EFFECT OF 2,4-D AND HEXAZINONEON SOIL DEHYDROGENASE ACTIVITY IN SUGARCANE CULTIVATED SOILS IN NZOIA SUGARCANE PLANTATIONS

Abstract

Herbicides have been used extensively all over the world and have become indispensable pact of high and cost effective agricultural production. The adverse effect of these herbicides is not only to their targets but also extend to non-targeted organisms. These effects may have detrimental impacts such as disruption of ecosystems, reduced soil health and fertility among other environmental hazardous.Dehydrogenase enzymes, which are intracellular enzyme in microflora of soil, play a key role in redox processes, especially in decomposition of organic matters. The aim of thisexperiments was to study the effects of 2,4-D and Hexazinone; commonly used herbicides to control weeds in sugarcane plantations in Nzoia sugar company nuclear estates, on the variation of dehydrogenase activity as an indicator of microbial activities on such soils. The soil for experiment were collected 0-10 cm depth using soil auger by random sampling method from three sites on each farm and a composite sample was prepared from the three sub-samples. Soil parameters such as pH, temperature,moisture content, N, P, K, Mg and Ca were analyzed. The experiments were conducted under the field conditions of soil samples collected from two farms which had history of application of the herbicides for five years and an out-grower farm as a control farm. The soils were spiked with the two xenobiotics at the field application rate and analyzed for the dehydrogenase activity for a period of seven days using TTC method andbacterial colony forming units using nutrient agar methods.Experiments showed that hexazinone and a boosting activity to the microbial activity as indicated by overall DHA activity of 16.375±1.822 in farm F139, 21.970±3.448 in farm F212, 113.45±15.453 in farm OGF. On the other hand, 2,4-D had suppressing effect on microbial activity as shown by DHA activity of 0.532±0.120 in farm F139, 0.541±0.139 in farm F212 and 6.594±1.175 in farm OGF. The noted results of DHA activity were in reference to untreated soils from the three farms which were 4.529±0.408 in farm F139, 6.103±0.341 in farm F212 and 21.578±3.234 in farm OGF. The two herbicides effects on the total microbial activity was also backed with bacterial density results which showed there was low bacterial count upon 2,4-D application 2.463±3.693*10^5 in untreated soil 2.487±5.607*10^5 in hexazinone treated soil and 2.007±4.194*10^4 in 2,4-D treated soil. All the farms had acidic soils with other parameters with the normal range.