Introduction related to soil, plant, climate, and management

Introduction

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).

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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.

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.
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.

 

MATERIALS AND METHODS

Survey

In Karnataka state, the cocoa cultivation confined to the Uttara
& Dakshian Kannada, Shimoga, Mysore Devanagere, Kodagu, Mandiya,
Chickmagalore, Hassan and Tumkur districts. Cocoa is found to be compatible
intercrop in coconut/arecanut plantations.  Foliar diagnosis will provide a comprehensive
understanding on the nutrient behavior and proper interpretation of leaf
analysis data will help in identifying nutrient from management perspective.

In order to further build up the data bank a regional survey made
in the cocoa growing areas like vittal and puttur, where cocoa is intercropped
with the coconut and arecanut gardens. The survey consisted of interviews with
the growers and sampling of leaf tissue. The plot was assessed for tree health
and general maintenance and the grower was interviewed about block history and
maintenance. An attempt was made to calculate yields, but it was not possible
to make reliable estimates for most blocks as most smallholders do not keep
production records. The age of the cocoa trees is 10 years old and average
yield is 1.2 kg dry bean/tree /ha .The leaves chosen (2 per tree) were the
third leaf of a recently hardened leaf flush at mid-canopy height.

Theory of the CND approach

As indicated by Parent and Dafir (1992), plant tissue composition
forms a d dimensional nutrient
arrangement, i.e., simplex (Sd) made of d+1 nutrient proportions
including d nutrients and a
filling value defined as follows:

Sd = (N, P,
K,….,Rd):N>0,P>0,K>0,….Rd>0, N+P+K+…+Rd= 100           (1)

where 100 is the dry
matter concentration (%); N,P,K,… are nutrient proportions computed as
follows;

Rd=100-
(N+P+K+…)                                                                                       (2)

The nutrient
proportions become scale invariant after they have divided by geometric mean (G) of the d+1 components including Rd
(Aitchinson, 1986) as follows:

G=NxPxKx…xRd
1/d+1                                                                                 (3)

Row-centered log
rations are computed as follows:

VN=  ln (N/G),….,VZn=
ln(Zn/G)                                                                       
(4)

Expressions such as N=G; . . .Zn=G are multi-nutrient ratios, since
each nutrient is divided by geometric means of all the components (the
determined nutrients and the filling value). The row-centered log-ratios are
linearized (undistorted) estimates of the original components that are fully
compatible with PCA.

Principal Component Analysis (PCA)

A PCA was performed on row centered log-ratioed nutrient values
characterizing the high yielding population. The correlation matrix in PCA
generates a linear combination of standardized row centered log-ratios as
follows:

PCj = aij(VN-V*N)/SD*N+…….+a(D-I)j                                                              
   (5)

(VZn-V*Zn)/SD*Zn

where PCj is the jth
principal component, and aij to a(D-1)(D – 1) components
excluding R as specified above are PC score coefficients of standardized row
centered log-ratios. V*N to V*

Zn and SD*N
to SD* Zn are the CND norms (indicated by asterisks), i.e., mean and
standard deviation of each row centered log-ratios in the high yielding
population. The standardized variables (VN – V* N )/SD* N
to (VZn – V* Zn)/SD* Zn are the CND nutrient
indices.

Indices

In= (VN –
V* N )/SD* N ,………IZn=(VZn – V* Zn)/SD*
Zn                                       (6)

 

Analysis of samples

The foliar samples are cleaned with distilled water and dried in 70°C
for 72 hr and grinned by wiley mill. The ground sample was digested with
concentrated H2SO4 and total N concentration was determined by micro Kjeldhal
distillation. Another part of the samples subjected to digesting 1 g leaf
sample with 10 ml 9:4 (HNO3:HClO4) for P and S estimation by the
Vanadomolybdate and Turbidometric methods. K, Ca, Mg and micronutrients like
Zn, Cu, Fe and Mn analyzed by the Atomic Absorption Spectrophotometry method.

Compositional nutrient diagnosis norms were calculated using
Microsoft excel 2000 software ( Microsoft corp.,2000), and principle component
analyses(PCA) were performed using SPSS 12

 

 

 

 

 

Normal,
low and deficient concentrations (% dm) of nutrients in cocoa leaves according
different Authors

Source

 

 

 

 

 

 

 

 

 

 

 

Normal

Low

Deficient

Normal

Low

Deficient

Normal

Low

Deficient

Remark