Regresar

Effect of pesticides on the population of Azospirillum sp. and on ammonification rate in two soils planted to groundnut (Arachis Hypogaea L.)

Abstract:

Pesticides are usually applied simultaneously or serially for groundnut (Arachis hypogaea L.) crop protection. This type of pesticide application often leads to a combined contamination of pesticides and their residues in the soil. Pesticides used in groundnut cultivation - monocrotophos and chlorpyrifos, singly and in combination with mancozeb and carbendazim, respectively - were tested for their effects on the population of Azospirillum sp. and ammonification in two soils planted to groundnut in the Anantapur District of Andhra Pradesh, India. The size of the Azospirillum sp. population was initially low in both soils. Application of pesticides, singly and in combination up to 5.0 kg ha -1, significantly increased the population of Azospirillum sp. after 7 and 14 days of incubation in vertisol soil, whereas in laterite soil, the application of pesticides in the same combination up to 2.5 kg ha -1 increased the population of Azospirillum sp. in similar conditions. Mineralization of peptone-nitrogen was profoundly increased when soil was treated with pesticides, singly or in combination, at 2.5 kg ha -1 in both soils. Vertisol soil that received monocrotophos and chlorpyrifos singly at 5.0 kg ha -1 showed a considerable increase in ammonification rate after 14 days of incubation. Due to the synergistic and additive interactions between pesticides and microorganisms, the population of Azospirillum sp. and the rate of ammonification increased at particular concentrations of pesticides (i.e 2.5 to 5.0 kg ha -1), but at higher concentrations (7.5 and 10.0 kg ha -1) the pesticides exerted antagonistic interactions on the population of Azospirillum sp. and ammonification. © International Society for Tropical Ecology.