Silicon fertilization in soybean: Si rates, soils and water deficit

Abstract

The benefits of silicon (Si) fertilization in plants are still little-know for soybean, especially regarding the responses to Si rates on soluble Si in contrasting soils and Si uptake. In addition to increased yield, Si could minimize of water deficit effects in soybean, but results are still scarce. It will be tested the hypotheses: a) Si rates increase the uptake by aerial part of soybean, reaching a maximum value in function of soluble Si in sandy, medium texture and clay soils (phase 1); b) There is a maximum value of soluble Si in soils, which there is no increase on aerial part biomass of soybean in function of Si rates (phase 1); c) Increased Si absorption in soybean leaves provides higher chlorophyll content, phosynthesis, plant transpiration, stomatal conductance, water, nutrients and Si uptake and, consequently, greater biomass and grains with different responses in function of soil type (phase 1); d) Si absorbed increased drought tolerance by decreasing of electrolyte, increased of chlorophyll content, water potential, stomatal conductance, transpiration, photosynthesis and water, and nutrients absorption by roots of soybean (phase 2); e) Si provides lower decrease of biomass and grain yield in soybean underwater deficit compared to its absence (phase 2); f) Si deposition in leaves with fertilization in soil increases drought tolerance by enhancement on gases exchange (stomatal conductance, transpiration and photosynthesis) of soybean plants underwater deficit (phases 2 and 3). The study has three phases. In the phase 1, an experiment will be conducted in randomized blocks with four Si rates and three contrasting soils. In the phase 2, treatments with and without Si, presence and absence of water deficit imposed during beginning of flowering during 5 and 10 days will be evaluated. In phases 1 and 2, chemical analysis of soluble Si and soil fertility will be done and evaluations of lenght, aerial part biomass, Si and nutrients uptake, physiological evaluations (SPAD index, photosynthesis, transpiration, stomatal conductance, intrinsic efficiency of water use, CO2 concentration in the intercellular spaces, photochemical efficiency of photosystem II, clorophyll a e b, water relative content) and leaf water potential and electrolyte leakage only in leaves of phase 2. (AU)