In-Season Side-Dressing of Urea and Ammonium Nitrate to Cotton on No-Till Soils with High Residual Nitrogen and Pre-Plant Nitrogen Application

Abstract

It is essential to develop innovative approaches that can apply N more efficiently. The objective of this study was to examine in-season side-dress urea and ammonium nitrate (UAN) applications to cotton on no-till soils with high residual N fertility. A field trial was conducted near Milan, TN in 2011 and 2012 with strip plots in a RCB design with three replicates. The following six in-season side-dress fluid UAN treatments were compared: 1) zero N; 2) low uniform-rate N application of 56 kg·N·ha −1 ; 3) high uniform-rate N application of 78.4 kg·N·ha −1 ; 4) ordinary variable-rate N application algorithm for each sub plot based on the average Normalized Difference Vegetation Index (NDVI) value in that sub plot; 5) reversed variable-rate N application algorithm for each sub plot based on average NDVI of that sub plot; and 6) N application rate based on the average NDVI value in each strip plot. All plots received 26 kg·N·ha −1 as diammonium phosphate before cotton planting each year. Leaf N concentrations were mostly enhanced with all side-dress N applications ranging from 56 to 78 kg·N·ha −1 relative to zero N during early to late bloom although this upland field had high initial soil N fertility and received pre-plant application of 26 kg·N·ha −1 across the treatments each year. However, NDVI, plant height, and lint yield were rarely improved with side-dress N application. The three variable-rate N application algorithms consumed 7.8 to 12.3 kg·ha −1 more N than the low uniform-rate application of 56 kg·N·ha −1 , but 10.1 to 14.6 kg·ha −1 less N than the high uniform rate of 78.4 kg·N·ha −1 . Our results indicate that the current N recommendations for cotton in Tennessee may be too high on upland soils with high initial N fertility.

Ammonia Volatilization Loss and Corn Nitrogen Nutrition and Productivity with Efficiency Enhanced UAN and Urea under No-tillage

“…Nitrogen fertilizer is often applied on the soil surface in no-tillage production systems without any mechanical incorporation into the soil in many areas around the world such as the State of Tennessee 1 . Ammonium nitrate (AN) can be surface broadcast since it has a low potential for N loss to the atmosphere via ammonia volatilization 2 .…”

Nitrogen Consumption and Productivity of Cotton under Sensor‐based Variable‐rate Nitrogen Fertilization

“…Post‐harvest N content in soil profile is a vitally important indicator in environmental assessment. High levels of post‐harvest N in the soil profile have been increasingly observed in cotton and corn production systems in Tennessee and other states in recent years (Yin, 2015; Sharma and Bali, 2018). Bausch and Delgado (2005) found that in‐season N application according to ground‐based sensing technology significantly reduced residual NO 3 − –N level in the soil depth of 1.5 m. However, Yin (2015) noted that no significant effect on post‐harvest inorganic N (NO 3 − –N + NH 4 + –N) content in 60‐cm soil profile was observed under different in‐season N treatments.…”

“…High levels of post‐harvest N in the soil profile have been increasingly observed in cotton and corn production systems in Tennessee and other states in recent years (Yin, 2015; Sharma and Bali, 2018). Bausch and Delgado (2005) found that in‐season N application according to ground‐based sensing technology significantly reduced residual NO 3 − –N level in the soil depth of 1.5 m. However, Yin (2015) noted that no significant effect on post‐harvest inorganic N (NO 3 − –N + NH 4 + –N) content in 60‐cm soil profile was observed under different in‐season N treatments. Likewise, our results suggest that the use of in‐season sensor‐based VNMS do not significantly affect the post‐harvest residual N level in soil profile compared with FUNS, which might relate to the possibility that a larger amount of the applied N under FUNS was taken up by cotton plants, lost to deeper soil layers via nitrate leaching, and/or lost to the atmosphere via ammonium volatilization during the growing season and/or associated with the fact that the N application rates were reduced under VNMS relative to FUNS.…”