Nutrient Removal by an Apple Crop

Back in the early 70’s it was common to refer to the value of nutrients contained in a pound of apples. There were discussions with other horticulturists about that value being so many cents per pound and it was rationalized that yes a few pounds of apples is indeed worth between a nickel and a dime in terms of fertilizer value. This makes even more sense when we pay our fertilizer bills as an input for apple production. If we take this one step further we can indeed calculate what nutrients a large crop of apples will remove from an acre or hectare of managed orchard. 

This doesn’t include any nitrogen losses from pollen carried away by bees in the spring of the year. Pollen itself is a nitrogen sink and a mature higher density planting of apple could easily produce over 100 lbs per acre of pollen. Pollen is protein rich and nitrogen is part of the amino acid complex found in pollen. This also does not include nutrients taken up by the tree and used to build tree structure or for the feeding of beneficial flora and fauna in the orchard.

This past growing season (2006) could be characterized by the apparent lack of crop in some blocks of orchard in the south west and in contrast some of the heaviest yields for other blocks and different varieties. When picking crews are not moving as fast as you think they should, it could mean one of two things. Either the producer has done a poor thinning job in the orchard or the crop is so heavy that it is holding the crew back. We would like to think that it is for the second reason.

If we take a metric tonne of apples, to see how much of each nutrient is in it, it works out to what is shown in Figure 1.

Figure 1. Typical nutrient content of apples in grams per metric tonne.

Link to data equivalent table

Back in 1999 at an IDFTA meeting in Hamilton Ontario we heard from Dr. Wolfgang Drahorad of the South Tyrolean Advisory Services talking about how much nutrient is contained in a 45 bin/ac or 45 metric tonne per hectare yield. Those figures are shown in Table 1. 

In his talk, Dr. Drahorad explained that when deciding on how much fertilizer to use after harvesting a large crop of apples one has to look at the nutrient availability in the block by way of soil analysis. If the availability of nutrients is within a given standard, then it would make good sense to replace what was taken out by the crop plus a % more to account for other factors. Factors like nitrogen losses from pollen removal by bees or nutrient use in building tree structure have to be accounted for.

In our situation, we also have to account for nutrient use in the orchard for purposes other than fertilizing the trees. Some growers in Ontario may be using nitrogen on leaf litter to help resident bacteria break down scabby foliage. Some of this nitrogen will eventually end up as nutrient for the trees and can be considered as a fertilizer input.

In the Tyrolean district of Italy, where deficiencies are identified, it is recommended that nutrient supply should be increased by 50%. The supply should be reduced by 50% if there is a surplus of nutrients in the soil. A severe shortage of anything would trigger a doubling of quantities. If there is an outstanding or considerable surplus of soil nutrients, then the grower is advised to cut out uses for several years. In Ontario, it is common to maintain a foliar program of nutrients where soil applications are eliminated for one reason or another.

It is best to keep a soil/tissue testing service employed on a regular basis, as guesswork in fertilizing apples can result in a chronic condition of deficiency or oversupply and lost opportunity with any cultivar or block.