Cover crops are promoted as a valuable practice to reduce erosion and nutrient loss while improving soil health. Incorporating this practice into current production systems can be challenging.
“Farmers want to know if they can successfully implement cover crops, how they impact soybean yield, and if the practice supports their profitability,” says Dr. Trent Roberts, Associate Professor of Soil Fertility and Soil Testing for the University of Arkansas System Division of Agriculture. “We are collecting and analyzing data to provide both short-term and long-term answers to those questions.”
Roberts and his team have collected four years of data on cover crops in a variety of common Arkansas soil types and crop systems to date, with plans to continue the research for several more years with support from the Arkansas Soybean Promotion Board.
“The checkoff invests in research to keep soybean farmers on the leading edge,” says Doug Hartz, a professional farm manager based in Stuttgart and member of the Arkansas Soybean Promotion Board. “As a board we fund practical independent research that addresses challenges we are seeing in producer’s fields to improve their operations.”
This cover crop research has been designed to answer questions and identify trends in conditions and management systems common to Arkansas soybean producers. Trials are being conducted in three locations around the state:
Trials at the Rohwer Research Station in Rohwer, Arkansas, the southeast region of the state, have silt loam and clay loam soils common to corn-soybean or cotton rotations.
At the Pine Tree Research Station near Colt in eastern Arkansas, cover crop trials are conducted on soils that typically support soybean-rice rotations.
The sandy soils of the Vegetable Research Station in Alma, Arkansas, in the western part of the state provide another distinct soil type.
At each location, seven different cover crop species are planted in the fall. The cover crops include cereal rye, barley, black-seeded oat, Austrian winter pea, blue lupin, a blend of cereal rye plus crimson clover plus seven-top turnip, and a blend of black-seeded oat plus Austrian winter pea. These treatments are compared to traditional winter fallow. All the plots are terminated with burndown herbicides in mid-April before planting. The first years of data also include a comparison to winter wheat and double-crop soybeans.
“We are looking at both short- and long-term data because it may take several years for these systems to reach equilibrium with the combination of cover crops and no-till management,” Roberts explains. “Our goal is to develop agronomic and economic guidelines for cover crop options that work. We are starting to see trends that indicate fit and value for cover crops in our systems.”
Roberts says that initially his team focused on implementing cover crops. They found that regardless of biomass left from cover crops and the residue on the field surface, soybean emergence and stands were consistent at typical planting populations.
“Soybeans emerged through the cover crop residue from all the treatments well,” he adds. “Our plots in a variety of soil types, cover crop species and soybean plant populations found that we can get a vigorous stand using no-till management into the terminated cover crop. The soybeans push through the residue well.”
According to Roberts, aggregate soybean yield data following cover crops across locations and years showed that all the cover crop trials yield equal to or better than conventional winter fallow. Four treatments yielded significantly better than fallow – barley, Austrian winter pea, the blend of cereal rye, crimson clover and seven-top turnip and the winter pea-oat blend.
“We can confidently say cover crops don’t hurt soybean yields,” he says. “In fact, we saw yields in the cover crop systems increase over time. The best cover crop treatment average seven bushels per acre more than fallow.”
The profitability of a system is just as important as yield impact. For each plot, Roberts’ team calculates the input costs that vary between treatments and compares those differences to the return on investment. This provides the partial economic returns for each option.
Variable costs in these trials include cover crop seed, planting, burndown herbicides, fuel and labor compared to tillage fuel and labor costs for conventional winter fallow. Analysis found that winter fallow is actually one of the most expensive treatments, at a partial cost of $71 per acre, while the cover crop partial costs ranged from about $56 per acre for cereal rye on the low end to $74 per acre for blue lupin on the high end.
“To figure returns, we used the average value of soybeans over 10 years,” Roberts explains. “With the yield differences, we found that transitioning from conventional fallow and full tillage to no-till saves farmers enough in fuel and labor to pay for cover crops. With the combination of increased yields and lower costs, all the cover crop treatments returned more per acre than winter fallow except the blue lupin. Six of them delivered significantly higher returns.”
Influence on Soil Health
Throughout these four years of trials, Roberts and his team have been monitoring soil health conditions, like the soil health score and changes in soil organic matter.
“We haven’t seen any statistically significant changes in soil metrics yet, but because we are seeing higher yields, we know cover crops are impacting the soil and the production system positively,” he says. “Will we see bigger yield increases as soil properties start to change? We’re not sure, but this is the epitome of why we need to do long-term research like this. We may not continue to increase yields, but if we can increase efficiency and profitability, that’s just as good – if not better.”
He adds that they plan to focus more on soil properties and understanding the cause of increased yields in the next few years of this research.