Nitrogen application improved peanut yield and nitrogen use efficiency by optimizing root morphology and distribution under drought stress

Drought stress and nutrient deficiency are two main factors that restrict the growth and yield of peanut (Arachis hypogaea L.) in arid and semi-arid regions. However, the effects of N fertilizer on root growth and pod yield of peanut under different water conditions are unclear. The growth, root morphology, and pod yield of peanut were studied under different water and N combinations. Two soil water treatments were tested: Well-watered (WW, 80%-85% field capacity) and drought stress conditions (DS, 55%-60% field capacity). Three N treatments were tested: no N application (NN), moderate N (MN, 90 kg ha(-1)), and high N (HN, 180 kg ha(-1)). Results showed that pod yield of peanut was limited by drought and N deficiency. Compared with NN, peanut shoot DM and pod yield were improved by MN under DS, with an average increase range of pod yield of 16.2% in the 2 yr. The annual average root length density (RLD) in the deeper soil layer (40-100 cm) was 5.5% higher under DS-MN than DS-NN treatment. The N use efficiency (NUE) was 12.3% higher wider WW than DS treatment, and the NUE of MN was significantly higher than that of HN under different water treatments. Root lengths in 40-60 and 60-80 cm soil layers were also positively correlated with pod yield (r = 0.66** and 0.47**, respectively) and NUE (r = 0.60* and 0.85**, respectively). In this study, root growth in deeper soil was improved by MN application under DS, thus increasing yield and NUE of DS conditions.