Soil acidification as influenced by crop rotations, stubble management, and application of nitrogenous fertiliser, Tarlee, South Australia

Soil acidification, as influenced by N fertiliser, stubble management, and crop rotations, was investigated using soil samples from a long-term rotation trial at Tarlee, South Australia. With the effects of combination of treatment inputs (wheat-lupin, stubble retention and N-fertiliser application), the p[H.sub.Ca] (0-10 cm depth) declined from the starting value of 6.12 to 4.50 after a 14-year period. All of the treatments caused the soil pH to decrease. The mean acidification rates for the period 1978-1992 varied from 0.5 to 2.22 kmol [H.sup.+]/ha.year for different treatments. Although the rainfall at Tarlee (483 mm) is not sufficient to cause regular drainage events, it is likely that downward movement of N[O.sub.3.sup.-] in the soil profile has caused acidification in the surface soil. Also the retention of stubble caused more acidification than where there was regular stubble burning or removal. The acidification resulted in an increase in soil exchangeable Al and Mn and extractable Al and Mn, and the decrease in soil exchangeable base cations. The values for soluble Al (extracted in Ca[Cl.sub.2]) in 1992 were 1.58 and 2.45 mg/kg (0-10 cm depth) for the wheat-bean and wheat-lupin rotations, but the percentage of Al in the ECEC was low. It is not known whether this acidity has any impact on yields of field crops at this stage. But with soluble Al and the percentage of Al in ECEC increasing, it is possible that Al toxicity may occur in the high input-output cropping soils in South Australia. Additional keywords: acidity, pH, aluminium, manganese.
Introduction Soil acidification in its broadest sense can be considered as a summation of natural and anthropogenic processes that lower measured soil pH (Krug and Frink 1983). The intervention of [...]