Objective 1: Leaf nutrient thresholds The complete data from the quarterly field survey over three years in three citrus growing regions have been collated and checked. Final analyses are underway, including the Diagnosis and Recommendation Integrated System (DRIS) method for leaf nutrient analysis that provides protection from cross-correlation of variables and environmental effects. Objective 2: Determine soil conditions that favor root hair and VAM proliferation Starting in July, new seedling Carrizo plants were established for use. Six weeks after germination, 27 uniform seedlings were selected and divided into 3 hydroponic tanks (9 seedlings each). Tank 1, is a control fertilizer mix, including all nutrients and pH adjusted to approximately 7.0. Tank 2, is a reduced Phosphorus fertilizer, similar to Tank 1, except it has no soluble phosphorus and Triple Calcium Phosphate added as the sole source of phosphate. The pH of Tank 2 is approximately 7.2 (unadjusted). Tank 3, is the same as Tank 2, except we have added CaCO3 to the mixture to increase the pH (approximately 7.8) of the solution and reduce the amount of available phosphorus. Tank 3 is a replicate from the first series tanks using Murcott seedlings (successful root hair development). All 3 tanks receive an extra dose, 100 ppm, of calcium (calcium chloride). The added calcium and the pH at approximately 7, should drive the chemical reactions in solution towards the removal of available phosphorus, keeping the available phosphorus in the solution at the concentration that favors root hair development, while still providing enough phosphorus to keep the plants nutrition balanced. The Carrizo seedlings from all 3 tanks are healthy, showing no visual signs of nutrient deficiency, and with visible differences in root hair development. Observing with light microscopy, Tanks 1 and 2 show significant development of root hairs; while Tank 3 has some root hairs, they are in much fewer numbers. We are currently assessing the numbers of root hairs using Scanning Electron Microscopy (SEM). Several roots from each tank, along with roots from untreated Carrizo seedlings, have been selected, and prepared for viewing with the SEM. Currently we are taking images and counting root hairs to asses whether there are significant differences. The density of root hairs on several of the roots is so high, SEM has been difficult. Tanks 1 and 2 had sample prep issues relating to the sputter coating stage and needed to be resampled. Those results should be available soon.