Improvement of soil nutrient availability and enzyme activities in rainfed wheat field by combined application of organic and inorganic fertilizers

Objectives Combined application of organic and inorganic fertilizers can significantly improve soil microbial activity and improve soil nutrient supply. In order to give full play to the fertilizer benefits and achieve high and stable yields of winter wheat, it is necessary to understand the biochemical characteristics of soil under different nitrogen (N) application rates combined with application of organic fertilizer.

Methods Field positioning experiments were conducted for three consecutive years on winter wheat in a semi-humid and drought-prone areas of the southern Loess Plateau. Different N application rates (N 0, 75, 150, 225, 300 kg/hm²) combined with organic manure (0 and 30 t/hm²) were set up by split plot experiment. In jointing stage, heading stage, filling stage and maturity stage of winter wheat, 0−20 cm soil samples were taken to determine soil nutrients and enzyme activities by using conventional methods. During the harvest period, the grain yield of winter wheat was investigated.

Results 1) The highest yield of winter wheat was obtained when 150 kg/hm² of N rate was combined with organic fertilizer (N150 + M), and compared to the chemical N fertilizer application, organic and inorganic fertilizer application could ensure the stable yield and high yield of winter wheat when the N fertilizer rate was reduced by 19.1%, in addition, under the unsatisfactory weather conditions, the net income of winter wheat could also be maintained at a relatively stable and high level. 2) During the whole growth period of winter wheat, the combined application of organic and inorganic fertilizers significantly increased soil organic matter, total N, available P, readily available K, NO₃⁻-N content, and the activities of sucrase, alkaline phosphatase and urease in 0−20 cm soil layer by a mean of 18.2%, 27.4%, 149%, 31.4%, 27.6%, 4.0%, 4.7%, 1.5%, respectively, compared with that without manure, while it had no significant effect on catalase activity. Except the highest value of urease activity occurring in the N300 + M (the combination of manure with N 300 kg/hm²) treatment, the other indicators were the best treated with the N150 + M (the combination of manure with N 150 kg/hm²) treatment. 3) N application, organic fertilizer and growth period of winter wheat significantly affected soil invertase, alkaline phosphatase, catalase and urease activities, the interaction between N application rate and organic fertilizer significantly affected alkaline phosphatase activity, the interaction between N application rate and growth period of winter wheat significantly affected soil invertase, alkaline phosphatase and catalase activities, the interaction effect of organic fertilizer and winter wheat growth period significantly affected soil alkaline phosphatase and catalase activities, and the interaction effect of N application rate, organic fertilizer and winter wheat growth period significantly affected soil invertase activity. 4) There was no significant correlation between soil alkaline phosphatase and organic matter, urease and readily available potassium. The activities of soil invertase, alkaline phosphatase, catalase, and urease were all positively correlated with soil organic matter, total N, available P and readily available K.

Conclusions Soil nutrients, enzyme activities and winter wheat yields were closely related. The combined application of manure with chemical N 150 kg/hm² is recommended for enhancing sustainability of ecosystem of winter wheat field in the semi-humid and drought-prone areas of the southern Loess Plateau.