Soil nitrogen dynamics in winter cover crop-corn systems
1999
Vaughan, J.D. | Evanylo, G.K.
Understanding seasonal soil mineral nitrogen (N) dynamics under various cover cropping systems will aid in making supplemental fertilizer N recommendations for corn (Zea mays L.) using soil nitrate testing. A split-plot field study was conducted to track early season soil mineral N under corn grown after cover crops and to determine the usefullness of the presidedress soil nitrate test (PSNT) in cover crop-corn systems. The cover crop treatments rye (Secale cereale L.), hairy vetch (Vicia villosa Roth), rye+hairy vetch, and fallow were established as main plots to provide a range of soil N availability for a subsequent corn crop. The split plot treatment was sidedress fertilizer N rate, which consisted of six rates ranging from 0-250 kg N ha-1 in 50 kg increments. Soil was sampled throughout the growing season and corn was sampled at Hanway's corn growth stage 5 in the 0 kg N ha-1 check plots to assess periodic soil N availability. Soil N concentrations peaked between Hanway's corn growth stage 1 and 3 and were concentrated in the top 15 cm of the soil. Vetch and fallow treatments provided higher amounts of available N as indicated by soil and corn N concentrations and corn yields. Recommended PSNT sampling times resulted in critical soil [NO3(-)N] values that are similar to those used for PSNT fertilization; however, sampling to a depth of 15 cm may be adequate when a considerable portion of plant available N is supplied by cover crops. Addition of NH4-N to NO3-N testing did not improve the predictive capability of the soil test for supplemental corn N needs. The time of sampling may be delayed as much as two weeks without a loss of prediction accuracy.
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