Soil testing to a depth of 60 cm. in the spring is critical to planning an effective and efficient N management program. Post-harvest soil samples may help growers to select succeeding crops, which will make maximum use of the residual N after the potato crop.
The nitrogen demand by the crop during tuber bulking may be 2.2 to 3.0 kg/ha/day. Petiole nitrate sampling allows for in-season monitoring of the crop’s nutrient status. Collecting the 4th petiole from 30 – 50 randomly selected plants throughout the field (Fig. 10) is recommended. Tissue samples are often collected weekly to track changes in nitrate levels, and to plan supplemental fertilizer applications, should levels drop below optimum.
Critical petiole nitrate-levels decline as the potato crop develops and matures. Generally, petiole nitrate-N levels at tuber bulking are 15,000 ppm = sufficient. (Fig. 11)