Respostas agrofisiológicas de tipos de sorgo irrigados com água residuária

Abstract

Due to the reduction of water availability due to population growth, the reuse of wastewater from domestic, industrial and agro-industrial sources in agriculture is urgent. However, these sources of water generally have a greater number of ions, organic matter and also microorganisms compared to fresh water, which may pose a risk to human health, as well as salinization of the soil causing stress on plants. Therefore, to cultivate certain cultures it is necessary that they show a certain tolerance to the characteristics imposed by wastewater. Sorghum has a moderate tolerance to salinity and water deficit, in addition to being a crop with a multitude of applications that can be used for animal, human and ethanol production. In view of the above, the objective of the study was to evaluate the effects of wastewater on the soil and on cultivars of sweet, forage and dual-purpose sorghum in the first and second growing cycle. The experiment was carried out between August 10, 2015 and March 18, 2016, at the Experimental Station of the Agronomic Institute of Pernambuco - IPA, in the municipality of Vitória de Santo Antão - Pernambuco. The design was in causalized blocks consisting of 12 genotypes and three blocks, totalling 36 experimental units. The total fresh and dry mass productivity, as well as leaf, stem and panicle yield were evaluated in the two production cycles. Five soil collections were also made over time in order to monitor the supply of sodium, potassium, organic matter and monitor the variation in the hydrogen potential of the soil solution and the electrical conductivity of the soil saturation extract. Gaseous exchanges, net CO2 assimilation rate, transpiration, stomatal conductance and instant carboxylation efficiency were also measured in the prefloration and milky-paste stages in the two production cycles. With the obtained results it was possible to verify that the cultivation of sorghum with wastewater increases the production of fresh and dry mass in the second cut compared to the first. The types of forage sorghum, dual purpose and saccharine showed an increase in productivity of 28.7%, 10.1% and 5.5%, respectively, compared to the first cut. The net CO2 assimilation rate in the second cut double-purpose sorghum plants increased by 30.6% to the detriment of the first cut. The accumulation of organic matter in the soil, favoured by the application of residual water, minimizes the toxic effects of the presence of sodium in the soil.