A grazing simulation model: GRASIM A: Model development
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A comprehensive grazing simulation model, GRASIM, that links components of the pasture system was developed. The grass component of the model contains two main carbon compartments: storage and structure. It accounts for root growth and maintenance, shoot growth, shoot respiration, senescence, and recycling. Shoot growth is partitioned into leaf and stem. The soil profile is partitioned into two zones. The top zone is where water and nitrogen additions and uptake, water evaporation, and nitrogen transformations take place. Nitrogen transformations include nitrification, mineralization, uptake, volatilization, denitrification, and leaching. The lower zone activities include plant uptake of water and nitrogen. Soil water is budgeted using a simplified water balance that considers runoff after a heavy rainfall, evapotranspiration, water movement between layers, and leaching. Effects of nitrogen and water stresses on growth are included. GRASIM predicts daily growth rate, biomass accumulation, protein and fiber content, water and nutrient levels. The simulation model can be used to obtain a better understanding of the pasture system and determine management strategies which yield more efficient use of pastures both economically and environmentally. It generates information suitable for estimating the financial and environmental consequences of alternative dairy management strategies including partial mechanical harvest in the context of the year round feeding needs of the dairy herd. GRASIM can be used to evaluate stocking rate effect on supplementation and amount of harvested feed, and storage/harvest needs, and year to year variability.
