OUR OPINION ON MANGO NUTRITION

MANGO NUTRITION

Our recommendations are based on these opinions. These opinions will change as we learn more about Mango Nutrition.

From our experience, we consider the most important results of the soil test for mango crops to be pH, Phosphorus, Potassium, Calcium, Zinc and Boron.

Following are the levels of those elements we consider best for Mangos in the Top End:

We find that P stays in the soil a lot longer than K. So after the wet season, we recommend enough P to bring the level up to 70 ppm and then just leave it at that.

K is used by the trees in large quantities during the dry season and is easily leached out, therefore, even when enough has been applied to bring the level up, we still recommend additional applications of K in the dry season to maintain the level.

We have also seen some indication that applying P and K will stimulate a tree into flowering when it had not yet flowered.

We often recommend Tropigro Mango Flowering and Fruiting Fertiliser when both P & K are required and Muriate of Potash when only K is needed. Muriate of Potash is cheaper than Potassium Sulphate but Muriate of Potash is not good for salty soils and if a soil is very low in Sulphur, we sometimes recommend Potassium Sulphate.

We don't think Sulphur is very important for Mangos but if the Sulphur is extremely low, it would have some effect, so we recommend some Sulphur in that situation.

Gypsum is another form of Sulphur, and it also contains a lot of Calcium but if the pH is low ie acidic, we will recommend lime instead. Lime does not contain any Sulphur but it contains a lot of Calcium and increases pH also.

Soils in the Top End are normally on the acidic side. Lime normally needs to be applied every year because rain is rather acidic, and levels of Ca need to be maintained. In fact, depending on the pH, we normally recommend a minimum of two applications of Lime, one in April and one a month before harvest.

If the soil is more sandy than clay, it is better to apply Lime in smaller quantities but more frequently. That applies to fertiliser also.

Although pH should ideally be 6.5, the trees are quite tolerant and levels down to 5.5 and up to 7.0 won't affect the quality of the fruit if the levels of all the nutrients/elements are good.

Although some people are of the opinion that Mango trees should never be given any Nitrogen, we are of the opinion that Mango trees should get some Nitrogen during the year and that immediately after harvest is the best time of year to do it.

Tropigro 10-97 has 10%N, 9%P, 7%K, 11%S, 8%Ca and 0.06% Zn, so in most situations, it is ideal for mangos at that time of year. At $37 for 50kg, it is a good price, also.

It is important that mangos do not receive any Nitrogen from January until after harvest. It can inhibit the trees ability to flower and can cause trees to drop fruit and result in poor quality fruit.

Zinc and Boron are very important for quality fruit. For some reason, Zinc seems to be more effective when applied on the ground, rather than as a foliant spray. It is a good idea to apply zinc in lumps in well watered places. This helps stop zinc being locked up in the soil.

Boron works together with Calcium so it is good to apply both at the same time. In fact Boron also needs to be applied evenly so we recommend Solubor for that reason. Calcium uptake relies on Boron.

As an added Calcium boost for the trees, we recommend Dextrolac Calcium Spray be applied weekly during fruit set. That is until the fruit is the size of golf balls. The smaller the fruit, the more benefit the calcium spray is to the fruit.

K, Ca and Mg all compete with each other. So when K and Ca are applied, the level of Mg will reduce.

We often want to reduce Mg because excess levels of Mg inhibits the uptake of K and Mg does not seem to be important in Mango trees. Excess Mg will result in green coloured fruit, even when it is ripe.

With all fertilisers and soil conditioners, it is only necessary to apply them under the canopy of the trees. Generally the roots of the tree only go about as far as the canopy, so applications outside that area are a waste of money.

All nutrients/elements are important for good quality fruit, but if we had to select one as the most important, it would be Calcium.

Poor quality fruit is almost always lacking in Calcium and there is never any disadvantage in having more Calcium in the soil, as long as the ratios are okay.

Those ratios are Ca:Mg which should be between 5:1 to 10:1 when using ppm, not % cation saturation.

For Ca:K it should be between 2:1 and 5:1 also in ppm.

Less Important Elements

Organic matter: ideally between 1-3% but in the top end it is usually very low. There is not any practicable solution and it is not that important.

Conductivity: should be less than 0.2. Conductivity measures total salt content. It is normally quite low because of our sandy soil and high rainfall.

Nitrate Nitrogen: should be less than 10 ppm. The level of N fluctuates so much that looking at the tree is probably a better indication of the level of N.

Sulphur: should be greater than 12 ppm but we have never seen any adverse reactions to low levels of Sulphur.

Sodium: a type of salt. Should be less than 1 ppm. Not usually a problem.

Chloride: another type of salt. Should be less than 250 ppm. Not usually a problem which is why we can recommend Potassium Chloride instead of Potassium Sulphate. Potassium Sulphate is a good form of Potassium but is significantly more expensive than Potassium Chloride.

Copper: should be 0.3 - 10 ppm, however if insecticides which contain copper have been sprayed onto the trees, no additional copper should be applied.

Manganese: should be 4-50 ppm but it is also important to be aware of sprays such as Mancozeb which contain Manganese. Those sprays may not affect the soil analysis but are still present on the trees.

Iron: should be 4-100. It is best to spray iron chelate as a foliant spray because it is difficult for the tree to take up iron.