Whilst many farms create a nutrient management plan, checking its appropriateness and adjusting the plan is also necessary to avoid sub-or-super optimal nutrient applications, causing unnecessary costs, pollution and compromised production levels. Checking (i.e. observations or sensing of crop structure and colour) is most important as rapid growth begins, and nutrient uptake becomes greatest. Checking allows a manager to determine whether their plan is working for each crop. Observations may include plant or shoot density, ground cover, height, and leaf colour. Additionally, crop analyses can diagnose in-season nutrient deficiencies. Hand-held, tractor-mounted or satellite-bourn sensors may use spectral reflectance indices to build a picture of the crop, gauge its nutrient requirements and inform adjustments to initial plans. Amendments may be required to rates or timings of nutrient applications to accomodate recent effects of weather and soil conditions on growth, nutrient uptake and crop potential. Adjustments to the plan such as a reduced nitrogen rate must ultimately be checked through the final step of Crop Nutrition Management: Reviewing.