| A long-term field experiment was conducted to study the effect of long-term inputs of green manure on soil physical properties, content of water-stable aggregates and its size distribution, content and distribution and storage of aggregate-associated organic carbon and nitrogen, characteristics of soil fertility, microbial properties, enzyme activities, Sustainable productivity and soil quality of a reddish paddy soil based on a double cropping system from Key Field Monitoring Experimental Station for Red Soil Eco-environment of Ministry of Agriculture, Qiyang County, Hunan, China. It can provide the theoretical basis for improving the soil fertility and soil quality in the reddish paddy soil, the utilization of farmland, and developing the sustainable and effective technology to improve the nutrient use efficiency. The main results were as follows:The soil bulk density in all green manure treatments was significantly reduced compared with the winter fallow treatment. Soil porosity under green manure applications was significantly higher than under the winter fallow. The 0.25-5 mm water stable aggregates and aggregates stabilities in the plow layer (0-15 cm depth) were higher in green manure treatments than in the fallow treatment. The mean weight diameter and normalized mean weigh diameter of aggregates were larger in the green manure treatment than in the winter fallow treatment. Soil given green manure retained both a higher water holding capacity in the plow layer soil, and a larger volume of moisture at all matric potentials (-10,-33 and -100 kPa). The free and weakly combined C and R2O3-combined C were significantly correlated with the stability of soil aggregates.Organic carbon is mainly enriched in 1-5mm water stable aggregates, followed by the >5mm water stable aggregates after a long-term winter planting green manure, and organic carbon is mainly enriched in >0.5mm water-stable aggregates in long-term winter fallow plot treated. Total N is mainly enriched in the larger size water-stable aggregates, in particular,>2mm water-stable aggregates, which indicated that large-size water-stable aggregates plays an important role in transformation of soil total N. Large-size water-stable micro-aggregates have a strong enrichment and physical protection on soil organic carbon and nitrogen. Long-term winter planting green manure can increase the content of organic carbon and total N of water-stable aggregates. C/N ratio of large aggregate is higher than that of small aggregate, C/N ratio of 2-5mm aggregate is the highest, C/N ratio is decreasing tendency with the decrease of particle size of soil aggregates. Long-term winter planting green manure treatment can improve C/N ratio of 2-5mm aggregates, and which has little effect on the C/N ratio of other size aggregates. Soil organic carbon and nitrogen stocks higher in >5mm water-stable aggregates and <0.25mm water-stable micro-aggregates in all plot treated. Long-term winter planting green manure, especially Chinese milk vetch can improve the storage of <5mm aggregate-associated organic carbon and nitrogen.Long-term winter planting green manure incorporation treatments increased soil total organic carbon (TOC), liable organic matter (LOM), total nitrogen (TN), available nitrogen (AN), slowly available potassium (SLK) and available potassium (AK) compared with the R-R-WF treatment. The soil nutrient status in treatments with long-term winter planting green manure incorporation were significantly improved compared with the winter fallow treatment; all these properties in the treatment with winter planting Chinese milk vetch were the most obvious. In the meantime, long-term winter planting green manure incorporation treatments could significantly decrease the soil pH in the Typic Hapllc-Stagnic Anthrosis (pH6.6 in initial soil). The productivity of long-term winter planting green manure plots treated was higher than that of the winter fallow-treated plots. Compared with the winter fallow-treated plots, the organic matter returned to the soil, soil organic matter and labile organic matter were higher in the winter planting green manure plots treated.The amounts of microbial populations, microbial biomass carbon (SMBC), microbial biomass nitrogen (SMBN), soil respiration, activities of urease, lnverstase and dehydrogenase were increased, and metabolic quotient (qCO2) was decreased in long-term winter planting green manure incorporation treatments. The microbial characteristics in the treatments with long-term winter planting green manure incorporation were significantly improved as compared with the winter fallow treatment. All these properties in the treatment with winter planting Chinese milk vetch were the most obvious. In the meantime, amounts of microbial populations, SMBC, urease and dehydrogenase were positively correlated with TOC, TN, AN, SLK and AK. Amounts of microbial populations, SMBC and qCO2 were positively correlated with rice yield.Sustainable yield index (SYI) and partial productivity (PFP) of long-term winter planting green manure treated plot was improved. Long term winter planting green manure and incorporate can significantly improve the nutrient status of paddy soil, soil health, soil fertility, and sustainable rice production of reddish paddy soil. Trends in grain yield, SYI and PFP of fertilizer appear promising tools to measure sustainability of fertilizer management practices. Soil organic carbon content, showing the least consistency with the effect of fertilizer management practice on yield, did not prove a reliable index of sustainability in this study.A soil quality index (SQI) based on four soil functions (i.e. the soil ability to resist physical degradation, supply plant nutrients and storage, resist biochemical degradation and sustain crop productivity) was derived for each treatment using bulk density (BD), maximum water holding capacity (MWHC), porosity (POR), normalized mean weight diameter (NMWD), pH, cation exchange capacity (CEC), plant available nutrients, soil organic matter (SOM), microbial biomass, soil enzymes and rice yield. The soil ability to resist physical degradation, to supply plant nutrients and storage, to resist biochemical degradation and to sustain crop productivity of the winter green manure treatments is much stronger than the winter fallow treatment. The soil ability to resist physical degradation of R-R-RG treatment is the strongest. The soil ability to supply plant nutrients and storage of R-R-MV treatment is the strongest. The soil ability to resist biochemical degradation of R-R-RP treatment and R-R-MV treatment are the strongest. The ability to sustain crop productivity R-R-RP treatment is the strongest. Soil quality index ratings ranged from 0.552(R-R-WF treatment) to 0.632(R-R-MV treatment) among the four treatments. SQI and soil functional class of the R-R-MV treatment are the highest, the three winter green manure treatments are higher than the winter fallow treatment obviously. Long-term winter planting-green manure improved the physical, chemical and biochemical properties of reddish paddy soil and therefore improved the comprehensive soil quality. |
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