Importance of monitoring soil fertility in coffee farming

Coffee crops in Brazil, in general, were established in areas with low to medium fertility soils. The poverty of these soils and the plants' need for an adequate supply of nutrients require coffee growers to look for efficient ways to correct the acidity and fertilize the soils of their crops.

The months of July and August in most coffee producing regions coincide with the end of the harvest. During this period, many coffee growers carry out soil analysis with the aim of monitoring soil fertility, especially in crops that had high productivity and whose plants absorbed a large amount of nutrients from the soil.

To replace these nutrients absorbed by plants, it is necessary to obey two laws of soil fertility: the Law of Minimum and that of Diminishing Increments. The Minimum Law states that “crop production is limited by the nutrient that is least available in the soil, even if all the others are available and in adequate quantity”. The Law of Diminishing Increments warns about the fact that if “adding increasing doses of a nutrient, the greatest increase in production will be obtained with the first dose, but with successive applications of the nutrient the production increments will be smaller and smaller”.

From a balanced supply of nutrients to the plants, they will have sufficient growth and development to produce fruits and, consequently, coffee beans. However, in addition to the balanced nutrition of coffee plants, other factors such as the availability of water must be considered so that nutrients can be absorbed, distributed and translocated by the plant. Other abiotic factors (high temperatures, drought, among others) and biotic factors (attack by pests and diseases, among others) throughout the crop cycle must be mitigated by the adoption of good agricultural practices and crop management in the field (Good Agricultural Practices and of Property Management - Normative Instruction No. 49 of 24/09/2013 - Specific Technical Standards for Integrated Coffee Production).

Once coffee plants have balanced nutrition and the presence of other growth and development factors at adequate levels such as water, light, CO2, O2 and heat, coffee fruits will have better formation, uniform maturation and, consequently, organoleptic and ideal nutraceuticals for good quality drinks, as long as good practices are also followed in the harvesting, post-harvesting, processing and storage phases.

The balanced recommendation of nutrients will be known through the interpretation of chemical and physical analyzes (soil texture) and the content of organic matter present in the soil. However, the correct interpretation of the results of these analyzes will be obtained if the samples sent to the laboratory were collected observing basic criteria, such as: the area to be sampled must be divided into plots of no more than 10 hectares; Each plot must be as homogeneous as possible, in relation to vegetation, topography, time of use, productivity and applications of acidity correctors (limestone, among others), gypsum and fertilizers; Areas that differ in the landscape, for example, in slope, drainage, color and/or type of soil, use and previous treatments, should be sampled separately.

The use of appropriate tools, the homogenization of samples in relation to the profile sampled, the packaging of these samples in suitable containers for sending to accredited laboratories to carry out these analyses, among other precautions, are also fundamental for correct interpretation (Sampling and Care in Soil Collection for Fertility Purposes).

 It is recommended that the collection of soil samples for the purpose of evaluating fertility and also the interpretation of analysis results be guided and interpreted by agronomists from technical assistance and rural extension. For more information, it is suggested that coffee growers access the publication Coffee Manual: Managing Coffee Plantations in Production – EMATER MG, available for download at Observatório do Café do Coffee Research Consortium, coordinated by Embrapa Coffee.

According to the interpretation of the soil analysis, correction of acidity through liming, if necessary, should be carried out before fertilization. Likewise, the correction of aluminum in the subsurface must be done after liming with the application of agricultural gypsum.

The supply of nutrients to coffee plants through soil fertilization occurs in two periods: first, from August to December, a period in which coffee plants are in vegetative growth, and, after the first rains (September-October) when emit the flower; and second, from January to March, a period in which there is a greater need for nutrients for fruit granulation.

Depending on the assessment of the nutritional status of coffee plants, foliar fertilization may be necessary to complement the nutrient levels required by the plants that were not supplied by soil fertilization. The period indicated for this fertilization practice corresponds to the months of December and January to March.

The dosage of essential nutrients for the development of the coffee plant (Nitrogen, Phosphorus, Potassium, Calcium, Magnesium, Sulfur, Iron, Manganese, Zinc, Boron and Copper) varies according to the cultivar/variety of coffee, whether in the seedling phase or by time of planting and, also, in the case of an already established crop, according to the phenological state of the crop in the field: flowering and fruit expansion, fruit graining and fruit maturation.