Zhoukou is located in the southeast of Henan Province, China, which is the core area of grain production. Lime concretion black soil is one of the main low-yield soil types in this region, which has the characteristics of heavy clay, compact soil layer, poor aeration and low organic matter content, so it is urgent to carry out the task of improving the soil fertility. Biogas slurry contains a variety of nutrients, which can improve soil physical and chemical properties, increase soil enzyme activity, improve crop biological properties and promote crop growth.
In this study, we systematically analyzed the effects of different proportions of combined application of biogas slurry and chemical fertilizer on the physicochemical properties and enzyme activities of different soil layers in the of lime concretion black soil of the Huang-Huai-Hai Plain, as well as the effects on the growth and development of winter wheat, and determined the appropriate amount of biogas slurry suitable for Zhoukou area, so as to provide a scientific basis for the improvement of the soil of the of lime concretion black soil, and provide a reference for the application of biogas slurry in Ukraine, the improvement of soil texture and the realization of sustainable agricultural development.
There were significant differences between different soil layers, and between each treatment and CK (сontrol). After adding biogas slurry, the soil bulk density was significantly reduced, especially BS50 (50 % nitrogen from biogas slurry and 50 % nitrogen from fertilizer during winter wheat planting) soil bulk density was the smallest, and it was within the suitable bulk density range for winter wheat, which was conducive to the growth and development of winter wheat and the increase in yield. Long-term application of chemical fertilizer significantly decreased the number of large aggregates and increased the number of small aggregates, and application of biogas slurry was beneficial to increase the aggregates with diameter more than 2 mm. The stability of soil aggregates varies in different soil layers and under different treatment conditions. Biogas slurry treatment is beneficial to increase the MWD (mean weight diameter) of 0-10 cm, 10-20 cm, 20-40 cm force-stable aggregates and waterstable aggregates, with BS50 being the largest. The size order of MWD of force-stable aggregates and MWD of water-stable aggregates in the vertical direction is 0-10 cm>10-20 cm>20-40 cm, and both decrease with the increase of soil depth. The combined application of chemical fertilizers and biogas slurry made the MWD of force-stable and water-stable aggregates significantly higher than those of other treatments, increasing the stability and agglomeration of the soil. In the 0-10 cm soil layer, BS50 has the smallest percentage of aggregate destruction (PAD) value of 36.52, which is 45.0 % and 46.74 % lower than CK and CF respectively. The single application of chemical fertilizer CF will make the stability of soil aggregates worse and destroy the aggregation of aggregates; while the combined application of organic fertilizer and chemical fertilizer will reduce the degree of damage to aggregates and facilitate the aggregation of aggregates. Reasonable fertilizer application, especially the BS50 treatment of biogas slurry and chemical fertilizers, has positive significance in maintaining the stability of soil aggregates and improving soil quality.
CF treatment can reduce pH, and application of biogas slurry can increase pH. The application of biogas slurry in agricultural planting can significantly increase the nitrogen content of the soil, thereby satisfying the absorption of nutrients by crops. In 0-10 cm, 10-20 cm, and 20-40 cm, the total nitrogen content is highest by the BS50 treatment. The application of biogas slurry could improve the supply level of soil available phosphorus, but increasing the proportion of biogas suspension to BS75, B100 leads to a decrease in phosphorus content. In different soil layers, the available potassium content of BS50 treatment combined with biogas slurry and chemical fertilizer was the highest. The soil organic matter content increased with the increase of biogas slurry. In 0-10cm, 10-20 cm and 20-40 cm soil layers, the soil organic matter content was in such order as BS100>BS75>BS50>BS25>CF>CK. Also, the use of biogas suspension increased the activity of sucrose, urease, phosphatase, and catalase in the soil.
The yield ofwinter wheat with BS50 treatment was the highest, compared with CF, BS25, BS75 and BS100, the increases were 30.79 %,13.61 %, 4.31 % and 34.06 %, respectively. BS50 is the optimal combination of biogas slurry and chemical fertilizer, which can well match the nutrient demand of winter wheat at different growth and development stages, ensure the continuous supply of nutrients, promote winter wheat nutrient growth and nutrient accumulation, and achieve the best level of winter wheat yield.
