​Installed fertilization in coffee

Conilon coffee trees (Coffea canephora) grown in commercial plantations stand out for their high productive potential and high nutritional requirements. Fertilization recommendations, based on soil analysis and expected productivity, have been widely used and should be adjusted with the help of leaf analysis. However, this recommendation does not consider the specific requirements of genotypes, being generally advised.

Much of the vegetative growth of the coffee tree occurs simultaneously with the fruit production phase, which is why, in this phase, there is a greater demand for nutrients. However, it is in the fruits where the greatest accumulation of dry matter occurs, throughout the one-year production cycle, corresponding to 45% of the total dry matter accumulated in the coffee tree (Figure 1). However, it must be considered that other parts of the plants, such as roots and trunks, accumulate part of the dry matter in previous years. Therefore, it can be suggested that there is a greater need in the year for fruit formation, which could be greater than 50%, in the case presented by Bragança, in 2005.

Figure 1 - Partition of the dry matter of Conilon coffee. Adapted from Bragança (2005)

Nutrient losses

Most of the nutrients added to the soil through the use of fertilizers quickly become unavailable to the coffee plant. The main factors involved in this process are chemical reactions that occur in the soil in contact with fertilizers. The leaching of ions, volatilization of ammonia, interaction between antagonistic nutrients and fixation and precipitation reactions, mainly, stand out.

In nitrogen fertilization, the most significant losses occur through the leaching of nitrate (NO₃^-) and by the volatilization of ammonia (NH₃⁺). In the case of NO₃^- the compound has low chemical interaction with minerals in the soil, which means it is subject to leaching and can reach surface waters or groundwater. And, in the case of NH₃⁺, the greatest losses occur due to the volatilization of the compound, as a result of the breakdown of the urea molecule, which normally occurs in the soil, under natural conditions.

As for phosphate fertilizer, the chemical reactions of this element with soil minerals (iron oxides, Fe, and aluminum, Al, mainly) make P unavailable for absorption by the plant. In Brazilian soils this situation is widespread, being common in cerrado regions, where the soils are highly weathered. In an acidic environment, this P can also be precipitated with Fe and Al oxides, mainly. Therefore, the practice of liming, appropriately, is one of the strategies that increase the efficiency of phosphate fertilization, however, it is important to note that excessive liming, in addition to unbalancing the bases in the soil (Ca, Mg and K, mainly), is harmful to the plant, the phosphate fixation reactions with Ca are also increased, inducing precipitation of the compound formed.

As for potassium fertilization, K in the soil has a simpler dynamic in tropical soils, compared to N and P. The main losses of K occur through leaching, mainly due to the low adsorption capacity of this element to soil minerals. The loss of K is potentiated by conditions of low soil K concentration, low soil cation exchange capacity and excessive precipitation. In these situations, K fertilization should be split throughout the crop cycle, with the aim of increasing fertilizer efficiency.

Installment according to the maturation cycle

Genotypes of Conilon coffee trees have different maturation cycles, which can influence the accumulation rates of dry matter and nutrients in the fruits. Therefore, knowledge of the dynamics of fruit formation and growth is important for establishing periods of greatest nutritional demand and for defining the best fertilization strategies for coffee crops.

The greatest vegetative growth of the Conilon coffee tree occurs between the beginning of October and the first half of May. This fact occurs for practically all Conilon coffee genotypes, with some particularities (Partelli et al, 2013). Therefore, it is suggested that the greatest nutritional demands for vegetative growth occur between October and May. On the other hand, between June and September there are the lowest growth rates, characterized as a period of vegetative rest for the Conilon coffee tree (Figure 2). The low vegetative growth at this time of year and the mild temperatures during this period are justified, as the Conilon coffee tree shows reduced vegetative growth when subjected to temperatures below 17ºC.

Figure 2 - Vegetative growth rate of groups of branches C. canephora CV. Ipiranga 501. The bars represent the standard error of the mean. Nova Venécia, ES

Similarly, the highest rates of nutrient accumulation occur from October onwards. However, the intensity of accumulation varies depending on the fruit maturation cycle of each genotype (example: nitrogen - Figure 3). Genotypes with a shorter fruit maturation cycle have a faster accumulation of dry matter and nutrients. Note: Marré (2012) presents the accumulation curves of all nutrients in his master's thesis carried out at Ufes/Ceunes.

Figure 3 - Nitrogen accumulation in the fruits (in percentage of the total accumulated) of four Conilon coffee genotypes, from anthesis to fruit maturation. Bars represent standard error of the mean. Nova Venécia, ES

In practical terms, for example, until December 6th, the Conilon 12V and 10V coffee genotypes had approximately 60% of the N accumulated in the fruits, reaching 90% by the beginning of February. Genotypes 13V and Ipiranga 501 presented values ​​below 20% until the beginning of December, reaching a maximum of 40% in mid-February. Thus, from February onwards, genotypes 12V and 10V would practically no longer need N for fruit formation. On the other hand, late maturing genotypes (13V and Ipiranga 501) still require large amounts of N until close to harvest (June and July).

Final considerations

The Conilon coffee tree uses 80% of N between the months of September and February for genotypes with an early and medium fruit maturation cycle. While in late and super late genotypes, the greatest N requirement begins from October onwards and remains until harvest (June to July). Thus, the N requirement for Conilon coffee varies according to the fruit maturation cycle.

It is suggested that fertilization management should be specific for each Conilon coffee tree genotype. Genotypes with an early fruit maturation cycle have a higher initial rate of accumulation of dry mass and nutrients. Therefore, they need to be fertilized earlier compared to late fruit ripening genotypes. Therefore, fertilization of the Conilon coffee tree must occur at times of highest rates of nutrient accumulation, especially those nutrients that present significant losses.

Click here to read the article in Revista Cultivar Grandes Culturas, issue 175.