Study On Characteristics And Simulation Of Organic Carbon Decompositon Of Several Main Soils In South China

The thesis studied characteristics of soil organic carbon(SOC) pools and their decomposition of several major soils in South China, based on three-pool-and-first-order dynamic theory and combined with laboratory incubation. On this basis, it explored to create a universal model for SOC decomposition, which is linked with soil basic physical and chemical properties.The results were as follows:There was significant difference in topsoil SOC while no significant difference in second-layer-soil SOC between regions. Content of topsoil SOC of different soils had such sequence as red soil>gley paddy soil>water-logging paddy soil>yellow soil>limestone soil>hydromorphic paddy soil>vegetable soil>submerged paddy soil>yellow brown soil> loamy soil. Content of SOC under different land-use had such sequence as swamp>forest and woodland>paddy field>bush>meadow>dry land.The size of total SOC pool decided that of each constituent SOC pool, while proportion of the constituent SOC pool had significant difference between soils due to effects of soil type, land use and external environment. Content of topsoil Ca,CS and Cr was respectively0.061～1.23g-kg-1,3.12～23.06g-kg-1and1.08～24.21g-kg-1, while proportion of Ca,CS and Cr was respectively0.55～5.01%,15.88～73.20%and25.36Y79.11%.Content of second-layer Ca,CS and Cr was respectively0.033～0.41g·kg-1,0.86～10.61g-kg-1and0.41～13.02g-kg-1, while proportion of Ca,CS and Cr was respectively0.81-7.35%,20.43～81.68%and17.10～77.66%. The Cs and Cr constituted95～99%size of SOC, and they always changed simultaneously. The proportion of Ca and Cr in topsoil was higher than that in second-layer, while the proportion of Cs had opposite order. The proportion of three pools had significant difference between soil types, which could be used as important basis for distinguishing different soil types. The proportion of Cr in natural soil was higher than that in farmland soil.The SOC decomposition process could be divided into three stages, that is fast decomposition stage(0-15d), slow decomposition stage(15-30d) and balanced decomposition stage(30-incubation ending). Divergence of SOC decomposition rate under different soil types mainly displayed in first30days. The peak and balance value of SOC decomposition curve both had significant difference between soil types, while the peak was decided by content of SOC especially content of Ca. The proportion of balance value ranged from7.62%to19.90%. Of natural soils, the SOC decomposition rate of yellow soil and red soil under different vegetation respectively had such sequence as scrub growth>evergreen broadleavedforest>Masson’spine forest>moso bamboo forest and evergreen broadleaved theropencedrymion> evergreen broadleavedforest>Masson’spine forest>Masson’spine forest. Comparison of SOC decomposition among types of soils was as follows:yellow soil deviated not far from red soil, but they were significantly higher than yellow brown soil and limestone soil. Of different age of stand, the SOC decomposition increased with forest age. Of agricultural soils, the SOC decomposition sequence under different cropping patterns,soil types and cultivation terms of years were as follows: weeds>peanut ground>orangery, hydromorphic yellow clayed soil>gley yellow clayed soil>submerged yellow clayed soil>water-logging yellow clayed soil and unreclaimed land>new dry land>old dry land. Accumulated CO2-C release amount derived from SOC decomposition was0.262-4.080g-kg-1, which comprised0.96-4.58%of the total SOC.Exponentiation model (kc=a×tb), exponential model and logarithmic model(kc=a X ln(-b X ln(t))) could be exactly used to portray SOC decomposition rate curve. Exponentiation model successfully simulated characteristics of SOC decomposition according to certain soil physical and chemical properties. The regression equation for the parameter was: a=-6.156+7.707×SOC+6.096×Cr-7.918RSON, b=-1.471+0.064×C/N. Exponentiation model (y=axtb) and polynomial model(y=ax3+bx2+cx+d) could be used for fitting accumulated CO2-C release amount curve, and cubic polynomial had achieved better accuracy.