Temporal and spatial distributions of nitrate-nitrogen in two 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 amendments showed significantly different nitrate-nitrogen (N) concentrations in time and space. The sludge-amended field had high nitrate concentrations in the root zone (1.5 m) throughout the season. Whereas, the fertilized field showed low nitrate-N concentrations during the same period. 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 sludge-amended field had very large reserve of nitrate-N in the profile. The spatial variabilities, as determined by the % coefficients of variations (CVs) of eight cores per sampling event, of nitrate-N distributions where large in both fields, 69% and 90% for the sludge and fertilizer field, respectively. The estimated nitrate-N leaching losses were much higher in the sludge-amended than the fertilized field. Significant leaching losses in the sludge-amended field were likely the result of year-to-year sludge residue accumulations that mineralize and release nitrate-N in the zone of incorporation (0-30 cm).