Temperaturesum - start application ?

Through the temperaturesum, T-sum, the optimum moment to start the first fertilizer application can be determined. On this page you can view the actual average T-Sum for the Netherlands. As soon as a value of 450 has been reached the moment for the first application is there.
More detailed T-sum information can be found at the website of Lumbricus

T-sum When to start with the first application
Lumbricus soil en plant growth