Variation Characteristics Of Organic Carbon And Its Fractions In Soil Of Alfalfa Grassland With Different Growing Years

To investigate the variability of soil organic carbon and its fractions in alfalfa grassland with different growth years, this research select four growth years(2a,4a,11 a,16a), taking samples deep into1 m at different growth stages with dormancy stage, returning green stage, branching stage, florescence stage, seed-setting stage; and measure the grass yield. The results showed as follow:1. At branching stage, alfalfa grass yield decreased with the increase of growth years, the highest grass yield was found in 2a alfalfa(The fresh yield were 36190.000 kg?hm-2). And at florence stage,seed-setting stage, alfalfa grass yield increased first then decreased with the increase of growth years,the highest grass yield was found in 11 a alfalfa(The fresh yield were 50126.667 kg·hm-2, 57186.667 kg?hm-2). A significant difference was found at each growth stage in 11 a alfalfa grass yield(p<0.05).2. Soil organic carbon in different growth period of alfalfa was mainly concentrated in 0-60 cm soil layer, and decreased with the increase of soil depth. Soil organic carbon in 2a decreased with the growth stage, 4a showed a trend of decreasing and then increasing, 11 a and 16 a showed a increasing trend. Soil organic carbon in the regreening stage increased first and then decreased with the growth years, and in the rest stages, soil total organic carbon decreased with the increase of the growth years,indicating that soil organic carbon were affected by the growth stage and growth years.3 Distribution characteristics of organic carbon fractions in soil of alfalfa grassland with different growing years shows that: 1). The soil organic carbon fractions of alfalfa were mainly concentrated in the 0-60 cm soil layer, showing a surface assembled, and decreased with the increase of the soil depth. 2)The organic carbon fractions in each growth years of alfalfa decreased with the growth stage. 3) ROC(Readily oxidized organic carbon) in returning green stage, Particle organic carbon(POC) in returning green stage, florence stage, Dissolved organic carbon(DOC) in seed-setting stage,and Light fraction organic carbon(LFOC) in florence stage increased with the growth years, and in the rest stages, soil organic carbon fractions decreased with the growth years.4. Correlation analysis showed that: Only ROC showed a highly significant(P<0.01) or significant(P<0.05) negative correlation with growth years, while others showed a different correlation,indicating that different organic carbon fractions in soil of alfalfa showed the difference in time and space with the change of growth stage and growth years.