Fertiliser requirements of luceme cut for hay in northern Southland

Abstract

Three field trials were laid down, on established luceme (Medicago sativa L.) stands and continued for 2,3 or 4 years. On two sites fertilisers applied were potassium chloride (0 and 200 kg/ha) and single superphosphate (0,200.400 and 800 kg/ha), while on the third site potassium chloride (0, 100 and 200 kg/ha), sulphur (0,25,50 and 100 kg S/ha as gypsum) and phosphorus (0,18,36 and 72 kg P/ ha as monocalcium phosphate) were applied. Lucerne was harvested at the hay stage with 2 or 3 cuts per year. Consistent annual yield responses to 200 kg/ ha of potassium chloride application occurred at all sites. At the site where 100 kg/ha was applied it produced about 95% of maximum yield but nil K gave 8594% of maximum yield. Responses to superphosphate treatments were recorded at two sites with the major response considered to be due to phosphorus. 200 - 400 kg/ha of superphosphate was sufficient for near maximum response. Response to both phosphorus and sulphur occurred at site 3 with 18 kg/ha phosphorus and 25 kg/ha sulphur being sufficient for near maximum response. Results indicate that a soil P test of 13 and K test of 6 should support approximately 95% of maximum yield. Herbage P and S concentrations associated with near maximum yields were slightly higher than indicated in current standards for plant analysis interpretations, but K concentrations agreed with current standards. Maintenance fertiliser requirements derived from this trial series are similar to those predicted from AgResearch's fertiliser recommendation models. Keywords Medicago sativa, potassium, phosphorus, soil test, plant analyses, sulphur, fertiliser