南充市农地资源可持续利用探讨

农地资源的可持续利用是实现农业可持续发展的基础.在分析南充市农地资源特点的基础上,阐述了农地利用中存在的主要问题,并就合理利用农地提出了农地资源可持续利用的主要原则、对策与措施.     

EFFECTS OF WATERSHED REPRESENTATION ON RUNOFF AND SEDIMENT YIELD MODELING1

ABSTRACT: This paper evaluates the effects of watershed geometric representation (i.e., plane and channel representation) on runoff and sediment yield simulations in a semiarid rangeland watershed. A process based, spatially distributed runoff erosion model (KINEROS2) was used to explore four spatial representations of a 4.4 ha experimental watershed. The most complex representation included all 96 channel elements identifiable in the field. The least complex representation contained only five channel elements. It was concluded that oversimplified watershed representations greatly influence runoff and sediment yield simulations by inducing excessive infiltration on hillslopes and distorting runoff patterns and sediment fluxes. Runoff and sediment yield decrease systematically with decreasing complexity in watershed representation. However, less complex representations had less impact on runoff and sediment‐yield simulations for small rainfall events. This study concludes that the selection of the appropriate level of watershed representation can have important theoretical and practical implications on runoff and sediment yield modeling in semiarid environments.     

SIMULATING THE IMPACT OF DRAINAGE DESIGN IN A COLD CLIMATE WITH ADAPT1

ABSTRACT: Surface and subsurface drainage make crop production economically viable in much of southern Minnesota because drainage allows timely field operations and protects field crops from extended periods of flooded soil conditions. However, subsurface drainage has been shown to increase nitrate/nitrogen losses to receiving waters. When engaging in drainage activities, farmers are increasingly being asked to consider, apart from the economic profit, the environmental impact of drainage. The Agricultural Drainage and Pesticide Transport model (ADAPT) was used in this study to evaluate the impact of subsurface drainage design on the soil water balance over a two‐year period during which observed drainage discharge data were available. Twelve modeling scenarios incorporated four drainage coefficients (DC), 0.64 cm/d, 0.95 cm/d, 1.27 cm/d, and 1.91 cm/d, and three drain depths, 0.84 m, 1.15 m, and 1.45 m. The baseline condition corresponded to the drainage system specifications at the field site: a drain depth and spacing of 1.45 m and 28 m, respectively (DC of 0.64 cm/d). The results of the two‐year simulation suggested that for a given drainage coefficient, soils with the shallower drains (but equal DC) generally have less subsurface drainage and can produce more runoff (but reduced total discharge) and evapotranspiration. The results also suggested that it may be possible to design for both water/nitrate/nitrogen reduction and crop water needs.     

NITROGEN AND ORGANIC MATTER LOSSES IN NO‐TILL CORN CROPPING SYSTEMS1

ABSTRACT: Intensive cropping systems based on mechanical movement of soil have induced land degradation in most agricultural areas due to soil erosion and soil fertility losses. Thus, farmers have been increasing fertilization rates to maintain an economically competitive crop yield. This practice has resulted in water quality degradation and lake eutrophication in many agricultural watersheds. Research was conducted in the Patzcuaro watershed in central Mexico to develop appropriate technology that prevents nonpoint source pollution from fertilizers. Organic matter (OM) and nitrogen (N) losses in runoff and nitrate (NO₃‐N) percolation in Andisols with corn under conventional till (CT) and no‐till (NT) treatments using variable percentages of crop residue as soil cover were investigated for steep‐slope agriculture. USLE type runoff plots were used to collect water runoff, while suction tubes with porous caps at 30, 60, and 90 cm depth were used to sample soil water solutes for NO₃‐N analyses. Results indicated a significant reduction of N and OM losses in runoff as residue cover increased in the NT treatments. Inorganic N in runoff was 25 kg/ha for NT without residue cover (NT‐0) and 6 kg/ha for the NT with 100 percent residue cover (NT‐100). Organic matter losses in runoff were 157 and 24 kg/ha for the NT‐0 and NT‐100 treatments, respectively. Nitrate‐N percolation was evident in CT and NT with 100 percent residue cover (NT‐100). However, NT‐100 had higher NO₃‐N concentration at the root zone, suggesting the possibility of reducing fertilization rates with the use of NT treatments.     

CHARACTERIZATION OF INORGANIC PARTICLES IN SELECTED RESERVOIRS AND TRIBUTARIES OF THE NEW YORK CITY WATER SUPPLY1

ABSTRACT: Individual particle analysis (IPA) by scanning electron microscopy interfaced with automated image and X‐ray analyses was used to characterize inorganic particles in five reservoirs and four tributaries located within the Catskill and Delaware systems of the New York City water supply. Individual particle analysis provides combined elemental and morphologic characterizations. Results are presented in terms of particle projected area per unit volume (PAV), consistent with optical impacts, and partitioned into seven generic particle types according to composition. Minerals of terrigenous origins, particularly clay minerals, dominated the inorganic particle populations of all the study systems except one downstream reservoir. Higher PAV levels were observed in the Catskill system. Particle dynamics represented by PAV were driven primarily by runoff, while the reservoirs were also greatly influenced by the timing of sediment resuspension promoted by drawdown of the surface and fall mixing. The benefit of the serial configuration of the reservoirs in decreasing inorganic particles with progression downstream towards the city is demonstrated. The patterns in PAV levels among the study systems generally tracked those of more common metrics of impacts of suspensoids, including mass concentrations of suspended solids, turbidity, and Secchi disc transparency.     

REGION,LANDSCAPE, AND SCALE EFFECTS ON LAKE SUPERIOR TRIBUTARY WATER QUALITY1

ABSTRACT: In 1998 and 1999, third‐order watersheds in high mature forest (HMF) and low mature forest (LMF) classes were selected along gradients of watershed storage within each of two hydrogeomorphic regions in the Lake Superior Basin to evaluate threshold effects of storage on hydrologic regimes and watershed exports. Differences were detected between regions (North and South Shore) for particulates, nutrients, and pH, with all but silica values higher for South Shore streams (p < 0.05). Mature forest effects were detected for turbidity, nutrients, color, and alkalinity, with higher values in the LMF watersheds, that is, watersheds with less that 50 percent mature forest cover. Dissolved N, ammonium, N:P, organic carbon, and color increased, while suspended solids, turbidity, and dissolved P decreased as a function of storage. Few two‐way interactions were detected between region and mature forest or watershed storage, thus threshold based classification schemes could be used to extrapolate effects across regions. Both regional differences in water quality and those associated with watershed attributes were more common for third‐order streams in the western Lake Superior drainage basin as compared with second‐order streams examined in an earlier study. Use of ecoregions alone as a basis for setting regional water quality criteria would have led to misinterpretation of reference condition and assessment of impacts in the Northern Lakes and Forest Ecoregion.     

农用改性硝酸铵拒爆机理及工业化可行性研究

对农用硝铵作改性处理,通过筛选和优化实验确定了改性硝酸铵配方。结果表明,当硝酸铵中添加3%的改性剂GXJ1,10%的改性剂GXJ2时,产品在1mm铁皮管约束下的雷管感度试验条件下具有拒爆特性。改性硝酸铵总养分与普通硝酸铵相当,并且颗粒强度高,不易粉化、结块和吸潮,具有优良的肥料品质。同时还利用X射线衍射分析、扫描电子显微镜分析对改性硝铵的拒爆机理作初步探讨。最终,建立了改性硝酸铵的脱水性能、流动性能、凝固性能、颗粒强度的评价方法,并进行了工业化可行性研究。     

Sustainability of Current Agricultural Practices in The Cameron Highlands, Malaysia

Cameron Highlands is a mountainous region with steep slopes. Gradients exceeding 20^∘ are common. The climate is favourable to the cultivation of tea, sub-tropical vegetables and flowers (under rain-shelter). Crop production is sustained by high fertiliser and manure applications. However, agriculture in this environment is characterised by high levels of soil erosion and environmental pollution. A study on the sustainability of these agro-ecosystems was conducted. Results indicated that soil loss was in the range of 24–42 ton/ha/yr under vegetables and 1.3 ton under rain-shelter. Sediment load in the vegetable sub-catchment reached 3.5 g/L, 50 times higher than that associated with flowers under rain-shelter and tea. The sediments contained high nutrient loads of up to 470 kg N/ha/yr. The N, P and K lost in runoff from cabbage farms was 154 kg/season/ha, whereas in chrysanthemum farms it was 5 kg. In cabbage farms, the N, P, and K lost through leaching was 193 kg/season/ha. The NO₃–N concentration in the runoff from the cabbage farms reached 25 ppm but less than 10 ppm in runoff from rain-shelters. Inorganic pollution in the rivers was within the acceptable limit of 10 ppm. The sustainability of the agro-ecosystems is in the order of tea { > } rain–shelter ≫ vegetables.     

Class: an Essential Aspect of Watershed Planning

A study of a watershed planning process in the Cache River Watershed in southern Illinois revealed that class divisions, based on property ownership, underlay key conflicts over land use and decision-making relevant to resource use. A class analysis of the region indicates that the planning process served to endorse and solidify the locally-dominant theory that landownership confers the right to govern. This obscured the class differences between large full-time farmers and small-holders whose livelihood depends on non-farm labor. These two groups generally opposed one another regarding wetland drainage. Their common identity as “property owner” consolidated the power wielded locally by large farmers. It also provided an instrument – the planning document – for state and federal government agencies to enhance their power and to bring resources to the region. The planning process simultaneously ameliorated conflicts between government agencies and the large farmers, while enhancing the agencies’ capacity to reclaim wetlands. In this contradictory manner, the plan promoted the environmental aims of many small-holders, and simultaneously disempowered them as actors in the region’s political economy. An erratum to this article is available at .     

The Ethics of Constrained Choice: How the Industrialization of Agriculture Impacts Farming and Farmer Behavior

The industrialization of agriculture not only alters the ways in which agricultural production occurs, but it also impacts the decisions farmers make in important ways. First, constraints created by the economic environment of farming limit what options a farmer has available to him. Second, because of the industrialization of agriculture and the resulting economic pressures it creates for farmers, the fact that decisions are constrained creates new ethical challenges for farmers. Having fewer options when faced with severe economic pressures is a very different situation for farmers than having many options available. We discuss the implications of constrained choice and show that it increases the likelihood that farmers will consider unethical behavior.