Using Reflection Measurements and Modeling to Minimize N Application in Potatoes.

The application of N on potatoes in The Netherlands is often higher than is necessary to achieve maximum physical or economic yield. We investigated whether reduction in N use can be achieved by splitting the N dose and calibrating the second application to crop N status. Data from several years of experiments show that actual N uptake can be estimated by means of reflection measurements. This provides a basis for adjusting the second application of N. The simplest model to determine the size of the second application considers only the difference between actual N content at canopy closure and a single target N content at that time. Application of this model resulted in savings of up to 35-40 kg N ha^-1 yr^-1. A more detailed model may additionally consider the period before canopy closure and the effects it has had on crop and soil conditions. We discuss the advantages and disadvantages of various models when used to calibrate N application to potatoes.