Optimizing Irrigation and Nitrogen Fertilizer Regimes to Increase the Yield and Nitrogen Utilization of Tibetan Barley in Tibet

Abstract

Nitrogen (N) fertilization plays a pivotal role in the nitrogen transport process and yield formation of field-grown Tibetan barley (Hordeum vulgare L., qingke in Chinese); however, little is known about its interaction with irrigation regimes. Here, we performed a control experiment to investigate the effects of irrigation regimes (primary irrigation and double irrigation, mentioned as W1 and W2) and N levels (0, 90, 120, and 150 kg ha−1, mentioned as N0, N9, N12, and N15) on the nitrogen accumulation, translocation, and utilization of Tibetan barley in the Tibetan Plateau during the spring barley seasons in 2022. The results showed that the highest yield (6242.28 kg ha−1) and aboveground biomass (12,354.13 kg ha−1 for anthesis; 15,827.9 kg ha−1 for maturity) were achieved in W2N15 as compared to other treatments. The maximum grain N accumulation (117.66 kg ha−1), the N translocation (54.16 kg ha−1), and the post-anthesis N accumulation (63.5 kg ha−1) were achieved in the W1N15 treatment. The N utilization efficiency increased with irrigation frequency and decreased with N application; however, the conclusion given by the N agronomic efficiency is contrary to this trend. The grain yield had significant positive correlations with the grain N accumulation (W1: r = 0.98; W2: r = 0.97) and N translocation (W1: r = 0.84; W2: r = 0.94), but significant negative correlations with the N harvest index (W1: r = −0.95; W2: r = −0.95) and N utilization efficiency (W1: r = −0.9; W2: r = −0.85). The path analysis revealed that the factors related to N utilization (β = 0.875) and the factors related to N translocation (β = −1.426) were the significant direct contributors towards grain yield. The influence of N application (total effect = 0.922) on the grain yield was much stronger than that of the irrigation regime (total effect = 0.324). Our findings can guide future efforts in designing sustainable water and N fertilizer management strategies for Tibetan barley in the Tibetan Plateau.