Solar stress in young coffee plantations
Aspects as latitude, geography and altitude of a region determine its weather conditions; there is a noticeable change in environmental conditions from sea level to the high mountains and therefore there is a certain type of crops that could be planted in specific areas.
Before planting any crop, farmers should be aware of environmental conditions in their location; by observing the type of local vegetation we can have a pretty good idea of the overall weather over the year, for example, if you only see cactus and woody bushes with small leaf size, you could have the impression that place is generally warmer, with lower water availability than in a rain forest or jungle.
Also, we need to have into consideration parameters such as exposure to sunlight, wind, rainfall, overall temperature over the ground surface and erosion rate change considerably after the transformation of native forest or jungle into farming land, in other words, microclimatic conditions also are affected by agriculture.
The countryside landscape can change according to which crop is profitable at a certain time, a typical example would be when farmers cut their coffee plantations due to low market price to grow instead of short term crops. Bearing in mind that the change from a perennial crop as coffee to a short cycle crop as veggies can affect the microclimatic conditions over the soil after some time. Once the farmers decide to return to coffee they must deal with degraded soil with low organic matter content, high solar radiation, high evaporation rate, exposure to the wind in other words: tough conditions for young plants.
What can the producer do to improve the microclimatic conditions in their land before the arrival of coffee plants? If you are a farmer planning a coffee plantation, you shall think overhead, considering that coffee plants come from a nursery provided with all the essentials to fulfil the basic needs, once at the field they are going to be exposed to stress and their performance and survival capacity would be tested.
The main sources of stress for young coffee plants growing in soils previously used for short term crops is excessive exposure to sunlight and water deficit. As you may know, photosynthesis is a very important process made by plants (also by algae and cyanobacteria) which allows the transformation of carbon dioxide (CO2), water (H2O) and sunlight into glucose and oxygen (O2); a continue photosynthesis process due to high sunlight exposure would increase the demand of water to compensate the increase of temperature in the leaf surface, but if for any reason there is not enough water available for the roots and the plant tissue suffer water deficit and sun damage; stress symptoms appear.
The stress symptoms frequently are shown as yellowing of the leaves, abnormal shape, low growth or presence of certain fungal disease; the occurrence of stress symptoms won’t necessarily represent a big danger for the plantation if farmers apply decent fertilization practices unless there are heavy abnormalities or damage in the roots due to pests or incorrect labour during the nursery.
On the right, you can see that young coffee plants in the nursery don’t show any sign of stress but after a couple of months on the field, the same plants may struggle a little bit due to high sunlight (Left).
Farmers can include shade into their plantations to progressively decrease the impact of sunlight over the plant surface and therefore reduce the need for water intake by the roots to compensate for the high photosynthesis rate.
Observations of stress in young plants in the field
Recently in January 2021 we visited “La Puerta” in Trujillo State (Venezuela) located around 1900 meters high were a small group of farmers supported by a small private company in the hospitality sector wanted to reintroduce the cultivation of coffee on land previously used for vegetables; despite that the overall weather of this location is suitable for coffee, young coffee plants were presenting stress symptoms by lack of shade.
Sharing field observations with farmers
As field technicians, while visiting farmers we must explore the farms and recollect observations about their current status for further analysis and make suitable recommendations. We observed that the soil was lacking organic matter with low moisture retention due to the lack of shade by secondary crops or trees, offering poor microclimatic conditions for the development of the young coffee plants.
We advise a progressive inclusion of secondary crops into the plantation like beans, corn (short term shade) and banana (middle term shade) between the rows of coffee in order to make better use of the land while the trees that would work as long term shade grows. Also, periodical applications of foliar organic/chemical fertilizers mixtures shall be done to help the plant to stand the process of acclimation while the temporally and semi-permanent shade grows.
However, full exposure coffee plantations are supposed to be more productive than those under the shade, but the need for water and nutrients are higher and most farmers can’t allow themselves to cover high production costs.
The team of Insidejobcoffee would advise smallholders from around the world to prevent plant stress due to excessive sunlight and make efficient use of land by growing secondary crops while allowing the coexistence of coffee with native trees, to protect and recover soil from erosion and also preserve biodiversity in the farm.
As an additional comment; while visiting the field always bring a hat and solar cream; protecting your skin is as important as protecting the leaves of coffee plants.
Author: Eduardo Matos Santiago
Biologist- Agronomist at Inside Job Coffee
Masters in Economy and Science in Coffee