施氮时期对玉米土壤硝态氮含量变化及氮盈亏的影响

Effect of nitrogen application time on dynamics of nitrate content and apparent nitrogen budget in the soil of summer maize fields

在“郑单 95 8”(9株 / m2 )组成的土 -植系统 ,研究了不施氮、基施氮 +10叶展追氮、基施氮 +吐丝期追氮和基施氮 +乳熟期追氮共 4个处理下 0～ 2 0 0 cm的土壤 NO- 3- N含量在夏玉米生长期间的变化和土壤氮素的表观盈亏量 ,结果表明 :2 0 cm以上的土壤 NO- 3- N含量以大口期为界、2 0 cm以下的土壤 NO- 3- N含量以吐丝期为界前降后升。在 0～ 2 0 cm土层 ,与不施氮相比 ,施氮能增加土壤 NO- 3- N含量 ,而且吐丝期和乳熟至成熟阶段的 NO- 3- N含量在 10叶展期和吐丝期各自追氮后均显著增加。在 2 0～4 0 cm土层 ,乳熟期的 NO- 3- N含量施氮后明显比不施氮高。在 80 cm以下土层 ,施氮后的土壤 NO- 3- N含量明显比不施氮高 ;追氮期相比 ,后一追氮处理在乳熟期和成熟期的 NO- 3- N含量均比前一追氮处理明显增加 ,其中成熟期基施氮 +乳熟期追氮处理在 16 0～ 2 0 0 cm土层的 NO- 3- N含量比基施氮 +吐丝期追氮处理 (为 2 5 .3m g N/ kg(干土 ) )高 16 %。土壤氮素的表观盈余发生在吐丝期之前且 80 %以上盈余量出现在大口期前 ,表观亏损出现在吐丝期以后且其亏损量在乳熟期前后各占一半。经玉米季后 ,本试验中不施氮处理出现表观盈余 (为 5 6 .3kg N/ hm2 ) ;施氮后表观盈余量增加 。

Applying N at high rate year by year in high maize yield production in China resulted in increasing basal soil N content and decreasing N fertilizer utilization efficiency. Moreover, it caused severe underground water pollution in many areas. Therefore, agricultural researchers are facing how to optimally use N fertilizer. There were a lot of researches on the relationship of N fertilizer application with crop growth and yield components. Due to high precipitation and temperature, soil N mineralization and fixation by microbes was active during summer maize growth season in China. Objective of this study was to determine the effect of N application time on dynamics of nitrate content and apparent nitrogen budget in the soil of summer maize fields.A field experiment was carried out at the Wuqiao Experimental Station of China Agricultural University in north China in 2002. Four nitrogen application treatments were zero N, basal N plus dressing N at 10-unfolded-leaf stage, basal N plus dressing N at silking stage, and basal N plus dressing N at dough stage. Both rates of basal N and dressing N were 90 kg/hm^2. The trial was completely randomized design with three replicates. Plot size was 6 m by 6 m.The soil in the trial field was light salted loam in 0~130cm soil layers and loam in 130~200cm soil layers. Before sowing, the field was irrigated once and not ploughed. Maize cultivar Zhengdan 958, an erectophile type with high yield potential, was sown on June 10 and thinned to 9 plants/m^2 at 5-unfolded-leaf stage. P_2O_5 and K_2O were applied by dressing at the rates of 105 and 120 kg/hm^2, respectively, on the day of sowing. An irrigation of 45 mm was done on August 3. From June to July, total precipitation was 110 mm and each rainfall was less than 20 mm. There was rainfall of 45mm on August 26. During whole growth season, total precipitation was 196.3 mm, which was one third of total precipitation in a normal year. Soil samples were taken with a soil auger at five maize growth stages (i.e. sowing, female floret differentiation, silking, dough, and maturity). The samples were divided into different soil layers in 20cm increment from surface to 100cm depth, 100~130 cm, 130～160 cm, and 160~200 cm. Two sub-samples were taken per plot, mixed for each layer and then frozen immediately. Before analysis of mineral N including nitrate and ammonium, the soil samples were defrosted, mixed fully, and sifted with a 2-mm-sieve. Twenty grams of each sample was extracted with 100 ml of 1 mol/L KCl on a horizontal shaker for 1 hour and then filtered with quantative filter. Soil nitrate was determined with the Salicylic Acid Colorimetric Method and ammonium by the improved Ninhydrin Colorimetric Method. Five plants were taken per plot at the same time of soil sampling. Plant samples were exposed at 105℃ for half hour and then dried at 80℃. Total N content was analyzed with the Kjeldahl Digestion Method. Based on reported results, the amount of mineralized N increased by fertilization approximately equals to the amount of fertilizer N fixed by microbes, the apparent budget of soil N (ABSN) could be calculated by following formula: ABSN=TAONmin+RAN-TARN-ACUN where TAONmin the total amount of original mineral N, RAM=the rate of applied N, TARN=the total amount of residual mineral N, ACUN=the amount of crop uptake N. The findings of the trial showed that in the 0~20 cm soil layer, the nitrate content was higher in the N-applied plots than in the zero N plots regardless of application time. The nitrate content at silking and from dough to maturity increased when N was dressed at the 10-unfolded leaf stage or at silking stage. In the 20~40 cm soil layer, the nitrate content at dough stage decreased in all N-applied treatments in comparison with the zero N treatment. In 80~200 cm soil layer, the nitrate content from N-applied time to maturity increased in comparison with zero N treatment. The nitrate content of the treatment of N dressed at dough stage was higher than that of the treatment of N dressed at silking stage or at the