Determination of soil water tension for irrigation management of sweet sorghum

Abstract

Culturing of sweet sorghum is being considered as an excellent option for ethanol production, from an agronomical and industrial point of view. At present, information regarding the best soil water tension for beginning sweet sorghum irrigation is not available; hence, this study aimed to determine the adequate soil water tension under field conditions for beginning irrigation of four cultivars of sorghum. Two experiments were conducted at Nova Porteirinha, MG, in a randomized block design with subsubdivided plots having four replications. Each experiment comprised six treatments of soil water tension (plots)-20, 40, 60, 80, 100, and 120 kPa-for resuming sweet sorghum irrigation, and four sweet sorghum cultivars (subplots)-BRS 508, BRS 509, BRS 511, and CMSXS647. After planting, the soil water level in the plots was elevated to field capacity (10 kPa), and then the treatments were applied. During treatment application, irrigation was resumed when the soil water tension reached the limit established in order to elevate the soil water tension to 10 kPa. The amount of water replaced during each irrigation was determined by generating a soil water retention curve for the experimental area. The following parameters were evaluated: green mass production, juice volume, soluble solids (Brix), and tons of Brix per hectare (TBH). The different soil water tensions and cultivars, agricultural year, and interaction between tension and year significantly affected (p ≤ 0.05) the characteristics evaluated, according to the F test. The agronomical characteristics of the evaluated cultivars showed linear relationship with water supply in the soil. According to TBH, irrigation of sweet sorghum needs to be performed when the soil tension reaches 20 kPa. The TBH values did not differ significantly among the four cultivars at the 5% significance level according to Tukey test. ResumoA cultura do sorgo sacarino vem sendo considerada uma ótima opção, sob os pontos de vista agronômico e industrial, para a produção de etanol. Como não há informações sobre a melhor tensão da água do solo para o início da irrigação do sorgo sacarino, objetivou-se determinar em campo a tensão de água do solo adequada para o início da irrigação de quatro cultivares. Foram conduzidos dois experimentos, em Nova Porteirinha, MG, no delineamento em blocos casualizados, no esquema de parcelas subsubdivididas, em quatro repetições. Cada um dos experimentos foi constituído por seis tratamentos de tensão da água do solo (parcelas); 20, 40, 60, 80, 100 e 120 kPa, para o reinício da irrigação do sorgo sacarino, e de quatro cultivares de sorgo sacarino (subparcelas): BRS 508, BRS 509, BRS 511 e CMSXS647. Após o plantio, as parcelas tiveram a umidade do solo elevada à capacidade de campo (10 kPa), quando a partir de então foram aplicados os tratamentos. Durante o período de aplicação dos tratamentos, sempre que a tensão de água no solo atingia o limite de tensão estabelecido, o sistema de irrigação do tratamento era acionado, funcionando o tempo necessário para ...