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The importance of Green Manure Cover Crops
Green
manure cover crops (GMCC) are the cornerstone of sustainable agriculture and
should always be included in sound crop rotations. In a no-till system cover
crops are incorporated biologically and not by tillage implements. To flatten
cover crops and lay them on the ground a knife roller should be used. Pictures
and dimensions of a knife roller can be seen in: Green
manure cover crops should: Ø
be of
low cost (seeds) Ø
be
easy to seed and manage Ø
provide
good weed control and shading Ø
produce
a positive residual fertilizer effect on following cash crops Ø
they
should not compete in area, labor, time and space with cash crops The
use of green manure cover crops and crop rotation are the key factors for the
unprecedented growth of no-tillage especially in Brazil and Paraguay. Only
those farmers that have understood the importance of these practices are
obtaining the highest economic benefits from this system. While in some regions of the world
no-till farmers concentrate on avoiding tillage, Latin American farmers have
understood that adequate production and management of crop residues, and of
cover crops, are key issues in the no-tillage system. Cover
crops do not cost but will pay. When practiced in monoculture or even in double
cropping, i.e. when the same crop or crops are repeated on the same land each
year, no-tillage is an imperfect and incomplete system, in which diseases,
pests and weeds tend to increase and profits tend to decrease. Adaptive
research in this area and technology development, are the most important
factors to make no-tillage work, that is, take advantage of all the benefits of
the system, reduce weed pressure and increase economic returns! Good
knowledge about green and dry matter production and profitability of green
manure cover crops, how to fit them into different crop rotations and what
residual effect we can expect of each GMCC planted before the main cash crops
is essential for dissemination of their use. A number of publications have
contributed in filling this knowledge gap in Latin America (Sorrenson and
Montoya, 1984; Monegat, 1991; Derpsch, et al., 1991; Derpsch and Calegari,
1992; Calegari et al., 1992, Kliewer, et al., 2000). Several publications on
the use of cover crops have appeared in the US in the last decade, i. e.,
(Cover crops for clean water, W. L. Hargrove, Ed. 1991; Managing Cover Crops
Profitably, SAN - SARE, 1998: www.sare.org).
There is increasing information on cover crops also in web sites. Some very
recommended web sites with comprehensive information on this topic are:
http://www.ianr.unl.edu/pubs/FieldCrops/g1146.htm#ccs
(Univ. of Nebraska)
http://www.kbs.msu.edu/extension/covercrops/home.htm
(MSU, Michigan)
http://www.gov.on.ca/OMAFRA/english/crops/facts/cover_crops01/covercrops.htm This last one from Ontario, Canada. Other interesting sites on cover crops are
Many more sites can be found using normal
search machines. According to USDA-ARS (2002). "No matter
where you farm, there are cover crop species that meet your need" In a
no-till system the use crop rotation and cover crops is much more important
than in conventional tillage systems. Experience has shown, that tillage
negates cover crops. We have also to remember that cover crops are essential
for producing the mulch needed in the no-tillage system. Cover crops have to be
integrated in the agricultural system of each farm and show their beneficial
effects. Cover crops, in combination with no-tillage and crop rotations ensure
the sustainability of agricultural production. “But, rotation isn’t just a
helter-skelter array of crops” (Rick Bieber, 2000). Without the knowledge of
positive or negative residual effects of one species on the succeeding crop,
any attempt of organizing a crop rotation is merely a theoretical model. Not
only legumes are adequate green manure cover crops. Black oats for instance (Avena
strigosa Schreb) are planted on 3,2 million ha only in the States of Paraná
and Rio Grande do Sul in Southern Brazil. They are planted on more than 300.000
ha in Paraguay. Provide soil cover for: Ø no-tillage Ø increasing water infiltration into
the soil Ø reducing water evaporation Ø reducing soil temperature Ø protection against erosion Ø reducing weed infestation Ø accumulation of organic matter in
the soil Ø adding and recycling nutrients Ø improve soil structure Ø promotion of biological soil
preparation Adding of organic matter in the soil is often
mentioned in the literature as one of the main objectives of cover crops, but
this can in general and especially in warmer climates only be achieved in the
no-tillage system. Cover crops are a key element to make
sustainable agriculture possible and have shown the following benefits in Latin
America: Ø Higher economic returns when appropriately
chosen Ø Reduce the need for herbicides and
pesticides Ø Improve yields of following cash
crops Ø Conserve soil moisture (when
properly managed) Ø Prevent soil erosion Ø Enhance organic matter content of
the soil Ø Provide nitrogen Ø Avoid leaching of nutrients and
improve soil fertility Ø Reduce fertilizer costs Literature: Calegari, A., Mondardo, A., Bulisani, E.A.,
Wildner, L.do P., Costa, M.B.B., Alcantara, P.B., Miyasaka, S. e Amado, T.J.C.
1992: Adubação verde no sul do Brasil, AS-PTA, Rio de Janeiro, 346 p. Derpsch, R. e Calegari, A., 1992: Plantas
para adubaçãao verde de inverno. IAPAR, Londrina, Circular 73, 80p. Derpsch, R., Roth, C.H., Sidiras, N. and Köpke,
U., 1991. Controle
da erosão no Paraná, Brasil: Sistemas de cobertura do solo, plantio direto e
preparo conservacionista do solo. GTZ, Eschborn, SP 245. Hargrove,
W. L., 1991: Ed. Cover Crops for Clean Water. Proceedings of an international
conference. West Tennessee Experiment Station, April 9 – 11, 1991, Published by
the Soil and Water Conservation Society. Kliewer, I.,
Casaccia, J., Vallejos, J., Derpsch, R., 2000: Cost and herbicide
reduction in the no-tillage system by using green manure cover crops in
Paraguay. Proceedings 15th ISTRO Conference, Fort Worth, Texas, USA, July 2 – 7, 2000 Monegat, C., 1991: Plantas de cobertura do
solo. Características e manejo em pequenas propriedades. Chapecó (SC). Ed. do Autor, 336 p. SAN – SARE, 1998: Managing Cover Crops
Profitably, SAN Handbook Series Book 3, Sustainable Agriculture Network,
National Agricultural Library, Beltsville, MD 20705-2351, www.sare.org >Sorrenson, W.J., Montoya, L.J., 1984:
Implicações econômicas da erosão do solo e de práticas conservacionistas no
Paraná, Brasil, IAPAR, Londrina, GTZ, Eschborn ( no publicado), 231 p. USDA-ARS,
2002: Sustainable Agricultural Systems Laboratory. Cover Crops in Agriculture –
An Old New Concept. www.barc.usda.gov/anri/sasl/covercrops.html |