Soil and pasture responses to lime on dry hill country in central Hawke's Bay, New Zealand

Abstract

Small plot trials were established with four combinations of aspect and slope (north‐easy, north‐steep, south‐easy, south‐steep) with initial soil pH 5.6, 5.4, 5.6, and 5.4, respectively) on hill country under low annual average rainfall (800 mm yr–1) near Waipawa in central Hawke's Bay. At each site, lime at 0, 0.5, 1.0, 2.0, 4.0, and 8.0 t ha–1 was applied once in November 2000 to increase soil pH to 5.4–5.6, 5.5–5.8, 5.7–5.9, 5.7–6.0, and 6.0–6.4, respectively for each rate of lime after 1 year. Soil exchangeable aluminium (Al) levels measured in November 2003 were above the critical level of 3 μg g–1, where root growth is restricted, on the north‐steep and south‐steep sites (4.48 and 5.23 μg g–1), just above on the south‐easy site (3.02 μg g–1) and below on the north‐easy site (1.45 μg g–1). At the north‐steep and south‐steep sites, soil Al was reduced below the critical level at rates of 0.5 and 1.0 t lime ha–1 and higher, respectively. There was no significant response in dry matter (DM) yield to lime measured at any site in Year 1 (December 2000‐November 2001), or for the north‐easy and north‐steep sites in Year 2 (December 2001‐November 2002) or Year 3 (December 2002‐November 2003). Lime had no significant effect on legume cover (19–61% in any one year) on the north‐easy site. Lime increased legume cover in years 2 and 3 (14–56%) on the north‐steep site. In Years 2 and 3, there was a significant DM yield response levelling off at 1.0 t lime ha–1 on both the south‐easy and south‐steep sites. On the south‐easy site, there was a significant response in legume cover to 0.5 t lime ha–1 and greater in Year 2, and 4.0t lime ha–1 and greater in Year 3 while on the south‐steep site there was a significant response in Year 2 to 1 t lime ha–1 and greater and in Year 3 to 2 t lime ha–1 and greater. Where a south aspect and easy slope favours legume growth in dry hill country, low rates of lime (1t ha–1) can result in a worthwhile pasture yield response, especially where soil Al levels are greater than 3 μg g–1.