Impact Of Organic Wastes Towards Heavy Metals Behavior In Soil-rice System And Rice Growth And Yield

Heavy metals in the soil pose a great threat to the environment and ultimately to the humans through bioaccumulation.A variety of heavy metals are reported to enter the food chain through uptake by the major crops therefore instigating a vicious cycle of being transferred and retransferred across various trophic levels.This continuum is a threat to the quality and quantity of principal staple foods for instance paddy rice.In this regard the most notorious element is Copper(Cu) for its efficient mode of uptake by grains and its lethal impact on grain production.Many organic and inorganic substrates associated with crops include potential sources of heavy metals.One such example is that of organic fertilizers whose main purpose is to increase the fertility of soil by providing essential nutrients,and to increase crop production by limiting the heavy metals bioavailability.Another utility is the provision of contaminant free food.Contemporary literature recognizes these organic fertilizers including manures as source of contaminants like Cu.The present research was conducted to evaluate the effect of heavy metal Cu on the growth and production of paddy rice.Different levels of Cu pollution were explored.The response of manure to Cu pollution in soil and on to rice growth, production and quality was assessed.A pot experiment was conducted to investigate the utilization of organic waste,its contribution towards heavy metals accumulation in the soil and possible effect on crop growth and production.The results indicated that lower levels 100 and 200 mg kg^-1 of Cu did not affect the plant height,number of tillers,and plant biomass,while higher levels of Cu from 400 to 800 mg kg^-1 caused significant reduction.No significant effect on SPAD value(without injured leaf symptoms,necrosis or chlorosis) was observed even at 800 mg kg^-1 of Cu.The addition of 1%manure along with low Cu levels(100 and 200 mg kg^-1 ) had a positive effect on the growth of rice(plant height,number of tillers and plant biomass).However,higher levels of Cu with 1%manure significantly reduced rice growth with a relatively more reduction with Ck1,compared to Ck0.The application of 3%manure with 100 and 200 mg kg^-1 had a significantly negative effect on growth parameters but in combination with higher doses of Cu(400 and 600 mg kg^-1,except for 800 mg kg^-1) it improved plant growth.The rice yield was severely affected at higher concentrations except for 100 mg kg^-1 of Cu compared with Ck0.A reduction in the grains yield of 30.11%,64.32%and 72.50%was observed at 400,600 and 800 mg kg^-1 of Cu respectively,compared with Ck0.While at 1%manure level an increase in the yield was observed for 100,200 and 400 mg kg^-1 of Cu respectively indicating a positive effect of manure on the grain yield.Higher Cu levels 600 and 800 mg kg^-1 reduced grain yield of 38.32%and 40.92%respectively when used with 1%manure.In contrast to 0%and 1%manure the average grain yield for 3%manure decreased at 100 and 200 mg kg^-1 of Cu,with reduction of 61.95%and 51.7%respectively.The effective panicles,filled grains per panicle and total grains per panicle decreased with the increased levels of Cu at 0%manure except for 1%manure at 200 and 400 mg kg^-1 of Cu.At 3%manure all these parameters decreased for 100 and 200 mg kg^-1 of Cu,while they increased at 400 and 600 mg kg^-1 of Cu compared with Ck3.For 1000 grains weight no significant differences were found for all the Cu concentration at 0%,1%and 3%manure levels.Regression analysis indicated a positive and significant(p＜0.01) correlation with effective panicles, filled grains per panicle,total grains per panicle and total grains per pot at 0%,1%and 3%manure.While a significant correlation between effective panicles per pot and total grains per pot(r² = 0.915^**) suggested that the more effective panicles the more will be the grains(yield).Roots,and shoots Cu concentration increased with the increase levels of Cu at 0% manure.Whereas,addition of 1%and 3%manure decreased the Cu content in the root by 2.29 to 1.5 and 2.55 to 1.5 fold for 100 to 800 mg kg^-1 of Cu,respectively.Cu contents in the shoots at tillering stage were higher but decreased as the growth of rice proceeds.Cu concentration increased consistently with the elevated Cu levels at 0%manure. Similarly Cu concentration in grains also increased with the increasing levels of Cu at 1% manure but the overall accumulation was less compared to 0%manure.For 3%manure less Cu was accumulated in grains at 100 and 200 mg kg^-1 but at higher doses significant accumulation was occurred as compared with Ck3.Relationship between roots,shoots and grains showed that Cu contents in the shoots and grains were significantly correlated with the Cu contents in the roots,as the Cu contents in the roots decreased at 1%and 3% manure,less Cu was transferred to the grains. The dynamic behavior of extractable Cu showed that it significantly decreased from planting to tillering stage for all the levels of manure.A reduction of 8.06,5.12,1.90, 1.18 and 1.25 folds were found at 0%manure from planting to harvesting stage.Similarly, the extractable Cu also decreased from planting to harvesting stage at 1%and 3%manure and decrease was more pronounced for the lower doses where reduction of 4.25,2.77 and 1.54 folds at 1%manure and 4.41,2.38 and 1.56 folds at 3%manure was obtained at 100, 200 and 400 mg kg^-1 respectively.The total Cu contents in the soil tend to increase with the addition of manure as the availability decreased due to addition of manure.The correlation between extractable Cu and the Cu in the grains was non significant(r² = 0.373) and indicated that 3%manure substantially decrease the availability of Cu to the grains.The correlation between the extractable Cu and Cu contents in the plants showed that higher the extractable Cu higher will be the Cu contents in the plant.