Influence of soil cover on the field moisture regimes of two "cerrado" oxisols: LVE and LVA

Abstract

During the 1978/1979 agricultural season a research was carried out in two "cerrado" oxisols: LVE (Typic Haplustox) and LVA (Haplustox-Acrustox) having the following covers: bare soil, rice (Oryza sativa L., cv. IAC-25), corn (Zea mays L., cv. C-111X) soybean (Glycine max L., cv. UFV-1), to conduct observations on the field water regimes under wet and dry conditions taking place throughout the crop growing season. Results show that available water in the 0.1 - 1.0 bar range was 11 and 13% (% dry weight) for the LVE and LVA soil respectively. Soil matric potencial from 5 to 115 cm depth ranged from 0.1 to 0.3 bars during the rainy season, with no great influence of the soil cover. Crop growth was not affected by conditions resulting from prolongued high soil matric potential. During the drought period (20/2 – 5/3) the greater variations in soil matric potentials were observed in the upper 5 cm (bare soils), due to soil water evaporation. This effect was much greater in the LVE soil than in the LVA soil. Water extraction by rice, corn and soybean crops in the LVE soil extended down to 45, 60 and 115 cm, respectively which explains the sensitivity to drought shown by rice crops and drought tolerance shown by soybean crops. Evapotranspiration during the drought period were the following: LVE soil, rice cover = 3.69 mm/day; LVE soil, corn = 4.27 mm/day; LVE soil, soybean cover = 5.31 mm/day. Water uptake in the upper soil 30 cm was: rice>soybean = corn and below the 30 cm depth was: soybean>corn>rice.