Modelagem de sistemas aplicada à produção de forragem e ao uso da água, nas condições atuais e sob mudanças climáticas, no semiárido brasileiro

Abstract

The study was performed using techniques of mechanistic / stochastic modeling and Systems Dynamics to understand the flows and management of water and forage in animal production systems in the semi-arid, also from the perspective of climate change. The study was divided into: (1) use of modeling to estimate stocks and forage on offer in livestock units in the semi-arid, (2) estimate of the buffel and current grass supporting capacity under the climate change scenario and (3) modeling of the water balance of a ruminant production system in the semi-arid region. In the first study, it was intended to restructure the Stabilized Forage Guarantee System and to present the methodology: guaranteed biomass production management system for the Brazilian Semi-arid “Asa Branca System. For application of the technique, simulation models using PHYGROW program of buffel and massai grasses and cactus pear were used, adhesion tests and generation of synthetic series at @RISK© software were performed. The models, first obtained for Limoeiro do Norte-CE, were derived for a property leased in Quixeramobim-CE. Different models of use of the areas were stipulated and analyzed by the guarantee concept. It was verified that, as the cactus pear is inserted in greater proportions in the property, the variation of the total production of the system is smaller, acting with a buffering element of the natural oscillation of the forage supply of the native pasture. With a 95% guarantee, the intermediate model of inclusion of cactus pear (Model 03) shows an increase potential of approximately 293,000 kg of DM in the property. In the second study, simulations using PHYGROW were carried out to assess the possible future impacts of climate change on the carrying capacity of buffel grass and current grass, using the global climate models CNRM-CM3, MIROC5 and MRI-CGCM3, considering the scenario RCP 4.5. The future interval of 38 years was considered for the Apodi plateau region, Limoeiro do Norte-CE. There was an adequate correlation between the climatic models and the initial model of crop growth by PHYGROW. The scenarios presented for the two forages evaluated are positive, indicating a support capacity estimated at 1.5 to 2.5 AU ha-1 and stabilized over the simulated period. In the third study, the objective was to demonstrate the impact of water consumption from a ruminant production system in a small reservoir. The water use model was developed using the Vensim PLE™ software for a hypothetical property located in Petrolina, Pernambuco, Brazil. The reservoir capacity and evaporation, infiltration and runoff rates were estimated from the literature and rainfall was estimated using the probability density function in the @RISK© software. The use of irrigation, water consumption of the family property, and water consumption by goats, sheep and cattle were estimated in the literature. In the horizon of 30 years, in only five of these the maximum capacity of the reservoir was reached. In the most demanding water scenarios, years are observed where the weir dries completely, making animal production unfeasible. Using the proposed model, it was possible to estimate, using practical and real indicators, combinations to find the best way to use water, depending on the type of herd and the use of irrigation.