不同氮肥和密度对直播油菜冠层结构及群体特征的影响

以华油杂62为材料,10月5日机械直播,在中氮(180 kg N hm–2)和高氮(270 kg N hm–2)2个水平下设置5个密度(15×104、30×104、45×104、60×104和75×104株hm–2)处理的裂区试验,研究产量、冠层结构、农艺和光合特征等指标。结果表明,2个氮水平下,分枝起点高度和冠层倒伏角度均随密度增加而增加,根颈粗和冠层高度均随密度增加而降低。在45×104株hm–2密度范围内,低效分枝比例随密度增加而减少。中氮水平下,45×104株hm–2和60×104株hm–2处理产量较高,在2921.2~3109.8 kg hm–2之间。高氮水平下,30×104株hm–2和45×104株hm–2处理产量较高,在3607.2~3772.4 kg hm–2之间,与其对应的初花期叶面积指数和结实期角果皮面积指数分别为3.72~3.94和4.21~4.34;初花期和结实期的透光率分别为6.1%~7.4%和16.4%~18.1%;群体有效角果数为65.5×106~68.7×106 hm–2。与传统的移栽油菜相比,直播油菜通过"减氮增密"栽培措施,在纯氮用量270 kg hm–2条件下,2种密度(30×104和45×104株hm–2)均可获得3600 kg hm–2以上产量,且适度密植可降低根颈粗,冠层相对集中,利于机械收获。

Effects of Nitrogen Fertilizer and Planting Density on Canopy Structure and Population Characteristic of Rapeseed with Direct Seeding Treatment

Cultivar Huayouza 62 was planted by mechanical seeding on 5 October with two nitrogen rates (180 and 270 kg ha^–1) and five planting densities (15×10⁴, 30×10⁴, 45×10⁴, 60×10⁴, and 75×10⁴ plant ha^–1). The differences of yield, canopy structure, agronomic traits and photosynthetic characteristics were studied. The results showed that with the increase of density, starting point of branch and lodging angle of canopy enhanced, while root collar diameter and height of canopy declined. In the density range of 45×10⁴ plant ha^–1, the low effective branch proportion lowered with the increase of density. Densities of 45×10⁴ and 60×10⁴ plant ha^–1 resulted in higher yield from 2921.2 to 3109.8 kg ha^–1 than other densities under middle nitrogen rate. Densities of 30×10⁴ and 45×10⁴ plant ha^–1 did higher yield from 3607.2 to 3772.4 kg ha^–1 than other densities under high nitrogen rate, and the corresponding suitable values of leaf area index (LAI) at beginning flowering stage, pod area index (PAI) at seed filling stage, light transmittance of bottom at beginning flowering stage, light transmittance of canopy at seed filling stage, and effective pod number were within the ranges from 3.72 to 3.94, from 4.21 to 4.34, from 6.1% to 7.4%, from 16.4% to 18.1% and from 65.5×10⁶ to 68.7×10⁶ ha^–1, respectively. Compared with traditional transplanting rapeseed, the direct seeding rapeseed could obtain high yield exceeding 3600 kg ha^–1 by reducing nitrogen rate and increasing density with 270 kg ha^–1 nitrogen fertilizer under both densities of 30×10⁴ and 45×10⁴ plant ha^–1. Reasonable plant density can effectively reduce the root collar diameter and the height of canopy, and concentrate pod maturing, which would help promote mechanical harvesting in rapeseed production.