ABSTRACT

The increasing demand for sugarcane residue to produce industrial biofuels competes with organic-matter inputs to tropical soils for increasing fertility. Soil nitrogen (N) availability to plants and carbon (C) storage can be optimized by the selection of substrate types and quantities. We tested whether substrate-induced microbial growth increases soil N mineralization and C stabilization as substrate inputs increase. The effects of substrate additions (cane sugar, leaf litter, and humic acid extracted from filter cake) on microbial growth and N availability were studied using C3/C4 plant C isotopic signatures in a sandy soil of northeast Thailand. The initial growth of microbial biomass in cane sugar-amended soil caused a short-term flush of N derived from the native soil organic matter within 3 days, whereas in the soils amended with leaf litter or humic acid, N was retained in microbial biomass or dissolved organic matter, respectively. Net mineralization of the native soil organic N was maximized by sugar addition at a dosage corresponding to 10 folds of microbial biomass-C. The efficacy of substrates stabilized in the heavy density fraction (>1.6 g cm⁻³) followed the order: leaf litter > humic acid > sugar. Soil net N mineralization can be promoted by sugar inputs (e.g., bud node) at an early growth stage, while leaf litter and humic acid inputs can increase C storage efficiently in the sandy soil without increasing risks of N starvation and loss when they are applied at several tons of C per hectare at least 3 weeks before planting.

摘要

生产工业生物燃料对甘蔗渣的需求不断增加，与向热带土壤输入有机物以提高肥力相竞争。可以通过选择基质类型和数量来优化植物对土壤氮（N）的利用率和碳（C）的存储量。我们测试了底物诱导的微生物生长是否随着底物输入的增加而增加了土壤的氮矿化和碳稳定。在泰国东北的沙质土壤中，使用C3 / C4植物C同位素特征研究了底物添加（蔗糖，枯枝落叶和从滤饼中提取的腐殖酸）对微生物生长和氮利用的影响。甘蔗糖改良土壤中微生物生物量的初始生长导致3天之内短期冲刷了源自天然土壤有机质的氮，而在用枯枝落叶或腐殖酸改良的土壤中，氮分别保留在微生物生物量或溶解的有机物中。通过添加相当于微生物生物量C的10倍的糖分，天然土壤有机氮的净矿化作用得以最大化。基材的功效稳定在高密度部分（> 1.6 g cm⁻³）遵循以下顺序：凋落物>腐殖酸>糖。在生长期初期，糖输入（例如芽节）可促进土壤净氮矿化，而凋落物和腐殖酸的输入可有效提高沙质土壤中的碳储存量，而施用氮时则无饥饿和损失的风险。种植前至少3周每公顷排放几吨碳。