Conversion of Arizona chaparral to grass increases water yield and nitrate loss

Converting an Arizona chaparral watershed to grass cover by using a soil application of karbutilate granules increased streamflow and the nitrate content of the water. Nitrate concentrations in streamflow from an untreated control watershed remained less than 1 ppm throughout the study, whereas nitrate from the treated watershed increased during the first posttreatment year to a maximum concentration of 56 ppm, with an annual weighted mean concentration of 16 ppm. Maximum concentrations of 60 and 69 ppm occurred during the third and fourth posttreatment years, when annual mean concentrations were 66‐ and 100‐fold above normal. After 11 years the annual mean concentration was still 14‐fold above normal. The mean nitrate concentration of the streamflow from the treated watershed for the entire 11‐year period was 29‐fold greater than that for the control watershed.