Nutrient budgets: sustainability assessment of rainfed lowland rice-based systems in northeast Thailand

In northeast Thailand, the sustainability of rainfed lowland rice-based systems, the dominant land-use system (LUS) in the region, is a concern for the welfare of the population in this relatively poor region. Poor soil fertility and low inputs are seen as major causes of this lack of sustainability. In this context, the assessment of nutrient budgets is seen as a powerful tool for the assessment of critical components of the sustainability of this particular LUS. Biophysical, socioeconomic, and management-related data on the farming systems were collected for 30 farms in Ubon Ratchathani Province, northeast Thailand. A relational database system (RDBS) was developed to manage and analyze the data. The RDBS includes a calculation procedure for the semi-automatic generation of partial nutrient balances. Partial nutrient balances are good indicators for some critical components of sustainability, and important for decision support on soil fertility management when considered with the additional factors that are required for a full nutrient balance.For the rice-based systems of 30 farms, mean partial balances were 12 kg N ha⁻¹, 8 kg P ha⁻¹, and 7 kg K ha⁻¹ per year. Large variations in partial N, P, and K balances exist among different farms and, even more so, for different land utilization types (LUTs). The LUTs are distinct cropping system–management combinations that occur down to the subfield level. Many of the partial balances assessed were negative.Farmers manage nutrients for similar parcels of land in very different ways. This results in the observed large variation in partial nutrient balances, even for the same type of land use within the same farm. These results confirm the high inter-farm and intra-farm variability for partial balances of N, P, and K of several preliminary studies. Farmer interviews and field surveys revealed that different socioeconomic factors appear to be related with inter- and intra-farm variability in nutrient budgets. In addition, the socioeconomic component of the case study revealed that diversification of income sources, particularly off-farm employment, had a larger impact on household income than rice production. Furthermore, while many less well-off households had a greater reliance on rice production, many farms with high off-farm and non-rice farm income had a higher total production of rice.The nutrient balance approach, starting with partial nutrient balances, may become an important component of a dynamic and site-specific decision support tool (DST) for nutrient management, and a relational database of the form used in this study may become a key element.     

改进层次分析法在土壤重金属污染评价中的应用

将层次分析法进行了必要的改进 ,并应用于土壤重金属污染的评价 .评价结果表明 :改进层次分析法比模糊综合评判法以及一般层次分析法更为合理 .     

化学农药对土壤微生物的影响

农药的使用势必对土壤微生物产生影响，由于土壤中的微生物处在共生状态，而土壤中的很多物质分解是靠微生物来完成的，因此微生物受农药影响而发生的各种变化，都会对物质分解过程（如碳、氮循环），植物的生长发育，以及植物病理等产生影响。该文概述了农药对土壤微生物的６个方面影响，并提出了还需进一步研究的方向。     

Assessment of labile phosphorus fractions and adsorption characteristics in relation to soil properties of West African savanna soils

A large proportion of total P in the soils of the area is unavailable to plants and consequently P is the second most limiting nutrient. The labile and moderately labile phosphorus fractions and adsorption characteristics of surface and subsurface horizons of eleven soil profiles in the derived savanna (DS) and the northern Guinea savanna (NGS) of West Africa were assessed. The labile P fractions are the resin and HCO₃-extractable inorganic (Pi) and organic (Po) P. The moderately labile fractions are the NaOH-extractable portion of soil P in the Hedley sequential procedure. In the DS soils, the resin P, considered the most readily available fraction, varied from 1 to 14 mg kg⁻¹, HCO₃-Pi ranged from 3.3 to 11, and HCO₃-PO was between 4 and 12 mg kg⁻¹ in the surface horizon. In the NGS, the topsoil contained 1.5–3 mg kg⁻¹ of resin P, 5–8 mg kg⁻¹ of HCO₃-Pi, and 7.5–9.7 mg kg⁻¹ of HCO₃-Po. Sodium hydroxide-Po was the largest of the fractions in all the soils studied. It ranged from 23 to 55 mg kg⁻¹ in the topsoil. In general, the labile P levels were higher in soils of the DS than of the NGS and were related to the oxalate-extractable Fe (Fe_ox), and Al (Al_ox) as well as to soil texture. The subsoil of Kasuwan Magani (profile KS 9–21 cm) required 153 mg P kg⁻¹ to maintain 0.2 mg P l⁻¹ in solution (standard P requirement), and Danayamaka (profile DD 7–32 cm) required 145 mg P kg⁻¹. These could translate to 214 and 200 kg P ha⁻¹ if a plow layer of 10 cm is assumed. Because these are within the plow layer, more P fertilizer would be needed for crop production than in the other soils. The standard P requirement and the adsorption maxima were related to Fe_ox and Al_ox, dithionite-Fe (Fe_d), and texture. The increase in labile P content with decreasing Fe_ox and Al_ox could imply that management practices capable of reducing the activities of Fe and Al in solution might improve P availability.     

Soil water depletion under various leguminous cover crops in the derived savanna of West Africa

Leguminous cover crops have the potential of making cropping systems in the tropics sustainable if they would not deplete resources such as soil water and nutrients to the detriment of companion crops. Therefore, a study was carried out at Alabata, Ibadan, southwestern Nigeria, to evaluate the effects of leguminous cover crops on soil water suctions in 1993 and 1994 in order to assess the possibility of integrating them into the farming systems of the savanna zone of West Africa. In 1993, 13 leguminous cover crops (Aeschynomene histrix, Centrosema brasilianum, Centrosema pascuorum, Chamaecrista rotundifolia, Cajanus cajan, Crotalaria verrucosa, Crotalaria ochroleuca, Lablab purpureus, Mucuna pruriens, Psophocarpus palustris, Pseudovigna argentea, Pueraria phaseoloides and Stylosanthes hamata) were planted in a randomized complete block design with four replications. Maize and natural fallow (mainly Chromolaena odorata and Imperata cylindrica) were included as comparisons. Only six of the legumes (A. histrix, C. pascuorum, C. cajan, C. ochroleuca, M. pruriens, and P. phaseoloides) were included in the measurements in the 1994 new plots. Soil water suctions at various stages of legume growth were measured at daily or weekly intervals (depending on the frequency of rainfall events) using tensiometers installed at 0–15 and 15–30 cm soil depths. Soil water suctions exceeding 10 kPa (theoretical field capacity) were observed mainly between 6 and 12 weeks after planting (WAP), and by 20 WAP when cover crops had matured and rainfall frequency was very low. Soil water suctions were significantly related (r²>0.80) to dry matter between 8 and 10 WAP. The studied cover crops were classified in three groups which can be used as a guide for choosing the legumes in tropical farming systems. Soil water depletion was markedly influenced by growth characteristics of legumes and distribution of rainfall during the rainy season. Leguminous cover crops conserved soil water after their growth needs were satisfied.     

土壤石油烃类污染治理方法述评

本文介绍了土壤中石油烃类的危害，在土壤中的主要存在形态及迁移转化情况；概述了近年来国内外治理土壤石油烃类污染和各种方法，并从场外治理和现场治理两个角度分别对各种物理、化学和生物治理方法的优缺点、可行性进行了述评；同时对联合运用多种技术，实行综合治理进行了讨论．     

上海市土壤中人工放射性水平调查及评价

调查了１９８９－１９９０年上海市土壤中及黄浦江水系底泥中，人工放射性核素的含量。调查共设３２个点，结果表明，上海市土壤中的人工放射性核素含量，＾９０Ｓｒ、＾１３７Ｃｓ、总β的比活度均值分别为２、４１±０．７８、３．１４±１．４７、７１７．０±１３５．９Ｂｑ／ｋｇ，属正常本底水平。土壤中人工放射性核素的比活度在全市范围内分布没有明显差别，波动范围不大。土壤中＾１３７Ｃｓ的比活度比＾９０Ｓｒ高，这与土     

沈阳市水土流失现状及对策措施探讨

针对沈阳市水土流失现状、成因及对策进行了初步探讨 ,并对沈阳市水土流失现状 ,提出了防治对策和措施 ,着重强调了政府的政策导向在综合防治水土流失中的重要作用     

铅生产项目土壤环境影响评价简析

通过再生铅项目的建设对土壤环境的影响评价，评述建设项目所在区域的土壤环境质量分级标准及评价区域环境土壤现状：从正常工况和非正常工况2方面预测污染物铅排放对土壤环境的潜在污染，并定量分析其危害程度：指出铅排放对人体健康及植被、农作物的危害，提出污染防治措施和监测方案。     

Eight years of annual no-till cropping in Washington's winter wheat-summer fallow region

The tillage-based winter wheat (Triticum aestivum L.)-summer fallow (WW-SF) cropping system has dominated dryland farming in the Pacific Northwest USA for 125 years. We conducted a large-scale multidisciplinary 8-year study of annual (i.e., no summer fallow) no-till cropping systems as an alternative to WW-SF. Soft white and hard white classes of winter and spring wheat, spring barley (Hordeum vulgare L.), yellow mustard (Brassica hirta Moench), and safflower (Carthamus tinctorius L.) were grown in various rotation combinations. Annual precipitation was less than the long-term average of 301 mm in 7 out of 8 years. Rhizoctonia bare patch disease caused by the fungus Rhizoctonia solani AG-8 appeared in year 3 and continued through year 8 in all no-till plots. All crops were susceptible to rhizoctonia, but bare patch area in wheat was reduced, and grain yield increased, when wheat was grown in rotation with barley every other year. Remnant downy brome (Bromus tectorum L.) weed seeds remained dormant for 6 years and longer to heavily infest recrop winter wheat. There were few quantifiable changes in soil quality due to crop rotation, but soil organic carbon (SOC) increased in the surface 0–5 cm depth with no-till during the 8 years to approach that found in undisturbed native soil. Annual no-till crop rotations experienced lower average profitability and greater income variability compared to WW-SF. Yellow mustard and safflower were not economically viable. Continuous annual cropping using no-till provides excellent protection against wind erosion and shows potential to increase soil quality, but the practice involves high economic risk compared to WW-SF. This paper provides the first comprehensive multidisciplinary report of long-term alternative annual no-till cropping systems research in the low-precipitation region of the Pacific Northwest.