Studies were carried out to determine whether there is any difference in the health risk involved in growing carrots and spinach on sludge-amended soils when a 90-day sludge application-to-planting interval and sludge application-to-harvest intervals are used for further pathogen reduction. The health risk was determined by enumerating the Most Probable Number (MPN) of Faecal Coliform (FC) recovered from both vegetables and identifying the different types of enteric bacteria recovered at harvest. The spinach and carrots were grown on four different soil types unto which a 3 year old sludge (type 1 sludge) and three month old sludge (type 2 sludge) had been separately applied at different rates. Two sludge application-to-planting and sludge application-to-harvest interval were used. A higher number of FC were recovered from carrots (1.5 log10 MPN/10 g-1.8 log10 MPN/10 g) than spinach (<1.5 log10 MPN/10 g) grown on same soil type with identical type of sludge applied at the same rate. More FC was recovered when a 0±3 day sludge application-to-planting interval was used as opposed to a 90 day sludge application-to-planting interval. Soil type, sludge age and sludge application rate affected the amount of FC recovered. The implications of these results on the specification of time interval in Regulations guiding the growth of vegetables on sludge-amended soil are discussed.
Veronica M. Ngole , 2007. The Effect of Sludge Application-to-Planting Interval on the Number of Coliforms Recovered from Vegetables Grown on Sludge-Amended Soils. Journal of Applied Sciences, 7: 3756-3761.