Response of grain yield and nitrogen utilization efficiency of spring wheat to green manure incorporation amount in oasis irrigation district

Objectives  Continuous cultivation of spring wheat causes excessive N fertilizer input and reduction in N fertilizer utilization efficiency in Hexi Oasis Irrigation Region. Green manure ( Vicia villosa Roth) could be incorporated into soil after wheat harvest to achieve a high-efficient N management system but the optimal amount of green manure incorporation is not known and requires investigation.

Methods  A field experiment was conducted from 2018 to 2020. The spring wheat was first cultivated with N 180 kg/hm² (N₁) and without N application (N₀). After the wheat harvest, green manure (Vicia villosa Roth) was incorporated into field at different rates i.e., no green manure (G₀, control), incorporation of 15000 kg/hm² (G₁), 30000 kg/hm² (G₂), and 45000 kg/hm² (G₃) green manure to the field at full blooming stage. N uptake, grain yield and N use efficiency of the wheat cultivated after green manure application were investigated.

Results  Green manure incorporation significantly increased aboveground N accumulation of spring wheat. Compared to N₁G_0, N accumulation of wheat in N₁G₁, N₁G₂, and N₁G₃ treatments increased by 8.7%‒9.3%, 15.3%‒16.6%, 11.9%‒12.3%. Compared to N₀G₀, N accumulation of wheat in N₀G₁, N₀G₂, and N₀G₃ increased by 3.3%‒4.0%, 4.6%‒5.6%, 5.9%‒8.4%. In the two years, N rate, green manure returning amount and their interaction effects significantly affected the translocation amount, translocation rate and contribution of nitrogen from leaves and stems to panicles. Among all green manure treatments, N₁G₂ treatment had the highest translocation and contribution value. Compared with N₁G₀, the N transfer amount of leaf-ear and stem-ear increased by 38.8%‒49.5% and 49.1%‒64.7%, the corresponding N transfer rate increased by 8.0%‒21.5% and 13.0%‒14.9%, and the contribution rate to grain increased by 11.0%‒26.0% and 25.6%‒31.3%, respectively. N₁G₂ treatment had the highest grain yield, N harvest index and N use efficiency. The fitting equation revealed that optimal nitrogen use efficiency could be obtained by incorporating green manure amount of 30000 kg/hm² into the field.

Conclusions  In arid oasis irrigation area, incorporation of green manure at the rate of 30000 kg/hm² combined with 180 kg/hm² N application can be used as an efficient management technique for increasing grain yield and N use efficiency of spring wheat.