Fertilisers for lotus and clover establishment on a sequence of acid soils on the east Otago uplands

Abstract

Abstract Results of 5 trials investigating the effect of phosphorus, sulphur, and lime on Maku lotus and clover yields during the first 3 years after plant establishment are presented. The trials were located on upland yellow‐brown earths and podzolised yellow‐brown earths (Cryochrepts and a Placaquept), forming an altosequence between 750 and 1 160 m, in which soil pH decreased and rainfall increased with altitude. Lotus and clovers both responded to applied sulphur on all sites. Strong responses to phosphorus were recorded at all sites after corrections had been made for sulphur deficiency and limitations of soil acidity. Responses to lime were related to soil pH. Lotus showed no response to broadcast lime except on the most acid site (topsoil pH 4.4). Clover responses to lime ranged from 42–48% (on sites of pH 5.2‐4.8) to 93–470% (on sites of pH 4.6‐4.4). In Year 1, yields were very low at all sites and trials were not harvested. The highest mean annual yields in Years 2 and 3 were less than 3 000 kg/ha. With adequate fertilisers, clover yields exceeded Maku lotus yields on sites above 1 000 m altitude (topsoil pH 4.6 or lower), but on sites at 855 and 760 m (pH 4.8 and 5.2 respectively) lotus yields exceeded those of clovers. Despite the severe phosphorus deficiency of all sites, phosphorus requirements of legumes were moderate. An initial phosphorus application of 20 kg/ha followed by 10 kg/ha annually gave over 60% of maximum clover yield on the sites where clover outyielded lotus, and over 90% of maximum lotus yield on the sites where lotus outyielded clover. As soil acidity and organic matter content of topsoils increased, clover treatments without applied gypsum showed an increasing response to lime. This was interpreted as being the result of lime‐induced sulphur mineralisation. This interpretation was supported by a significant increase in topsoil sulphate levels on limed treatments not receiving gypsum in Trial 1.