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

摘要

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.