Determining your Orchard Nutrition Needs

This year, several orchards have experienced either severe nutrient deficiencies or toxicity problems.  When examining the problem and trying to find out a solution, I have come up with the following conclusions as to the reason why nutrition problems occur in the orchard:

· Most growers do not do a routine leaf analysis.
· Most growers do not do a routine soil analysis.
· Most growers use visual observations to determine the orchard nutrient requirements.
· Most growers follow the same fertilizer application from year to year, especially if the trees do not show any visual problems.

Optimal mineral nutrition is essential for high productivity and growers should become involved in the long-term management of the orchard nutritional needs in order to avoid problems of deficiencies and toxicities, maximize productivity, and reduce the application of unneeded fertilizers. 

Practices growers should follow in order have long term management of the orchard nutrition needs:


Leaf tissue analysis on a regular basis (at least every other year)

· Regular sampling is more valuable than using leaf analysis only when nutritional problems are evident because a series of analyses over a period of years can indicate approaching nutritional problems.
· Leaf analyses are a good indicator of the success of either fertilizer sprays or soil amendments.
· Leaf analysis can confirm visual symptoms that suggest deficiencies or toxicities.
· Using leaf analyses enable growers to better manage their orchards.  When specific deficiencies are identified, large responses are possible.

Soil analysis on a regular basis (at least every third year)

· It is absolutely foolish to design a fertilizer program without knowing the pH because nutrient availability is pH dependent.
· Soil test can reveal a cause of a nutrient problem and is most useful when it supplements leaf analysis.
· If the leaf analysis suggests a deficiency and the soil analysis suggests adequate levels, one might suspect that additional factors are involved
· If low tissue levels are accompanied with low soil levels, the grower is much more certain of the source of the problem.
· The most important soil test that could serve as a guide for the interpretation of foliar levels of Mn, Fe and Zn is soil pH.

Factors to consider when determining the orchard fertilizer program: 

Season differences:

· Concentration of mineral within any given tissue is a reflection of the nutrient uptake, growth, transport, and remobilization of the nutrient within the plant.  Climatic factors affect all these processes and may explain some differences in mineral concentration that occur within the same tissue in different years.
· Transpiration and uptake can have profound effect on the elemental composition of the plant tissues.  Temperature and soil moisture, coupled with relative humidity, determine the amount of transpiration from plant leaves.
· Nutrient availability for root uptake is a summation of those nutrients that are intercepted by plant roots, nutrients in the soil reaching the plant root by mass flow (nutrient and dissolved substances are transported in the flow of water to the root that results from transpirational water uptake), and those reaching the root by diffusion (the movement of nutrient and dissolved substances from a high concentration to a low concentration).
· Diffusion appears to be the main mechanism supplying K to the plant root while mass flow amounts for a large portion of the Ca.  Thus, leaf K and Ca would be differently influenced not only by the soil supply, but also by soil moisture, air temperature, and transpiration. 

Crop load

The first prerequisite to understand the effect of crop load on leaf nutrient levels is to recognize the differences in elemental content compared to foliage.
· In both stone and pome fruits, concentration in the fruit of mobile elements, e.g. K may be similar to that in the foliage while an immobile element such as Ca may be <5% of the levels in the foliage.
· Increasing crop load decreased the total N requirement of the trees.  It takes more N to grow excess leaves, braches, and roots than fruit.
· Crop load can reduce K in the leaves.



Plant vigor

There is a concept of nutrient balance that states that if any element is deficient to the extent of limiting growth, when corrected, may result in deficiency of other elements because of the increased growth demands on the marginal supplies.

· Often when little of no growth happens, nutrients are often concentrated and deficiencies may not be apparent.
· Excessively vigorous trees may show deficiencies due to a dilution effect rather than an actual deficiency.

Pruning

· Pruning results in a dwarfing effect on the tree, but induces vigorous growth near the pruned area.  A general concentration of all nutrients can result from pruning.

Orchard floor management

Cover crops change water relations, alter root distribution, change root temperatures, and compete for plant nutrients.

· If lack of moisture restrict root activity to less-fertile subsoil, large differences in K and other surface concentrated nutrients may appear.

Nutritional interactions

· The optimal value of one mineral element may depend on the levels of another and Modifying one nutrient will likely alter another
For example, adequate Zn levels may differ depending on the P status
· The sum of cations, (i.e., K, Ca, and Mg) in milliequivalents, usually is not changed.  As one element is added, the other two usually decrease.
· Increasing the application of K or Mg is reflected not only in a decrease in the foliar concentration of the element not applied, but foliar levels of Ca are often decreased
· High K levels could result in lowering of Ca and Mg by 40 and 50%, respectively.
· In the interpretation of leaf analyses, levels of K in the mid to upper portions of the sufficiency range, coupled with low foliar Ca would warrant restriction in future use of K fertilizers.
· Evidence shows that increasing the soil P levels lowers foliar levels of Zn
In the interpretation of Zn foliar level concentrations, it appears that the soil Zn levels are the utmost importance, but that the uptake, translocation, or utilization of Zn can be altered with an increase in the P levels.