[Effects of Straw Returning with Lime on SOC and Carbon Pool Management in Acidic Paddy Soil].

Soil acidification and low SOC are the main limiting factors in acidic paddy soils. Straw returning with lime is an effective measure to alleviate soil acidification and improve soil fertility; however, its interaction effects on SOC and carbon pool management are still unclear. To investigate the impact of straw returning with lime on the organic carbon pool of acidic paddy soil, field experiments were conducted on acidic paddy soil in Baiyun District and Huiyang District of Guangdong Province. The changes in soil total organic carbon (TOC), water-soluble organic carbon (DOC), active organic carbon (LOC), particulate organic carbon (POC), microbial biomass carbon (MBC), carbon pool index (CPI), stable organic carbon (IOC), carbon pool activity (L), carbon pool activity index (CPAI), and carbon pool management index (CPMI) were analyzed under three treatments (CK, conventional fertilization; RS, straw returning+conventional fertilization; RS+L straw returning with lime+conventional fertilization). The results demonstrated that compared with that in CK, the TOC, LOC, POC, and MBC in the RS+L treatment were significantly increased by 10.24%-17.79%, 34.49%-44.37%, 19.27%-23.59%, and 33.36%-43.26%, respectively (P<0.05). Compared with that in CK, the RS+L treatment significantly increased the DOC content during the early growth stage (15-45 days after transplanting) of rice (P<0.05) but had no significant influence on the DOC content during the late growth stage of rice. Compared with that in RS, the TOC, LOC, POC, and MBC in the RS+L treatment were increased by 2.15%-6.95%, 1.17%-17.90%, 4.27%-8.65%, and 12.99%-14.53%, respectively. Compared with that in CK, the RS+L treatment significantly increased IOC and CPI by 8.32%-15.57% and 14.00%-20.00%, respectively (P<0.05). Compared with that in the CK treatment, the RS treatment significantly increased CPI by 14.00%-18.00% (P<0.05). No significant differences in L, CPAI, or CPMI were detected among the different treatments. The soil pH in the RS+L treatment was significantly higher than that in the CK treatment (P<0.05). No significant differences in rice yield were detected among the different treatments. Principal component analysis demonstrated that rice yield was primarily correlated with DOC, LOC, CPAI, and CPMI but its contribution to SOC and carbon pool management index was low. Principal component analysis also indicated that straw returning with lime could improve soil pH and nutrient contents of acidic paddy soil, driving the formation and accumulation of organic carbon fraction such as MBC and POC, thus boosting the increase in SOC. In conclusion, straw returning with lime is beneficial to the accumulation of MBC, POC, LOC, and IOC in acidic paddy soil to improve the content and stability of soil total organic carbon, which is an effective way to improve the carbon sequestration of acidic paddy soil.

[Effects of Early Rice Straw Returning with Reducing Potassium Fertilizer on Late Rice Yield and Soil Fertility].

Rice straw is an important organic fertilizer in the region for double-cropping rice in South China. To reveal the effects of early rice returning with reducing potassium fertilizer on the yield of late rice and soil fertility, field experiments were carried out in Baiyun and Huiyang district in Guangdong province. The biomass, K content, and yield of late rice and the soil fertility properties, such as soil available potassium, soil organic carbon, bacterial diversity, and bacterial community structure were analyzed under three treatments (CK, conventional fertilization; RS, straw returning with conventional fertilization; RS-K, straw returning with reducing 20% potassium fertilizer). The results showed no significant differences in the biomass and yield of late rice between the RS-K treatment and CK treatment. Compared with that in CK, the RS treatment significantly increased the K contents of rice by 3.97% (Baiyun) and 6.91% (Huiyang). The K contents of late rice under the RS-K treatment were significantly lower than that under the CK treatment during the early growth period in rice, but there was no significant difference between them during the late growth period. Compared with that in CK, the soil available K in the RS treatment increased by 13.90% (Baiyun) and 21.67% (Huiyang) (P<0.05), and the soil available K in the RS-K treatment also increased by 3.56% (Baiyun) and 4.23% (Huiyang). Compared with that in the CK treatment, the soil dissolved organic carbon increased significantly in the RS and RS-K treatments (P<0.05). Compared with that in CK, the straw returning treatments (RS and RS-K) significantly improved the Chao1 and Shannon indexes of soil bacteria (P<0.05). Straw returning treatments (RS and RS-K) increased the relative abundance of Proteobacteria, Actinobacteria, and Nitrospirae compared with that in CK, whereas they decreased the relative abundance of Acidobacteria, Bacteroidetes, and Firmicutes. Redundancy analysis showed that the soil bacterial community was mainly influenced by soil organic carbon, dissolved organic carbon, microbial biomass carbon, available P, and available K. In summary, early rice returning could increase soil available K and K content in late rice. Early rice straw returning with reducing potassium fertilizer had no negative impacts on the growth and yield of late rice and could also improve soil organic carbon and the diversity of soil bacteria. Therefore, early rice straw returning with reducing potassium fertilizer can guarantee the grain yield of late rice and improve soil fertility.

[Adsorption-desorption Characteristics of Fermented Rice Husk for Ferrous and Sulfur Ions].

To understand the potential of rice husk to fix Fe2+ and S2- ions, the sorption of Fe2+ and S2- by fermented rice husk was studied by using batch incubation experiments in the present study. The effects of adsorption time, Fe2+ and S2- concentration, pH, the temperature and ionic strength in adsorption reaction solution on the sorption were investigated. Therefore, the stability of Fe2+ and S2- adsorbed by fermented rice husk was further validated by desorption experiments performed under similar conditions as adsorption. The results showed that, the adsorption kinetics of Fe2+ (r = 0.912 1) and S2- (r = 0.901 1) by fermented rice husk fits the Elovich kinetics equation, and Freundlich isotherm model could simulate the isotherm adsorption processes of Fe2+ (R2 = 0.965 1) and S2- (R2 = 0.936 6) on fermented rice husk was better than other models. The adsorption processes on fermented rice husk were non- preferential adsorption for Fe2+ and S2, while the adsorption process of Fe2+ on fermented rice husk was spontaneous reaction and the adsorption process of S2- was non-spontaneous reaction. The adsorption processes of Fe2+ and S2- on fermented rice husk were endothermic process since high temperature could benefit to the adsorption. The adsorption mechanism of Fe2+ on fermented rice husk was mainly controlled by coordination adsorption, the adsorption mechanism of S2- on fermented rice husk was mainly controlled by ligand exchange adsorption. The adsorption processes of Fe2+ and S2- on fermented rice husk showed greater pH adaptability which ranged from 1.50 to 11.50. With the increasing of ionic strength, the amount of adsorbed Fe2+ on fermented rice husk wasincreased in some extent, the amount of adsorbed S2- on fermented rice husk was slightly decreased, which further proved the adsorption of Fe2+ was major in inner sphere complexation and the adsorption of S2- was major in outer complexation. The desorption rates of Fe2+ and S2- which was adsorbed by fermented rice husk were lower in different pH or ionic strength conditions, the desorption rates were all below 10 percentage which proved that the adsorption stabilities of Fe2+ and S2- on fermented rice husk were superior. The above results indicated that, the adsorption abilities to Fe2+ and S2- on fermented rice husk were better and had greater environmental adaptability. The Fe2+ and S2- adsorbed by fermented rice husk showed higher stability, and were not easy to release again.

[Wastewater pollution characteristics from typical intensive pig farms in the Pearl River Delta and its ecological risk assessment].

Based on the wastewater quality investigation data from March 2009 to November 2011, wastewater qualities from typical intensive pig farms were assessed in the Pearl River Delta by single and comprehensive pollution index model. The results showed that key pollutants of piggery wastewater were fecal coliform (FC), total phosphorus (TP), chemical oxygen demand (COD) and biochemical oxygen demand (BOD), with their average mass concentrations of 1.98 x 10(9) CFU.L-1, 158.61 mg.L-1, 5 608.68 mg.L-1 and 1984.34 mg.L-1, respectively; key pollutants of biogas slurry were FC, TP, ammonia nitrogen (NH+4 -N) and suspended substance (SS), with their average mass concentrations of 8. 10 x 10(6) CFU.L-1, 81.76 mg.L-1, 476.24 mg.L-1 and 464.58 mg.L-1, respectively. Under the effect of wastewater pollutants, environment surrounding of typical intensive pig farms was seriously polluted, which decreased gradually from piggery wastewater to biogas slurry, and comprehensive pollution indices were 11.41, 6.91, 5.27, respectively. The risk analysis showed that the high-risk wastewater could never be discharged directly and irrigated crops. After the anaerobic treatment, FC, TP, NH+4 -N and SS were still strong factors with the potential ecological risk in the biogas slurry. In the long run, the ecological risk still exists for direct discharge or irrigation of them, and it is necessary to apply further treatment.

[Effects of microbial agent inoculation on bacterial community diversity in the process of pig manure composting].

PCR-DGGE method was adopted to study the effects of inoculating exogenous microbial agent on the bacterial community diversity in the process of fresh pig manure high-temperature aerobic composting. Exogenous microbial agent inoculation promoted the composting process, with the high-temperature period being advanced by 2 days than that of non-inoculation. DGGE pattern analysis showed that during composting, the dominant bacteria changed significantly, with the Shannon-Wiener index of bacterial community at different composting periods varied obviously. The sequencing of DGGE-distinguished bands showed that Clostridium stercorarium subsp. thermolacticum sp. was the dominant group in the whole composting process. Uncultured bacteria Bacillus coagulans sp. and Clostridium thermocellum sp. became the main groups on the 10th and 16th day after microbial agent inoculation, while uncultured Firmicutes sp. and delta proteobacterium became the dominant groups on the 5th and 16th days in the treatment non-inoculation, respectively. Un-dominant group Ureibacillus thermosphaericu sp. and uncultured Silvimonas sp. appeared in the late period of well rotted composting, while uncultured soil bacteria mainly appeared in the initial and high-temperature periods. UPGMC cluster analysis showed that exogenous microbial agent inoculation obviously affected the bacterial community structure in different composting periods, and the main component analysis of DGGE patterns in composting process showed that the bacterial community was mainly affected by the exogenous microbial agent inoculation.

[Effects of slow/controlled release fertilizers on the growth and nutrient use efficiency of pepper].

Pot trails were conducted from 2003 to 2005 to study the effects of slow/controlled release fertilizers on the growth and nutrient use efficiency of pepper. The results indicated that in comparison with conventional splitting fertilization (T1), basal application of polymer-coated controlled release fertilizer (T2) enhanced the single fruit mass and vitamin C concentration, improved the root activity, and increased the fruit yield by 8.4%, but no significant effect was observed on the dissoluble sugar concentration in fruit. NH4MgPO4-coated controlled release fertilizer (T3) increased the dissoluble sugar concentration by 5.67%, but had less effect on single fruit mass and vitamin C concentration. Under the application of T3, the root system had a vigorous growth at early stages but became infirm at later stages, resulting in a lower yield. Comparing with T1, the application of 3 slow release fertilizers increased the dissoluble sugar concentration in fruit, enhanced the root activity, but had less effect on the yield. All test slow/controlled release fertilizers increased the use efficiency of N, P, and K significantly, with an exception for T2 which increased the use efficiency of N and K but decreased that of P. It was demonstrated that an appropriate application of slow/controlled release fertilizers could enhance pepper' s root activity and improve nutrient use efficiency.