Trends in some soil test data over a 14-year period in New Zealand

Abstract

To establish long-term trends in soil fertility in New Zealand pasture lands, data for Olsen phosphate (Olsen P), pH, and QuickTest (QT) calcium (Ca), magnesium (Mg), and potassium (K) from 246 000 soil samples submitted to a commercial soil sampling laboratory from 1988 to 2001 were analysed. Each record was categorised according to year, land use (dairy, sheep/beef including deer), soil “group” (sedimentary, volcanic, pumice, peats, rest), and regions. Olsen P values were, on average, higher on dairy farms than sheep/beef farms and lower on sedimentary soils than other soils (P > 0.05). Sedimentary and volcanic soils had higher QT K than pumice and peat soils (P > 0.05). Regional differences were largely explained by differences between land use and soil group distribution. However, given this distribution, average Olsen P values were higher in the Waikato, Bay of Plenty/Taupo and Taranaki regions, the east coast of both islands generally had higher average pH, K, and Mg soil test values, and the West Coast region had lower average soil test values than most other regions. Over the 14-year period, Olsen P followed an asymptotic increase, reaching the asymptote between 1994 and 1997 depending on land use and soil group. For the period 1997–2001, 30–65% of samples from dairy farms had Olsen P levels above the range required for near-maximum pasture production. QT Mg decreased consistently by about 0.35 QT units year−1 when QT Mg was 25. The database provides a tool for looking at soil test trends over time on a national basis to assess the sustainability of soil fertility management practices on pastoral farms. © 2004 Taylor & Francis Group, LLC.