Excessive soil N, applied late in the season delays maturity of the tubers and result in poor skin set, which harms the tuber quality and storage properties. Potatoes are a shallow-rooted crop, generally growing on sandy, well-drained soils. These soil conditions frequently make water and N management difficult since nitrate is susceptible to leaching losses. On these sandy soils, it is recommended that potatoes receive split applications of N during the growing season. This involves applying some of the total N requirement prior to planting and applying the remainder during the season with side-dress applications or through the irrigation system by Nutrigation™ (fertigation).
The period of highest N demand varies by potato variety and is related to cultivar characteristics, such as root density and time to maturity. Petiole analysis during the growing season is a useful tool, allowing growers to determine the N status of the crop and respond in a timely manner with appropriate nutrients.
A balanced ammonium / nitrate ratio is very important at planting time. Too much ammonium-nitrogen is a disadvantage as it reduces root-zone pH and thereby promotes Rhizoctonia disease. Nitrate-nitrogen enhances the uptake of cations such as calcium, potassium and magnesium, required for elevated specific gravity values.