适宜氮肥可提高人工羊草的抽穗数和种子产量

【目的】 施用氮肥是禾本科牧草种子高产的关键管理措施之一。为提高羊草种子产量，在人工羊草地上探讨施用氮肥对羊草种子产量及其构成因子的影响，以期为羊草种子生产提供理论和实践依据。 【方法】 试验于 2013～2015 年进行，以中科 2 号羊草 Leymus chinensis (Trin.) Tzvel ‘Zhongke No.2’] 为材料，设置 5 个氮肥处理水平，分别为 N 0、60、120、180、240 kg/hm2，氮肥在返青期 (4 月上旬) 和种子完熟后 (7 月下旬) 施入，两个时期各施 1/2，羊草种子完熟时测定种子产量和产量构成因子。 【结果】 施氮量和年际对种子产量影响显著。随生长年限延长，羊草种子产量逐年增加。2013 年和 2014 年种子产量随施氮量增加呈先增加后降低的趋势，2013 年施用氮肥 104.9 kg/hm2 时羊草产量最高，为 395.2 kg/hm2，但氮肥对种子产量影响不显著，2014 年施用氮肥 173.5 kg/hm2 时产量最高，为 857.8 kg/hm2，较不施氮肥显著增加 56.0%。2015 年种子产量随施氮量增加而增加，施用氮肥 180 kg/hm2 时种子产量达较高水平为 1865.0 kg/hm2，与施用氮肥 240 kg/hm2 差异不显著，较不施氮肥显著增加 206.5%。通径分析结果表明，种子产量与抽穗数呈极显著正相关 ( r = 0.883， P < 0.01)，抽穗数对种子产量的直接作用最大为 0.717，分蘖数对种子产量的间接作用最大为 0.689，且主要是通过抽穗数产生，抽穗数对种子产量的贡献最大。2013 年施用氮肥羊草抽穗数差异不显著，其后两年随氮肥施用量增加抽穗数的变化趋势与产量相同。三年连续施用氮肥使 2014 年和 2015 年抽穗数显著增加，对种子生产有利。施用氮肥显著增加羊草植株穗长、小穗花数、结实粒数/穗和结实率，而对千粒重和小穗数影响不显著。抽穗数与穗长、千粒重和小花数/小穗呈显著负相关。 【结论】 随生长年限增加，羊草种子高产所需施氮量增大，羊草适宜施氮量为 104.9～180.0 kg/hm2，2013 年以施氮 104.9 kg/hm2 为宜，而 2014 年和 2015 年则以 180 kg/hm2 左右为宜。抽穗数是影响种子产量的最关键因子，不受当年施用氮肥的影响，而与前一年种子完熟后施氮量和 8～10 月降雨量相关。抽穗数增加导致的穗长、千粒重和每小穗花数减少，可以通过添加氮素来给予补偿。

Effects of nitrogen fertilizer on seed yield and yield components in artificialLeymus chinensis grassland

Objectives]The application of nitrogen fertilizer is one of the key measures to increase seed yield of Gramineous forage. In this study, a field experiment was conducted in artificialLeymus chinensis(Trin.) Tzvel grassland to understand the effects of nitrogen fertilizer on seed yield and its components, and to provide theoretical and practical basis for management of artificialLeymus chinensis(Trin.) Tzvel grassland.Methods]The experiment was conducted from 2013 to 2015 withLeymus chinensis(Trin.) Tzvel ‘Zhongke No.2’ as materials. The experiment included five nitrogen level treatments (N 0, 60, 120, 180, 240 kg/hm2) with three randomized blocks. In each treatment, half of N fertilizer was applied at green stage (late March) and half at harvest stage (late July). Seed yield and yield components were measured at harvest stage.Results]The experimental years and N fertilizer had significant effects on seed yield. The yield increased gradually with experimental years. However, the seed yield was initially increased and then decreased in 2013 and 2014. In 2013, the optimal N rate was 104.9 kg/hm2with a highest seed yield of 395.2 kg/hm2, but the yield was not significantly affected by N fertilizers. In 2014, the optimal N rate was 173.5 kg/hm2with a highest seed yield of 857.8 kg/hm2, which was 56% higher than control treatment. In 2015, seed yield increased with N rate, with the highest yield of 1865 kg/hm2at N rate of 180 kg/hm2, which was 206.6% higher than control treatment. The results of path analysis indicated that seed yield was significantly correlated with spike number (r= 0.883,P< 0.01). Spike number had largest direct path coefficient to seed yield (0.717) among all the variables, while tiller number had the highest indirect effect on seed yield through spike number, indicating that spike number contributes most to seed yield. Spike number was not affected by N treatmetn in 2013, but had similar responding pattern to N treatment to seed yiled in 2014 and 2015. The spike number increased significantly in 2014 and 2015 by consecutive application of N fertilizer among the three years. Furthermore, the application of N fertilizer significantly increased spike length, florets/spikelet, grain number/spike and seed setting rate, but did not affected 1000-seed weight and spikelet/spike.Conclusions]The optimal amount of N fertilizer for seed yield was 104.9–180.0 kg/hm2and increased with planting year increasing (104.9 kg/hm2in 2013 and 180.0 kg/hm2in 2014 and 2015). The spike number was the key factor influencing yield, which was not affected by N fertilizer application of current year, but was influenced by the precipitation from August to October and the amount of N fertilizer after mature stage in the previous year. The negative direct coefficient for spike number to spike length, 1000-seed weight and florets/spikelet could be offset by adding N fertilizer.