Sodium deficiency in sheep pastures : A dissertation submitted in partial fulfilment of the requirements for the Degree of Bachelor of Agriculture Science with Honours at Lincoln University

Abstract

Sodium (Na) is not essential for plant growth however it is required by grazing ruminants. Natrophobic species are usually deficient for animal nutrition (<0.10% Na) while natrophiles have adequate Na contents except for location induced deficiencies.

Samples of common pasture plants were collected from pastures south of the Rakaia River (0 to 110km from the coast) to measure Na content in relation to proximity to the coast. This showed that coastal sea spray increased Na content by up to 600% within 200m of the coast and continued to have an effect up to 40km inland. Further inland from this, the average Na contents decreased slowly, probably due to increasing rainfall and negligible atmospheric salt. Browntop and cocksfoot were deficient from 5 and 20km inland respectively while ryegrass and white clover were both marginal (approximately 0.10%.Na) from 40km and 80km inland respectively.

A march grazing experiment at Ashley Dene investigated the effectiveness of sowing Na rich chicory, plantain and white clover alongside a stand of natrophobic lucerne with the aim of increasing the average Na content of the herbage on offer to sheep. Lambs fed 70% lucerne and 30% Na rich species grew faster (75g/hd/d) than lambs fed lucerne only (20g/hd/d) and lucerne plus a salt lick (26g/hd/d). However, the lucerne was droughted and mature (50% flower) with leaf Na levels of 0.10 to 0.15%. Therefore, none of the trial groups were deficient in Na and the liveweight gain differences were most likely due to the superior feed quality of the Na rich species compared to mature lucerne. The Na content of rapidly growing lucerne was 0.03 to 0.05% in spring 2002. The autumn and spring Na contents of chicory (0.74% and 0.35% respectively), plantain (0.60 and 0.58%) and white clover (0.24 and 0.14%) indicated that mixtures of these species with natrophobic forages/ pastures can produce swards with adequate, average Na levels.

Further replicated experiments on Na deficient luceme are necessary to investigate the effectiveness of supplementing with Na rich species. More work is also required to predict environmental influences on plant Na content.