Abstract
The major objectives of this study were to compare nutrient leaching losses from two contrasting cropping systems, a monocropped annual (MA) and a multiple-cropped perennial (MP), and to describe the observed differences in terms of relatively easily-obtained water balance information. A method of characterizing cropping systems in terms of sensitivity to nutrient leaching loss is discussed. A capacity-parameter based model of water and solute movement was modified to include the effects of a fluctuating water table. Profile soil-water content, calculated using the model, closely approximated measured values over a 98-day period. Nutrient leaching losses were estimated from model-calculated deep percolation values and measured soil solution nutrient concentrations. Soil solution concentrations of NO3-, K +, Ca2+ and Mg2+ at a depth of 90 cm were approximately constant over the 242-day measurement period. Losses of the latter three elements were significantly greater, by 2-15 times, in the MA system. Estimated loss of N03 --N from the MA plot was 56 kg ha-l and approximately 1 kg ha-l from the MP system. Model simulations indicated that little residual fertilizer NO3- would be available to a subsequent crop in the MA system. These calculations were extended to develop another parameter, the solute residence time within the crop root zone. The slightly greater solute residence time of the MP system was not sufficient to explain the much larger leaching losses from the MA system; this was attributed to more efficient nutrient retention and uptake capabilities of the MP system. The solute residence time may prove most useful for comparison of similar cropping systems under different soil and climatic conditions.
