Productivity and soil nutrient evolution under long-term conventional fertilization in irrigation silting soils

Objectives Irrigation silting soil is an important soil type for grain and economical crop production in the northwest region of China. Studying the yield and soil fertility evolvement under long-term fertilization will provide reference for choosing proper strategy to improve soil fertility and high yields.

Methods Seven national farmland quality monitoring field were established in typical irrigation silting soil regions during 1988−2004, four of them located at Yinchuan, Wuzhong and Shizuishan regions in Ningxia, and the other three located at Hetian region in Xinjiang Autonomous Region. The yield data were collected, and the yield variation coefficients and sustainability yield index were calculated. The soil total N, available P and available K contents were collected, and the soil fertility contribution index to the yields of wheat, maize and rice were calculated. The relationship between yield increment and soil nutrient contents were also calculated.

Results After the long-term conventional fertilization, the wheat yield showed an increasing trend over time, reaching the highest point (7.58 t/hm²) at 2004, and then remained stable. The wheat yield in 2016 was about 2 times higher than the initial year. There has been an increasing trend of maize production over time, with an average production of 9.8 t/hm² in 2016, which is about twice of the initial year. As the relative short years for rice production, the rice yield was not significantly changed. Compared with no fertilization, conventional fertilization increased the average yields of wheat, maize and rice by 3.43, 3.20 and 1.21 times, respectively, and the sustainability of yield index by 18.8%, 148% and 13.9%, respectively. The fertility contribution index of wheat and maize were consistent during the years, with a slight downward trend, while that of rice was increased at an annual rate of 0.0125. The total soil N content was increased from 0.4 g/kg to 1.1 g/kg, and the contents of available P and K changed little over 28 years. The increment of wheat and maize yield was linearly positive correlated with soil total nitrogen contents. The average nitrogen fertilizer agronomy efficiency of wheat, maize and rice were 9.8, 16.8 and 27.4 kg/kg respectively.

Conclusions Conventional application of chemical fertilizers (mainly nitrogen fertilizer) has effectively increased the yield of maize, wheat and rice, but the increasing intensity showed decreasing with time. The soil total nitrogen content is increasing, and available P and K contents are stable at irrigation silting soil. Therefore, reasonable nitrogen fertilizer is still the most important and necessary for keeping stable and high crop yields, and soil fertility is also need to be improved for efficient crop production in irrigation silting soils in the Northwest of China.