稻草全量还田下氮肥运筹对双季晚稻产量及其氮素吸收利用的影响

Effects of nitrogen management on yield and nitrogen utilization of double cropping late rice under total rice straw incorporation

【目的】稻草还田和合理的氮肥运筹不仅可以改良土壤和培肥地力,提高农作物产量和品质,还可以减少因过量施用氮肥带来的环境污染。随着水稻机械化收割的快速发展,稻草全量原位还田面积迅速扩大。因此,研究稻草全量还田后合理施用氮肥十分必要。本文通过早稻机收稻草切碎全量还田后晚稻氮肥运筹试验,探索该条件下晚稻氮肥的合理施用技术。【方法】以超级晚稻品种淦鑫688为试验材料,设计4个施氮(N)水平(0、120、180、240 kg/hm2)基蘖穗肥比例为5∶2∶3,并在180 kg/hm2水平下增设稻草不还田对照处理和稻草全量还田下基蘖穗肥不同施氮比例处理(5∶0∶5、5∶1∶4、5∶2∶3、5∶3∶2、5∶4∶1、5∶5∶0)。旨在分析不同处理间水稻产量、产量构成和氮素吸收利用的差异。【结果】稻草全量还田下,施氮量在180 kg/hm2以下时产量随施氮量的增加而增加,之后则下降,处理间差异极显著。随施氮量的增加,有效穗数显著增加,而结实率则显著下降,施氮处理每穗粒数和千粒重显著高于不施氮处理。在相同施氮水平下,因为有效穗数、结实率和千粒重显著提高,所以稻草全量还田产量极显著高于不还田处理,增幅8.83%。稻草全量还田同一施氮水平下,施氮比例为5∶2∶3处理产量极显著高于其他处理,其每穗粒数和千粒重均为最高,有效穗数随分蘖肥比例的增加而减少,处理间结实率差异不显著。稻草全量还田后,随着施氮量增加,其氮素总积累量、氮肥表观利用率、氮素的吸收率和百公斤籽粒的需氮量也显著提高,且与施氮量呈极显著正相关。但氮素收获指数和氮肥生理利用率均随施氮量的增加而降低。同一施氮水平下,全量还田处理水稻氮肥农学利用率和生理利用率均显著高于不还田处理。相关分析表明,氮素总积累量与产量呈二次抛物线极显著正相关,氮肥表观利用率、氮素吸收率与产量呈极显著正相关。稻草全量还田相同施氮水平下,随着穗肥施氮比例降低,其氮素总积累量、中期的积累量和比率下降,其氮肥的表观利用率、收获指数和氮素的吸收率也随之降低,但前期的氮素积累量和比率则升高。氮素的农学利用率和生理利用率均表现为随着穗肥比例的减少呈先增加后降低趋势,均以施氮比例为5∶2∶3处理处理最高,不施穗肥处理最低。各施氮比例处理中,穗肥的施氮量与氮素的总积累量、中期积累量、氮肥的表观利用率、收获指数和氮素吸收率呈极显著正相关,氮肥的农学利用率和生理利用率与产量显著正相关。【结论】稻草全量还田后配施适量的氮肥可以提高晚稻产量,本试验以配施N 180 kg/hm2产量最高;在施纯N 240 kg/hm2以内,施氮越多,氮素积累量越多,相应的氮肥表观利用率、氮素的吸收率和百公斤籽粒的需氮量也越大。总施氮量相同条件下,以基肥∶分蘖肥∶穗肥为5∶2∶3的施氮比例水稻产量,氮肥农学、生理利用率均为最高,此结果可作为双季稻区稻草全量还田后的推荐施氮比例。

Objectives Rice straw incorporation and appropriate nitrogen ( N ) management can not only improve soil fertility and crop yield, but also reduce environmental pollution. With the rapid development of mechanized harvest, the area of in situ total incorporation of rice straw is expanded rapidly. Thus, it is important to determine reasonable N fertilization regimes under the total incorporation of rice straw. The objective of this study is to investigate the proper management for late rice under total incorporation of chopped early rice straw by a combine harvester. [Methods]Using a late rice variety ( Ganxin 688 ) as materials the experiment included four N rates (0, 120, 180 and 240 kg/hm2) with a ratio of 5:2:3 for basal, tillering, and panicle initiation, respectively. At the same time, under the N rate of 180 kg/hm2 , a control treatment without straw return and different N application ratios (5:0:5, 5:1:4, 5:2:3, 5:3:2, 5:4:1, 5:5:0 for basal, tillering, and panicle initiation, respectively) under total incorporation of rice straw were arranged. Rice yield, yield components, N absorption and utilization in different treatments were investigated. [Results]The yield increased with increasing N application rates, and was highest at the N rate of 180 kg/hm2 under total incorporation of rice straw. The number of effective panicles increased with increasing application rates, while the percentage of filled grains showed the opposite trend. In comparison with no straw retention, the higher yield under straw retention mainly attributed to the higher number of effective panicles, percentage of filled grains and 1000-grain weights, with an increase of 8. 83% in yield. Under the same N rate, the yield, number of grains per panicle, and 1000-grain weight were the highest at the N ratio of 5:2:3. The number of effective panicles decreased with increasing N proportions at the tillering stage, while the percentage of filled grains showed no significant differences among treatments. Under straw incorporation, the N accumulation, N recovery efficiency (NRE), N uptake rate (NUR) and N requirement for producing 100-kg grain increased with increasing N application rates. However, N harvest index ( NHI ) and nitrogen physiological efficiency ( NPE) decreased with increasing N application rates. Under the same N rate, the nitrogen agronomic efficiency ( NAE ) and NPE under total incorporation of rice straw were significantly higher than those under no straw incorporation. The correlation between yield and N accumulation was quadratic. NRE and NUR were significantly positively correlated with yield. Under the same nitrogen rate with total incorporation of rice straw, total N accumulation ( TNA) , N accumulation ratio in middle stage, NRE, NHI, and NUR were decreased with decreasing N proportions at panicle initiation, whereas N accumulation and ratio in early stage were increased. Both NAE and NPE were increased at first, but then decreased with decreasing N proportions at panicle initiation with the highest at the ratio of 5:2:3. The N application rate at panicle initiation was significantly positively correlated with TNA, N accumulation in middle stage, NRE, NHI and NUR, while NAE and NPE were positively correlated with yield. [Conclusion]The highest yield achieved when the N application rate is 180 kg/hm2. The N accumulation, NRE, NUR and N requirement for producing 100-kg grain increased with increasing N application rates from 0 to 240 kg/hm2. Under the same N application rate, the highest yield, the highest NAE and NPE can be achieved with the N application ratio of 5:2:3 for basal, tillering, and panicle initiation, respectively.