Effects of rate and time of nitrogen application on growth, leaf nutrient contents and yield of sugarcane at Kilombero sugar estates

A field study on the effects of rate and time of nitrogen fertilization on growth, leaf nutrient contents and yield of sugarcane (Saccharum officinarum) variety N. Co.376 was conducted at Kilombero Sugar Estates in Morogoro region during the 1982/83 cropping season. Four rates of N and three different times of application were tested in factorial combination in a randomized block design using a plant cane crop. The N rates wete 0. 100. 200 and 300 kg N/ha applied as ammonium sulphate. The times of application were (i) all the N applied at planting, (ii) all the N applied at three months, and (iii) N applied in two split dose: one half at planting, and the rest at three months. The crop was grown for twelve months. The germination, stalk population counts, and the heights of the plants were determined. The N, P, K, Ca and Mg nutrition of the crop wete assessed by analysing cane leaves sampled from two-and four-months old plants. The yield and quality of the crop were determined at harvest time. The germination was good and was not affected by the treatments. Nitrogen fertilization increased stalk population, and cane growth significantly. Nitrogen application increased the concentration of N in the leaves sampled at the two ages. For the two months samples the leaf N concentration ranged from 1.87% to 2.29%, while for the four months samples the concentration ranged from 1.38% to 1.94%. Leaf N concentrations in the four months old plants were highly correlated with sucrose contents in the plants cane yield and sugar yield suggesting that leaf N concentration could be used predicting concentration sugar yield a of 1 .78%was established. The concentrations of P, K Ca, and Mg were considered to be within the adequate range for the crop. All rates of N increased cane yield significantly but sugar yield increased with increase in applied N only up to 100 kg N/ha. Further increase in N did not cause further increase in sugar yield mainly because of the negative effect of higher rates of N on sucrose accumulation in cane plants. In addition, nitrogen application reduced the quality of the juice; i.e. the brix, pol and juice purity. Time of application did not have any significant effect on any of these parameters. The results of the study suggest that the optimum rate of N for sugar production in Ruaha area of Msolwa Estate is around 100 kg N/ha and that all the N can be applied in the furrows at planting. Also leaf analysis technique can be used for assessing the sufficiency of N in cane plants.