Nitrogen loss by volatilization of nitrogen fertilizers applied to coffee orchard

Ammonia volatilization (N-NH3) is one of the main pathways of Nitrogen loss reducing nitrogen use efficiency in coffee orchard. This work aimed at quantifying ammonia volatilization (N-NH3) losses from N-sources to be used in coffee plantations fertilization in Brazil. The experiment was conducted in the field on a dystrophic red latosol (Ferralsol in FAO’s classification) at the Coffee Research Sector, University of Lavras, MG, Brazil. The experimental design was of complete randomized blocks with three repetitions of the following treatments: conventional urea, ammonium nitrate and urea + 0.15% Cu and 0.4% B, urea + anionic polymers, urea + elementary sulfur (S0) + polymers, and urea + plastic resin. These N sources were split into three doses of 150 kg ha-1 and band applied. The N-NH3 losses by volatilization and variations of pH (H2O) were measured, before and after N application. The N-sources contributed to reduce the soil pH, measured after the third nitrogen fertilization. The N-NH3 losses by volatilization (average from three applications) was as follows: urea + anionic polymers (35.8%) > conventional urea (31.2%) = urea + S0 + polymers (31.0%) > urea + 0.15% Cu + 0.4 % B (25.6%) > urea + plastic resin (8.6%) = ammonium nitrate (1.0%).


INTRODUCTION
The agronomic efficiency of conventional fertilizers and the reduction of nitrogen (N) loss are the main objectives in fertility management because these practices reduce the production costs and negative environmental impacts (Trenkel, 2010;Fan et al., 2010).The increase in the efficiency of N fertilization of field crops has been a major concern for decades (Chien;Prochnow;Cantarella, 2009).Intensive research aims at solving the threat of N loss in the form of ammonia.
Technologies directly related to FAE include key soil and crop components such as improving the soil profile to create appropriate conditions for the development of the root system; fertility monitoring and nutrition based on soil and plant analysis; and soil acidity amendment.In this context, a slow and controlled release of stabilized N sources has been a goal to increase the fertilization efficiency and reduce the adverse environmental effects.Indeed, the objectives of any type of N fertilization are to avoid losses due to volatilization, leaching and denitrification (Chien;Prochnow;Cantarella, 2009;Trenkel, 2010).
Several inhibitors have been identified in those three groups of compounds, including those that are utilized most frequently in major cropping areas of the world: a) NBPT, Cu and B; b) sulfhydryl; c) urea analogs; and d) molecules that react with nickel (Krajewska;Zaborska;Chudy, 2004).
In addition to stabilized urea , there is another group that belongs to the coated or encapsulated fertilizers.These fertilizers are produced via the addition of compounds that cover the urea granules, reduce their exposure to water and air, and block volatilization.Various products have been developed to suit ammonia volatilization and enhance urea efficiency, thus creating ample innovation possibilities; the products include sulfur, polymers, polystyrene, polyesters, polyurethane, fatty acids, latex, petroleum by-products, magnesium and calcium phosphate, gypsum, Azadhiractha (Neem tree) extract and wax (Trenkel, 2010;Chien;Prochnow;Cantarella, 2009).
These coating substances act as granule sealants, control the dissolution rate and the time required to release the nutrient and allow the synchrony between availability and demand by crops.These fertilizers are divided into three main groups, according to the covering agent: 1) sulfur; 2) sulfur added to polymers; and 3) polymeric and polyolefin matrices (Trenkel, 2010).The controlled release of nutrients from N fertilizers by these coating agents is considered a promising technology for improving the efficiency of N fertilization (Yang, 2012).
The use of these innovative N sources has been restricted to certain crops, especially in developing countries, because efforts were devoted to mastering the technology (Shoji, 2005;Du;Zhouw;Shaviv, 2006;Du et al., 2008;Yang, 2012).However, with a Chinese contribution and the installation of fertilizer plants in various countries, the slow-release nutrient sources have become available for the agricultural production, especially those coated with sulfur, sulfur and polymers or polymers alone (Sanders;Mazo;Mazo, 2008;Lupwayi et al., 2010;Ogle;Sims, 2012).
Certain N sources have been developed with the use of value-added compounds, which restrict their application to nurseries, horticulture, orchids, golf pitch and lawns.The high cost of coating the granules has been the limiting factor in extending their use to large-scale agriculture (Trenkel, 2010;Yang, 2012).
Considering the value of these innovative fertilizer sources, the aim of this work was to evaluate the N-NH 3 loss through the volatilization of the conventional sources of urea and urea coated with 0.15% Cu and 0.4% B, plastic resins and with polymers and elementary sulfur added as polymers.

MATERIAL AND METHODS
The experiment was conducted between August 2013 and August 2014 on a dystrophic red latosol (Ferralsol in the FAO's classification) at the Coffee Research Sector of the University of Lavras, Minas Gerais state, Brazil.The climate, according to Köppen, is classified as Cwa.The average annual temperature recorded between 1961 and 1994 was 19.4 °C, and the average rainfall during the same period was 1,530 mm.The rainfall was concentrated between October and March and was followed by a long dry period in the remaining six months.Before setting the experiment, soil samples were collected at 0-20 cm depth.To prepare for the analysis, sods were broken into fine particles; the soil was sieved using 4 mm mesh and allowed to air dry.Subsequently, the soil was further sieved with 2 mm mesh, and sub-samples were taken for chemical and physical analyses (Table 1).
The following chemical determinations were made: pH, 1:2.5 soil and water; (H+Al), 0.5 mol L -1 Ca(OAc) 2 at pH 7.0; exchangeable Ca 2+ , Mg 2+ and Al 3+ using 1.0 mol L -1 KCl extractant and titrimetry; P and K using Mehlich-1 extractant and colorimetry (P); flame photometry (K); carbon oxidation with potassium dichromate; Zn, Mn and Cu using Mehlich-1 extractant; and atomic absorption spectrophotometry.The values for an effective CEC (t), CEC at pH 7.0 (T) and the rates of base saturation (BS %) and aluminum (m) were indirectly obtained using potential acidity values, exchangeable bases and exchangeable aluminum.
The experiment had a complete randomized block design with three replications, and it included the following treatments: urea, ammonium nitrate, urea + Cu + B, anionic polymer-coated urea, sulfur 7.9% (elementary sulfur = S 0 )coated urea + polymers and plastic resin-coated urea.All of the nitrogen fertilizers were applied manually in three nitrogen fertilization times: November/1 st fertilization, January/2 nd , and March/3 rd .The fertilizations occurred at equal rates of 150 kg ha -1 , i.e., a total of 450 kg ha -1 of N was used in a single coffee season.
The fertilizer characteristics are as follows: a) Urea -granular urea with 45% N; b) Urea + 0.15 % Cu + B: Urea fertilizer prilled with 44.6% N and with 1.5 g kg -1 of Cu in the form of copper sulfate and 4 g kg -1 of B in the form of boric acid.Both copper sulfate and boric acid had particle sizes less than 0.015 mm and were evenly spread over the granules in the rotating drum (Heringer, 2008); c) Anionic polymer-coated granular urea: anionic polymer-coated urea with 41% of N. Polymers had negative charges to retain ammonium (NH 4 + ; positive charge) that was dissolved in the soil solution near the urea granules.d) Sulfur-coated urea + polymers (Blend): Urea coated with an elemental sulfur layer and an organic polymer that acted as a sealing wax for the sulfur layer.The proportion of polymer coated sulfur urea represented 30%, and the remaining 70% was composed of the total N in the form of conventional granular urea (with no coating) for an immediate N release.This blend of coated urea allowed a controlled nitrogen release due to the presence of a physical barrier, which prevented its dissolution in water.The total nitrogen content was 40%, with 7.9% elemental sulfur (S 0 ).According to the supplier, the nitrogen is released for up to three months; e) Urea coated with a copolymer of ethylene acrylic.This formula of coated urea consisted of a primary controlled release polymer-coated technology.The polymer was springy and controlled the nutrient release by diffusion according to the temperature and humidity.All of the mentioned fertilizers are commercial products.
The experimental plots had 12 equally spaced plants (3.7 m between rows and 0.7 between plants).The harvest area had 10 plants because we excluded the borders.
The experimental area was amended with 1.74 t ha -1 lime, equivalent to 100% calcium carbonate, as indicated by the soil analysis 60 days before the maintenance fertilization.The rate of nitrogen was 450 kg ha -1 and potassium maintenance equal 300 kg ha -1 K 2 O split into three doses applied every 60 days from 19/11/2013.The phosphate fertilizer source was applied in a single dose.The respective sources were potassium chloride (60% K 2 O) and super phosphate (20% P 2 O 5 ).Micronutrients such as boron, zinc and copper were applied on the leaves.
During the experiment, soil samples were collected at a depth of 0-5 cm to assess the pH variations in the layer where the N fertilizers were applied.
The rate of ammonia volatilization was determined by a semi-open static collector adapted from the methods described by Lara-Cabezas (1999).Polyvinyl chloride tubes (20 cm in diameter and 50 cm long) were inserted in the soil at a depth of 5 cm under the tree canopy (0.35 m from plagiotropic branches).Two rubber foam discs (0.02 g cm -3 density and 2.5 cm thick) of same diameter as the tubes were imbibed in phosphoric acid (H 3 PO 4 ) and glycerin and placed inside tubes at 25 and 45 cm from the soil surface.The upper foam had the function of avoiding contamination from the lower foam.Evaluations on the volatilized ammonia were made at one, two, three, four, five, seven, nine, twelve, fifteen, nineteen, twenty-three and thirty days after the N fertilizers' application.On the third N application, the evaluations were extended  (1) and texture (2) of coffee orchard area.Chemical analysis (1)   pH (H2O) P K + S Zn Cu Mn B Fe Ca 2+ Mg 2+ Al 3+ (H+Al) t T m BS OM 1 P-rem ___________________ mg dm -3 ________________________ _____________________ cmol c dm -3 _____________________ _______ % _______ g kg -1 mg L to sixty-six days after the fertilization or until the fluxes of ammonia were still detected.The determination of the N that was captured from volatilization was made as follows: the foams were washed with distilled water over a porous tile Buchner funnel and with the help of a vacuum pump.The extracted volume from the foams was measured, and aliquots were transferred to test tubes and distilled in semi-micro Kjeldahl.
The data for every treatment were subjected to an analysis of variance using the SISVAR 4.3 ® statistical program (Ferreira, 2011).Linear, quadratic, logarithmic and exponential models were tested, and we chose the one that had the highest regression coefficient; the significance level was set at p≤0.05 for the F test.

RESULTS AND DISCUSSION
There was a significant influence of the nitrogen fertilizer sources in the in the daily and accumulated N loss for the three N fertilizations of the coffee orchard (p≤0.05).The variations in accumulated (Figure 1a) and daily volatilization (Figure 1b) were associated with rainfall, temperature and relative air moisture (Figure 1c) during the 27 days after the first fertilization (Figure 1).
The accumulated and daily ammonia loss of the first fertilization varied significantly with the time of application and the N fertilizer sources (p≤0.05; Figure 1a, 1b).The urea, urea + anionic polymers and Urea + S 0 + polymers had the highest volatilization peaks of 5%, 5.7%, and 6.1%, respectively, at the 2 nd day after the band application of N. The coated urea with 0.15% Cu and 0.4% B had the maximum volatilization in the 3 rd day (6.2%; Figure 1b).
The accumulated rainfall after the first application was 333.4 mm, with 0.6, 0.8, 1.2, 12.6, 33, 30, and 0.4 mm of precipitation between the 1 st and 8 th days.In the same period, the mean air temperature was 22.2°C (Figure 1c).
The urea + plastic resin did not show a high loss of N-NH 3 , and the maximum daily volatilization between the 5 th and 14 th days for this N source was 0.26% and 0.33% of the total N applied, respectively.The exception of urea + plastic resin in relation to the others nitrogen fertilizers was the high rates of N-NH 3 loss that occurred during the first seven days after the first application.The sequence of accumulated N-NH 3 loss was, in decreasing order, urea + anionic polymers (32.6%) = urea + S 0 + polymers (29.6%) = conventional urea (28.3%) > urea + 0.15% Cu + 0.4% B (25.4%) > urea + plastic resin (1.4%) = ammonium nitrate (0.7%).It became evident that the urea + plastic resin and the ammonium nitrate are similar with regards to the reduced N loss by volatilization.Currently, the ammonium nitrate has a lower price in the Brazilian fertilizer market compared with the urea + plastic resin (Figure 1a).
The copper and boron, among several substances, compounds and chemical elements, are the ones that most inhibited the urease activity in the soil.There are three mechanisms involved in the inhibition of urease.The first is based on a reaction of the inhibiting substances with sulfhydryl, which blocks the active site of the enzyme.Ions such as Ag + , Hg + and Cu 2+ cause an inhibition that is proportional to the solubility of the metal-sulfite product.In the second mechanism, compounds similar to urea, such as thio-urea, methyl-urea, and replaced urea, compete to inhibit the urease activity, which render them inefficient when high N doses are applied in the form of urea.The third mechanism to inhibit the urease activity is based on the addition of molecules that react with the Ni present in the enzyme (Krajewska;Zaborska;Chudy, 2004).
Another chemical element that inhibits the urease enzyme is boron, which is routinely added in the form of boric acid (H 3 BO 3 ) to fertilizers for two purposes: supply the boron element as a nutrient and diminish the N loss by volatilization.The maximum urease inhibition in the region of urea solubility occur in pH values from 6.2 to 9.3, which indicates that only the neutral trigon anion H 3 BO 3 0 can inhibit the urease, instead of the H 4 BO 4 .Due to its structural similarity to urea, the boric acid molecule is also considered an analog substrate.Boric acid almost exactly replaces the water molecules bonded to Ni in the center of reaction (Benini et al., 2004).
The effect of adding Cu, B and S to the urea reduces the N loss compared with that observed by adding urea alone in maize and sugar cane (Faria et al. 2013;Nascimento et al. 2013).
The rainfall after the second N fertilization was 16.2 mm at day one and 82, 1.2, 7, 67.4,5.6, 0.6 and 0.4 mm in the period between the 2 nd and 8 th days (Figure 2c), with a reduced N loss in the form of ammonia.
The maximum daily N volatilization from the urea + polymers (9.8 %), urea (8.4 %) and urea + S 0 + polymers (7.3%) occurred on the 2 nd day.The copper and boron-coated urea delayed the volatilization peak (6.1%) in the 2 nd N application (Figure 2b).As observed in the first application of N sources, the ammonium nitrate and urea + plastic resin showed no peaks of daily volatilization of N-NH 3 .The addition of plastic resin was, therefore, effective for the gradual release of N from the granules to the soil solution.Coating the urea granule with resin causes a reduction in the dissolution rate.In the presence of water, the resin membrane becomes permeable by diffusion, and the N release begins inside the granule.The solution formed at the beginning of the dissolution permeates gradually through the coat, contrary to the water flow, and releases N to the soil by diffusion (Du et al., 2006;Du et al., 2008;Trenkel, 2010;Ogle;Sims, 2012;Yang, 2012).
The nitrogen fertilizer with a controlled release such as the urea + resin used in this study possess advantageous attributes such as a reduction in the number of applications, N-NH 3 loss by volatilization, leaching and denitrification, as well as labor requirements and application costs (Ogle;Sims, 2012;Wilson;Rosen;Moncrief, 2010;Wang;Cui;Zhou, 2011).Therefore, the urea + resin is more advantageous when it is applied in one dose at the beginning of the coffee season than when it used in the three split applications that are usually applied in Brazil.Moreover, these sources contribute to the synchrony between the release and absorption curve (Yang, 2012).However, one limitation is the high cost of their production due to the type of materials that are required to coat the granules.The use of these sources has been restricted to value crops (Trenkel, 2010;Yang, 2012) and, eventually, to field crops when their market price is high.
The urea with controlled release promoted a high efficiency compared with the regular urea in the rice cultivation by increasing the N availability near the root system and the absorption by plants.Similarly, it promotes an enzymatic activity related to the N metabolism.This relative efficiency allowed a reduction in the N dose and positively impacted the production costs and the effects on the environment (Wang, 2011).
The rainfall after the 3 rd application of N fertilizers was 159.6 mm, and it was the least of these three periods, with 4.8, 0.4, and 12.4 mm on the 2 nd , 3 rd , and 4 th days, respectively.The mean temperature was 21.7 °C.The low rainfall contributed to an increase in the accumulated ammonia loss.The relative air moisture was > 75% on 16 of the 30 days after the N application (Figure 3c), which contributed to a rapid urea dissolution in the soil.In addition, the low rainfall kept the dissolved urea near the soil surface and exposed it to volatilization.
The volatilization daily peak from the urea + 0.15% Cu and 0.4% B occurred on the 7 th day (8.1%) after the 3 rd application.This peak coincided with the one from the urea + S 0 + polymers, though the ammonium daily loss in the preceding and following days reached high values, which contributed to a reduced volatilization compared with the regular urea.A similar situation was observed with the urea + polymers, which promoted an N-NH 3 loss of 9.6% on the 3 rd day after the 3 rd N application.The urea + plastic resin had 3.8% volatilization 48 days after the N was applied and reached values near zero near the 66 th day from the application.
Therefore, in the 2 nd and 3 rd N fertilizations of the coffee orchard, the ammonium nitrate did not contribute to the N-NH 3 loss by volatilization, irrespective of the weather conditions.
Currently, there are few scientific databases (Fenilli, 2007) related to daily and accumulated loss of N-NH 3 by volatilization from conventional (ammonium nitrate, urea and ammonium sulfate) and slow and controlled-release as well as stabilized fertilizers applied in Brazilian coffee orchards.On average, over the three N fertilizations, the urea + 0.15% Cu + 0.4% B and the plastic resin-coated urea reduced the losses of N-NH 3 compared with the pure urea (Table 2).
The N loss associated with ammonium nitrate was only 1% of the total, as expected from similar studies on coffee orchards.From the total of 450 kg ha -1 in three doses applied during 2013/2014, only 4.5 kg ha -1 N-NH 3 was lost to the atmosphere as ammonia.The urea coated with polymers showed a loss of 35.8%, which is higher than the loss observed for conventional urea (31.2%).
The high loss of ammonia from anionic polymerscoated urea is due to the inefficacy of the additive formulation added to the urea that retains the ammonium in the negative charges of the polymer.This outcome reinforces the idea that coffee farmers should benefit from knowing the features of each technology and its efficiency before using it.Table 2: Accumulated N-NH3 loss from fertilizers (Conventional urea, ammonium nitrate, urea + 0.15% Cu + 0.4% B, urea + anionic polymers, urea + S 0 + polymers and urea + plastic resin), in 1 st , 2 nd , 3 rd and total of three split nitrogen fertilization (450 kg ha -1 ) N, in coffee orchard.

N-Fertilizer
1 st fertilization 2 nd fertilization 3 rd fertilization Mean The pH in the soil surface layer (0-5 cm) is one of the chemical attributes that mostly affects the volatilization of ammonia to the atmosphere, and an increase in its value accelerates the loss (Watson et al., 2008;Menendez et al., 2009).In this study, the soil pH in the 0-5 cm layer was reduced from the 1 st to the 3 rd N fertilization of coffee (Table 3).With the N application in the form of urea, the mean soil pH value after the 3 rd fertilization was 6.33, and after the last fertilization, it decreased to 4.07; for the ammonium nitrate, the variations were 6.35 and 4.41.
Several technologies used to enhance the efficiency of fertilizers were developed in the 1950s.However, fertilizers with an enhanced efficiency represent less than 1% of the total fertilizer used worldwide, though their prices have been decreasing.
The polymer-coated fertilizers (controlled release technology such as urea + resin) are eight to 12 times more expansive in terms of cost than the conventional fertilizers.Sulfur-coated urea is common in the Brazilian market and is the least expensive, though it is nearly twice as costly as regular urea.Moreover, sulfur-coated urea has been commercialized both alone and in the form of blends/mixtures.The urease inhibitors added to urea result in extra costs of approximately 15 -30% (Azeem, 2014;Timilsena et al., 2015).
Table 3: Values of pH in water at 0-5 cm soil layer and N-NH 3 loss (%) from conventional urea, ammonium nitrate, urea + 0.15 % Cu + 0.4% B, urea + anionic polymers, urea + S 0 + polymers and urea + plastic resin in the dose of 150 kg ha -1 (Average of three fertilizations).Means followed by the same lower case letter in the columns and upper case letter in lines do not differ from each other by the Skott-Knott test (p≤0.05). (1)pH in water at 0-5 cm depth before 1 st fertilization;
Currently, the cost of technologies in a decreasing order is controlled release > slow release > stabilized nitrogen fertilizers.To summarize, it is necessary to develop a new generation of cost-effective, slow, controlled-release and stabilized nitrogen fertilizers and to develop or improve the infrastructure of fertilizer plants in Brazil to reduce their cost.Advances in the nitrogen fertilizer technology could reduce the ammonia loss in coffee orchards.There are several fertilizers and technologies on the Brazilian market, such as those evaluated in this study.

Table 1 :
Soil chemical analysis