Effects Of Fertilizer Reduction Combined With Humic Acid Bio-fertilizer On Soil Characteristic And Growth Of Kidney Bean

Northeast black soil area is the largest commodity grain reserve base in China.However,the prolonged reclamation time and long-term mono-application of chemical fertilizers have deteriorated the soil quality in the area,the land productivity has decreased,and the contribution of chemical fertilizers to grain yield has been decreasing year by year.The development of an effective"Combination of use and nourishment"model has become an urgent bottleneck in agricultural production in the black soil areas of Northeast China.In this study,a two-year field trial was conducted on kidney beans with six treatments.The six treatments were:local conventional fertilizer application（CF）,fertilizer reduced by 20%（RF）,and fertilizer reduced by 20%with different amounts of humic acid bio-fertilizer 45.0 kg·hm^-2（RFH1）,67.5 kg·hm^-2（RFH2）,90.0kg·hm^-2（RFH3）,112.5 kg·hm^-2（RFH4）.To study the effects of chemical fertilizer reduction with humic acid bio-fertilizer on soil physicochemical properties,as well as plant nutrient uptake,carbon and nitrogen metabolism,antioxidant properties and yield composition were studied to clarify the effects of homemade humic acid bio-fertilizer on the restoration of degraded black soil areas and the growth of legume crops under maize-legume crop rotation system,and to provide reference for the conservation and utilization of arable land in black soil areas in China.The results of the study showed that:1.Fertilizer reduction with humic acid biofertilizer can reduce soil capacity,and at the same time promote the generation of soil water-stable large agglomerates,increase the proportion of soil large agglomerates with diameters of 5～2mm and 2～1mm,and improve soil physical structure.The mean weight diameter of soil aggregates in the RFH1 and RFH2 treatments in the 2021 and 2022trials was significantly increased by 26.0%and 12.3%,17.6%and 10.6%compared to the CF treatment.Soil capacity was reduced to 1.45 g·cm^-3 and 1.38 g·cm^-3,1.45 g·cm^-3 and 1.37 g·cm^-3.2.Fertilizer reduction with humic acid biofertilizer increased the relative abundance of the fungus Ascomycota and the bacteria Proteobacteria,which promoted the diversity of soil fungi and bacteria.Fertilizer reduction with humic acid biofertilizer improved soil enzyme activity to a certain extent,especially in the nutrient growth period.Soil alkaline phosphatase,sucrase,urease and protease activities were increased by 11.8%～34.6%,10.1%～48.4%,10.4%～14.7%and 13.7%～35.2%,respectively,in the treatment with humic acid bio-fertilizer compared with CF control.3.Fertilizer reduction with humic acid biofertilizer increases the nutrient supply of soil to some extent.The contents of soil alkaline nitrogen and effective phosphorus in RFH2 treatment in2021 were significantly increased by 10.1%～15.8%and 12.7%～25.3%,respectively,compared with CF treatment;the contents of soil alkaline nitrogen in RFH2 treatment in 2022 were significantly increased by 15.1%～21.1%compared with CF treatment.4.Fertilizer reduction with humic acid biofertilizer increased the accumulation of nitrogen,phosphorus and potassium in the plant and maintained the nutrient uptake capacity of the plant no less than the amount of conventional chemical fertilizer application.Plants in RFH2 treatment in2021 and 2022 showed significant increases in nitrogen content by 10.6%～18.9%and 9.3%～11.8%,phosphorus content by 16.0%～26.6%and 11.5%～16.8%,and potassium content by 13.8%～21.1%and 15.5%～19.7%,respectively,compared with CF treatment.5.Fertilizer reduction with humic acid biofertilizer had a more significant effect on photosynthetic carbon metabolism while enhancing plant carbon and nitrogen metabolism,and the plant carbon to nitrogen ratio increased.With the increase of humic acid biofertilizer dosage,the metabolic activity of the plants showed a parabolic pattern,with the peak occurring in the RFH3treatment,and the soluble sugar and soluble protein contents of the leaves significantly increased from 11.5%to 49.0%and 13.0%to 26.7%,respectively,in the two-year experiment compared with the CF treatment;the carbon to nitrogen ratio of the plants increased from 1.08 to 2.61 to 1.31 to3.07.6.Humic acid biofertilizer reduced the accumulation of reactive oxygen species by inducing the enhancement of superoxide dismutase and catalase activities in plants,and enhanced the peroxide-scavenging enzyme system and ascorbic acid-glutathione cycle activity,which in turn enhanced the scavenging of H₂O₂.The malondialdehyde content of RFH2 treatment was significantly reduced by 13.1%～40.7%and 20.2%～37.5%in 2021 and 2022,respectively,and the superoxide anion radical content was significantly reduced by 15.7%～32.9%and 14.2%～25.3%compared to CF treatment.7.Fertilizer reduction with humic acid biofertilizer promoted the growth and yield formation of kidney bean plants.The RFH2 treatment had the highest seed yield in both the 2021 and 2022trials and significantly increased by 32.8%and 52.4%compared to the RF treatment and 24.7%and21.5%compared to the CF treatment,respectively.Humic acid biofertilizer can improve the physical properties of soil,activate soil nutrients,promote the growth and nutrient uptake of kidney beans,enhance plant resistance and carbon and nitrogen metabolic activity,which in turn reduces the adverse effects of reduced chemical fertilizer application and improves the number of seedling retention and single plant yield formation capacity of the population.From a comprehensive analysis,the treatment of 20%reduction in conventional chemical fertilizer application with 67.5 kg·hm^-2 of humic acid bio-fertilizer（RFH2）could obtain better results.