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Plant analysis gives a direct indication of the
nutritional status of the plant and may show a strong correlation with yields
(Ahn, 1993; Foster and Prabowo, 2002). Plant chemical analysis may be another
helpful tool in establishing fertilizer requirements. The plant’s nutritional
status is the net effect of variables related to soil, plant, climate, and
management (Ahn, 1993).

In perennials, nutrient deficiencies can be
detected through plant (Usually leaves are used) in the analysis and corrected
before they have an effect on production (Ahn, 1993; Smilde, 1985). Foliar
diagnosis will provide a better understanding on the nutrient uptake and the
it’s proper interpretation will help in providing idea about the plant nutrient
status.

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Cocoa
(Theobroma cacao L.) is a
preferentially alogamous tropical woody species formerly in the Sterculiaceae
family (Cuatrecasas, 1964) and reclassified in the Malvaceae family (Alverson et al., 1999) which originates from the
tropical rainforests of the Americas. Cocoa is grown almost exclusively within
10°N and 10°S of the equator; predominantly grown in the tropical areas of
central and south America, Asia and Africa (Marita et al., 2001). Here, the
climate is warm and humid and thus suitable for growing cocoa (Hartemink and
Donald, 2005).

 It is considered one of the most important
perennial crop in the planet, Global annual production of cocoa currently
exceeds 4 million tons. However, while global demand for sustainable cocoa is
growing annually by 2 to 3 %, while Africa still contributes about 72% of the global
supply (ICCO, 2015). Cocoa is a major source of export earnings for many
producing countries; mostly it is commercially exploited for seed output mainly
for chocolate manufacturing and consumed in Western Europe and the United
States (ICCO, 2012, 2015). However, derivatives and by products of cocoa can
also be transformed in cosmetics, fine beverages, jellies, ice creams.

Around
80–90% of global cocoa production occurs on smallholder farms, by about 5–6
million cocoa farmers worldwide (WCF, 2014). Estimated at Ghana is around 400
kg/ha (Aneani and Ofori-Frimpong, 2013) while potential yields modeled at 5000
kg/ha under rainfed conditions (Zuidema et al., 2005)

As
cocoa is a perennial, the duration of its productive life should also be taken
into consideration when assessing productivity. Trees come into bearing after
2–6 years depending on the variety and location (Wessel, 1971; Wood and Lass,
1985). To
achieve high productivity, cocoa requires a soil abundant in nutrients (Wessel,
1971). The importance of several other soil characteristics, such as pH and
organic matter, is largely due to their influence on the availability of
nutrients.

Although
nutrients have different functions in the development of the tree (e.g., canopy
formation, flowering, pod production), all nutrient deficiencies will
ultimately lead to decreased yields. It is hypothesized that pod production is
fundamentally determined by the available nutrients in the tree at different
stages from flower initiation to pod maturity (Hutcheon, 1976). Soil nutrient
levels have declined and can no longer support productive cocoa (Appiah et al.,
2000). Critical
values for leaf nutrient analysis are referred to for cocoa (Table 14).

Variations in cocoa leaf nutrient content do not
necessarily indicate variations in the nutritional status of the cocoa tree. A
main problem with using cocoa leaf analysis is that cocoa leaf nutrient content
depends on many factors. These include leaf age, the development of new leaves,
fruit bearing, light intensity, and seasonal effects.

Soil nutrients in cocoa plantation are being mined annually via
cocoa harvest (Ogunlade et al.,
2009).  Opeyemi et al, (2005) reported that an effective use
of fertilizer on cocoa would help not only to improve yield but also has the
advantages of profitability, product quality and environmental protection. Soils under cacao are often
depleted and acidic because of long-term cultivation with minimal fertilizer
input, loss of nutrients through erosion and leaching, and removal by the
harvested crops 3. This therefore implies that
fertilizer usage should be considered as a key factor in maximizing cocoa
production; the possibility of nutrition-related limitations to productivity
has been raised in the past but not examined in detail.

            In India, Cocoa was introduced in
the early part of 20th century and now it has become one of the
important horticulture crops and where it is largely confined to southern
states, viz., Kerala, Karnataka, Tamil Nadu and Andhra Pradesh. The total area
under this crop is 46,318 ha with a production of 12,954 MT (DCCD, 2011). In
terms of production, India ranks nineteenth in the world.  Large area of cocoa cultivation is under
irrigated coconut and the progressive growers who opt for mixed cropping,
better market opportunities have made cocoa as an undisputable intercrop in the
state. However, the productivity is low which is only 2 kg dry beans tree-1 as
against the potential yield of upto 4 kg tree-1 through improved production
techniques.

As the
demand for cocoa in India is more (30,000 MT) than the present supply (12,954
MT), cocoa production needs to be intensified (DCCD, 2011). Cocoa production
envisages techniques to improve yield through drip and fertigation, nutritional
management. Nelliat (1984) concluded that cocoa was a heavy feeder of
potassium. A good crop of cocoa removes as much as 170 kg of K ha-1.
Potassium is also the principal element present in the pods of cocoa
(Fassbender et al., 1985). Omotoso
(1975) reported that a crop of 1000kg dry Cocoa beans removed about  20kg N, 41kg P and 10kg K  and where the method of
harvesting  (as in Nigeria) involves the
removal of pod husks from the field, the amount of potassium removed increased
more than five folds.  Wessel (1971)
reported that there is a steady decline in almost all the nutrients with length
of cultivation of cocoa. Ogunlade and Aikokpodion (2006) reported that
phosphorus is grossly inadequate for optimum cocoa yield in cocoa ecologies of
Nigeria. 

Nutrient demands of the cocoa trees will fluctuate
throughout the year. For instance, according to Santana and Cabala-Rosand
(1982), N demand is greater during leaf fall and shoot production. In
April/May, young fruits are setting, while in September, the developing pods
have their greatest demand for nutrients (Wessel, 1971). Jadin and Snoeck
(1985) suggest that further splits would lead to better uptake. For instance,
Mg is best applied in November, at the end of the second rainy season in West
Africa. However, they acknowledge that many different times of fertilizer
application are not economically feasible. They advise three application times
during the West Africa. However, they acknowledge that many different times of
fertilizer application are not economically feasible. They advise three
application times during the year. According to Jadin and Snoeck, 1985, P
should be applied before flowering, half of K and all Ca and Mg during
flowering, and the other half of K 2–3 months later.

Plant analysis has been considered a very practical approach for
diagnosing disorders and formulation fertilizer recommendations (Kelling et al. 2000). Plant analysis, in
conjunction with soil testing, becomes a highly useful tool not only in
diagnosing the nutritional status but also an aid in management decisions for
improving the crop nutrition. Approaches to diagnosing
leaf nutrient status can be estimated by Compositional Nutrient Diagnosis (CND)
(Parent and Dafir, 1992;). For CND, the high-yield subpopulation is selected
from a crop survey database. This technique has been effectively utilized for
the establishment of nutrient norm and for identification of yield limiting
nutrients in fruit crops like banana (Raghupathi
et al, 2002,). With the background, present study was conducted
with the following objectives, To study the present status of nutrients in
cocoa growing enterprises of Puttur region of Karanataka and To develop CND
norms for identification of common yield limiting nutrients.

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