Potentials of chemical fertilizer reduction for wheat production in Hexi oasis irrigation area under long-term application of green manure

Objectives We studied the effects of decreasing different ratios of chemical fertilizer on yield stability of wheat, and the changes in soil fertility contribution to crop yield under long-term application of green manure, to provide a scientific basis for the efficient and sustainable development of wheat production in Hexi oasis irrigation area in Gansu Province of China.

Methods Field experiments were conducted consecutively for 12 years in Hexi oasis irrigation area from 2009 to 2020, the tested crop was spring wheat. The experimental treatments were composed of no fertilizer (CK), 100% chemical fertilizer (CF), and reducing the chemical fertilizer rate by 0%, 10%, 20%, 30%, 40%, and 100% respectively at the base of applying green manure 30000 kg/hm² per year. The cumulative yield, sustainable yield index (SYI) and its coefficient of variation (CV) were investigated. A grey linear model was used to quantitatively analyze the dynamics of yield and soil fertility contribution rate to yield under green manure application.

Results As the experiment progressed, the cumulative contribution rate of fertilizer to wheat yield exhibited an increasing trend under green manure application except for 100% reduction of fertilizer application, and there was no significant difference between treatments in the contribution rate of fertilizer to wheat yield, reaching about 60% in 2020. The cumulative soil fertility contribution rate of CK decreased from 57.41% in 2009 to 34.24% in 2020. Reducing less than 40% of chemical fertilizer did not decrease the average yield of entire 12 years, compared to 100% chemical fertilizer treatment (CF). However, higher chemical fertilizer reduction rate exhibited rising yield CVs and declining SYIs. The grey linear model revealed that the yield dynamics of chemical fertilizer reduction less than 40% was significantly higher than CF treatment. The 40% fertilizer reduction treatment recorded lower yield than CF from the ninth experimental year. Wheat yield (y) and chemical fertilizer reduction rate (x) had the regression relationship of y=−0.292x²+11.917x+6667.34, with the theoretical maximum yield at the reduction rate of 20.41%. The yield was mainly correlated positively with plant height, spike length, fertile spikelet number, and grain number per spike.

Conclusions On the basis of continuous application of green manure at 30000 kg/hm² per year, reducing 20%～30% of local chemical fertilizer input will increase wheat yield, enhance the yield stability, and the soil fertility contribution to yield, that will increase the chemical fertilizer efficiency and the sustainability of wheat production in Hexi oasis area of Gansu.