Interactive effect of tillage and wood ash on heavy metal content of soil, castor shoot and seed

Organic waste when used as soil amendment improves the fertility status of soil and crop yield, but unrestricted application on soil could lead to accumulation of heavy metals to a level, toxic to plants themselves and the animals that consumes them. Thus a field experiment was conducted in three (3) different planting seasons using three tillage methods (mound, ridge, flat) and four different rates (0t/ha, 2t/ha, 4t/ha, 6t/ha) of wood ash to evaluate the effect of tillage and wood ash on heavy metal; copper (Cu), boron (B) and lead (Pb) content of soil and uptake by castor shoot and seed. Data generated from the study was analyzed using crop start version 7.2 and mean separation was done using least significant difference (LSD0.05). The findings from the study showed that the interactive effect of tillage and wood ash on heavy metals content of soil, castor shoot and seed were significant (P<0.05). The values obtained decreased as the planting season increased, while the amount was found to increase as the rates of wood ash application increased. For soil heavy metal contents it was observed that tillage methods had no effect on virtually all the parameters assessed. The values obtained from ridge and flat were higher when compared to the value of mound with regard to soil and castor shoot heavy metal contents. The result of the shoot also show that interaction of flat and wood ash at the rates of 2t/ha, 4t/ha, and 6t/ha (Ft2, Ft4, Ft6) show statistically similar results. The result of heavy metal content of seed indicated that tillage method had no effect in most of the heavy metal contents of the castor seed, while Cu in 3rd year planting season were not significant among the rates of wood ash applied. The interaction effect of ridge and wood ash at the rates of 2t/ha, 4t/ha and 6t/ha (Rd2, Rd4, Rd6) on Cu, 1st and 2nd season were statistically similar, while the result from mound method was found to increase the seed up take of most of the tested parameters. The observed values of these tested parameters (Cu, B, Pb) in wood ash amended plots in the three planting seasons were within acceptable limits.