Proper fertility management is necessary to maintain fruit tree productivity, maximize the quality and health benefits of the fruit, and optimize the profits for the producer and processor. Soils of the arid Intermountain West are often characterized as calcareous, low in organic matter and high in salts. This can result in micronutrient deficiencies as well as poor nutrient cycling and uptake requiring orchardists to provide nutrients to promote healthy growth and yields. Regular soil and foliar nutrient testing to monitor for excesses or deficiencies can provide growers with a roadmap for orchard nutrition and should guide fertilizer inputs in addition to visual observations of tree growth and yields. Before applying any fertilizer, however, growers should also consider any potential barriers to uptake due to poor soil conditions including high or low soil moisture, temperature and compaction resulting in limited root growth and nutrient uptake (Dupont, et al. 2020). For more information on soil health, promoting healthy roots and soil biota’s role in nutrient cycling visit WSU Tree Fruit Soil & Nutrition.
Soil and Leaf Analyses
Soil analyses are useful for determining mineral nutrient availability in soil before orchard establishment. For existing orchards, a soil test every three years provides useful information for interpreting leaf analysis results and modifying fertilization programs. For example, if soil test indicate sufficient levels of a given nutrient that is deficient in foliar tests, this would suggest that poor nutrient uptake by the trees is the issue and could be due to poor root growth or soil pH.
Leaf analysis indicates the concentration of nutrients that are actually present in the tree foliage. If leaf samples are taken correctly and the results are interpreted properly, they provide a good tool for developing an effective fertilization program.
Leaf samples should be collected about 60 to 70 days after petal fall and after terminal buds have set, which generally corresponds to late July or early August. Undamaged leaves about twelve nodes downward from the terminal end of shoots will provide the most representative sample. Each sample should consist of about 100 leaves collected from several trees in the sample area. Do not mix leaves from different varieties, soil conditions, tree vigor, or crop load. Record observations on terminal shoot length, thickness, crop load, and fruit size, because these will enable meaningful interpretation of the observed nutrient concentrations in tree leaves. Choose a trusted lab with experience analyzing foliar samples from tree fruits and follow their instructions for preparing and sending samples.