FERTILIZATION

Once established, fruit trees need to be fertilized each spring to ensure that new healthy growth occurs and fruit will be large and tasty. Remember trees are not fertilized the year of planting. The main nutrient needed by fruit trees is nitrogen. Nitrogen can be applied in organic or synthetic chemical form. The most common form of commercial fertilizers are ammonium sulfate, ammonium phosphate or a special fruit tree fertilizer usually found at the nursery. Most fertilizer containers have three numbers listed in the form of x-x-x, i.e. 10-10-10. The first number is the % nitrogen (N) by weight found in the container. The second number is phosphorous (P) and the third is potassium (K). Most soils in Arizona have enough P and K to support fruit tree growth. Sandy or porous soils may lack these two nutrients, and should be applied prior to planting or can be mixed in the backfill soil. The amount of fertilizer to apply each year will depend on the size or age of the tree. Regardless of the kind or type of fertilizer used always apply amounts based on the nitrogen content expressed on the label.

Table 4. Important Factors in Selection of Apple Rootstocks

	Clonal Stocks
Factor	M.9	M.26	M.7	MM.106	MM.111	Seedling
Tree size as % of a standard seedling rootstock	30	45	55	75	80	100
Support Needed	Yes	May	May	No	No	No
Yields
a. early	++	+	+	+	-	-
b. heavy	++	+	+	+	+	-
Adaptability
a. wet soil	-	-	-	-	+	?
b. dry soil	+	+	+	+	+	+
c. heavy soil	-	+	-	-	+	+
d. light soil	+	+	+	+	+	+
e. cold temperature	?	+	-	-	+	+
f. hot temperature	+	+	+	+	+	+
Disease Resistance
a. collar rot	?	?	+	-	+	+
b. fireblight	-	-	+	?	+	+
Spacing in Feet Between Trees for Spur type (add 2' between each tree for non-spur type trees). Use the smallest spacing for poor soils and the largest spaching for excellent soils.	8'-12'	10'-14'	10'-16'	12'-16'	14'-18'	16'-20'

Fertilizer should be applied in the spring of the year just prior to bud-break. This time of application will coincide with the first spring irrigation. If a complete fertilizer is used i.e. a 10-15-10, apply the amount based on nitrogen content. The table at left is a guide for the amount of nitrogen to apply.

Fertilizer should be applied in the spring of the year just prior to bud-break. This time of application will coincide with the first spring irrigation. If a complete fertilizer is used i.e. a 10-15-10, apply the amount based on nitrogen content. The table at left is a guide for the amount of nitrogen to apply.

When applying fertilizer spread, (do not band) beneath the branches to the drip line around the entire tree. Incorporate into the soil and water. Organic fertilizers such as animal manure can supply some nitrogen. If manure is to be used as a source of nitrogen have its nitrogen content determined. Never use fresh manure on fruit trees. Make sure it has been composted or rotted.

Sometimes trees will develop micronutrient problems during its lifetime. The two most frequent micronutrient deficiencies are iron and zinc. In many cases iron deficiency is caused by overwatering in the spring. This is corrected by increasing the length of time between irrigations. Both nutrient deficiencies can be induced by high soil pH, and in particular by heavy based caliche soils. Iron deficiency symptoms are characterized by yellow leaves with green veins on the youngest leaves. Zinc deficiency symptoms are characterized by small narrow leaves that occur as tufts at the end of shoots. In addition, leaves can have yellow splotches between the veins.

The quickest way to correct these deficiencies is to use foliar applications of the deficient nutrient when leaves are young and will absorb the spray material. For zinc deficiencies use a form of zinc chelate. Do not use zinc sulfate as it will defoliate most fruit trees. For iron problems use iron sulfate or chelate. It will take several applications to correct the problem.