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Corn Yield and Nitrate Loss in Subsurface Drainage from Midseason Nitrogen Fertilizer Application

USDA-ARS, National Soil Tilth Lab., 2150 Pammel Dr., Ames, IA 50011

View larger version (37K): [in a new window]   Fig. 1. Location of the field within Iowa and the USA and the layout of tile drains, sumps, locations of high (H), medium (M), low (L), and responsive (R) N-fertilizer treatment plots and distribution of Okoboji silty clay loam, Harps loam, Ottosen clay loam and Kossuth silty clay loam soils as determined by Brevik et al. (2000).

View larger version (28K): [in a new window]   Fig. 2. Example of daily discharge rate and cumulative discharge depth from a tile drain for one of the low N-fertilizer treatment plots for 2002 through 2005. Cumulative precipitation for each year is also shown.

View larger version (28K): [in a new window]   Fig. 3. Chlorophyll (SPAD) values for corn relative to SPAD values from a nonlimiting N strip and the 95% confidence limits for different dates in 2002 and 2004. The N treatments for corn were H = 199 kg ha–1, M = 138 kg ha–1, L = 69 kg ha–1, R = 69 kg ha–1 of N applied at V1 to V3 with another 69 kg ha–1 N side-dressed at midseason (V16), and Z = no N fertilizer. Dotted horizontal line is at the 0.95 sufficiency threshold value. The dashed vertical line is the time of the midseason N application to the R treatment.

View larger version (21K): [in a new window]   Fig. 4. Residual soil NO3 concentration vs. depth for each N treatment after harvest in 2002 through 2005. The N treatments for corn were H = 199 kg ha–1, M = 138 kg ha–1, L = 69 kg ha–1, and R = 69 kg ha–1 of N applied at V1 to V3 with another 69 kg ha–1 N side-dressed at midseason (V16). No N fertilizer was applied to soybean. Corn was harvested in even years, soybean in odd years. Horizontal bars, where present, represent least significant difference where an F test was significant ( = 0.05).