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Trends in Fertilization of Avocado and Litchi Orchards

1. Trends in orchard management strategies

Sub-tropical orchard crops industry remains relatively young in SA and is currently very vibrant. Being mindful of:

- the smaller properties of the “average” farm; - orchard blocks that are typically 2-5ha big;- farms developing over decades

Recent developments brought alteration and moves in their general development and management and the nutritional strategies followed for these crops. I randomly list some bigger moves

1 The availability of precision farming tools has made decision making pre-plantation development and post-planting practical and meaningful – later more.

2 Better soil preparation techniques and technologies are used – I like the way that Gerhard Mostert refers to these practices as long term oxygen management practices. We also term them risk mitigation strategies. Phytophthora, the subtropical fruit grower’s nightmare is a symptom of compaction (Joubert, 1993) and crusting and resulting low oxygen levels in the soil.

3 A renewed focus shift to the importance of soil amelioration is seen – specifically the ratios between the cations, i.e., K:(Ca+Mg) and Ca:Mg and a new focus onto the management of acid saturation levels. Cost and efficiency of liming and gypsum applications are frequently tabled. o Losses of micro fine amelioration product particles are lamented and alternative

“pilled” and liquid based products are punted… generally at prices that is in my view too high.

4 As people become more aware of the negative implications of compaction, inclusive of crusting a lot of products that potentially can act as soil conditioners are sold many mainly being Ca and humic acid combinations.

5 Shade netting and for example the influence of shade netting on quality and water use

6 Integration of and holistic management practices looking at: o understanding that soil management is criticalo the focus on canopy management that

directly influence yield through light interception, productivity of plants and labour (especially in avocado and litchi that is

hand harvested) and quality (efficiency of spraying and crop protection in general)

o root- and general tree health (quoting Arnold Botha of Westfalia that related recently: “when the client started with a Phytophthora treatment program the visually obvious Boron deficiencies went away”)

7 Irrigation systems are relooked and the belief that trees can sense the size of the emitter that irrigates the tree is at last fading away. We see more new plantations that are drip irrigated.

8 Irrigation management (irrigation scheduling is not only talked of – it is practiced) through capacitance probes, good old tensiometers and other methods.o water quality (the 2016 low water availability and Komati River salt loads lead to all

manner of induced foliar deficiencies and salt burn symptoms in Litchi and burn in avocado’s on the Crocodile)

9 Lower or let us say more directed priority placed on foliar applied nutrients – trees take up the nutrients applied through the roots when they are healthy. Strategic foliar applications to assist in carry-over or out-of-season crops in avocado or for specific reason (Lovatt 1999, 2016) and to assist in reserve levels in alternate bearing situations.

10 New areas are explored and planted! Developments in the traditional sugar areas in SA, and in neighbouring and central African countries as well as in the traditionally Mediterranean areas --- the temperate and stone fruit crops’ habitat are exciting.

Hopefully we will make the same quantum leaps in yield that those crops made over the past 2 decades. Our industry is currently just aversive to the intense level pruning and management we hear of…

New varieties in both avocado and litchi are asking us to re-look norms.

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2. Soil mapping and irrigation block planning and other trends

- New farms start differently…- When soils are properly mapped and characterised - then block layout could be planned and row directions selected. - Then only follows integration with the irrigation designer or engineer.

- Irrigation blocks do not have to be square… Management blocks should fit the soil… to make the long term (20-30-40 year) orchard developments sustainable.

Figure 1. Soil mapping and block layout example – top 30cm WHC of and resulting block layout and suggested drainage lines drawn in.

- Trends are for bigger farms but smaller management blocks- Simpler (even at cost) centralised irrigation control – dedicated sub-mainlines- Central control of irrigation and fertigation- Installation of drainage (especially where marginal soils are planted)- Tighter control over water resources is predicted- Continuous irrigation and the low-flow drip irrigation philosophy

- Ridging which comes as a separate lecture…- Controlled release fertilizer shotguns for young plantations- Mixes and blends and sexy brand names- Increased number of contenders in the half-organic space

- Adapting fertilization to the realities on farm:o Supplementary / full irrigation leads to different avocado production potentials and

therefore nutrients applied should be different (Takete & Meyer, 1996)o Softer half-organic products where annual applications are in bigger portionso Fertigation trends

Through micro sprinklers (fortnightly dumps) Conventional drip (fortnightly or weekly dumps)

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Low-flow continuous drip – peroxide management and continuous fertigation

One of the negative spinoffs of the new technology – the precision mapping tools into orchard crops is that non-specialists are suddenly advising growers out of their field of expertise. It also points to a direct need for more trained and better people in the field…

Just because it is laminated does not make it good…

I have seen fancy laminated bound documents for young avocado plantations in Nelspruit where high volume fertilizer dumps are planned 5/6 times per annum through 2 low flow drip-emitters per tree in stead of continuous fertigation spread over the season… Soluble fertilizer was not even specified… Mature tree avocado norms are used for young trees etc. Advisors must make sure that they understand the clients’ situation before they give their advice.

3. Avocado nutrition trends

1 Physiological disorders, post-harvest quality and shelf life is critical in avocado that is almost exclusively ship-exported.

- Much avocadoes are sold ripe and ready in SA and in our export markets and nutritional status influences:

o cold damage in field, cold storage damage ---- Low No speed to ripening --- Low N and low K levels delay ripeningo Quality is a synergy of Ca; K; N and trace-elements inclusive of Copper (difficult due

to spraying..)

2 Traditional dumping of fertilizers, poor timing and focus on the NPK-macro elements have led to a very critical minimalistic view of nutrition strategies.The pendulum has swung in different directions over the decades. For many years the focus rested on quality rather than quantity. We now believe that both are important aims…

a. It could be achieved through integrated management, especially pruning,b. Proper irrigation management andc. Feeding the trees through a program containing the spectrum of nutrients.d. Timeous and efficient management of Phytophthora

Aims are pushed a little to the heavier side rather than in the middle road of the leaf analysis norms.

3 A renewed focus on the role of Calcium and Potassium, Boron and other trace elements are seen. Aims to correct the soil K status to 5-7% of the CEC is expensive but aimed for over the course of a few years.The use of Calcium nitrate as a source of N and Ca especially in the early part of the season whilst transpiration through the fruit is still active.

4 Chlorine salts are generally mistrusted but it becomes clearer that it is an EC management

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issue more than KCl being a problem.

5 Although the use of cattle manures has reduced due to chlorine contamination, the Global Gap regulations as well as in some situations Phosphate levels that build-up to toxic levels over seasons. One of the bigger Limpopo avocado producers apply 10m3 of fungal dominated compost per ha at start of season. Avos are litter feeders.

6 Growth regulator use requires precise timing but it is an established practice especially in the more vigourous varieties and areas for growth control but also fruit quality and sustaining yields.

7 Most advisors place high value on the use of leaf and other analysis as the starting point of a program. Fruit nutrition levels are also monitored periodically after fruit set

8 The bulk of the fertilizer is applied (simpler in buffered soils) from August/September to Nov/December, especially in the earlier varieties with some fertilising of N continuing into January and February in the later hanging or heavier bearing varieties or blocks.

Tree reserve levels should be built (after harvest --- in April, whether the harvest is done by that time or not) – at least 15 to even 50% of annual nutrition is applied at this time to carry trees towards August – the start of the new fertilizer season. It is timed when flower buds are seen.

9 Alternate crops should be managed differently, supporting on-crops and reducing vigour in off-crop and late hanging fruit draws a lot of reserve out of the trees and this should be managed

10 New areas… late fruit… Mediterranean examples… at the 2016 SAAGA symposium we were awed by the Californian avocado fertilizing strategies.

11 Different varieties are managed differently and the norms are being looked ata. Pinkerton requires more Cab. Hass receives a greater portion of its N earlier in the seasonc. New high yielding varieties with different character are being planted like:

i. Carmen that is a heavy feeder and bearer and the Alternate bearing is a concern to, proposing the two are interlinked…

ii. Maluma that is prolific but seems to be sensitive… use Pinkerton norms maybe?

iii. we are still learning to understand these varieties and fresh look at nutrition strategy is required

Summary: Trends in Avocado nutrition1 Aiming for yields and not only for quality2 Following tree phenology3 Aiming to strengthen crops during the post-harvest phase (April) to build reserves for the

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follow-up flowering4 Rapid expansion of the industry into new areas and with new varieties will require different

thinking.4. Litchi Phenology, alternate bearing and flush control

1 Litchi is being farmed with for many years, but we still consider our understanding rudimentary – it was still taken almost a wild crop when I spent time at UP mainly due to

a. Alternate bearing (Monselise & Goldschmidt, 1982)b. Long youth phase

2 Some important progress has been made over the past few decades both in China and locally in understanding litchi physiology and phenology.“Normally” when litchi flowers there would be a crop (of course it is more complex than this):

a. On and off years are correlated to years with and without flowering…b. But we have had much difficulty in controlling alternate bearing – we could describe

it in detail… (Schoeman 1998)

In Fig 2, the litchi phenology (Cronje, 2016a) show the annual progress, note the after-harvest flushes, the period of carbon reserve build-up and the indicated time for flush control. The growth cycles and the importance of the timeous flush maturity and temperature control seen in Fig 3 (Huang & Chen 2015).

Fig. 2. Outline of chronological progression of main growth stages in ‘Mauritius’ litchi in South Africa (generalized).

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Fig. 3. Litchi growth cycles

3 Climate – Cold signal

4 Cronje, 2016b proposed that flush control could be done via selected or combined (carefully) a. timeous full cover Ethapon applications after the final acceptable after-harvest flushb. spot spraying with Ethapon managing developing flushc. girdling i.e. Chinad. water stress during the dormant phasee. stress inducing K2SO4 foliar sprays

5 Cronje and Ratlapane (2017) published optimised strategy for breaking the alternate bearing cycle, in this case getting flowers on annual basis means having strong bearing branches with mature flush and dormant buds ready to receive the flower induction signal by cool temperatures.

Fostering strong bearing branches- Timing of nitrogen is moved backwards to the start of harvest or even earlier to promote

rapid flush development after harvest (best correlation in hotter areas) and build tree N reserves (all areas) and post-harvest starch levels.

- It is critical to give the orchard time to harden off one or two after-harvest flushes in cooler and hotter areas respectively, before dormancy is forced with the use of Ethapon. This is so that carbohydrate reserves could be built

- Pruning immediately after harvest is most beneficial

6 Phenological work by Cronje et al (2017) showed flush development can be manipulated by N applications and that splitting N before and after harvest had the best results on building of reserve levels, subsequent flowering, fruit set and yield in both cooler and hotter production areas. The current recommended split out of this work is:

a. 30% just before harvestb. 20% after harvest (even prior to pruning)c. 30% prior to or at floweringd. 20% at fruit set

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7 Figure 4 (Cronje & Ratlapane, 2016) indicates Litchi flushing and flowering patterns based on fertilizer timing.

Fig. 4 Litchi flushing and flowering patterns in 2013-16 based on fertilizer timing at a trial site in Malelane

8 Foliar sprays - During the opening of the first male flowers Zn, Cu and B is applied to enhance

fertilization- At female flower opening (anthesis) N and Ca is applied to assist with energy for set

and cell wall strength- At fruit set (after all male flowers have dropped; when one of the conjoined fruitlets

start growing) and again at 2g stage Ca will enhance cell wall strength. Calcium nitrate work better than Calcium chloride

- Fruit size enhancement sprays with synthetic auxins (Maxim) can be done at 2g stage

- After-harvest flush targeted foliar applications of Zn, B- In some situations, potassium sulphate is applied in the post-harvest phase to

enhance reserve levels and induce dormancy – as potassium reserve levels have previously been shown to be correlated to alternate bearing

9. Fruit cracking, Fruit browning and abnormal growth

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- Physiological disorders are found in all cultivars but are worse in some seasons,- Specific varieties more prone (Early Delight) indicating some level of genetic control –

high returns warrants finding the management strategy…- Low moisture during early fruit development and heavy rains during later stages causes

cracking in the rapid aril growth stage (Fig 5, 6)- Calcium is a big role player, especially levels of structural Calcium (Fig. 7) as it induces

spongy tissue formation that contribute to pericarp extensibility and therefore cracking resistance.

i. Uptake is via the transpiration stream whilst fruit has functioning stomata, but some level of phloem transport is seen and a positive relationship between the living seed (hormonal control) and calcium increases in fruit (Fig. 8, 9)

Fig. 5. Litchi fruit showing aril

Fig. 6. Zig-zag pattern of litchi pericarp expansion

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Aril

Fig. 7. Cracked fruit has comparatively lower levels of structural Calcium than normal fruit.

Fig. 8. Fruit with killed seed stopped taking up more Calcium

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Fig. 9. Early seed development is essential for Ca uptake.

- Other Ca related physiological disorders like fruit browning and abnormal fruit growth are indicated in Figure 10 a & b (Yao, 2015b)

Fig. 10 a & b. Calcium related physiological disorders Abnormal growth (a) and Fruit browning (b).

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Summary: Trends in litchi nutrition

- Better understanding in litchi reduces alternate bearingo Flush controlo Fostering strong bearing branches – timing of nitrogen applicationso Increased focus on calcium nutrition for the control of physiological

disorders- Re-evaluation of the timing of leaf sample analysis. In SA we sample during the fruit

rapid expansion stage, in China on mature Autumn shoots (Yao, 2015a)- Increasing soil organic contents (Yao, 2015b) through combination of organic

manures and fertilizers- Chinese work from 2009-2012 seems to indicate that the N:K ratio is important in

increasing yield and for post-harvest quality and shelf-life.

5 References

Cronje, R.B., 2016a. How well do you know your litchi trees? SUBTROP Journal 2016:1.Cronje, R.B., 2016b. Flush control in litchi – Importance and Methods. Presentation at Tzaneen litchi study group March

2016.Cronje, R.B. & Ratlapane, I.M., 2017. Optimising the use of Ethapon for warm early-season production areas. SALGA

Yearbook, Vol 23, p 33-40.Cronje, R.B., Ratlapane, I.M. & Mostert, G.P., 2017. Fostering strong bearing branches after harvest to increase the yield

potential of litchi. SALGA Yearbook, Vol 23, p 41-48.Huang, X. & Chen, H., 2015. Studies on shoot, flower and fruit development in Litchi and strategies for production

improvement. Keynote address at 2015 SALGA Research Symposium, Nelspruit.Joubert, D., 1993. Relationship between soil compaction and Phytophtera root rot of citrus. MScAgric. Dissertation, Univ.

Pretoria.Lovatt, C.J., 1999. Timing Citrus and Avocado Foliar Nutrient Applications to Increase Fruit Set and Size. Hort Technology,

Oct 1999, p 607.Lovatt, C.J., 2016. Foliar nutrition in Avocado. Presentation to 2016 SAAGA Research Symposium, Tzaneen.Mallett, J.B., Koch, C.D., Visser, P.A. & Botha, A.J., 1985. Tillage-related soil compaction and its effect upon maize grain

yields on a Viljoenskroon fine sand. S. Afr. J. Plant Soil 2, 52-56.Monselise, S.P., Goldschmidt, E.E., 1982. Alternate bearing in fruit trees. Hort. Rev., 4, 128-173.Schoeman, S.P., 1998. Alternate Bearing - Challenge to Fruit Producers. Seminar presented as partial fulfillment of the

requirements for the B.Sc.(Agric) degree in the Department Plant Production and Soil Sciences.Van Der Watt, H. v. H. & Claassens, A.S. 1990. Effect of surface treatments on soil crusting and infiltration. Soil Technol. 3,

241-251.Yao, L., 2015a. Evaluation on soil fertility of litchi and longan orchard and nutrient status of litchi leaf in China. Keynote

address at 2015 SALGA Research Symposium, Nelspruit.Yao, L., 2015b. Nutrient management in litchi. Keynote address at 2015 SALGA Research Symposium, Nelspruit.

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