Nitrogen Requirements of Potatoes

Nitrogen fertilizer applications, for maximum fertilizer efficiencies and crop yields, should be based on the N required by the crop during its various growth stages. The objectives of this paper were to identify the N requirements of the potato plant (Solanum tuberosum L.) during growth and to evaluate selected soil and plant tissue tests as indicators of the plant's N status. Growth analysis data and soil and petiole NO3-N concentrations were obtained at predetermined time intervals from N fertilization treatments in replicated field studies on a coarse-silty mixed, mesic Durixerollic Calciorthrid soil. Maximum early tuber growth occurred when leaf area index was between 2.5 and 3.2 and the tops contained between 79 and 100 kg N ha-1 at the start of linear tuber growth. A preplant N fertilizer application between 67 and 134 kg ha-1 gave these characteristics under the experimental conditions. The maximum dry matter production rate per day (approx. 250 kg ha-1) occurred when there was between 80 and 140 kg N ha-1 in the plant tops and roots. An average tuber growth rate of 0.75 Mg ha-1 day-1 required a N uptake rate of 3.7 kg ha-1 day-1 to prevent the loss of N and dry matter from the tops and roots. Sufficient N was available for this rate when the soil NO3-N concentration was > 7.5 mg kg-1 (0.46-m soil depth), corresponding to 15 000 mg kg-1 NO3-N in the fourth petiole. Soil and petiole NO3-N concentrations may be used to adjust the N fertilization rates during the growing season. This practice has the potential of increasing the overall N fertilizer use efficiency and final tuber yields within the climatic, disease, and variety limitations