Comparison of split nitrogen appliacation strategies in leek (Allium porrum) to reduce N fertilization on sandy soils in the Netherlands

High nitrogen (N) fertilization to maximize production of leek (Allium porrum L.) combined with low N recovery can lead to considerable nitrogen pollution of the environment. A field trial was conducted in 2002 and 2003 on a sandy soil in the Netherlands. To synchronize N supply and N demand, two strategies of sequential split nitrogen application (SNA) were compared: 1) SNA-soil: in which the split N applications are the difference between standardized crop demand and the available amount of mineral N in the soil for each period; 2) Crop Scan method: in which the split N applications are derived from comparing the actual crop nitrogen status to the desired nitrogen status, using crop reflectance measurements and a crop growth model. Total fertilizer application according to Crop Scan method in 2002 saved 65 kg N ha-1 compared to recommendation of SNA-soil, maintaining maximal production. In 2003 the total N application of SNA-soil and Crop Scan were respectively 95 and 113 kg N ha-1, whereas a N application of 45 kg N ha-1 was sufficient. The Crop Scan method overestimated the N application needed in 2003 because it did not account for the high mineral N content in the soil. SNA-soil overestimated the N application needed in autumn in both years. Combination of Crop Scan measurements, to assess plant N need, and soil N analysis may cover the flaws, which each method separately showed.