| The fertile black soil in Northeast China is one of the main grain-producing regions in China.However,due to the continuous increasing fertilizer input in recent years,the organic matter layer has become thinner and soil degradation has been severe.The purpose of this study is to reduce chemical fertilizer input but maintain the yield,and at the same time to increase the fertility of black soil by applying organic fertilizer.These eight conventional physical and chemical indicators of the soil at each time point were analyzed,and the structure and the average weight diameter of the soil aggregates were characterized;then the activities of soil catalase,sucrose invertase,urease,nitrite reductase,nitrate reductase and nitrogen cycling-related functional genes copy numbers that represent the biological properties of the soil were determined.Finally,maize yield,nutrient element content of maize plants,nitrogen,phosphorus and potassium fertilizer use efficiency were analyzed to assess the bioorganic fertilizers for improving the balck soil fertility.The main findings are as follows:(1)In terms of soil physical and chemical indicators and physical structure,the application of bioorganic fertilizer can significantly improve soil nutrients,increase the available phosphorus,available potassium,the content of organic matter in the soil and increase the soil pH.At the end of the experiment,when the total nitrogen fertilizer input was reduced by 30%,the contents of soil total potassium and available potassium in the treatment with bio-organic fertilizer were significantly increased by 27%and 14%compared with single fertilizer application,respectively.Compared with the background soil and chemical fertilizer,the maximum pH of bioorganic fertilizer treatment was increased by 0.55 and 0.59 units,respectively,and the highest organic matter content was increased by 19%and 8%,respectively.These results showed that bioorganic fertilizer can improve the nutrient supply of the soil,and reducing the application of nitrogen fertilizer did not reduce the content of soil nutrient elements.At the same time,the application of bioorganic fertilizer and organic fertilizer can increase the proportion of high-quality large-and medium-sized aggregates in the soil and increase the average weight diameter(MWD)of the aggregates.Compared with the background soil and single application of fertilizer,the highest increase was 35%and 14%respectively,indicating that bioorganic fertilizer improved the stability of soil aggregate structure.(2)In terms of the biological characteristics of the soil,the enzyme activities were varied greatly between the different periods in the same treatments,but it can still be concluded that the bioorganic fertilizer improved the activities of the 5 soil enzymes and is generally follow the trend that bioorganic fertilizer is greater than organic fertilizer and single application chemical fertilizer.In the 2017 harvest season,compared with the single application of chemical fertilizers,the activities of urease,sucrose invertase,and nitrite reductase applied by bioorganic fertilizers were increased by 10%,41%,and 65%,respectively,the differences were significant;in the 2018 harvest season,the nitrite reductase and urease of bioorganic fertilizer treatments increased by 19%and 10%,respectively,compared with the single application of chemical fertilizers,and the differences were also significant.In terms of nitrogen cycling functional genes,the changes between different treatments are not clear.Except for the bacterial 16S Rrna gene,the copy number of genes is always higher in bioorganic fertilizer treatments than in other treatments.Bioorganic fertilizer treatment increased the copy number of specific genes in the soil in a specific period.In October 2017,the 16S rRNA gene copy number of bioorganic fertilizer treatment reached 1×1010.39,an increase of 0.47 orders of magnitude compared to NPK treatment.In May 2018,the copy number of the nifH gene in bioorganic fertilizer treatment reached 1×109.97,which was an increase of 0.96 orders of magnitude compared to NPK treatment.At the same time,it was also found that the sensitivity of bulk and rhizosphere soils response to fertilization treatment is different.Compared with bulk soil,rhizosphere soil is significantly affected by fertilization.In the rhizosphere soil in October 2018,the bioorganic fertilizer significantly increased the copy numbers of nifH,16S rRNA,and nirS genes compared to other treatments,reaching 4.26×1010,1.15×1012 and 2.49×106,respectively.In addition,whether it is bulk soil or rhizosphere soil,bioorganic fertilizer can increase the total number of bacteria,and single application of chemical fertilizer significantly reduced the total amount of bacteria in the soil,while increasing the copy of functional genes involved in denitrification in the rhizosphere soil,which showed that bioorganic fertilizer can promote the biochemical process of soil.(3)In terms of corn yield and the utilization rate of various fertilizers,compared with the conventional application of chemical fertilizers,the application of bioorganic fertilizer can significantly increase corn yield,the biomass index of the corn growth period,and the corn mature plants.Especially the content of nitrogen,phosphorus and potassium in the grain.In the 2018 harvest season,the output of bioorganic fertilizer treatment reached 13987kg/hm2,which was an increase of 21%and 62%compared to NPK and CK treatments,respectively.The application of bioorganic fertilizer can significantly improve the partial productivity and agronomic utilization efficiency of nitrogen,phosphorus and potassium fertilizers.The partial productivity of nitrogen,phosphorus and potassium fertilizers treated by bioorganic fertilizer in 2018 were 92.50(kg/kg),150.81(kg/kg)and 277.49(kg/kg)increased by 17%compared with NPK;the agronomic utilization efficiency of nitrogen,phosphorus and potassium treated by bioorganic fertilizer in the same year was 34.81(kg/kg),56.77(kg/kg)and 104.45(kg/kg)NPK,the ratio was increased by 61%.In addition,the partial productivity of nitrogen fertilizer in the three treatments involving fertilizer reduction was significantly higher than that in the three full-fertilization treatments.Finally,by calculating the correlation between each soil characteristic and nitrogen fertilizer utilization efficiency,the nitrogen fertilizer utilization efficiency and the current crop yield,the amount of bioorganic fertilizer input,and the average weight diameter of soil aggregates(MWD),soil pH,potassium element(TK&AK)It is positively correlated with the content of five kinds of enzymes in the available potassium,soil biological indicators,and AOA gene copy number,and negatively correlated with the total input of nitrogen fertilizer and the nitrogen content in the soil..This study analyzed the correlation between each soil characteristic and fertilizer utilization rate by charactering the conventional soil physical and chemical indicators,physical structure,soil biological indicators,crop yield and fertilizer utilization efficiency,and finally concluded that bioorganic fertilizer can be significantly improved soil nutrients,the soil physical structure,the soil biochemical process activities and the crop yields,improved the using efficiency of various fertilizers,and can effectively fertilize the black soil in the Northeast.However,reducing the application of nitrogen fertilizer on the basis of conventional fertilization has no obvious negative effect on the characteristics and yield of the soil,and it can also significantly increase the partial productivity of nitrogen fertilizer.At the same time,the input of chemical fertilizers has a better effect. |
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