Black Soil Carbon Nitrogen And Its Fraction In Response To Long-Term Fertilization

Cropland soil organic carbon and nitrogen are key factors of soil fertility and crop production, and they are the basic of sustainable development of agriculture. They are also related to global climate change. Agriculture management measures such as fertilization affect the cycle of soil organic carbon and nitrogen. Northeast China is one of the main food production areas, which is now facing the loss of soil organic carbon (SOC) and total nitrogen(TN). We analyzed SOC, TN, their fractions and revealed the effects of long-term fertilization on SOC, TN and their fractions of black soil. We also analyzed the response of SOC and its fraction to system carbon input of black soil. Results are as given follows:1. Compared with control, the application of manure, manure plus mineral fertilization and straw did not only increase the crop production, but also contribute to accumulation of SOC and TN. SOC and TN of surface soil was more sensitivitive to fertilization than subsurface soil. As to normal fertilization, SOC of surface soil in Harbin reached16.25g·kg-1under nitrogen fertilizer plus manure (NM) treatment. Compared with control (CK), NM increased SOC by25.8%. TN of surface soil in Harbin reached1.62g·kg-1under NM treatment, and compared with CK, TN increased by30.0%. As regarding to hign amount of fertilization, SOC of surface soil in Harbin reached16.69g·kg-1under nitrogen plus phosphorus and manure (N2P2M2) treatment. Compared with CK2, N2P2M2increased SOC by25.0%. TN of surface soil in Harbin reached1.77g·kg-1under N2P2M2treatment, and compared with CK2, TN increased by32.8%. The SOC and TN stock was not sensitive to fertilization, there was no significant difference between different treatments. Soil carbon to nitrogen ratio was not sensitive to fertilization, and soil C/N maintained about10.2. Fertilization affected soil carbon and nitrogen fraction. Soil microbial biomass carbon(SMBC) and soil microbial biomass nitrogen (SMBN) of surface soil was higher than that of subsurface soil. Long-term application of manure(manure, manure plus mineral fertilizer) and straw increased the SMBC and SMBN, but manure was better than straw. Long-term application of manure and straw increased the percentage of SMBC in SOC(SMBC/SOC)and percentage of SMBN in TN(SMBN/TN), and manure was more significant than straw. Application of mineral fertilizer alone did not increase the SMBC and SMBN, and also had little effect on SMBC/SOC and SMBN/TN. As to normal fertilization in Harbin site, the value of surface soil SMBC/SOC under NPKM treatment reached1.92%. And compared with CK, this value increased by43.6%. The value of SMBN/TN reached2.88%, which inceased by187.1%compared with CK. While as to high amount fertilization in Harbin site, the value of surface soil SMBC/SOC under N2P2M2treatment reached1.90%, which increased by40.1%compared with CK2.The value of SMBN/TN reached2.20%, which increased by121.0%compared with CK2.3. Dissolved organic carbon(DOC) and dissolved organic nitrogen(DON) of surface soil was higher than that of subsurface soil. Long-term application of manure and manure plus mineral fertilizer increased DOC and DON significantly. Application of straw also increased DOC and DON, but the effect was not as significant as manure. Mineral fertilizer had little effect on DOC and DON. Long-term application of manure also increased DOC/SOC and DON/TN. As to normal fertilization in Harbin site, the value of surface soil DOC/SOC under NPKM treatment reached0.54%. Compared with CK, this value increased by72.9%. The value of DON/TN reached1.72%, which increased by75.0%compared with CK. While as to high amount fertilization in Harbin site, the value of surface soil DOC/SOC under M2treatment reached0.62%, which increased by94.7%compared with CK2. The value of DON/TN reached1.60%, which increased by43.3%compared with CK2.4. Long-term application of manure increased the percentage of SOC, TN in coarse sand and clay(Harbin site). As to surface soil, NPKM increased the percentage of SOC in coarse sand by191.3%compared with CK, while M increased the percentage of SOC in clay by45.0%. However, NPKM increased the percentage of TN in coarse sand by179.3%compared with CK, while M increased the percentage of TN in clay by47.3%compared with CK. Manure also had positive effect on the SOC and TN accumulation in coarse sand and clay, which was very important to carbon sequestration.5. SMBC, SMBN, DOC, DON, coarse sand SOC were very sensitive to fertilization, and they reflected the activity of SOC and TN. Besides, they reflected the change of fertility in response to fertilization.6. The black soil in northeast China is facing the decreasing in SOC and TN, and long-term application of manure can slow down the decrease in SOC and TN. There is a positive correlation relationship between the change of SOC and carbon input. Besides, there is a positive correlation relationship between SMBC, DOC, coarse sand SOC, clay SOC and system carbon input. With the increasing of carbon input, these indexes will increase.