Fertilizer decisions for fruit crops should be made based on scientific evidence of need. This is accomplished using tissue analysis (foliar samples) every 1-2 years and soil analysis every 3-4 years. A tissue analysis indicates the levels of macro and micro nutrients present in the plant. A single method is used for the analysis with optimal levels of each nutrient established for specific fruit crops. Foliar sampling of tree fruit is done at approximately 60 to 70 days after petal fall.
A soil analysis indicates the levels of macro nutrients (not nitrogen) and some micro nutrients available in the soil, as well as soil pH. There are several methods (Modified Morgan, Morgan, Mehlich 3) used by labs with standards based on the particular method.
When decisions are made based on previous experience, a grower could be missing interactions of elements that are hindering production and/or quality. This can also lead to the over or over-application of nutrients. Although recommendations on fertilizer containers have a scientific basis, they are considered a maintenance amount and are not reflective of the nutrient needs of a specific farm site. Plant age does not take into account specific plant needs, or soil nutrient levels. When fertilizer decisions are based on visual appearance, reductions in crop yield or quality may have already occurred. Diagnosing based on appearance alone does not take into account nutrient interactions.
Excessive rates of certain nutrients can cause interactions leading to deficiencies of other nutrients. For example, high rates of nitrogen can lead to an induced potassium deficiency which has a negative impact on winter hardiness and fruit size. An over application of potassium can lead to an induced deficiency of calcium. The lack of scientific evidence when making fertilizer decisions can result in over- as well as under-applications of many nutrients. The resulting imbalance can affect yield, quality, and may contribute to ground or surface water contamination. An excess amount of phosphorus doesn’t impede plant growth but creates environmental problems that are well documented. Nutrient imbalances can also affect the longevity of a planting which can have an economic impact on a farming operation. Nutrient deficiencies can result in stunted growth, reduced fruit yield and quality, and overall reduced plant health. Excessive rates of nutrients can cause a delay in fruit maturity, an over-abundance of vegetative growth, reduced bud set, and an increase in insect and disease problems. Improper soil pH for a crop can lead to nutrient deficiencies and toxicities affecting fruit quality and plant health.
Tissue nutrient standards for stone fruit have been established and are the following.
|Nitrogen||3 to 4.2 % peach (2.4 to 3.4 % other stone fruit)|
|Phosphorus||0.08 to 0.33 %|
|Potassium||1.3 to 1.9 %|
|Calcium||1.3 to 2.0 %|
|Magnesium||0.4 to 0.7 %|
|Boron||25 to 50 ppm|
|Iron||80 to 500 ppm|
|Manganese||35 to 135 ppm|
|Copper||7 to 12 ppm|
|Zinc||25 to 50 ppm|