混播种类和群体结构对豆禾牧草混播系统氮素利用效率的影响

为从物种多样性和空间结构方面阐明豆禾牧草混播系统高效生产机制,将混播种类(单播、2种牧草混播、4种牧草混播和6种牧草混播)、混播群体空间结构(行距+同行/异行/异行阻隔)作为影响因素,从豆科牧草固氮能力、转氮效率、氮素营养竞争、种间相容性和生产性能分析和比较豆禾牧草在不同混播方式中氮素固定、转移和利用效率对混播系统生态功能的贡献程度。结果表明:1)混播处理的牧草产量、N产量均显著高于单播(P<0.05),生产性能显著提高;但生产性能未随混播种类的增加而提高,异行混播+30 cm行距的混播群体结构具有较高的生产性能。2)固氮量随混播种类的增加而呈下降趋势,转氮量和转氮率随混播种类的增加而呈先下降后上升的趋势,而固氮率和贡献率变化不明显;异行混播+30 cm行距的混播群体结构具有较高的转氮量、转氮率和贡献率。3)营养竞争比率随混播种类的增加变化不明显,豆科牧草相对产量和相对产量总和随混播种类的增加而呈增加趋势;异行混播+30 cm行距的混播群体结构具有较高的豆科牧草相对产量和相对产量总和,但营养竞争比率较低。4)牧草产量与转氮量呈极显著正相关(P<0.01),而相对产量总和与氮素营养竞争比率呈极显著负相关(P<0.01)。因此,混播种类对于豆禾牧草混播系统生产性能的提升作用有限,高养分利用效率的物种组合可能更为关键;通过混播群体空间结构的优化可以使豆禾混播牧草根系氮素固定、转移、利用途径和效率得到提高,为混播系统生产性能的提升提供了重要途径。

Effects of species diversity and community structure on nitrogen use efficiency of mixed legume+grass pastures

This study investigated species diversity and effects of species spatial distribution on forage yield in mixed grass+legume pasture communities. N fixation, N transfer and N utilization efficiency in leguminous forage under different planting patterns with intermixed grasses were evaluated to gain insight into N fixation ability, N transfer efficiency, N nutrition competition, interspecies compatibility and production performance. The results showed: 1) Both the forage yield and N yield in mixed pastures were significantly higher than in monoculture (P<0.05), However, productive capacity of mixed pastures did not increase with increasing number of grass species. A row spacing of 30 cm intercropping treatment+different line mixed treatment had higher productive capacity than other planting patterns. 2) The amount of nitrogen derived from air (W_N) declined with increasing grass content. The amount of nitrogen derived from legume (W_Nt) and percentage of nitrogen derived from legume (P_Nt) showed a curvilinear response with lowest values at intermediate levels of grass species, while, the percentage of nitrogen derived from air (P_N) and contribution of biological nitrogen fixation (C_BNF) were comparatively unchanged. Again, the treatment Row spacing of 30 cm+intercropping treatment had higher W_Nt, P_Nt and C_BNF values than other treatments. 3) No changes in competition ratio (C_Rpm) were observed, but the relative yield and relative yield total of legume increased with increasing grass species content in the mixtures. The relative yield and relative yield total of legume in row spacing of 30 cm+intercropping treatment were higher and the C_Rpm value was lower than for other spacing patterns. 4) Forage yield was significantly correlated with the W_Nt value (P<0.01), and relative yield total was negatively correlated with C_Rpm value (P<0.01). Therefore, species diversity had a limited impact on the productivity in mixed pastures, and high nutrient use efficiency species would be theoretically more important. Optimization of the spatial structure of legume-grass mixtures can improve biological N fixation, N transfer, N utilization, and N use efficiency. These principles potentially provide new methods to improve the productivity of mixed legume+grass pastures.