Organic No-till: N release from roll-killed hairy vetch and crimson clover.

By: Mary Parr, Dr. Chris Reberg-Horton, and Dr. Julie Grossman

In collaboration with the Organic Grains Research group, Mary Parr, graduate student in the Soil Science department at NCSU, has been investigating nitrogen (N) fixation and release in a system involving roll-killed winter legume cover crops followed by no-till organic corn. She has quantified the total amount of N in the biomass of hairy vetch, crimson clover and Austrian winter pea at the time of roll-kill, and is in the process of calculating the portion of this N coming from the atmosphere vs. the soil. Beginning with corn planting in May 2009, she monitored the decomposition and release of fixed N from hairy vetch and crimson clover mulches that had been roll-killed. One of the novel ways in which she quantified N released from the decomposing mulch was by using “resin probes” inserted into the soil that collected the N released by mulch over a two week period. She found that the hairy vetch plants contained up to 195 lb N per acre by mid May, and crimson clover between 120 and 140 lb N per acre. As a rolled surface mulch, N from the hairy vetch cover crop was made available more quickly to the corn crop – with peak availability between 2 and 6 weeks, but the crimson clover N did not become available until later in the season – between 6 and 10 weeks after planting. This experiment was conducted at the Tidewater station in Plymouth NC, and the Piedmont station in Salisbury NC and it will be repeated on both sites in the coming year.