Model calculations of nitrate leaching during the growth period of potatoes.

To estimate the amount of nitrate lost due to leaching during the growth period of potatoes and the amount of mineral nitrogen present in the soil at harvest time, i.e. residual mineral nitrogen, calculations were performed with a previously derived simulation model for the response of potatoes to nitrogen. In the calculations those factors were varied that were considered to affect the amount of nitrate lost due to leaching: precipitation in spring and summer, soil type, mineralization rate of soil organic matter, and amount of fertilizer nitrogen applied. It was calculated that the total loss of nitrogen, i.e. the amounts leached in spring plus the amounts accumulated as residual soil mineral nitrogen, were similar in a loamy sand and a clay loam. The greater loss by leaching from the sand was offset by the greater accumulation of mineral nitrogen in the loam. Under normal conditions of precipitation and mineralization the total loss increased from about 20 kg N/ha at a fertilizer nitrogen application rate of 200 kg N/ha to about 190 kg N/ha at a rate of 400 kg N/ha. At a high rate of mineralization, an application as low as 100 kg fertilizer N/ha resulted in a total loss of about 60 kg N/ha. It was concluded that little nitrate leaching occurs when the current nitrogen fertilizer recommendations are followed, provided that mineralization in the soil proceeds at an average rate. When high mineralization rates are likely to occur, however, the recommendations should be lowered. (Abstract retrieved from CAB Abstracts by CABI’s permission)