The effect of two lime sources on short-term changes in soil pH under Marlborough hill country pasture

The effect of fine slurried lime applied at 200 kg/ha on soil pH at two depths was compared with 400 and 2500 kg/ha of local agricultural (ag) lime in the presence and absence of sulphur (S) superphosphate 20, in Marlborough hill country for one year. In the absence of fertiliser all lime treatments significantly raised soil pH in the top 25 mm for the 355 days after application. Initial responses declined from day 14 or 35 to day 138 before increasing at day 355. Fine lime did not significantly alter pH in the 25-75 mm zone until day 355. The low rate of ag lime significantly raised pH in the 25-75 mm zone for the whole year. The high rate of ag lime significantly increased pH in the top 25 mm over the other lime treatments for the 355 days and over the fine lime treatment in the 25-75 mm zone from day 35. In the presence of fertiliser in the top 25 mm, fine lime significantly increased pH at day 14 only, and low ag lime at day 355 only. The high rate of ag lime significantly increased pH over the control from day 14 and over the other lime rates from day 35. In the 25-75 mm zone the high rate of ag lime significantly increased pH over the control and the low ag lime rate from day 71 but was significantly better than fine lime from day 35. It is likely that rain immediately after application and higher than average annual rainfall hastened the release of fine and intermediate particles of lime. However provided lime meets the accepted criteria for particle size distribution and maximum size it is the rate of application which dictates the magnitude of response. In Marlborough hill country it was 43% cheaper to aerially apply 400 kg/ha of ag lime compared to 200 kg/ha of fine lime with the added benefit of a greater residual effect beyond one year. Keywords: agricultural lime, fine lime, slurry, soil pH