WO2014091279A1

WO2014091279A1 - Controlled-release nitrogen fertilizer using biochar as a renewable support matrix

Info

Publication number: WO2014091279A1
Application number: PCT/IB2012/057245
Authority: WO
Inventors: Rodrigo Javier NAVIA DIEZ; Robinson Eugenio Betancourt Astete; María Cristina DIEZ JEREZ; Noelia Zoila SEPÚLVEDA RAMÍREZ; Gustavo Aner CURAQUEO FUENTES; Mara Ximena CEA LEMUS; Claudio Andrés TORO AEDO; Aixa GONZÁLEZ RUIZ; María Eugenia GONZÁLEZ QUIJÓN
Original assignee: Universidad De La Frontera
Priority date: 2012-12-12
Filing date: 2012-12-12
Publication date: 2014-06-19
Also published as: BR112015013462A2; BR112015013462B1; BR112015013462A8

Abstract

This invention is directed to an ecofertilizer comprising a granular organic urea-based controlled release nitrogen fertilizer using biochar as a renewable support matrix. It also relates to a process for the production of a controlled-release nitrogen fertilizer, such as, the ecofertilizer of this invention. Biochar is obtained by low temperature pyrolysis at 300°C of agricultural wastes; and is used as a renewable matrix for nitrogen impregnation. Subsequently, urea impregnated onto biochar is encapsulated using a biodegradable polymer. The encapsulation was carried out by a precipitation method. The controlled-release nitrogen fertilizer developed exhibited substantially complete nitrogen availability as plant nutrient.

Description

CONTROLLED-RELEASE NITROGEN FERTILIZER USING BIOCHAR AS A

RENEWABLE SUPPORT MATRIX

FIELD OF THE INVETION

The invention has application in the production of fertilizers, particularly in the production of controlled release nitrogen fertilizer by urea impregnation onto biochar.

The invention relates to an ecofertilizer comprising a granular urea-based controlled release nitrogen fertilizer using biochar as a renewable support matrix, and the production process thereof. Biochar is obtained by low temperature pyrolysis at 300°C using residual biomass as feedstock.

The ecofertilizer of the invention accomplishes with new features regarding nitrogen up-take efficiency for specific cultivars by effectively promoting the slow nitrogen release in up to 30 days. This controlled nitrogen release from the biochar matrix also increases the production yield of two tested wheat cultivars at field scale in up to 20%. BACKGROUND

Fertilization is one of the key elements of crop production; it can accelerate plant growth, both in its aerial and radical parts. It can also alter the nutritional composition of tissues, with effects on the level of reserves, the ability of attachment and resistance to water and cold stress and diseases, among others.

Regarding to the main fertilizers used in agriculture, the global consumption of nitrogen (N), phosphorus (P) and potassium (K) in 2005/06 was 93.2, 37.1, and 25.8Mt y^"1, respectively (IFA, 2007). 55% of the nutrients were used for cereal production, 12% for oilseed crops, 11% for grass land, 11% for commodities, 6% for root crops and only 5% for fruit and vegetable production.

In this context, nitrogen is the most widely applied plant nutrient. It has often been singled out for its adverse effects on the environment as well as on human and animal health. The estimated worldwide nitrogen fertilizer consumption by agriculture in 2000 was 85.5 Tg, of which 60% was destined for cereal production. However, only 33% of the total N applied for cereal production is actually removed in the grain. This implies that the overall efficiency of N utilization for food production is low. This leads to significant economic losses that become higher and higher due to the continued increase in nitrogen fertilizer prices as a result of the scarcity of fossil fuels. Especially, urea is a widely used solid nitrogen fertilizer for agricultural production due to its low cost. After being applied to soil, it can be rapidly hydrolyzed to N¾ and CO₂ by soil urease, followed by NO₃ formation through nitrification. In agriculture, urea is more than half of applied N fertilizer, and this comprise 40% of the global annual urea consumption. However, the N recovery by crops from urea is often as low as 30-40%, with a potentially high environment cost associated with N losses via NH₃ volatilization, NO₃ leaching and N₂0 emission.

These losses are the result of many chemical, physical and biological processes, whose magnitude is affected by several factors such as: temperature, soil pH, cation exchange capacity (CEC), organic matter, and dose coverage and fertilization location.

One way to improve nutrient yield and specifically the efficiency of nitrogen use while reducing the environmental hazards is by using controlled-release fertilizers (CRFs). CRFs have been known for several decades. A major focus on CRFs research remains nowadays focused on environmental protection issues. CRFs are designed to release their nutrient contents gradually and to coincide with the nutrient requirement of a plant. This ensures an improved effectiveness of fertilizing through minimizing the losses between application and absorption, thus avoiding the losses by runoff, leaching and N volatilization.

The literature describes the CRFs as a granular nutrient core material containing at least one water soluble fertilizer compound, and a substantially water-insoluble coating applied on the core material. The fertilizer composition is structured to provide a Gaussian nutrient release rate curve over time with the maximum of the release rate occurring between 1 and 18 months after exposure of the fertilizer composition to moisture, according to US6139597 (Tijsma et al. 2000). Moreover, the European Committee for Standardization (CEN) states that a fertilizer can be described as controlled or slow release if the nutrient release, under defined conditions including that of a temperature of 25 °C, meets all the following criteria, a) no more than 15 % in 24 hours, b) no more than 75 % in 28 days and c) at least about 75 % released at the stated release time.

The nutrient release in conventional fertilization (e.g. urea) lasts 30-60 days, which given a 100- 120 day long crops growth cycle means that a fertilizers must be applied 2 or 3 times. In comparison, the CRFs release their nutrients slowly and gradually during the whole vegetation season consequently, they need to be applied only once, which reduces greatly both time and energy consumption.

Nowadays, CFRs development is an important topic of research, focusing mainly on obtaining a system in which a granule of fertilizer is encapsulated, i.e. it is coated with an inert layer. However, the use of coating materials may result in high production cost and even soil contamination after their release into soil. The CRFs value is 3-4 times more expensive than conventional fertilizers, this being the main reason for their limited use. However, these costs can be offset by a decrease in the application and purchase of fertilizers.

To solve these problems, conventional fertilizers are mixed with agricultural and industrial organic wastes and polymeric materials, forming a mixing with N-rich and high-quality organic fertilizer.

Biochar is among these products, it is a carbon-rich material obtained from the incomplete combustion of lignocellulosic biomass in the absence of oxygen and low temperatures. In recent years, the application of biochar as a soil amendment has attracted worldwide interest. This practice is positioned as a new approach to promote a significant carbon dioxide (C0₂) sinks in terrestrial ecosystems, in long-term. In addition, the production of biochar and its subsequent application to the ground would deliver benefits in both soil fertility and crop production.

Along with the benefits described above, this material exhibits certain characteristic, such as increased capacity to adsorb organic and inorganic pollutants compounds in comparison with other forms of organic matter. It also presents a high cation exchange capacity and negative surface charge. Due to these features, biochar is positioned nowadays as a low-cost adsorbent compared with activated carbon.

Despite the benefits that come with the addition of biochar to the soil, some patents and studies suggest the modification of this material before being incorporated into the soil. These modifications include the addition of one or more nutrients either by a direct mixing process, encapsulation and/or pelletizing, among others.

U.S. Patent No. 5,676,727 to Radlein et al. disclosed a process for making organic slow release nitrogenous fertilizers from products obtained of the flash pyrolysis of biomass. They proposed to use a chemical reaction to combine a nitrogen compound containing the NH₂ group with the pyrolysis products. The bio-oil obtained in the process contains high concentrations of carbonyl, carboxyl and phenolic functional groups and it is likely that these groups are largely responsible for the reaction with ammonia. This invention consists of use of bio-oil and charcoal N-rich derived from fast pyrolysis process by the formulation of an efficient biodegradable slow-release nitrogen fertilizer.

Similarly, other works used peanut shell pellets pyrolyzed under mild conditions at 400 °C, for developing a slow-release nitrogen fertilizer. In this study, similar conditions and principles to those propose by Radlein et al. are used. This charcoal also provided the baseline material for further nutrient addition by reaction of pyrolysis of oil with urea to add more bioavailable nitrogen. However, the reactivity of products used in the development of CRFs will depend on the feedstock used in the pyrolysis as well as the reactor operating conditions. WO/2005/054154 to Kotaka disclosed a method for obtaining nitrogen fertilizers considering the use of charcoal as an adsorbent. The method includes fermentation of organic matter from agricultural waste to produce ammonia gas, which is subsequently adsorbed by the charcoal. The resulting product is used as a nitrogenous fertilizer.

Another method for obtaining a slow release fertilizer considers the mixture of ammoniated superphosphate granules and potassium chloride, water, plaster (CaS0₄-2H₂0) and charcoal. The plaster gives a high resistance to the product; it also makes possible pelletizing the mixture. Moreover, due to the high surface area presented by charcoal, it tends to smooth the release rate by absorbing extra concentration of fertilizer when the release rate is high and by releasing or desorbing the fertilizer when the release rate is low.

Other forms to obtain nitrogen-enriched charcoals are by chemical modifications of charcoals already formed by thermo-chemical treatment of common raw material. These last procedures involve reactions with various reagents introducing the nitrogen groups, as well as the reaction sequences. For instance, the oxidation of carbon preceding the reaction with ammonia or its derivatives (ammonium carbonate, hydrazine, hydroxylamine and urea) with the carboxyl groups either naturally occurring in charcoal or artificially introduced by performic oxidation, or the nitration of carbon followed by hydrogenation of the nitro groups introduced.

Much attention is being paid to ammoxidation of charcoals, which consists of the direct reaction of active carbons with the mixture of air and ammonia. Depending on the method used, the nitrogen content of the charcoal varies, the same as the chemical nature of nitrogen groups.

This practice has been described in the formulation of slow charcoal-based release nitrogen fertilizer using chemical reaction between a nitrogen source and lignocellulosic matrices. However, this method has been used nowadays to obtain the activated carbons through nitrogen group introduction.

Basically, the mechanism of CRF action includes a system in a granule (conventional fertilizers), which is encapsulated or coated. After a fertilizers application, water penetrates through a membrane into a granule. Then, nutrients are dissolved and the arising osmotic pressure leads to a partial rupture of the membrane, which allows the release of active compounds to the soil. In recent years, CRFs production has focused mainly on obtaining organic fertilizers of determined particle size and specific physical-chemical characteristics. Recent studies present a trend towards production of biochar-based fertilizers incorporating nitrogen in a process of direct mixing, encapsulation and/or pelletizing. Various materials were found to be suitable for encapsulating or coating purposes. The most important of these include wax and sulfur and organic polymers such as polyolefins, polyethylene, kraft pine lignin, cellulose acetate, sodium alginate, among others. SUMMARY OF THE INVENTION

BRIEF DESCRIPTION OF THE FIGURES

Figure 1: Schematics of the process of the present invention.

Figure 2: Distribution of field tests (T0-T3, TS) in two experimental sites.

Figure 3: Components Percentage proportion of encapsulated mixture.

Figure 4: Nitrogen stability of encapsulated mixture during 6 months.

Figure 5: Ammonium release (NH₄ ⁺) concentration into deionized water of encapsulated mixture at 25°C and l00 rpm.

Figure 6: Ammonium release (NH₄ ^"1") percentage into deionized water of encapsulated mixture at 25 °C and 100 rpm.

Figure 7: Test results of ecofertilizer applications on two different cultivars (Mg ha^"1). DETAILED DESCRIPTION OF FIGURES

Figure 1: The schematics illustrates input of biochar with the particle size of less than 5 mm, preferentially of < 2 mm to the marmite (1); input of urea to the marmite (2); input of water to the marmite (3); particles of biochar in suspension (4); granules of urea in suspension (5); a mixer (6) and a thermocouple (7) for monitoring the process temperature between 100°C and 200°C, more preferentially at 150°C, within said marmite. After of a period of time between 1 hour and 12 hours, more preferentially for 8 hours of impregnation process, the solution is removed from marmite (8), and then the biochar impregnated with nitrogen is filtered from the aqueous solution (9). The content of nitrogen in biochar in this process was determined (10), and then biochar impregnated with nitrogen and 5% sodium alginate solution, were mixed (11) at a 3: 1 (w/v) mixing ratio. The mixture is transferred to the PVC cylinder with openings (12) of about 4 mm of diameter. The solution is mixed for maintaining the mixture and drip constant. After that, the sample is precipitated in a 0.5 M CaCl₂ (13). The spherical beads were left in the CaCl₂ solution for 10 min to ensure complete gelling. Once complete gelling the beads were separated from the CaCl₂ solution (14). Finally, beads are filtered and rinse twice with distilled water (15), and then beads were dried at room temperature overnight to constant weight (16).

DETAILS OF THE INVENTION

The object of the present invention is the development a granular organic controlled-release nitrogen fertilizer, comprising a source of nitrogen, a support matrix, and a biodegradable polymer coating or encapsulation in a biodegradable polymer.

In a particular embodiment of the invention, the granular organic controlled-release nitrogen fertilizer uses preferentially urea as a nitrogen source, but there are other sources of nitrogen than can be used.

In a further embodiment of the invention, the support matrix is biochar. In a more preferred embodiment, the biochar is in the form of particles of less than 5 mm, more preferentially less than 2 mm.

Other embodiment of the invention considers sodium alginate as a biodegradable polymer coating or encapsulation medium.

The invention also considers the process for the production of the granular organic controlled- release nitrogen fertilizer, wherein said process comprises the following steps:

a) obtaining biochar by slow pyrolysis of a biomass source;

b) impregnating the biochar obtained in the previous step with a nitrogen source, producing biochar particles impregnated with nitrogen;

c) coating or encapsulating the biochar particles impregnated with nitrogen with a biodegradable polymer.

In step a) of the process, the biochar is obtained by low temperature pyrolysis of a biomass source. Preferentially, the temperature of pyrolysis ranges between 300°C and 600°C, more preferentially between 300°C and 500°C. In a further embodiment, the pyrolysis is carried out for a period of time between 100 and 400 minutes, more preferentially between 120 and 315 minutes. In a further more specific embodiment, the biomass source is oat hull. In a further embodiment, the particle size of biochar obtained by low temperature pyrolysis is reduced to a size of less than 5 mm, preferentially, less than 2 mm.

In step b) of the process, impregnation of biochar with a nitrogen source is performed in liquid phase. The impregnation reaction is carried out in a suitable reactor at a temperature between 100°C and 200°C, more preferentially at 150°C. The impregnation reaction is carried out with constant agitation for a period of time between 1 hour and 12 hours, more preferentially for 8 hours. In a more particular embodiment, the solvent used as a liquid phase is a polar solvent. In a more preferred embodiment, the solvent used is water. For the impregnation reaction, the biochar and nitrogen source are present in a weight ratio of biochar:nitrogen source from 2:1 to 1:2, more preferentially 1:1. In a more specific embodiment, the polar solvent is present in a weight ratio of biochar:nitrogensource:polar solvent from 1:1:1 to 1:1:10, more preferentially 1:1:5. Further different ratios are also encompassed in the present invention, such as for example, the weight ratio of biochar:nitrogensource:polar solvent can be from 1:2:10 to 1:2:1, from 2:1:10 to 2:1:1. Finally, when the period of time of the impregnation reaction has ended, the mixture is left to cool at room temperature and the reaction gases are released. Once the reaction gases have been released, the polar solvent is separated by filtration, obtaining biochar particles impregnated with nitrogen.

In the final step c), the biochar particles impregnated with nitrogen obtained in the previous step are encapsulated or coated with a biodegradable polymer. In a more preferred embodiment, the biodegradable polymer is sodium alginate, although the present invention also encompasses the use of other biodegradable polymers, including cellulose acetate and ethyl acetate (both using formamide as solvent). In a more specific embodiment, the biodegradable polymer is dissolved in a suitable solvent, for example water. The ratio of biodegradable polymer: solvent is from 1:100 (1% in weight) to 1:10 (10% in weight), more preferentially 1:20 (i.e. 5% in weight). The biodegradable polymer/solvent mixture is mixed with the biochar particles impregnated with nitrogen obtained in the previous step, in a ratio of (biochar particles impregnated with nitrogen): (biodegradable polymer/solvent) from 10:1 (weigh volume) to 1:1 (weight:volume), more preferentially 3:1 (weight: volume). The mixture formed is added, dropwise, to a CaCl₂ solution allowing the drops to from gellified beads. In a more specific embodiment, the gellified beads have a size between 1 and 5 mm, more preferentially between 2 and 3 mm. Finally, the gellified beads are dried at room temperature overnight.

APPLICATION EXAMPLES

Biochar production The process used for obtaining biochar was slow pyrolysis. The carbonization experiment was performed in a pyrolizer with capacity to process 5 kg of raw material. The reactor was purged with N2 at a flow of 5 L min ¹. Oat hull was used for biochar production and the temperature of pyrolysis was of 300 °C, the time to reach T_max was 195 min and the processing time for T_max was of 120 min and the total time of pyrolysis was 315 min. The mass balance of slow pyrolysis process showed in Table 1.

Table 1. Mass balance of slow pyrolysis process of oat hull pyrolyzed at 300 °C

Products %

Biochar 41

Bio-oil 24

Synthesis gas* 35

obtained by difference

The biochar obtained from slow pyrolysis of oat hull at 300 °C (BO300) was characterized physically and chemically (Table 2).

Table 2.Physico-chemical characterization of BO300

Nitrogen impregnation onto biochar using urea as a nitrogen source

Impregnation process onto biochar (BO300) was carried out in a marmite with a 60 liter capacity (Figure 1). In the process urea was used as nitrogen source. Previously to the reaction, the size particle of BO300 was reduced at < 2mm.

The temperature of reaction was of 150 °C and was monitored with a thermocouple. The impregnation of biochar was performed in liquid phase, using water as solvent; the proportions used were 1:1:5 biochar:nitrogen:water, respectively. Process parameters are shown in Table 3. The reaction was carried out at 150°C during 8 h with constant agitation. After cooling and releasing the reaction gases, the solvent was separated by filtration. Table 3. Parameters and their ranges used in the urea impregnation process onto biochar (BO300)

Parameter Value Unit

Biochar (BO300) 6 kg

Urea 13 kg

Water 30 L

Reaction time 8 h

Temperature 150 °C

The total nitrogen content of the solid and liquid phase samples were then determined by jeldahl method for total nitrogen (APHA, 1998). The moisture content of the solid phase was measured by drying the sample in an oven at 100 + 5°C for approximately 24 h.

Encapsulation of the mixture between biochar impregnated with nitrogen and sodium alginate

(SA) The solution of sodium alginate (SA) (Aldrich Chemical) was prepared by dissolution of the solid polymer in distilled water, the concentration of solution was 5 wt%. This was followed by mixing biochar (undried solid) with the SA. The mixing ratio was 3:1 (w/v) of biochar and SA, respectively.

The resulting mixture was arranged in a cylinder of PVC with openings of about 4 mm of diameter at the bottom, the mixture was stirred vigorously until uniform and then slowly added dropwise to a 0.5 M CaCl₂ solution, where the drops turned to white beads immediately because the sodium alginate in the drop was cross-linked by Ca²⁺at once. The spherical beads were left in the CaCl₂ solution for 10 minutes to ensure complete gelling and then separated from the solution. The encapsulated mixture was dried at room temperature overnight.

Stability of nitrogen content in the time of encapsulation

To study the stability of encapsulated nitrogen content at certain time intervals (1, 5, 15 and 30 days and 6 months) a sample of encapsulated mixture was taken and the content of total nitrogen was measured by the Kjeldahl method.

Ammonium release of encapsulated mixture in water To study the release behavior of encapsulated mixture in water, the following experiment was carried out: 1 g of encapsulated mixture was mixed with 200 mL of deionized water and kept in a beaker properly covered and incubated in an orbital shaker at 100 rpm for different periods at 25 °C. All of the following tests were carried out in triplicate, and the average value was taken as the result. At certain time intervals (1, 5, 10, 15, 20, 25 and 30 days), 100 mL of aqueous solution was retired, for nitrogen determination, and an additional 100 mL of water was injected into the bottles to maintain a constant amount of solvent. The amount of N in the aqueous medium was estimated by the Kjeldahl method.

Application in field tests

Two different types of soil were selected to perform the field test of the developed ecofertilizer. In Figure 2 ecofertilizers field tests description is shown.

Results Nitrogen impregnation onto biocharusing urea as a nitrogen source

The result of total nitrogen content presented in Table 4 shows an increase in total nitrogen content in the BO300 after impregnation process. The process of impregnation at high temperatures (150 °C) showed a significant increase in the content of total nitrogen.

As for the moisture, biochar impregnated with nitrogen was dried at 105 +5°C for approximately 24 h resulting in a 50.43% of moisture.

Table 4. Total nitrogen content in the solid and liquid phase after the ammoxidation process

Phase Total nitrogen content (%)

Solid (BO300) 18.97+1.8

Liquid 13.14+1.6

Gaseous* 67.89

*obtained by difference

(SA) Once the humidity percentage was obtained, it was performed the mixing of biochar impregnated with nitrogen and sodium alginate; the mixing ratio was made 3:1 (w/v). The resulting mixture was arranged in a cylinder with openings of about 4 mm of diameter and, by means of dropping, the sample was precipitated in a solution of CaCl₂ 0.5 M. The spherical beads were left in the CaCl₂ solution for 10 min to ensure complete gelling and then separated from the solution, rinsed twice with distilled water, and dried at room temperature overnight. Finally, the proportion of the components of encapsulate is shown in Figure 3. While the average diameters of dry samples were of 2-3 mm.

Stability of nitrogen content of encapsulated mixture

The stability of the nitrogen content over time was evaluated, to rule out the loss by NH₃ volatilization of encapsulated mixture. It can be seen from Figure 4 that the nitrogen content is constant during the evaluated time. It is observed that first day the total nitrogen content is of 12.09 ±1.98% and at the 30th day the nitrogen content remains in 13.24+1.23%.

Ammonium release test of encapsulated mixture in water

One of the most important characteristics of the encapsulated mixture prepared by the method of this invention was its slow-release property. Figure 5 shows the ammonium slow release behaviors of encapsulated mixture in deionized water. It is seen in the figure that the release of NH₄ ^"1" during the first 10 days exhibits an exponential behavior and then abruptly decreases. From Figure 6 it can be seen that on day 5, 17.90% of the ΝΗ₄ ⁺ was released, between day 5 and day 15a 36.68% was released, while at day 30 a 39.59% NH₄ ⁺was released.

DETAILED DISCUSSION OF THE INVENTION

Nitrogen impregnation onto biochar using urea with nitrogen source The reaction of biochar with urea at elevated temperature (150°C) showed highest nitrogen enrichment of biochar (18.97+1.8). Other works used the same nitrogen source, but at a higher temperature (300°C), reporting values between 13 and 16.7% in the total nitrogen content in the charcoal.

This increase in nitrogen content could be explained by the presence of urea by-products after thermal decomposition. Nitrogen is likely to be in the form of amides, free NH and NH₂, bonded NH and NH₂, or NH₄ ⁺ species. All the findings so far suggest that the chemistry of the reaction of coal with urea is very complex, not only because of the heterogeneity of the charcoal structure but also because of the variety of N-reagents that can arise from urea and can react independently with charcoal. Encapsulation of the mixture between biochar impregnated with nitrogen and sodium alginate

(SA)

In recent years, a number of studies have greatly paid attention to the preparation and utilization of polysaccharide super absorbents because of their biodegradability, biocompatibility, renewability and nontoxicity. In particular, sodium alginate (SA) is a renewable and biodegradable natural polymer that is used in a variety of commercial applications because of its capacity for gelatinization.

The technique of precipitation of SA in CaCl₂ has been widely described for the obtained of CRF. Basically the method consists in the cross-linking between Na⁺ and Ca₂ ⁺. The stability of spherical beads depends of SA and Ca²⁺ concentration of solutions. However, a disadvantage in using CaCl₂ as precipitation bath is the need to change at certain intervals the CaCl₂Solution.

Stability of nitrogen content of encapsulated mixture in time

Before the release of the encapsulated mixture test it was necessary to assess the stability of the nitrogen content in time and rule out the loss of NI¾such as for example due to volatilization, so knowing the initial concentration of the encapsulated mixture to be used, also gives an idea of the period time that the final product can be stored once produced. According to the values obtained, no difference was seen between the total nitrogen content at first day and 30^th day (12.09+1.98% and 13.24+1.23%, respectively).

The literature does not report the evaluation of stability of active ingredient in the CRF in time. But it does mention that the viability of CRF depends of storage conditions such as temperature, humidity, among others as well as the polymeric material used in the formulation.

Ammonium release test of encapsulated mixture in water

CRFs are a granular nutrient core material containing at least one water soluble fertilizer compound, and a substantially water-insoluble coating applied to the core material. The fertilizer composition is structured to provide a Gaussian nutrient release rate curve over time with the maximum of the release rate occurring between 1 and 18 months after exposure of the fertilizer composition to moisture. However, the release time depends on environmental conditions and the properties of the polymers used to formulate of CRF. According to data obtained for the NH₄ ⁺ release of the encapsulated mixture in deionized water at 25 °C, the release does not follow this behavior, since the release of NH₄ ⁺ during the first 10 days exhibits an exponential behavior and then abruptly decreases. It is expected that this behavior is maintained in soil, with the difference that release is slower compared to deionized water.

With the sum of NH₄ ⁺release lower than 15% on the 3rd day and not above75% on the 30th day, this indicated that the slow release character of the encapsulated mixture prepared herein agrees with the standard of slow release fertilizers of the Committee of European Normalization (CEN). As for the conventional CRF the use of a double-coated in the preparation of slow-release urea has been reported. The fertilizer was prepared by cross-linked poly(acrylic acid)-containing urea (PAAU) (the outer coating), polystyrene (PS) (the inner coating), and urea granule (the core) with a total nitrogen content of 33.6%, whose ΝΗ₄ ⁺ release rate was 100% in 18 days in same conditions used in these studies. Note that the stability of the encapsulated mixture in liquid medium and under stirring was approximately 15 days

Field test

In Figure 7, the effect of ecofertilizer application on two different cultivars (Mg ha^"1) was tested, namely wheat (Triticumaestivum) A) Crac cultivar in the experimental site Maquehue and B) Impulso cultivar in the experimental site El Retiro. The nitrogen content of the encapsulated mixture after the application on field test was 1.62% in average.

Claims

WHAT IS CLAIM IS:

1. Granular organic contra lled-release nitrogen fertilizer comprising a nitrogen source, a support matrix, and a biodegradable polymer coating or encapsulation medium.

2. Granular organic controlled-release nitrogen fertilizer according to claim 1, wherein the nitrogen source is selected among urea.

3. Granular organic controlled-release nitrogen fertilizer according to claim 1, wherein the support matrix is biochar.

4. Granular organic controlled-release nitrogen fertilizer according to claim 3, wherein the biochar matrix is in the form of particles of less than 5 mm.

5. Granular organic controlled-release nitrogen fertilizer according to claim 1, wherein the biodegradable polymer coating is selected among sodium alginate, cellulose acetate and ethyl acetate (both using formamide as solvent).

6. Granular organic controlled-release nitrogen fertilizer according to claims 2 and 3, wherein the nitrogen source is impregnated onto the biochar.

7. Process for the production of a controlled-release nitrogen fertilizer comprising the steps of:

a. obtaining biochar by slow pyrolysis of a biomass source;

b. impregnating the biochar obtained in the previous step with a nitrogen source, producing biochar particles impregnated with nitrogen;

c. coating or encapsulating the biochar particles impregnated with nitrogen with a biodegradable polymer.

8. Process for the production of a controlled-release nitrogen fertilizer according to claim 7, wherein in step a) of the process, the biochar is obtained by low temperature pyrolysis of a biomass source, with the temperature of pyrolysis between 300°C and 500°C.

9. Process for the production of a controlled-release nitrogen fertilizer according to claim 7, wherein in step a) of the process, the biochar is obtained by low temperature pyrolysis of a biomass source with the temperature of pyrolysis between 300°C and 500 °C.

10. Process for the production of a controlled-release nitrogen fertilizer according to claim 7, wherein in step a) of the process, the biochar is obtained by low temperature pyrolysis carried out for a period of time between 100 and 400 minutes.

11. Process for the production of a controlled-release nitrogen fertilizer according to claim 7, wherein in step a) of the process, the biochar is obtained by low temperature pyrolysis carried out for a period of time between 120 and 315 minutes.

12. Process for the production of a controlled-release nitrogen fertilizer according to claim 7, wherein the biomass source is selected among oat hulland pine bark.

13. Process for the production of a controlled-release nitrogen fertilizer according to claim 7, wherein in step a) of the process, the size of the obtained biochar is reduced to less than 5 mm.

14. Process for the production of a controlled-release nitrogen fertilizer according to claim 7, wherein in step a) of the process, the size of the obtained biochar is reduced to less than 2 mm.

15. Process for the production of a controlled-release nitrogen fertilizer according to claim 7, wherein in step b) of the process, impregnation of biochar with a nitrogen source is performed in liquid phase.

16. Process for the production of a controlled-release nitrogen fertilizer according to claim 7, wherein in step b) the impregnation reaction is carried out at a temperature between 100°C and 200°C.

17. Process for the production of a controlled-release nitrogen fertilizer according to claim 7, wherein in step b) the impregnation reaction is carried out at a temperature of 150°C.

18. Process for the production of a controlled-release nitrogen fertilizer according to claim 7, wherein in step b) the impregnation reaction is carried with constant agitation for a period of time between 1 hour and 12 hours.

19. Process for the production of a controlled-release nitrogen fertilizer according to claim 7, wherein in step b) in the impregnation reaction, the biochar and nitrogen source are present in a weight ratio of biochannitrogen source from 2:1 to 1:2.

20. Process for the production of a controlled-release nitrogen fertilizer according to claim 7, wherein in step b) in the impregnation reaction, the polar solvent is present in a weight ratio of biochar:nitrogensource:polar solvent from 1:1:1 to 1:1:10.

21. Process for the production of a controlled-release nitrogen fertilizer according to claim 7, wherein in step b) in the impregnation reaction the polar solvent is present in a weight ratio of biochar:nitrogensource:polar solvent from 1:2:10 to 1:2:1 or from 2:1:10 to 2:1:1.

22. Process for the production of a controlled-release nitrogen fertilizer according to claim 7, wherein in step b) the mixture is left to cool at room temperature and the reaction gases are released, and once the reaction gases have been released, the polar solvent is separated by filtration, obtaining biochar particles impregnated with nitrogen.

23. Process for the production of a controlled-release nitrogen fertilizer according to claim 7, wherein in step c) the biochar particles impregnated with nitrogen are encapsulated or coated with a biodegradable polymer.

24. Process for the production of a controlled-release nitrogen fertilizer according to claim 23, wherein the biodegradable polymer is dissolved in a suitable solvent from 1% in weight to 10% in weight.

25. Process for the production of a controlled-release nitrogen fertilizer according to claim 23 and 24, wherein the biodegradable polymer is sodium alginate and the solvent is water, and the sodium alginate/water mixture is mixed with the biochar particles impregnated with nitrogen in a ratio of (biochar particles impregnated with nitrogen):(sodium alginate/water) from 10:1 (weight: volume) to 1:1 (weight: volume).

26. Process for the production of a controlled-release nitrogen fertilizer according to claim

25, wherein the mixture of biochar particles impregnated with nitrogen and sodium alginate/water is added, dropwise, to a CaCl₂ solution allowing the drops to form gellified beads, and the gellified beads have a size between 1 and 5 mm.

27. Process for the production of a controlled-release nitrogen fertilizer according to claim

26, wherein the gellified beads are dried at room temperature overnight.