Nitrogen and Water Distributions in Fertilized Sandy Soil During Irrigation and Drainage

Abstract

Nutrients applied to citrus growing in subsurface-drained acid, sandy soils of Florida are subject to movement through the soil and possible loss through drainage water especially after intense rainfall. The primary objective of this investigation was to determine the spatial distributions of soil water pressure head and concentrations of nitrogen (NO3-N and NH4-N) in the soil solution after fertilization and irrigation of citrus in a subsurface-drained Spodosol. The soil treatments were: (i) shallow tillage and shallow liming (ST), and (ii) deep tillage and deep liming (DTL). Tensiometers and solution sampler cups were placed at several soil depths and lateral distances on either side of a subsurface drain. Results showed transport of water and nutrients in the ST soil was rapid relative to DTL soil. Two-dimensional contours of equal soil-water pressure revealed that, after a 3.4-cm irrigation, slower drainage in DTL soil relative to ST raised the water table near the soil surface (to within 30 cm), of the DTL soil, whereas the water table in the ST soil rose to only about 80 cm from the soil surface. Observed distributions of NO3-N and NH4-N concentrations in the soil solution exhibited considerably higher spatial variability than soil water pressure head distributions for both soils. Concentrations of NO3-N were always higher than NH4-N in either soil. Rates of drainage were higher for ST than DTL soils. Over a 2-week period, the amount of NO3-N in the drainage water from ST soil was four times greater than from DTL soil. We concluded that NO3-N was less susceptible to leaching loss in the DTL soil than in the ST soil.