Straw - wheat, oat, barley, whatever kind - is known to be a good algae and nutrient cleaner-upper on farm ponds. A recent two-year Penn State research reveals it even more effective in no-till corn fields.
Straw left in the field after small grain harvest will reduce nitrogen leaching into waterways. But it may also reduce following no-till corn yields and economic return, according to research conducted in Penn State's College of Agricultural Sciences.
The study evaluated three different quantities of straw residue spread on research plots that were later planted with hairy vetch. Anna Starovoytov, a recent Penn State ecology master's recipient conducted the study.
A corn grain crop was later no-till planted into the vetch/straw residues. The residue affected the magnitude of nitrogen's peak amount in soil - and the timing of that peak. The timing is important to corn nitrogen uptake when it needs it the most.
"Legume cover crops, such as hairy vetch, have been considered as an alternative or supplement to synthetic nitrogen fertilizers that may improve the sustainability of agricultural systems," says Starovoytov, now at Northgate Environmental Management, Inc., Oakland, Calif. "Such cover crops can contribute substantial amounts of nitrogen to subsequent crops, as well as protect soils from erosion and promote overall soil quality."
Legumes tend to release nitrogen more slowly than synthetic fertilizers, possibly leading to more synchrony with crop demand. That doesn't mean nitrogen from legumes can't be lost from the system.
Cereal crop straw ties up N
One way to minimize the losses is to add crops with carbon-rich residues, such as cereal grains, into the rotation, noted Starovoytov. Adding straw residues to hairy vetch cover crops tended to lower soil inorganic nitrogen content compared to treatments with only legume residues.
On average, soil inorganic nitrogen was 7.3% lower in the fields with straw residue. But reduced N availability negatively impacted corn yields, which fell 16% below the county average during one year of the study.
And since straw residues can be baled and marketed, it also reduced economic return. The study didn't show that retaining nitrogen with straw residue offset that income loss.