Effect of aqueous neem(Azdirachta Indica A Juss) leaf extract on selected soil chemical and biological properties

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Chewe, Lubungo Aswell
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The University of Zambia
Zambia has soils with low plant available nutrients due to leaching, depletion of organic matter and acidification. One way of addressing this situation is by the application of organic materials such as aqueous neem leaf extract. No known documented research has been conducted in Zambia to evaluate the effects of neem products on soil biological and chemical properties when used as a soil amendment. Possible effects may include the addition of nutrients which may be used by the soil microorganisms or the chemicals that may have negative impacts on soil microorganisms resulting in reduced activity and population. This study was a greenhouse experiment designed to evaluate the effects of aqueous neem leaf extract on selected soil chemical and biological properties when applied as a soil amendment. Five treatments of neem leaf concentrations in replicates of four were arranged in a Completely Randomized Design. The aqueous neem extract concentrations included 2 %, 5 %, 10 %, 15 %, 20 % and 0 % as a control. The leaf extract was applied to 5 kg of soil in each plastic pot on a weekly basis for the first five consecutive weeks. In addition, each week, for ten consecutive weeks, 100 g of soil was removed from each pot. The soil which was removed from the pots was incubated for 7 days and analysed for soil microbial biomass and activity using the Chloroform Fumigation and Incubation (CFI) method and soil respiration method, respectively. Neem leaves used for making the extract had 2.58, 1.77, 1.5, 0.4 and 0.1 % of Ca, K, N, Mg and P respectively. These levels of nutrients were comparable to those in Confrey and Tithonia commonly used for making leaf extracts. The results also showed that 10 % and 20 % concentrations of aqueous neam leaf extract were significantly different from each other. The results at week 10 showed that there were non-significant differences among treatments 2 %, 5 % and 15 % but cumulative soil microbial activity at 10 % concentration of aqueous neem leaf extract had increased by 16 % from the control. This increase in the microbial activity can be attributed to increasing amounts of the nutrients available to the soil microorganisms. Microbial activity at 20 % concentration of aqueous neem leaf extract reduced by 3 % compared to the control attributable to the possible toxic effects of the secondary metabolites at this high concentration. The cumulative soil microbial biomass for 2 %, 5 % and 10 % concentrations of aqueous neem leaf extract had reduced by 19 %, 10 % and 3 % respectively. An increase in cumulative soil microbial biomass was recorded at 15 % and 20 % by 8 % and 4 % respectively.
Soil science. , Soil management--Zambia , Neem products