Factors Affecting on Soil Organic Matter and Organic Carbon Fractions under Agricultural Soils of Upper Northern Thailand

Abstract

     This study proposed the effect of agricultural land uses on soil organic matter (SOM), soil organic carbon (SOC), and labile soil carbon fractions (LSCF), and the relationship between organic carbon fractions and SOM and SOC agricultural soil in the upper northern region. Soil samples were collected from the difference of crop-land use types (i.e. paddy soil, maize, and longan plantation) from the upper north of Thailand (i.e. Lampang, Phrae, Nan, Payao, Lampoon, Chiang Rai, Mae Hong Son, and Chiang Mai) were sampled by the grid method (1 grid = 10×10 km2) at a depth of 0-30 cm, and then the SOM, SOC, and LSCF were analyzed by reference methods from soil samples. The soil data were analyzed by Two ways and One way ANOVA, and the relationships between LSCF to SOM and SOC were calculated by the Principal Component Analysis method. The results showed that the higher means of SOM and SCF (e.g. WSC, C-FPSF, and C-LPSF) contents in maize soil than rice soil. Meanwhile, the longan soil had the highest proportion of SFC/SOC (% of SOC) (P<0.05) (about 13.398-17.814%), which was higher than that of rice and maize soil samples. As for the location effects, Phrae province had the highest content of SOM, while Chiang Rai province had the highest content of SOC. The LSCF were related to the SOC and SOM, which differ according to the crop-land uses. In this study, the amount of SOM, SOC, LSCF, and LSCF/SOC in rice soil (i.e. paddy soil) was lower than longan soil. As a result of soil management such as tillage and synthesis fertilizers could affect the LSCF a higher than longan plantation. The rice soil was plowed and contributed to a high decomposition rate. Meanwhile, possibly a high SOM formation rate in maize soil, there was high LSCF content and corresponding high SOM content. There was the highest percentage of LSCF/SOC which was consistent with high SOM content. Because the plant residues were continuing input in the longan plot area, there were minimum soil disturbances also. There was a combination of organic and chemical fertilization, that enhanced the Negative Priming. These could be the reasons that the amount of SOM and SOC in the longan soil was higher than in the paddy soil. Additionally, these soil data were the spatial study. They came from many pieces of information (i.e. soil type, quantity and type of clay mineral, geography, soil property, climate, and geomorphology of various provinces). These affect the formation and decomposition of SOM, SOC, and LSCF within crop-land types and in the condition of various provinces. The SOM, SOC, and LSCF could be assessing soil health indicators. Moreover, they were the capability of the modulators of Carbon cycling, which could be contributing to the carbon sequestration in the agricultural soils. That could be for soil health improvement and the mitigation of climate change.