ABSTRACT
Information on the relationship between agricultural practices and solute movement in soil has been collected from the long-term Bet Dagan Permanent Plots field experiment, in which the effect of fertilization on crop yield under Mediterranean climatic conditions has been intensively studied since 1960. Soil samples representing 60 (5 x 4 x 3) NPK fertilizer combinations were analyzed for different chemical properties, mainly the concentration of solutes (NO3, Cl, SO4, Na, K, Ca, Mg) in soil saturation extracts. The samples were taken from a depth of 2.1 m in 1986 and 1987, and also from a depth of 12.0 m in some cases in 1987. The mean annual rainfall for the above period was 524 mm, and it was greatly exceeded by the potential evapotranspiration.
The pattern of solute distribution in soil was closely related to crop yield and dry matter production. The higher the yield, the greater the transpiration and the smaller the quantity of rain or irrigation water available for leaching. The Cl level in the soil saturation extract along the 2–12-m profile of the zero fertilizer treatment ranged between 3 and 5 mM, while that found in the optimum fertilization treatment was 6–27 mM. No Cl was added through fertilizer in either case. The distribution of Na and Mg, not originating from fertilizer, was also greatly affected by leaching. However, mainly due to exchange and precipitation- dissolution processes, their distribution pattern differed from that of CL
The level of NO3 in soil was greatly influenced by the plant, both directly through uptake and indirectly through its effect on leaching. The present data show that proper fertilization of irrigated crops can greatly improve yield and slow down solute movement through the soil profile.
