A successful fertilizer program helps provide top yields of high quality potatoes while maximizing returns on fertilizer investment. As fertility programs become more specialized, one factor which cannot be overlooked is the source of nitrogen in the fertilizers applied to the crop. In general, the nitrogen source used in potato fertilizer is not critical in the overall effectiveness of the fertilizer. There are, however, some differences in the way various nitrogen sources behave in the soil and knowledge of these differences can be useful.
Plants use only the nitrate form directly.
However, nitrogen supplied in the ammonium form is converted to the nitrate form by soil micro-organisms during the growing season. If only the nitrate form of nitrogen is taken up by plants, one might logically expect that fertilizers containing only nitrates would be preferable. This is not normally the case, however, because nitrates are also highly subject to leaching losses. If only nitrate-nitrogen were applied in the spring and heavy rains occurred before the nitrogen is taken up by the plant, substantial nitrogen losses could occur resulting in crop deficiencies. An ideal nitrogen program is one that employs both ammonium and nitrate sources which, in turn, provides a steady and adequate supply of nitrate-nitrogen to the growing crop.