适宜播期提高农牧交错带春小麦产量和水氮利用效率

Optimal sowing dates improving yield, water and nitrogen use efficiencies of spring wheat in agriculture and pasture ecotone

为了明确农牧交错带播种期对春小麦的产量、生育期和资源利用效率的影响，从2011年到2012年在内蒙古进行了小麦分期播种试验。试验共设置了5个播种期，从4月26日开始至6月5日结束，每播期间隔10 d。结果表明，随着播期的推迟，5月6日之后播种的各处理小麦产量显著降低，最后播种的小麦产量相比4月26日播种的减产63.3%～72.3%，对应的收获指数和千粒质量也大幅下降，主要是由于小麦晚播后抽穗至成熟阶段日平均温度降低所致。播期导致各生育阶段所需要的天数特别是播种到出苗期产生差异，但全生育期所需要的生理发育时间（发育最低温度Tb为0，最适温度To为20℃）在不同年份和播种期处理下均没有显著差异，稳定为95.3个生理日数（当每日平均温度均为最适温度时所需要的发育天数）。水分利用效率随着播期推迟呈现明显降低的趋势，与4月26日播种处理相比，最后播种处理的水分利用效率降低了68.8%～74.3%，主要是晚播小麦麦穗干物质质量占地上部干物质质量的比例降低，营养体生长过旺，增加了各生育期内的日耗水量。不同播期下，春小麦地上部植株氮素累积吸收量为14.0～17.0 g/m2。播种期对春小麦氮素累积吸收量没有显著影响。但由于早播处理小麦的收获指数和产量较高，所以氮素的吸收转化利用效率显著高于晚播处理。在农牧交错带适时早播春小麦不但可提高产量，而且还能大幅度提高水氮资源的吸收利用效率，这对该区域实现春小麦高产和稳产有着实际指导意义。

Agriculture and pasture ecotone are typical ecologically vulnerable areas. Crop productivities and the agricultural sustainability are greatly affected by climate change in these areas. Field experiments were conducted from 2011 to 2013 in Inner Mongolia （41＆#176;06′N, 111＆#176;28′E） to investigate the influence of planting dates on yield and phenology of spring wheat and potential of improving resource （water and nitrogen） use efficiencies. The experimental field was located in arid and semiarid climate zone, where mean annual temperature was 2.7℃, annual growing degree days （＆gt;0 ） was about 2553 （℃＆#183;d）, the average annual rainfall was only 354 mm mainly in July and August accounting for 80%precipitation in the whole growing season. Five sowing dates was designed from 26 April to 5 June with a 10-day interval. The results showed that the yields after 6 May were significantly （p＆lt;0.05） decreased due to delayed sowing dates. Compared to early sowing date （26 April）, the yield of the late sowing date was reduced by 63.3%to 72.3%due to the obvious reduction in daily temperature from the growth stages of heading to maturity. Harvest index （HI） and grain weight per 1000 seeds were also affected by sowing dates. The early sowing （26 April and 5 May） treatments had higher HI. But after 16 May, the HI decreased significantly （p＆lt;0.05）. The grain weight per 1000 seeds decreased from 44.65 to 20.73 g with the delaying of the seeding dates, which had a trend similar with HI. It indicated that low values of HI and grain weight contributed to yield decrease when sowing after 26 May. Phenology of wheat as expressed in calendar days were different between years and sowing dates, especially from sowing to emergency, but the phenology based on physiological development time （PDT） was similar with a constant value of 95.3 days （the days required to complete whole development stage at optimal temperature condition） between years and sowing dates. Water use efficiency （WUE） was significantly （p＆lt;0.05） decreased by delaying sowing dates. Compared with early sowing treatments, the WUE of late sowing dates were reduced by 68.8%to 74.3%probably due to the reduction of ratio of spike over above-ground dry matter in late sowing treatments （i.e. more vegetative growth and bigger canopy than early sowing treatments）. Total nitrogen uptake by above-ground biomass ranged from 14.0 to 17.0 g/m2 for different sowing dates, however, the difference was not statistically significant （p＆gt;0.05）. As the early sowing treatments showed higher （p＆lt;0.05） yield and HI, nitrogen use efficiency （NUE）, the transformation of nitrogen uptake to the economic yield was significantly （p＆lt;0.05） higher in early sowing treatments than in late sowing treatments. Therefore, the best sowing date should be earlier than 6 May, and early sowing before 6 May could improve yield, water and nitrogen use efficiencies of wheat in the agriculture and pasture ecotone.