Otimização da irrigação das culturas da soja e do milho no sistema sulco-camalhão em terras baixas.

Abstract

The physical-hydric characteristics of lowland soils have historically led to the predominance of flood-irrigated rice cultivation. However, the insertion of rainfed crops, such as soy and maize in succession and/or in rotation with rice, brings improvements to the production system, in addition to contributing to productive competitiveness in the lowlands. Since the irrigation of rainfed crops in this environment is recent, it is necessary to know the water demand for the rational irrigation management of these crops. The objective of this study was to optimize the irrigation of soybean and maize crops cultivated in the furrow-ridge system based on the calibration and adjustment of parameters of a soil water balance (BH) model. For this, the work consisted of the following steps: (a) calibration of a BH model, using the crop coefficient (Kc) from the regional literature, in the 2019/20, 2020/21 and 2021/22 harvests from different locations production in Rio Grande do Sul; (b) estimate of relative water consumption; (c) assessment of water productivity; (d) estimate of the crop coefficient Kc (NDVI) for soybean and maize through the relationship between the vegetation index (IV) Normalized Difference Vegetation Index (NDVI), and Kc (FAO-56); (e) estimation of ETc(NDVI) from Kc (NDVI); (f) Propose a relationship between crop grain yield and VIs: NDVI, SAVI (Soil-Adjusted Vegetation Index), EVI (Enhanced Vegetation Index) and SR (Simple Ratio); (g) adjust the CN parameters and initial abstraction rate (λ) of the Curve Number method of the Soil Conservation Service (SCS-CN), through observed runoff data in order to estimate runoff and infiltration in land soils casualties. The results indicate that the BH model calibrated with parameters available in the literature was efficient, with an average increment of 29 sc ha-1 in the irrigated soybean areas. Water deficiency classified as high risk occurred during the critical periods of non-irrigated soybean and maize in the different lowland regions of Rio Grande do Sul. Water productivity in soybean and maize production is variable, depending on the local distribution of precipitation, especially during the crop's reproductive period, in addition to the characteristics of the soil, cultivar and agronomic management adopted. However, it proved to be more efficient for maize. The Kc values estimated from the processing of remote sensing data provide more accurate information to determine the water demand of soybean and maize crops, promoting better water use efficiency in the furrow-ridge system. The NDVI and SR IVs were the most adequate to estimate the productivity of soybean and maize crops. The modified model SCS-CNm, adjusting CNm = 56.16 and λm = 0.1, showed the best fit, with efficiency E = 0.83. Thus, in order to use BH in optimizing irrigation, it is necessary to use adequate estimates of crop evapotranspiration as well as surface runoff and water infiltration in lowland soils.