Nitrogen irrigation in conilon coffee production

An adequate supply of water and nutrients is essential for the growth and productivity of coffee plants. Therefore, the use of irrigation and nutrition management, when adopted in a rational and judicious manner, are tools that can help the producer to obtain better results.

The periodicity of coffee tree growth is associated with several environmental factors, such as the supply of water and nutrients. The occurrence of water deficit in certain phases of the phenological cycle, such as that preceding the beginning of flowering, can compromise crop productivity.

Most of the conilon coffee plantations in Espírito Santo occupy areas in the north and northwest regions, which are considered marginal, with low altitudes, higher temperatures, with low fertility soils and which constantly suffer from problems of low water supply (BUSATO et al., 2007), making balanced fertilization and correct water management essential for improving productivity and product quality. In this sense, the adoption of irrigation aims to ensure adequate management of the crop and allows for increases in productivity that can vary from 20% to 260% (SILVA; REIS, 2007).

Irrigation in Coffee Farming

Among the irrigation systems commonly used in irrigated coffee farming in the North of Espírito Santo, localized systems (conventional drip, microjet drip and microsprinkler) and sprinkler systems (central pivot, conventional and fixed sprinkler) stand out. Although localized systems have greater potential for water savings, associated with high uniformity and application efficiency, in recent years there has been a trend towards the implementation of new fixed sprinkler systems. In this sense, irrigation management constitutes a very important technique from an economic and environmental point of view in an irrigated agricultural activity, providing water and energy savings, increasing crop productivity and improving product quality (BONOMO et al., 2013 ). Therefore, by adopting appropriate management, it is often possible to use the irrigation system in less time than it was designed, thus saving in terms of operation, with direct impacts on electricity and labor costs.

Irrigation promotes increased production, as crop productivity is compromised when critical periods of water deficiency occur during the flowering and fruiting phases until approximately the eighteenth week after flowering.

Supply of Water and Nutrition with Nitrogen in the Coffee Plant

Nitrogen (N) is one of the nutrients most affected by water supply in the soil, especially during the fruiting phase, when it is intensely transported from the leaves to the fruits, whether in an adequate or deficient supply condition. The crop's response to N is closely related to the water supply in the soil, as it is essential for the plant's vital functions.

Normally, the dose of N used in coffee plants is based on a general recommendation, according to productivity expectations, and is rarely carried out using plant analysis. When carried out, this monitoring is carried out by chemical analysis of the N content in the dry mass of the leaves. These procedures are costly, time-consuming and must be carried out in appropriate locations and by people with some level of education (FONTES, 2011).

In this sense, the determination of the N content in the plant by rapid diagnostic techniques, including biometric or plant growth characteristics such as branch length, leaf area and leaf dry mass and characteristics or N indices associated with color intensity leaf green and chlorophyll, perhaps it could be a useful and viable tool in N management in coffee plants.

The quantification of growth or N indices in coffee trees as a function of nitrogen fertilization levels translates into a prognosis of the crop's productive potential, in the field, and also allows adapting the management of N fertilization to optimize fertilizers and less impact on the environment.

With the objective of evaluating the productivity of the conilon coffee tree irrigated under doses of nitrogen, an experiment was carried out on a rural property in the municipality of Colatina, Rio Doce basin, northwestern region of Espírito Santo. The local climate is Tropical Aw, according to the Köppen climate classification. The region is characterized by hot lands, high temperatures, rugged relief and the occurrence of droughts, with irregular rainfall throughout the year and dry winters, with an average annual rainfall of 1.100 mm.

The species used was the conilon coffee tree (Coffea canephora), in production and the experiment was cultivated with a spacing of 3,0 meters between rows and 1,5 meters between plants. At this spacing, the crop was managed with traditional pruning and thinning, maintaining 5 stems/plant - 6 stems/plant, equivalent to 13.333 stems/ha, as recommended by Fonseca et al. (2007).

The N doses were applied in the form of urea fertilizer (45% N), divided into four applications during the year, 30% in October, 30% in December, 25% in February and 15% in the month of June.

Six doses of nitrogen (N) were tested: 0 kg/ ha/ year, 110 kg/ ha/ year, 220 kg/ ha/ year, 440 kg/ ha/ year, 880 kg/ ha/ year and 1320 kg/ha^/ year of N, and its influences on growth and productivity characteristics, in two harvests: 2012/2013 (1st Harvest) and 2013/2014 (2nd Harvest).

Characteristics evaluated in the experiment

a) Length of orthotropic and plagiotropic branches - measured with the aid of a tape measure;

b) Number of nodes in the orthotropic and plagiotropic branches - obtained by counting.

c) Leaf area - measurements were taken on the 3rd or 4th pair of leaves counted from the apex of plagiotropic branches located in the middle third of the coffee plants, identified as the Diagnostic Leaf (FD) and the Oldest Leaf (FV) of the same branch, on each side of the plant.

d) Productivity of processed coffee - the plants evaluated were harvested by stripping the cloth when their grains were approximately 80% mature. At the time of harvest, the volume (liters) and mass (kg) of the grains harvested in each fertilization plot were measured. The production results were then transformed into productivity in bags of 60 kg/ha of processed coffee.

It was found that there was a positive effect of N doses on the growth of plagiotropic (Figures 1A, 1B, 2A and 2B) and orthotropic (Figures 3A, 3B, 4A and 4B) branches, respectively, and on the number of nodes in plagiotropic branches. and orthotropics of conilon coffee plants in all evaluation periods, which were November 2012 (E1), December 2012 (E2), February 2013 (E3) and June 2013 (E4).

It was observed that the growth of the branches was greater in the first evaluations, reducing until the last evaluation, since the highest growth rate of the coffee tree is concentrated in the summer. Furthermore, as time passed, the branches became older.

The doses of N provided a significant increase in the growth of branches, both orthotropic and plagiotropic, and in the number of nodes, showing that these growth characteristics were directly related to nitrogen fertilization and that it is possible to use it as an auxiliary tool in nutritional diagnosis nitrogen from the conilon coffee tree.

Similar results of increasing fertilization levels in irrigated coffee plants during the production phase were obtained by Costa et al. (2010) and Guimarães et al. (2010) who found that irrigated coffee trees grow throughout the year.

Studying the N factor in each evaluation period, it is noted that there was a positive effect of N doses on the leaf area of ​​the diagnostic leaf in all evaluation periods, in December 2012 (E1), February 2013 (E2), June 2013 (E3), October 2013 (E4) and December 2013 (E5), with an increase in the values ​​of this characteristic with the increase in N doses.

The use of the leaf area of ​​the diagnostic leaf is more appropriate than the use of the area of ​​the older leaf, since the former is considered physiologically more active and better represents the condition of the plant. Furthermore, the diagnostic leaf is easier to access on the plant, which means faster measurement in the field, while older leaves are more likely to have suffered from biotic or abiotic stress.

The greater the N supply, the greater the leaf area (BIEMOND; VOS, 1992; ANDRIOLO et al., 2006) of the conilon coffee tree, showing that the expansion of the leaf area was sensitive to the effect of N.

An adequate supply of N, maintaining levels within the appropriate ranges recommended by Gomes and Partelli (2013), is essential for the continuous growth of coffee plants throughout the year, including in autumn-winter, despite occurring at a lower rate.

It was found that there was an effect of N doses on the productivity of processed coffee (bags/ha) of the conilon coffee tree in the two harvests evaluated (1st harvest - 2012/2013 and 2nd harvest - 2013/2014) (Figures 7A and 7B). 

In the 1st harvest evaluated, the average productivity was 130,4 bags/ha. The dose of 830,2 kg/ha of N provided the maximum productivity of processed coffee among the levels studied, which was 144,8 bags/ha. An interesting fact is that the dose of N necessary to obtain 90% of maximum productivity (130,1 bags/ ha) was 251,3 kg/ ha, that is, a 10% reduction in maximum productivity resulted in a reduction of 69,7% of the applied N dose.

In the 2nd harvest evaluated, the average productivity was 94,5 bags/ha. The dose of 815,2 kg/ha of N provided the maximum productivity of processed coffee among the levels studied, which was 120,5 bags/ha.

The N dose responsible for 90% of maximum productivity (108,5 bags/ha) was 430,3 kg/ha. Analyzing these results in a similar way to the analysis of the results of the previous harvest, it can be seen that a 10% reduction in maximum productivity provided a 47,2% reduction in the dose of N applied.

The recommendation for N fertilization for the conilon coffee tree in Espírito Santo for a productivity of 137,4 bags/ ha is 560 kg/ ha of N and for a productivity of 114,5 bags/ ha is 500 kg/ ha of N (PREZOTTI et al., 2007).

It can be seen that the 1st harvest has an average productivity 27,47% higher than the 2nd harvest. In the 1st harvest, the plants were noticeably more vigorous, with a greater number of branches in production. With pruning, the plant's architecture was changed and in the 2nd harvest, the number of branches in the vegetative stage was greater and, therefore, younger.

Silva (2014), in an experiment carried out with conilon coffee in São Mateus, ES, observed that the plants in the 2011/2012 harvest had better structure, with a greater number of branches and leaves and, consequently, obtained a productivity of 127,0 bags/ ha, much higher when compared to the productivity of the 2012/2013 harvest, which was 92,0 bags/ha. The productive branches reduce their vigor after the second or third harvest and there is no compensatory growth to maintain high productivity (BRAGANÇA et al., 2007).

Regarding the analysis of the biennial production, Valadares et al. (2013) found that over eight evaluated harvests of Arabica coffee in Martins Soares, Minas Gerais, greater production stability was obtained in treatments with higher doses of N. Therefore, the greater supply of N provided a lower biannual production period. The authors reinforce that in the biennial analysis, the relationship between fertilization and greater productive stability can be attributed, essentially, to N fertilization.

It was found in the field that irrigation tends to enhance the effect of fertilizer doses, thus resulting in a greater total number of plagiotropic branches, enhancing production.

Camilo Busato, Cristiani Campos Martins Busato, Edvaldo Fialho dos Reis, Fábio Luiz Partelli, Federal University of Espírito Santo

Article published in issue 203 of Cultivar Grandes Culturas.