Assessment of some phosphatic sources for possible accumulation of heavy metals in chilli (Capsicum annuum L.)

Abstract

Rock phosphate sources collected from different locations were analysed for both phosphorus content and heavy metals namely cadmium and lead. Those sources which analysed relatively higher content of heavy metals were included for conducting a pot culture experiment using chilli (Capsicum annuum L.) as test crop. To derive meaningful comparison in the study, partially acidulated rock phosphates as well as direct water soluble source of cadmium and lead were also applied to assess their bioavailability to plants. The influence of organic matter when applied alone or in conjunction with heavy doses of heavy metals was also assessed in the study. The pot culture experiment was conducted in the Vegetable Research Farm, Department of Olericulture, Vellanikkara during the kharif season of 1996, with chilli as the test crop. The entire fertilizer management was based on package of practice (N, P and K at 70, 40 and 25 kg ha-1) recommendation. Five different sources of P selected for the pot culture experiment were (1) Maton rock phosphate, (2) Mussorie rock phosphate, (3) Gafsa rock phosphate, (4) Rajasthan rock phosphate and (5) Single superphosphate. The maximum content of cadmium (55 mg kg-1) was recorded in Gafsa rock followed by 25 mg Cd kg-1 for the Maton rock and single superphosphate analysed the least concentration of cadmium (15 mg kg-1 Highest lead content of 230.5 mg Pb kg-1 was analysed in Maton rock while lowest (38 mg kg-1) in Musoorie rock. All the other sources maintained their heavy metal concentration in between these extremes. In general, the shoot portion of test crop chilli recorded highest cadmium uptake while root portion noted the maximum lead uptake. The least uptake of heavy metals was noted in the chilli fruit, which is the edible part of the plant. This indicates that the heavy metal load in the fruit portion is much less when compared to other plant parts, irrespective of the sources used. The same trend was evident when either partially acidulated P sources or direct source of heavy metals (through water soluble salts) were applied. However, the uptake of cadmium and lead from those sources remained higher in plant parts. Application of organic matter in conjunction with a heavy dose of heavy metals to soil resulted in a significantly higher uptake of cadmium and lead in all plant parts. Analysis of the available cadmium and lead in the post-harvest soil samples indicated negligible build-up of these metals in soils. However, direct application of higher levels of heavy metals permitted higher cadmium and lead extraction in the post-harvest soil samples. Application of partially acidulated rock sources to soils, though could cause enhanced uptake of heavy metals, could not show higher residual effects of heavy metals in post-harvest soil samples.