Dr. Modesto Mojena Graverán / Part II
In the previous article, I discussed making coffee plantations more productive, sustainable, and profitable. Proper management of the coffee plantation and fertilization are key, but it’s natural to have many questions. Therefore, today I will explain how to decide which type of fertilization to apply. The best way to know this is by adequately answering the following questions: How much fertilizer should be used? Which form of nitrogen the plants assimilate will be better, Nitrate Nitrogen or Ammoniacal Nitrogen?
The amount to apply is directly related to the yield we want to obtain from our coffee plantation. Therefore, we must consider three fundamental aspects: the nutrient demand, which is the amount of nutrients a plant can absorb from the soil solution to achieve a certain yield; the nutrient contributions of the soil, which will depend on its physical and chemical characteristics; and finally, the difference between demand and contribution, which is supplied through fertilization.
Other aspects to consider for the calculation of fertilizers are their source and efficiency in the soil, meaning the amount or percentage of the applied fertilizer that is absorbed by the plant during the growth cycle and the application periods. It’s also important to identify the type of crop (new, ratoon, or in production) and the root system, physical and chemical soil conditions, the fertilizer source, and the cultivation system.
In general, it is estimated that in coffee plantations with rainfed or furrow irrigation, nitrogen efficiency is 45 to 55%, phosphorus is 10 to 20%, and potassium is 50 to 65%. To achieve greater efficiency, fertilizers should be applied according to how nutrients are absorbed by the plant during crop development. Now let’s learn a little more about these key elements.
Nitrogen
Nutrient requirements for coffee vary according to the phenological phase of the crop. Of the elements that the coffee plant obtains from the soil to meet its normal nutritional needs, nitrogen (N) is probably the essential nutrient that most limits its development, and determines the productive behavior of the plant, and thus the yields.
There are many arguments justifying the use of adequate doses of nitrogen fertilizers and the implementation of appropriate practices for their application. So, which form of nitrogen the plants assimilate will be better, Nitrate Nitrogen or Ammoniacal Nitrogen?
According to Malavota, 1976, nitrogen is mainly present in the soil in the organic form (98%), with only 2% in the inorganic form represented by ammonium ions (NH4+), ammonia (NH3), nitrate (NO3-), nitrous oxide (N2O), nitrogen dioxide (NO2-), nitric oxide (NO), and nitrite (NO2-). NH4+ and NO3- are the most important chemical forms for plant nutrition, as the rest are gaseous forms lost from the system through the denitrification process.
It is important to note that the plant absorbs 80-90% of nitrogen in the form of NO3-, which is immediately available to the plant. This form of nitrogen enhances the absorption of cations such as K+, Ca++, and Mg++ synergistically and is not lost through volatilization. Ammoniacal nitrogen sources can also be directly absorbed by the plant, although in a relatively smaller percentage (10-20%).
The ammoniacal form of nitrogen (N-NH4+) can interfere with the absorption of potassium (K+), calcium (Ca++), and magnesium (Mg++) ions, which are also required in high amounts. Ammoniacal forms of nitrogen are converted to nitrates in the soil by bacterial processes (nitrification). For these processes to occur efficiently, the soil must meet conditions of pH, temperature, moisture, and oxygen availability, which frequently are not at optimal levels, delaying the transformation of ammonium to nitrate.
Plants under N-NO3- nutrition exhibit better growth and higher yields. A 100% N-NO3- nutrition can increase the pH of the rhizosphere, which favors the assimilation of soil nutrients, an important aspect in coffee-producing areas where the pH is acidic (3-5.5).
During a survey in the coffee-growing regions of Caldas, Quindío, Risaralda, and southern Huila in Colombia, as well as in Jinotega, Nicaragua, we found that many producers use fertilizers such as Urea or Ammonium Sulfate directly or in NPK mixes for their nitrogen contributions to the crop, as they are commercial products relatively cheaper than other nitrate-based products like potassium nitrate.
However, it is crucial to know the source, as, during the nitrification process, ammonium releases H+ ions, which accumulate in the soil and are primarily responsible for soil acidification. This is very detrimental as it can lead to the release of aluminum and manganese, damaging roots, and poorly developing seedlings. Additionally, these H+ ions will displace the soil cations potassium (K+), calcium (Ca++), and magnesium (Mg++), causing a loss of base saturation and soil imbalance.
Nitrogen application should relate to the phenological phase of the coffee crop. Generally, nitrogen is the element with the highest response in coffee production. Fertilization with 200-300 kg/ha/year yields good results. In general, an optimal partitioning of nitrogen in coffee would be 35%, 30%, and 35% of the total dose post-harvest, post-flowering, and fruit development, respectively. Excessive nitrogen application can increase low-density beans.
If you found this reading interesting, stay tuned for next week when I will talk about phosphorus and potassium.
Dr. Modesto Mojena Graverán
Is an Agronomist Engineer with a PhD in Agricultural Sciences from the Agrarian University of Havana. With more than 30 years of field experience, Specialist in plant nutrition, agroecology, and sustainable agriculture, among others. He has over 20 publications on plant nutrition, production systems, and agronomic management of tropical and subtropical crops. He has participated in various national and international scientific research and events and, is currently the R&D Manager at SQM Commercial in Mexico and Commercial Manager for Central America and the Caribbean.
