EEUU: Learn potato-nutrient management

Because of an extensive nutrient requirement and a relatively shallow root system -- most roots are within the top foot -- the crop is often responsive to applied nutrients, particularly the three primary macronutrients, which are nitrogen, phosphorus and potassium.

Nutrient management research throughout the years has provided some insight into optimizing nutrient inputs to enhance yields and minimize losses to the environment. More recently, improving soil health in potato cropping systems has also been a focus.

There are several strategies available to increase nitrogen use efficiency. Of all the essential nutrients, nitrogen is the one most often limiting for potato production. It is also susceptible to leaching losses as nitrate under conditions of excessive rainfall or unpredicted rainfall following irrigation. There are several strategies that can be used to improve nitrogen use efficacy by potato.

The first is to select a realistic target nitrogen rate. Then, split applications to meet the demands of the crop. That means applying the bulk of the nitrogen at emergence and beyond. The fastest rate of nitrogen uptake occurs between tuber initiation and initial tuber bulking. Depending on cultivar, that can occur between 20 to 30 days after emergence.

Enhanced efficiency fertilizers such as polymer-coated urea or urea coated with nitrification inhibitors applied at emergence can extend nitrogen availability through the bulking period. The benefits of enhanced efficiency fertilizers primarily occur during seasons with excessive rainfall.

To determine nitrogen needs during the growing season, petiole nitrate analysis remains the most sensitive tool. Periodic testing of petioles from tuber initiation through the bulking period is recommended. If petiole nitrate decreases to less than the critical level when conditions are conducive for tuber bulking, application of soluble nitrogen via fertigation is suggested.

Current research is evaluating the use of remote sensing with drones to schedule nitrogen applications. The advantage of remote sensing is that spatial variability in nitrogen status within a field is more easily determined than with spot checking of petioles.

Fumigation increases nitrogen use efficiency but does not change the optimal nitrogen rate. Soil-borne diseases such as Verticillium wilt and root knot nematodes can limit potato root health and the ability to take up nutrients. A short-term fix to those diseases is to use fumigation such as Vapam or Chloropicrin. Research has found that if soil-borne diseases are present at high levels in a soil, the use of fumigation can increase nitrogen use efficiency but does not significantly affect the rate of nitrogen required to optimize yields. At the recommended nitrogen rate of 240 pounds of nitrogen per acre for Russet Burbank, nitrogen uptake in fumigated plots increase by 50 pounds of nitrogen per acre over non-fumigated plots, indicating that there is better use of applied nitrogen and potential for less leaching with fumigation. Unfortunately, the effects of fumigation are short-lived, and repeated use of fumigation is necessary during the years potatoes are grown. Current research is evaluating the use of cover crops, composted manure and biofumigation using mustards to reduce or use in combination with chemical fumigation.