Capacidade de campo e a retenção de água em três solos de Minas Gerais

Resumo

A study was conducted on soils from three regions of Minas Gerais, Capinópolis, Sete Lagoas and Viçosa, to verify the properties of these soils with respect to the commonly accepted concept for field capacity and the movement and retention of soil moisture. Theretention trials were conducted with columns of soil in the laboratory 2, 16, 40, 150, and 360 days after irrigation at the top of the column. A series of columns was inverted in order to determine gravitational and capilary movement. The retention curve against matric suction was determined with a pressure plate and pressure membrana for the three soils. The moisture equivalent was determined with a Centrifuge International Moisture Equivalent model ME.

Field plots were studied in Viçosa with plastic covered and uncovered, devegated plots to compare with the laboratory results. The soil profile was sampled toa depth of two meters. Soil moisture inthe columns showed accentuated downward movement from two to 360 days and showed a curve similar to the nexpectedu field capacity curve onlyat the second day, even though the Viçosa soil showed a retention force of more then one bar at that time.

In the Viçosa field plots, due to the large quantity of water added the dry subsoil layer was also wet, at least to a depth of two meters. This resulted in the absence of a hydraulic gradient between moist soil and dry soil immediately below, thus anulling the downward movement of moisture with time. The inverted columns indicated that gravitational moisture movement had essentially no influence in the laboratory study. The percent of moisture retained under a force of one-third bar was consistently well above the moisture equivalent for all three soils,