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High light use efficiency is an important factor for yield improvement during the growing season for winter canola. This study explored the evaluation method of high light use efficiency during the whole growth period in order to screen high light use coefficient of crop genotypes in canola producing areas of Southwest China. The pot experiment was conducted with sixty canola cultivars which had already been planted in the crops planting areas of the middle and upper reaches of Yangtze River. The plant height, root neck diameter, number of pods per main inflorescence, pods per plant, dry weight of shoots, seed weight per plant, pericarp weight per plant, ratio of pericarps to seeds weight per plant, seeds number per pod and 1000-grain weight were investigated under the shading treatment of reducing the incoming solar light by 20%. The high light use coefficient of canola cultivars was evaluated comprehensively by principal component analysis, membership function, cluster analysis and stepwise regression analysis. With these analyses, the original twelve indices related to light use efficiency could be synthesized into the four independent indices which represented 86.4% of all the investigated information of canola with high photosynthetic efficiency. Sixty varieties were classified into three groups by cluster analysis, and ZS12, GYZ6, FY792, RHY6, CZY3 and ZYZ19 displayed higher light use efficiency; such 18 varieties as XDZY9, XY1, YY50 and so on, were medium light efficient ones; and the rest 36 varieties such as LY9, ZYZ781, SG127 and so on, fell to the relatively lower light use efficiency categories. The comprehensive evaluation in this study had screened such four indicators as the stem dry weight per plant, the pod number per plant, the seed number per pod and the 1000-seed weight, which could be regarded as identification indicators for high light use efficiency of canola.

Direct seeded canola (Brassica napus L.) has become increasingly popular in China's key canola-producing regions. The studies on the K response of direct-seeded canola performance are limited. This research aimed to investigate the K utilization efficiency and canopy radiation interception rate of direct seeded winter canola at various K application rates. Two seasons field trials were done with five K levels (0, 75, 150, 225, and 300 kg K 2 O ha -1 ) utilizing two key local cultivars (Huayouza no. 9 and Zhongshuang no. 11) in Southwest China. Canola yield rose by 17.9%-82.6% in 2017-2018 and 21.1%-73.6% in 2018-2019 when K was applied, compared to Kunfertilized. Canola yield go up rapidly at first and then gradually when K ingestion grew, demonstrating the phenomena of K luxury consumption. As K levels rose, internal utilization efficiency, agronomic efficiency, and physiological efficiency all decreased. In canola pod development and maturation period, 150 kg K 2 O ha -1 intercepted the most solar radiation (73.8%), while K-unfertilized treatment intercepted the least (61.6%) on average. The K supply rates had a significant effect on canopy radiation interception and K absorption in winter canola. When K application exceeded a specific rate, luxury consumption occurred. Canola's luxury K consumption was mostly stored in the pericarp and plant stem.

Summary Rationally higher population density is crucial for seeking a balance that meets lodging resistance and maximizes seed yield in mechanized direct-seeded winter canola. In this study, a split-plot experiment with two cultivars (Huayouza9 and Zhongshuang11) and eleven planting densities (12–105 plants m-2) was conducted in a two-season field experiment to evaluate the high planting density in this cropping system and improve its production efficiency. Seed yield noticeably increased in planting density up to 80 plants m-2 in Zhongshuang11 (2187 kg hm-2) and 60 plants m-2 in Huayouza9 (2943 kg hm-2). The seed yield of Huayouza9 did not differ significantly from the local target seed yield. Higher plant density curtailed the luxurious vegetative growth of individual canola plants at the density of no less than 60–80 plants m-2, and high seed yield was derived from the increased ratio of main raceme and branch seed weight in winter canola. An increase in plant densities contributed to the reinforced sunlight interception at the pod-filling stage, providing a larger canopy photosynthetic area for the rapid growth of more canola pods at higher densities (60–105 plants m-2). Lodging resistance and breaking resistance decreased sharply with the plant density increasing from 12 to 60 plants m-2 while remaining almost steady as it further increased from 60 to 105 plants m-2 for Huayouza9 and Zhongshuang11. Hence, the population density of 60 plants m-2 reached a balance between lodging resistance and maximized seed yield in mechanized direct-seeded winter canola in China.

Phosphorus (P) fertilization is a crucial practice for winter rapeseed (Brassica napus L.) production. With the shift to a direct seeding cropping system, the P fertilizer supply should be re-evaluated for the requirement of direct-seeded winter rapeseed in southwest China. A two-factor field experiment was conducted in 2017-18 and 2018-19 in the region. The experiment aimed to investigate the responses of a wide range of P levels (0, 45, 90, 135, and 180 kg P ha −1 ) on yield, P-efficiency, and canopy sunlight interception of direct-seeded winter rapeseed. The results demonstrated that winter rapeseed yield was enhanced as the P fertilizer rate increased from 0 to 90 kg P ha −1 , and excessive P fertilizer supply did not significantly contribute to higher grain yield at high P levels. Rapeseed produced 7.1-10.1 kg seed ha −1 to supply 1 kg P ha −1 average across different five P levels from 0 to 180 kg P ha −1 .Phosphorus efficiency significantly firstly increased (0-90 kg P ha −1 ) and then progressively decreased with the rise of P levels (around 120 kg P ha −1 ). Greater P fertilizer rates were absorbed by the stem and pericarp while playing a negligible role in boosting winter rapeseed yield. When the target yield of 3000 kg ha −1 was set, the corresponding winter rapeseed canopy area index should be 1.42-2.71 to facilitate yield formation depending on the growth stages. Meanwhile, it intercepted 30.8%-88.7% of sunlight by the rapeseed canopy. A reduced P-fertilizer level of 90-120 kg P ha −1 was recommended to obtain target yield with less environmental risks in direct-seeded winter rapeseed planting regions.