Biological Regulation Of Nitrogen Uptake And Growth Of Maize In Acid Soil Of Southern Henan Province

Soil acidification is one of the important factors threatening China’s agricultural production.Soil acidification affects soil physical and chemical properties,reduces soil quality,and then affects plant nutrient utilization and crop growth.Soil organisms are important parts of soil ecosystem,and play an important role in improving degraded soil physical and chemical properties and promoting plant nutrient absorption and growth.In this study,pot experiments were conducted to explore the mechanism of nitrogen over-fertilization accelerating soil acidification and its effect on crop growth in central and southern Henan.Field experiments were conducted to explore the synergistic improvement effect of earthworms and mycorrhizal fungi interaction on maize growth in acidic farmland.The results showed that: 1.In acidic soil,there were different effects of nitrogen fertilizer application on soil acidity with or without maize planting,and the coexist of maize planting and nitrogen over-fertilization（ammonium chloride）had the greatest impact on soil acidification.There was no significant change of soil pH in all nitrogen fertilizer treatments without maize planting;with maize planting,soil pH decreased with the increase of nitrogen fertilizer application rate by 0.26-0.64 units,and the lowest soil pH was in 1.5-fold recommend N fertilizer application amount（1.5N）.With or without maize planting,1.5N treatment significantly reduced soil CEC,increased soil water-soluble K⁺,Ca²⁺ and Mg²⁺ contents,indicating that nitrogen over-fertilization would reduce soil buffering capacity and accelerate the loss of soil nutrients such as K⁺,Ca²⁺ and Mg²⁺.The activities of soil urease,dehydrogenase,cellulase and acid phosphatase were significantly increased by applying nitrogen fertilizer to maize.Treatment 1.5N and NX significantly reduced maize biomass and nitrogen use efficiency.Compared with CK,the aboveground biomass,root biomass and nitrogen use efficiency decreased by 24.3%,56.6% and48.9%,respectively.Excessive nitrogen application decreased the absorption of K,Ca,Mg and other elements beneficial to maize growth,but increased the absorption of Al and Fe which may be toxic to plants.2.In acid farmland,earthworms,mycorrhizal fungi or their combined inoculation can significantly increase the biomass and yield of maize.Compared with the controls,earthworms,mycorrhizal fungi and the cooperation of earthworms and mycorrhizal fungi increased maize yield by 28.7%,15.7% and 22.8% in mild acidic farmland respectively,and by25.3%,12.6% and 11.6% in severe acid farmland,respectively.In acid farmland,the interaction of earthworm and mycorrhiza significantly increased the contents of nitrogen,phosphorus,potassium,sodium and magnesium ions in maize shoot,and increased the maize biomass and yield.Earthworms and mycorrhizal fungi decreased the soil pH value of mild acid soil in varying degrees,but had no significant effect on the soil pH value of severe acid soil.Earthworms,mycorrhizal fungi and their cooperation could significantly increase the content of ammonium nitrogen in acid farmland soil,and significantly increase the nitrification rate of severe acid soil at silking stage and mature stage.In the mature stage,earthworm and mycorrhiza significantly increased soil microbial biomass nitrogen and soil microbial biomass phosphorus.Earthworm and mycorrhizal fungi significantly increased the activity of acid phosphatase in the whole growing season,and increased the urease activity at the jointing and silking stages.In a word,this study found that maize planting and excessive application of nitrogen（ammonium chloride）can accelerate soil acidification and nutrients loss,decrease plant N use efficiency,inhibit crop nutrient absorption（K,Ca,Mg）and growth;earthworm and mycorrhizal fungi can synergistically increase soil microbial biomass,soil enzyme activity,promote nutrient absorption of maize aboveground,and then improve maize yield in acidic farmland.