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The tree and its surroundings

The bush that produces coffee is referred to as the coffee tree. It grows naturally in tropical regions and belongs to the Rubiaceae family, which consists of over 500 different genus and 8,000 species. One of these genus is the Coffea, which is constituted by trees, bushes and reeds and composed of by more than 10 civilized species, that is, species cultivated by man and 50 wild species.

The coffee tree is recognizable by its simple opposing leaves, with frequently well developed stipules. Its flowers are small, tubular and white. The fruit is a drupe with two seeds and a sugary pulp.

The coffee beans or seeds are contained within the fruits of the coffee tree, which at maturity turn red and are thus referred to as coffee cherries.  Each of these consist of an exterior skin that covers a sweet pulp, which respectively covers the seeds surrounded by a fine, golden membrane.

The fruit of the coffee tree whose seeds are roasted and ground and used for human consumption is composed of by:

  • An external layer known as the pulp.
  • A sugary gelatin substance that is referred to as mucilage.
  • A hard shelling that is referred to as parchment or simply as the shelling.
  • A thinner layer commonly known as the film.
  • And finally the grain or almond which is the part of the fruit (drupe), which is roasted and ground in order to make drinkable coffee.

The taxonomy of coffee, its botany and physiology, and the characteristics of the plant, such as its roots, stem and branches, leaves, flowers, fruits and seeds are unique, and thus the objective of analysis and investigation undergone by specialized research centers such as Cenicafé. 

A Crop that should adapt to its Environment

As we have seen in the History of Coffee, this product originates from the tropical regions of Africa, and has adapted to other tropical and subtropical regions in the Americas, Asia and Oceana.

In the case of Arabica Coffee which is a specie more vulnerable to plagues and diseases than its parent specie the Robusta Coffee its adaptation is more inclined to subtropical regions or to tropical regions with greater elevations. These elevated regions tend to have less extreme weather with milder average temperatures. Robusta Coffee, consequent to its Meridional African origin, adapts easier to less elevated and inhospitable tropical regions.

Within tropical mountainous regions with significant elevations, such as East Africa (Kenya, Tanzania, and Ethiopia) and the tropics within the Americas, such as Colombia, it is possible to produce coffee near the equator in elevations of up to two thousand meters above sea level. In these regions of lesser latitude and greater elevation, the average annual temperature permits the production of very high quality coffee.

Arabica Coffee in higher elevations requires a unique climate (temperature, precipitation, sunlight and humidity) and soil for its cultivation. For this reason and although the origin of the genus is tropical, not all tropical regions are apt for its cultivation.

The Taxonomy of Coffee

Coffee belongs to the Rubiaceae family and the Coffea genus. There are many species of coffee trees and different varieties of each species. The most important commercial species that belong to the Coffea genus are known as Coffea arabicaLinneo (commonly referred to as Arabica or Arabiga) and Coffea canephora Pierre Ex-Froehner (commonly referred to as Robusta).

 

Botany and Physiology

  • The coffee tree belongs to the Rubiaceae family. This family has the following easily discernable features:Leaves sprout in pairs.
  •  Leaves are not divided and its borders are smooth.
  •  The flowers contain the reproductive organs of both sexes, thus the flowers are hermaphrodites.

Generally, each fruit has two seeds. The Root

This is a very important organ through which the plant absorbs the water and nutrients necessary for its growth and production. A healthy root guarantees that substances are accumulated and later used to nourish the leaves and fruits, and allow the tree to remain anchored.

The coffee tree has a taproot that penetrates vertically up to 50 centimeters soil without physical limitations. From this root sprout other thick axial roots that extend horizontally and serve as support for thinner roots known as feeder roots. The feeder roots of the coffee tree are very superficial and are responsible for absorbing water and mineral nutrients. Slightly more than half of these roots are found within the first ten centimeters of depth and 86% are found in the first thirty centimeters of depth.

 

The Stem and Branches

The stem or trunk and the primary branches form the skeleton of the coffee tree.

The most prominent aerial features of the morphology of the coffee plant have to do with two types of shoots:

  • Orthotropic, morphological features that grow vertically and compose the principal stem and offshoots.
  • Plagiotropic, morphological features that grow horizontally and refers to the primary, secondary and tertiary branches.

Several types of buds are found within the knots of the principal stem:

  • Those that serve as the origin of primary branches.
  • Those that remain dormant until the moment of pruning, or cutting the stem (known in Spanish as Zoca), and give rise to new offshoots.
  • Other buds that form flowers.

The primary branches cannot be renewed. When a primary branch is lost the coffee tree looses an important segment for the production of its fruits. The cherries harvested from the coffee tree are mostly produced by younger branches. The greater number of younger branches the better the harvest will be.

 

 

 

The Leaves

The leaves are a fundamental organ of the coffee tree. The bush uses them for photosynthesis, transpiration, and respiration.

At first, a coffee tree branch would generate a pair of leaves approximately every 15 to 20 days.

Independently of the density of the plantation, a coffee tree with one year of maturity has on average approximately 440 leaves. After the second year the density of the plantation as well as the amount of sunlight that a coffee tree receives reflects notably on its quantity of leaves.

Coffee leaves last approximately for one year. The duration of the lifespan of such leaves is significantly reduced by droughts, high temperatures, and poor nutrition.

The growth of leaves and branches can be increased by:

  • Applying fertilizers.
  • Pruning.
  • Weeding.
  • Increasing the amount of sunlight exposure.

 

The Flower

The flowers are the designated reproductive plant organs. The flowers evolve into fruits, and without flowers there would not be a harvest.

The coffee flowers appear at the branches' nodes, towards the base of the leaves, in groups of 4 or more. They grow over a very short tallit called a glomerulus. At the base of each leaf there are 3 to 5 clusters.

The quantity of flowers present at any specific moment depends on the quantity of knots previously formed in each branch.

The coffee tree's flower formation process can last between four to five months, following the subsequent stages:

  • Floral initiation and differentiation.
  • A short latency period.
  • Rapid rejuvenation of the floral bulb.
  • Blossoming of the bulb.

The final stage of floral development is conditioned by the suspension of the latency period and this can only be brought about by the presence of rain after a prolonged dry spell, a sudden drop in temperature, or by an intense fog at the end of the dry period.

The floral fertilization occurs when a grain of pollen makes direct contact with the floral ovaries. Self-fertilization occurs when the ovary receives the pollen from the same flower, which is common in Arabica trees as opposed to Robusta trees, where cross pollination needs to occur.

Knowledge of the flowering process of the coffee tree permits coffee growers to establish:

  • The adequate distribution of the coffee plantation.
  • Estimates regarding the amount of manual labor required for the harvest.
  • Cultural practices as well as the management of pests and diseases.
  • Estimates of cash flows throughout the year and identification of periods and origins of potential problems that can affect the quality of the harvest.

 

The Coffee Bean

The fruits and seeds are the result of the union of the grain of pollen and the ovary. Although 32 weeks is the average time from flowering to harvesting, in some regions within Colombia, it can take up to four additional weeks, depending on specific conditions.

 There are four distinguishable stages throughout the development of the coffee fruit.

Pinhead Stage

  • The bean barely undergoes any noticeable change in their size and weight.
  • This stage begins at the moment of fertilization and lasts until roughly the sixth week.

Rapid Expansion Stage

  • During this stage the bean grows rapidly in size and weight as the locules that contain the ovaries swell with rapid cell expansion of the integument.
  • The integument is a cavity that will later be filled by the embryo (coffee bean).
  • The size to which the integument swells depends on the moisture present in the soil.
  • Water is neededat this stage; otherwise a drought will limit the size of the integument and therefore the size of the final bean causing the "black bean" defect.
  • This stage is also referred to as the stage where the milky grain is formed.
  • This stage lasts from the sixth week up to the sixteenth week after fertilization.

 Endosperm Growth Stage

  • During this stage the external growth of the bean is barely noticeable while the endosperm (coffee bean) consumes and replaces the integument.
  • A layer of the integument will remain and will surround the bean. This is the silver skin.
  • At this stage the bean is jelly like, but will gain dry matter over the following months.
  • The fruit requires a significant amount of nutrients throughout this time.
  • The almond is hardened.
  • If the coffee tree lacks water the fruit will not finish developing well and the grain can become shriveled.
  • This stage lasts from the sixteenth to the twenty-seventh week after fertilization

Cherry Ripening Stage

  • The cherry pulp continues to grow and the endosperm will consume 70% of the total photosynthesis produced by the coffee tree, thus stalling the growth of the coffee tree.
  • After the beans are fully formed the fruit will change from a green to yellow to a bright red color. At this stage the coffee is ready for harvesting.
  • This stage lasts from the twenty-seventh to the thirty-second week after fertilization.

 

The Coffee Seed

The seed is composed of by two parts: the bean and the parchment (hull).

The bean is hard and green in color. It is covered by a silver skin when it is dry and by an embryo that is a very small plant that grows and feeds off the bean during the first couple months of its development.

Protecting the seed there is a covering referred to as parchment, which is itself covered by a sugary substance referred to as the mucilage or pit. The red or yellow part of the mature coffee cherry is referred to as the pulp (mesocarp). When the coffee is dried is known as a parchment coffee.

 

The Optimal Climate for Coffee Cultivation

The climate is a combination of atmospheric conditions that characterize a region:

Temperature

Rainfall

Humidity

Wind Factor

Sunlight

Cloud Coverage

Understanding the climate is important for knowing where, when and how to grow coffee and in which moment to harvest it. 

 

Components of the Climate

Temperature

  • The optimal region to grow Arabica coffee in Colombia is found where the average annual temperature varies between 19 and 21.5 degrees centigrade, in higher elevations.
  • In colder climates where the average annual temperature is less than 19 degrees centigrade, coffee trees face tougher conditions to grow. They may be less developed, produce lower harvests, and the harvest is distributed throughout the year.
  • In warmer climates, where the average annual temperature is greater than 21.5 degrees centigrade, the productive lifespan of the coffee tree is shorter; the harvest comes sooner and is more concentrated. Coffee rust attacks are more and severe and plagues such as the coffee berry borer and the leaf miner become more prevalent.

Rainfall

  • It is generally considered that the adequate amount of rainfall for the coffee tree is between 1,800 and 2,800 millimeters per year, and equally distributed throughout the year.
  • Periods of excessive rainfall favor the presence of diseases such as the Pink disease and the American Coffee Leaf Spot Disease.
  • Excessive rainfall can also affect the flowering of the coffee tree by either diminishing it or destroying it altogether.
  • Excessive droughts can cause the coffee tree to become dehydrated and thus lead to its defoliation and or increment the attacks of plagues such as the red spider mite, leaf miner or the coffee berry borer.

Air Humidity or Relative Humidity

  • This climate component can present large variations between the day and the night. In the coffee region the air is usually humid.

Wind Factor

  • This climate component is responsible for transporting water vapor and clouds, causing other climate components, such as rainfall, temperature, and sunlight to vary.
  • In general the regions most apt for coffee cultivation are characterized by gentle winds.

Sunlight and Cloud Coverage

  • The principal source of energy for plants is solar radiation, which varies according to the amount of cloud coverage present and the orientation of the mountain folds in relation to the direction of the sun. Sunlight is commonly expressed by the amount of hours in which it is present during a specific time period.
  • Sunlight in coffee regions is typically present between 1,600 and 2,000 hours per year (4.5 to 5.5. hours per day). 

 

The Soil in which Coffee is Cultivated

  • The soil is the upper layer of earth where plant roots develop.
  • The soil is essential for the coffee tree because it allows it to anchor and supplies it with the necessary water and nutrients for its growth, development and production.
  • The soil is derived from the slow disintegration and decomposition of rocks caused mainly by erosion from water, temperature and wind. In some regions this process is accompanied by volcanic ash. As time goes by, these particles mix with animal and vegetable residue, thus resulting in soil or vegetative layer of earth.
  • The soil is composed of by solid substances (organic and inorganic), water and air.

Physical Properties of Soil

The principal properties of soil are its: Color, Texture, Structure, Porosity, Permeability, and Effective Depth.

Color

In general terms, black soil indicates a rich amount of organic material. In general, the darker the soil the better it is for coffee cultivation.

Texture

This property is in relation to the size of the soil grains and particles.

  • The smaller grains and particles are referred to as clay.
  • The larger grains and particles are referred to as sand.
  • The intermediate sized grains and particles are referred to as silt.
  • The quantity and proportion in which these particles are found in the soil determines its texture.
  • Depending upon the grains or particles that are found in greater quantities in the soil, one can describe the soil as clayish, silty or sandy.
  • When the particles are found in equal proportions, the texture is referred to as loam, the best soils to cultivate coffee are those referred to as loam.
  • Each texture provides the soil with particular properties, such as its porosity, richness in nutrients amongst others.

Structure

This component refers to how the particles or grains of soil are grouped, and thus reflects directly on the growth and penetration of the coffee tree roots.

  • It is very important in terms of the permeability of the soil, in the difficulty to work the soil, and the inherent resistance of soil erosion.
  • The structure of the soil can be improved or impaired depending upon the way that the coffee is grown.
  • The best structural type of soil for coffee cultivation is granular.

 Porosity and Permeability

When the particles and grains of soil are grouped together to form masses of compact earth, there are remaining spaces between them of various sizes denominated pores which are occupied by water and air.

The permeability refers to the velocity in which water and air circulates or moves through these pores.

  • Sandy soils are of high permeability and clayish soils are of low permeability.
  • The best soils for coffee cultivation are loamy soils, in which the permeability is moderate.

Effective Depth

This component refers to the vertical distance that roots can easily penetrate in search of water and nutrition.

  • The greater the effective depth of the soil is, the stronger the coffee tree will develop.
  • In general, the ideal soil for coffee cultivation permits the roots to penetrate up to 80 centimeters in a vertical direction.
  • Erosion caused by inadequate weeding practices diminishes the effective depth of the soil.

The best soils to cultivate coffee are loamy, structurally granular, well aerated, moderately permeable, and offer a good effective depth.

Chemical Properties of the Soil

The most important of these properties are its Ph Balance or Acidic Level, fertility and proportion of organic matter. These are determined in a laboratory through careful chemical analysis of the soil.

Ph Balance or Acidic Level

  • This measure varies between 1 and 14. Good quality soil for coffee cultivation should have an acidity level between 5 and 5.5.
  • Soils with acidity level below 5 or above 5.5 are not recommended for coffee trees.

Fertility

This soil property is closely in relation to the quantity of nutrients available for the plants.

The nutritional elements most required for healthy coffee trees include: Nitrogen, Phosphorous, and Potassium.

Coffee trees need in less volume the following nutritional elements: Calcium, Magnesium, Sulfur, Iron, Zinc, Manganese, Boron, and Copper.

The lack of any of these nutrients will affect the normal growth and development of the coffee plantation as well as it potential productivity, in terms of both its quality and the volume of coffee produced.

A soil that is either mildly or poorly fertile can be improved through the application of fertilizers. Thus, it can be said that for the cultivation of coffee physical conditions of the soil are more important than its fertility.

Organic Material

  • This component is represented by decomposed plant and vegetable residuals.
  • The decomposed coffee pulp also supplies organic material to the soil.
  • Organic Material is very important for having a highly productive coffee plantation. It has a decisive influence on the improvement of the physical conditions of the soil, favoring the retention of humidity and is the principal substratum for the development of small organisms allowing an important source of nutrition for coffee trees.
  • Good soils for the cultivation of coffee should consist of at least 8% organic material.
 

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