Effect of different forms and sources of arsenic on crop yield and arsenic concentration

Two greenhouse experiments were conducted to investigate the effects of different sources of As application on the yield of ryegrass (Lolium perenne L.) and barley (Hordeum vulgare L.) and the arsenic concentration in crop tissue. The soils used were a sand and a loam soil. In the first experiment (3 yr), As was applied either as sodium arsenite or as disodium hydrogen arsenate at the rate of 0, 2, 10, 50, and 250 mg As kg^?1 soil in year 1. In years 2 and 3, only the residual effect of As applied in year 1 was investigated. In the second experiment (5 yr), a NPK(16-7-12) fertilizer containing 10, 100 and 3000 mg As kg^?1 as sodium arsenite was applied at rates of 750 and 600 mg kg^?1 to ryegrass and barley, respectively, with lime and without lime. Arsenite had more inhibitory effect on crop yield than arsenate. Although the residual effect persisted up to year 3, it was found to be dependent on As application rate, soil type, and crop species. Only minor differences in As concentration in crops between arsenite and arsenate sources were observed. The yield reduction and the increase of As concentration in crops was highly related to As application rates. The As rates of 50 and 250 mg As kg^?1 resulted in significant yield reduction and marked increase of As concentration in both crops and these rates could be considered as critical for both crops. The application of As containing fertilizer had little or no effect on crop yield. The As concentration in both crops was little affected by the fertilizer containing up to 100 mg As kg^?1 but the concentration increased several folds when the fertilizer containing 3000 mg As kg^?1 was applied. The application of additional P to the treatment containing 3000 mg As kg^?1 fertilizer only slightly increased crop yields but it increased As concentration in ryegrass markedly. The repeated application of As containing fertilizer up to a period of 5 yr, even at 3000 mg As kg^?1 level, generally did not affect either the yields or the As concentration in both crops although a slight increase of As concentration in barley grain over the years was observed. In both experiments, the yield reduction and the increase in As concentration in crop tissue were lower in the loam soil than in the sand and barley straw cointained much higher As than barley grains, indicating that greater proportion of the As taken up by this crop was retained in the vegetative organs.