Crescimento e produtividade da mandioca sob níveis de irrigação

Abstract

Understanding the soil-water-plant-atmosphere relationships and the productive responses of cassava to irrigation depth is essential to increase the productivity of this crop in the Coastal Plateaus of Alagoas. For this reason, this research aimed analyze the growth, productivity and physiological aspects of cassava according to irrigation levels. The experiment was carried out at the Campus of Engineering and Agricultural Sciences (CEAS) of the Federal University of Alagoas (FUAL), from June 2019 to June 2020. The statistical design used was randomized blocks, with four repetitions. The treatments were six levels of irrigation, depending on the evapotranspiration of the crop – ETC (L0 = 0% (rainfed), L1 = 40%, L2 = 80%, L3 = 120%, L4 = 160% and L5 = 200% of ETC). And the growth and production variables analyzed were: plant height, number of leaves, length and diameter of the stem, number , length and diameter of commercial roots, leaf area index (LAI) and fresh and dry matter productivity of: root , stem and leaf, fresh and dry total biomass (root, stem and leaf), per hectare, and harvest index. The physiological variables analyzed were: liquid photosynthetic rate, internal CO2 concentration, transpiration, leaf temperature, stomatal conductance, instant water use efficiency, potential quantum yield and effective quantum efficiency of photosystem II and SPAD index. In this research, the total depth was defined as total irrigation plus the effective rain. The average air temperature during the search period was 25.1°C, the average relative humidity was 74.2%, and the total accumulated rainfall (rain) was 1,847 mm. Of this total, 212 mm occurred in the period when the crop was irrigated, from October 2019 to March 2020. This it resulted in an effective rain of 522 mm and, in rainfed crops, was estimated a water deficit of 508 mm and an excess of 1,323 mm. The accumulated reference evapotranspiration (ET0) was 1,454 mm and the ETC was 1,030 mm in the 355 day cassava cycle. The maximum LAI was 7.6, the maximum length of commercial roots, 49 cm, the highest root yields and total biomass were 94 and 149 t ha-1, respectively. The total depth of maximum mean economic efficiency, with prices from R $ 180.00 to 400.00 reais per tonnes of cassava, was 911 mm that produced 94 t ha-1 of cassava roots. Meanwhile, the maximum root and total dry matter productivity were 47 and 69 t ha-1, respectively, the highest harvest index was 0.66. And, the maximum physiological variables were: photosynthetic rate, 22.5 μmol of CO2 m-2 s-1; transpiratory rate and stomatal conductance 4.0 and 0.35 μmol of H2O m-2 s-1, respectively; internal concentration of CO2 of 245 μmol m-2 s-1; maximum effective quantum efficiency was 0.68 and the maximum SPAD index was 57. In general, irrigation can generating a higher index of leaf area, root length and increase of productivit roots and total biomass of 194 and 99% in the cassava crop, in the region of Rio Largo, AL.