The effects of nitrogenous fertilizers on selected physiochemical parameters and heavy metal loads within Nzioa nucleus sugarcane estate farms in western Kenya

Abstract

Continued use of nitrogenous fertilizers and biosolids in farming is known to affect the soil pH of the farms leading to acidic environment that promotes solubility;bioavailability and mobility of heavy metals. In addition, these fertilizers also contain residues of heavy metals that accumulate in soils and water bodies over time. Nzoia <.,.. Sugar Company in western Kenya uses nitrogenous fertilizers in sugarcane farming and the effect of these agrochemicals on the environment were yet to be determined. Heavy metals and physicochemical parameters cause a great threat to the environment and human health if the levels go beyond allowable limits. The Presence of heavy metals in the aquatic environment also affects some physicochemical parameter like dissolved oxygen and chemical oxygen demand which become harmful to the aquatic animals and plants when they exceed certain limits. River Nzoia is already reported to be affected by heavy metals and physicochemical parameters like total phosphate, nitrate-nitrogen and dissolved oxygen beyond international levels. Therefore, there was need to determine point sources of the above parameters in order to suggest possible mitigation procedures. Nzoia sugarcane nucleus farms were used to represent sugarcane farming in the whole sugar belt region where Nzoia River transverses. Two factor completely randomized block design was used in sampling. Triplicates of surface water, surface sediments and top soil samples from the farms, canals and River Kuywa (a river that traverses the nucleus to join River Nzoia) were collected. Sampling was done twice in the year (dry season when there was no nitrogenous fertilizer application and wet season a week after nitrogenous fertilizer application). A pH meter, a mercury thermometer, a turbidity meter and an electrical conductivity meter were used to measure pH, temperature, turbidity and . electrical conductivity respectively insitu. Ultraviolet spectrophotometric screening method, closed reflux colometric method, Wrinklers' method, Anils' method and Okalebos' method, were used in determining nitrate-nitrogen, chemical oxygen demand, dissolved oxygen, total phosphates and total organic carbon respectively, whereas AAS (AA-6200, Shimadzu) was used to analyze heavy metals. The data was analyzed using . Analysis of variance (ANOVA) (p ::;0.05) (two factor experiment) and students t-test (P ::;0.05) used to check the variations. The research found out that lowering of soil pH by nitrogenous fertilizers affected the concentrations of heavy metals in the soils and the surrounding aquatic environments. The nitrogenous fertilizers used in the farms were also found to contain residues of heavy metals. Presence of heavt metals into the aquatic environment increased water conductivity levels and reduced dissolved oxygen in water due to bioavailability and reoxidation processes respectively. Surface runoffs and soil erosions in the sugar plantations were the major transport agents of the heavy metals in soils to aquatic environments as was determined from high water turbidity values during the long wet season.In addition the surface runoffs and soil erosion were also transporting the nitrate and phosphate residues from the fertilizers applied to aquatic environment leading to pollution of the water.