Response of potato to potassium fertilization and growth retardants under short day conditions

Abstract:

While nitrogen receives the bulk of attention in potato nutrition research, potassium quietly governs tuber bulking rate, dry matter partitioning, and post-harvest quality—yet it is often under-applied in tropical short-day production systems. Simultaneously, excessive vine growth under warm, humid conditions diverts assimilates away from tubers, reducing harvest index. This research examined the interactive effects of four potassium levels (0, 75, 150, and 225 kg K₂O ha⁻¹) and three growth retardant treatments (control, chlormequat chloride at 1,500 ppm, and paclobutrazol at 100 ppm) on growth, tuber yield, and quality of potato cultivar Diamant under short-day conditions at Can Tho, Vietnam. The experiment followed a factorial randomized block design with three replications during the winter 2022-23 season. Potassium at 150 kg K₂O ha⁻¹ combined with paclobutrazol produced the highest marketable tuber yield (28.7 t ha⁻¹), 43.6 percent above the zero-K control without retardant. Paclobutrazol reduced plant height by 18.3 percent and increased the tuber-to-shoot dry matter ratio from 2.8 to 4.1. Tuber dry matter content peaked at 21.4 percent under K₁₅₀ + paclobutrazol, whereas tubers from the zero-K control contained only 17.8 percent dry matter. Potassium uptake was 38.7 percent higher when K₁₅₀ was paired with paclobutrazol compared to K₁₅₀ alone, suggesting that retarded vine growth redirects nutrient absorption toward tubers. These results indicate that moderate K fertilization combined with a growth retardant spray at 40 days after planting can markedly improve tuber yield and quality in short-day tropical potato production.