化肥配施不同剂量有机肥对黑土团聚体中有机碳与腐殖酸分布的影响

摘要

【目的】团聚体的形成为土壤有机碳的稳定提供了重要的物理保护，施用有机肥影响着土壤团聚体的形成，量化有机肥施用剂量与团聚体有机碳稳定性之间的关系对于阐明农田土壤有机碳的固碳机制具有重要意义。【方法】以黑龙江省海伦市国家野外科学观测研究站为平台，选择连续10年进行化肥配施不同剂量有机肥处理[0、7.5、15、22.5 t/(hm2·a)]的黑土为研究对象，将团聚体分组与腐殖酸提取相结合，分析了不同粒径团聚体中有机碳和腐殖酸的含量与光学特性。【结果】1)与单施化肥相比，化肥配施有机肥增加了大团聚体(>0.25 mm)的分配比例与团聚体的平均重量直径，二者均随着有机肥剂量的增加而逐渐升高，回归拟合分析表明，团聚体的平均重量直径与有机肥剂量之间呈现显著的正相关关系(P =0.03)。2)2～0.25 mm团聚体是黑土有机碳的主要贮存场所，约占有机碳总量的64.8%～68.8%，大团聚体中有机碳的含量与储量均随着有机肥剂量的增加而逐渐升高，<0.053 mm团聚体中有机碳含量与储量则维持在较稳定的水平。3)各粒级团聚体中腐殖酸碳含量以0.25～0.053 mm团聚体最高，各粒级团聚体中腐殖酸碳占有机碳百分比之间的差异不显著。化肥配施有机肥提高了各粒级团聚体中腐殖酸碳的含量，使团聚体对有机碳的固持能力增加，且各粒级团聚体中腐殖酸碳的含量随着有机肥剂量的增加逐渐升高。4)化肥配施有机肥增加了各粒级团聚体中腐殖酸的 E4/E6比值，表明其分子结构简单化，且以>2 mm和0.25～0.053 mm团聚体中腐殖酸 E4/E6比值的增加最显著。【结论】在黑土中，长期连续进行化肥配施有机肥，促进了团聚体的形成，改善了耕层土壤结构，增加了团聚体中有机碳的积累与固持能力，并使各粒级团聚体中腐殖酸的结构“年轻化”，这种促进作用在高剂量有机肥施用下更为显著。实际生产中，在短期内可通过适当提高有机肥的施用量以提高黑土肥力及其固碳能力。%[Objectives]Aggregates provide important physical protection for soil organic carbon. Organic amendments strongly influence aggregate formation and its organic carbon stability, quantifying the relationships between organic manure addition rate and stability of organic carbon in aggregates could provide valuable information for better understanding in soil organic carbon sequestration mechanism.[Methods]This experiment was carried out based on a 10-year field experiment in National Observation Station of Hailun Agroecology System. Soils were selected from four treatments amended with different rate of organic manure [0, 7.5, 15, 22.5 t/ (hm2·a)] plus mineral fertilizer. Aggregate fractionation and humic acids extraction was used to analyze the distribution of soil organic carbon and content and optical characteristics of humic acid in different size of aggregate fractions.[Results]1) Compared with application of mineral fertilizer alone, addition of mineral fertilizers plus organic manure increased the proportion of macroaggregates ( > 0.25 mm) and mean weight diameter which was gradually increased with the addition rate of organic manure. Significant linear correlation between the value of mean weight diameter and organic manure addition rate was observed (P = 0.03). 2) Soil organic carbon was mainly distributed in 2–0.25 mm aggregates, accounting for about 64.8%–68.8%. Organic carbon content and stock in macroaggregates increased with the increasing organic manure rate. However, no significant differences were showed both in organic carbon content and stock in small microaggregates among treatments. 3) Humic carbon content in microaggregate (0.25–0.053 mm) was higher than other aggregates, but no significant difference in the percentage of humic carbon was found among different aggregate fractions. The content of humic carbon in each aggregate fraction increased significantly after application of organic manure plus mineral fertilizer, thus its capacity in organic C retention increased. The humic carbon content gradually increased with the increasing addition rate of organic manure. 4) Application of organic manure plus mineral fertilizer increased the E4/E6 ratio of humic acid in each aggregate fraction, particularly in the aggregate of > 2 mm and 0.25–0.053 mm, which indicated that the structure of humic acid tended to become simpler.[Conclusions]In black soil, continuous application of organic manure plus mineral fertilizers is effective to improve surface soil structure through promoting the formation of aggregates, increase carbon sequestration in aggregates, and simplify the structure of humic acid in aggregates, these beneficial effects are greater in soil amended with high rate of organic manure. Therefore, the addition rate of organic manure could be properly increased in order to improve soil fertility and carbon sequestration.