Effects of salinity and fertigation practice on cotton yield and 15N recovery

The purpose of optimal water and nutrient management is to maximize water and fertilizer use efficiency and crop production, and to minimize groundwater pollution. In this study, field experiments were conducted to investigate the effect of soil salinity and N fertigation strategy on plant growth, N uptake, as well as plant and soil 15N recovery. The experimental design was a 3x3 factorial with three soil salinity levels (2.5, 6.3, and 10.8dSm-1) and three N fertigation strategies (N applied at the beginning, end, and in the middle of an irrigation cycle). Seed cotton yield, dry matter, N uptake, and plant 15N recovery significantly increased as soil salinity level increased from 2.5 to 6.3dSm-1, but they decreased markedly at higher soil salinity of 10.8dSm-1. Soil 15N recovery was higher under soil salinity of 10.8dSm-1 than those under soil salinity of 6.3dSm-1, but was not significantly different from that under soil salinity of 2.5dSm-1. The fertigation strategy that nitrogen applied at the beginning of an irrigation cycle had the highest seed cotton yield and plant 15N recovery, but showed higher potential loss of fertilizer N from the root zone. While the fertigation strategy of applying N at the end of an irrigation cycle tended to avoid potential N loss from the root zone, it had the lowest cotton yield and nitrogen use efficiency. Total 15N recovery was not significantly affected by soil salinity, fertigation strategy, and their interaction. These results suggest that applying nitrogen at the beginning of an irrigation cycle has an advantage on promoting yield and fertilizer use efficiency, therefore, is an agronomically efficient way to provide cotton with fertilizer N under the given production conditions.