Sugarcane straw is a potential feedstock to increase bioenergy production. However, leaving straw on the soil surface is important to sustaining soil organic matter (SOM). We conducted a field experiment to evaluate the impacts of two years of straw removal on SOM in a sugarcane area – on an Eutric Nitisol in south-eastern Brazil – with low straw production (7 Mg ha–1). The experiment was a randomised complete block design (four blocks) with four rates of straw removal: (i) no removal, (ii) medium removal, (iii) high removal and (iv) total removal. We evaluated straw decomposition, soil carbon (C) and nitrogen (N) stock (0–30 cm), labile C, and microbial biomass C and N (0–10 cm). Increases in the straw removal rates reduced decomposition, with 30–42% of the initial straw amount remaining on the soil after one year (first year) and 33–38% remaining at the end of the second year. During the first year, no effect was found on soil C (8 kg m–2) and N (0.7 kg m–2) stocks; however, during the second year, total straw removal reduced soil C stock by 10% (0–30 cm) compared with no straw removal. Straw removal rates negatively affected the labile C (6–10% and 20–25%, first and second year respectively) and microbial C (correspondingly 10–15% and 21–27%). Microbial N was not altered in the first year, but decreased 26% due to straw maintenance (no removal) during the second year. Total straw removal decreased the C management index (CMI) by 15% (first year) compared with no straw removal. However, during the second year, all rates of straw removal decreased the CMI: by 15% for medium, 22% for high and 26% for total removal. Our findings indicate that any straw removal in areas with low straw production negatively affects SOM, initially through reduction in labile C pools. Although slight impacts on soil C and N stock were detected, reduction in straw-derived inputs stimulates microbial utilisation of soil C pools, and consequently reduces SOM over time.

中文翻译：

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甘蔗秸秆维护对防止巴西中南部地区 Nitisol 土壤有机质消耗的重要性

甘蔗秸秆是提高生物能源产量的潜在原料。然而，将秸秆留在土壤表面对于维持土壤有机质 (SOM) 很重要。我们进行了一项田间试验，以评估在秸秆产量较低（7 Mg ha-1）的甘蔗地区（巴西东南部的 Eutric Nitisol），两年的秸秆移除对 SOM 的影响。该实验是随机完整块设计（四个块），具有四种秸秆去除率：（i）无去除，（ii）中等去除，（iii）高去除和（iv）完全去除。我们评估了秸秆分解、土壤碳 (C) 和氮 (N) 储量（0-30 厘米）、不稳定碳以及微生物生物量碳和氮（0-10 厘米）。秸秆去除率的提高减少了分解，一年（第一年）后，最初的秸秆数量的 30-42% 保留在土壤中，第二年末剩余 33-38%。在第一年，没有发现对土壤碳（8 kg m-2）和 N（0.7 kg m-2）库的影响；然而，在第二年，与没有去除秸秆相比，完全去除秸秆使土壤碳库减少了 10%（0-30 厘米）。秸秆去除率对不稳定 C（第一年和第二年分别为 6-10% 和 20-25%）和微生物 C（相应地为 10-15% 和 21-27%）产生负面影响。第一年微生物 N 没有改变，但由于第二年的秸秆维护（没有移除），微生物 N 减少了 26%。与不清除秸秆相比，全部秸秆清除使 C 管理指数 (CMI) 降低了 15%（第一年）。然而，在第二年，所有秸秆去除率都降低了 CMI：中型降低了 15%，高去除率 22%，总去除率 26%。我们的研究结果表明，在秸秆产量低的地区，任何秸秆去除都会对 SOM 产生负面影响，最初是通过减少不稳定的碳库。虽然检测到对土壤 C 和 N 库的轻微影响，但秸秆来源输入的减少刺激了土壤 C 库的微生物利用，从而随着时间的推移降低了 SOM。