Modelagem técnica e econômica da irrigação deficitária para diferentes métodos de aplicação de água na cultura do milho

Abstract

The deficit irrigation is often required to overcome periods of drought and limited water availability. To reduce the impacts on production, water deficits need to be applied during less sensitive stages of crop development. However, to select the appropriate irrigation management, it is necessary to assess, properly, if the economic impacts of deficit irrigation are economically viable. To understand the process of water loss from crops, such as soil water evaporation and crop transpiration allows a better assessment of irrigation management practices in relation to deficit irrigation. This study sought to determine the basal crop coefficients appropriate for corn through the calibration and validation of SIMDualKc model, using the methodology of dual coefficients, separating crop transpiration and soil surface evaporation; to assess crop and water productivity, as well as water economic productivity for corn in relation to different levels of water deficit and under different irrigation systems and their economic viability, considering different alternatives for center pivot and drip irrigation. A set of experiments was conducted using different strategies of full irrigation and deficit irrigation through the methods of sprinkling and drip irrigation during the years 2011 to 2012. The simulation s results of the SIMDualKc model showed a good agreement between the simulated value of available soil water and the value observed during the crop cycle. The initial and mid Kcb calibrated values were, respectively, 0.20 and 1.12 and the end Kcb was 0.2 for corn grains and 0.8 for corn harvested for silage. Evaporation was lesser than 9% of the crop evapotranspiration in both drip and sprinkling irrigation, indicating, thereby, the possibility of using crop residues for water conservation. The economic results show that deficit irrigation was highly dependent on corn prices, while changes in the costs of water and labor had a low impact in relation to the economic results. The results also show that the deficit irrigation applied in periods of rain is easy to implement, unlike deficit irrigation for periods of reduced precipitation when only a small stress is economically feasible. Although improving water productivity and irrigation performance, the adoption of center pivot systems can favor irrigation deficit for supplementary irrigation when rainfall is frequent. The economic viability of using irrigation deficit in maize by the system of drip irrigation under surface was dependent on the cost of installing the system, mainly the fixed cost and life cycle of the lateral lines.