连续施用氮肥对旱地土壤氮素状况的影响

Effect of continuously applying nitrogen fertilizer on the nitrogen in dryland soil

在半湿润易旱地区红垆土上进行的大田试验表明，连续施用氮肥显著影响硝态氮在土层中的残留累积、０～２０ ｃｍ 土层微生物体氮和矿物固定态氮。当每作施氮量达到１１２５ ｋｇ／ｈｍ ２ 时，则发生残留硝态氮的累积，并随施氮量增加，残留量增加，当每作施氮量低于 ７５０ ｋｇ Ｎ／ｈｍ ２ 时，不会出现硝态氮的残留累积。补充灌水后，作物产量、吸氮量和氮肥利用率提高，则累积的残留硝态氮显著下降。微生物体氮和施氮水平及作物产量之间的关系：施肥加灌水，作物地上、地下部分生长量增加，土壤中作物残体增加，能源物质充分，微生物体氮相应增加。施肥和灌水对矿物固定态氮的影响与对残留硝态氮和微生物体氮的影响不同，与试验开始时相比，不施氮，矿物固定态氮显著下降，施氮后却保持着试验开始时的水平，表明施用氮肥对维持土壤矿物固定态氮库的稳定具有重要意义。

Field trials conducted on Honglou soil in subhumid area prone to drought show that continuous N fertilization effected significantly nitrate nitrogen accumulation, microbial biomass N (MBN) and mineral fixed N (MFN) in soil. The effects on nitrate accumulation and MBN content depended on N fertilizer rate and crop yields. NO - 3 accumulating occured when N fertilizer reached at 112.5 kg/hm 2 and increased with N fertilizer rate rised. When 7.5 kg or less N per hectare were applied, no NO - 3 accumulated. Crop yield, N uptake and N fertilizer use efficiency increased while the amount of residual nitrate in soils reduced under irrigation. MBN had correlation positively with N rate and crop production. MBN content in soils increased because of a plenty of energy material resulting from the increase of crop residue in soils. This occurred when crop biomass of abovergroud part and root rised after fertilizer and water were applied. The effects of fertilizer and water supply on MFN were different from that of residual NO - 3 and MBN. MFN in no fertilized soils declined remarkably while in fertilized soils maintained at the level when the trial started. It indicated that N fertilization played an important role in stablizing MFN pool of soils.