Salt Resistant Citrus – Are Citrus Trees Salt Tolerant

Salt Resistant Citrus – Are Citrus Trees Salt Tolerant

If you are a seaside resident and wish to experience the joys of freshly plucked citrus from your very own tree, you may be wondering, “Are citrus trees salt tolerant?”. The salt tolerance of citrus trees is notoriously low. That said, are there any salt resistant citrus varieties and/or are there any ways of managing salinity in citrus trees?

Are Citrus Trees Salt Tolerant?

As previously mentioned, citrus trees vary in their salt tolerance but most rank rather sensitive to salinity, particularly on their foliage. Citrus can tolerate up to 2,200-2,300 ppm of salt on their root systems but a moderate 1,500 ppm of salt sprayed on their leaves can kill them.

Scientists are, however, working on developing salt resistant citrus trees but, at this juncture, there are none on the market. The key then is managing salinity in citrus trees.

Managing Salinity in Citrus

Coastal residents or people irrigating with well water or reclaimed water with a high salt content are limited in what they can plant in the landscape. What causes soil salinity? A number of factors, including water evaporation, heavy irrigation, and chemical fertilization, cause salt to build up naturally in soil. Coastal denizens have the added problem of salt spray, which can destroy foliage and potential fruit.

Salt in soil inhibits the growth of many plants or kills them. Because salt ions attract water, there is less water available to the plants. This results in drought stress even if the plant is well watered, as well as leaf burn and chlorosis (yellowing of the leaves).

So how can you mitigate the effects of saline on plants? Add plenty of compost, mulch, or manure to the soil. This will provide a buffering effect from the salt. This process may take a few years to come to fruition but is well worth the effort. Also, don’t over fertilize, which only compounds the problem, and irrigate regularly yet moderately. Planting atop ridges is beneficial as well.

If you are not directly on the beach, citrus can be container grown as well, which can help you manage the salinity in the soil.

If this all seems too much and you decide to wash your hands of growing citrus, switch gears. There are a number of salt tolerant plants available, including many fruiting trees, so instead of having fresh squeezed O.J. in the morning, go for something a little more exotic like Cherimoya, Guava, Pineapple, or Mango juice.


A Guide to Citrus Nutritional Deficiency and Toxicity Identification 1

Stephen H. Futch and David P. H. Tucker 2

Citrus trees in commercial and dooryard plantings can exhibit a host of symptoms reflecting various disorders that can impact their health, vigor, and productivity to varying degrees. Identifying symptoms correctly is an important aspect of management, as inappropriate remedial applications or other actions can be costly and sometimes detrimental. Nutritional disorders addressed in this publication are an important aspect of citrus tree symptomology. Symptoms of deficiency or toxicity may have different forms of expression on foliage, stems, roots, and fruit, and may not in all cases resemble those illustrated in various publications. Symptoms can vary considerably from mild/incipient to chronic, particularly on foliage, and can also be expressed in leaf size. Because availability of some micronutrients like Zn, Mn, and Fe are soil-pH related, deficiency symptoms of these three elements may often occur simultaneously within a tree canopy and sometimes mask each other within a single leaf. To the untrained eye, nutritional disorders may be confused with herbicide, fungicide, physiological, and stress-related toxicities and physiological disorders. When in doubt, seek advice before committing to costly and perhaps inappropriate corrective measures.


SERIES 26 Episode 27

Sophie gets some top citrus-growing tips from 'Mr Citrus'

I'm in the South Australian Riverland, around 260 kilometres north-east of Adelaide. It's irrigation country, where water from the Murray is used to grow beautiful fruit. But it's the citrus I'm here for - the fruit trees that so many home gardeners ask us questions about - and to get some answers, I'm lucky enough to meeting with Australia's 'Mr Citrus' - Ian Tolley.

Ian became absorbed with growing citrus in his early twenties. Now he's meant to be semi-retired, but he seems as busy as ever! "Whilst birthdays keep rolling along, it doesn't diminish my passion for all things citricultural. I was meant to be an engineer in the family tradition and that just didn't happen because I quit just before I graduated. The reason was that my father was beginning to develop an orchard and nursery - and I fell in love with that. I'm still in love with citrus!

In 1966, after many years of horticultural study and hands-on experience, Ian won a Churchill Fellowship that took him to orchards in South-east Asia, the USA and Israel where he set about solving citrus growing problems and his work's been recognised with a medal of the Order of Australia.

Today, Ian's going to share his essentials for citrus success.

First things first. "Well, make up your mind that the variety is what you want, get the right rootstock, make sure that you plant it properly, make sure the nutrition is ok and learn to shape the tree - you're there for life," says Ian.

WHAT ROOTSTOCK TO CHOOSE

"Make your own mind up," says Ian, "because generally, no matter where you're living, you can grow a good variety, so long as you get the right rootstock - that's the important thing - so the selection of the variety's not as important as having the rootstock because that does so many things for you. We're aiming to put a root system underneath your variety which is resistant to plant pests and diseases in the soil. We're also going to influence the maturity of the fruit, we're going to improve the quality of the fruit - all of those things are very important - so we need to select the right rootstock for the right area, the right soil, the right climate - all of those factors."

'Troyer' and Carrizo'

Trifoliata and 'Flying

'Cleopatra' and

'Emperor' mandarin

Sour orange

(rough Seville)

DISEASE/PESTS

ENVIRONMENTAL TOLERANCES

Mandarins (excl.

Source: Ian Tolley

Now to Ian's second essential for citrus success - planting. The principles are the same, Ian says, whether planting into a container or in the ground. "When your tree arrives, soak it thoroughly. Stick it straight into a bucket of water and let the bubbles come up. That's it."

Ian also suggests something that might surprise many gardeners. After soaking the plant, he washes all the potting media from the tree's roots! He says it's important to act quickly then, whilst the roots are still wet. "It's important that the roots are being protected by a moisture barrier. Now we make sure the tree goes into a pot of fresh mix - ensuring the soil level is the same as in the original container."

"Settle the plant in, then put some mix around it without piling it in. Don't damage it - spread the roots out over the whole of the pot."

Ian also supplements his potting media. "It's regular potting media, with chicken manure with additives - a couple of cupfuls - mixed in. Then we want to make sure it stays there, so here's the magic formula - zeolite. It's a rare earth, mined in Australia. I usually put in, for instance, a tablespoon for a medium to large pot.

Mixed up, that locks the fertiliser with the nutrients, in the potting media so that when the start to grow, they can pick it up at any time. cuts the fertiliser use in about half!" (Zeolite attracts and retains ammonium, potassium, calcium & magnesium, as well as trace elements.)

The Magic Temperature

Ian also says it's worth waiting until the air temperature is right. "The magic temperature - 14 degrees centigrade. When the temperature starts to go above 14 degrees, you've got root development. Just keep on planting while that's happening.

But by the end of summer, we need to stop planting because the temperature's going to be cooling and root growth will stop. "That's right - we want establish the tree before that happens. In cold soil, the roots will rot and then because you love your plant so much, you will keep watering - just in case it needs it - and that contributes to its death."

Fertilising

Fertilising is a huge and complicated subject, but Ian has a basic rule for feeding citrus. "Yes, I do - it's just monthly, without fail, summer or winter."

"I always use organic, composted chicken manure but you need to have additives." Ian adds trace elements from boron to zinc to ensure a good, balanced, feed. "And liquid seaweed, which helps to boost all the activity in the soil and so make the whole thing a living, active thing for the tree to take advantage of."

"Also, Sophie, don't waste your fertiliser with over-watering. We don't want to flood the plant - then all the fertiliser's gone. Make sure you've added enough water to just have the odd few drips out of the bottom of your pot."

And he says the plant will tell you when it needs water. "Ask the plant! You just go to its leaves and if the leaves are shiny and really firm and cool - more than anything, they're cool to your touch - then you know the plant is happy, so go away. Wait until you can come back and say, 'Oh. It's not cool, so it's not transpiring,' so you need to water. Do it now."

BARK CARE AND PRUNING

Sophie wants to know why all Ian's potted citrus trees have white trunks. "Sunburn control," he says. "Sunburn's a very serious matter. It can kill trees. Just use ordinary white exterior paint every 5 to 7 years - something like that - and you've got protection." Milk paint or whitewash will also have a similar effect, but needs to be applied more frequently.

However, this is just for his potted plants. Trees in the ground that have a canopy shading their trunk don't need the extra barrier.

And that brings us to the last of Ian's tips for citrus success - pruning. "I'd much prefer to call it shaping. This tree is in its second year. In the first year, I cut the top off - just snipped it. It gives lots of bushy growth, but a little bit of suckering. Remember - citrus trees grow fruit on the tips of their terminals. We're aiming for a shape like a pear drop - an upside-down pear - that's what we're aiming for.

Don't use secateurs! From this distance, you can't see what you're doing and it's quite dangerous. Throw them away," says Ian. He suggests using something larger, but just as sharp - like shears. "That's the key. Stand back and work out where you want to go and you can get straight in."

Even with trees planted in the ground, "I don't want to let them grow higher than two 2 metres. If you're getting a normal crop year after year, you don't have to worry, but if you see a very light crop coming your way, that's red for danger. That's the year to start shaping your tree - taking down the number of terminals. That means you start to get the tree back to a normal crop, every year."

"Well, thank you so much for having us, Ian," says Sophie. "It's been an absolute privilege."

"Well it's a pleasure for me too, Sophie. It's nice to have that opportunity to just explain a little bit about my passion!"


Soil examination

Digging the pit

Soil pits are usually dug in representative parts of a planting, using a backhoe or spade.

Dig pits about 4 m long at right angles to the direction of water flow and wheel traffic, and as close as possible to the trees.

Dig pits about 1 m deep. One metre is ideal — citrus feeder roots rarely penetrate below that depth however, the most important inspection area is the first 50 cm.

Trim the pit walls with a flat-edged implement to remove smeared soil left by the backhoe bucket and to expose undisturbed soil. Examine the sides of the pit for compacted layers and tree roots.

What to look for

  1. A wet layer (sometimes below the compacted or smeared zone) may indicate that:
    • drainage is poor
    • the roots cannot properly extract the water.

Record the depth and thickness of the damaged layer as a future guide to how deep you should dig.

  • Continuous stable macropores (large pores). These indicate that the soil is not damaged. Macropores are important for water entry and drainage. They are created by roots swelling and shrinking, and soil fauna such as earthworms and ants that connect the subsoil to the surface.
  • What to test for

    1. Clod stability when wet. Test the stability of clods and aggregates by immersing them in water. You can test topsoil and subsoil in the field or at home:
      1. Drop three air-dry clods (2.5 mm diameter) into a dish of irrigation water. Do the same using a dish of rainwater, for comparison.
      2. Examine after 5 minutes, then leave undisturbed for about 2 hours.

      If the clods are intact after 5 minutes, this usually means that soil conditions are excellent for plant growth. This is because there is enough organic matter to act as a glue between particles. This, in turn, means that the channels between aggregates and clods are likely to remain open after wetting, so allowing water to drain quickly and roots to penetrate easily. And when the soil dries, there are no hard crusts or flakes.

      If the clods fall apart in water, there is not enough organic matter to stabilise microaggregates (about 0.25 mm diameter). This collapse is known as slaking. Most irrigated soils in Australia behave this way.

      Although slaking is generally undesirable, you can still grow a good crop in such soils, particularly when there is enough swelling clay to create a loose, self-mulching surface after wetting and drying.

      If the clods slake when tested in water, leave them for a further 2 hours. If the water then looks milky, this means that the microaggregates have dispersed into individual particles of sand, silt and clay. The clay particles block soil pores so that wet soil is waterlogged and dry soil is very hard.

      In the field, dispersion shows on the soil surface after heavy rain and subsequent drying, with light-coloured sand separating from the clay. Dispersion is most obvious in dark clay soils. The main cause of dispersion is an excess of sodium and (possibly) magnesium on the clay particles. It indicates that gypsum may be required.

      This test for slaking and dispersion gives an early indication of the soil’s structural stability. However, you should also collect soil samples for laboratory testing, as chemical analysis provides detailed advice about gypsum requirements.

      Salinity. Salinity is a serious problem and is expensive to overcome. Laboratory testing is necessary if, on a moist soil surface, there are dark greasy areas that form salty-tasting white crystals as the soil dries. Other signs of salt include unusually crumbly soil and a water table within 2 m of the surface.

      Do not confuse salt (mainly sodium chloride) with calcium carbonate (lime). A simple test is to apply a low-strength solution of hydrochloric acid to the deposits. If it effervesces or fizzes, the deposit is lime.

      Laboratory testing

      Sometimes you need to have field observations verified by chemical and physical laboratory analysis.

      Important soil information, for example texture, sodicity and salinity, can sometimes be obtained from existing soil surveys. However, if good quality survey information is not available, collect soil samples from pits or holes for analysis.

      Three sampling depths are recommended at citrus sites:

      • 0–15 cm
      • 15–30 cm
      • 30–60 cm.

      Five subsamples from across the pit or from five spade holes throughout each planting should be bulked to make up each sample. Soil testing laboratories can provide information on how to take soil samples.

      Soil analysis

      Send the samples to a NATA-accredited laboratory (National Association of Testing Authorities for a full analysis, including:

      • exchangeable sodium percentage (ESP), which is the primary way of measuring a soil’s tendency to disperse
      • exchangeable calcium:magnesium ratio (a secondary way of measuring ESP)
      • electrical conductivity (a measure of salinity, which also affects soil dispersion)
      • organic matter content (a way of measuring a soil’s tendency to slaking)
      • effective cation exchange capacity (sum of the most common exchangeable cations) of surface soil (an index of the ability of the soil to self-regenerate by shrinking and swelling).


      Water Quality Guidelines for Trees and Vines

      Author:

      Stephen R. Grattan
      Plant-Water Relations Specialist
      University of California, Davis
      Jim Oster
      Soils and Water Specialist
      University of California, Riverside

      Drought Tip 92-19 is a publication series developed as a cooperative effort by the following organizations:

      California Department of Water Resources - Water Conservation Office
      Department of Land, Air and Water Resources University of California
      USDA Drought Response Office
      USDA Soil Conservation Service
      If you have comments or suggestions, please email [email protected]

      Last reviewed December 19, 2002

      Drought Tip 92-19
      Water Quality Guidelines for Trees and Vines

      Agricultural soils and irrigation water contain varying amounts and types of salts, but a soil is not considered saline unless the concentration of salts in the crop rootzone is high enough to reduce crop growth and yield. Tree and vine crops are generally more sensitive than field crops to salinity, chloride, sodium, and boron.

      Salinity affects tree and vine performance in two ways. First, the plants must acclimate themsoelves to a saline environment in order for water to become available. This process requires energy the plant normally uses for growth and production. Second, chloride, sodium, and boron can reduce yields because of speicifi ion toxicity. Sensitive trees and vines can accumulate these elements in leaves, causing leaf burn or in limbs or new shoots affecting the yield potential the next season. The two processes can operate simultaneously and can reduce crop yield.

      All tree andvine crops can tolerate some salts in the rootzone without harm to yield or plant quality. The maximum amount of salt the plant can tolerate in the rootzone without reduction in growth or yield is called the "salinity threshold". Beyond this level crop yields are reduced in proportion to the salt concentration in the rootzone.

      Effective irrigation management is important anytime, regardless of the availability of water, but becomes essential during a drought. After irrigation water and its dissolved salts move into the crop rootzone, the plant extracts "pure water", for the most part leaving the salts behind. The amount of salt in the rootzone will increase over time unless more water than the crop uses is applied. This excess water controls soil salinity levels by leaching some of the salt from the rootzone. The fraction of applied water that moves downward through the rootzone and is not used by the crop is called the "leaching fraction".

      Soil salinity is expressed as the electrical conductivity of the saturated soil extract (ECe) (with the units usually expressed as mmhos/cm or dS/m). rootzone salinity (ECe) increases as the leaching fraction decreases for a given irrigation water salinity (ECw). Increasing the leaching fraction when using a more saline irrigation water can result in the same average rootzone salinity as using a less saline irrigation water with a lower leaching fraction. In short, if a more saline water must be used because of drought, applying more water to increase leaching can lessen the effects of salinity on plant growth.

      Table 1 lists water quality guidelines for the most commonly grown tree and vine crops in California. These guidelines assume that the soil is well-drained -- that is, that adequate soil aeration exists for root respiration and disease control -- and that the leaching fraction is 0.15. Under these conditions the relationship between average rootzone salinity (ECe) and ECw is ECe = 1.5 ECw. It is also assumed that all other factors (such as fertility, irrigation scheduling, and pest control) are managed for optimal crop performance. The ECw values given in the table represent the maximums that can be continuously used to achieve the given yield. For example, the ECw values at 100% yield represent the poorest quality water that, if used continuously, will produce ECe levels equal to the salinity thresholds.

      Toxicity to Specific Elements

      Unklike most annual crops, tree and vine crops are generally susceptible to boron and chloride toxicity. Tolerances vary among species and rootstocks. Tolerant varieties and rootstocks restrict the uptake and accumulation of boron and chloride in leaf tissue. Boron concentrations in the irrigation water exceeding 0.5 to 0.75 mg/L can reduce plant growth and yield. Climatic effects are also important. In the cool moist coastal climates, irrigation waters with boron concentrations exceeding 1 mg/L are used successrfully on treee and vine crops.

      Chloride moves readily with the soil water, is taken up by the plant roots, translocates to the shoot and accumulates in the leaves. Table 2 contains maximum permissible concentrations of chloride in the irrigation water (assuming a 15% leaching fraction) that various rootstocks or cultivars can tolerate without experiencing leaf injury. Injury does not necessarily mean a reduction in yield or vice-versa. Chloride injury usually begins with a chlorosis (yellowing) in the leaf tip and margins and progresses to leaf burn or drying of the tissue as ijury becomes more acut. Chloride injury can also result from direct leaf absorption during overhead sprinkler irrigation.

      Short-term Versus Long-term Use of Water

      These guidelines are based on the long-term use of the given water quality. Poorer quality water can be tolerated if used on a short-term basis.

      If good quality water is used for one-third of the irrigation season, saline water with an ECw that would cause a 25% to 50% yield reduction if used continuously (Table 1) may be used for the remaining season with little or no yield reduction. Caution is advised in using this irrigation strategy since reduced growth and increased levels of chloride and boron in the soil and plant tissue could reduce yields in future years. Sufficient rainfall or good quality water is needed the subsequent year to leach most of the salts from the upper tow or three feet of the rootzone. In some soils, good quality water following saline water could cause reduced soil-water infiltration, creating an ideal environment for root diseases.

      Table 1. Estimated crop yield using irrigation water of various qualities over the long-term. Potential yields are based on a 15% leaching fraction.

      Yield Potential %* Rating**
      Tree and Vine Crop 100 90 75 50
      ECw (mmhos/cm)
      Almond*** 1.0 1.4 1.9 2.8 S
      Apricot*** 1.1 1.3 1.8 2.5 S
      Blackberry 1.0 1.3 1.8 2.5 S
      Boysenberry 1.0 1.3 1.8 2.5 S
      Date Palm 2.7 4.5 7.3 12.0 T
      Grape 1.0 1.7 2.7 4.5 MS
      Grapefruit 1.2 1.6 2.2 3.3 S
      Orange 1.1 1.6 2.2 3.2 S
      Peach 1.1 1.5 1.9 2.7 S
      Plum 1.0 1.4 1.9 2.9 S

      *Based on data from E.V Maas, 1990, "Crop Salt Tolerance." In: Agricultural Salinity Assessment and Management, ed. K.K. Tanji. ASCE Manual No. 71. ASCE.
      **Sensitive (S), moderately sensitive (MS), moderately tolerant (MT), and tolerant (T), to soil salinity.
      ***Tolerance is based on growth rather than yield.

      Table 2. Maximum chloride concentrations that various tree and vine crops can tolerate without developing leaf burn. (Assumes long-term effects and a 15% leaching fraction.)

      Yield Potential %* Rating**
      Crop Rootstock or Cultivar Maximum recommended chloride concentration* in the Irrigation Water
      ppm meq/L
      Avocado West Indian 180 5
      (Persea Americana) Guatemalan 140 4
      Citrus Sunki Mandarin, Grapefruit, Cleopatra Mandarin, Rangpur lime 590 10
      Citrus Sampson tangelo, rough lemon**, sour orange,Ponkan mandarin 350 10
      Citrus Citrumelo 4475, trifoliate orange, Cuban shaddock, Calamondin, sweet orange, Savage citrange, Rush citrange, Troyer citrange 240 7
      Grape Salt Creek, 1613-3 950 26
      (Vitis spp.) Dog ridge 710 20
      Stone fruit Marianna 590 17
      (Prunus spp.) Lovell, Shalil 240 7
      Yunnan 180 5
      Cultivars
      Berries*** Boysenberry 240 7
      (Rubus spp.) Olallie blackberry 240 7
      Indian Summer raspberry 120 3
      Grape Thomas seedless, Perlette 470 13
      (Vitis spp.) Cardinal, black rose 240 7
      Strawberry Lassen 180 5
      (Fragaria spp.) Shasta 120 3


      *These concentrations may exceed the salinity threshold and cause yield reduction in some crops.
      **Data from Australia indicates that rough lemon is more sensitive to Cl than sweet orange.
      ***Data available for one variety of each species only.


      How to Grow Navel Orange Trees

      Protect navel orange trees from the cold by wrapping them in blankets or clear plastic sheets during a freeze.

      Fruit can be left on the navel orange tree without it over ripening.

      Navel oranges are susceptible to pests such as the Asian leaf miner, but this pest will not kill the tree.

      Keep the soil around the navel orange tree moist while the tree is young.

      Do not allow 1- and 2-year-old navel orange trees to produce fruit. Pluck off any fruit that grows to allow the tree to focus on growing.

      Navel oranges are familiar to almost everyone as the oranges you find in the super market. While Valencia oranges are used for juice making, navel oranges are grown mostly for their fruit. While oranges are native to India, navel oranges are a hybrid of sweet oranges, created in Brazil. They are the hardiest of all oranges grown and do well in light frosts, so long as they are protected. There are a few varieties to choose from, many that will remain hardy in USDA zones 8 to 11. Navel orange trees are easy to grow in the right climate.

      Choose a variety of navel oranges to grow. There are dwarf navel orange trees, but they do not grow much fruit. Pineapple and Cara cara are other varieties of navel oranges. Cara cara has pink flesh.

      • Navel oranges are familiar to almost everyone as the oranges you find in the super market.
      • They are the hardiest of all oranges grown and do well in light frosts, so long as they are protected.

      Choose a spot in your garden for the orange tree. The tree needs to be planted in full sun near the south side to protect it from cold. Planting near a wall is acceptable. Well-drained soil is a must. Plant orange trees away from grass and other plants.

      Plant your navel orange tree in the spring after the last frost. Dig a hole for the navel orange tree. It must be deep enough to accommodate the root ball, about 2 to 3 feet deep and 3 feet wide. Place the tree in the hole and fill it with water. Allow the water to soak in. Fill the hole with soil and pat down.

      Water your navel orange tree once a week for 10 minutes each watering. Be sure the soil absorbs all the water while it is young. Once it is more than a year old, water it only once every other week for 10 minutes each watering.

      Add one cup of water-soluble 10-10-10 fertilizer to navel orange trees in the late winter.

      Prune your navel orange tree in the spring while the tree is dormant before and new growth. Remove dead, damaged or crossing branches at the base of the tree. Give branches a space of about 6 to 8 inches. No other pruning is needed.


      Today’s techniques

      Today, soil management in citrus plantings is predominantly aimed at the following areas:

      1. Correcting/minimising soil acidity

      • Monitor the soil pH regularly using soil analysis. Collect samples from similar areas within the orchard at depths of 0–15 cm and 15–30 cm. For new sites also sample at 60 cm. Select several test sites as standards for monitoring long-term changes in pH.
      • Apply lime to counter the acidifying effects of nitrogen fertilisers or to improve the pH of new sites. Intersperse the lime with dolomite or magnesite, depending on the exchangeable calcium:magnesium ratio (the ideal is 2:5). Application rates of 1.5–2.5 t/ha should be based on results from soil analysis.
      • For new or replanted sites, apply the lime 6–8 weeks before planting. Work in the lime as deeply as possible and use sufficient to achieve a soil pH of 6.0–7.0 in the plant row.
      • In established orchards, broadcast superfine lime in the plant row where nitrogen fertilisers are applied. The usual time is June/July, but any time when heavy rains are not expected is suitable. In the future it may be possible to inject lime into the subsoil, using deep-slotting/Agrowplow® implements currently being developed.
      • Use the least acidic forms of nitrogen such as urea or ammonium nitrate, and reduce sulfate forms of fertiliser such as ammonium sulfate.
      • To reduce leaching, apply nitrogen fertilisers in small amounts at frequent intervals. Alternatively, apply nitrogen through irrigation water (fertigation) a third of the way through the irrigation cycle.
      • To avoid overwatering and leaching out of plant nutrients (which increases soil acidity), monitor the soil water, using a tensiometer.

      2. Improving plant nutrient supply

      • To avoid nutrient availability problems associated with the pH being too low or high, maintain soil pH at 6.0–7.0.
      • For short-term control of micronutrient deficiencies such as zinc, magnesium and manganese, use foliar fertilisers as needed.
      • To improve organic matter content, apply slow-release organic fertilisers (e.g. poultry manure) at 2 t/ha in late summer/autumn. Organic fertilisers are particularly important on sandy soils, increasing the organic matter and decreasing nutrient loss from leaching.

      3. Maintaining and improving soil structure and drainage

      • Install agricultural tile pipes to improve drainage. Locate drains above the impermeable clay layer.
      • Plant trees on raised beds. Sow green manure crops and apply organic matter (for example, animal manure).
      • Mulch along the tree rows.
      • Sow and maintain a permanent sod between tree rows.

      4. Weed control

      • Mulch the tree rows, using organic matter or weed matting.
      • Sow and maintain a permanent sod between rows.
      • Use a registered knockdown herbicide in plant rows, as required.

      5. Improving irrigation infiltration

      • Make irrigation efficient by using water-scheduling aids such as tensiometers.
      • Reduce orchard traffic when soil is wet.

      Watch the video: Why your citrus tree is losing leaves and how to fix it!