Dairy farm nutrient management model. 1. Model description and validation

Intensive dairy farming results in significant phosphorus (P) emission to the environment. Field data indicates that farm-gate P surplus is highly positive in Finland and strategies to mitigate the surplus are needed. The objectives of this study were to build a P cycle model for dairy farms (1) and to validate the model with independent field data (2). The dairy farm nutrient management model (“Lypsikki”) described in this paper includes three sub-models: (1) soil and crop, (2) dairy herd and (3) manure management. The model is based on empirical regression equations allowing estimations of crop and milk yields in response to increased fertilisation and nutrient supply, respectively. In addition, the model includes a dynamic simulation model of the dairy herd structure and calculation of the farm-gate nutrient surplus. The model was validated with independent annual (average for 1-4 years) farm-gate P surplus data from 21 dairy farms. Model simulations were conducted using two levels of soil productivity, mean (M) and low (L). The model validation indicated a strong relationships between model-predicted and observed farm-gate P surplus: (M: R² = 0.77 and L: R² = 0.80). The line bias between the model-predicted and observed data was negligible and insignificant (P > 0.6) suggesting a robustness of the model. The mean biases were relatively high and significant (M: 4.7 and L: 1.8 kg/ha, P < 0.001), but evidently related to overestimation of crop yields that has to be taken into account when using the model on a single farm. The prediction error of the model (observed minus predicted P surplus) was significantly correlated to the difference between simulated and observed P import in feeds (M: R² = 0.55 and L: R² = 0.51). This suggests either that all the dairy farms did not fully exploit the possibilities in the crop production or that all the model assumptions are not correct. The effects of purchased feed and fertiliser P and exported milk P (per cow or cropping area) on farm-gate P surplus were of the same magnitude in both observed and simulated data. This implies that the model developed can be used as a management decision tool to find strategies to mitigate P surplus on dairy farms.     

Economic evaluation of current and alternative dual-purpose cattle systems for smallholder farms in the central Peruvian highlands

In four communities in the Peruvian Andes, 56 farmers were interviewed every three months over a period of one year. Information linked to milk and cattle production such as activities, inputs (labour, means of production, capital) and outputs (milk, cheese, animals) were recorded using a closed-ended questionnaire. The communities were divided into two groups with low (LC) and high (HC) level of dependence on income from milk and animal sales. The survey results showed that cattle production on the LC farms was based on less land and a smaller herd (3.32 ha/farm, 1.06 lactating cows) than on HC farms (10.28 ha/farm, 4.19 lactating cows). The data from the survey and the results of the nutritional analyses of 74 feed samples were introduced into a model that applied linear programming techniques in order to estimate the farm household income under the current production systems and evaluate the economic impact of improved forage varieties for hay production. Furthermore, the economic viability of other changes in fodder and herd management was tested. Both groups were characterised by a dual-purpose system generating a gross income from the sale of both, milk and live animals in the amount of -21 (LC) and +1057 US$/farm and year (HC). Due to higher production costs for forages and better access to markets, LC communities were characterised by an integrated crop–livestock system whereas in the HC group income was mainly based on livestock. Introduction of improved and fertilized barley for hay production, was estimated to increase the annual farm income to 127 and 1257 US$ for LC and HC, respectively. This increase was accompanied by an increment of the animal number. Maintaining the animal number but increasing the milk production/cow by feeding additional forage was a less profitable option generating 50 and 1221 US$ of income per farm and year for LC and HC, respectively. The production of hay was limited by high costs (external labour) in LC communities and the restricted availability of family labour in the HC group. A scenario based on the use of improved cow genotypes led to the highest estimated annual farm income for HC communities (1280 US$) but was less favourable for LC. The modelling results showed that the best development strategy depends on various factors such as production costs, access to the markets and to irrigation and availability of different feed resources.     

Replacement policy in dairy herds on farms where heifers compete with the cows for Grassland—part 1: Model construction and validation

It is difficult to evaluate quantitatively the effect of different replacement rates on dairy farm profitability and dairy herd improvement. Computer simulation models were developed to tackle this problem and to formulate hypotheses that might be useful for research and advisory purposes.A model was constructed and validated against actual average yields of heifers entering the national herd of England and Wales over the period 1962–1976. It was used to generate information on the initial state of herds that could be used in experiments. A second model was adapted from this generation model to handle the replacement situation where heifers are reared on the farm where they are to be used and compete with the cows for grassland.     

Assessment and management of poor quality waters for crop production: A simulation model (SWAM)

A simulation model has been prepared for assessing water quality to judge its suitability for irrigation. When water is classified as poor quality water (saline/sodic/saline-sodic) utilizing standard norms for Indian agro-climatic conditions, the model determines the potential of the water for direct application. Further, it also evaluates management strategies based on conjunctive use of fresh and saline waters. For this purpose, the model requires water quality data, crop data, soil data and rules established in the expert system rule-base. Data are compiled in data files which can be updated. For conjunctive use of saline and fresh waters, an irrigation scheduling sub-model has been modified to include a soil salinization-desalinization module based on layer-wise equilibrium theory. The module was independently tested using field data. The model SWAM has been successfully tested using data from a number of field experiments. Sodic waters of 16.2 meq l⁻¹ residual sodium carbonate would require 2.73 t ha⁻¹ of gypsum for each 20 cm of water applied to the soil. Field observations usually attest to this requirement. Likewise, saline water of 16 dS m⁻¹, when applied to a wheat crop in conjunction with fresh water of 0.5 dS m⁻¹, would yield optimally in case two saline water irrigations are followed by one fresh water irrigation in a normal rainfall year with an initial soil salinity of 2.98 dS m⁻¹. Some more useful data sets are analyzed and compared with results from field experiments. In our opinion, the model which is based upon recent guidelines can be applied to the classification of waters and their management. The minor changes necessary to apply the model to other conditions can be easily carried out.     

Simulated comparisons of breeding plans for beef production—Part 1: A dynamic model to evaluate the effect of mating plan on herd age structure and productivity

A computer program to simulate beef production is described. The model is based on the principles of industrial dynamics and constructed in the simulation language DYNAMO. This dynamic model is composed of subroutines that simulate herd structure for a cow herd and a production herd composed of calves from the cow herd. Additional subroutines model pre-weaning and post-weaning growth of the calves.The portion of the model that simulates the herd structure includes ten age classes of cow. The subroutine which models the portion of the herd between 2 and 9 years of age utilises twelve variables to describe the events that occur in the herd during the passage of a year. The age structure of the herd is influenced by the breeding system and the way in which the herd is managed.The production herd is modelled by sequential subroutines. These subroutines follow the number and growth of calves weaned from the cow herd until they are sold at 32, 52, 67 or 85 weeks of age. Mating plans utilising different breeds can be simulated in combination with various management options.     

A method for exploring sustainable development options at farm scale: a case study for vegetable farms in South Uruguay

The methodology presented in this paper aims at analysing whether there is room for improvement of vegetable farmers’ income in Canelón Grande (Uruguay), while reducing soil erosion and improving physical and biological soil fertility, and to gain insight in the influence of farmers’ resource availability on the opportunities for sustainable development. The (generic) approach we developed to support re-design of farming systems in this region is unique in dealing with complex temporal interactions in crop rotations and spatial heterogeneity on farms in one integrated method, while revealing trade-off between economic and environmental objectives. Rather than an arbitrary sub-set, all feasible crop rotations were generated, using a tool named ROTAT. The crop rotations were combined with a range of production techniques according to pre-defined design criteria to create a wide variety of alternative production activities at the field scale. We used process-based simulation models supplemented with empirical data and expert knowledge to quantify inputs and outputs of production activities. We developed a mixed integer linear programming model (MILP), named Farm Images, to allocate production activities to a farm with land units differing in soil quality, while maximising or minimising socio-economic and environmental objectives, subject to constraints at the farm level. Production activities comprised current practices as well as activities new to the area. We used Farm Images to design farm systems for seven existing farms in Canelón Grande with different resource availability. The farm systems designed by the model had higher family income than current systems for six of the seven farms studied. The estimated average soil erosion per ha decreased by a factor of 2–4 in the farm systems proposed compared to the current systems, while the rate of change of soil organic matter increased from negative in the current systems to +130 to +280 kg ha⁻¹ yr⁻¹ in the proposed farm systems. The degree to which the objectives could be achieved was strongly affected by farm resource endowment, i.e., particularly by the fraction of the area irrigated, soil quality and labour availability per ha. The study suggests that decreasing the area of vegetable crops by introducing long crop rotations with pastures and green manure during the inter-crop periods and integrating beef cattle production into the farm systems would often be a better strategy than the actual farmers’ practice.     

Life cycle assessment of greenhouse gas emissions from beef production in western Canada: A case study

A life cycle assessment (LCA) was conducted to estimate whole-farm greenhouse gas (GHG) emissions from beef production in western Canada. The aim was to determine the relative contributions of the cow-calf and feedlot components to these emissions, and to examine the proportion of whole-farm emissions attributable to enteric methane (CH₄). The simulated farm consisted of a beef production operation comprised of 120 cows, four bulls, and their progeny, with the progeny fattened in a feedlot. The farm also included cropland and native prairie pasture for grazing to supply the feed for the animals. The LCA was conducted over 8 years to fully account for the lifetime GHG emissions from the cows, bulls and progeny, as well as the beef marketed from cull cows, cull bulls, and progeny raised for market. The emissions were estimated using Holos, a whole-farm model developed by Agriculture and Agri-Food Canada. Holos is an empirical model, with a yearly time-step, based on the Intergovernmental Panel on Climate Change methodology, modified for Canadian conditions and farm scale. The model considers all significant CH₄, N₂O, and CO₂ emissions and removals on the farm, as well as emissions from manufacture of inputs (fertilizer, herbicides) and off-farm emissions of N₂O derived from nitrogen applied on the farm. The LCA estimated the GHG intensity of beef production in this system at 22 kg CO₂ equivalent (kg carcass)⁻¹. Enteric CH₄ was the largest contributing source of GHG accounting for 63% of total emissions. Nitrous oxide from soil and manure accounted for a further 27% of the total emissions, while CH₄ emissions from manure and CO₂ energy emissions were minor contributors. Within the beef production cycle, the cow-calf system accounted for about 80% of total GHG emissions and the feedlot system for only 20%. About 84% of enteric CH₄ was from the cow-calf herd, mostly from mature cows. It follows that mitigation practices to reduce GHG emissions from beef production should focus on reducing enteric CH₄ production from mature beef cows. However, mitigation approaches must also recognize that the cow-calf production system also has many ancillary environmental benefits, allowing use of grazing and forage lands that can preserve soil carbon reserves and provide other ecosystems services.     

Replacement policy in dairy herds on farms where heifers compete with cows for grassland: Part 2-Experimentation

Replacement policy is not easy to determine on dairy farms where heifers compete with cows for grassland. Using a computer simulation model of this farm situation, two factorial experiments were conducted to evaluate quantitatively the effect of different replacement rates on profitability and herd improvement.The variables changed in herds of average health and very good health were replacement rate (0·14, 0·22, 0·30), age at first calving (36, 24 months), calving index (13, 12 months) and AI sire merit (standard, premium). Initially, the experimental herd had average health, a replacement rate of 0·22, a calving index of 13 months, calved its heifers at 36 months and had been using standard bulls for many years.After 15 years, the increase in the level of a sinking fund when the age at first calving was reduced was between three and five times greater than when premium bulls were used, calving index was reduced or herd health was improved. There was a major interaction between replacement rate and age at first calving.Yield per cow was significantly reduced (P≤0·001) by reducing the age at first calving and significantly increased when premium bulls (P≤0·001) were used or when herd health was improved (P≤0·05).Some treatments were not tested as expected due to the restraining effect of a 13-month calving interval on the availability of cows for breeding pure in a seasonally calving herd.     

基于Web的奶牛场管理信息系统

介绍基于JSP+SPrvlet+Javabean模式开发的、适合中型奶牛场使用的奶牛场管理信息系统,分为牛群管理、产乳管理、牛群繁殖、统计与分析、养牛场管理及系统管理功能6个方面,可以对奶牛及奶牛场各种技术数据进行分析与综合整理,是一种实用、经济和操作简便的奶牛场信息资料管理系统.     

Simulation of production systems in East Africa by use of interfaced forage and cattle models

A forage model and a cattle production model were interfaced and adapted for tropical production conditions in East Africa. The objectives of the modelling were to structure and conceptualise a complex system for better comprehension, thereby determining constraints on a traditional African grazing system. The model was designed to simulate the physical linkages between the scarce resource of forage and the outputs of cattle, meat and milk. The effects of improved management practices were examined for a traditional village livestock grazing system. Verification and validation for the baseline village herd were carried out using several different sources of data. A combination of a restricted breeding season, supplemental feeding during the dry season and a seasonal sales policy resulted in a 40% increase in net revenue to village producers above the baseline for a ten-year period.     

Identifying and controlling critical sources of farm phosphorus imbalances for Vermont dairy farms

Lake Champlain, located between Vermont, New York, and Quebec exhibits eutrophication mainly due to continuing phosphorus (P) losses from upstream nonpoint source areas. Several state and local agencies have initiated efforts aimed at assessing and identifying critical sources areas for P loss. To augment these efforts, accounting of farm P inputs (in purchased animal feed and fertilizers) and P outputs (in milk, meat, or off-farm sales of harvested crops or other products) is needed as a means of determining potential P build-up in farm soils. When farm P inputs exceed P outputs, P surplus occurs on the farm. This leads to potential soil-P accumulations and risk of P loss in runoff, negatively impacting the quality of receiving water bodies. In this study, a combination of farm record data and a model-based approach, using the Integrated Farming System Model (IFSM), was used to estimate farm P inputs and outputs, identify root causes of farm P imbalances, and explore viable P balancing strategies. Three Vermont dairy farms with varying farm systems (grass-based organic farm, fully confined farm, and a mixed system farm with high-producing confined dairy cows and grazing heifers) were studied. These farms were found to have P surpluses ranging from 5.5 kg/ha to 18.7 kg/ha on annual basis. This study also identified critical causes of P imbalances for each farm and suggested farm specific alternative strategies needed to address the P imbalances. By balancing farm P inputs and outputs, potential accumulation of soil-P can be prevented. As a result, maximum benefits can be obtained from land treatment measures implemented to control off-field P loss without the additional concern of continuing P build-up that could reduce their effectiveness.     

A quantitative framework for livestock development planning: Part 2—The determination of livestock requirements

This paper describes the structure, inputs and outputs of models designed to quantify livestock requirements for the achievement of specified production targets. The component relationships of the models describe physical production processes and population dynamics. Input data consist largely of productivity parameter values. The main output of the models is a summary of required herd size and structure.     

Farm types for beef production and their economic success in a mountainous province of northern Vietnam

The objective of this study was to compare the management and economic success of beef production by three types of farm in northwestern Vietnam. The potential of household farms to supply beef for the market and their competition with large farms were examined.The fieldwork was done in 2007 on 73 farms consisting of 58 small mixed farms (small farms), 10 medium mixed farms (medium farms) and 5 specialised large-scale beef farms (large farms) in Son La province. The three types of farm differed in ethnicity (Thai, H’mong, and Kinh), remoteness (lowland, highland), production objectives (subsistence, market output), degree of specialization (mixed farm, specialised beef farm) and integration of production (single farmers, cooperative). Data on biological productivity, inputs and outputs, and the social contribution of cattle production were collected by household and key person interviews, participatory rural appraisal tools and cattle body measurements. Economic values were derived by assessment of market or replacement costs. Quantitative data analysis was done with linear models (PROC GLM) in the SAS software (version 9.1).Lowland small farms had higher costs for cattle production than the highland farms (0.8 Mill. VND head⁻¹ year⁻¹ compared with 0.02 Mill. VND head⁻¹ year⁻¹, respectively). The large farms had high production costs, with an average of 2.5-3.6 Mill. VND head⁻¹ year⁻¹. Cattle brought high benefits of non-cash values to the household farms. The total revenue from cattle was in the range 4.5-11.5 Mill. VND head⁻¹ year⁻¹, which depended on the use of non-market functions of cattle on the household farm. The value of net benefit/kg live weight (LW) of lowland small farms with an average of 39,000 VND/kg LW was significantly higher than that of the medium and small farms in the highlands (26,000 VND/kg LW). However, the small farms kept fewer cattle than the medium farms (average of 2-4 cattle/farm compared with 9 cattle/farm, respectively) because of forage and labour shortages and have no option to further develop cattle production. Keeping larger numbers of cattle based on available natural pasture brought high benefit from stock value as farm liquidity to only the medium farms. This was the most promising type of farm for future development of beef production, given its actual success and the availability of underutilised resources. Large-scale farms suffered high economic losses of 0.3-1.4 Mill. VND cattle⁻¹ year⁻¹, due to the lack of professional management, high feed costs and low animal performance, and showed no potential for developing cattle production.     

Development of DRAIN-WARMF model to simulate flow and nitrogen transport in a tile-drained agricultural watershed in Eastern Canada

A new watershed model, DRAIN-WARMF, was developed to simulate the hydrologic processes and the nitrogen fate and transport that occur in small, predominantly subsurface-drained, agricultural watersheds that experience periodic freezing and thawing conditions. In this modeling approach, surface flow is simulated using a watershed scale model, WARMF, and subsurface flow is estimated using a field-scale model for subsurface-drained shallow water table fields, DRAINMOD 5.1. For subsurface flow calculations, the watershed is subdivided into uniform cells, and DRAINMOD is run on each cell with inputs based on the individual hydrologic characteristics of the cell. The coupling results in a distributed parameter model that calculates the total flow at the outlet of a watershed as well as the nitrogen losses. The model was evaluated for the St. Esprit watershed, located approximately 50 km northeast of Montreal. Simulations were carried out from 1994 to 1996; data from 1994 and 1995 was used for model calibration and data from 1996 was used for model validation. The new model was able to adequately simulate the hydrologic response and nitrate losses at the outlet of the watershed. Comparing the observed daily flow/monthly nitrogen with the model's outputs over the validation period returned an R² value of 0.74/0.86 and modeling efficiency of 0.72/0.83. This clearly demonstrates the model's ability to simulate hydrology and nitrogen losses occurring in small agricultural watersheds in cold climates.     

Long-term solute dynamics and hydrology in irrigated slowly permeable soils

Summary A simple model is given, based on mass conservation of a non-transformed non-absorbed solute or ion (such as the chloride ion), which allows long term trends in the concentration of this solute to be predicted. The method involves solution of an implicit equation for the long term through-drainage flux below the maximum depth of sampling. A knowledge of the initial chloride ion concentration in the soil depth of interest, and its value after a known application via irrigation water provides sufficient information for the model to be applied. The model is applied to data from an irrigated slowly permeable swelling clay soil. A drainage flux of 8 cm yr^–1 beneath paddy rice was inferred, and some twenty-five years after commencement of irrigation an equilibrium soil salinity of 22 meq/l at saturation was predicted.     

A model to find and test decision rules for turnout date and grazing area allocation for a dairy cow system in spring

Use of grazing is decreasing in dairy cow systems in many European countries. However, pasture has a lower production cost than most conserved forage. Furthermore, agronomic decision rules are available to provide dairy cows with sufficient quality and quantity of dry matter. The decline in use of grazing is partly due to organisational difficulties in planning the grazing period. Land use at the farm level requires that this plan must be made in September, about 6 months before the turnout date. This area planning depends on the decision rule used for the turnout date. So we propose to search for a combination of area planning and turnout decision rules that allows a dairy herd to be fed in the spring by means of grazing without any risk of an interruption in the feeding. For this we propose to use a simulation model combining a grass growth model and a model for scheduling the farmer's decisions. A test of a turnout date rule showed that it is necessary to use an area allocation decision rule that depends on the turnout date rule and not the converse. We therefore proposed another turnout date rule based on the available herbage per ha and we calculated the area to allocate on the basis of this turnout rule.     

Optimization model of an irrigation reservoir for water allocation and crop planning under various weather conditions

This paper develops a non-linear programming optimization model with an integrated soil water balance, to determine the optimal reservoir release policies, the irrigation allocation to multiple crops and the optimal cropping pattern in irrigated agriculture. Decision variables are the cultivated area and the water allocated to each crop. The objective function of the model maximizes the total farm income, which is based on crop–water production functions, production cost and crop prices. The proposed model is solved using the simulated annealing (SA) global optimization stochastic search algorithm in combination with the stochastic gradient descent algorithm. The rainfall, evapotranspiration and inflow are considered to be stochastic and the model is run for expected values of the above parameters corresponding to different probability of exceedence. By combining various probability levels of rainfall, evapotranspiration and inflow, four weather conditions are distinguished. The model takes into account an irrigation time interval in each growth stage and gives the optimal distribution of area, the water to each crop and the total farm income. The outputs of this model were compared with the results obtained from the model in which the only decision variables are cultivated areas. The model was applied on data from a planned reservoir on the Havrias River in Northern Greece, is sufficiently general and has great potential to be applicable as a decision support tool for cropping patterns of an irrigated area and irrigation scheduling.     

A stochastic simulation model for evaluating forage machinery performance

The selection of machinery on a dairy farm is the focus of the study. A simulation model is constructed that evaluates alternative forage machinery complements on New York State dairy farms. Attention is focussed on the machinery use, forage crop production and concentrate purchase. The key measure of performance is the total cost of acquiring feed for the dairy herd. The total cost includes the machinery investment and operating costs and the cost of feeds required to supplement that produced on the farm.The simulation model, written in Fortran, utilises a daily timestep. Each day the feasibility of machinery operation is determined, machinery operations are scheduled and the end of day status is determined.     

Modelling the impacts of group ranch subdivision on agro-pastoral households in Kajiado,Kenya

Pastoral communities in East Africa are facing considerable challenges arising from shifts in land tenure policy from communal to individual landholdings and high human population growth rates. Over the last 30 years, livestock-to-human ratios have generally declined to levels that will no longer support pure pastoralism. Many Maasai have thus diversified into cultivation, wage labour, and small businesses. Livelihood expectations are rising, with concomitant increases in the need for cash. We describe the modification of PHEWS, a simple rule-based model that tracks cash flow and calories in agro-pastoral households. We use it, coupled to Savanna, a sophisticated ecosystem model, to quantify some of the effects of subdivision and land fragmentation on household livestock numbers and on food security. For the group ranches simulated, model outputs indicate that subdivision results in substantial reductions in livestock numbers, partially because households have to sell more animals to generate the cash needed, with serious long-term consequences on herd sizes and food security. If subdivision occurs, even to parcels as large as 196 km², livelihood strategies may need to be modified to maintain current levels of household well-being. Model results have been discussed in community meetings in southern Kajiado, but more work is needed on communication mechanisms to utilise more effectively the results of imperfect but useful integrated assessments of complex problems concerning land use and human well-being.