长期施肥下褐土易氧化有机碳及有机碳库的变化特征

本研究探讨了24年长期施肥对褐土土壤有机碳(TOC)、有机碳储量(TOCs)、净固碳效率(NCSE)和碳库管理指数(CPMI)的影响,为评价褐土土壤碳库变化与质量及科学施肥提供理论依据。研究以褐土肥力与肥料长期定位试验为平台,通过9个处理[A组:不施肥处理(N_0P_0、CK);B组:单施无机肥处理(N_1P_1、N_2P_2、N_3P_3和N_4P_4);C组:有机肥与无机肥配施处理(N_2P_1M_1、N_3P_2M_3和N_4P_2M_2);D组:单施高量有机肥处理(M_6)]测定土壤TOC与易氧化有机碳(ROOC)含量,并计算TOCs、NCSE及CPMI等相关指标。结果表明,在不同土层不同时期施用较高量有机肥配施无机肥及施用高量有机肥(N_3P_2M_3、N_4P_2M_2和M_6)均可提高TOC和ROOC含量,且随土层深度加深提升作用减弱。TOCs、NCSE与0~20 cm土层TOC含量在时间和空间上的变化规律基本一致。施用高量有机肥(C组、D组)可有效提高TOCs,A组、B组的TOCs均值分别比C组、D组低76.77%与17.36%。长期施肥处理可提高NCSE,尤其是施用有机肥处理可显著提高NCSE。NCSE为D组C组A组=B组;D组NCSE为1 152.27 kg·hm~(-2)·a~(-1),是C组的2.51倍,B组的16.20倍。与试验前相比,C组和D组的CPMI无显著变化,且C组与D组间差异不显著,但A组与B组比试验前降低16.38~40.02。与A组(CK)相比,B组中N1P1处理与C、D组处理显著影响CPMI,提高了23.30~45.67。在0~40 cm土层CPMI与ROOC含量呈显著正相关,CPMI可以很好地指示有机碳的变化。可见,施用高量有机肥或者较高量有机肥与无机肥配施可极显著提高褐土土壤TOCs、NCSE和CPMI,即施用高量有机肥或者较高量有机肥与无机肥配施(N_3P_2M_3和N_4P_2M_2)有利于褐土有机碳的固存,可减少无机肥的施用量,使土壤性质向良性方向发展,培肥土壤。

Characteristics of readily oxidizable organic carbon and soil organic carbon pool under long-term fertilization in cinnamon soils

The effects of 24 years of long-term fertilization on total organic carbon (TOC), total organic carbon storage (TOCs), net carbon sequestration efficiency (NCSE) and carbon pool management index (CPMI) of cinnamon soils were analyzed in order to provide theoretical basis for the evaluation of soil carbon pool change and quality, and to guide scientific application mode of fertilizers in cinnamon soils. Using data from long-term experiment on soil fertility and fertilizer use history, TOC and ROOC (readily oxidizable organic carbon) contents were analyzed and the relative indexes for TOCS, NCSE and CPMI were calculated for 9 different treatment conditions. The treatments included Group A[no fertilization treatment (N₀P₀, CK)], Group B[single application of inorganic fertilizer treatments (N₁P₁, N₂P₂, N₃P₃ and N₄P₄)], Group C[mixed organic and inorganic fertilizers treatments (N₂P₁M₁, N₃P₂M₃ and N₄P₂M₂)] and Group D[single application of high amount of organic fertilizer treatment (M₆)]. Results showed that the application of medium and high organic manure (N₃P₂M₃ and N₄P₂M₂) increased the contents of TOC and ROOC in different soil layers and in different periods, but the promotion effect decreased with increasing soil depth. TOCS, NCSE and TOC had similar trends in both time and space. TOCS increased with increasing application of organic fertilizer (Group C, Group D), with 76.77% and 17.36% lower for average of Group A and Group B than that for Group C and Group D, respectively. Long-term fertilization improved net carbon fixation efficiency and the application of organic fertilizer significantly improved NCSE. NCSE decreased in the order of Group D > Group C > Group A > Group B. NCSE for Group D was 1 152.27 kg·hm^-2·a^-1, which was 2.51 times that of Group C, and 16.20 times that of Group B. Compared with CMPI before the experiment, there was no significant difference in CPMIs of Group C and Group D; while CPMIs of Group A and Group B decreased by 16.38-40.02. Also compared with control, the application of low-level inorganic fertilizer treatment (N₁P₁) and application of organic fertilizer of Group C and Group D significantly increased CPMI by 23.30-45.67. There was a significant positive correlation between CPMI and ROOC in the 0-40 cm soil layer, which implied that CPMI was a good indicator for organic carbon change. As noted, the application of high amount of organic manure or high amounts of organic and inorganic fertilizers (N₃P₂M₃ and N₄P₂M₂) significantly improved soil TOCS, NCSE and CPMI. In other words, application of high amounts of organic fertilizer increased organic carbon sequestration, decreased the application of inorganic fertilizer and enhanced better soil development and soil fertility.