy vetch was planted promptly after harvest of summer vegetables. Photographed at the beginning of December on a farm on Cape Cod, MA, a thick mat of cover crop has largely closed the niche for winter weeds. on the right, a delay in cover cropping has allowed a mat of common chickweed to grow. Figure credit: Mark Schonbeck, Virginia Association for Biological Farming.

Schedule bare soil periods for limited times only, and only with specific purposes. These could include a period of cultivated fallow to draw down weed seed banks, to weaken invasive perennial weeds, or to germinate and remove weeds in a stale seedbed and allow soil warming before planting a vegetable. Another strategic fallow technique is to mow promptly after vegetable harvest to stop weed seed formation, then delay tillage for a few weeks to give the farm's cleanup crew of ground beetles, crickets, field mice, and other weed seed predators a chance to consume a substantial percentage of any weed seeds formed and shed prior to harvest. In each of these examples, the weed niche has been deliberately opened in a way that facilitates the reduction of weed populations.

Advanced and Experimental Techniques for Closing Off Weed Niches

Innovative growers and researchers continue to explore and develop new ways to reduce niches for weeds. Whereas these methods have not performed consistently enough to be recommended for widespread application, they can give excellent results when used skillfully in certain circumstances. Some of these techniques include:

• Intercropping or companion planting
• Interseeding or overseeding cover crops into established vegetable crops
• No-till cover crop management prior to vegetable planting
• Living mulches—low-growing ground covers between crop rows or beds
• Self-seeding winter annual cover crops

Intercropping

Intercropping is the practice of growing two or more cash crops within a single bed or in alternating rows across the field, to optimize crop use of resources and to minimize space and other resources available to weeds. Vegetable crops grown together should differ in maturity date, plant architecture, rooting depth and structure, and nutrient demands in ways that reduce competition among the crops and increase total competition against weeds. Crop combinations should be chosen that have neutral or positive biochemical interactions with one another—that is, no adverse allelopathic effects—and complementary needs for light, moisture, and nutrients. This practice of companion planting is widely used in ancient traditional food gardening systems, as well as some intensively managed market gardens today.

Examples include: lettuce between rows of tomatoes, in which the lettuce shades out early-emerging weeds, and is harvested before it competes with the tomatoes (Fig. 3); spinach between Brussels sprouts (similar relationship); or quick-growing greens (heavy feeders for N, tolerant of partial shade) between widely spaced trellised rows of tall snow or snap peas, which fix their own N. The Native American “three sisters” system combines corn, runner beans, and squash, whose complementary architecture utilizes space and resources effectively, and usually yields more food per unit area than any one of the crops grown alone. The corn provides support for the beans, the beans fix nitrogen, and the squash vines rapidly cover ground between corn hills or rows and suppress weeds.

Figure 3. Charlie Maloney of Dayspring Farm in Cologne, VA (Tidewater region) intercrops lettuce and bok choy with his high-tunnel tomatoes, thus producing two crops while virtually eliminating niches for weeds in his production beds. The greens are ready to harvest just as the tomatoes enter their rapid growth phase and begin to occupy the whole bed. Figure credit: Mark Schonbeck, Virginia Association for Biological Farming.

Another form of intercropping alternates widely spaced rows of large vegetables like tomatoes or winter squash with swaths of cover crop such as buckwheat. The latter is allowed to grow and suppress weeds for several weeks, then cut before it begins to compete with the vegetables, and left on the soil surface as a mulch that retards later-emerging weeds.

Interseeding or Overseeding

Interseeding or overseeding of cover crops into a standing cash crop can eliminate the empty niche following harvest. Red, white, crimson, and subterranean clovers; Italian ryegrass; winter rye; and oats have sufficient shade- and traffic-tolerance to become established under the cash crop, then grow rapidly after it is harvested and cleared. Red clover is especially shade-tolerant with a “light compensation point” near 6% of full sun, so that its seedlings can become established even under a winter squash or pumpkin canopy. Combining a clover with a grass may fill the postharvest niche more thoroughly than either alone.

Some vegetable growers, especially those living in colder climates with short growing seasons, broadcast cover crops into established vegetables just before a final shallow cultivation to remove existing weeds and incorporate the cover crop seed. Essentially, this strategy utilizes the time after the vegetable crop’s minimum weed-free period to begin growing a cover crop in lieu of late-emerging weeds. Success depends on sufficient moisture and seed–soil contact to get the cover crop established.

Veteran vegetable grower and author Eliot Coleman has refined this approach, using a multirow push-seeder to drill cover crops between vegetable rows immediately after the final cultivation. Drilling can give better seed–soil contact, uniformity and stand establishment than broadcasting. Coleman (1995) developed an eight-year rotation for central Vermont (hardiness zone 4) that includes eight different vegetables, seven of them overseeded with various clovers and other cover crops (Fig. 4).

Figure 4. Eliot Coleman, author of The New Organic Grower, uses a five-row push seeder to plant cover crops between rows of vegetables when the latter are at midgrowth. After vegetables are harvested and cleared away, the young clover cover crop rapidly covers the ground, effectively closing the niche between the vegetable and subsequent cover crop, while fixing nitrogen. Figure credits: Mark Schonbeck, Virginia Association for Biological Farming.

Grubinger (2004) has documented other successful cover crop overseeding practices used by organic farmers. Hank Bissell of Lewis Creek Farm in Starksboro, VT interseeds rye manually into fall brassicas to obtain winter and spring cover after the vegetables are finished. In early July, Will Stevens of Golden Russet Farm in Shoreham, VT seeds hairy vetch into winter squash. The vetch becomes established under the squash, covers the ground when frost kills squash foliage, and grows until the following May, thereby shutting out weeds while fixing a lot of nitrogen.

No-till Cover Crop Management

No-till cover crop management entails mowing or rolling a mature cover crop to create an in situmulch, into which vegetable starts or large seeds can be planted. This eliminates the bare-soil period between a cover crop and the subsequent vegetable, as well as tillage-related stimuli to weed seed germination. Under favorable conditions, the mulch from a high-biomass cover crop can delay the onset of weed growth for four or more weeks after vegetable planting. However, results in terms of weed control and vegetable yield have been inconsistent. Additional research is needed to refine this technique and define circumstances in which it is most likely to succeed.

Living Mulch

Living mulch consists of one or more low-growing ground cover species—for example, low-growing legumes such as white Dutch clover; dwarf perennial ryegrass; and creeping red fescue—maintained between crop rows or beds by periodic mowing. The goal is to replace tall, competitive, hard-to-manage weeds with low-growing perennial vegetation that suppresses weeds and protects the soil, while having minimal impact on crop yield. This approach works well for woody perennial crops like blueberries, grapes, and orchard fruits. However, it has been found difficult to keep living mulches from reducing vegetable yields by competing for moisture or nutrients. Living mulch has been used successfully in alleys between plastic-mulched beds of either annual vegetables or perennial crops.

The living mulch and some of its variants remain subjects of experimentation by scientists and farmers. A dying mulch consists of a winter annual grain, such as rye, planted in early spring to suppress or supplant between-row or between-bed weeds in spring planted vegetables. As summer heat builds, the winter annual living mulch declines and dies back while the vegetables enter their rapid growth and maturation phases. Another form of dying mulch is a non-winter-hardy cover crop, such as oats or buckwheat, sown in mid to late summer ahead of fall garlic planting. When the cover crop frost-kills, it becomes mulch through which the garlic emerges at the end of winter. In Pennsylvania, organic vegetable farmers Anne and Eric Nordell plant garlic into standing oats + field peas in October, which later winter-kill to provide at least some of the mulch required to suppress spring weeds in the garlic.

Self-seeding Winter Annual Cover Crops

Certain varieties of winter annual cover crops like subterranean clover, crimson clover, bigflower vetch, and Italian ryegrass can be grown as self-seeding cover crops. The cover crop is allowed to set seed and die down naturally in late spring, then followed by warm-season vegetable crops. The seeds germinate in late summer under the vegetable, thus regenerating the cover crop for the following winter without the need for postharvest tillage and seedbed preparation. The cover crop seed must be sufficiently summer-dormant that it does not emerge too early and compete with the vegetable, yet must establish sufficient stands to outcompete fall weeds. Farmers Jean Mills and Carol Eichelberger use crimson clover and annual ryegrass as self-seeding cover crops for certain vegetables on their farm in Coker, Alabama (Fig. 5).

Figure 5. The crimson clover and Italian ryegrass growing beneath these fall broccoli emerged from seed shed by an earlier cover crop the preceding spring. Hot summer weather kept the seeds dormant until the onset of autumn, at which time the vegetable was sufficiently established so that the emerging ryegrss and clover did not compete significantly. The photo was taken November, 2005 at Jean Mills and Carol Eichelberger's Tuscaloosa CSA in Coker, AL. Figure credit: Mark Schonbeck, Virginia Association for Biological Farming.

Minimizing Weed Niches in Small and Larger Scale Vegetable Production

Farmers and gardeners have developed many site-specific strategies for closing off weed niches in annual vegetable cropping systems. The details depend on climate, soil conditions, weed flora, crops grown, available equipment, and scale of operation. Growers who have limited land area tend to use more labor-intensive approaches aimed at maximum year round production of desired crop plants, and can afford to do some hand weeding during crop production. Farmers working larger acreages seek labor-efficient means to reduce weed pressure prior to planting the vegetable crop, thus minimizing weed control labor during crop production.

Over the past 40 years, Alan Chadwick and John Jeavons pioneered and developed the BioIntensive Minifarming method for sustainable food production in communities with limited land, machinery, and financial resources. Biointensive minifarming aims to make maximal use of every square foot of land to produce either food or biomass (grass–legume cover crops) to use for mulch or making compost. This system is characterized by very tight crop rotations with 60% of the time in cover crops, close plant spacings, companion planting, and multiple cropping (Jeavons, 2006). While labor intensive, this approach is highly productive and leaves little space for weeds to invade or compete. The few weeds that do emerge are pulled manually before they set seed, and composted.

Eric and Anne Nordell, who manage a six-acre vegetable farm in Pennsylvania primarily with draft horses, have developed an approach to weed management that they call bioextensive. Their strategy is to "weed the soil, not the crop", and their crop rotations include only one market crop every two years (Nordell and Nordell, 2006). The rest of the rotation is devoted to two high-biomass, weed-excluding cover crops, separated by a brief (4–6 week) cultivated fallow during the nonproduction season to draw down weed seed populations. Timing of fallow, cultivation implements (all horse-drawn), and methods are adjusted according to the existing weed flora—very shallow for small-seeded annuals; deeper for quack grass, dandelion, and other perennials. In the production year, the final cover crop is shallow-incorporated (minimizing tillage depth to reduce weed seed germination) a few weeks before vegetable planting. The Nordells find that this system greatly reduces weed control labor during vegetable production.

Another approach used on farms with sufficient land is to follow several years of intensive annual cropping with one to three full years under a perennial sod cover crop, such as red clover–timothy–orchardgrass. The perennial covers are planted, sometimes with a nurse crop of oats or other cereal grain, either after a vegetable harvest, or as an overseed into a standing vegetable crop. In addition to rebuilding the soil, the perennial cover effectively closes the niche for annual weeds-of-cultivation like lambsquarters and pigweeds, so that they cannot reproduce, and their weed seed bank declines through seed predation and decay. View the followng video clips for some ingenious and effective uses of perennial cover crops to build fertility and reduce weeds in organic vegetable production:

References and Citations

• Coleman, E. 1995. The new organic grower: A master's manual of tools and techniques for the home and market gardener. 2nd ed. Chelsea Green Publishing, White River Junction, VT.
• Grubinger, V. 2004. Farmers and their innovative cover cropping techniques [VHS tape/DVD]. University of Vermont Extension, Burlington, VT.
• Jeavons, J. 2006. How to grow more vegetables and fruits, nuts, berries, grains and other crops than you ever thought possible on less land than you can imagine. 7th edition. Ten Speed Press, Berkley, CA.
• Nordell, E., and A. Nordell. 2006. Weed the soil, not the crop: A whole-farm approach to the weed-free market garden. Small Farmer's Journal 30 (3 - summer): 53–58.
• Schonbeck, M., and R. Morse. 2007. Reduced tillage and cover cropping systems for organic vegetable production. Virginia Association for Biological Farming information sheet No. 9-07. (Available online at: http://www.vabf.org/docman/information-sheets/reduced-tillage-and-cover-cropping-systems-for-organic-vegetable-production/view) (verified 23 March 2010).

이렇게 재미나고 좋은 농사법이 있습니다.

그런데도 농약에 의존하여 땅을 망가뜨리고, 생태계를 어지럽히겠습니까?

Abstract

Organic mulches can suppress annual weeds and offer other important benefits, such as organic matter, nutrients, moisture conservation, soil protection, and moderation of soil temperature. Drawbacks include costs and labor of application, limited efficacy on perennial weeds, delayed soil warming, and the potential to carry weed seeds and harbor pests.

Hay, straw, and fresh-cut forage or cover crops are among the most versatile and widely-used organic mulches. They can suppress weed germination and emergence when applied at reasonable rates, are fairly easy to apply, reduce evaporative losses of soil moisture while allowing rainfall to reach the soil, and provide other benefits. Caution is needed to avoid bringing in weed seeds or herbicide residues with hay from off-farm sources. Tree leaves, chipped brush, and other forest-based mulches are often beneficial to small fruit and other perennial crops, but may not be an economical option for weed control at a multi-acre scale. This article explores in greater depth the properties, uses, advantages, and disadvantages of a variety of organic mulch materials.

Introduction

Organic mulch materials include grain straw, fresh or old hay, fresh-cut forage or cover crops, chipped brush, wood shavings, tree leaves, cotton gin waste, rice or buckwheat hulls, and other crop residues. Hay and straw are among the most widely used organic mulches in organic horticulture. Cover crops can be grown to maturity (flowering), mechanically killed, and left on the soil surface to provide an in-situ organic mulch for no-till planting. Leaf mold (decomposed tree leaves), compost, and aged manure have also been used as organic mulches, although their crumbly texture may not provide as effective a barrier to weed seedlings as other materials.

Organic mulches suppress weeds in several ways. First, they block seed germination stimuli by intercepting light, reducing soil temperature, and greatly dampening day–night temperature fluctuations. As a result, fewer weed seeds germinate under the mulch than in uncovered soil. Second, the mulch physically hinders emergence of those weeds that do germinate. If the mulch is thick enough to prevent light from reaching the trapped seedlings, they eventually die. Third, some mulch materials, such as grain straw and fresh-cut forages like sorghum-sudangrass, release natural substances that inhibit weed seedling growth for several weeks after application, a process known as allelopathy. Finally, organic mulch can enhance crop growth and competitiveness against weeds by conserving soil moisture and moderating soil temperature.

Straw and other organic mulches effectively block emergence of most weeds germinating from seed, although grasses and large-seeded broadleaf weeds may require a greater thickness of material than small-seeded broadleaf weeds, which have more delicate seedlings. Perennial weeds arising from rootstocks, rhizomes, tubers, or other vegetative propagules can penetrate most organic mulches.

Weeds that have already emerged at the time of mulch application should be cultivated or hoed out before spreading mulch; simply laying the organic materials over established weeds is less effective. once the weeds break through the mulch, they will enjoy the same mulching benefits as the crop, and will grow vigorously.

Usually, some weeds will eventually emerge through an organic mulch. Fast-growing, canopy-forming crop like sweet potato, squash, or snap bean often shade-out these late emerging weeds. In slower-growing, less competitive vegetables like onion and carrot, manual weeding or application of additional mulch may be required to maintain satisfactory weed control.

Hay

Hay is often used to mulch horticultural crops in regions such as southern Appalachia, where the predominant farming systems include hay production, and old hay is more affordable than straw and other materials. Hay has some drawbacks and must be chosen and used with care. However, it is fairly easy to apply in small scale plantings, and is usually beneficial to soil quality and crop production (Fig. 1). A hay mulch of about 3–4 inch thickness can:

• Reduce emergence of weed seedlings, especially small–seeded broadleaf annuals.
• Provide habitat for beneficial organisms, including ground beetles and other weed seed consumers.
• Allow air and rain to reach the soil.
• Moderate soil temperature during hot weather.
• Conserve soil moisture.
• Prevent soil crusting and erosion.
• Keep pumpkins, melons, and other fruiting crops out of direct contact with soil, and therefore cleaner.
• Add significant amounts of organic matter and slow-release nutrients, especially potassium (K).

Figure 1. (a) Garlic mulched with hay immediately after planting in October; photographed in April. (b) Tomato mulched with hay after the crop became established, several weeks before the photo was taken. The mulch delayed weed emergence and provided favorable conditions for crop growth. Photo credit: Mark Schonbeck, Virginia Association for Biological Farming.

Hay also has some significant drawbacks, in that it:

• Does not suppress most perennial weeds.
• May contain weed seeds (Fig. 2) or herbicide residues (see Sidebar).
• Can harbor slugs, squash bugs, voles, and other pests.
• Can keep the soil too cool or wet, slowing crop growth or maturation.
• Can accentuate frost damage by keeping the soil's radiant heat from reaching crop foliage.
• Can build up excessive soil K levels when used year after year.

Not all hay is alike. Grass hay is lower in nitrogen (N) and phosphorus (P), higher in K, and more persistent and weed-suppressive than legume hay. Because of its high cargon-to-nitrogen (C:N) ratio, grass hay has sometimes been reported to tie up soil N. However, this is most likely to occur when the hay is incorporated into the soil, not when it is applied to the surface as a mulch. A grass–legume mix (such as timothy–alfalfa, fescue–red clover, or rye–hairy vetch) yields a more balanced mulch that provides slow release nutrients to soil life and crops, and persists long enough to provide several weeks of weed suppression.

Fresh hay is more pleasant to spread but more likely to contain large numbers of viable weed seeds than old, spoiled hay. Second or third cuttings of hay are especially likely to have weed seeds (Mohler and DiTommaso, unpublished). Leaving hay bales or rolls in the rain for a year or so reduces weed seed viability, but moldy hay can be nasty and hazardous to handle, and does not provide as clean or long-lasting a mulch. A better solution is to grow and harvest mulch hay on farm, taking care to cut the mulch crop before viable seeds are formed. Mulch hay can be derived from perennial forages or annual cover crops (rye, sorghum-sudangrass, etc.). Note that repeated hay harvests from a given field can deplete soil nutrients, notably P, K, and calcium (Ca). Crop rotations that alternate annual or perennial mulch crops with vegetables that receive the mulch can promote better nutrient balance by minimizing the nutrient depletion of hay harvest while avoiding the potential K excesses from repeated mulch application.

Applying hay manually is most feasible at a small scale, for example, a half acre of a high value crop. A few farmers have used bale choppers to mechanize application of hay or straw in small rectangular bales. Large rolls (round bales) are commonly unrolled between rows of widely spaced crops like tomato, a job which usually requires a tractor to place the ~1,000 lb roll at the beginning of the crop row, and two people to unroll it.

A number of farmers have streamlined on-farm harvest and application of mulch by using a flail chopper and forage wagon for harvest, and then pitchforking the fresh-cut forage off the wagon as it is pulled slowly along crop rows (Kittredge, 2008–09a). Other producers, including David Stern of Rose Valley Farm in upstate New York, grow alternate rows of vegetable and cover crop (e.g., potato and sorghum-sudangrass), and periodically mow the cover crop, blowing the clippings into the vegetable row as mulch (Schonbeck, 2007). This approach saves the labor and costs of curing, baling, and storing hay. However, fresh grass or legume "green chop" has been reported to promote certain soil-borne pathogens for a short period after application (Mohler and DiTommaso, unpublished); thus, fresh-cut forage mulches should be tested on a small area for each crop before field-wide application.

Some tips for optimal use of hay mulch for weed control:

• Grow and use on-farm hay if practical.
• Check sources of off-farm hay for weed seeds and herbicide residues before purchasing.
• Apply mulch when crops are well established, and soil temperature and moisture are optimum for the crops being grown (exception: fall planted garlic is mulched immediately after planting).
• Hoe or cultivate at the beginning of a warm sunny day, wait 12–36 hours to let uprooted weeds die, then spread mulch (applies to all organic mulches).
• Use enough hay to suppress most weed seedlings, about 3–4 inches or 5–10 tons per acre.
• Monitor soil nutrient levels, especially K.
• Rotate mulched vegetables with non-mulched crops or hay production.

Straw

Straw, defined here as the stalks and other residues left after harvest of a mature grain, is similar to hay in texture, potential for soil protection and moisture conservation, weed suppression, and application methods. Straw differs from hay in that it:

• Has higher carbon to nitrogen (C:N ratio).
• Provides a cleaner, more persistent mulch that is slower to decompose, and more effective in keeping the fruit of pumpkin and other vine crops clean.
• May carry seeds of the grain crop itself, but is less likely to carry other weed seeds.
• Has somewhat lower K levels and slower K release.
• Is lighter colored and more reflective, hence it may cool soil more than hay.

Because straw is so much less likely to introduce serious new weed problems than hay, organic horticultural farmers located in or near grain-producing regions where straw is available and affordable often prefer straw over hay. The high C:N ratio of straw precludes much release of N from mulch to the current year's crop, but usually does not lead to tie-up of soil N, as long as the mulch lies on top of the soil and is not tilled in.

The dramatic soil cooling under straw can delay crop growth (Fig. 3); however it can be beneficial for cool weather crops like potato, in which tuber growth is inhibited by soil temperatures above 70°F (Fig. 4a); and for other crops during hot summer weather (Fig. 4b). For example, tomato shows optimal nutrient uptake and production at root zone temperatures of 70–85°F, and becomes stressed at higher temperatures (Abdul-Baki and Teasdale, 1994, Tindall et al., 1990, Tindall et al., 1991); thus, it often performs better in organic than in plastic mulches during the heat of summer. Bright, reflective straw can intensify heating of crop foliage under a row cover, resulting in crop damage (Kittredge, 2008–09a), and may also increase damage from frosts.

Figure 3. The light colored grain straw was applied too early in the season. The mulch has suppressed weeds, but also seriously delayed soil warming and tomato growth (compare to plastic mulched tomato in upper left). Photo credit: Mark Schonbeck, Virginia Association for Biological Farming.

Figure 4. (a) Potato tuber yields are often enhanced by the cooler soil conditions under a straw mulch. (b) The straw was applied after the soil had warmed to optimal temperatures for eggplant, and is now helping the crop thrive during intense summer heat. A few weeds have emerged at this point, but are unlikely to affect yield in the vigorous, established eggplant crop. Photo credit: Mark Schonbeck, Virginia Association for Biological Farming.

Rye, wheat, and other grain crops cut for mulch at an earlier stage of maturity (e.g., head emergence or pollen shed) are richer in nutrients and less likely to immobilize soil N than straw left by grain harvest. Rye, triticale, and other winter grains cut at the milk stage (before the seeds become viable) yields excellent straw for mulch, and minimize the risk of volunteer cereal grains becoming a weed (Fig. 5). Cereal grain cover crops rolled down at the milk stage are particularly popular for no-till pumpkin production, as they help keep the fruit clean, reduce soilborne diseases, and promote even color development (Ron Morse, Virginia Tech, pers. comm.).

Figure 5. Self-seeding of cereal grain occasionally causes a weed problem in straw mulch. In order to avoid this problem, some farmers grow their own grain straw for mulch, and harvest the mulch crop before seeds become viable. Photo credit: Mark Schonbeck, Virginia Association for Biological Farming.

Tree Leaves

Hardwood leaves that fall naturally in autumn are sometimes used as mulch in vegetable production (Fig. 6a). They are rich in calcium (Ca) and micronutrients, contain small to moderate amounts of N, P, and K, and decompose gradually to form leaf mold, a humus-like material that is valued by horticulturists. Millions of suburban residents rake up autumn leaves for disposal, and a growing number of farmers and other entrepreneurs accept leaves for mulch or for making compost. Leaves are often used for berries and some other perennials that tolerate or prefer some acidity. Pine needles (pine straw) are lower in nutrients, more persistent, and more acidic than hardwood leaves, and can be especially useful for blueberries, which require a low pH (Fig. 6b). Tree leaves are much less likely than hay to carry the seeds of agricultural weeds; however, they have been observed to carry tree seeds (especially maple or ash), which germinate into vigorous seedlings that readily emerge through the mulch.

Figure 6. (a) onion mulched with tree leaves gathered the preceding autumn at Potomac Vegetable Farms in Vienna, VA, near Washington, DC. (b) New blueberry planting in Floyd, VA mulched with pine needles (foreground) and grain straw (background). Photo credit: Mark Schonbeck, Virginia Association for Biological Farming.

Some disadvantages of tree leaves as a mulch include:

• A tendency to mat down when wet, creating soggy or airless soil conditions.
• A tendency to blow away in the wind when dry, or to blow onto and smother young crop seedlings.
• Labor intensive application, not feasible at a larger scale.
• Presence of trash (cans, glass, plastic, etc.) in municipal leaves or yard waste.

The soil benefits of tree leaves can also be realized by including them in compost piles, or making leaf mold (leaves aged for 1–2 years until crumbly), which is an excellent soil amendment or potting mix ingredient.

Chipped Brush, Wood Shavings, Bark

These forest product mulches are most often used on perennial crops such as berries (Fig. 7) and ornamental perennials, many of which like a somewhat acidic soil rich in mycorrhizae and other beneficial fungi supported by these materials. They tend to be coarser and higher density than hay or straw, require higher tonnage per acre to suppress weeds, and may not be economical for most larger-scale applications. Other characteristics include:

• High C:N ratio.
• Relatively long lived.
• Allelopathic properties when fresh, especially walnut and some conifers (softwoods).
• Provide calcium (Ca), micronutrients, and small amounts of N, P, and K.
• Formation of stable humus when fully decomposed.

Figure 7. A perennial variety of strawberry in a garden in Floyd, VA thrives and yields well in a mulch of chipped brush, aged about one year before application. Photo credit: Mark Schonbeck, Virginia Association for Biological Farming.

Wood based or bark mulches should be aged for at least a year outdoors before application near crop rows, to minimize possible allelopathic suppression of crop growth. However, fresh chipped brush can be useful for suppressing weeds in paths or alleys between beds. one grower in New Jersey has had excellent results with 1–2 year old hardwood chips as mulch, and 8–11 year aged hardwood chips as a soil amendment for blueberry (Kittredge, 2008-09b).

Wood chip and bark mulches should not be piled against the bases of trees or shrubs, as this can promote the development of fungal diseases. Limit mulch depth to 1–2 inches adjacent to and within 6–12 inches from the base, then increase the depth further away.

Sawdust

Sawdust is chemically similar to other wood products, but because it is so finely divided, it has the following disadvantages as a mulching material:

• Tends to mat down and keep soil wet and airless.
• Can tie up soil N as small particles or soluble carbohydrates leach into the soil.
• Can be quite allelopathic against crops for a short time.
• May be penetrated by some weeds, and may provide a good germination medium for wind-borne weed seeds.
• May be washed away by heavy rain on sloping fields (Fig. 8).

Figure 8.(a) An intense rainstorm has washed a fine sawdust mulch away from newly planted blueberries. (b) The same storm damaged soil structure in un-mulched beds (right and background), whereas chipped brush held firm, protecting both soil and crop (left foreground). Several years after these photos were taken, the blueberry bushes mulched with sawdust remained visibly smaller than those in other mulches, as a result of N immobilization by the fine sawdust. Photo credit: Mark Schonbeck, Virginia Association for Biological Farming.

Compost

A few growers use compost as mulch, although the quantities required for effective weed suppression may not be economically feasible. In a study in Virginia, 1½–2 inches of leaf mold compost (50–90 tons per acre) did not suppress weeds quite as well as 4 inches (~8 tons per acre) of hay (Fig. 9) (Schonbeck, 1998). Compost is much more effective and economical to use as an ingredient in potting mixes (at 10–50% of total volume), or as a soil amendment at 1–10 tons/ac to inoculate the soil with beneficial organisms, provide slow-release nutrients, and improve soil structure. Higher application rates, such as those used in the study, commonly leads to excessive levels of P, K, and some micronutrients in the soil. The surplus P and K can favor the growth of weeds over crops in subsequent years.

Figure 9. Mulching with compost (a) A municipal compost, based primarily on tree leaves, was applied at 50 tons per acre in this trial. (b) By midsummer, considerably more weeds emerged through the compost than through a 4–inch (~8 tons per acre) hay mulch. Photo credit: Mark Schonbeck, Virginia Association for Biological Farming.

Manure

Manure is not recommended as a mulch for weed control. Many weed seeds pass through livestock digestive tracts unharmed, and the readily available nutrients in the manure stimulate weed growth. Lambsquarters (Chenopodium album) and spiny amaranth (Amaranthus spinosus)are just two of many nutrient-responsive weeds that are frequently spread in manure. Furthermore, uncomposted manure cannot be applied to USDA certified organic vegetable crops within 90–120 days of harvest, and applying sufficient manure to suppress weed seedling emergence from the soil is likely to create gross excesses of soil P and K.

Other Organic Residues

Crop residues—especially materials like cotton gin waste, rice hulls, peanut hulls, and buckwheat hulls—may be available in quantity in certain locales. Their ability to suppress weeds may vary, depending on texture and possibly chemical properties. Care should be taken to avoid crop residues that carry crop pathogens, weed seeds, or herbicide residues. Buckwheat hulls have been reported to attract cats using the mulched bed as a litter box, and thus may not be a good choice in neighborhoods with high cat populations.

Living Mulch

For many years, some growers have experimented with living mulches—perennial or annual cover crops growing between crop rows—in an effort to build soil quality while suppressing weeds. Experience has shown that living mulches allowed to grow in close proximity to crops often compete with the crop for moisture or nutrients, resulting in lower yields. However, in wide-spaced plantings, such as berries, alleys can be maintained in a perennial living mulch, while the area near crop rows are kept free of competing vegetation and mulched with straw, wood chip,or other organic materials (Fig. 10). Living mulches can also be planted in 2–3 foot wide strips between permanent vegetable beds to create firm, mud-free paths for tractor and foot traffic; define where workers and u-pickers should walk, and provide habitat for beneficial insects. Clippings from periodic mowing of the living mulch can be used to supplement organic mulch in crop beds.

Figure 10. A perennial living grass–clover mulch, maintained by regular mowing, maintains soil quality and suppresses weeds in alleys, while a 4-ft-wide zone for each row of blueberries is kept free of competing vegetation and mulched with straw and clippings from the alleys, to allow the new planting to become established. The grass-covered alleys also provide a better surface for foot traffic and minimize soil damage in u-pick berry fields. Photo credit: Mark Schonbeck, Virginia Association for Biological Farming.

References Cited

• Abdul-Baki, A. A., and J. R. Teasdale. 1994. Sustainable production of fresh market tomatoes with organic mulches. USDA Farmers' Bulletin FB-2279.
• Kittredge, J. 2008-09a. Mulching at Pleasant Valley Farm. The Natural Farmer 2(79): 32–39 (Winter 2008–09). (Available online at:http://www.nofa.org/tnf/Winter2008.pdf) (verified 12 Jan 2012).
• Kittredge, J. 2008-09b. 24 acres of mulch. The Natural Farmer 2(79): 13–18 (Winter 2008–09). (Available online at: http://www.nofa.org/tnf/Winter2008.pdf) (verified 12 Jan 2012).
• Mohler, C. L., and A. DiTommaso. Unpublished. Manage weeds on your farm: a guide to ecological strategies; version 5.1 (Cornell University, Dec. 4, 2008).
• Plaksin, E., and R. Bynum. 2007. Contaminated hay ruins crops. Growing for Market 16: 1, 4–7. (Available online at:http://www.growingformarket.com/articles/20071220_28) (verified 12 Jan 2012).
• Schonbeck, M. W. 1998. Weed suppression and labor costs associated with organic, plastic, and paper mulches in small-scale vegetable production. Journal of Sustainable Agriculture. 13: 13–33. (Available online at: http://dx.doi.org/10.1300/J064v13n02_04) (verified 12 Jan 2012).
• Schonbeck, M. W. 2007. Beating the weeds with low-cost cover crops, intercropping, and steel. The Virginia Biological Farmer 30: 7–8.
• Tindall, J. A., R. B. Beverly, and D. E. Radcliffe. 1991. Mulch effects on soil properties and tomato growth using micro-irrigation. Agronomy Journal 83: 1028–1034. (Available online at: https://www.crops.org/publications/aj/abstracts/83/6/AJ0830061028) (verified 12 Jan 2012).
• Tindall, J. A., H. A. Mills, and D. E. Radcliffe. 1990. The effect of root zone temperature on nutrient uptake of tomato. Journal of Plant Nutrition 13: 939–956. (Available online at:http://dx.doi.org/10.1080/01904169009364127) (verified 12 Jan 2012).

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