TEMPORAL AND SPATIAL DISTRIBUTIONS OF NITRATE-NITROGEN IN 2 FURROW-IRRIGATED SEMIARID SOILS AMENDED FOR SLUDGE AND FERTILIZER

A statistical comparison of data collected from two cotton production fields with a history of either commercial fertilizer or sludge amendm ents showed significantly different nitrate-nitrogen (N) concentration s in time and space. The sludge-amended field had high nitrate concent rations in the root zone (1.5 m) throughout the season. Whereas, the f ertilized field showed low nitrate-N concentrations during the same pe riod. Both fields showed significant increases in nitrate-N following pre-plant irrigation events, and significant decreases of nitrate-N in the root zone during the growing season. Following harvest, the sludg e-amended field had very large reserve of nitrate-N in the profile. Th e spatial variabilities, as determined by the % coefficients of variat ions (CVs) of eight cores per sampling event, of nitrate-N distributio ns where large in both fields, 69% and 90% for the sludge and fertiliz er field, respectively. The estimated nitrate-N leaching losses were m uch higher in the sludge-amended than the fertilized field. Significan t leaching losses in the sludge-amended field were likely the result o f year-to-year sludge residue accumulations that mineralize and releas e nitrate-N in the zone of incorporation (0-30 cm).