Nitogen is a difficult element to fertilize for because of its movement from and to different pools in the environment. Tissue analysis has been used sucessfuly to prdict nitrogen need in several crops including sugar beets, potatoes onions and wheat. There are many other crops where tissue analysis has been used to more efficiently apply N. Wheat total nitrogen analysis has been used as a protein predictor and as well as an estimate of how much N needs to be added in order to get a desired protein level at harvest. Post harvest N analysis can be used as N adequacy test in wheat. The easiest and most transient measurement to make in plants is nitrate. Nitrate in plant tissue can be used to estimating supply and adjust fertilizer rate. Petiole analysis in potaoes has been used to indicate supply and adjust fertilizer rates. Nitrate in onion roots is a more recent management tool used to manage fertilizer rate.