氮肥和种植密度对带状种植小麦抗倒能力的影响及边际效应

西南地区小麦以套作为主，因有效穗不足而使产量受到严重制约。本研究目的是提出该地区套作小麦高产栽培的适宜密度和氮肥施用量，提高小麦生育后期的抗倒伏能力，确保有效穗和最终产量。2009-2010和2010-2011连续两年度，选用主推品种川麦42，在纯氮120 kg hm^-2和180 kg hm^-2 2个施氮水平下，按60、120、180、240和300万株 hm^-2密度进行带状种植，对小麦群体发展、茎秆形态特征和倒伏机械特性进行了行间差异分析。结果表明，边行、次边行和中间行均随种植密度的增加茎蘖数和有效穗增多，但单株干物重及其在穗中的分配比例下降，茎秆质量降低。群体发展和个体质量在拔节后表现出显著的边行优势，成穗率、有效穗、单茎干物重、节间粗度、茎壁厚度、节间充实度和机械强度均以边行最优；同时密度对边行优势有显著影响，在180万株 hm^-2密度下，边行的有效穗基本达到饱和；密度继续增加时次边行和中间行的有效穗显著增加，并伴随株高和重心高度增加、单茎干物重降低、干物质分配在穗中的比例减小、节间充实度和茎秆机械强度急剧下降、倒伏时期提前、倒伏指数和倒伏程度增加。增加施氮量有提高中间行茎秆机械强度和降低倒伏指数、增强茎秆抗倒伏能力的趋势，但总体表现不显著。因此认为，120~180万株 hm^-2种植密度有利于套作小麦个体和群体质量的协调，是南方丘陵旱地带状种植小麦抗倒高产的适宜种植密度。

Lodging Resistance of Winter Wheat in Response to Nitrogen and Planting Density and Border Effect under Relay Intercropping Condition

Southwest is the third largest wheat producing area in China, where wheat/corn relay intercropping is the typical cultivation mode. In this area, wheat is harvested in a relatively low yield due to deficiency of effective spikes. The objective of this study was to modulate spike enhancement and lodging resistance of wheat in the relay intercropping system through optimizing plant density and nitrogen application rate. Using Chuanmai 42, the major wheat cultivar in local production, a two-year field experiment was carried out in Sichuan Province from November 2009 to May 2011 under two-factor split-plot design. The main-plot was for N application rate at 120 kg ha^-1 and 180 kg ha^-1, and the sub-plot was for plant density in five levels (0.6, 1.2, 1.8, 2.4, and 3.0 million plants per hectare). The border effects on wheat population quality, stem morphology, and stem mechanical strength were investigated at different growth stages. The quantities of tillers and effective spikes in edge, second, and central lines were all enhanced with the increase of planting density; however, the biomass and its distribution proportion in spike were reduced, resulting in declined stem quality. Under the same density, border advantage was significant after jointing stage, when the edge line showed higher levels than the second and central lines in spike rate, number of effective spikes, plant dry weight, outside diameter, wall thickness of culm, internode filling degree, and mechanical strength. Plant density influenced the border effect on number of effective spikes, with the maximum effective spikes in plant density of 1.8 million plants per hectare; even higher density stimulated significant increases of the spike number in the second and central lines in company with the increased plant height and height of gravity centre, the decreased plant weight and biomass distribution proportion in spike, and the dramatically declined internode filling degree and mechanical strength, which resulted in the occurrence of early lodging and high lodging degree and lodging area percentage. Nitrogen application had positive effects on lodging index and mechanical strength of the central line, but the general effects were not significant in the two nitrogen treatments. Suggestively, plant density of 1.2–1.8 million per hectare is optimal for relay intercropping wheat in the hill area of Southwest China based on its lodging resistance and border effect on plant growth and yield formation.