Potassium nitrate has been used overseas to regulate mango flowering and Ayr researchers David Catchpoole and Ian Bally have tested it on local cultivars under local conditions. Early results look promising although more work is needed to confirm the results.
The fertiliser, potassium nitrate, has been reputed to result in earlier flowering in some mangoes eg: Carabao in the Philippines. Yet there are no written reports of a response in Kensington to nutrient sprays.
This trial involved spraying potassium nitrate and trace elements on the leaves of different varieties of mango trees before they started flowerIng in June. Sprayed trees of the varieties Early Gold, Haden, Zillate, Keitt, Palmer and Irwin all flowered earlier, better, and more evenly, when compared with unsprayed trees.
Not all cultivars were affected in the same way. Van Dyke flowered earlier when sprayed, but the unsprayed trees caught up by the end of August. The spray technique did not significantly affect earliness of flowering in Kensington, R2E2, Nam Doc Mai, Glenn, Isis or Kent.
The sprays substantially increased the fruit yield of most cultivars even when there had been no effect on flowering. R2E2 yield increased by 95% to 82kg per tree, Irwin yields increased 132%, Haden increased by 116% and Keitt yield improved 52%.
Other cultivars showed less response. Kensington Pride yield increased by 30% with the sprays, Zillate improved by 27%, while there was no response with the cultivar Kent. The low yields recorded by Palmer were because the trees were only two years old.
The spray used was made up as follows:
|To 100 litres of water add:|
|Potassium Nitrate||2.6 kg|
|Sodium Molybdate||8 g|
|Ferrous Sulphate||6 g|
|Boric Acid||4 g|
|Zinc Sulphate||0.6 g|
The mix can be difficult to dissolve when mixed, so it may be easier to mix the equivalent quantities of trace elements in the chelate form.
The spray was applied three times (beginning in late May, after the leaves had hardened off), leaving a fortnight between sprays. Each tree was sprayed until dripping. This took about 7 litres per tree for 8-year-old trees, about 4 metres high.
Trace elements were included in the foliar spray, as recent work by DPI has showed the importance of trace elements for good fruit set. A trial with grafted Kensington plants grown in a hydroponic system with nutrients containing different amounts of trace elements, showed a big increase in fruit set up to pea size when each of the trace elements iron, boron, zinc, manganese, copper and molybdenum were supplied at high levels.
DATE: November 1993
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