Evaluating Termination Methods of Four Winter Annual Leguminous Cover Crops for Optimizing Nitrogen Synchrony.
Brown, M. I.. 2012. North Carolina State University, M.Sc.
Abstract
In agroecosystems, synchronizing availability of legume nitrogen (N) to cash crop
need is essential to efficiently utilize cover crops as a fertility source. Winter annual legume
cover crop termination can be achieved through both tillage and non-tillage methods.
However, the chosen approach may affect legume decomposition rate and consequent N
mineralization by impacting availability to decomposer soil microorganisms. We predict that
termination method in combination with biomass nitrogen content will govern rates of
mineralization. Our objective is to evaluate various legume species and termination methods
to determine nitrogen release rates in corn following winter annual legumes. In this study,
four leguminous winter cover crop species, Austr ian winter pea, hairy vetch, and balansa and
crimson clovers, were terminated using a roller-crimper, flail mower, disk, or an herbicide.
Bi-weekly inorganic soil tests and Plant Root Simulator ion resin probes were used to
measure plant available NO3-
-and NH4
. Cover crop biomass, total carbon, and total nitrogen
were measured for each species prior to termination. Mineralized nitrogen was most
available from Austrian winter pea and hair y vetch across all termination methods at six to
ten weeks after kill. Disked hairy vetch contributed the greatest plant available nitrogen
amongst all 16 combinations. Biomass contributions of cover crops ranged from 2.4 Mg ha-1 to 9.7 Mg ha-1
in crimson clover and balansa clover, respectively. Crimson clover, Austria n
winter pea, and hairy vetch averaged greater than 7 Mg ha-1 over three years. Balansa clover
was the lowest contributor of both biomass and biomass nitrogen (2.4 Mg ha-1 and 40.3 kg ha-1, respectively). Hairy vetch had the greatest overall average biomass nitrogen of 226.4 kg ha-1, while Austrian winter pea averaged 188.71 kg ha-1 and crimson clover averaged 181.1 kg ha-1
. Corn yield was not consistent with inorganic and PRS™ probe measurements of
nitrogen. Results show though termination technique in combination with cover crop species
does influence nitrogen contributions from winter annual leguminous cover crops.
