Effects Of Four Crops On Soil Environment Under Two Different Nitrogen-adding Treatments

In order to explore the effects of cotton,sorghum,maize and soybean on soil nutrient,enzyme activity,humus and it's optical properties in soil-crop system,we used potted experiment and rhizosphere bag methods to find out the differences and study the mechanism of the rhizosphere environment.The following conclusions are drawn:?1?In the process of growth,the plant's root system will secrete a large number of low-molecular organic acids,releasing into the rhizosphere soil environment,enhancing soil acidity and lowering pH value.The rhizospHere soil's pH of high nitrogen crops is lower than that of low nitrogen.The pH of cotton roots is the lowest in four crops,the value is:5.30.Crops can effectively increase the content of organic matter in rhizosphere soils.Under the high nitrogen,the enrichment effect of rhizospHere organic matter was more remarkable,and the rhizospHere of cotton,sorghum,maize and soybeans were:3.9%,8.4%,17.7%and 6.2%respectively.The organic matter in the rhizospHere of maize is the highest of the other three crops.?2?Low nitrogen treatment level more suitable crops to the soil's ammonium nitrogen and available nitrogen accumulation.High nitrogen crops can cause the root of ammonium nitrogen to be absent?contrast to the bare soil?.The rhizospHere of low nitrogen corn,soybean and sorghum was higher than the bare soil of 8.31mg kg^-1and 7.6mg kg^-1,and the rhizospHere of low nitrogen sorghum was higher than that of non-rhizospHere:1.13mg kg^-1.The crop growth has a certain enrichment effect on the soil nitrate nitrogen,and the low nitrogen treatment of maize and soybean rhizospHere is higher than the non-rhizosphere of9.3mg kg^-1and 5.26mg kg^-1.The rhizospHere enrichment rate of high nitrogen cotton and maize was 56.5%and 16.1%.The rhizospHere alkali nitrogen's solution of low nitrogen cotton,maize and sorghum was 51.6%,68.3%and 60.9%,higher than that of non-rhizosphere,the presence enhancement effect of high nitrogen sorghum?rhizosphere higher than the non-rhizosphere 45.5%?,but the other three crops were not significant.The effect of crop growth on the rhizosphere enrichment of available pHospHorus was not significant,and the root deficiency was remarkable.?3?Crop growth inhibits catalase activity in soils,and the enzyme activity of the high nitrogen treatment lower than the nitrogen treatment.The effects of different crops and different nitrogen levels on soil urease activity,nitric nitrate reductase activity and nitrite reductase activity varied in rhizosphere.Overall,the activity of urease in low nitrogen treatment level is higher than that of high nitrogen treatment level,and the significant level of rhizosphere effect is higher than that of nitrogen.The RhizospHere urease activity of low nitrogen sorghum and soybean was 52.8%and 72.1%,higher than that of non-rhizosphere.The rhizospHere of high nitrogen corn and soybeans was 98.2%and 40.6%higher than that of non-rhizospHere.?4?Nitrate reductase activity in rhizosphere soils of low nitrogen cotton,sorghum and maize is 18%,31.4%and 8.7%higher than that of non-rhizosphere.Nitrate reductase activity in the rhizospHere soils of high nitrogen sorghum and maize was 30.7%and 16.2%higher than that of non-rhizosphere.In addition to cotton,the growth of three crops can increase the activity of nitrite reductase in the rhizosphere soil,low nitrogen sorghum,corn and soybean nitrate reductase activity is 12.8%,7.4%and 4.1%higher than that of non-rhizosphere respectively.The activity of nitrite reductase in the rhizosphere of high nitrogen sorghum and soybean was 7.5%and 4.5%higher than that of non-rhizosphere.The crop roots can release amylase directly,and the activity of amylase in potted soils of this study is significantly higher than that of bare soils.?5?The accumulation of humic substances in the rhizosphere of crops was remarkable in low nitrogen treatment,and the deficiency of humus under high nitrogen treatment was remarkable.The RhizospHere aggregation rate of low nitrogen cotton,sorghum and maize was 28.6%,30.4%and 3.7%.The root deficiency rate of high nitrogen cotton,sorghum,maize and soybean was:5.7%,16.7%,12.3%and 9.8%.Crop growth reduces soil HA/FA ratios.?6?The Humus optical properties of crops E465/E665 and?lgK are significantly greater than the rhizosphere.But the value of E265/E325 is different,low nitrogen cotton,maize and soybean rhizosphere are 1.6%,0.5%and 2.6%higher than the non-rhizosphere,and the difference between the rhizosphere and non-roots of sorghum is not significant.The rhizospHere E265/E325 of high nitrogen cotton,maize and sorghum were 3.1%,3.2%and0.5%higher than the non-rhizosphere,and the roots of soybean were 0.5%lower than the non-rhizospHere.?7?The effects of different plant growth on soil environment are not the same.High concentrations of nitrogen fertilizer are not necessarily conducive to the improvement of the soil environment.The results of this study showed that in more cases,the improvement of soil physicochemical properties,enzyme activity and other fertility factors in low nitrogen level were higher.