减氮增密对西南丘陵区旱地直播油菜根系发育及水分利用的影响

以氮肥施用量N1(108 kg·hm~(-2))、N2(144 kg·hm~(-2))、N3(180 kg·hm~(-2))及种植密度D1(15×10~4株·hm~(-2))、D2(22.5×10~4株·hm~(-2))、D3(30×10~4株·hm~(-2))、D4(37.5×10~4株·hm~(-2))设置12个处理,以当地传统种植方式(N3D1)为对照,在生态脆弱、水土流失严重的西南丘陵区研究了油菜不同生育期根冠比(R/T)、根系形态、土壤蓄水量以及经济产量、水分利用效率、经济收益对不同氮肥施用量及种植密度的响应。结果表明:施氮量极显著影响油菜蕾薹期、角果期及成熟期的R/T与角果期的总根长和根系总表面积,同时显著影响蕾薹期的总根长和根系总体积;种植密度极显著影响蕾薹期R/T及角果期根系总体积,同时显著影响蕾薹期的根系总表面积和根系总根体积。角果期为地上部生物量积累速率最大时期,根冠比相较蕾薹期减小55.5%,而苗期的根冠比与经济产量呈显著负相关(r=-0.673~*)。氮肥减施可以有效增加土壤蓄水量和生育期总耗水量,且氮肥减施40%后更为显著,前者表现为N1N2N3,后者则为N3N2N1;相较N3,N1和N2下的各处理平均总耗水量分别减少5.03%和3.24%。在N2下,经济产量和水分利用效率则随着种植密度的增加而显著增加;经济收益与水分经济收益也表现出显著增长的变化趋势,其中,N2D3、N2D4处理较对照每公顷经济收益增加290.73元和503.37元,水分经济收益提高2.72%和9.93%。N2D3或N2D4处理能促进油菜产量、土壤蓄水量及经济收益的增长,并显著提升水分利用效率及水分经济收益,可作为西南丘陵区直播油菜减肥增效优化种植方式。

Effects of dense planting with less nitrogen fertilizer on root system development and water use efficiency of direct-sowed rapeseed in hilly dryland area in southwest of China

In the hilly area of southwestern China where the eco\|environment is fragile and soil erosion is serious, the combination of optimal fertilization and population regulation is of great significance for coping with seasonal drought, achieving high and stable yield, and saving fertilizer in rapeseed production. A two\|factor split plot experiment was designed, in which nitrogen fertilizer (pure N) was the main treatment and planting density was the sub\|treatment. There were three levels of N fertilizer including N1 (108 kg·hm^-2), N2 (144 kg·hm^-2), and N3 (180 kg·hm^-2), and four levels of planting density including D1 (150 000 plants·hm^-2), D2 (225 000 plants·hm^-2), D3 (300 000 plants·hm^-2), D4 (375 000 plants·hm^-2). There were 12 treatments in total, in which N3D1 (traditional planting mode) was used as control. The root\|shoot ratio, root morphology (root length, root surface area and root volume) and soil storage capacity at different growth stages, as well as economic yield, water use efficiency (WUE) and economic benefit of rapeseed under different N fertilizer and planting density were analyzed. The results showed that the amount of N application significantly affected the root\|shoot ratio, total root length and total surface area of the bud stage, pod stage and maturity stage, and significantly affected the total root length and total volume of the bud stage. The planting density significantly affected the root\|shoot ratio at the bud stage and the total root volume during the pod\|setting stage and significantly affected the total root surface area and total root volume of the bud stage. During the period of pod stage, the biomass accumulation rate of the above mentioned part was at the maximum, and the root\|cap ratio of this period was 55.5% lower than that of the bud stage. In addition, root\|crown ratio at seedling stage was negatively correlated with economic yield (r=-0.673^*). The reduction of N fertilizer effectively increased the soil water storage and total water consumption during the growth period, and it was more significant after 40% reduction of N fertilizer. The former is N1>N2>N3, while the latter is N3>N2>N1. Compared with N3, the average total water consumption of each treatment under N1 and N2 decreased by 5.03% and 3.24%. Under N2, the economic yield and water use efficiency increased significantly with the increase of planting density; both economic returns and water economic returns showed similar and significant growth trends; Among them, N2D3 and N2D4 increased the economic returns per hectare by 290.73 yuan and 503.37 yuan, and the economic returns on water increased by 2.72% and 9.93%. So, the N application rate of 144 kg·hm^-2 and the planting density of 300 000 plants·hm^-2 or 375 000 plants·hm^-2 is an optimal planting mode for saving fertilizer and increasing efficiency in the production of direct sowed rapeseed in dryland in the hilly area of southwestern China.