Soil Nitrogen Supply (SNS) is a measure of the nitrogen (N) available to the crop from the soil. The N fertilisation rate for a crop can be calculated as the difference between the total N requirement for the crop and the SNS. SNS includes a) the soil mineral N, b) the potential N that may continue to be mineralised, c) the amount of N already capatured by the growing crop. Estimates of crop N uptake should occur at the time when soil mineral and potentially mineralisable N are estimated. Methods include the following: 1) Estimating crop N uptake using plant biomass. This can be performed by either estimating the number of shoots/m2 or the Green Area Index (GAI). 2) Measuring crop N uptake using commercial lab analysis. A quadrat can be used to collect a known area of plant material to convert the N concentration to kg N/ha. 3) Remote sensing based estimations of crop N uptake using satelite data or drone data. Several online platforms or apps provide biomass imagery, and someprovide an estimation of crop N content. In each case it is important that estimates of crop N uptake are added to estimates of SMN and further potential mineralisable N to calculate SNS.