红壤区玉米-大豆间作中作物氮素利用的根际生态学研究

Pig farming is one of major livestock industry in red soil region of Southern China, accounting for about 1/3 of the total slaughtered fattened hogs in China. Corn as the main feed resource, accounting for only 2.85% of the country's corn production in red soil region of Southern China, lack of corn which limiting the development of pig breeding in red soil region of Southern China. Vigorously develop the local corn is an important way to maintain the sustainable development of pig breeding, but the red soil has high acidity, low nutrient, sticky, compaction， and other limiting factors, so how to effectively plant corn become an important issue in the red soil area. Cereal-legumes intercropping systems have several major advantages in total crop yield and land use efficiency, the efficient utilization of natural resources (light, water, and nutrients), and control of pests and diseases. Based on previous work and the characteristics of hilly red soil zone, our study will fully use the advantage of cereal-legumes intercropping system, combined pot and field experiments to optimize nitrogen rate of corn-soybean intercropping systems in the red soil, reveal the law of corn nitrogen uptake under the high yield; meanwhile, use the denaturing gradient gel electrophoresis fingerprint to analyze the dynamic of nitrogen related rhizophere microbial community, and reveal the maize rhizosphere ecology mechanism of crop nitrogen uptake through in-depth analysis of the relation of crop nitrogen accumulation with micro-environment of crops' rhizosphere and change of nitrogen related microbial community composition. The project trying to use the cereal-legume intercropping to improve crop nitrogen utilization efficiency, reduce inputs of chemical fertilizers and pesticides, slow down the soil acidification, reduce the cost of agricultural production and the risk of environmental pollution of farmland. At all,the project will provide a theoretical basis for expanding corn yield efficient ecological cultivation in red soil region of Southern China.

生猪养殖是南方红壤区主要畜牧产业之一，生猪年出栏量约占全国1/3,但作为主要饲料源的玉米产量仅占全国的2.85%，需从外地输入大量玉米，限制了生猪养殖的发展。大力发展本土玉米是维持生猪养殖可持续发展的重要手段，但红壤存在酸、瘦、粘、板等多种限制因素，如何有效发展红壤区玉米种植是一个重要问题。本研究在前期工作基础上，立足南方红壤丘陵区域特点，利用禾本科-豆科间作优势，通过盆栽试验结合田间定位研究优化红壤区玉米-大豆间作模式的施氮量，揭示红壤区间作条件下的玉米氮素吸收利用规律，同时利用变性梯度凝胶电泳图谱技术监测作物根际氮相关微生物群落变化，深入探讨作物氮素吸收、根际微环境和氮相关微生物群落组成变化来阐明红壤区玉米氮素吸收的根际生态学机制。整个项目试图通过禾本科-豆科间作促进作物氮素吸收、减缓红壤酸化、降低农业生产成本和农田环境污染的风险,以期为扩大南方红壤区玉米高产高效生态种植提供理论依据。

本项目通过设置三个种植模式和五个施氮水平的盆栽试验系统研究了玉米-大豆种植系统中作物干物质和氮素累积量，土壤养分和土壤微生物群落组成的相互关系。主要研究结果表明：（1）红壤地玉米-大豆间作种植模式在施氮水平（150 kg/hm2）下较玉米单作没有显著降低玉米孕穗和收获期的玉米干物质量和氮素累积量，且玉米果穗干物质量较单作有显著增加。过高的施氮（225或300 kg/hm2）没有显著增加间作系统中作物氮素累积量。（2）玉米-大豆间作降低了红壤地pH、有效磷和速效钾，有利于提高土壤碱解氮含量。施氮显著影响了红壤地pH和速效钾，没有明显影响土壤全氮和碱解氮。（3）施氮水平显著影响了红壤地玉米根际土壤细菌群落α多样性指数。玉米-大豆间作模式下的根际土壤细菌群落β多样性指数高于单作模式下的，且间作模式下N2、N3水平的β多样性指数高于N1和N4的。PCoA分析结果表明施氮显著影响了根际土壤细菌群落的组成。T-test分析表明，相比不施氮，玉米-大豆间作和施氮显著影响了根际土壤细菌群落属水平的比例，部分差异菌属（Rhizomicrobium，Nitrosospira，Rhodoplanes等）与土壤氮循环密切相关。（4）土壤速效钾在玉米孕穗期和收获期与作物生物量和氮素累积量都呈极显著的负相关性。典型关联分析（CCA）表明，土壤速效钾与玉米孕穗期施氮处理下根际土壤细菌群落有明显的负相关，对玉米收获期根际土壤细菌群落有明显的正相关。（5）1年两季大田玉米试验进一步验证了玉米-大豆间作模式下施氮（150 kg/hm2）能够节约生产成本，维持较高的作物产量和土地生产力。试验结果为进一步研究红壤区玉米种植模式下作物-土壤-微生物相互协同作用和玉米-大豆间作种植模式下合理施氮提供了一定的参考依据。