Annona Species Monograph.pdf - Crops for the Future

Chapter 10. Agronomy
Content of Potassium
Tree Age
(meq/100 g of soil) 3 years old 3-6 years old 6 years old
0.40 0-20 0-40 6-60
Source: Torres and Sánchez (1992).
The observation of deficiency symptoms, as a field analytical technique, is a
fast and low cost method. When used with soil and leaf analyses it is very
important for determining the nutritional status of annonas. The main general
physiological characteristics and symptoms of deficiencies on annona trees
are discussed below, following Avilan (1975), Navia and Valenzuela (1978),
Mengel and Kirkby (1987), Torres and Sánchez (1992) and Silva and Silva
(1997).
Nitrogen - When the supply of N from the roots is inadequate, N from the
older leaves is mobilized to feed the younger parts of the plant. Symptoms of
nitrogen deficiency on cherimoya seedlings start at 40 days after sowing,
with reduction of the plant and leaf sizes. The progression of the deficiency
promotes an intense yellowing of the leaf and then its abscission. In soursop,
the seedling shows a reduction in height, and leaf yellowing and abscission
occur more quickly than in cherimoya. The leaf blade also shows a greenyellow
chlorosis and changes texture. Symptoms of nitrogen deficiency in
sugar apple seedlings are irregular bud development and lack of branches.
The leaves are small and show dusty spots; abscission occurs later.
Phosphorus - In cherimoya seedlings, deficiency symptoms become evident
60 days after sowing. Irregular chlorosis occurs in the basal leaves and most
show a darker green colour. As the deficiency develops, the leaves become
small and irregular in shape, coffee coloured spots develop on the blade, then
abscission occurs in these affected leaves. Deficient soursop plants only grow
50% as fast as fertilized plants and the leaves show a necrosis on the blade
edges. Sugar apple seedlings also show reduced growth with thin shoots and
their leaves develop abnormal brown spots at their apices and on the blade
edges.
Potassium - Due to its great mobility, potassium moves from old organs to
new ones easily. In general, deficient plants do not have the ability to
transport carbohydrates produced in the leaves to the other plant organs.
Potassium deficiency in cherimoya seedlings appears at 50 days after sowing,
and shows intermediate symptoms that are between phosphorus and nitrogen
deficiency. Brownish spots start from the apex and basal parts of the leaf
blade, and gradually coalesce. In soursop, the leaf symptoms appear in the
8th month after sowing with a reduction in size and an abnormal yellowing,
then leaf abscission. Sugar apple trees show retarded growth and dryness of
108