Modeling an irrigation management strategy for minimizing the leaching of atrazine

Possible contamination of water resources by applied pesticides (including insecticides and herbicides) is a problem currently confronting irrigated agricultural production. Best management practices have to be adopted to minimize pesticide transport and leaching under irrigated conditions. A field capacity/mixing-cell model (IRRSCHM) and a model that uses Richard’s equation and the convection–dispersion equation to describe water and contaminant dynamics in soils (LEACHP) were used to assess the leaching of atrazine (a herbicide) under corn receiving different levels of early-season irrigation. The early-season irrigation levels were 11.1, 16.8, 23.3, and 28.8 cm out of corresponding seasonal irrigation levels of 31.2, 39.6, 45.5, and 53.1 cm. The objectives were to (a) use a modeling approach to evaluate water management effects on atrazine leaching, and (b) assess the feasibility of using IRRSCHM and LEACHP to guide irrigation for minimizing atrazine leaching.IRRSCHM and LEACHP simulations deviated from the measured atrazine profile, but both models predicted reasonably well the progression in atrazine leaching with increasing water application. Additionally, atrazine pulses predicted by IRRSCHM were ahead of those by LEACHP but lagged behind those observed under the different irrigation levels. Similarly, both models underestimated atrazine leaching, with IRRSCHM leaching estimates being closer to the observed than the LEACHP estimates. For example, the atrazine profile’s center of mass position at 143 days after application, ranged from 34.2 to 49.4 cm for IRRSCHM, 23.8 to 34.7 cm for LEACHP, and 40.6 to 60.9 cm for the measured atrazine profile under irrigation levels that ranged from 31.2 to 53.1 cm of water. Based on accurate predictions of the trends in atrazine leaching in relation to different irrigation levels, IRRSCHM and LEACHP could be used for preliminary assessment of the likely amount of atrazine leaching, resulting from targeted irrigation management strategies.     

Decision-making processes for crop management on African farms. Modelling from a case study of cotton crops in northern Cameroon

Recent work on decision processes on French farms and irrigated systems in Africa has shown that farmers plan their cyclical (recurrent) technical operations, and that one can model this planning process. Taking the case of cotton crop management in North Cameroon, we show that with certain adjustments, modelling of this kind can also be done for rainfed crop farming in Africa. The adjustments are needed to take account of the differences in social status between different fields on one farm and the implications of the fact that farm work is primarily manual. This produces decision models with a similar structure to that described for technical management of an annual crop break in a temperate climate using mechanised implements. Not only do these models give us a detailed understanding of the variability of farming practices, we can also classify them into categories according to weather scenarios yield level as a function of weather scenario. We show that one can attribute farms to these types of model using simple indicators concerning work organisation. By analysing North Cameroon farmers' decision processes for managing cotton crops we can thus produce an effective tool for organising technical supervision of farmers at the regional level: advisers can work with these decision model types by measuring some simple indicators at farm level to predict which types of model are applicable, without the onerous work of constructing individual decision models.     

食用豆联合收获减损技术与策略分析

食用豆是我国重要的食用作物,推进其机械化收获提质减损是促进产业发展的重要手段。由于食用豆种类多、地域分布广、种植模式多样,其高效收获装备较为缺乏,是当前生产中迫切需要解决的短板技术问题。结合国内外食用豆产业发展现状、当前联合收获技术研究成果和食用豆机械化收获的特殊性,在对现有联合收获技术的适用性进行分析的基础上,提出适合我国食用豆生产的机械化减损收获技术策略。主要措施包括综合考虑宜机化品种筛选及配套种植农艺、联合收获各环节协同作用和机手收获技能减损。利用以上手段可有效降低收获割前损失、割台损失、脱粒损失和清选损失,同时通过集成应用低损收获割台、高效脱粒清选和物料低损输送技术,可大幅降低食用豆联合收割机作业损失率,减损效果显著。     

一种识别天车吊具运动的新方法

针对传统天车吊具防摆过程均为人眼识别,现对其进行数字化改造,用相机代替人眼进行吊具运动识别,根据实际天车吊具结构,搭建实验室天车吊具识别实验台,由于天车工作的复杂性,对天车吊具添加发光二极管增强目标物的特征性.利用RGB颜色分割法对吊具运动图像进行识别,识别后的吊具图像具有很高的准确性和稳定性.     

Rainfall simulation to identify the storm-scale mechanisms of gully bank retreat

Gully erosion is one of the main causes of soil loss in drylands. Understanding the dominant mechanisms of erosion is important to achieve effective erosion control, thus in this study our main objective was to quantify the mechanisms involved in gully bank retreat as a result of three processes, falling of entire soil aggregates, transport of soil material by splash and by water running along gully banks (runoff), during rainfall events. The study was conducted in the sloping lands of the KwaZulu-Natal province, a region that is highly affected by gully erosion. Artificial rain was applied at 60 mm h⁻¹ for 45 min at the vertical wall of a gully bank typical to the area. The splash material was collected by using a network of 0.045 m² buckets. The sediments in the running water were assessed by sampling the runoff collected from a microplot inserted within the base of the bank, and collecting the fallen aggregates after the rainfall simulation was complete. Results indicated that the overall erosion for the simulation was 721 g m⁻² h⁻¹. Runoff erosion proved to be the dominant mechanism and amounted to 450 g m⁻² h⁻¹, followed by splash and fall down of aggregates (about 170 g m⁻² h⁻¹). Gully bank retreat occurred at a rate of 0.55 mm h⁻¹ and assuming that the soil bulk density is 1.3 g cm⁻³, this corresponds to a retreat of 8.8 mm y⁻¹. Extrapolations to the watershed level, where about 500 m² of gully bank are observed per hectare, would lead to an erosion rate of 4.8 t ha⁻¹ y⁻¹. These limited results based on a simulated storm show that the three main mechanisms (runoff, splash and fall down of aggregates) are responsible for the retreat of gully banks and that to mitigate gully erosion, appropriate measures are required to control all three mechanisms. Further research studies are needed to confirm and to scale up, both in time and space, as these data are obtained at one location and from a single artificial storm.     

Planning and management of a complex water resource system: case of Samanalawewa and Udawalawe reservoirs in the Walawe river,Sri Lanka

The Samanalawewa and Udawalawe reservoirs were built to harness the hydro-energy and irrigation potentials of the Walawe river in Sri Lanka. The recently completed Samanalawewa reservoir primarily generates hydropower while the Udawalawe reservoir, which was built in the 1960s, supplies water mainly for irrigation. With the addition of the Samanalawewa reservoir, located upstream of the Udawalawe reservoir, the Government of Sri Lanka is planning to increase the irrigated area of the Udawalawe reservoir. The Samanalawewa reservoir is expected to act as an additional storage for irrigation water supply. A study was carried out to investigate the operational behavior of these two reservoirs. The model used in the study is based on stochastic dynamic programming (SDP) and simulation techniques. Since, the direct application of SDP for two reservoirs is limited by the dimensionality of the problem, a sequential decomposition method is employed in the model. The algorithm employed breaks down the system into single-reservoir subsystems and subsequently, each subsystem’s operation is individually optimized using a SDP based optimization model and then simulated using a reservoir operation simulation model. The results indicate the usefulness of optimization techniques in planning reservoirs and deriving operational policies for them. The inclusion of the Samanalawewa reservoir reduces the irrigation water supply deficits at the Udawalawe reservoir.     

Economic assessment of shade-cloth covers for agricultural irrigation reservoirs in a semi-arid climate

We assess the economics of investing in suspended shade-cloth covers (SSCCs) in agricultural water reservoirs (AWRs) to reduce evaporation losses and save water for irrigation in arid and semi-arid areas. In particular, we examine the use of SSCCs in the Segura River Basin (southeastern Spain). The decision to install a cover depends on the potential evaporation losses, reservoir characteristics, cover effectiveness, the value of water, filtration requirements, water salinity, government subsidies and the installation, operation and maintenance costs. The economic viability of the investment increases with the value of the saved water, i.e., with water scarcity, and is greater when water quality is poor. Hence SSCCs can be helpful in arid and semi-arid regions facing water shortages and water quality problems. The farm-level decision to install a cover depends largely on the cost of purchasing water, when water is generally available, and the profit from increased crop production or enlarged farmlands, when water is scarce.     

Controlled water table management as a strategy for reducing salt loads from subsurface drainage under perennial agriculture in semi-arid Australia

Recent community based actions to ensure the sustainability of irrigation and protection of associated ecosystems in the Murrumbidgee Irrigation Area (MIA) of Australia has seen the implementation of a regional Land and Water Management Plan. This aims to improve land and water management within the irrigation area and minimise downstream impacts associated with irrigation. One of the plan objectives is to decrease current salt loads generated from subsurface drainage in perennial horticulture within the area from 20 000 tonnes/year to 17 000 tonnes/year. In order to meet such objectives Controlled Water table Management (CWM) is being investigated as a possible ‘Best Management Practice’, to reduce drainage volumes and salt loads.During 2000–2002 a trial was conducted on a 15 ha subsurface drained vineyard. This compared a traditional unmanaged subsurface drainage system with a controlled drainage system utilizing weirs to maintain water tables and changes in irrigation scheduling to maximize the potential crop use of a shallow water table. Drainage volumes, salt loads and water table elevations throughout the field were monitored to investigate the effects of controlled drainage on drain flows and salt loads.Results from the experiment showed that controlled drainage significantly reduced drainage volumes and salt loads compared to unmanaged systems. However, there were marked increases in soil salinity which will need to be carefully monitored and managed.     

Modelling the Drying Kinetics of Maize in a Microwave Environment

Microwave drying of grains is fundamentally different from either convection or conduction drying. Drying of cereal grains appears to proceed mainly in the period when the drying rate is decreasing (in the falling rate period), a characteristic of internally controlled diffusion. However, the analytical solution to Fick's second law of diffusion for a homogeneous, isotropic sphere with constant initial and boundary conditions does not adequately describe the drying behaviour. In an attempt to overcome this problem, the moisture ratio was written in terms of the surface moisture content rather than the equilibrium value. The associated surface drying coefficient, as determined by an iterative technique, was found to be expressible as a linear function of the initial free moisture content of the grain. The resulting empirical model better described the observed drying kinetics. This approach also resulted in good fits to independent data from experiments on convective drying of rough rice, microwave drying of wheat and combined microwave-fluidized bed drying of wheat.     

Identification of nitrate leaching hot spots in a large area with contrasting soil texture and management

Identification of nitrate (NO₃) leaching hot spots is important in mitigating environmental effect of NO₃. Once identified, the hot spots can be further analyzed in detail for evaluating appropriate alternative management techniques to reduce impact of nitrate on groundwater. This study was conducted to identify NO₃ leaching hot spots in an approximately 36,000 ha area in Serik plain, which is used intensively for agriculture in the Antalya region of Southern Turkey. Geo-referenced water samples were taken from 161 wells and from the representative soils around the wells during the period from late May to early June of 2009. The data were analyzed by classical statistics and geostatistics. Both soil and groundwater NO₃-N concentrations demonstrated a considerably high variation, with a mean of 10.2 mg kg⁻¹ and 2.1 mg L⁻¹ NO₃-N for soil and groundwater, respectively. The NO₃-N concentrations ranged from 0.01 to 102.5 mg L⁻¹ in well waters and from 1.89 to 106.4 mg kg⁻¹ in soils. Nitrate leaching was spatially dependent in the study area. Six hot spots were identified in the plain, and in general, the hot spots coincided with high water table, high sand content, and irrigated wheat and cotton. The adverse effects of NO₃ can be mitigated by switching the surface and furrow irrigation methods to sprinkler irrigation, which results in a more efficient N and water use. Computer models such as NLEAP can be used to analyze alternative management practices together with soil, aquifer, and climate characteristics to determine a set of management alternatives to mitigate NO₃ effect in these hot spot areas.     

Developing a reliable strategy to infer the effective soil hydraulic properties from field evaporation experiments for agro-hydrological models

The Richards equation has been widely used for simulating soil water movement. However, the take-up of agro-hydrological models using the basic theory of soil water flow for optimizing irrigation, fertilizer and pesticide practices is still low. This is partly due to the difficulties in obtaining accurate values for soil hydraulic properties at a field scale. Here, we use an inverse technique to deduce the effective soil hydraulic properties, based on measuring the changes in the distribution of soil water with depth in a fallow field over a long period, subject to natural rainfall and evaporation using a robust micro Genetic Algorithm. A new optimized function was constructed from the soil water contents at different depths, and the soil water at field capacity. The deduced soil water retention curve was approximately parallel but higher than that derived from published pedo-tranfer functions for a given soil pressure head. The water contents calculated from the deduced soil hydraulic properties were in good agreement with the measured values. The reliability of the deduced soil hydraulic properties was tested in reproducing data measured from an independent experiment on the same soil cropped with leek. The calculation of root water uptake took account for both soil water potential and root density distribution. Results show that the predictions of soil water contents at various depths agree fairly well with the measurements, indicating that the inverse analysis is an effective and reliable approach to estimate soil hydraulic properties, and thus permits the simulation of soil water dynamics in both cropped and fallow soils in the field accurately.     

Modelling the requirement of the young growing pig for dietary protein

Achieved protein retention in young pigs (<20 kg) is less than the maximum potential attained later in the growth period. Knowledge of this former rate is a prerequisite for response prediction and the determination of dietary protein requirement, but its simulation has been complicated by the presumption of a single value for maximum daily rate of protein retention (Pr̂) characteristic of a pig type, and by the consequent need for some mechanism to account for the down-sizing of protein retention in early life. Commonly this is achieved by a single value for Pr̂ ranging from 100–200 g according to sex and genotype, and the unsatisfactory assumption of some arbitrarily given minimum ratio, often 1:1, for lipid to protein in the gain of young pigs. More satisfactory simulation and prediction of response can be achieved (i) by use of a Gompertz function rather than a single value to describe the potential for protein growth, Pr̂ = B.Pt.ln (Pt̂/Pt), where B is the growth coefficient, Pt the present protein mass and Pt̂ the ultimate mature protein mass; (ii) by understanding that amino acids disappearing from the terminal ileum in ideal balance are not necessarily fully available, even when supplied at levels which are less than requirement; and (iii) by dispensing entirely with the concept of a minimum lipid:protein retention ratio.     

引江大型灌区的治理规划与灌排调度

1　灌排区基本情况1.1　地理概貌江汉平原由于长江、汉水的冲积成土过程的影响 ,地势从西北向东南倾斜 ,地面高程在 5 0～ 2 5ｍ(吴淞基面 ,下同 )以下。平原内部受网状水系的泥砂沉积过程中的水力泥砂的分选作用 ,以及地形局部差异的影响 ,形成了相对高差数米至十余米的沿江高地和河间湖洼地相分布的地貌特点。四湖地区位于江汉平原腹地 ,因区内有长湖、三湖、白露湖和洪湖四大湖而得名。区域面积 115 47ｋｍ2 ,行政区划有荆州市、荆门市、潜江市等 8个县 (市 )、区 ,耕地约 42 .6 7万ｈｍ2 ( 6 40万亩 )。四湖地区的西北部的丘陵地区是漳…     

Modelling weekly rainfall data for crop planning in a sub-humid climate of India

In this study, two and three-parameter probability distributions have been compared to identify the most appropriate distribution to describe the weekly rainfall data in a sub-humid climate of India. The “best” distribution among different data sets has been identified using probability plot and Anderson–Darling (AD) test for goodness-of-fit, along with the appropriateness of estimated percentiles. One single probability distribution has not been found appropriate to represent all the data sets though Weibull distribution has been found promising for most of the data sets. Gamma probability distribution, which is generally employed for describing weekly rainfall data, was found to grossly approximate the underlying process. Likelihood ratio (LR) test revealed that three-parameter distributions did not significantly improve the fit over two-parameter distributions within the same family. The developed models for different data sets have been employed for computing minimum assured amount of rainfall at different probability levels. Minimum assured rainfall at 40% probability level was found to be in close agreement with the long-term average weekly rainfall data as depicted by L2 and Chebycheff norms. The effect of departure from minimum assured rainfall at 70% probability level on yield of rainfed maize in the region has also been studied using the available experimental data collected from three different field experiments. The effect of intervening drought was found to be most serious in reducing the crop yield by 37–58% as compared to other scenarios representing rainfall amount and its distribution under a sub-humid climate.     

Simulation of the management of a rabbit population for meat production

A population model for a 100 doe rabbit enterprise was constructed in which the effect on output of various management decisions could be simulated. The question of how many young female stock to retain as replacements for dead or culled breeding stock was examined in detail. The optimum level was found to be when the combined number of mature and immature female replacements was maintained between 25 and 35 replacement does for a population of 100 breeding females. At this level was possible to maintain a regular and predictable output of rabbit carcases. With a larger population of 500 does, the optimum level for the replacement pool remained between 25 and 35 replacement does for each 100 breeding females.     

Simulated effect of drainage water management operational strategy on hydrology and crop yield for Drummer soil in the Midwestern United States

The hypothetical effects of drainage water management operational strategy on hydrology and crop yield at the Purdue University Water Quality Field Station (WQFS) were simulated using DRAINMOD, a field-scale hydrologic model. The WQFS has forty-eight cropping system treatment plots with 10 m drain spacing. Drain flow observations from a subset of the treatment plots with continuous corn (Zea mays L.) were used to calibrate the model, which was then used to develop an operational strategy for drainage water management. The chosen dates of raising and lowering the outlet during the crop period were 10 and 85 days after planting, respectively, with a control height of 50 cm above the drain (40 cm from the surface). The potential effects of this operational strategy on hydrology and corn yield were simulated over a period of 15 years from 1991 to 2005. On average, the predicted annual drain flows were reduced by 60% (statistically significant at 95% level). This is the most significant benefit of drainage water management since it may reduce the nitrate load to the receiving streams. About 68% of the reduced drain flow contributed to an increase in seepage. Drainage water management increased the average surface runoff by about 85% and slightly decreased the relative yield of corn crop by 0.5% (both are not statistically significant at 95% level). On average, the relative yield due to wet stress (RYw) decreased by 1.3% while relative yield due to dry stress (RYd) increased by 1%. Overall, the relative crop yield increased in 5 years (within a range of 0.8-6.9%), decreased in 8 years (within a range of 0.2-5.5%), and was not affected in the remaining 2 years. With simulated drainage water management, the water table rose above the conventional drainage level during both the winter and the crop periods in all years (except 2002 crop season). The annual maximum winter period rise ranged between 47 cm (1995) and 87 cm (1992), and the annual maximum crop period rise ranged between no effect (2002) and 47 cm (1993).