Adequate N management is one of the most important factors required to obtain high yields(Fig. 7) of excellent quality potatoes. An adequate early season N supply is important to support vegetative growth.
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.