耕作与轮作方式对黑土有机碳和全氮储量的影响

土壤有机碳(SOC)及全氮(TN)对土壤肥力、作物产量、农业可持续发展以及全球碳、氮循环等都具有重要影响。为探索不同耕作和轮作方式对耕层黑土SOC和TN储量的影响,本文以吉林省德惠市进行了8 a的田间定位试验中层黑土为研究对象,对免耕、垄作和秋翻三种耕作方式及玉米-大豆轮作和玉米连作两种轮作方式下SOC和TN在各土层的含量变化进行了分析,并采用等质量土壤有机质储量计算方法,对比分析了不同处理对0～30 cm SOC和TN储量的影响。结果表明,与试验开始前相比,玉米-大豆轮作系统中,秋翻下SOC和TN储量均有所降低;免耕显著增加了0～5 cm SOC及TN含量,但SOC在亚表层亏损,导致其储量并未增加;而垄作处理下SOC及TN含量在0～5、5～10 cm的均显著增加,0～30 cm储量亦分别增加了4.9%和10.7%。玉米连作系统的两种耕作处理(免耕和秋翻)下SOC和TN储量均有所增加,且TN储量增幅均高于玉米-大豆轮作系统,其中免耕下TN储量增幅是玉米-大豆轮作的3.2倍。所有处理下C/N均呈降低趋势,其中垄作0～5 cm C/N由12.05降至11.04,降低幅度分别是免耕和秋翻的3.2和2.8倍。综上可知,对质地黏重排水不良的中层黑土,玉米-大豆轮作系统下免耕并不是促进SOC固定的有效形式,而垄作则促进了黑土SOC和TN的积累,这不仅有利于土壤肥力的改善,而且是使农田黑土由CO2"源"变为"汇"的有效形式之一。与玉米-大豆轮作相比,玉米连作下三种耕作方式都有利于SOC和TN积累。

Tillage and rotation effects on soil organic carbon and total nitrogen stocks of a black soil

Soil organic matter is of crucial importance to soil fertility, crop yield, agricultural sustainable development and global carbon and nitrogen cycling. This study was undertaken to evaluate the tillage and rotation effects on soil organic carbon (SOC) and total nitrogen (TN) storage of a Black soil in Northeast China. Three tillages and two rotations were involved in this study, including no-tillage (NT) and moldboard plow (MP) which were in combination with 2-year corn-soybean rotation (CS) and continuous corn (CC), and ridge tillage (RT) which was under 2-year corn-soybean rotation (CC) only. The SOC and TN stocks calculated based on samples collected in 2009 were compared with the initial values when the study was initiated in 2001. In the CS system, SOC and TN stocks (equivalent mass basis) decrease under MP practice. NT leads to a significant increase in SOC and TN contents in the 0-5 cm; however, SOC contents show a notable decrease at 5-20 cm depth, leading to a 2.6% reduction in SOC storage in the plow layer (30 cm). Under RT, both SOC and TN contents increase significantly in the 0-5 cm and 5-10 cm, which lead to 4.9% and 10.7% increase in SOC and TN storage, respectively. In the CC system, SOC and TN stocks increase under both MP and NT, and the increase of TN is 3.2 times higher than in CS system. The C/N ratio declines under all treatments. The C/N ratios in RT soil drop form 12.05 to 11.04 in the 0-5 cm, with a decreasing amplitude of 3.2 and 2.8 times greater than NT and MP, respectively. The results indicate that neither MP nor NT is efficient in promoting SOC sequestration under corn-soybean rotation in the poorly-drained clay loam soil. Ridge tillage, however, promotes SOC and TN accumulation and this indicates that it not only could improve soil fertility but also result in turning farmland soil from carbon source to carbon sink. In addition, continuous corn cropping is more favorable in SOC and TN sequestration than the corn-soybean rotation system.