Differential response of short- and long-duration cassava cultivars to applied mineral nitrogen

The differential response of two contrasting cassava cultivars to different rates of soil-applied nitrogen (N) on the number of tuberous roots, harvest index, yield, nitrogen uptake, and fertilizer-nitrogen-use efficiency was studied over a period of 2 years on a typic Plinthustults in Kerala state in Southern India. The experiment was laid out in a split-plot design with two popular cultivars of cassava, namely Sree Vijaya (6 months) and M-4 (10 months) in the main plots, and eight urea-N rates (0, 12.5, 25, 50, 75, 100, 150, and 200 kg ha⁻¹) in subplots. Half of the N was applied at the time of planting and the other half 60 d later. The study revealed significant differences between the two cultivars regarding their response to fertilizer-N application. The tuberous-root yield of the short-duration cultivar Sree Vijaya increased significantly up to 100 kg N ha⁻¹ whereas the yield of the long-duration cultivar M-4 increased significantly only up to 50 kg N ha⁻¹ rate. Also the N-use-efficiency parameters (i.e., agronomic, recovery, and physiological efficiencies) were higher in Sree Vijaya than in M-4 but declined at N rates beyond 100 kg ha⁻¹. The more efficient N use in the short-duration cultivar was associated with a higher N uptake and a more efficient internal use.