尿素施用量对小麦根际土壤微生物数量及土壤酶活性的影响

在大田高产条件下，研究了不同尿素施用量下两种不同穗型小麦品种“兰考矮早8”和“豫麦49—198”根际微生物数量和土壤酶活性的变化。结果表明：微生物数量随小麦生育时期的进行呈规律性变化，其中微生物总量在拔节期和抽穗期时数量较多。尿素施用量对小麦根际微生物数量和酶活性均产生一定的影响，并且处理间差异达到显著水平。两个小麦品种根际微生物总量、细菌、放线菌、真菌数量随着尿素施用量的增加呈先上升后下降的趋势，但两个品种根际微生物数量最高时的尿素量略有差异。同一生育时期，随着尿素施用量的提高，土壤蛋白酶、过氧化氢酶呈先增加后降低的变化趋势，以他（391kg／hm^2）或T3（586kg／hm^2）处理的酶活性较高，T4（782kg／hm^2）处理的酶活性略有降低；脲酶活性则呈上升趋势，以T4（782kg／hm^2）处理的脲酶活性最大。表明适宜尿素施用量有益于小麦根际微生物数量和酶活性的提高，过高则微生物数量和酶活性下降。

Effects of urea application rate on the quantity of microorganisms and activity of enzymes in wheat rhizosphere

Application of nitrogen(N)fertilizer is one of the best ways to increase winter wheat(Triticum aestivum L.)grain yield and quality.However,incorrect application of N fertilizer,especially excessive N application,has been raising serious environmental and economic problems.Urea is the most popular N fertilizer used for wheat in China.In order to investigate the effects of urea application rate on the quantity and activity of soil microbes and enzymes in high-yielding wheat fields,split plot experimental designs with three replications were conducted at the Experimental Station of Henan Agricultural University,Zhengzhou,Henan,with different N treatments for two years.Two wheat cultivars,Lankaoaizao8 and Yumai49-198,and four urea treatments,T1,T2,T3 and T4,were used.T1,T2,T3 and T4 received 0,391,586 kg/hm2 and 782 kg/hm2 urea,respectively.The urea rates in T2,T3 and T4 were split with 50% of the total amount at presowing and the remaining 50% at jointing stage.Plots were 3 m wide and 7 m long.Each treatment received same amount of P(P2O5,150 kg/hm2)and K(K2O,150 kg/hm2)before sowing.Soil in the 020 cm rhizosphere was sampled for each treatment at turning greening stage,jointing stage,heading stage and inflorescence,respectively.All the soil close to the wheat root in 020 cm depths were mixed to make one sample and placed in plastic bag,then transported to the laboratory for subsequent analysis.A part of each soil sample was sifted with a 1-mm sieve for the analysis of microbial quantity,the rest was air-dried for the determination of soil enzyme activity.Results showed that the total numbers of microbes reached the maximum value at jointing and heading stage,and the urea application rate had significant effect on the quantity of microorganisms and activity of enzymes in wheat field.Significant differences among urea treatments were observed as well.Change of microorganisms population in rhizosphere soil of both cultivars showed a single-peaked curve with the increase of urea application rate.The maximum population of microbes in rhizosphere soil was recorded with T2 in Yumai49198 and with T3 in Lankaoaizao8.At all growth stages,the enzyme activity of protease and catalase increased with applied urea rate until 586 kg/hm2.Larger amounts of urea decreased their activities.Urease activity increased with increasing urea rate and maximum activity was observed with T4.The results suggested that optimal urea application rate would lead to increase the quantity and activity of microbes and enzymes activity in soil.