大豆和玉米影响后茬作物氮素供应的研究进展

Research advances on the mechanisms of soybean and maize influence nitrogen supply in subsequent crops

【目的】为提高轮作系统的生产力和土壤肥力的可持续性,我们从作物根系形态、残留养分有效性和土壤结构等方面,综述了大豆和玉米生产对土壤物理特性和后茬作物氮素供应能力的影响机理及原因。【主要进展】大豆根系呈网状分布,分枝侧根多,生长过程中新老根频繁更替,收获后土壤团聚体由原来的简单形态变为多级复合形态,团聚体内部孔隙增多,利于后茬作物的根系发育。大豆形成的稳定土壤团聚结构也是土壤氮素循环的良好基础,可有效提升土壤有机氮的总矿化和转化量,增强土壤对后茬作物的供氮潜力。玉米生产一般氮肥施用量较高,故收获后残留在土壤中的肥料氮相对较多。残留氮以NO;-N和微生物氮形态存在的比例高,由于NO;-N在土壤中不稳定、易损失,因此,不易于为后茬利用。大豆秸秆C/N低,翻压还田后易于被土壤微生物利用,加速土壤氮循环,易于后茬作物的吸收利用。加之豆科作物生长过程中死亡的根瘤和根形成的沉积物数量大,根系分泌物含有较高的甘氨酸和丝氨酸,且根际沉积物C/N较低,更易矿化转化为后季作物的重要氮源。因此,大豆较玉米更有利于后茬作物的生长和氮素营养。【展望】为更好地利用轮作优势,需要在以下几方面加强研究:提高大豆残留氮素高效利用的关键驱动因素比例;减少玉米收获后土壤残留氮素损失的氮素管理方法;残留氮素转移转化过程中的根–土–微生物互作机制。由于秸秆腐解会加快土壤有机碳的释放,因此减少大豆秸秆还田带来的轮作周年CO_(2)等温室气体的排放,提高土壤的碳汇功能也将成为今后研究重点。

【Objectives】We reviewed the effects of soybean and maize production on the soil’s physical properties and nitrogen supply capacity to subsequent crops from crop root morphology and residual nutrient availability. We aim to examine how soil texture could increase the rotational system’s productivity and sustain soil fertility. 【Major advances】 Soybean roots are reticular in shape with many branches and lateral roots.New roots rapidly replace the old roots during the whole growing period. This stabilizes the soil texture and shows a multistage complex form rich in internal aggregate pores, conducive to the root development of the subsequent crops. After soybean cultivation, the ensuing stable soil aggregate structure lays a good foundation for soil N cycling, such as increasing the total soil organic nitrogen mineralization and transformation and enhancing the potential of soil N supply to the subsequent crops. Maize requires a high N fertilizer application, leading to a corresponding high residual N in the soil. The residual N is mainly in the form of NO;-N and microbial nitrogen.NO;-N is unstable and easily lost in soils, reducing its availability for use by subsequent crops. Soybean straw has a low C/N ratio and is easily utilized by soil microorganisms after returning to the field, accelerating the soil N cycle and N use by subsequent crops. Soybean roots have many dead root nodules, sediments formed by roots during the growth process, high levels of root exudates such as glycine and serine, and a low C/N ratio of sediments. This further increases their mineralization and transformation into an important N source for later crops. Therefore, the N supply capacity of soils after soybean cultivation is better than maize. 【Expectations】A beneficial crop rotation should consider proportion of key factors that can improve the efficient utilization of residual soybean nitrogen(N), N management for minimal loss after maize production, and the mechanism of root-soil microbial interaction during N transfer and transformation. Since straw decomposition can accelerate soil organic carbon release, reducing greenhouse gas emissions such as annual CO_(2) and improving soil carbon sink are worthy of future research.