Corn Yield and Nitrate Loss in Subsurface Drainage Affected by Timing of Anhydrous Ammonia Application
2015
Jaynes, D. B.
Surprisingly little research has examined the corn (Zea mays L.) yield, N-use efficiency (NUE), and water quality implications of N fertilizer timing. Anhydrous ammonia (AA) was applied either in the fall after harvest (F) at 196 kg N ha⁻¹, in the spring before planting (PP), or as an early sidedress (SD) at rates of 168 kg N ha⁻¹ on replicated plots within a producer’s field used to grow corn and soybean [Glycine max (L.) Merr.] in a 2-yr rotation. The field was underlain with subsurface drainage pipes (tiles) which were used to collect drainage and nitrate lost from the root zone for each plot. A fourth treatment was added when the initial fall N application was accidentally over applied by threefold on two plots (FH), allowing us to follow this one time over application over 4 yr. There were no significant differences among treatments for soybean yield. Over the two corn years, yields for the FH and SD treatments were at least 1.5 Mg ha⁻¹ greater than for the F and PP treatments. The NUE and partial factor productivity for N (PFPN) metrics in corn followed similar patterns; SD > PP > F > FH and SD > PP = F > FH, respectively. Flow-weighted annual N concentrations in the tile drainage were significantly different and followed the pattern FH > F > SD > PP. Effects of the over application of N for the FH treatment could still be measured after 4 yr and impacted yield and nitrate losses well after the first year. Considering yield, NUE, and nitrate losses, sidedressing N was clearly superior to fall application in a corn–soybean rotation.
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