Long-Term Effect of Phosphate Fertilization on Cadmium Uptake by Oat and its Accumulation in Soil

Abstract

Phosphate fertilizers contain varying amounts of cadmium (Cd) and other heavy metals as contaminants from phosphate rock (PR). Periodic applications of these fertilizers could result in measurable accumulations of Cd in soils and in harvested crops. A long term field study for fifteen cropping seasons (1992-2006) was conducted on an experimental plot located at the Norwegian University of Life Sciences (As, Norway) to evaluate the effect of application of cadmium enriched phosphate fertilizer on Cd uptake by Oat (Avena sativa) and its accumulation and availability in soil. Treatments consisted of three NPK fertilizer sources containing 1, 90, 381 mg Cd kg-1 P and applied at the rate of 0.03, 2.7, 11.43 g Cd ha-1yr-1, respectively. Surface soil samples (0-20 cm), collected after harvesting of oat in 1992, 1995, and 2006, and were analyzed for total and extractable Cd, pH, dissolve organic carbon (DOC) and PO4 3-. Plant samples collected in 1992, 1995, 1997, 2002 and 2006 were analyzed total Cd. Plant Cd generally decreased with increased soil pH throughout the experimental period except 1992. Increased input of Cd through fertilizers increased the Cd concentration in soil but the Cd concentration in oat grain remained unaffected. Ammonium nitrate (NH4NO3 -) extractable Cd in the soil increased with increasing rate of Cd through different sources but it decreased with increased pH throughout the experimental period with minor exceptions. Plant Cd did not show any significant correlation with extractable Cd in soil and hence the Cd input through fertilizers did not significantly affect the concentration of Cd in oat grain. Model (WHAM) prediction of Cd uptake by plants showed that crop yield, pH and DOC in combination explained about 57% of the variation in Cd uptake and DOC (r2=0.47, p<0.0001) was the most important factor. However, in individual years (e.g.2006) the combination of FA-Cd and yield did in fact explain 92% of the Cd-uptake.