Potato (Solanum tuberosum L.) has high phosphorus requirement for optimum growth and yield. Thus, under
P deficiency, growth and yield are considerably reduced. An experiment was conducted in a controlled growth
chamber on the effect of P supply on morphological and physiological plant parameters of three potato genotypes
having contrasting P efficiency. The genotypes were CGN 17903, CIP 384321.3 and CGN 18233. They
were grown under two P levels [100 mg P kg-1 soil (low P) and 700 mg P kg-1 of soil (high P)]. Treatments were
arranged in a completely randomised block designs with six replications. Low P supply reduced shoot dry matter
yield, relative growth rate, leaf number, whole plant relative leaf expansion rate, total leaf area per plant, plant
height and net assimilation rate of P-inefficient genotype, more than that of the P-efficient genotypes. However,
low P supply did not affect net photosynthetic rate per unit leaf area, leaf dark respiration rate, chlorophyll
fluorescence rate and electron transport rate of both P-efficient and inefficient genotypes. P-efficient genotype
CGN 17903 allocated more dry matter yield to the leaf which might have enabled higher light harvesting, hence
contributing to high biomass accumulation of this genotype.
Total N uptake for potato crops in southern Idaho usually ranges from about 150 to 250 lb N/acre, depending on cultivar and yield potential. At harvest, about 60-65% of the total plant N is contained in the tubers, while about 30% remains in the vines. During tuber bulking, potato plants require about 2.0 to 3.0 lb N/acre/day depending on tuber growth rate.
About 60% of the seasonal N requirement is taken up by 75 days after planting. Consequently, adequate N must be available to the crop early in the season to allow for sufficient canopy development. Research shows that about 150-180 lb N/acre from soil and fertilizer sources is required by the time the rows begin to close to provide for optimum canopy development and yield. However, excessive N availability prior to tuber initiation can delay tuber bulking by up to 2-3 weeks, reducing tuber yields by as much as 80-120 cwt/acre. Excessive early-season N can also increase the susceptibility to brown center and hollow heart. Excessive late-season N applications usually reduce specific gravity and skin set, and increase the potential for nitrate leaching.