Studies On Characteristics Of Soil Organic Matter And Its Relate To Soil Quality In Reddish Paddy Soil Under Long-term Fertilization

A long-term field experiment with the double rice and winter fallow cropping system was conducted based on the Key Field Monitoring Experimental Station for Reddish Paddy Soil Eco-environment in Wangcheng, Ministry of Agriculture, China, to study the effect of long-term application of fertilizers on the soil organic carbon and productivity. The treatments selected in this study were:CK (no any fertilizer applied), NP (N, P fertilizers), NK (N, K fertilizers), NPK(N, P, K fertilizers), NK+PM (N, K plus pig manure), NP+RS(N, P plus rice straw) and NPK+RS (N, P, K plus rice straw). The aim of the research was to study the effects of long-term fertilization systems on the characteristics of different soil organic matter and it's components, the dynamic change of soil organic matter and labile organic matter, the characteristics of water stable aggregates distribution and organic carbon in water stable aggregates, soil physical properties, chemical properties and biochemical properties, soil productivity and the relationship between soil organic matter and soil quality. The main results were as follows:The results showed that soil organic matter (SOM) content increased or decreased with cropping year in different treatments under different fertilization system. SOM content was tended to decrease in long term no fertilizer (CK) and NP application (NP) treatment, while SOM content was tended to increase in long term fertilizer application (NK, NPK, NK+PM, NP+RS and NPK+RS). Soil organic matter accumulation process in NPK, NK+PM, NP+RS and NPK+RS treatments are still in the stage of steady growth, and its increasing trend with duration of experiment was a significant positive linear correlation. Soil organic matter accumulation process in long term NK treatment is in the stage of slow growth, and its increasing trend with duration of experiment was a positive linear correlation. Soil organic matter content in no fertilizer (CK) and long term NP treatment was tended to decrease, and its decreasing trend with duration of experiment was a significant negative linear correlation. Long term balance of NPK fertilization and integrated fertilization with organic manure and chemical fertilizers can increase the content of soil labile organic matter, and the effect of integrated fertilization with organic manure and chemical fertilizers on the accumulation of soil labile organic matter was higher than chemical fertilization alone.There were significantly difference(p<0.05) in different treatments of soil organic carbon (SOC), easily oxidizable organic carbon (EOC), microbial biomass carbon (MBC), light fraction organic carbon (LFOC), humic acid organic carbon (HA-C) and fulvic acid organic carbon (HF-C) in plow layer of reddish paddy soil after 54season rice cropping in 27 years. SOC, EOC, MBC, LFOC, HA-C and HF-C in long-term combination application of chemical fertilizers (NP, NK and NPK) with organic manure (PM or RS) were significantly higher than those in long-term chemical fertilizer application (NP, NK and NPK) alone(p<0.05). The proportion of active organic carbon to soil organic carbon was MBC< LFOC< EOC. SOC was positively related to EOC(p?0.01) and LFOC(p<0.05).There were significant differences in the content of different size water-stable aggregates among all treatments under the long-term different fertilizer system. The content of water-stable aggregates in the>5mm size fraction were the highest among different size fractions, and then in the<0.25mm of all treatments. Long-term alone application of chemical fertilizer such as NP, NK or NPK decreased organic carbon in water-stable aggregates of all particle size compared with no fertilizer application treatment (CK), while long-term combined application of chemical fertilizer(NK, NK or NPK) with organic manure (PM or RS) increased organic carbon content in aggregates of all particle size significantly(p<0.05). In all the treatments, the contribution of organic carbon in different size water-stable aggregates fraction to organic carbon in whole soil was the highest in the>5 mm fraction, accounting for 46.71%-60.52%(mean 54.31%), and then was in the<0.25 mm water stable aggregates, accounting for 22.42%-29.71% (mean 26.35%). Long-term combined application of fertilizer combined with organic manure was an effective method to increase the stability of soil water-stable aggregates and organic carbon content in different size soil aggregates and to improve soil structure.Contents of soil organic carbon (SOC), labile organic carbon (LOC), high labile organic carbon (HLOC) and moderate labile organic carbon (MLOC) decreased with the increasing of soil depth. Contents of SOC, LOC, HLOC and MLOC were significantly different among the different soil layers. Long-term application of fertilizer combined with organic fertilizer significantly increased the contents of organic carbon in 0-15cm and 15-30cm soil layer, while the increasing effect was not observed in 30-45cm soil layer. The contents of LOC, HLOC and MLOC were significantly different among different treatments in 0-15cm,15-30cm and 30-45cm soil layer. There was obviously different in SOC content in 0-15cm soil layer among different treatments, but significant difference was not observed in 15-30cm and 30-45cm soil layers among different treatments.There were significant difference in soil physical properties such as bulk density, particle density and soil porosity among all treatments in long-term different fertilizer system. Long-term combined application of chemical fertilizer with the PM or RS decreased markedly soil bulk density and particle density, and increased the porosity. Compared with no fertilizer application treatment (CK), long-term fertilizer application (NP, NK, NPK, NK+PM, NP+RS and NPK+RS) significantly increased the mean weight diameter (MWD) of water-stable aggregates(p<0.05). Combined application of the PM and RS with fertilizer help to formation of 5-0.5mm water-stable aggregate and hence increased soil structure stability and soil physical quality compared with application of fertilizer alone. pH value in soils within long-term combined application of the PM, RS with chemical fertilizer was decreased compared with the initial soil, but electrical conductivity (EC) was not different with the initial soil. Contents of TOC, total N, available N and available P within long-term combined application of the PM, RS with chemical fertilizer were higher than those within CK treatment and the corresponding application of fertilizers alone. The TOC, total N, Available N, Available P and Available K within NPK treatment were obviously higher than those in NP and NK treatment. Significant differences of the soil pH value and EC were not observed between NPK treatment and NP or NK treatment. Long-term combined application of PM, RS with fertilizer increased soil enzyme activity significantly, and hence help to improve soil biochemical environment for crops. Rice yield was higher in treatments for combined application of fertilizer with PM and RS than in corresponding fertilizer application alone. Sustainable yield index(SYI) in NPK treatment was higher than in NP or NK treatment. Rice yield was significantly or extremely significantly positive correlated with soil TOC, total N, Available N, Available P, soil enzyme activity, MBC and MBN, which may act as valuable indexes for evaluation soil quality.Soil total organic carbon(TOC) and different labile organic carbon fraction (EOC, MBC and LFOC) have significant relationship with the soil physical, chemical and biochemical parameters such as soil bulk density, particle density, porosity, total N, available N, available P, enzyme activity and soil respiration. Accumulation of TOC and LOC were beneficial to improve soil physical, chemical and biochemical properties. Rice yield and sustainable yield index(SYI) were positively correlated with TOC different labile organic carbon fraction (EOC, MBC and LFOC). Long-term combined application of pig manure (PM), rice straw(RS) with chemical fertilizer increased amount of N, P and K uptake by rice, and there was positive correlation between TOC or LOC and N, P, K absorption. Soil TOC, EOC, MBC and LFOC have positive relationship with soil quality index(SQI), which suggested soil total organic carbon and labile organic carbon play a important role in soil quality. In the rice planting areas of south China, long-term combining application of fertilizer with organic manure could obviously improve soil physical-chemical environment and its biological activity, and also the comprehensive quality.