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High density planting-an approach to
increase citrus yields
By
M. Azher Nawaz1, Dr.Waqar Ahmed2, M. Mithal
Jiskani3
1. Agriculture Officer, Agriculture Extension Office Dhanote, Lodhran.
2. Associate Professor, Institute of Horticultural Sciences, University of
Agriculture, Fiaslabad.
3. Assistant Professor, Sindh Agriculture University Tando Jam, Sindh.
 Citrus
is an important genus of family Rutaceae in the plant kingdom. Citrus fruits are
cultivated in more than fifty-two countries of the world which are concentrated
at 40° North and South of equator. Citrus fruit rank at the top in world
production and trade among tree fruits. It is highly prized and economically
remunerative. Citrus fruits have special importance due to their distinct
flavors and therapeutic values. It is an established fact that grapefruit juice
is enriched with antioxidants therefore used as anati-cancer agent by a large
population of the world. Moreover, citrus fruits are rich in vitamin C with fair
amounts of vitamins A & B. Besides this, they are rich source of minerals
(calcium, phosphorus and iron). The juice is very refreshing, delicious and
soothing. Citrus fruit comprise about 40% of the total fruits produces in
Pakistan and it is cultivated over an area of 185,400 hectares with an annual
production of about 1.67 million ton. (FAO. 2005). More than 95% of citrus is
being produced in the province Punjab and 70% of citrus grown in Punjab is under
Kinnow. In fact Kinnow has monopolized the citrus industry of Pakistan. Pakistan
is bestowed with suitable climate and soil conditions to grow citrus. Even then,
Production of citrus fruits is very low in Pakistan as compared to other leading
citrus producing countries whereas population of Pakistan is increasing rapidly;
there is problem of feeding large number of human beings with limited cultivated
area. So to meet the needs of ever increasing population of the country as well
as for export it is imperative to improve the yield of kinnow mandarin both in
terms of quantity as well as quality with ever limiting resource of cultivated
lands.
In most orchards with standard planting, the trees are set at the corners of
square or rectangles of such size as to accommodate the trees when fully grown.
The full distance allowed from tree to tree will not normally be required by the
trees for early ten to fifteen years, and in the meantime inter plantings can
often be done to take the advantage from the fallow land. The majority of citrus
planted in Pakistan are spaced at 22 ft ? 22 ft or 20 ft ? 22 ft giving 90 and
99 trees per acre, respectively. But the tendency since 1990 has been towards
closer planting distances. Results of earlier work on density have indicated
that closer spacing produce more fruit per acre. A number of grooves have been
planted as “hedgerow” plantings on an 11 ft ? 22 ft spacing.
Several countries, including Australia, have higher yields from high-density
citrus orchard (>500 tree/ha) as compared to low-density orchards (<500
trees/ha). To date these higher yields have been more evident during the 4 to 10
years period after establishment. In Australia average annual yield in excess of
60 tones/ha have been obtained from 6-year-old “Valencia” orange trees at a
density of 2500-5000 trees/ha. Current interest in higher density orchards has
been stimulated by a number of factors. These include the irreversible reduction
in the availability for prime citrus land through urbanization. The establishing
energy costs involved in the use of farm machinery for pest control and
harvesting operations etc. The higher costs and reduced availability of water
for irrigation and greater difficulties involved in obtaining suitable labor for
hand harvesting particularly in orchards where much ladder work is required.
Thus shortage of land, energy, water and skilled harvesting labor, together with
higher fixed costs which require a more rapid return on capital have all
contributed to the trend toward higher planting densities evident in several
countries including USA.The major advantage of high density planting is higher
convenience and efficiency of tree care, plant protection operations, harvesting
and early production of commercial yields. Early productivity shortens
investment period and enables quick supply of fashionable market demands for
newly developed fruits. Furthermore tree spacing has become an increasingly
important consideration in citrus rootstock management because of the benefits
of higher tree density on early production and financial returns.
Citrus plantings should be planed so that the biological and management aspects
are interrelated to maximize economic return. Due to changes in labor wages,
government regulations, and tree loss rates require continual evaluation of
citrus plantings to establish optimum system. In Florida a number of changes
have occurred which affect returns from citrus production; land values and taxes
have increased, certain zoning laws favor the agricultural production;
availability of good land for citrus has decreased; citrus on poor soil type
results in smaller tree size due to various limiting factors; loss of trees to
diseases has increased; and there have been tremendous increase in capital
expenditures for equipments and irrigation, interest rates, and labor costs.
Because of these changes, it appears that citrus production in the future must
make more efficient use of the limited amounts of good land provision for more
rapid recovery of investment capital in order to provide maximum average net
return. So, tree spacing has become an increasingly important consideration in
citrus rootstock management because of the benefits of higher tree density on
early production and financial returns. As by high-density plantation we can get
earlier return on investment; better spray coverage at less cost, easy
harvesting and return to fulfill production sooner after tree damage or removal.
At closer plant spacing Kinnow plants grow taller than its normal pattern of
spreading canopy and it was due to competition among plants for light
interception in close spacing, owing to which plants get more height. In closer
spacing, plants also compete for nutrients which may cause lower and inferior
quality fruits. Canopy volume reflects the efficient use of nutrients light and
water. At wider spacing plants have spherical type canopy because they have
enough space for canopy spread. At wider spacing plants received more light
around the canopy and lateral buds proliferate effectively leading to lateral
branch development. As a response to more light interception at higher branches,
the pattern of growth in Kinnow mandarin changed to upright as against
spreading. This very particular behavior of canopy development in relevance to
plant height needs regular pruning for canopy management. While at wider spacing
number of trees ha-1 are less due to which cumulative yield is low. So a
moderate planting distance along with canopy management is required for early
and more return. As the value of land increasing and the available land for
cultivation is decreasing, in this condition high density plantation is very
important and effective as a greatest amount of fruit bearing volume per hectare
would be attained.
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