A pasture growth model for use in a whole-farm dairy production model

A generalised climate driven pasture growth model is described and evaluated by comparison to field observation. The model describes dry matter production and green-dead tissue flow dynamics for grazed temperate swards, especially perennial ryegrass (Lolium perenne). The model includes a unique feature to account for light interception by non photosynthetic tissue. Extrapolation across environments occurs by the interaction of climate variables with three parameters that tune the model to a site. These parameters reflect the influence of soil fertility and sward species composition on production patterns. They are: (1) the efficiency of radiant energy use for photosynthesis, (2) the timing of reproductive development and (3) the relative efficiency of radiant energy use in vegetative compared to reproductive swards. Initial parameter settings were derived from data from a sheep grazing experiment in New Zealand. In this paper the ability to describe pasture production under dairy grazing at a different site is confirmed. When the three available parameters were calibrated for the dairy site, all but two of the 42 seasonal estimates of pasture production were within the 95% confidence interval for mean measured production. The model is being used as a component of a whole-farm dairy production model.     

LP analysis in a tank irrigation system for near real representation and optimal allocation of area

There is a wide gap between an ideal situation and actual conditions existing in the field of irrigation management in any tank irrigation system in India. To bridge this gap, a near real time analysis through LP modeling of the existing situation and the best allocation policy is attempted for the Aralikottai tank system. The actual conditions are simulated at each sluice command level whereas the best operational policy is attempted for the entire system as a whole. The analysis is conducted separately for a drought year (1988) and a surplus year (1990) with the available five year data from 1988 to 1992. The major conclusions indicate that the late transplantations of the rice crop and the excess water application during the periods of water availability (leading to water stress during the last stages of crop maturity) are the causes of the meagre benefits in a drought year. Also, in a surplus year the excess water application over the entire cropping season resulted in under utilization of land resources and moderate benefits. The existing status of irrigation can be improved to obtain the maximum benefits from the tank command area based on the quantification done.     

A preliminary model to investigate culling and replacement policy in dairy herds

Replacement policy in dairy herds is not easy to determine when heifers are both home-reared and compete for land with the cows. The difficulty lies in evaluating quantitatively the advantages and disadvantages of low and high replacement rates. A computer simulation model was developed to examine the effects of different replacement rates on genetic improvement in yield per cow, milk output and farm profit at two levels of culling for reasons other than insufficient yield.The working hypothesis suggested by the results is that profitability falls as replacement rate increases because the number of cows able to be milked and the maturity of the herd over-ride the gains in milk yield per cow due to genetic improvement by yield culling and the greater use of a sire of high genetic merit.     

A framework for estimating the extent and severity of drought,based on a grazing system in south-eastern Australia

The National Drought Policy of Australia was ratified by the Commonwealth, States and Territories in 1992. However, before it was fully implemented, one of the most severe droughts on record was already establishing itself across Australia. The Commonwealth government, therefore, devised measures to determine which areas had been exposed to exceptional drought so that financial assistance could be directed as effectively as possible. Six criteria were agreed to nationally, namely meteorological, agronomic, and environmental conditions, water supply, net farm income, and the spatial extent of the drought. Assessments during 1994–1995 had to account for the wide range of environments and farming systems. Useful data were often at a premium. In this paper we describe some of the ways in which these criteria have been estimated and assessed. Ways in which simulation models can be used to objectively estimate the extent and severity of drought are also demonstrated and discussed.     

A dynamic bio-economic model to simulate optimal adjustments of suckler cow farm management to production and market shocks in France

Tactical adjustments to seasonal weather conditions and beef price may generate additional income or avoid losses in French beef cattle farms. Due to the length of the suckler cow production cycle, adjustment decisions may impact not only on current production and profit but also on future farm outcomes. To better understand the consequences of shocks and subsequent production adjustments on the evolution of farm earnings and production over time, we built a dynamic recursive bio-economic farm model. Our model introduced simultaneously the possibility of adjusting herd size and herd composition, diet composition and diet energy content, as well as crop rotation, haymaking and feed stocks, taking into account both their short- and long-term consequences. An application is provided to test impacts of crop yield and beef price shocks of different intensities. Main simulated adjustments to face unfavourable weather shocks are (1) purchased feed in order to maintain animal production objectives, and (2) area of pasture harvested for haymaking. Very severe beef price shocks induce forced sales. Weather shocks affect farm net profit not only of the current year but also of the following years. Profit losses caused by unfavourable weather conditions are not compensated by gains in favourable ones and this differential is amplified when intensity of shocks rises.     

I. A decision support system to improve planning and management in large irrigation schemes

This paper describes a decision support system (DSS) that was developed to improve planning and management for the large irrigation schemes in the Alentejo region of Portugal. The system was designed to help in the analysis and evaluation of the crops and crop systems that can potentially be cultivated, together with identification of limitations affecting crop selection and crop yields. It integrates socio-economic and biophysical data at the field level to analyse the performance of an irrigation scheme in terms of the adoption of irrigation by farmers and farmers’ incomes. The final output is given in the form of specific actions and policies for the irrigated areas. The DSS was designed initially to be used in the Alqueva project, a large irrigation scheme that is under construction in Alentejo. Nevertheless, the final framework is generic in nature, being suitable for planning and policy evaluation in other large irrigation schemes.     

A field test of a conceptual computer simulation model for predicting water and salt distribution

Summary The unsaturated flow and unsaturated chemistry submodels of a conceptual computer simulation model, developed at the United States Bureau of Reclamation to predict water and salt behaviour in soils, were tested under field conditions. The comparison of results was done with data obtained from an irrigation trial with alfalfa over a period of four years. The model simulated the actual physical and chemical processes taking place in the soil to a fair degree of accuracy. The predicted moisture contents compared reasonably well with ob served data, especially in the soil layers between 480 and 1200 mm (Figs. 1 and 2, Tables 3 and 4). The simulation of moisture distribution was more accurate for plots receiving a high irrigation frequency than for plots given a low irrigation frequency. On a depth-weighted-mean scale, the predicted salt concentration of the soil layers shallower than 1200 mm was within 11% of the observed data. However when the salt content of the soil layers between 1200 and 1920 mm was taken into account, the percentage error increased to about 40% (Table 6). The results indicate that this simulation model can be extremely useful in predicting the long and short term effect of irrigation water on the root zone of a soil. Field data are however at all times needed to calibrate the unsaturated flow model for specific soil types.     

VegSyst, a simulation model of daily crop growth, nitrogen uptake and evapotranspiration for pepper crops for use in an on-farm decision support system

The VegSyst simulation model was developed to assist with N and irrigation management of sweet pepper grown in plastic greenhouses in the Mediterranean Basin. The model was developed for use in an on-farm decision support system with the requirement for readily available input data. Dry matter production (DMP), crop N uptake and crop evapotranspiration (ET_c) are simulated on a daily basis. DMP is calculated from daily fraction of intercepted photosynthetically active radiation (PAR), PAR radiation, and radiation-use efficiency. Fraction of intercepted PAR is calculated from relative thermal time. Crop N uptake is calculated as the product of DMP and N content which is described by a power function of DMP. ET_c is the product of daily reference evapotranspiration (ET_o) using an adapted Penman–Monteith equation, and a daily simulated crop coefficient value. The VegSyst model for soil-grown, greenhouse pepper was calibrated in one crop and validated in three different crops. In the validation, the model accurately simulated crop growth, N uptake and ET_c. Relative to measured values, simulated DMP at final harvest was 0.89–1.06, and crop N uptake was 0.97–1.13. Simulated cumulative ET_c for complete crops was 0.95–1.05 of measured values.     

LUSE,a decision support system for exploration of rural land use allocation: Application to the Terra Chá district of Galicia (N.W. Spain)

This article describes LUSE, a system for exploration of rural land use allocations (total area devoted to each kind of use) by multiobjective linear programming methods. The objectives pursued are maximization of gross margin, employment in agriculture, land use naturalness and traditional rural landscape, and minimization of production costs and use of agrochemicals. The constraints on the areas devoted to the land uses considered in addition to those imposed by their joint and individual availabilities, are that they must reach levels considered to satisfy existing demand for those uses or their products, and that the areas devoted to maize and fodder must be sufficient for maintenance of dairy farm production. The program generates comprehensive samples of the Pareto-optimal set, and also allows interactive convergence on a solution that is satisfactory to the decision-maker or interactive exploration of the Pareto-optimal set. The system is currently parameterized for use in an area of Galicia (N.W. Spain), but is easily adaptable to other geographic locations.     

Prototype decision support system based on the VegSyst simulation model to calculate crop N and water requirements for tomato under plastic cover

The simulation model VegSyst was calibrated and validated for tomato grown under plastic cover. Calibration was conducted with an autumn–winter soil-grown crop, and validation with five crops with differences in season, cropping media, and site. VegSyst accurately simulated daily dry matter production (DMP), N uptake, and ET_c. Comparing simulated and measured values by linear regression, slope and intercept values were not statistically significantly different (P < 0.05) from 1 and 0, respectively. Slopes between simulated and measured values indicated average differences of 4, 2, and ?1 % for DMP, N uptake, and ET_c, respectively. Model performance was good with autumn–winter and spring cropping cycles, and in soil and substrate. A prototype decision support system (VegSyst-DSS) based on VegSyst was developed to calculate daily irrigation and N fertilizer requirements and nutrient solution [N] for fertigated tomato. N fertilizer requirements are based on crop N uptake and consider soil mineral N, and N mineralized from manure and soil OM and the N efficiency of each N source. Irrigation requirements are based on ET_c and consider application efficiency and salinity. VegSyst-DSS requires very few inputs which are all readily available to farmers and advisors. Scenario analysis compared a scenario representative of local farming practice, where N supplied from soil is not considered, with scenarios with different amounts of N supplied from soil mineral N at planting and mineralization of soil OM and of manure. Relative to the scenario representative of farmer practice, VegSyst recommendations resulted in reductions of 34–65 % in fertilizer N.     

Management of water consumption in agriculture A model for the economic optimisation of water use: application to a sub-humid area

This paper present a set of solutions for new irrigation transformation in a sub-humid area such as Salvatierra (Alava, Spain). The research is based on the choice of crop rotation (cultivated species and its degree of participation) being able to economically optimise the use of available water for irrigation. Hence, we will be able in helping make decisions to plan, from origin, the transformation of a dry area into an irrigated area. To do this, a model of economic use of water has been used in an area with climatic features very similar to a large part of Europe, representing an interesting scenario compared to the places where the model had not been applied. Crops taking part in this rotation to optimise use of water are mainly vegetables, with high water needs, that coexist together with crops for dryland farming even in conditions of lack of water. Crops for dryland farming allow an interesting diversification of activity as well as an average resource assignment to the farms that make possible to cultivate many farms at a time, which obviously implies socio-economic benefits for the achievements in the zone.     

Bases for farm resource allocation in the traditional farming system: A comparative study of productivity of farm resources in abakaliki area of Anambra State,Nigeria

A study was carried out to determine the returns in utilisation of farm-resources in the production of three crop enterprises. These returns determined the productivity of resources in yam-based crop mixture (YBCM), cassava-based crop mixture (CBCM) and rice enterprises.The results show that of the three crop enterprises considered in the survey year, YBCM received special attention in the resources allocated. Prime land, prime labour and a large proportion of household cash were allocated to the production of YBCM relative to other crop enterprises. Cost-return analysis indicated that all scarce resources such as labour, land and capital were more productive in monetary terms in CBCM and rice enterprises than in YBCM.The cultural value of yam in YBCM transcends the monetary and food security values. It includes intangible value such as social status. The special place of yam in the crop production system militates against practical solutions such as the transfer of farm resources from the less productive (YBCM) to the more productive enterprises. Thus it is that improved management techniques such as the use of higher-yielding yam varieties, increase in cropping densities and the use of fertilizers need to be explored as a means of improving the returns of the resources used in the YBCM enterprises.     

Mathematical relationships and computer routines for a model of food intake,liveweight change and wool production in grazing sheep

The model predicts the selection of herbage from pastures containing green and dry clover and grass, intake of digestible organic matter and nitrogen, and changes in liveweights and wool growth in Merino wethers. Details of the prediction relationships and their derivation are given. Sensitivity analyses were done and the reason for poorer predictions on clover dominant pasture found and corrected.     

FARMFLOW—A dynamic model for phosphorus mass flow,simulating conventional and organic management of a Swedish dairy farm

A farm systems mass-balance calculation model, FARMFLOW, was applied to a case study comparing organic and conventional management of a Swedish experimental dairy farm, Öjebyn. Parameterisation of the model is implemented using detailed field data from the Öjebyn farm where the two management systems have been run parallel for more than 11 years. Simulations were made to compare the stocks, flows and resulting balances of phosphorus (P) in the two systems during six crop rotations (36 years). In addition, a maximum animal density scenario was tested, in order to analyse the effects of increased production intensity. Results show that FARMFLOW can be a useful tool for analysing the impact of management on internal farm P dynamics, as well as imports and exports. The organic management results in a higher proportion of internal P flows whereas the conventional system relies more on imports of P in feed and mineral fertilisers. In both management systems, the crop rotation cause large temporal and spatial variation in the application of manure P to the soil system. The resulting field specific soil P accumulation can indicate which fields to target with changed fertilisation management. In the maximum animal density scenario, both management systems led to an application rate of manure P in excess of crop demands.     

Environmental decision support system development for seasonal wetland salt management in a river basin subjected to water quality regulation

Seasonally managed wetlands in the Grasslands Basin on the west-side of California’s San Joaquin Valley provide food and shelter for migratory wildfowl during winter months and sport for waterfowl hunters during the annual duck season. Surface water supply to these wetlands contain salt which, when drained to the San Joaquin River (SJR) during the annual drawdown period, can negatively impact water quality and cause concern to downstream agricultural riparian water diverters. Recent environmental regulation, limiting discharges salinity to the SJR and primarily targeting agricultural non-point sources, now also targets return flows from seasonally managed wetlands. Real-time water quality management has been advocated as a means of continuously matching salt loads discharged from agricultural, wetland and municipal operations to the assimilative capacity of the SJR. Past attempts to build environmental monitoring and decision support systems (EDSS’s) to implement this concept have enjoyed limited success for reasons that are discussed in this paper. These reasons are discussed in the context of more general challenges facing the successful implementation of a comprehensive environmental monitoring, modelling and decision support system for the SJR Basin.     

A model for recycling of feed nutrients in a crop,animal and biogas system in India

In northern India, with triple cropping intensity of fodder crops and recycling of feed nutrients in a milch animals and biogas system, from 1 ha of land it is possible to produce 82·63 GJ of energy and 906·11 kg of protein from milk; 263·93 kg of N; 148·93 kg of P₂O₅ and 90·94 kg of K₂O fertilizer from biogas slurry and 2897 kilowatts of power per annum for farm operation from biogas using the Kirloskar biogas engine. Traditional systems of wheat and rice cultivation can produce 93·87 GJ of energy and 654·25 kg of protein from food grain per hectare per annum. The recycling of feed nutrients in the available straws of rice and wheat crop can yield an additional 16·31 GJ of energy and 166·97 kg of protein from milk; 81·23 kg of N; 56·00 kg of P₂O₅ and 25·14 kg of K₂O fertilizer from biogas slurry and 1097 kilowatts of power per hectare annually from biogas.     

A framework for priority non-point source area identification and load estimation integrated with APPI and PLOAD model in Fujiang Watershed, China

The non-point source (NPS) pollution is difficult to manage and control due to its complicated generation and formation. In large scale watersheds, the priority sources areas (PSAs) identification is an important and necessary process for efficient aquatic environmental management. Here, a framework for the PSAs identification and pollution load estimation in PSAs screened for Best Management Practices (BMPs) is proposed. Fujiang Watershed, a branch of Jialingjiang, the upper reach of Yangtze River, was chosen for evaluation of the method proposed here. The entire Fujiang Watershed was divided into 21 subbasins, after which the Agricultural Pollution Potential Index (APPI) was used to identify the PSAs, and a modified runoff coefficient was introduced to mitigate the impact of the rainfall heterogeneity in the process. Next, the identified PSAs were further divided into 34 subbasins, after which quantification of the pollution load was conducted using the Pollution Load (PLOAD) model. The results indicated that there are five subbasins have much higher NPS pollution load intensities, with an average value of 6.05 t/km²/year for TN and 0.31 t/km²/year for TP. According to the cluster analysis on land use structure, these five subbasins were featured by higher proportion of agricultural land, suggesting a need for better fertilizer application management. The method developed here provided a helpful framework for conducting NPS pollution management in a large watershed.     

A universal agro-hydrological model for water and nitrogen cycles in the soil-crop system SMCR_N: Critical update and further validation

Agro-hydrological models have widely been used for optimizing resources use and minimizing environmental consequences in agriculture. SMCR_N is a recently developed sophisticated model which simulates crop response to nitrogen fertilizer for a wide range of crops, and the associated leaching of nitrate from arable soils. In this paper, we describe the improvements of this model by replacing the existing approximate hydrological cascade algorithm with a new simple and explicit algorithm for the basic soil water flow equation, which not only enhanced the model performance in hydrological simulation, but also was essential to extend the model application to the situations where the capillary flow is important. As a result, the updated SMCR_N model could be used for more accurate study of water dynamics in the soil-crop system. The success of the model update was demonstrated by the simulated results that the updated model consistently out-performed the original model in drainage simulations and in predicting time course soil water content in different layers in the soil-wheat system. Tests of the updated SMCR_N model against data from 4 field crop experiments showed that crop nitrogen offtakes and soil mineral nitrogen in the top 90 cm were in a good agreement with the measured values, indicating that the model could make more reliable predictions of nitrogen fate in the crop-soil system, and thus provides a useful platform to assess the impacts of nitrogen fertilizer on crop yield and nitrogen leaching from different production systems.     

Adaptation to Agenda 2000 (CAP reform) and optimisation of the farming system of French suckler cattle farms in the Charolais area: a model-based study

French suckler farmers need advice on the implications of the Agenda 2000 CAP reform for their farms and, in particular, on the incentives it offers for a more extensive mode of production. To support the dialogue between advisers and farmers, and thus help farmers with their decision-making, we constructed a linear programming (LP) model that optimises the farming system of the northern Massif Central Charolais suckler cattle farms, which may be either mixed (crop-livestock) or specialised (livestock). This model, called Opt'INRA, incorporated all of the production activities presently encountered in this zone, together with the constraints of the CAP premium attributions. We used it to study how, on the basis of their 1999 data, two farms, representing two situations frequently encountered in the Charolais area (a mixed crop-livestock farm and a specialised livestock farm), could best adapt to Agenda 2000.According to the model, for both of the farms studied, the economic impact of Agenda 2000 is relatively low, albeit negative. The adaptation of the system when possible does not lead to a significant increase in the gross margin of this farms. Agenda 2000 did not encourage farmers to extensify their farming system. On the other hand, this CAP reform discourages them from intensifying.