Potassium and Water-Deficient Conditions Influence the Growth, Yield and Quality of Ratoon Sugarcane (<i>Saccharum officinarum</i> L.) in a Semi-Arid Agroecosystem

Groundwater and soil potassium deficiencies are present in northern India. Sugarcane is a vital crop in the Indian Punjab; it is grown on approximately 91,000 hectares with an average yield of 80 tonnes ha⁻¹ and a sugar recovery rate of 9.59%. The role of potassium (K) fertilizer under both sufficient and deficient irrigation in ratoon sugarcane crops is not well documented. We conducted a split-plot ratoon cane experiment during 2020–2021 at the Gurdaspur Regional Research Station of Punjab Agricultural University, India, on K-deficient soils. Main treatments were fully irrigated (I₁) and water stressed (I₀) conditions, with sub-treatments reflecting K fertilizer application rates of 0 (M₁), 67 (M₂), 133 (M₃), and 200 (M₄) kg K ha⁻¹. The ratoon sugarcane performance was assessed in terms of growth, productivity, sugar quality and incidence of key insect pests. At harvest, trends in the growth and yield parameters in I₁ were improved over the I₀ treatment, with cane height (+12.2%), diameter (+3.3%), number of internodes (+5.4%), biomass yield (+7.6%) and cane yield (+5.9%) all higher, although little significant difference was observed between treatments. Ratoon cane yield under irrigation was 57.1 tonnes ha⁻¹; in water-stressed conditions, it was 54.7 tonnes ha⁻¹. In terms of sugarcane quality parameters, measured 12 months after harvesting the initial seed crop, values of Brix (+3.6%), pol (+3.9%), commercial cane sugar percentage (+4.0%) and extractable sugar percentage (+2.8%) were all higher in the irrigated treatments than the water-stressed plot. Irrigated treatments also had a significantly lower incidence of two key insect pests: top borer (<i>Scirpophaga excerptalis</i>) was reduced by 18.5% and stalk borer (<i>Chilo auricilius</i>) by 21.7%. The M₃ and M₄ treatments resulted in the highest cane yield and lowest incidence of insect pests compared to other K-fertilizer treatments. Economic return on K-fertilizer application increased with increasing fertilizer dosage. Under the potassium-deficient water-stressed conditions of the region of north India, a fertilizer application rate of 133 kg K ha⁻¹ is recommended to improve ratoon sugarcane growth, yield, and quality parameters and economic returns for sugarcane farmers.