| A modeling procedure was developed to allocate water in an optimal manner in pasture lands managed under Short Duration Grazing plus Sprinkle Irrigation (SDG + SPI). Three fundamental phases were considered: (1) creation of a design and operation procedure for SDG + SPI, (2) generation of crop production functions through the use of model PLANTGRO, and (3) utilization of System Simulation (SS) and Discrete Dynamic Programming (DDP) to make optimal water allocation by means of the Maximization of Net Benefits method. The following four computer programs were written to attain the objectives of this study: (1) program SDGSPI, which computes all practical design alternatives for a SDG + SPI system, (2) programs PCDCRA and FIXSTRM, which simulate the numerical behavior for any design with unrestricted water supply and a fixed or variable stocking density, (3) program DYPROG, which finds the optimal water allocation under restricted water supply and fixed or variable stocking densities.;The model used crop and climatic data corresponding to tropical conditions: Panicum maximum Jacq., in Aragua State, Venezuela. The results indicate that the best designs correspond to the block IV which includes projects 16 through 19. Block IV has the following characteristics: 20 plots, 9 rotations per year, 2 days of time of grazing, 2 animal groups, rest period equal to 36 days, irrigation frequencies of 8 days (project 16), 10 days (project 17), 20 days (project 18), and 40 days (project 19). Neither a single project nor a single alternative were optimal for all situations simulated. Thus for instance, project 19 showed a better performance for low stocking densities (1 and 2 an/ha), whereas projects 17 and 18 shared the best solution for 3 to 6 animals per hectare. With the results obtained, it was possible to build Tables of Decision and Tables of Operation which permit selection of the best design and best operation for availability of water between 0 and 130 cm and stocking densities between 1 and 6 an/ha. |
