By Don Comis
An organic crop rotation is at least as sustainable as no-till farming or chisel tillage in terms of nitrogen loss and corn yields, according to an Agricultural Research Service (ARS) study. The five-year study showed that a three-year rotation of organic corn, soybeans, wheat and a legume cover crop had nitrogen losses and corn yields similar to those on land where either chisel-tillage or no-till farming had been used.
The organic rotation relied on poultry litter, soybeans and a hairy vetch legume cover crop as nitrogen sources. The study showed the highest risk of leaching nitrogen to groundwater was on fields with no-till or chisel tillage where both commercial fertilizer and poultry litter had been used. Future studies are planned to measure or estimate leaching losses.
Michel Cavigelli, an ARS soil scientist at the Henry A. Wallace Beltsville (Md.) Agricultural Research Center, and Steve Green, an ARS soil scientist research associate, are studying nitrogen losses with organic and other farming systems. The study is part of a farming systems project begun in 1996 to compare the sustainability of organic and conventional farming. Minimizing losses of nitrogen and other nutrients is a key element of both environmental and economic sustainability.
Cavigelli and Green used measurements and estimates to get an initial picture of nitrogen inputs and losses. They are conducting additional studies to improve their ability to more accurately estimate the amount of nitrogen added naturally by soybean plants.
The scientists got their poultry litter–both composted and noncomposted–from commercial farms on Maryland’s Eastern Shore. They studied corn-soybean rotations, mostly with winter wheat, using various levels of tillage.
Green presented this research at the American Society of Agronomy’s recent annual meeting in Seattle, Wash., along with a report on the risk of phosphorus loss from erosion. He found the risk of losing phosphorus from soil erosion was similar for both the organic system and land that was chisel-plowed, but the risk was lower with a conventional no-till system.
ARS is the U.S. Department of Agriculture’s chief scientific research agency.