INFILTRATION IN RESPONSE TO WATER-QUALITY, TILLAGE, AND GYPSUM

Maintaining adequate infiltration into cropped soils is a continuing problem in the Trans-Pecos region of Texas due to the accumulation of electrolytes from irrigation water. The objectives of this study were to determine the effect of (i) number of years of irrigation, (ii) applied water quality, (iii) tillage, and (iv) surface-applied powdered gypsum on field infiltration rate and amount. Infiltration rate into a Hoban silt loam (fine-silty, mixed, thermic Ustollic Calciorthid) at Pecos, TX, was measured with a rainfall simulator in field experiments with different irrigation amounts and qualities of applied water treatments or tillage and powdered-gypsum treatments. Electrical conductivies from the soil surface (0-50 mm) increased 300% after the first year's irrigation and remained relatively constant with continued irrigation. Infiltration rate and amount increased when the soil salinity and sodicity decreased or the salinity of the applied water increased. Tillage increased infiltration in the order of plow-disk > double-disk > compacted = control. The application of powdered gypsum to the soil surface increased infiltration amount by an average of 38% in tilled or compacted soil, where the surfaces had been disturbed. Powdered gypsum did not affect the infiltration amount where the soil surface was undistrubed. These data indicate that (i) sufficient electrolytes from irrigation water will accumulate in one growing season to reduce infiltration and (ii) field applications of powdered gypsum will increase the infiltration into tilled or disturbed soils.