Effects of irrigation and nitrogen interaction on soil NO₃^－-N transport, nitrogen use efficiency and water use efficiency in wheat

To provide theoretical basis for the culture of strong gluten wheat (Triticum aeativum L.), the effects of irrigation and nitrogen interaction on water consumption, soil NO3-–N transport, nitrogen use efficiency and water use efficiency were studied using winter wheat cultivar Jimai 20 which had high grain yield and high process quality. Three nitrogen fertilization levels ( N 0 kg/ha (N0), N 180 kg /ha (N1) and N 240 (N1) kg/ha), and four irrigation treatments W0 (no irrigation), W1 (irrigation before sowing, at jointing and at anthesis stage), W2 (irrigation before sowing, before winter, at jointing stage and at anthesis) and W3 (irrigation before sowing, before winter, at jointing stage, at anthesis and during grain filling), with 60 mm water each time) were adapted. The results were as follows. (1)Soil NO3-–N content in 0–140 cm soil layers at anthesis and maturity was increased with the increase of N fertilizer rate. At the same N fertilizer rate, increasing irrigation rate reduced soil NO3-–N content in 0–80 cm soil layers and increased that in 120–140 cm soil layers at maturity. The treatment N1W1 promoted wheat plant uptake N and resulted in a reasonable soil NO3-–N content within 0–80cm soil layer and 100–140 cm soil layer respectively, at maturity. (2) With the increasing of N fertilizer, the grain yield increased first then decreased. Treatment N1 had the highest grain yield in the end. Under the N level of N1, W1 had higher grain yield, higher grain N absorption, higher N use efficiency, higher agronomic efficiency of N fertilizer and higher N partial factor productivity. However, no significant differences between these index were found under W2 level, (3) Nitrogen application promoted the utilization of soil water. With the increase of N fertilizer rate, the soil water consumption and the ratio of it to total water consumption significantly increased. Under the N1 level, W1 had the highest water use efficiency (WUE). Additional water supply reduced WUE significantly and enhanced water consumption index from the blooming stage to maturity. Under the experiment station, the treatment N1W1 ( N 180 kg per ha and 3 times irrigation (before sowing, at jointing stage and at anthesis) was recommended due to its high grain yield, high process quality and high NUE and WUE.