Mango: Calcium
A key for
good Mango yield and quality
Calcium
is increasingly recognised as a key to mango production in the Northern
Territory for both yield and quality. Observation on yields indicates
some of the low yields and fruit drop problems may be the result of low
calcium levels and we are becoming more convinced that calcium is
essential for good quality, particularly good skin colour. The evidence
at the moment is only by observation. Recent research from Africa
indicates that mangoes use a lot of calcium – 10 times that
of
phosphorus and magnesium.
Leading growers in North Queensland
have long recognised the importance of calcium. Research by DPIF in the
Northern Territory has indicated that growers’ opinion that
calcium is important is possibly correct. Most Northern Territory soils
including Katherine are very low in calcium – around one
quarter
of recommended levels. Soil levels should be at least 1000 ppm; most
Northern Territory soils are only 250-300ppm.
Not only is the
amount of calcium important but the ratio of calcium to magnesium. This
should be at least 5:1 calcium to magnesium (expressed as meq/100g) The
quality reports have shown the best coloured fruit come from orchards
high in calcium, low in magnesium. Unfortunately many Top End soils
including Katherine have ratios less than 2:1 (expressed as meq/100g).
Magnesium
is present in many Northern Territory water supplies and for mangoes
this is a problem. It makes fruit green and soft. The amount of calcium
and magnesium in water supplies is variable so soil testing is crucial
to get levels right. Test your soils to ensure you have at least
1000ppm calcium and your calcium:magnesium ratio is at least 5:1. NTHA
provide a free interpretation service to members.
Calcium can be
applied as lime, gypsum or dolomite. Dolomite generally is not
recommended for mangoes as it is high in magnesium. Lime is used to
increase pH and gypsum is used to increase calcium where pH is OK or
high. Foliar sprays of calcium around flowering and fruit set have also
been used to improve yield and quality. Current indications are that
calcium should be applied at flowering (soil and foliar), after harvest
(optional), and especially at the end of the wet season after the heavy
rains to set the tree up for good calcium levels before flowering.
The
amounts of lime or gypsum required on most Top End soils are large. The
recommendations to date have generally been too low. They fail to take
into account wet season leaching and the negative effects of high
magnesium in most irrigation water. Mangoes appear to use a lot of
calcium. Most growers have taken 2-3 years to get their calcium levels
and their calcium:magnesium ratio right. Applications of 20kg/tree,
three times a year for 2-3 years are not uncommon so get your soil
tested. Leaf analysis can be used as a guide but can be misleading as
calcium increases naturally as leaves age. It is important to realise
that other elements also have to be corrected to get the maximum
benefit.
Boron is essential for the best calcium response and
should be applied at up to 50gms per mature tree. It is also important
to have phosphorus, zinc and potassium levels right. The bottom line is
get your soil tested. The best time to test soil (in Northern
Territory) is December to February before the main time for application
in March.
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