长期绿肥利用下红壤性水稻土有机碳和可溶性有机碳的垂直分布特征

为了探讨长期绿肥翻压对红壤性水稻土有机碳(SOC)和可溶性有机碳(DOC)垂直分布的影响,利用在江西丰城水稻田进行了8 a的长期定位试验,研究了不施肥不种植绿肥(CK)、不施肥种植绿肥(M)、施用化肥(F)和施用化肥并种植绿肥(F+M)4个处理下土壤SOC和DOC的垂直分布特征,以及SOC和DOC的计量关系。结果表明,早稻和晚稻季土壤SOC和DOC含量随深度变化可以用S函数描述,拟合曲线的决定系数分别为0.928~0.966和0.876~0.975,均达到极显著(P<0.01)水平。施用化肥或绿肥还田(F、M和F+M处理)主要影响了表层(0~20 cm)土壤的SOC和DOC,20 cm以下土层各处理的SOC和DOC差异不显著。绿肥还田(F+M和M处理)显著(P<0.05)提高了表层土壤的SOC和DOC,而化肥处理(F)仅显著(P<0.05)提高了表层土壤的SOC。与CK相比,M、F、F+M处理的早稻季表层土壤SOC含量分别显著(P<0.05)提高了51.1%、80.9%、92.8%,M、F+M处理的早稻季表层土壤DOC含量分别显著(P<0.05)提高了12.9%、46.2%,M、F、F+M处理的晚稻季表层土壤SOC和DOC含量分别显著(P<0.05)提高了66.6%、81.3%、81.2%和37.1%、10.8%、45.2%。表层土壤DOC含量随SOC呈线性增长,晚稻季DOC随SOC增长率要高于早稻季。施肥降低了土壤DOC/SOC,但施用绿肥减缓了DOC/SOC下降。可见,绿肥不仅有利于土壤有机碳提高,同时有利于土壤有机碳生态功能的稳定。

Vertical distribution of soil organic carbon and dissolved organic carbon in reddish paddy soil under long-term green manure utilization

The objective of this study was to evaluate the effects of long-term application of green manure on the distribution of soil organic carbon (SOC) and dissolved organic carbon (DOC) in reddish paddy soil. Soil samples were collected from the 8 years' long-term experiments located in Fengcheng City, Jiangxi Province. Four treatments were carried out in the experiment: CK (no fertilizer), F (only chemical fertilizers), M (only green manure), F+M (green manure plus chemical fertilizers). The green manure was Chinese milk vetch (Astragalus sinicus L.). The vertical distribution of SOC and DOC in soil layers and the quantitative relationship of SOC and DOC were investigated. The results showed that, the variation of SOC and DOC contents with soil depths could be described by S-function in early rice and late rice season. The determination coefficients of function equations were 0.928-0.966 and 0.876-0.975, which reached significant level at P<0.01. The application of chemical fertilizers or green manure (treatment F, M, and F+M) affected SOC and DOC contents in the topsoil (0-20 cm). There was no significant difference in SOC and DOC in deep soil (>20 cm) within different treatments. Green manure treatments (F+M and M) significantly (P<0.05) increased SOC and DOC in topsoil, while chemical fertilizers treatment (F) only significantly (P<0.05) increased the SOC content in topsoil. Compared with CK, the contents of SOC in topsoil treated with M, F and F+M in early rice season were significantly (P<0.05) increased by 51.1%, 80.9%, 92.8%, respectively, and the contents of DOC in topsoil treated with M and F+M in early rice season were significantly (P<0.05) increased by 12.9% and 46.2%, respectively; while the contents of SOC and DOC in topsoil treated with M, F and F+M in late rice season were significantly (P<0.05) increased by 66.6%, 81.3%, 81.2% and 37.1%, 10.8%, 45.2%, respectively. The DOC content of topsoil increased linearly with SOC, and the increase ratio of DOC with SOC in late rice season was higher than that in early rice season. The long-term application of chemical fertilizers reduced DOC/SOC, yet green manure could mitigate DOC/SOC decrease. Green manure could not only increase soil organic carbon, but also benefit the stability of soil organic carbon ecological function.