The response of Italian ryegrass to sodium, lime and potassium on an acidic Natal soil

Abstract

Unless corrected, soil acidity and K deficiency frequently limit growth of intensive temperate pastures on highly weathered soils in South Africa. A field trial, with Italian ryegrass (cv. Midmar), was established on a Himeville sandy clay loam (typic Hapludox) for two seasons to test the possibility that Na applications could assist in the correction of these problems. Four levels of Na, lime and K were applied in an unreplicated 4³ factorial design. Significant responses to all treatments were recorded. In the first season, the response to 200 kg ha⁻¹ Na as NaCI was 1526 kg dry matter ha⁻¹: Sodium responses were possibly due to enhanced P uptake, or Na substitution for K, or a combination of the two mechanisms. No consistent lime × Na interaction was observed. The need for continual monitoring of K levels in intensively used pastures was highlighted. Also shown was the important effect of K and Na on the mineral balance of the herbage produced: Potassium depressed herbage Ca, Mg and Na concentrations, and Na depressed herbage Ca and Mg where herbage K was low, but had no effect on herbage K. Where soil P and K reserves are marginal, production of ryegrass pastures in the cool part of the season may benefit from Na applications.