耕作方式对紫色水稻土有机碳和微生物生物量碳的影响

以位于西南大学的农业部紫色土生态环境重点野外科学观测试验站始于1990年的长期定位试验田为对象,研究了冬水田平作(DP)、水旱轮作(SH)、垄作免耕(LM)及垄作翻耕(LF)等4种耕作方式对紫色水稻土有机碳(SOC)和微生物生物量碳(SMBC)的影响。结果表明,4种耕作方式下SOC和SMBC均呈现出在土壤剖面垂直递减趋势,翻耕栽培下其降低较均匀,而免耕栽培下其富集在表层土壤中。同一土层不同耕作方式间SOC和SMBC的差异在表层最大,随着土壤深度的增加,各处理之间的差异逐渐减小。在0—60 cm剖面中,SOC含量依次为:LM(17.6 g/kg)>DP(13.9 g/kg)>LF(12.5 g/kg)>SH(11.3 g/kg),SOC储量也依次为:LM(158.52 Mg C/hm2)>DP(106.74 Mg C/hm2)>LF(93.11 Mg C/hm2)>SH(88.59 Mg C/hm2),而SMBC含量则依次为:LM(259 mg/kg)>SH(213 mg/kg)>LF(160 mg/kg)>DP(144 mg/kg)。与其它3种耕作方式比较,LM处理显著提高SOC含量和储量以及SMBC含量。对土壤微生物商(SMBC/SOC)进行分析发现,耕作方式对SOC和SMBC的影响程度并不一致。SMBC与SOC、全氮、全磷、全硫、碱解氮、有效磷均呈现极显著正相关(P<0.01),与有效硫呈显著正相关(P<0.05);表明SMBC可以作为表征紫色水稻土土壤肥力的敏感因子。

Long-term tillage effects on soil organic carbon and microbial biomass carbon in a purple paddy soil

Changes in soil organic carbon (SOC) storage are closely related to soil quality and the long-term sustainability of agriculture. Accurate assessments of the effects of tillage system on soil organic matter sequestration are needed. A small difference in SOC contents can substantially change soil C storage estimates because the terrestrial carbon pool is so large. Sequestration of C in soils represents a mechanism to reduce atmospheric CO₂ levels, but the extent to which soils can sequester C varies with climate, cropping system, and tillage practices. Soil C sequestration represents the accumulation of soil organic matter, and is the difference between C inputs by plants and organic matter decomposition. Hence, microbial activity is an important factor influencing C sequestration potential in soils. The impacts of different tillage systems on SOC and soil microbial biomass carbon (SMBC) were studied in this paper. The tillage experimental site (30°26'N, 106°26'E) is located at the farm of Southwest University in Chongqing, China. The experiment was initiated in 1990 and included four tillage treatments: 1) conventional tillage with rotation of rice and winter fallow system (DP), where regular tillage practices were used for rice with three times of plowing and harrowing annually, and after the rice harvest, the field was submerged with water; 2) conventional tillage with rotation of rice and rape system (SH), where tillage was the same as in the DP treatment, but the field was alternately submerged and drained for rice and rape cultivation; 3) no-till and ridge culture with rotation of rice and rape system (LM), where ridges (five in each plot) with the top of 25 cm width were intervened with the ditches of 30 cm width and 35 cm depth, with no tillage practices performed, rape cultivated on the top of the ridges with the water level being maintained just to the bottom of the ditch, and the field submerged in water to cultivate rice after rape being harvested; 4) tillage and ridge culture with rotation of rice and rape system (LF), where ridges were made as in LM treatment, but ridges were made every year for cultivating rice after rape harvest. Soils sampling at the depths of 0-10, 10-20, 20-30, 30-40, 40-50 and 50-60 cmwere performed with a soil drill after the rape harvest in the spring of 2009. The results showed that the contents of SOC and SMBC both decreased with the increase of soil depth under four tillage systems; however LM treatment enriched SOC and SMBC contents near the soil surface. The differences of SOC and SMBC contents in the same soil layer among the four tillage systems were the largest in 0-10cm soil layer and the lowest in 50-60cm soil layer. In the whole soil layer(0-60cm), the order of SOC contents was LM(17.57 g/kg) > DP(13.91 g/kg) > LF(12.50 g/kg) > SH(11.29 g/kg), SOC storage was LM(158.52 MgC/hm²) > DP(106.74 MgC/hm²) > LF(93.11 MgC/hm²) > SH(88.59 MgC/hm²), and SMBC contents was LM(258.88 mg/kg) > SH(213.23 mg/kg) > LF(159.71 mg/kg) > DP(144.08 mg/kg). Compared with the other three treatments, LM treatment significantly increased the content and storage of SOC, and SMBC content. Analysis of microbial quotient showed that tillage systems had different impacts on SOC and SMBC. SMBC were significantly correlated with soil organic carbon, total nitrogen, alkali-hydrolyzed nitrogen, total phosphorus, effective phosphorus, total sulfur and effective sulfur which suggested SMBC could be a sensitive indicator for characterizing changes of purple paddy soil fertility in Southwest China.