Long-term organic farm research findings
The gold standard of research is long-term findings. These demonstrate lasting trends and a greater likelihood of predicting future outcomes.
Michael Cavigelli, retired lead scientist with USDA-ARS’s Farming Systems Project (FSP), presented “Findings from the Beltsville Long-Term Cropping Systems Project” at the recent Cornell Organic Field Crops & Dairy Conference.
Researchers established long-term agricultural research (LTAR) plots to “provide robust data to calibrate and validate simulation models,” Cavigelli said. “We do the same thing every year; farming is a long-term process.”
Since every year’s weather is different, using the same growing practices in a long-term study helps account for variability.
By using a long-term model, researchers can measure gradual changes. The FSP in the study established one of five U.S. LTAR plots in 1996 to look at no-till and organic practices. They’re the only LTAR with no-till and three different organic treatments.
The FSP includes no-till (NT), chisel till (CT), organic two-year rotation (Org2), organic three-year rotation (Org3) and organic six-year rotation (Org6). NT and CT management include mineral fertilizers, herbicides, University of Maryland recommendations and input and wheat straw harvested.
The rotation plots included poultry litter, potassium, sulfate, between-row cultivation, unharvested wheat straw and farmer input. The control area was hand-weeded and was NT.
“That translates to a 35% yield loss to weeds in the organic system,” Cavigelli said of the control. “Weeds are an important part of it.”
For example, the corn grain yield from 1996 – 2024 in non-drought years was highest in NT, followed by CT, Org6, Org3 and then Org2.
“Soybeans show a similar trend, but some benefit with no-till,” Cavigelli said.
These findings prompted researchers to look at crop varieties better suited to the Mid-Atlantic region.
“The seed may not be suited for this area,” Cavigelli said. “A lot of seed was coming from the Midwest.”
The grain yield for corn was “pretty close” some years, he added. Soybeans indicated a similar trend, but some benefits from NT management.
“We could quantify the effect in the Farm Systems Project organic, then conventional,” Cavigelli said.
The percent of weed coverage corresponded with the percent of yield lost. The average was highest in both for Org2, followed by Org 3, Org 6 and then NT. This left researchers with further questions as to why grain yields were lower in organic vs. conventional systems. Was it weed competition, plant available soil nitrogen or crop varieties?
A trial beginning in 2009 looked at corn variety impact on grain yields. The researchers used two planting dates – early May and late May – along with two crop varieties, conventional TA seeds and organic Blue River seeds and managed with NT. Overall, the earlier planting date for organic seeds resulted in the highest percent of the conventional seed crop.
“In wheat yield, it’s not that big of a difference,” Cavigelli noted.
As for soybeans, the yields were lower in FSP organic than in conventional systems. Cavigelli noted that every 1% increase in weed cover resulted in a 0.26 bushel/acre decrease on soybean yield.
“Weed competition explains all the differences between conventional and organic soybean yields at FSP,” he noted.
The mean annual net returns from 2006 – 2014 showed Org6 as highest, followed by NT, then a near tie between Org2 and Org3; CT came in last.
“The six-year rotation, we’re getting better returns than the shorter rotations and the conventional,” Cavigelli noted. “The standard deviation in conventional is similar to organic short-term rotation.”
He posed the question, “At what price premiums do organic returns equal those from conventional production?” The research points to 60% of the premiums.
Regarding soil organic carbon, the group’s initial hypothesis was that NT was better than CT because of increased carbon mineralization with tillage.
“You need long-term studies to evaluate that,” Cavigelli said. “Soil organic carbon comes from plant residue, manure, et cetera. You put it on the soil like putting money into the bank. Much of it decomposes as you till.”
Studying the effects of cumulative carbon and nitrogen inputs indicated that “burying carbon may be a better way to sequester carbon than NT in some situations,” Cavigelli said. “Carbon sequestered at depth should be more stable than on the surface of NT soils. When initial soil organic carbon is high, it is hard to sequester additional carbon, but perennial crops outperform annuals.”
The Org6 plot was the only one to show zero change in soil carbon.
In addition, “the agronomic benefits or soil organic matter is critical in all systems, not just organic,” Cavigelli said. “There was a yield of 150 bushels for organic with no nitrogen. It shows the importance of organic matter.”
Cavigelli feared that using poultry litter as a source of nitrogen may have caused excess nitrogen in FSP organic systems. After some research, he concluded that long-term alfalfa and poultry litter inputs led to sufficient soil PAN for corn.
“Applying poultry litter at reduced rates – less than 50% – optimized corn yield in shorter rotations. Farms using long-term poultry litter and legumes can reduce input costs and nitrogen losses. The impacts of STP in long-term corn needs to be considered.”
