Avaliação de sorgo (Sorghum bicolor (L.) Moench.) e milheto (Pennisetum glaucum (L.) B. R.) sob diferentes níveis de água no solo.

Abstract

This investigation was carried out to study the effects of different water contents in the soil, applied by irrigation, on yield and forage quality of sorghum [Sorghum bicolor (L.) Moench] and millet [Pennsietum glaucum (L.) R. Br.]. Sorghum and millet plants developed in medium texture alluvional soil, in 9L plastic container, arranged according to a complete random design with 2x4 treatments (2 species x 4 water levels in the soil), and 5 replications for each treatment, totaling 40 containers for the first experiment, and 40 containers for the second experiment. Water replacement levels were 100% (1T1), 75% (1T2), 50% (1T3), and 25% (1T4) in the experiment 1, and 100% (2T1), 80% (2T2), 70% (2T3), 60% (2T4) in the experiment 2. The treatment with 100% of water replacement was used as the reference for the calculation of the amount of applied water in the other treatments in both experiments. Data of aboveground fresh and dry matter and root dry matter were collected, as well as data on water use efficiency. Forage evaluation was made by means of percentage of dry matter (DM), neutral detergent fiber (NDF) and acid detergent fiber (ADF). In experiment 1, both species showed severe reduction in fresh biomass production due to soil water deficit. In this case, sorghum tended to produce more than millet, except in treatment with 50% of water replacement. The production of aboveground dry matter presented an accentuated reduction when soil water availability was reduced, especially for the treatment that received 25% of the maximum water consumption, when dry matter production reduced to 57.9% and 66.6% of the maximum yield, respectively for sorghum and millet. Root dry matter was also severely reduced in this treatment. Water consumption tended to be higher for millet than for sorghum plants. Water use efficiency increased with the reduction of soil water availability. In this case, sorghum was more efficient in 100 and 25% water replacement treatments, while millet was more efficient in the 75 and 50% water replacement treatments. ADF contents decreased with the reduction of water availability in the soil for both species. Sorghum NDF showed the same trend, while sorghum DM increased. In experiment 2 only production variables were considered, and showed similar trend of that observed in experiment 1, with reduction of aboveground fresh and dry matter, as well as root dry matter, as the water supply was reduced from 100% to 60% of the maximum demand. However, biomass reduction between treatments was less pronounced than the observed in experiment 1. Sorghum showed a better response to water deficiency, and water supply starting from 70% of the maximum demand provided good results in both species, comparable to the one observed on the 100% water supply treatment.