Characteristics Of Stabilized Organic Carbon In Soils Of Dryland And Paddy Under Long-term Fertilizations

Soil organic matter (SOM) is not only the key point for cropland soil fertility, but also has close relation with global climate change. Long-term fertilization in cropland can significantly affect soil total carbon content, and could also have different impacts on various soil carbon factions. This study focused on different soil carbon fractions and its relation to soil total carbon content, to provide scientific basement for choosing suitable management tool for soil fertility improvement. Specifically, topsoil samples (0-20 cm) were collected from a paddy soil (red soil, fertilization for 31 years) and a dry land soil (brown earth, fertilization for 28 years) under different long-term fertilization treatments. The treatments in paddy soil contained control (CK), chemical NPK fertilizer (NPK); combined application of manure with fertilizer(NPKM7/3, NPKM5/5, NPKM3/7); and in dryland soil, they contained control (CK), chemical NPK fertilizer (N2), combined application of manure with fertilizer (M1N1P1, M2N2, M4N2P1). Using physical-chemical combination fractionation method, soil samples were separated to no-protection groups (cPOM, LF), physical-protection groups (μagg, iPOM), chemical-protection groups (H-dsilt, H-dclay), biochemistry-protection groups (NH-dsilt, NH-dclay), physical-chemical-protection groups (H-μsilt, H-μclay), and physical-biochemistry-protection group (NH-μsilt, NH-μclay). The effects of long-term fertilizations on various carbon fractions and soil total carbon contents in paddy soil and dry land soil were discussed. The main results were as following:1) Both in paddy soil and dry land, long-term application of manure or its combination with fertilizer increased soil total carbon and nitrogen content/stock, but application of only chemical fertilizer did not change them. However, all fertilization treatments did not change soil C:N ratios.2) Long-term fertilizations had different impacts on various soil carbon factions. Both in paddy soil and dry land, manure application or its combination with chemical fertilizer increased soil carbon content in cPOM fraction, but did not change it in clay and silt fractions.3) Paddy soil and dry land soil had contrasting carbon distribution among soil fractions. In the paddy soil, carbon in cPOM fraction occupied the highest proportion (50%) in soil total carbon. In the dry land, however, μagg fraction occupied the highest carbon proportion (35%).The above results suggested that, although dry land soil and paddy soil had different carbon sequestration mechanism, the effect of long-term fertilization on carbon in soil fractions and total soil were similar between the two soils. These results will provide scientific basement for evaluating carbon dynamics under long-term fertilization and choosing suitable management tool to improve soil fertility.