Evaluation of maturity levels and heavy metal content in composts made from rice straw

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Use of compost is rising due to challenges associated with use of synthetic farm inputs. To ascertain the suitability of compost with plant growth, phytotoxicity level of compost should be evaluated before its use as a plant growth medium. Compost maturity tests are performed to assess compost phytotoxicity before its application to soil. Abundant rice straw produced in Mwea Rice Irrigation Scheme in Kenya was used in the present study to produce five composts treated differently with either chicken droppings (T1), commercial effective microorganisms (T2), locally formulated microbial consortium (T3), donkey dung (T4) and without inoculation (T0) (control). Humification index (HI) of each of the five compost types were tested. Germination index (GI) and Plant growth index (PGI) bioassays were performed using tomato (Solanum lycopersicum L.) crop. Levels of lead, copper, zinc and cadmium were measured in an Atomic Absorption Spectrophotometer (AAS). HI in all the five compost types was generally high ranging from 2.57- 11.05 %. Cadmium, lead, copper and zinc were all at detectable but varying concentrations in the composts. PGI values ranged from 93.05- 241.88 % while GI values varied from 182.33±4.63- 275.67±5.49 %. The results indicate that all the compost types were mature and suitable for use in crop farming

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