半干旱农田生态系统作物根系和施肥对土壤微生物体氮的影响

Effects of crop root and fertilizer on soil microbial biomass nitrogen in semiarid farmland ecological system

盆栽和大田试验表明,作物根系显著影响土壤微生物体氮的含量。在田间试验条件下,根际土壤微生物体氮比非根际土壤平均高出N54 7μg/g;盆栽试验中,根际土壤微生物体氮平均含量为N77 1±13 6μg/g,而非根际土壤为N65 2±17 0μg/g,差异达显著水平,根际微生物体氮含量为非际根际土壤的1 10～2 04倍。施肥能明显增加土壤微生物体氮含量,但影响程度因肥料种类而不同。秸秆和富含有机物质的厩肥对土壤微生物体氮的影响远大于化学肥料,而且土壤微生物体氮含量随秸秆施用量增加而增加。在红油土上进行的20年长期田间定位试验结果表明,对不施肥和施氮磷处理,0—20cm土层的微生物体氮分别是N102 2和110 4μg/g;在施氮磷的基础上,每公顷配施新鲜玉米秸秆9375kg、18750kg、37500kg和厩肥37500kg时,相应土层微生物体氮分别是N147 5、163 2、286 4和265 3μg/g。培养条件下,当有效能源物质缺乏时,微生物对NH+4-N的同化固定能力远大于NO-3-N,但在加入有效能源物质葡萄糖后,微生物对2种形态氮的固定量大幅度增加,且对2种形态氮的固定量趋于一致。

The pot and field experiments were conducted to study the effects of root and fertilization on soil microbial biomass nitrogenin semi-arid farmland. The result showed that fertilization and crop root increased obviously the soil (microbial) biomass nitrogen amounts, the microbial biomass nitrogen in rhizosphere soil being as high as 1.10—2.04 times as that in non-rhizosphere soil indicated that roots played a great role in increasing its amounts. Different fertilizer or (manure) had different impacts, the effects of straw and manure with rich organic material on soil microbial biomass were (larger) than chemical fertilizer, and the soil microbial biomass nitrogen amount raised with increase of straw application rate. A long-term experiment conducted on a manual loessial soil showed that without fertilizers, the microbial biomass nitrogen at 0—20cm depth was N 102.2μg/g, and N 110.4μg/g with application of both N and P fertilizers, whereas addition of 9375kg, 18750kg, 37500kg fresh maize straw and 37500kg of organic manure per hectare in a year on the (basis) of applying N and P fertilizers raised the microbial biomass nitrogen to N 147.5, 163.2, 286.4 and 265.3μg/g, respectively. Adding organic manures or crop residues provided energy source for soil microorganisms, thereby stimulated their reproduction and growth. Applying chemical fertilizers increased the growth of shoots and roots of crops, therefore increased the organic materials in soil and the microbial biomass nitrogen also raised accordingly. The incubation experiment showed that the ability of fixation of ammonium nitrogen into microbial biomass was much higher than that of nitrate nitrogen but in case the available energy material such as glucose was applied the nitrogen immobilized by microorganisms from the 2 forms of mineral nitrogen increased in a large scale, meanwhile, the fixed amounts were almost similar.