An additional tool that can be used for long season crops such as eggplant, pepper, potato, tomato, squashes, sweet corn, and pumpkin is plant tissue analysis. While leaf tissue laboratory analysis can be used to verify symptomatic deficiencies in any nutrients, it can also be used to detect sufficiency levels of critical nutrients such as N, P, K, Ca and Mg. If performed early enough in the season, corrections can be made by topdressing, side dressing, or fertigation. Prior to making nutrient corrections, other potential issues should be addressed first, such as incorrect pH, inadequate soil moisture, root disease or insect infestation. Leaf tissue analysis requires collecting an adequately sized sample (from all over a planting) of whole leaves from designated locations in the plant canopy. These locations vary among crop species and specific sampling and handling instructions are available from university and private laboratories. For the purpose of comparison, laboratory reports will also present results in tabular form alongside reference sufficiency ranges of nutrient concentrations for the crop tested. Nutrient status of some crops can also be determined using laboratory testing of whole leaf petioles, and for nitrate-N and K, it is possible to test petiole sap in-field using a portable meter.