Corn N Supply from Annual and Living Mulch Cover Crops.

White clover is an excellent candidate cover crop for the living mulch system because of its perennial stoloniferous growth habit.  Development of the system requires managing competition between the clover and row crop, including the N dynamics between the two.  The interaction between the two crops is complex and involves clover growth and N fixation, chemical suppression of the clover, the impact of crop shading on clover mass and N release, and regrowth of the clover for subsequent years.  A study was established to examine the N dynamics between corn and cover crops (white clover= WC, crimson clover=CC, cereal rye=CR) under irrigated conditions (6 reps). CR plots were fertilized with 50 kg/ha N at corn planting, and WC, CC and CR were top-dressed with 50, 100 and 200 kg N/ha, respectively, at the corn 6^th leaf stage.  All residues and herbage were sampled weekly using frame quadrats to estimate mass and N content in each from which N release was calculated.  A calibrated rising plate meter was also used to predict herbage mass in WC.  All samples were analyzed for N using NIR and wet chemistry.  NIR performed poorly in predicting N in residue samples.  Wet chemistry provided predictable N supply from CC and CR to the corn because of their annual growth habit.  The estimated supply of N from the WC varied depending upon a) laboratory method of N determination in residue/herbage and b) method of WC mass determination.  All methods underestimated the N uptake by the corn crop.