Annona Species Monograph.pdf - Crops for the Future

Chapter 10. Agronomy
the apical leaves. Deficient plants may flower, but there will be no fruit set.
A high content of K induces Mg and Zinc deficiencies.
Calcium - Calcium is an immobile nutrient and its deficiency affects the
zones of intense growth first. The symptoms of calcium deficiency in leaves
of cherimoya seedlings appear after 30 days. New leaves show interveinal
chlorosis. At 70 days, the apical meristem of cherimoya dies and the leaves
stop growing and become twisted. In the leaves of soursop seedlings, calcium
deficiency occurs later than in cherimoya (120 days), although the symptoms
are similar. The best ratio of Ca:Mg is 3:1, a higher ratio can increase Mg
deficiency.
Magnesium - The first symptoms of deficiency are generally shown in the
oldest leaves because Mg is a mobile nutrient. In cherimoya seedlings this
begins at 50 days. An interveinal chlorosis then starts to become visible in
the new leaves. In soursop, chlorosis is progressive, turning the leaves
necrotic.
Sulphur - This nutrient has low mobility, both in the plant and in the soil,
especially in soils with low organic matter content and high C/N ratios.
Therefore, the first symptoms of sulphur deficiency occur in the young
leaves. The new leaves of cherimoya seedlings are notably smaller than the
old ones after 75 days of sulphur deficiency, and the new leaves present an
overall yellowing. Similar symptoms are also detected in the leaves of
soursop seedlings.
Boron - Similar to calcium, this nutrient is immobile; therefore, the first
symptoms of boron deficiency occur in young leaves. In cherimoya seedlings
the leaf symptoms appear after 70 days. The upper leaves turn intense green,
with some chlorosis. At 140 days, leaf chlorosis becomes more intense.
Symptoms are similar on the leaves of soursop seedlings.
Iron - Like calcium and boron, iron is relatively immobile and the first
symptoms occur in the young leaves. The initial symptoms are partial
chlorosis (yellowish green), then the leaf blades become totally yellow,
except over the veins.
Zinc - Plants suffering from zinc deficiency often show chlorosis in the
interveinal areas of the leaf. These areas become pale green, yellow, or white.
Unevenly distributed clusters of small, stiff leaves are formed at the top of
the young shoots; this symptom is known as rosette or little-leaf.
109