Effect of superphosphate with and without nitrogen on grain yield, grain size, nitrogen, phosphorus, and sulphur concentrations, and baking quality of ‘Karamu’ wheat

Abstract

The effects of superphosphate rates up to 1000 kg/ha with and without 56 kg/ha nitrogen (N) on the yield, grain size, nutrient concentration, and baking quality of ‘Karamu’ wheat were investigated on blocks which has previously grown three - seven wheat crops. ‘Karamu’ grown on land which had had seven previous wheat crops compared to three previous crops, gave lower grain yields but no change in grain weight or % N concentration. There was a small drop in bake score and an increase in the % phosphorus (P) and % sulphur (S) concentrations in the grain grown on land which had had a greater number of crops. There was no significant interaction between years in wheat and the fertiliser treatments. Grain yield increased with superphosphate rates up to 500 kg/ha but 90% of the maximum grain yield was produced at 250 kg/ha. There was a large response to N. Grain weight was increased by superphosphate additions but reduced by N. Superphosphate increased the P, N, and S grain uptake particularly with added N, but it reduced the N concentration in the grain, reduced the N: P ratio, and had no effect on the S concentration and the N: S ratio. The S concentration was influenced more by the background effect of the number of previous wheat crops than by the fertiliser applied. The bake score of ‘Karamu’ was improved by addition of N but was markedly depressed by addition of superphosphate with and without N, changing the wheat quality from acceptable to unacceptable. Bake score was highly correlated with fertiliser treatments. Although across-treatment relationships were established with N, P, grain weight, and the N: P ratio, no within-treatment relationships were found. No relationship was established between bake score and grain S concentration even though it was in the deficient range. These results provide some possible explanation for the wide variation in bake score found in commercial samples of ‘Karamu’ wheat.

Keywords:

• wheat
• baking quality
• superphosphate
• nitrogen
• sulphur
• phosphorus
• fertiliser
• grain yield
• bake score