Sewage Sludge Influences Nitrogen Uptake, Translocation, and Use Efficiency in Sunflower

A better understanding of crop and soil response to biosolids is necessary for optimizing their use as soil amendments. The present study examined the influence of sewage sludge application on N accumulation, partitioning, translocation, and N use in sunflower and on soil properties compared with mineral fertilizers. Treatments included the application of sewage sludge (9, 18, and 36 Mg dry weight ha−1 year−1), an inorganic fertilizer (138 kg N plus 55 kg P2O5 ha−1 year−1), and a non-amended control. Sewage sludge increased early crop growth rate and N uptake at levels similar to or even greater than those obtained with the inorganic fertilizer. Nitrogen translocation was correlated with nitrogen translocation efficiency (r = 0.66*); both parameters appeared to be associated with source and sink attributes. Nitrogen use efficiency and nitrogen uptake efficiency were decreased with increasing rates of sewage sludge following a quadratic response curve. The estimated nitrogen use efficiency of sewage sludge-added N was greater than that of the inorganic fertilizer when sewage sludge was applied at agronomically realistic rates (< 26 Mg ha−1 in the first year or < 18 Mg ha−1 in the second year). Sewage sludge application increased soil organic matter and Olsen P compared with the control. Soil electrical conductivity in sewage sludge treatments remained at acceptable levels and soil concentrations of DTPA-extractable trace elements were similar to those of the control or the inorganic fertilizer. In the light of these findings, treated municipal sewage sludge may be used in sunflower intended for biodiesel production replacing mineral fertilizers serving as alternative sewage sludge disposal method.