早稻施氮对连作晚稻产量和氮肥利用率及土壤有效氮含量的影响

于20022～005年,在湖南长沙采用连续定位试验,研究了早稻施氮对连作晚稻产量、氮肥利用率、土壤有效氮含量的影响。试验设早稻施氮/晚稻不施氮、早稻施氮/晚稻施氮、早稻不施氮/晚稻不施氮、早稻不施氮/晚稻施氮4个处理。结果表明,在连续4年早季施氮的条件下,连作晚稻施氮处理的平均产量为6.45.t/hm2,地上部干物质重12.13.t/hm2,氮素吸收量183.6.kg/hm2,分别比连作晚稻不施氮处理增加28.4%、35.1%和103.5%,均达到显著水平;在连续4年早季不施氮的条件下,连作晚稻施氮处理的平均产量为6.61.t/hm2,地上部干物质重12.14.t/hm2,氮素吸收量165.6.kg/hm2,分别比不施氮处理增加33.4%、37.6%和95.6%,均亦达到显著水平。连作晚稻在早季不施氮和早季施氮两种情况下氮肥利用率不同,前者的氮肥生理利用率显著高于后者,增幅为37.8%,两者的氮肥农学利用效率、吸收利用率差异不显著,但前者4年氮肥农学利用效率平均值比后者高18.1%,吸收利用率低6.8个百分点。早晚两季均不施氮小区土壤碱解氮含量均明显低于其他施氮小区,但没有出现随试验年度加长而连续下降的趋势;当早稻或晚稻其中有一季施用了氮肥,或者两季均施用了氮肥的小区,土壤碱解氮含量差异不显著。说明连作晚稻产量主要受当季施氮量的影响,而受早季施氮量的影响较小;早季不施氮小区的连作晚稻氮肥的农学利用效率、生理利用率比早季施氮小区高;在一定程度上降低稻田氮肥用量不会导致土壤背景氮含量的下降。

Effects of fertilizer-N application for double early rice on the yield,nitrogen use efficiency and soil nitrogen content of double late rice

To explore the effects of fertilizer-N application for early cropping rice on rice yield,nitrogen use efficiency and soil nitrogen content in late cropping rice.Long-term experiment with different N treatments in double rice cropping system was conducted on the farm of Hunan agricultural university by using random block design with 4 replications from 2002 to 2005.There were four N treatments: N fertilizer applied in early season but not in late season(ENL0),N fertilizer applied in both early and late seasons(ENLN),no N fertilizer applied in either early or late seasons(E0L0),and N fertilizer applied in late season but not in early season(E0LN).The results showed that when N fertilizer was applied for both early and late rice,the average yield,dry matter production and N uptake of late rice reached 6.45 t/ha,12.13 t/ha and 183.6 kg/ha,respectively,which were 28.0%,35.1% and 103.5% higher than those of ENL0,respectively.The average grain yield,dry matter production and N uptake of the E0LN treatment reached 6.61 t/ha,12.14 t/ha and 165.6 kg/ha,respectively,which were 33.4%,37.6% and 95.6% higher than those of E0L0 treatment,respectively.The agronomic efficiency,physiological efficiency and partial factor productivity of fertilizer N of E0LN increased by 18.1%,37.8% and 2.7%,respectively,but the recovery efficiency decreased by 6.8%,compared with those of ENLN.The alkali-hydrolyzed soil N content in plots without N fertilizer in either early or late season rice was significantly lower than that in plots with N fertilizer in either season,but did not decrease continuously over years.No significant difference of the soil N content was observed among treatments receiving N application in one or both seasons.The results indicated that the grain yield of double late rice was significantly affected by N fertilizer applied in late season but not by that in early season.The agronomic efficiency,physiological efficiency of N fertilizer in late cropping rice was higher without N fertilizer in early season than those with N fertilizer in early season.To some extend,reduce N fertilizer rate would not significantly reduce soil indigenous N content.