Limite crítico do potencial hídrico da soja durante os estádios vegetativo e reprodutivo

Abstract

With the advent of climate change, one of the main problems faced in the production of soybeans (Glycine max (L.) Merrill) in Brazil is the irregularity of the rainy season, which can reduce the water availability to the plants causing the water stress due to lack of water . The expressive water deficit during the vegetative and reproductive stages of the crop can cause physiological and morphological changes in the plants, such as the presence of poorly developed plants, abortion of the flowers, small number of pods, small grains and, consequently, low productivity. One solution to this problem is the installation of irrigation systems on rural properties. Brazil has 29.6 million hectares that can be irrigated, of which only 6.1 million are used. Despite using only 20% of the national potential, agriculture is responsible for the consumption of 75% of the national water flow. Thus, to expand the irrigated area in the country, it is essential to make use of irrigation management. Among the methods developed, the pressure chamber has been highlighted, as it can directly measure the water status of the plants, providing information on the actual condition of the crop at the time of reading the equipment. Based on the above, the objective of this study was to determine, from the pressure chamber, the critical water potential of the xylem in the vegetative and reproductive phases for maximum soybean development. For this, two experiments were carried out, one in the vegetative phase and the other in the vegetative phase, using a completely randomized design (DIC). The experiments were composed of two soybean cultivars, UFUS 6901 and BRASMAX Flecha IPRO (6266RSF). Both the first and the second experiment were performed at different water supply levels, with no water deficit (SDH), moderate water deficit (DHM) and severe water deficit (DHS). The levels of water supply were separated in the greenhouse in the different stands, each corresponding to a level of water deficit. Each table was composed of 2 cultivars and 5 replicates, totaling 10 treatments. In the vegetative phase the parameters were: plant height, stem diameter, leaf area, fresh and dry shoot mass, chlorophyll a and b, photosynthetic activity with IRGA and water potential of the xylem, using the Sholander chamber. In the reproductive phase, the parameters evaluated were: plant height, number of pods, number of pods with one, two and three grains, height of insertion of the first pod, number of nodes and water potential of xylem. All evaluations were conducted weekly, as well as pest and disease management when necessary. The treatments were tested using a joint analysis, aiming to determine the critical limit for the soybean crop. Xylem water potential greater than -0.54 MPa is not supradient for the development of the two stages of development.