Effect of pest controlling neem ( Azadirachta indica A. Juss) and mata-raton ( Gliricidia sepium Jacquin) leaf extracts on emission of green house gases and inorganic-N content in urea-amended soil

Abstract

Extracts of neem ( Azadirachta indica A. Juss.) and Gliricidia sepium Jacquin, locally known as ‘mata-raton’, are used to control pests of maize. Their application, however, is known to affect soil microorganisms. We investigated if these extracts affected emissions of methane (CH 4), carbon dioxide (CO 2) and nitrous oxide (N 2O), important greenhouse gases, and dynamics of soil inorganic N. Soil was treated with extracts of neem, mata-raton or lambda-cyhalothrin, used as chemical control. The soil was amended with or without urea and incubated at 40% and 100% water holding capacity (WHC). Concentrations of ammonium ( NH 4 + ) , nitrite ( NO 2 - ) and nitrate ( NO 3 - ) and emissions of CH 4, CO 2 and N 2O were monitored for 7 d. Treating urea-amended soil with extracts of neem, mata-raton or lambda-cyhalothrin reduced the emission of CO 2 significantly compared to the untreated soil with the largest decrease found in the latter. Oxidation of CH 4 was inhibited by extracts of neem in the unamended soil, and by neem, mata-raton and lambda-cyhalothrin in the urea-amended soil compared to the untreated soil. Neem, mata-raton and lambda-cyhalothrin reduced the N 2O emission from the unamended soil incubated at 40%WHC compared to the untreated soil. Extracts of neem, mata-raton and lambda-cyhalothrin had no significant effect on dynamics of NH 4 + , NO 2 - and NO 3 - . It was found that emission of CO 2 and oxidation of CH 4 was inhibited in the urea-amended soil treated with extracts of neem, mata-raton and lambda-cyhalothrin, but ammonification, N 2O emission and nitrification were not affected.