What Plants Need
A healthy, “happy” coffee plant is one that is able to produce the greatest number of quality seeds. There are three main factors influencing the “happiness” of a plant: genetics, the environment, and applied agricultural management. Since there is no exact formula to produce award-winning specialty coffee, farmers work to meet all the basic needs of plants so they are able to thrive. There are common biological necessities universal to all plants that make this possible. These essentials are sun, water, soil, and air; the four combine to provide the plant with the energy and nutrients necessary to sustain life. Certainly, different plants have adapted to require different specific conditions, depending on their histories and environments. However, all plants share these external factors that allow growth and reproduction—the only metrics of success a plant has.
Plants live in ecosystems. It doesn’t matter if the ecosystem is a natural one or an agricultural one. Either way, plants interact with their external surroundings and are dependent on soil, weather, microorganisms, temperature, humidity, and myriad other influences. Although a farmer may choose plants based on what is known about their genetics, the only factor that can be actively controlled each year after planting is the plantation’s agricultural management.
The following information is an introduction to plant biology and agricultural management on the coffee farm. It does not attempt to outline the difficult and high-risk situations that most coffee producers today are faced with. It is meant to present some basic biological factors to help non-agronomists understand some of the scientific complexities that go into maintaining a healthy, productive, high-quality coffee plantation. Use it as an overview, learn, and look to your producer relationships to get the human side of the story.
The Essentials for Life
It is critical to remember that whenever we take a “natural” plant out of the forest and use it for agricultural purposes, such as with coffee, its needs are changed. Agriculture is not nature. Coffee arabica is perhaps one of the more stubborn and sensitive of agricultural commodities. Since it is endemic to a very specific region (the highlands of Ethiopia and South Sudan), where it was born under an unusual set of genetic circumstances, it has a low level of genetic diversity with which to combat challenges (Lashermes, Combes, Robert, Trouslot, D’Hont, Anthony, et al., 1999). Also, it has only recently (in evolutionary time) been distributed throughout the world, which means that it has not had time to evolve to new climates and conditions. A C. arabica coffee plant in Indonesia, or Brazil, or Jamaica still grows best under the ideal conditions that its ancestors learned to love in the shaded understory of tropical forests in East Africa. This is one reason why it is so difficult to make C. arabica plants happy, and why this continues to challenge farmers all over the equatorial world.
To function, plants “inhale” and “exhale” the building blocks of life. The “inhale” is called photosynthesis, and the “exhale” is called respiration; both depend on water, energy from the sun, and nutrients. Plants take in nutrients and water from the soil through their roots.
There is always one major factor limiting a plant’s growth and reproduction (Larcher, 2003). This may sound bad, but in fact it is for the best—because we don’t want giant plants taking over the world and demolishing skyscrapers in a King-Kong-esque dramatic growth spurt. Usually, carbon (C), water (H2O), or nitrogen (N) will be the primary limiting factor. In the agricultural world, this often becomes macronutrients such as nitrogen (N), potassium (K+) and phosphorus (P). This is why farmers often have to irrigate or apply fertilizer to crops. In this day and age, perennial and wild plants are not often limited by carbon, as there is plenty of extra carbon in the atmosphere. However, in the case of annual crops (such as corn, soy, and wheat), carbon can become limiting, and adding peat or carbon-based composts can help alleviate this deficit. If you put a shade plant in sun, it will require more nutrients in order to keep up with the level of growth and production that will occur. If you add nitrogen, the plant will demand more phosphorus, potassium, and calcium to function properly. If you add more nutrients, the plant will therefore need more water. You get the idea. In this way, a plant is always, physiologically speaking, attempting to balance its available resources and allocate them to specific tasks relevant to sustaining life. What do humans do to make C. arabica coffee plants biologically happy? Plenty!
- Adequate Growing Conditions: Site Choice
Location is key for growing C. arabica. Site selection is one of the most important choices a farmer can make to ensure success. That being said, not all farmers have a choice of site; they may simply have a piece of land in proximity to a known coffee-growing area. Slope and aspect, topography, temperature, weather pattern, rainfall, seasonal change, and soil texture are not easy factors to alter (unless you construct a giant greenhouse around your coffee plants, which doesn’t seem feasible). The condition of the soil and history of the land can also influence the potential of a site. Practical and logistical considerations must be made in light of local harvesting techniques, irrigation, pruning, and other management practices.
- Adequate Water: Transpiration, Irrigation, and/or Soil Management
Creating an adequate water situation is key to maintaining a happy plantation of C. arabica plants. Many coffee farmers rely on rainfall as their only water source. Less frequently, irrigation systems are set up to maintain highly productive full-sun growing conditions. In these cases, commonly found in Brazil and Vietnam, where growth and therefore water demand are very high, automated systems have helped allow the expansion of coffee production (Snoeck & Lambot, 2009). In other instances, irrigation can be managed to facilitate flowering (Willson, 1999). The water balance of a coffee plantation is ideally maintained through soil and site selection. If this is adequate to begin with, a farmer is much less likely to need irrigation or soil additions to assure proper drainage. Coffee, like all plants, needs a minimum amount of water to remain healthy (i.e., not wilted) and functioning. This is because nutrients and minerals are absorbed by plants via capillary action, from their roots all the way up to the highest shoots. However, too much water in the soil can be detrimental. Roots need oxygen to survive and function, and shallow roots make erosion a topic of concern in certain coffee growing regions that experience periods of severe rainfall (Clifford & Willson, 1985; Snoeck & Lambot, 2009).
- Adequate Sun: Shade Management
Photosynthesis requires energy from the sun to convert CO2 from the air into sugars, which are plant food (Raven, Evert, & Eichhorn, 1999). However, the intensity of sunlight is important to C. arabica plants, and difficult to regulate naturally. Because C. arabica evolved as an understory plant, it can only utilize a limited amount of sun. In fact, too much sun can damage the photosynthetic tissues over time, eventually leading to decreased growth and production (Clifford & Willson, 1985). Young plants, like human infants, are particularly sensitive, which is why you often see coffee seedlings under cover. High temperatures associated with strong sunlight can also slow down photosynthesis by causing the plant’s pores (called stomata) to close up (Larcher, 2003).
- Adequate Nutrients: Soil Management
Nutrients beyond what a plant gets from air and water (carbon, oxygen, and hydrogen) are obtained through the soil. Roots act as little vacuums of water and nutrients, so that plants stay well hydrated AND healthy at the same time (Raven, Evert, & Eichhorn, 1999). Soil and its nutrients can be regionally specific, varying with local geology and parent material. So, depending on where a plantation sits in the world, soil management differs. In fact, it can be a micro-region-specific, very precise science, and some agronomists recommend having soils as well as foliar tissues analyzed multiple times a year to assure accurate nutrient management.
- Adequate Stimulation: Spacing and Pruning
Assuring that a coffee plantation will be healthy and productive for as long as possible requires active management, beginning with planting density, or plant spacing. It is essential to give each tree enough space to meet its needs, while at the same time considering yield per hectare. Depending on the cultivar utilized, adult C. arabica plants usually require 1-3 meters between plants. For example, when plants are spaced 2.5 meters apart, that results in 1600 plants per hectare; whereas, if spaced at 4 meters apart, the yield would be 625 plants per hectare (Rothfos, 1980). In situations where coffee is being intercropped with other types of plants, these decisions are more complex and depend on what sort of energy and water demands neighboring plants will have in relation to the needs of C. arabica.