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首页> 外文期刊>Nutrient Cycling in Agroecosystems >Integrating legumes to improve N cycling on smallholder farms in sub-humid Zimbabwe: resource quality,biophysical and environmental limitations
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Integrating legumes to improve N cycling on smallholder farms in sub-humid Zimbabwe: resource quality,biophysical and environmental limitations

机译：整合豆科植物以改善津巴布韦半湿润小农户的氮素循环：资源质量，生物物理和环境限制

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The release of mineral-N in soil from plant residues is regulated by their 'quality' or chemical composition.Legume materials used by farmers in southern Africa are often in the form of litter with N concentration <2%.We investigated the decomposition of Sesbania sesban and Acacia angustissima litter in the field using litterbags,and N mineralization of a range of legume materials using a leaching tube incubation method in the laboratory.The mass loss of the litter could be described using a modified exponential decay model: Y =(Y_0 - Q)e~(-kt)+ Q.The relative decomposition constants for Sesbania and Acacia litter were 0.053 and 0.039 d~(-1),respectively.The % N mineralized from fresh Sesbania prunings was 55% compared with only 27% for the Sesbania litter after 120 days of incubation under leaching conditions.During the same period,fresh prunings of Acacia released only 12% of the added N while Acacia litter released 9%.Despite the large differences in N concentration between Acacia prunings and its litter,the total mineralized N was similar,as mineralization from prunings was depressed by the highly active polyphenols.While N supply may be poor,these slow decomposing litter materials are potentially useful for maintaining soil organic matter in smallholder farms.In two field experiments with contrasting soil texture,Sesbania,Acacia and Cajanus produced large amounts of biomass(>5 Mg ha~(-1))and improved N cycling significantly(>150 kg N ha~(-1))on the clay loam soil,but adapted poorly on the sandier soil.There was a rapid N accumulation in the topsoil at the beginning of the rains in plots where large amounts of Sesbania or Acacia biomass had been incorporated.Despite the wide differences in resource quality between these two,there was virtually no difference in N availability in the field as this was,among other factors,confounded by the quantity of N added.A substantial amount of the nitrate was leached to greater than 0.4 m depth within a three-week period.Also,the incidence of pests in the first season,and drought in the second season resulted in poor nitrogen use efficiency.Our measurements of gaseous N losses in the field confirmed that N_2O emissions were <0.5 kg N ha~(-1).As we had measurements of all major N flows,we were able to construct overall N budgets for the improved fallow-maize rotation systems.These budgets indicated that,in a normal rainfall season with no major pest problems,reducing nitrate leaching would be the single largest challenge to increased N recovery of added organic N in the light textured soils.
机译：植物残渣中土壤中氮素的释放受其“质量”或化学成分的控制。南部非洲农民使用的豆科材料通常以凋落物的形式存在，氮含量＜2％。我们研究了芝麻的分解在田间使用小垃圾袋处理sesban和Acacia angustissima凋落物，并在实验室中使用浸出管孵化法对一系列豆类物料进行N矿化。可以使用修正的指数衰减模型描述垃圾的质量损失：Y =（Y_0 -Q）e〜（-kt）+ Q.Sesbania和Acacia凋落物的相对分解常数分别为0.053和0.039 d〜（-1）.Sesbania新鲜修剪的矿化N含量为55％，而仅27％在浸出条件下温育120天后，Sesbania凋落物。在同一时期，相思树的新鲜修剪仅释放了12％的添加的N，而Acacia凋落物则释放了9％。径迹及其凋落物，总矿化的氮相似，因为高活性的多酚抑制了修剪过程中的矿化。虽然氮供应可能不足，但这些缓慢分解的凋落物可能对保持小农户的土壤有机质有用。对比土壤质地的田间试验，Sesbania，Acacia和Cajanus在壤土上产生了大量的生物量（> 5 Mg ha〜（-1）），并显着改善了氮素循环（> 150 kg N ha〜（-1））。但在沙质土壤上适应性较差。降雨开始时，在大量掺入了塞斯巴尼亚或阿拉伯树胶生物量的土地上，表层土壤中氮迅速积累。尽管两者之间的资源质量差异很大，田间氮的有效性几乎没有差异，因为这与添加的氮量有关。在三周的时间内，大量的硝酸盐被浸出到0.4 m以上的深度。 ，第一季的虫害发生率和第二季的干旱导致氮素利用效率低下。我们对田间气态氮损失的测量结果证实，N_2O排放量<0.5 kg N ha〜（-1）。对所有主要氮流量进行了测量，我们能够为改良的休耕玉米轮作系统建立总氮预算。这些预算表明，在没有主要病虫害的正常降雨季节，减少硝酸盐淋失将是最大的挑战。增加了轻质土壤中添加的有机氮的氮回收率。

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