Potassium requirements of pasture on pumice soils

Abstract

Abstract On pumice soils at Mamaku near Rotorua (initial quick test (QT) K 4) and Pouakani near Whakamaru (initial QT K 2), pasture yield responses to applications of 0, 75, 150, 300 and 600 kg K/ha/yr (all as three equal split applications) plus 300 kg K/ha/yr applied once in the spring were measured for 3 years. There was a significant total pasture dry matter (DM) response to up to 150 kg K/ha/yr at Mamaku in two and to 75 kg K/ ha/yr in one of the first three years, but no significant difference (P<0.05) between 300 kg K/ha/yr applied once or as split applications. The contribution of clover to DM yield was increased significantly by up to 75 kg K/ha/yr in the second year and 150 kg K/ha/yr in the third year. In the fourth year when a common rate of 130 kg K/ha was applied to all of the K plots, there was a significant pasture and clover DM contribution response up to the previous 300 kg K/ha/yr at Mamaku. At Pouakani there was a significant pasture yield response to up to 300 kg K/ha/yr in the second and up to 75 kg K/ha/yr in the third year. There was no significant difference in pasture yield between a single spring application and three split applications of 300 kg K/ha/yr. Clover contribution to DM yield was increased significantly by up to 300 kg K/ha/yr in all of the first three years. In the fourth year, there was no significant difference in pasture DM yield between previous K treatments, but a carryover effect on clover contribution to pasture DM yield. Pasture relative yield (RY) was lower than the average derived from other trials on pumice soils at the same soil QT K levels and nearmaximum pasture yield (97% RY) was achieved at a lower soil QT K level (3-4) for these sites than for the overall average (5) . It was concluded that at these low QT K levels, high rates of K are required for maximum pasture production on pumice soils but these may not be economic. These higher rates of K increased soil QT K levels above the target range for near-maximum pasture production (7-10) at the end of the growth season, only for it to drop to below this range by the next spring because of high winter leaching rates. Therefore on those pumice soils where it is difficult to achieve the target range for soil QT K, it is recommended that K be applied at least three times in a growth season to ensure an adequate supply from fertiliser. Potassium requirements of pasture on pumice soils J. MORTON1, A. STAFFORD2 and M. HAWKE3 1 Ballance Agri-Nutrients, PB 2290, Hastings 2 Ballance Agri-Nutrients, PB 12503, Tauranga 3 MFH Consultancy, RD 4, Rotorua jmorton@ballance.co.nz Keywords: pasture yield response, potassium, soil quick test potassium, pumice soils