| [Object] The effect of different N and P fertilizer application rates on soil nutrient contents, maize growthand yield were investigated with a field experiment. Soil microbial biomass, enzyme activities, andmicrobial community functional diversity were also evaluated in this study. The objective is (1) to explorethe changes of soil nutrients, microbial community, and crop yield under different N and P fertilizerapplication rates;(2) to raise the input threshold of N and P fertilizer in maize land, and to provide a basisfor reasonable application of fertilizer.[Method] An field experiment was conduced in grey desert soil from2011to2013. The two partsexperiment were designed, the six application rates in N fertilizer experiment were set as0,225,300,375,450and600kg N/ha, which the local recommended N application rate was300kg/ha, and the P fertilizerapplication rate was75kg/ha. While the four application rates in P fertilizer experiment were set as0,75,150, and300kg P2O5/ha, which75kg/ha was the local P fertilizer application rate, and the N fertilizerapplication rate was300kg/ha.[Result](1) With the N fertilizer application rate increasing, the residual NO-3-N and NH+4-N contents in0-1msoil profile increased. Soil residual inorganic N showed a negative accumulation when the N applicationrate was less than225kg/ha, but accumulated significantly when N application rate was higher than300kg/ha.(2) The contents of Olsen-P, H2O-P, and CaCl2-P in soil decreased significantly under without Pfertilizer application condition. The content of Olsen-P was increased with P application rate increased. TheOlsen-P content of soil was keep balance when the P rate was75kg P2O5/hm2, but accumulatedsignificantly when the P rate was higher than150kg P2O5/hm2. There was the exponential relationshipbetween H2O-P and CaCl2-P contents and P application rate. The content of H2O-P was no significantchange when the P rate was less than150kg/ha, but increased markedly in P150and P300treatments.(3) The content of Ca2-P, Ca8-P and Fe-P were promoted significantly by the phosphorus rates andyears of applying P fertilizer, while the content of Al-P had small increase in the third year, O-P and Ca10-Phad no significantly change. And the content of Ca10-P and O-P had no significant correlation with othervarious forms of inorganic phosphorus. The correlation of the various forms of inorganic phosphorus foravailable P in the order is: Ca2-P> Ca8-P> Fe-P> Al-P> Ca10-P, O-P.(4) Soil microbial number, biomass and enzyme activity were significantly increased by applyingnitrogen fertilizer reasonably when the N rate were0to300kg N/ha. When the N rate was higher than300kg/ha, the urease activities significantly discreased, soil microbial biomass P and alkaline phosphataseactivities had no significant change; when the N rate was higher than375kg/ha, the number of bacteria,actinomycetes and fungi discreased significantly, soil microbial biomass C and N had no significant change;while the invertase activities was highest at the N rate450kg/ha. The AWCD value of soil microbialcommunity expressed that N225, N0>N600, N450>N375, N300.(5) The number of bacteria and fungi, microbial biomass N enhanced significantly with P applicationrate increased when the P rate were0to300kg/ha. The number of actinomycetes, microbial biomass C andP were discreased significantly，the invertase and alkaline phosphatase activities had no significantincreased when the P application rate was higher than150kg/ha. The AWCD value of soil microbialcommunity showed that P0, P300>P150, P75under P fertilizer treatment.(6) Dry matter weight, nutrients uptake, and yield of maize were promoted when the N fertilizerapplication rate were300-375kg/ha, but N uptake and N use efficiency of maize were reduced when the Nfertilizer application rate was higher than375kg N/ha. There were significantly parabolic relationshipbetween maize yield and soil inorganic N accumulation. When the soil inorganic N was no accumulation after maize harvest, maize yield was significantly lower than the maximum yield. After reaching themaximum yield of maize, soil inorganic N was accumulated significantly. Therefore, N fertilizerapplication rate at270-340kg/ha is a reasonable investment threshold in the study area, not only get highermaize yield and fertilizer use efficiency, but also reduce N source pollution risk.（7）The N and P accumulation of maize plant were increased with P application rate increased, and theN transportation to grain was significantly promoted by P application. The highest dry matter weight andyeild of maize were found in the150kg P2O5/ha treatment. But the growth and yield of maize werediscreased when the P fertilizer application was higher than150kg P2O5/ha. P fertilizer application rate at98-145kg/ha is a reasonable investment threshold in the study area, not only get higher maize yield andfertilizer use efficiency, but also reduce phosphorus source pollution.[Conclusion]Applying nitrogen fertilizer (300~375kg N/ha) could improve the soil microbial number, biomass andenzyme activities, and enhance the nutrient absorption of maize, increase the yield of maize, significantly.The soil inorganic nitrogen was kept balance at N rate260kg/ha. When the N fertilizer application rate washigher than300kg/ha, soil urease activities discreased significantly, soil microbial biomass P and alkalinephosphatase activities had no significant change, the accumulation of soil inorganic nitrogen increasedsignificantly, the yield of maize had no significantly increased and the nitrogen fertilizer using efficiencydiscreased. The soil microbial number, microbial biomass N, the invertase and alkaline phosphataseactivities enhanced significantly with P application rate increased. The soil available P was kept balance atP2O5rate75kg/ha. The soil water soluble were increased when the P2O5rate was96to99kg/ha. The soilavailable P was significant accumulation when the P2O5rate was150kg/ha. The optimum input thresholdof nitrogen and phosphorous fertilizer for the maize yield in study area were270~340kg/ha and98-145kg/ha, respectively. |
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