Accumulation of chromium from fertilizers in cultivated soils

Studies to determine whether chromium originating from fertilizers increases to toxic concentrations as a result of common applications of fertilizers were carried out in fields with a well-documented record of fertilizer application. Chromium contents ranged from 10-150 µg Cr/g soil in the 41 fields with long-term applications of N, P, and K fertilizers, silicate, and liming materials in seven agricultural experiment stations. Such values corresponded to natural background levels in soils. Increase of chromium concentration ranging from 20-50 µg Cr/g soil was detected in plots with heavy application of calcium silicate and fused magnesium phosphate (fused serpentine-phosphate) as soil amendments in Iwate and Tochigi Prefectural Agricultural Experiment Stations. On the whole, chromium contents in treated soils were not different from those in untreated soils and depended on the soil parent materials. Chromium applied showed a vertical distribution with higher amounts in the surface soils and/or subsurface soils than in subsoils, and seldom reached the zone below subsoils. In pot-experiments (500 cm2 pots), the application of fused phosphate at the rate of 100 g and 200 g for the Konosu and Tochigi soils, respectively, affected the growth of rice (Oryza sativa L.) markedly. On the other hand, fused phosphate application to komatsuna (Brassica rapa var. pervedes), affected only moderating the growth of the plants. Even the plants in which the effect was most pronounced, contained only small amounts of Cr at the maximum, i.e. less than 2.7 µg Cr/g in the tops and 2.0 µg Cr/g in the roots. In view of such low absorption, yield decreases did not appear to be caused by chromium toxicity, but by other factors. In conclusion, chromium present in fertilizers, silicate, and liming materials was not considered to be a sourse of man-induced contamination of cultivated soils.