Mineralization Characteristics Of Soil Labile And Recalcitrant Carbon/Nitrogen Under Different Long-Term Fertilization Systems

To reveal the mineralization characteristics of soil labile and recalcitrant carbon&nitrogen component under different long-term fertilization systems in China, black soil, fluvo-aquic soil and paddy soil was choosen from different regions as object of study.We regard soil efficient sectionalization as breakthrough point, and the fractions of labile and recalcitrant carbon&nitrogen were separated by particle-density method.Then combined with Megan Steinweg’s dry-wet mineralization training method to test the carbon and nitrogen mineralization parameters of different components.The mineralization characteristics of different components study offer theoretical reference for soil fertility measures and management of soil carbon or nitrogen pool. The main results and conclusions are showed below:(1) On the basis of improving original sieving equipment,compared with the results that sieved at mass of 50 g,the mass recovery rate of the black soil or fluvo-aquic soil sieved at mass of 300 g increased between 1 and 3 percent. Organic carbon or total nitrogen recovery rate was also having an improvement during 1 and 8 percent. There are no significant difference in liable or recalcitrant carbon(or nitrogen)content between the two sieving mass. In conclusion, the new machine can sieve 300 g soil sample at one time, it can be a simple and efficient way to get the soil liable or recalcitrant carbon and nitrogen components.(2) The Net-Carbon(Net-C) mineralization potential and mineralization contribution rate of soil labile or recalcitrant carbon can be changed under different fertilizer treatments.The Net-C mineralization potential of upland soil labile carbon under different fertilizer treatments were higher than that under CK treatments by 27.08%—66.49%(except NPK of black soil).The Net-C mineralization potential of paddy soil labile carbon under NPKM was higher than that under CK by14.32%,but other fertilizer treatments had no improvement effect. The Net-C mineralization potential of upland soil labile carbon under NPKM treatment was 25.35 mg·kg-1·d-1, which was increased by 39.29%than NPK(18.20 mg·kg-1·d-1) and keep original level with NPKS(22.21 mg·kg-1·d-1) or higher. The Net-C mineralization potential of paddy soil labile carbon under NPKM treatment was 46.85mg·kg-1·d-1,which was higher than that under NPK and NPKS(40.98-41.15 mg.kg-1.day-1). But there were no significant influence betwen NPK and NPKS. In both upland and paddy soil, the Net-N mineralization potential of soil labile carbon was 1.4-2.0 times that of soil recalcitrant carbon. The Net-C mineralization potential of soil recalcitrant carbon in both upland and paddy siol had no significant difference among different fertilizer treatments. The mineralization contribution rate of upland or paddy soil labile carbon under NPKM was significantly improved than that under CK,but NPKS and NPK just had a slight increase or maintain the original level.In conclusion, The Net-C mineralization potential or mineralization contribution rate of upland soil labile carbon were more sensitive to different fertilizer measures than that in soil recalcitrant carbon. Under different fertilization measures, the Net-C mineralization potential of soil labile carbon was significantly higher than that of soil recalcitrant carbon.Long-term application of NPKM will improve Net-C mineralization potentials and contribution rate,which had a improvement effect better than NPKS and NPK. In paddy soil,the Net-C mineralizationpotential and contribution rate of soil labile carbon were significantly improved under NPKM, but not sensitive to other fertilizer measures.The mineralization potential of carbon in paddy soil was higher than that in upland.(3) Net-Nitrogen(Net-N) mineralization potential and mineralization contribution rate of soil labile or recalcitrant carbon had a different reaction to different fertilization measures.The Net-N mineralization potential of soil labile nitrogen(upland and paddy soil) under treatments of NPK, NPKS and NPKM were higher than that under CK treatments by 26.82%-137.10%(except NPK of black soil).The Net-N mineralization potential of upland soil labile nitrogen under NPKM treatment was 1.33mg·kg-1·d-1, which was higher compared with NPKS(0.96 mg·kg-1·d-1) and NPK(0.76 mg·kg-1·d-1). The Net-N mineralization potential of paddy soil labile nitrogen under NPKM treatment was 4.93mg·kg-1·d-1, which was higher compared with NPK(4.20 mg·kg-1·d-1). But there were no significant influence among other treatments.The Net-N mineralization potential of upland or paddy soil recalcitrant nitrogen had no significant difference among different fertilizer treatments. The average mineralization potential was 0.55 mg·kg-1·d-1 in upland soil and 3.96 mg·kg-1·d-1in paddy soil. The Net-N mineralization potential of soil labile nitrogen was higher than that of soil recalcitrant nitrogen in both black soil and fluvo-aquic soil. Among them, the Net-N mineralization potential of soil labile nitrogen was 1.5-2.0 times that of soil recalcitrant nitrogen. But the paddy soil showed no difference between the soil labile and recalcitrant nitrogen fractions. The mineralization contribution rate of upland soil labile nitrogen was influenced by different fertilizer measures in this order CK,NPK<NPKS<NPKM. The mineralization contribution rate of paddy soil labile nitrogen was not sensitive to different fertilizer measures,expect NPKM was higher than CK. There were no significant differences among the mineralization contribution rate of upland or paddy soil recalcitrant nitrogen under different fertilizer treatments. In conclusion, The Net-N mineralization potential and mineralization contribution rate of upland soil labile nitrogen were more sensitive to different fertilizer measures than that in soil recalcitrant nitrogen. The Net-N mineralization potential of soil labile nitrogen was significantly higher than that of soil recalcitrant nitrogen. Long-term application of fertilizer will improve Net-N mineralization potential or mineralization contribution rate of upland soil.The improvement effect is in the order of NPKM>NPKS>NPK. The Net-N mineralization potential of paddy soil labile or recalcitrant nitrogen was not sensitive to different fertilizer measures. The mineralization potential of nitrogen in paddy soil was significantly higher than that in upland.(4) In both upland and paddy soil, the microbial biomass carbon&nitrogen was significantly correlation with the mineralization potential of soil carbon&nitrogen in labile or recalcitrant fraction.The microbial biomass carbon&nitrogen of soil labile fraction was 1.20-2.75 times that of soil recalcitrant fraction. The microbial biomass carbon&nitrogen of upland soil labile fraction were sensitive to different fertilizer measures. The microbial biomass carbon(381.19 mg·kg-1) and nitrogen(39.96 mg·kg-1) under NPKM were improved than that under NPKS or NPK by 15.54%,29.10%The microbial biomass carbon&nitrogen of paddy soil labile fraction showed no differences among different fertilizer measures. There were no significant differences among the microbial biomasscarbon&nitrogen of upland or paddy soil recalcitrant fraction under different fertilizer treatments. The microbial biomass carbon&nitrogen in paddy soil was higher than that in upland.(5)The relative aboundance of Aquabacterium species between the labile and recalcitrant fraction in black soil under different fertilizer treatments, had significant differences. The relative aboundance of Aquabacterium species in labile fraction was 2-4 times than that in recalcitrant fraction.The species of Aquabacterium may be one of the reasons for the difference of mineralization ability between the soil labile and recalcitrant fraction.