Effects of polymer materials on the transformation and utilization of soil nitrogen and yield of wheat under drip irrigation

Nitrogen management is the key to improve crop yield. Polymer materials are widely used as water‐retaining agents in agriculture, but little is known about how polymer materials affect the transformation and utilization of soil nitrogen. This study focused on the effects of three polymer materials (humic acid extracted from cottonseed meal, H; modified polymer prepared by using polyacrylamide as main raw material, P; and composite polymer material composed of humic acid and modified polymer, HP) on the characteristics of soil and plant nitrogen accumulation in soils with/without plants under drip irrigation. The results showed that polymer materials increased the nitrogen accumulation and dry weight of leaf, spike axis + husk and grain, but decreased thos e of stem. Among them, the H treatment had the highest nitrogen uptake (34.5 kg·hm −2 ) after flowering stage, and the P treatment had the highest nitrogen transport (21.1% higher than no polymer materials, CK). Moreover, the wheat yields for the H and P treatments significantly increased by 19.7% and 12.6%, respectively. Polymer materials had an inhibitory effect on nitrogen fractions (soil total nitrogen (TN) and microbial biomass nitrogen (MBN) at the early stage of the culture, but there were significant improvements at the flowering and mature stages. The effects of polymer materials on the storage of TN and its fractions were different. Among them, the storages of soil TN, nitrate‐nitrogen (SNO 3 ‐ ‐N), and ammonium‐nitrogen (SNH 4 + ‐N) for the H treatment were increased, but the SNO 3 ‐ ‐N in soil with plants was decreased by 1,317 kg·hm −2 compared with that in soil without plants, and the decrease was the largest among the decreases caused by the three polymer materials; the soil SNO 3 ‐ ‐N for the P treatment was increased, but also the decrease in the SNO 3 ‐ ‐N was smaller than that for the H treatment; the SNO 3 ‐ ‐N for the HP treatment was increased, but the SNH 4 + ‐N was decreased. Redundancy analysis showed that humic acid and modified polymer materials mainly increased soil MBN, NH 4 + ‐N, and nitrogen accumulation of plant organs except for stem, which finally increases wheat yield.