Minerals in Soils and Forages Irrigated with Secondary Treated Sewage Water in Sebele, Botswana

Abstract

Production of forage using treated sewage water is a viable practice internationally. However, there is not much information on the heavy metal content of such forages. This study was conducted to determine the effect of sewage water on soils and forages irrigated with treated sewage water at Botswana College of Agriculture 's farm. The study was conducted for a period of 120 days using established forage pastures of rye grass (Lolium multiflorum) and lucerne (Medicago sativa). Heavy metals determined were Fe, Mn, Cu, Zn, Ni, Pb and Cd. Generally the treated sewage water contained relatively low levels of heavy metals. Zn, Ni and Mn concentration were below the detectable levels. In the sewage water while soils and plants had low levels of heavy metals. Comparatively the soil and plants heavy metal levels were much higher than those in the water and the difference was significant (p<0.05). There was some low correlation between trace element contents in the water and soil. In addition there was some significant difference (p<0.05) in heavy metal concentration in sewage water between the months during which the analyses were done. However, the sewage water, soils and forage mineral concentrations were within the internationally allowable heavy metal concentration with respect to irrigation, soil loadings and animal feeds. poor performance is largely attributed to low and variable effluent is generated per annum and discarded in rainfall as well as the occurrence of successive droughts. Gaborone alone as sewage . The use of sewage water for This calls for exploitation of other means of water sources irrigation is a positive way to dispose off sewage. Such to sustain the sector as underground water from huge volumes of water in a country with persistent boreholes, damming of rivers and sewage water. The latter droughts and unreliable rainfall can be of great agronomic being the most sustainable as it minimizes the cost of and economic importance. Irrigation with sewage water procuring portable or fresh water for agricultural use. can increase available water supply or release water for Concern for water quality denotes it's suitability and is alternative use. The utilization of sewage water also related to it's effect on the soil and plants and the contributes to cleaning of the environment, as the water management that may be necessary to control or is not discharged into water bodies that could otherwise compensate for a water quality related problem is the most get polluted. In addition to these direct economic benefits limiting factor in the use of sewage water for agricultural that conserve natural resources, this water contains a lot purposes. The principle for evaluating the quality of of nutrients and can serve as an alternative source to irrigation water deals with the total concentration and expensive chemical fertilizers. FAO estimated that typical composition of soluble salts in water . Soluble salts wastewater from domestic sources could supply all of the (2)