秸秆还田下双季稻田土壤团聚体碳氮磷含量及生态化学计量比特征

土壤碳氮磷等养分含量及其生态化学计量比对作物养分供应有重要影响,长期秸秆还田如何影响稻田土壤水稳性团聚体碳氮磷含量及生态化学计量比尚不清楚。本研究以双季稻田为研究对象,设置仅施化肥(CK)、低量秸秆还田+化肥(LS)和高量秸秆还田+化肥(HS)三个处理,于秸秆还田后的第9~10年测定土壤水稳性团聚体组成及其碳氮磷含量,分析土壤水稳性团聚体分布、平均重量直径及元素生态化学计量比,旨在明确长期秸秆还田下双季稻田土壤各粒径水稳性团聚体对碳氮磷养分的贡献及其生态化学计量比特征。结果表明,秸秆还田后的9~10年,与CK相比,HS和LS处理显著增加了>0.25 mm粒径水稳性团聚体(R0.25)的占比和平均重量直径(MWD);HS处理显著提高了>2 mm、0.25~1 mm、0.053~0.25 mm和<0.053 mm粒径水稳性团聚体总碳(TC)和总氮(TN)含量,且增加幅度最大的粒径为0.25~1 mm,分别为28.1%和22.9%,而对总磷(TP)含量无显著影响。HS和LS处理较CK显著提高了>2 mm粒径水稳性团聚体对于土壤TC、TN和TP的贡献率,有助于改善水稻的氮磷吸收。与CK相比,HS处理提高了各主要粒径水稳性团聚体(>2 mm、1~2 mm、0.053~0.25 mm和<0.053 mm)氮磷比和碳磷比,有利于提高稻田氮素有效性,且碳磷比未达到限制磷素供应的阈值而没有降低磷素有效性。研究表明,高量秸秆(6 t/hm2)还田提高了稻田水稳性团聚体的稳定性,提高了土壤碳氮储量,以及水稳性团聚体氮磷比,对于改善稻田土壤结构和氮素供应具有较好的效果。

Contents and eco-stoichiometric ratios of carbon, nitrogen and phosphorus of soil aggregates in double-cropping rice fields under straw incorporation

The contents and eco-stoichiometric ratios of soil carbon, nitrogen, and phosphorus have important effects on crop nutrient supply. It is still unclear how long-term straw incorporation affects the carbon, nitrogen, and phosphorus contents and eco-stoichiometric ratio of soil aggregates in paddy fields. In this study, the double-cropping rice field was taken as the research object, and three treatments of only applying chemical fertilizer (CK), low amount straw incorporation + chemical fertilizer (LS), and high amount straw incorporation + chemical fertilizer (HS) were set up. Soil aggregate composition and its contents of carbon, nitrogen, and phosphorus were measured in 9~10 years after straw incorporation, and the distribution, average weight diameter, and eco-stoichiometric ratio of soil aggregates were also analyzed, so as to clarify the contribution of soil aggregates with different particle sizes to carbon, nitrogen, and phosphorus nutrients and the characteristics of the ecological stoichiometric ratios under long-term straw incorporation in double cropping rice fields. The results showed that in 9~10 years after straw incorporation, compared with CK, HS and LS treatment significantly increased the proportion of water-stable aggregates with the particle size of > 0.25 mm (R0.25) and mean weight diameter (MWD). HS treatment significantly increased the total carbon (TC) and total nitrogen (TN) contents of water-stable aggregates with the particle sizes of > 2 mm, 0.25~1 mm, 0.053~0.25 mm and < 0.053 mm, and the particle size with the largest increase of TC and TN was 0.25~1 mm, with an increase of 28.1% and 22.9% respectively, but had no significant impact on the total phosphorus (TP) content. Compared with CK, HS and LS treatments significantly increased the contribution rate of water-stable aggregates > 2 mm to soil TC, TN and TP, which was helpful to improve the nitrogen and phosphorus uptake of rice. Compared with the CK, HS treatment improved the nitrogen phosphorus ratio and carbon phosphorus ratio of water-stable aggregates (> 2 mm, 1~2 mm, 0.053~0.25 mm and < 0.053 mm), which was beneficial for improving nitrogen availability in rice fields and did not limit phosphorus supply with the carbon phosphorus ratio not exceeding the threshold. This study showed that the high amount of straw (6 t/hm2) incorporation at can improve the stability of water-stable aggregates, increase soil carbon and nitrogen storage, and the aggregate nitrogen phosphorus ratio, which has a good effect on improving soil structure and nitrogen supply in paddy fields.