Post harvest nutrition in Apple - Q&A.

The mineral nutrition of trees crops has a major influence on their shoot growth and yield. Nutrition is even more important in apple and pear trees because good nutrient status improves the storage behavior (or fermentation if being made into cider) of our fruit. 

Q&A with James Hook – DJ’s Growers.

Q: What do you think of applying phosphorous (P) after fruit has been picked as a way of adding P to the orchard?

James Hook’s A: I am a newby to the apple industry but my understanding is phosphorus (particularly if nitrogen and potassium are found in high levels) is very important for apple fruit maturation because P is involved in several biochemical processes that take place after picking. There are significant relationships between soluble solids, between acidity and phosphorus which may increase the synthesis of nucleic acids and improve energy supply through adenosine phosphates (Kaack and Pedersen, 2014).

If fruit is deficient in phosphorous, but high in nitrogen and potassium then it reduces the storage performance of that fruit. Also phosphorous levels in combination with calcium are linked with skin firmness. Firmness is important in all horticultural crops that are transported and stored.

So, yes replenishing phosphorous after picking is important especially in orchards where fruit is not performing well in storage. 

Q: How would you approach an orchard that has low phosphorous and problems with skin firmness and storage.

I have a preference for using organic methods to improve the soil of orchards rather than using phosphate or foliar sprays or similar. I was cynical when I started out testing soil but I have changed 180 degrees over the last ten years. It just makes sense to me to build a healthy soil that provides the nutrients a tree needs rather than continually import nutrient in the form of mineral fertilisers. Needing to constantly add fertiliser to ‘prop’ up trees is a short term solution. Spraying harvested fruit is also an expensive and temporary solution. I would advocate getting the soil right and then monitoring nutrient uptake into the tree.

I would look at adding guano to the soil, steadily over a few seasons, as a long term approach to nutrient correction. I am prepared to recommend guano on the record because it supplies a natural source of phosphorous with the added benefit of being a high source of calcium.

Guano: a natural source of  phosphorous and calcium.

Guano is a granular product made from sea bird droppings, 2- 4mm in size, so it can be spread using the equipment farmers and contractors already have.  Guano offers a combination of soluble and slow-release phosphorous so it can be seasonally broadcast out to begin to boost soil levels. Guano’s phosphorous isn’t prone to lock up and becoming insoluble. As I mentioned it also contains calcium and has other good trace element levels as a bonus.

Q:  Is guano as effective as superphosphate or other phosphate fertilser stack up?

A: On Adelaide Hills soil types, clay loams and sandy loams, it is likely to be a more effective source of phosphorous because it has greater stability in our soil types.

The inherent problem with superphosphate fertilisers or MAP is that they are locked up in our soils. They are soluble phosphate concentrates which theoretically reduce transport costs in comparison to guano but their potential is not matched by their performance in my opinion. Phosphate is a triple negatively charged anion which means that it is strongly attracted to positively charged cations like calcium, iron and aluminium. The fact is that when P forms a bond with these other minerals it becomes insoluble and is no longer available to the plant. This “lock-up” can begin to occur within hours of application and is likely all tied up before spring begins.

Q: How does the price between conventional sources of P and Guano.

A: Guano is surprisingly good value for money per unit of Phosphourous. Guano is (0:14:0 and 26 calcium). I cross checked guano with the current price of single superphosphate (0:9:0) and triple superphosphate (0:23:0). Guano works out to be $62 a kilo of P while single super is $42.50 and triple super is $37.50 a kilo. 

While Guano does cost more per unit of P when you factor in its performance, stability and availability it is certainly a valid option.

James Hook is a director of DJ’s Growers and has a background in horticulture beginning with Wesfarmers Landmark in 2001 before founding DJ’s in 2007. Together with is wife he also runs the Lazy Ballerina cellar door located across the road from Kuitpo Forest.

Further  reading:

Kaack, K., & Pedersen, H. L. (2014). Effects Of Potassium, Phosphorus  And  Nitrogen  Fertilization  On  Endogenous  Ethylene And Quality Characteristics Of Apples (Malus Domestica L.). Journal of Plant Nutrition, 37(7), 1148-1155.