Evaluation of Percolation and Nitrogen Leaching From a Sweet Pepper Crop Grown on an Oxisol Soil in Northwest Puerto Rico

A study was conducted to evaluate the influence of agricultural lime (CaCOî) on the movement and uptake of inorganic nitrogen for a sweet pepper crop (Capsicum annuum) grown on an Oxisol soil (Coto clay) in northwest Puerto Rico. The Coto clay soil, which contains the 1:1 kaolinite mineral, has a low pH (4 to 4.5). The 1:1 type clays are known to possess a net positive charge at low pH, resulting in the adsorption of negatively charged ions such as nitrate. From an environmental standpoint this characteristic of the 1:1 clay is favorable, since nitrate leaching, a major cause of groundwater pollution in many areas, is reduced relative to soils with net negative charge. However, agricultural plants, such as sweet peppers, favor a higher soil pH (approximately 6.5), which can be obtained by the application of agricultural lime. This application, however, may have the negative effect of increasing the potential for nitrate leaching, as the net charge in the soil particles becomes positive with increasing pH. This paper describes the results of a nitrogen leaching analysis for two sweet pepper crop seasons. The analysis was based on multiplying the daily percolation flux through the soil profile by the measured concentration of nitrogen below the root zone. Irrigations were scheduled using the pan evaporation method for estimating crop water requirements. No significant difference in nitrogen leaching was observed for the lime and no-lime treatments. This finding was attributed to the low nitrate retention capacity of this soil, even a low pH. The average percentages of nitrogen leached during the 1st and 2nd season, relative to the amounts applied, were 26% and 15%), respectively. Leaching events were associated with large rainstorms, suggesting that leaching of Ν would have occurred regardless of the irrigation scheduling method used.