Yield and Quality of Ratoon Sugarcane Are Improved by Applying Potassium under Irrigation to Potassium Deficient Soils

The current study was carried out at the experimental farm of Rana Sugars Ltd., Buttar Seviyan, Amritsar, Punjab, India, to identify methods to improve the yield and quality of ratoon sugarcane in potassium-deficient soils. The treatments comprised two levels of irrigation, resulting in plants which either received sufficient water (I-1) or were water-stressed (I-2), and four rates of potassium (K) application: 0 (K-1), 40 (K-2), 80 (K-3) and 120 (K-4) kg K2O ha(-1). The results showed that the irrigation levels did not influence crop parameters significantly, although all parameters presented higher values for I-1-treated plots. Compared to the K-1 (i.e., 0 kg ha(-1) K fertiliser applied) treatment, the K-2,K- K-3 and K-4 treatments yielded 11.16, 37.9 and 40.7%, respectively, higher millable canes and 1.25, 5.62 and 13.13% more nodes per plant, respectively. At 280 days after harvest of the first (plant) crop, the I-1 treatment provided ratoons which were up to 15.58% higher than those obtained with the I-2 treatment, with cane girths up to 7.69% wider and yields up to 7.29% higher than those observed with the I-2 treatment. While the number of nodes per plant did not differ significantly between treatments, there were significant differences in other parameters. Quality parameters (with the exception of extraction percentage) were significantly enhanced by the K-3 treatment. The benefit-to-cost ratio (B/C) was higher for the I-1 treatment than for the I-2, due to a reduced productivity associated with the I-2 treatment. At both irrigation levels, the K-3 treatment resulted in the highest quality parameters. K-1-, K-2- and K-4-treated plots presented more instances of insect infestations than plots receiving the K-3 treatment. Relative to the K-3 plots, infestation by the early shoot borer (Chilo infuscatellus) was 18.2, 6.0 and 12.2% higher, respectively, in plots that underwent the K-1, K-2 and K-4 treatments, while infestation by the top borer (Scirpophaga excerptalis) was 21.2, 9.21 and 14.0% higher, and that by the stalk borer (Chilo auricilius) was 10.7, 0 and 8.10% higher. Not all infestation differences between treatments were significant. Our research demonstrates that growing sugarcane in potassium-deficient soils with applications of 80 kg K2O ha(-1) under irrigation should be recommended to increase yield and quality while minimising insect infestation and to implement sustainable ratoon sugarcane production.