氮肥形态对冬小麦根际土壤氮素生理群活性及无机氮含量的影响

采用大田盆栽方法研究了硝态氮肥、铵态氮肥、酰胺态氮肥3种氮肥形态对冬小麦品种豫麦50生育中后期(拔节期、开花期、花后14 d、花后28 d)根际土壤氮转化相关微生物活性、酶活性和根际土壤NH+4离子、NO-3离子含量的影响。结果表明:随着生育期的推进,除脲酶外,氨化细菌、硝化细菌、亚硝化细菌、反硝化细菌和蛋白酶活性变化的均为"倒V"型变化特征,以花后14 d活性最强;而脲酶活性在拔节期最强,并且其活性远大于其它微生物及酶。氮肥形态对根际土壤氮素生理群及无机氮的影响不同。酰胺态氮肥促进了根际氨化细菌、反硝化细菌、脲酶、蛋白酶的活性,而硝化细菌、亚硝化细菌在硝态氮肥条件下活性较强。除拔节期外,土壤中NH+4离子在铵态氮肥处理下含量较高,NO-3离子在酰氨态氮肥处理下含量较高。因此,酰胺态氮能够促进小麦根际土壤有机氮的分解,硝态氮肥可以促进土壤中氨的转化,以利于小麦根系的吸收与利用。氮肥形态主要是通过影响土壤中氮素生理类群及酶的活性,从而影响土壤中无机氮的含量。

Effects of nitrogen form on the activity of nitrogen bacteria group and inorganic nitrogen in rhizosphere soil of winter wheat

Fertilization with different forms of nitrogen is an important measure to regulate nitrogen metabolism of wheat(Triticum aestivum L.).Soil microorganisms and enzymes play significant roles in nutrient transformation and decomposition.Their activities may affect how different forms of nitrogen fertilizer influence nitrogen metabolism in wheat.To understand the effects of nitrogen form on soil nitrogen bacteria group and soil enzyme activity,pot experiments using the wheat cultivar ’Yumai 50’ were carried out in a sandy loam at the Experimental Farm of Henan Agricultural University in 2009 and 2010.The soil contained 14.29 g/kg organic matter,1.50 g/kg total N,16.9 mg/kg Olsen-P and 195.95 mg/kg NH4OAc-K.Each pot(30 cm diameter,38 cm tall) was filled with 20 kg of sieved dry soil.Nitrogen forms were NH-2-N as CO(NH2)2-N,NH+4-N as NH4HCO3,and NO-3-N as NaNO3.The nitrification inhibitor dicyandiamide was applied to each pot.Prior to sowing,each pot received 3.06 g N,2.9 g P2O5,and 3.3 g K2O;an additional 2.04 g N was also applied to each pot during the wheat elongation stage.Seven plants from each pot were selected when the plants had five leaves.The experiment was arranged in a completely randomized design with 15 replications,and all pots were managed in the same way.Rhizosphere soil samples from a depth of 5—20 cm for each treatment were taken at elongation stage(March 25),anthesis(April 30),14 days after anthesis(May 14),and 28 days after anthesis(May 28).Soil samples were put into sterile bags and transported to the lab as quickly as possible.Part of each soil sample was sieved through a 1 mm screen for analysis of(1) the activities of amination,nitrobacteria,nitrite bacteria,and denitrifying bacteria and(2) inorganic nitrogen(NH+4-N and NO-3-N) contents,and part was air-dried for(3) determination of soil enzyme(urease and protease) activities.This study showed that the activity of nitrogen bacteria group and enzymes in rhizosphere soils planted with wheat responded differently to nitrogen form.Overall,amination,nitrobacteria,nitrite bacteria,denitrifying bacteria,and protease activities graphed as inverted "V"-shapes that peaked 14 days after anthesis.Urease activity peaked at the jointing stage and was much higher than the activities of amination,nitrobacteria,nitrite bacteria,denitrifying bacteria,and proteases in all studied stages.The different nitrogen forms had different effects on soil nitrogen bacteria group,soil enzyme activity,and inorganic nitrogen.When CO(NH2)2-N was applied to Yumai 50,the activities of urease,protease,and amination in the rhizosphere soil increased substantially.The content of NH+4-N in the soil was highest when NH4HCO3 was applied,and the content of NO-3-N in the soil was highest when CO(NH2)2-N was provided.Therefore,CO(NH2)2-N could promote decomposition and the use of organic nitrogen,and the conversion of ammonia in the soil was promoted under NaNO3.Nitrogen form affected the content of organic nitrogen in the soil by affecting nitrogen bacteria and the activities of enzymes in the rhizosphere.