Effects of Sewage-Sludge Application on Soils and Sunflower Yield: Quality and Toxic Element Accumulation

Sunflower nutrition, sewage-sludge nutrients, and trace-metals supply have been studied in detail, but separately. The objective of the present work was to study the effects of sewage sludge on sunflower yields and the accumulation of nutrients and trace metals in soils and in the crop. Three experiments with sunflower were therefore conducted on farms located in Buenos Aires Province, Argentina. The treatments were control, 7 t dry matter (DM) sewage sludge/ha, and 14 t DM sewage sludge/ha. Soils were Typic Argiudolls and a Typic Hapludoll. At physiological maturity, grains and aerial biomass were harvested. Nitrogen (N), phosphorus (P), and potassium (K) were determined and, after digestion with acids, cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb), nickel (Ni), and zinc (Zn) were analyzed with inductively coupled argon plasma emission spectrometry (ICPES). Soil samples were taken and analyzed for nutrients and Cd, Cr, Cu, Ni, Pb, and Zn. Only available P and nitrate-N increased in the soil after the application of sewage sludge. Sunflower yields increased by increasing grains per head. Individual grain weight, oil content, nutrients, and trace-metals concentrations were not affected, nor were the aerial biomass and its composition. Using sewage sludge according to standard regulations does not affect either toxic-metals uptake or sunflower quality.