Vertical and lateral movements of nitrate, phosphate and sulphate in soils around manure dumpsites and the potential environmental implications.

Abstract

Monitoring and quantification of nutrient movement in soils could help farmers and policy makers to formulate effective nutrient loss reduction strategies and waste management. The study was conducted to monitor and quantify vertical and lateral movements of nitrate-nitrogen (NO3-N), phosphate (PO4) and sulphate-sulphur (SO4-S) in soils around manure dumpsites in Abeokuta, southwest Nigeria. The dumpsites investigated include a flush-type poultry litter, poultry litter mixed with beddings of wood shavings and cattle and pig waste open dumpsites. Soils were sampled at depths of 0-20, 20-40, 40-60 and 60-80cm and at distances 2, 4, 6, 8, 10, 20, 40, 60 and 80m away from the dumpsites. Soil samples were analysed for some physical and chemical properties and NO3-N, PO4 and SO4-S contents. Results indicated that there were more nutrients in the soil around the poultry manure slurry dumpsite compared with others while the soil pH increased with increase in soil depth, across dump sites. There was evidence of leaching of salts, and this correlated positively with the soil organic matter content (r = 0.41, p < 0.01). The soils were polluted with NO3-N, PO4 and SO4-S as deep as 80-cm depth; these nutrient amounts were higher than the maximum allowable (40, 15 and 7mgkg-1, respectively) for southwest Nigerian soils. Due to high soil organic matter and for agronomic considerations, the soils are only suitable for cultivation at depths below 40cm and 8m away from the dump sites. There was significant pollution of the soils with nitrate, phosphate and sulphate, within 80m distance from the dump site. This has serious implications for ground water recharges and shallow well sunk around these areas. There is potential risk of NO3-N, PO4 and SO4-S consumption through such water sources.