Hydrogen oxidation activities in soil as influenced by pH,temperature, moisture,and season

Summary Hydrogen oxidation in soil was measured at low (1 ppmv) and high (300 ppmv) H₂ concentrations to distinguish between the activities of abiontic soil hydrogenases and Knallgas bacteria, respectively. The two activities also showed distinctly different pH optima, temperature optima, and apparent activation energies. The pH optima for the soil hydrogenase activities were similar to the soil pH in situ, i.e., pH 8 in an slightly alkaline garden soil (pH 7.3) and pH 5 in an acidic cambisol (pH 4.6–5.4). Most probable number determinations in the alkaline acidic soils showed that Knallgas bacterial populations grew preferentially in neutral or acidic media, respectively. However, H₂ oxidation activity by Knallgas bacteria in the acidic soil showed two distinct pH optima, one at pH 4 and a second at pH 6.4–7.0. The soil hydrogenase activities exhibited temperature optima at 35–40°C, whereas the Knallgas bacteria had optima at 50–60°C. The apparent activation energies of the soil hydrogenases were lower (11–23kJ mol^-1) than those of the Knallgas bacteria (51–145 kJ mol^-1). Most of the soil hydrogenase activity was located in the upper 10 cm of the acidic cambisol and changed with season. The seasonal activity changes were correlated with changes in soil moisture and soil pH.     

土壤呼吸影响因素研究进展

随着二氧化碳浓度的升高,全球变暖问题受到越来越多的关注。土壤是陆地生态系统最大的碳源,也是最大的碳汇。研究土壤呼吸作用对预测大气二氧化碳浓度变化,控制气候变暖,具有重要的意义。文章对土壤呼吸作用及其影响因素作了简要分析,为以后土壤呼吸方面的研究提供参考。     

Geostatistical Analysis of Yield,Soil Properties and Crop Management Practices in Paddy Rice Fields

Abstract

We examined the possible benefit of rational site-specific crop management practices in 17 paddy fields located in an area of 2.0 ha for the prevalence of precision agriculture methods on a cooperatively managed large-scale farm in Sakurai, Nara Japan. Data on grain yield, soil physicochemical properties and farmer's crop management practices were collected in each paddy field. Unhulled rice yield was estimated at a resolution of 5m ? 5m in an area of 1.2 ha using a yield-monitoring combine. The spatial distribution of the variations for the collected data was characterized using geostatistical procedures. The kriged map of the unhulled rice yield drawn from the results of geostatistical analysis indicated the potential value of rational site-specific crop management using the yield-monitoring combine. The ratio of spatially structured variation to the total variation of brown rice yield, that is, the controllable proportion to total variation, was 75.4%. Each yield component i.e., the number of spikelets per square meter, filled-spikelet percentage and 1000-grain weight contributed 33.7%, 54.7% and 11.6%, respectively, to brown rice yield. These three yield components combined contributed to 96.5% of the brown rice yield variation. The agronomic factors (soil fertility factor, early growth factor, N dressing and uptake factor) contributed 79.7%, 52.1% and 41.8%, respectively, to the variation of these three yield components. Therefore these agronomic factors accounted for 58.1% of the total variation of the brown rice yield and 77.1% (i.e. 58.1% out of 75.4%) of the spatially structured variation of the brown rice yield. This controllable proportion may be a criterion for the prevalence of site-specific crop management in large-scale farm management in general, although only one case study was conducted.     

Simulation and Prediction of Soil Organic Carbon Dynamics in Jiangsu Province Based on Model and GIS Techniques

Based on the databases of soils, meteorology, crop production, and agricultural management, changes in the soil organic carbon (SOC) of agro-ecosystems in Jiangsu Province were simulated by using a soil organic carbon model with a linkage of GIS. Four data sets of soil organic carbon measured from various field experiments in Jiangsu Province were used to validate the model. It was demonstrated that the model simulation in general agreed with the field measurements. Model simulation indicated that the SOC content in approximately 77% of the agricultural soils in Jiangsu Province has increased since the Second National Soil Survey completed in the early 1980s. Compared with the values in 1985, the SOC content in 2000 was estimated to increase by 1.0-3.0 g kg-1 for the north and the coastal areas of the province, and by 3.5-5.0 g kg-1 for the region of Tai Lake in the south. A slight decrease (about 0.5-1.5 g kg-1 ) was estimated for the central region of Jiangsu Province and the Nanjing-Zhenjiang hilly area. Model prediction for 2010 A.D. under two scena-rios, i.e., with 30 and 50% of the harvested crop straw incorporation, suggested that the SOC in Jiangsu Province would increase, and thus that the agricultural soils would have potential as organic carbon storage. The incorporation of crop straw into soils is of great benefit to increase soil carbon storage, consequently to benefit the control of the rise of atmospheric CO2 concentration and to maintain the sustainable development of agriculture.     

How do earthworms influence organic matter quantity and quality in tropical soils?

Earthworms are important regulators of soil structure and soil organic matter (SOM) dynamics; however, quantifying their influence on SOM cycling in tropical ecosystems remains little studied. Simulated rainfall was used to disrupt casts produced by Amynthas khami and their surrounding soil (control) into a range of small sized aggregates (50-250, 250-500, 500-2000 and 2000-5000 μm). To gain insight into how earthworms influence SOM biogeochemical composition in the aggregates, we carried out elemental and stable isotope analysis, and analytical pyrolysis (Py GC/MS). We also characterized their lignin component after oxidation with cupric oxide (CuO).The C content of smaller size fractions (<500 μm) in the control soil was higher than in the larger fractions. Our study therefore suggests that the aggregate hierarchy concept, which is used to understand soil aggregates and SOM dynamics in temperate soils, may not be applicable to the tropical Acrisol studied here. Earthworms modified SOM organization in soil aggregates. Although the isotope analyses were useful for highlighting SOM enrichment in the earthworm casts, aggregate fractions could not be classified according to particle size. Molecular analyses were necessary to indicate that SOM in all size fractions of casts consisted of relatively undecomposed material. Protection of the most labile SOM structures occurred in the smallest aggregate size fraction (50-250 μm). Py GC/MS showed that earthworm casts and control aggregates <2000 μm could be clearly distinguished according to the molecular properties of their SOM. Aggregates larger than 2000 μm, however, were most probably composed of all fractions and were not different. As a consequence, our results indicate that studies to determine the impact of earthworms on SOM turnover in soil are spatially dependant on the scale of observation.     

两种土壤栽培下姜黄挥发油的化学成分比较

采用GC-MS方法,对两种土壤栽培下姜黄挥发油的化学成分进行分析。结果表明：红壤土中栽培的姜黄挥发油含量（8.0％）明显高于沙壤土中栽培的含量（6.0％）;两种土壤栽培的姜黄挥发油中分别鉴定出34和33种化学成分,分别占总含量的64.095％和55.951％,主要成分均为倍半萜类和单萜类化合物。且红壤土栽培下姜黄挥发油中的芳姜黄酮等主要化学成分的含量大多高于沙壤土栽培的,栽培在红壤土的姜黄比栽培在沙壤土中的姜黄品质更好。     

土壤水分对谷子(粟)结实的影响及其生理效应

土壤水分对谷子结实的影响主要在结实阶段.土壤水分过少或过多,都能显著降低结实率、成粒数和产量.这一时期以保持土壤毛管持水量的70%左右对结实最为有利.供水不足,首先影响根系活性和体内水分状况,从而影响体内外气体交换,降低光合速率和呼吸强度,同时影响细胞膜透性,导致体内物质代谢过程改变,降低有机物质的积累,造成穗部营养贫乏,形成秕谷.土壤水分过多,通气不良,影响根系活性,降低伤流量,抑制体内代谢过程及物质运转,造成穗部营养不足,形成秕谷.