Lint yield and nitrogen use efficiency of field-grown cotton vary with soil salinity and nitrogen application rate

Abstract

Understanding salinity and fertilizer interaction is of great economic importance to improving crop yield and fertilizer use efficiency. The objective of this study was to investigate the effects of nitrogen (N) rate on cotton yield and N use efficiency (NUE), and relate this to the optimum N fertilizer rate under saline field conditions. To achieve this goal, we conducted a two-year experiment in two nearby fields with similar fertility but varying salinity, using a split-plot design in the Yellow River Delta of China. The main plots were assigned to moderate (electrical conductivity of soil saturated paste extract, ECe=6.3dS/m) and high (ECe=12.5dS/m) salinity levels, while N-free (0kg/ha), low (120kg/ha), moderate (210kg/ha) and high (300kgN/ha) nitrogen rates were assigned to the subplots. The high-salinity soil produced 35% lower biological yield but 8.9% higher harvest index than the moderate-salinity soil. Biological yields were increased by 30% at low N rate, 35% at moderate N rate and 37% at high N rate. Under moderate salinity, moderate N rate produced more lint than other N rates; under the high salinity field, the low N rate produced lint yield comparable to the high- and moderate-N rates, being about 33% greater than that from 0-N rate. Moderate N rate was superior to high N rate but comparable to low rate based on agronomic NUE (aNUE), physiological NUE (pNUE), internal NUE (iNUE) and N recovery efficiency (NRE) under moderate salinity; under high salinity, the low N rate produced the greatest aNUE and NRE, and higher pNUE and iNUE than high N rate. Our overall results supported the use of moderate N rate for moderate salinity cotton fields and low N rate for high salinity fields in the saline Yellow River Delta and other cotton-growing areas with similar ecologies.