Seminar Field Day - Boosting Avocados

The introduction of a field day involving farm visits, as an optional 5th day tag-on to the four day Certificate in Sustainable Agriculture, has proven a resounding success. This social and educational journey provides the perfect way of winding down from four days of intensive learning and allows for the potential development of relationships that may extend way beyond this experience. Our November seminar featured visits to a ginger farm, a blueberry farm and an avocado/macadamia/custard apple grower. In this segment I will focus upon the avocado grower as we conducted some trial work on this property for several weeks prior to the field day and it will be interesting to report on the results.

Henry Agostinelli had an NTS Soil Therapy™ analysis a couple of years ago and enjoyed good results on his treated macadamias but has not embraced full nutrition programs. Henry’s property features 600 assorted avocado trees yielding 5081 trays of high quality fruit. His 100 custard apple trees yield 556 x 8 kg trays and he also has 5 hectares of macadamias which were planted in 1996. Henry also grows strawberries on an adjoining property but it was the avocados that were to feature in our trial work. I am convinced that some of the experts have got it wrong with some aspects of avocado agronomy and this little trial offered an opportunity to highlight that fact.

Henry was gracious enough to allow us a row of established trees to treat. NTS agronomist, Nathan Pianeda, designed the trial and treated the designated area.

A Trio of Limiting Factors

There were three areas we chose to address in this trial:

1. According to the experts, avocados don’t respond well to foliar fertilisers – in fact it is often suggested that it is a waste of time as the shiny, waxy leaf will not absorb nutrients.
2. Avocados use more boron than any other crop and there can be good gains in using a stabilised form of boron to counteract the extreme leachability of this trace mineral.
3. Phytophthora is the major avocado pest and there are viable biological management strategies that are less intrusive than injecting with phosphorus acid.

I will deal with the foliar controversy first. Consultants often refer to a study where calcium nitrate was used as a foliar without generating a significant increase in leaf levels of calcium. This is cited as evidence of the ineffectiveness of foliar nutrition for avocados. There were several faults with this research. For a start, foliars are usually used to address trace element deficiencies or to top up major elements but never for total supply of a major nutrient like calcium. Secondly, it is true that the waxy avocado leaf does reduce uptake potential. That is why there should always be an oil-based wetter sticker used and there should also be an additive included to increase uptake potential. Neither of these two prerequisites were used in the trial in question so it is no surprise that good results were not forthcoming.We have found that Cloak™ Spray Oil is the perfect wetter-sticker* for avocado foliars. It consists of a combination of emulsified cold pressed canola oil and a high omega three fish oil derived from deep water species. The fish oil is a remarkable penetrant and it also contains very high levels of iodine which is beneficial in its own right.( Note: This product is not registered in Australia for use with agricultural chemicals including insecticides, herbicides and fungicides.)*

Fulvic acid is the material we use to increase uptake. This natural acid (which is also a chelating agent, a bio-stimulant and a plant growth promoter) is a cell sensitiser. Several research papers confirm the capacity of fulvic acid to increase the permeability of the cell membrane to increase nutrient uptake by up to 30%. When these two additives are combined with the avocado foliar there is no debating the response.

In Henry’s trial we selected our specialist avocado foliar, called Avo-Tech Triple Ten™, and this was applied 4 weeks prior to the field day. Seminar patrons attending the field day were left in no doubt as to the viability of avocado foliars. There was a major difference in colour and growth in the treated row in comparison to the untreated in just a few weeks. The Triple Ten™ formulation includes a high performance, Hot Mix NPK™ combined with a full range of chelated trace elements and a group of plant growth promoters.

Satisfying the Boron Hunger

The second focus in our trial involved the trace mineral, boron. Avocados are, in my opinion, the most boron hungry of all crops. It is unbelievable how much boron they can utilise and how much must be applied to achieve the luxury leaf levels we are seeking for maximum production. Boron is extremely important in a crop that has such a poor fruit to flower ratio. There is only a very small percentage of the mass of flowers that are converted to fruit and this is a central role of boron. This mineral increases the length of the pollen tube to boost the efficiency of pollination. One of the most productive strategies for any avocado producer is to apply a pre-flower foliar that includes the following:

Pre-Flower Foliar

• 10 kg of urea per hectare – as a source of amines to promote a reproductive response.
• 2 kg of solubor per hectare – as a boron kick to boost pollination.
• 700 grams of Tri-Kelp™ Soluble Seaweed Powder per hectare – as a natural growth promotant to improve reproductive response.
• 400 grams of NTS Soluble Fulvic Acid Powder™per hectare – as a cell sensitiser and chelating agent.
• 3 litres of Nutri-Key Shuttle Seven™per hectare – as a rich source of the trace minerals required to facilitate fruit set.
  

The problem with applying boron to the soil is that it is very easily leached. It is a negatively charged anion that can only be stored in the humus component of the soil (humus contains the positively charged sites to which boron can attach). Unfortunately, many of us have lost a large percentage of our humus over the past few decades and this has reduced the capacity to store boron in our soils. We have found that we can compensate for this decline in organic matter if we apply boron that is pre-complexed with humic acid. Humic acid is a natural material extracted from brown coal that can serve as a humus substitute. In fact, it is a humus concentrate with a remarkable CEC of 450.It performs all of the same functions as humus in a soluble humate granule. In orchard crops where boron must be added every year due to leaching, the addition of 25 kg of NTS Stabilised Boron Granules™ per hectare can supply luxury levels of boron to the plant for the full crop cycle and into the next. At this avocado field day we were able to show that an addition of boron humates a few weeks prior had resulted in significant increases in boron levels in the leaf.

Fighting Root Rot

The third consideration in the avocado trial involved the major pest in this industry, Phytophthora. The avocado tree evolved in America in fertile, well drained soils with plentiful rainfall and minimal disease pressure. Soil moisture is a major issue in Australian conditions. The tree is very sensitive to dry conditions and it also hates wet feet. In this context, drainage and poor irrigation practices become the major yield limiters as the trees are far more likely to be ravaged by root diseases like Phytophthora. There are other factors that can increase root rot pressure including the form of nitrogen present in the root zone. Nitrate nitrogen stimulates Phytophthora while ammonium nitrogen is antagonistic towards this pathogen.

Unstabilised urea, the most common choice of nitrogen in this crop, can be counterproductive because it converts to nitrates so rapidly. Conversely, there can be considerable gain in stabilising urea with humic acid or liquid zeolite to slow the conversion to nitrate nitrogen. Foliar urea is also a good nitrogen supply option as it reduces the nitrate lode in the roots. However, the best strategy is to introduce a blend of nitrogen fixing bacteria in large numbers to deliver a constant supply of ammonium nitrogen from the atmosphere. Ideally this blend should also include a range of phosphate solubilising organisms, as nitrogen fixers need phosphate to fuel the enzymatic reaction required to fix nitrogen. Such a blend could also supply a fungi species that specifically predates on root rot organisms.

The conventional treatment for Phytophthora involves injecting the trunk with phosphorus acid which is translocated down to the roots to kill the pathogen. This burning acid can compromise tree health and is not particularly sustainable.

Research released at the International Silica Conference in South Africa suggests that drenching the roots with liquid silica can be at least as effective as phosphorus acid in the management of Phytophthora.

The approach that we favoured for the purposes of the field day trial involved an inoculate called Nutri-Life 4/20™. This highly successful microbe blend can be manipulated to provide a largely bacterial workforce or it can be made fungal-dominant. In this instance we tested the soil life composition and discovered very high fungal numbers. This was largely due to wood chip mulching which provides abundant food for cellulose digesting fungi. The problem is that these fungi require a constant source of nitrogen to create the protein needed for constantly expanding hyphae and much of this nitrogen can be supplied by nitrogen fixing bacteria. They need their nitrogen in the ammonium form and this is partly why there is restriction of Phytophthora linked to ammonium nitrogen. Some cellulose digesting fungi also double as predators that eat Phytophthora. If they are supplied the right form of nitrogen they can more vigorously hunt down pathogens like Phytophthora.

We decided on the basis of the soil life analysis that the bacterial version of Nutri-Life 4/20™ was most appropriate and applied it at 100 litres per hectare 4 weeks before the field day. One week before the farm visit we retested the soil and found a 500% increase in bacteria. On the basis of past experience we would expect to see a significant reduction in Phytophthora after this change in microbe balance. Nutri-Life 4/20™ contains several species of nitrogen fixing organisms, three species of phosphate solubilisers and Pseudomonas fluorescens, a probiotic bacteria. This inexpensive blend also contains Trichoderma but numbers are relatively low in the bacterial version of the product.

In Conclusion

Field day attendees were able to witness the kinds of changes that can inspire a non-committed biological grower like Henry Agostinelli to delve more deeply into the wonders and undeniable potential of the biological approach. They were able to see some of the principles that had been learnt all week put into practice and were, hopefully, further “sparked” to return home and begin their own journey toward a more sustainable, more passionate future, working with nature rather than against her.