Effect of nitrogen application on soil nitrogen absorption and transformation under supplementary irrigation of peanut

Rainfed agriculture is a mode of critical production which relies on natural rainfall in arid and semiarid regions. However, it causes crop yield instability due to frequent insufficient water supply at key growth stages of crops. Thus supplemental irrigation based on soil moisture has been widely adopted as an alternative water-saving irrigation method. To determine the effects of different nitrogen (N) application rates on nitrogen absorption and distribution, yield of peanut and soil nitrate accumulation under rainfed or supplementary irrigation conditions, a split plot experiment was conducted using the 'Baisha 1016' peanut variety with different N and irrigation managements in semiarid region of West Liaoning Province. The aim of the study was to explore suitable water and N managements and provide support for "modulate N with water" in peanut cultivation in semiarid regions. The irrigation treatments included W0 (rainfed condition) and W1 (supplemental irrigation based on soil moisture with the lower limit of soil water content of 55% of field capacity). The N treatments included N0no N, N140 kg(N)·hm^-2, N260 kg(N)·hm^-2 and N380 kg(N)·hm^-2. The results indicated that biomass and plant N uptake were highest under W1N2 treatment (supplemental irrigation at N application rate of 60 kg·hm^-2) among all treatments at maturity stage of peanut. The yield and nitrogen accumulation of peanut increased with increasing nitrogen, but decreased at N3 dose. N application rate, irrigation mode and their interactions significantly affected yield, water use efficiency (WUE), N use efficiency (NUE)including N agronomic efficiency (NAE), grain N recovery efficiency (GRE) and apparent N recovery efficiency (NRE), and N harvest index (NHI). Total plant pod N accumulation greatly increased due to the optimal distribution of N nutrient in peanut, and accelerated N transfer from leaf to kernel under W1 treatment. This created beneficial effects on increasing total plant pod N accumulation, peanut harvest index, agronomic N efficiency and yield. Compared with W0, W1 increased peanut NHI, NAE and NRE by 2.13%, 78.57% and 25.90%, respectively. Soil nitrate content was highest in the 0-20 cm soil layer after peanut harvest, but decreased with increasing soil depth. The accumulation of soil nitrate N at the 0-60 cm soil depth increased with increasing N application rate. However, supplementary irrigation accelerated the leaching loss of soil nitrate N. It was concluded that W1N2 treatment had the highest yield (6 485.03 kg·hm^-2), WUE (2.02 kg·m^-3) and irrigation WUE (10.21 kg·m^-3). It was therefore recommended as the best combination for water and N to improve peanut yield under drip irrigation with plastic film mulching in semi-arid regions in Western Liaoning Province.