土壤硝态氮时空变异与土壤氮素表观盈亏研究Ⅰ.冬小麦

Studies on the spatio-temporal variations of soil NO_3^--N and apparent budget of soil nitrogen Ⅰ. Winter wheat

不同氮肥用量下对冬小麦生育期间土壤硝态氮时空变化特征及土壤氮素表观盈亏量的研究结果表明 ,氮肥用量不同 ,硝态氮分布特征有差异 ,并且随着冬小麦的生长 ,其变化也不同。在冬小麦快速生长阶段 ,作物吸收可在一定深度的土层出现硝态氮亏缺区。由于灌溉的影响 ,土壤表层硝态氮向深层淋洗严重 ,即使在低氮肥水平 ,土壤深层仍可观察到硝态氮含量升高现象 ,存在淋出 2 m土体的可能性。并且氮肥用量越高 ,土壤硝态氮含量越高 ,硝酸盐向深层淋洗也越严重 ,淋出 2 m土体的可能性和数量也相应增大 ;在冬小麦生长前期 (播种～拔节 ) ,即使在不施氮肥处理也有土壤氮素的表观盈余 ,随着施肥量的增加 ,在拔节～扬花也出现土壤氮素表观盈余 ,而扬花后各个氮肥处理均出现土壤氮素的表观亏缺。氮肥用量越高 ,小麦一生中土壤表观氮盈余量越大 ,1 m土体内平均最大盈余量达 1 99.8kg N/ hm2。研究表明 ,土壤氮损失是盈余氮素的一个主要去向 。

Nitrogen fertilization is a key factor of improving crop yield and quality, yet it is also a dangerous source of water and air pollution. In field ecological system, the negative effects to environment coming from the Nitrogen fertilizer (Nf) application in maize, rice and vegetable are paid close attention, but in wheat rarely taken into account. In order to find out the effects of Nf to environment and improve Nf use efficiency in winter wheat, the spatio\|temporal variations of soil NO - 3\|N and apparent budget of soil N were studied in high\|yield condition. A 2 year field trail was conducted at Wuqiao Research Station, Wuqiao county, Hebei Province in 1997～1999. Because of the identical trend in the 2 year' results and the limit of paper space, only the result in 1998～1999 was discussed here. The experiment was laid out in a split plot design, 5 doses of nitrogen were in the main plot and 6 genotypes were represented in the subplot with three replications. The 5 doses of nitrogen was 0, 90, 180, 270 or 360kg/hm 2, and the 6 genotypes was 915091 (early maturity, moderate spike), Hengshui 4041 (medium maturity, multi ear), 95021 (medium maturity, moderate spike), 6029 (medium maturity, big spike), Shannong 45 (medium maturity, moderate spike) and Taishan 021 (late maturity, big spike). The soil texture is a salted light loam soil but which turns clammy at deeper layer (about 130～170cm) and is a fine sandy loam soil at the layer of 170～200cm depth. Nf was divided as 2 split applications (50% basal + 50% at elongation stage, by broadcasting). The basal was applied together with 138kg P 2O 5/hm 2, 108 5kg K 2O/hm 2, 30kg ZnSO 4/hm 2 before ploughing. During the life winter wheat was given 3 irrigations (at re greening stage, elongation stage and 12d after flowering) except the 1 irrigation before ploughing. Soil samples were obtained from all plots at 4 growth stages [sowing, elongation(before fertilization), flowering and harvest] in 20cm increments to a depth of 100cm, but in genotype 915091, 95021 and Tai shan 021 the samples of 200cm depth were taken at 3 growth stages(sowing, flowering and harvest ) and it was divided as three layers from 100cm to 200cm(100～130cm, 130～160cm and 160～200cm). Mixing samples of multi boring per plot were taken with a soil auger and the sample was frozen immediately. The determination steps of soil mineral N (i.e. N min , including NO - 3 N and NH + 4 N) as follows: defrosted→mixed the sample fully and then sifted it with a 2mm sieve→10g of each sample were extracted with 0 1L of 0 01mol/L CaCl 2 on a horizontal shaker for 0 5 hour→filtered→N min were determined using an auto analyzer (TRAACS 2000). At the same time soil water content of each sample was determined, too. Plant samples were taken three times (at elongation, flowering and harvest stage). All the samples were killed at 105℃ for 0 5 hour and dried at 70℃. Total plant N was analyzed by the Kjeldahl digestion method. The estimating method of apparent budget of soil N (ABSN): after reviewed relevant studies, Zhu Zhao Liang showed that the increment of mineralized soil N after fertilization is approximately equal to the biological fixed rate of fertilizer N. So based on the assumption, the calculating formula of ABSN as follows: ABSN=(Total amount of original N min +Rate of applied N+Rate of mineralized N)-(Total amount of residual N min +Rate of uptake N by crop+Rate of fixed N)=(Total amount of original N min +Rate of applied N)-(Total amount of residual N min +Rate of uptake N by crop) The results of soil N min indicated, during the growth period of winter wheat the difference of soil NH + 4 N content among soil layers was smaller under different Nf level, while the change of soil NO - 3 N content(SNC) was very distinct, so only the spatio temporal variations of soil NO - 3 N was discussed here. At sowing SNC was maximum at the top layer, then decreased following soil depth deepened, and was minimum at the layer of 60～80cm depth.