Impact of human intervention on soil degradation in the Nilwala Project

Abstract

The present investigation was carried out in order to assess the soil development o f a human impacted site located near Kamburupitiya in the Matara district. The site previously under cinnamon cultivation was severely affected by the Nilwala Ganga Flood Protection Scheme in 1987. The soil has been cut down to the bed rock and removed from the site in order to construct dams. Representative soil samples (from 0-15 cm depth) were drawn randomly from the disturbed site and analyzed for pH, EC, bulk density, N, P, K and organic matter contents using standard methods. A neighboring site with the same soil type was used as the reference in order to compare the disturbed and undisturbed soils. Results revealed that the average bulk density, pH and EC o f the disturbed soil were 1.25 g/cm3, 5.35 and 36.25 p mhos/cm respectively. Whereas the corresponding values for the undisturbed soil were 0.87 g/cm3, 5.23 and 56.2 p mhos/cm. The values o f major nutrients (N, P and K) were 0.0088 %, 10.5 and 72.66 mg/kg for the disturbed soil and 0.095 %, 44 and 82.8 mg/kg for the undisturbed soil. The average organic matter contents „ o f the disturbed and the undisturbed soil were 0.24 and 1.09 % respectively. The observation made during the study revealed that the soil surface had been totally exposed due to severe erosion and therefore, the major reason for the significantly lower values of nutrients (organic matter, N, P and K) recorded in disturbed soil would be removal o f the bulk o f nutritive soil byerosion. Furthermore, the present findings indicate that even 18 years after the disturbance the development o f soil was quite poor and thus it may take some considerable period o f time to improve the soil for crop production.