麦秆还田对直播和移栽棉花产量及氮素吸收的影响

为明确长江流域棉区植棉对麦秆还田的响应及其对麦秆中氮素的吸收利用效果，采用田间试验，设置棉花直播冬小麦秸秆不还田（D-S）、棉花直播冬小麦秸秆还田（D+S）、棉花移栽冬小麦秸秆不还田（P-S）和棉花移栽冬小麦秸秆还田（P+S）4个处理。利用¹⁵N同位素示踪技术研究麦秆还田对直播和移栽棉花的产量、生物量、氮素吸收及秸秆氮利用率的影响。结果显示，麦秆还田可不同程度地增加直播和移栽棉花的产量、秸秆生物量和根系生物量。直播条件下，麦秆还田后棉花籽棉产量、叶片、茎秆、棉壳和根系生物量的增幅分别为7.8%、3.7%、4.6%、3.4%和14.6%；移栽条件下，麦秆还田后棉花产量及各部位生物量的增幅分别为5.9%、5.2%、5.6%、7.4%和7.9%。从棉花生物量和产量来看，各处理均表现为P+S>P-S>D+S>D-S。收获期，与麦秆不还田相比，麦秆还田后直播和移栽棉花的根系数、果枝数、叶片数、叶片SPAD、单株铃数和单铃重均有明显增加，而株高、根茎粗和衣分的差异并不显著。与D-S处理相比，D+S、P-S和P+S处理的棉株氮素吸收量分别增加14.4、34.6和51.1 kg·hm^-2，增幅达到9.0%、21.8%和32.2%。表观法和¹⁵N示踪法得出棉花季麦秆氮素的平均回收率分别为22.3%和11.5%，且移栽棉花对麦秆氮素的利用率高于直播棉花，表明棉花季大部分小麦秸秆氮素残留在土壤中。因此，在长江流域麦-棉轮作区，积极开展麦秆还田技术可增加直播、移栽棉花的产量和棉株氮素吸收，并减少化学氮肥施用，从而提高秸秆氮素养分的循环利用效率。研究可为作物秸秆资源利用和棉花季氮肥科学减量施用提供参考依据。

Influences of Wheat Straw Returning on the Yield and Nitrogen Uptake of Direct-Seeding and Transplanting Cotton

In order to investigate the response of cotton to wheat straw returning and the nitrogen absorption efficiency of cotton from wheat straw, field experiments were carried out in 2018, and 4 treatments were set, including direct-seeding cotton without wheat straw returning (D-S), direct-seeding cotton with wheat straw returning (D+S), transplanting cotton without wheat straw returning (P-S), transplanting cotton with wheat straw returning (P+S). ¹⁵N isotope tracer technique was used to study dry matter content, yield, nitrogen uptake and straw nitrogen (N) uptake of direct-seeding cotton (+D) and transplanting cotton (+P) by wheat straw returning (+S). The results showed that the yield, straw biomass and root biomass of direct-seeding and transplanting cotton were increased by returning wheat straw to the field. Under direct-seeding conditions, the yield and dry weight of cotton leaves, stems, husks and roots of treatment D+S were higher than those in treatment D-S by 7.8%, 3.7%, 4.6%, 3.4% and 14.6%, respectively, and the dry weights of cotton leaves, stems, husks and roots in treatment P+S were higher than those in treatment P-S by 5.9%, 5.2%, 5.6%, 7.4% and 7.9%, respectively. Judging from the biomass and yield of cotton, all treatments were as following: P+S>P-S>D+S>D-S. In the harvest period, the root coefficient, number of fruit branches, number of leaves, leaf SPAD, number of bolls per plant and weight of single boll of direct seeding and transplanting cotton in straw returning treatments were significantly higher than those in treatments without straw returning, while there were no significant differences in plant height, root thickness and lint percentage between treatments. Compared with D-S treatment, nitrogen uptake contents of cotton plants in treatments D+S, P-S and P+S were increased by 14.4, 34.6 and 51.1 kg·hm^-2, the increasing rates were up to 9.0%, 21.8% and 32.2%, respectively. Apparent method and ¹⁵N tracer method showed that the average recovery rate of straw-N in cotton season was 22.3% and 11.5%, respectively, and the N utilization rate of transplanted cotton was higher than that of direct-seeding cotton, where most of the wheat straw N was remained in soil during cotton season. Therefore, in the wheat-cotton rotation area of the Yangtze River Basin, active application of straw returning technology could increase the yield and N uptake of direct-seeding and transplanting cotton, reduce the application of chemical N fertilizer, thus improve the recycling efficiency of straw-N. The present research could provide reference basis for the utilization of crop straw resources and scientific application of nitrogen fertilizer reduction in cotton season.