Wu Jinshui

Soil Quality Changes and Quality Status: A Case Study of the Subtropical China Region Ultisol

Aims: To provide a soil quality assessment frame work and threshold limits for assessing soil quality in Ultisol of subtropical China region. Study Design: Selected minimum data set for soil quality assessment and threshold limits for the study were total carbon, nitrogen, soil pH and phosphorus, biomass carbon, nitrogen and phosphorus, maize grain and fresh potato tuber yields. Soil data (2000-2010), maize grain and fresh potato yield data (2000-2009) from a long term experiment under the Institute of subtropical Agriculture, China were analyzed using the SAS statistical package and means were graphically compared to determine threshold limits for selected data set and fitted into a soil quality model. Place and Duration of Study: The key Laboratory for Agro-ecological Processes in Subtropical Regions, Chinese Academy of Sciences; Institute of Subtropical Agriculture, Changsha, Hunan China long-term experimental site in Taoyuan county, conducted from the year 2000 to 2010. Methodology: Soils samples at the experimental fields were obtained from depths 0-20 cm using an auger at each replicate in triplicates and homogenized to obtain a composite sub sample, air-dried, sieved through 2.0 mm to obtain samples for analysis in the Laboratory. Parameters analyzed for were organic carbon concentration, measured by the combustion method using an automated C/N analyzer (Vario MAX CN, Elemental Co., Germany) while total nitrogen was by the Kjeldahl method of ISSCAS (1978). Microbial carbon, nitrogen and phosphorus levels were determined using the chloroform-fumigationextraction method (Jenkinson and Powlson, 1976; Vance et al., 1987; Brookes et al., Case Study

Spatial variation in organic carbon, nutrients and microbial biomass contents of paddy soils in a hilly red soil region

The contents of soil organic C (SOC), total N (TN), total P (TP), dissolved N (DN), Olsen-P, and microbial biomass C, N, P (BC, BN, BP) of 254 paddy soils (0–18 cm in depth) in a hilly red soil region of subtropical zone of China were studied. The results showed that the contents of SOC, TN, BC, BN and DN of paddy soils at the bottom of hills were 14.6%, 13.6%, 24.6%, 20.4% and 95.8% higher than those at the foothill, respectively. The Olsen-P content of paddy soils at the foothill was 33.3% higher than that at the bottom of hills. However, the differences in TP, BP and available P (the sum of BP and Olsen-P) contents were not significant between the two positions. In addition, the ratios of soil C/P, BC/BP and BC/SOC of paddy soils at the bottom of hills were 12.7%, 28.5% and 8.2% higher than those at the foothill, respectively, but the differences in ratios of soil C/N, BC/BN, BN/TN and BP/TP were not statistically significant between various positions.

稻田土壤 β -1, 4-葡萄糖苷酶活性对温度变化的响应特征

温度是土壤酶活性的关键非生物影响因子，调控着土壤物质周转过程.为了探究温度变化对稻田土壤有机质周转及其关键胞外酶活性的影响，设计室内培养试验，分别在5、15、25和35℃下测定亚热带稻田土壤BG（β-1，4-葡萄糖苷酶）活性，探究温度对土壤胞外酶活性及其与碳氮转化过程的影响特征.结果表明：稻田土壤中w（DOC）（DOC为可利用态碳）、w（NH4+-N）和w（MBC）（MBC为微生物生物量碳）在5~25℃下随着培养时间的增加而降低.在第15天时BG活性达到306.57~437.75 nmol/（g·h），并随温度的增加表现为先增后减，在第3、75天时，25℃下BG活性为184.46~207.60 nmol/（g·h）.土壤酶活性的Q10（温度敏感性）在15℃升至25℃时表现出正响应（Q10=1.5），而在5~15℃和25~35℃时Q10 < 1，表现为消除效应.土壤酶活性的变化是多因素共同影响的结果，温度作为关键影响因子，升温显著改变了土壤中w（DOC）、w（NH4+-N）、w（MBC）、w（MBN）（MBN为微生物生物量氮），进而影响土壤BG活性；土壤中w（MBC）对BG活性具有直接的显著负影响作用.研究显示，对参与稻田土壤碳转化BG酶活性的温度敏感性及其与土壤关键理化因子之间的耦合关系进行量化，有助于深入开展水稻土碳循环及其调控机制研究.