1. A double-coated slow-release water-retaining urea fertilizer comprises a fertilizer core, an inner-layer coated film, a binder and an outer-layer coated film, wherein the fertilizer core comprises talcum powder, urea, orange peel, tea and a slow-release aid, the inner-layer coated film comprises sodium alginate and chitosan, the binder comprises processed bletilla hyacinthine gum and polyethylene glycol, and the outer-layer coated film comprises a water-retaining agent.

2. The double-coated slow-release water-retaining urea fertilizer as claimed in claim 1, wherein the fertilizer core comprises the following components in parts by weight: urea: 50-58 parts of citrus peel: 12-20 parts of tea leaves: 5-10 parts of talcum powder: 10-20 parts of a slow release auxiliary agent: 4-7 parts of slow release auxiliary agent, wherein the slow release auxiliary agent is hydroxyethyl cellulose.

3. The double-coated slow-release water-retaining urea fertilizer as claimed in claim 1, wherein the inner coating is a mixture of sodium alginate and chitosan, preferably a composition in a weight ratio of 1.2-1.6: 1.

4. The double-coated slow-release water-retaining urea fertilizer as claimed in claim 1, wherein the treated bletilla gum is prepared by the following steps: pulverizing rhizoma bletilla gum, and sieving with 20 mesh sieve; 95% of ethanol, sodium hydroxide and the sieved and crushed materials in a weight ratio of 10: 0.8: stirring for 3 hours to obtain reaction liquid; neutralizing the reaction solution with a 732 strong acid ion exchange resin to pH = 7.5; filtering to remove resin, and freeze drying the filtrate to obtain treated bletilla hyacinthine gum.

5. The double-coated slow-release water-retaining urea fertilizer as claimed in claim 1, wherein the outer coating is a water-retaining agent, the water-retaining agent is a mixture of starch graft acrylate copolymer and acrylamide-acrylate copolymer in a weight ratio of 2.5-3.2: 1; preferably 2.6-3.0: 1.

6. The double-coated slow-release water-retaining urea fertilizer as claimed in claim 1, wherein the polyethylene glycol is polyethylene glycol 400; the weight ratio of the treated bletilla striata gum to the polyethylene glycol 400 is 0.6-0.7:0.3-0.4, preferably 0.65: 0.35.

7. A method for preparing a double-coated slow-release water-retaining urea fertilizer as claimed in any one of claims 1 to 6, characterized by comprising the steps of:

preparing a slow-release water-retention urea fertilizer kernel: adding urea particles into a granulator, spraying atomized water to wet the surfaces of the urea particles, adding 5-10 parts of talcum powder, after the talcum powder is uniformly coated on the surfaces of the urea particles, adding powder formed by mixing orange peels and tea leaves, continuously rotating the disc until the urea particles are completely coated, repeating the above operations, spraying atomized water, adding the rest talcum powder and the water-retaining agent, rotating the disc until the urea particles are completely coated, taking out the prepared particles, and drying to obtain the water-retaining slow-release fertilizer core;

2) preparing the inner envelope slow-release water-retention urea fertilizer: putting the prepared fertilizer core particles into a granulator, rotating a disc, spraying sodium alginate and chitosan solution, taking out, and drying to obtain the inner-coating water-retention slow-release fertilizer;

3) preparing a double-coated slow-release water-retention urea fertilizer: putting the dried fertilizer granules into a granulator, spraying the treated bletilla striata gum and polyethylene glycol solution, adding a mixture of a starch grafted acrylate copolymerization cross-linked substance and an acrylamide-acrylate copolymerization cross-linked substance, coating until the surfaces of the fertilizer granules are uniformly coated, and drying the coated granules to obtain the double-coated water-retaining slow-release fertilizer granules.

8. The production method according to claim 7,

in the step 1), the particle diameters of the talcum powder and the water-retaining agent are 50-100 μm;

in the step 1), the average particle size of the orange peel and the tea is 100-150 μm.

9. The production method according to claim 7,

in the step 2), the sodium alginate and chitosan solution is prepared by dissolving sodium alginate and chitosan in 70-80% ethanol solution, preferably 75% ethanol solution;

in the step 2), sodium alginate: and (3) chitosan: the weight ratio of the ethanol solution is (1.2-1.6):1 (47-52), preferably (1.2-1.6):1: 50.

10. The production method according to claim 7,

in the preparation method, in the step 3), the bletilla hyacinthine gum and polyethylene glycol solution is prepared by dissolving bletilla hyacinthine gum and polyethylene glycol in 70% -80% ethanol solution, preferably 75% ethanol solution;

in the preparation method, in the step 3), the bletilla striata gum: polyethylene glycol: the weight ratio of the ethanol solution is (0.6-0.7:) (0.3-0.4): (29-31), preferably 0.65:0.35: 30.

Background

Agriculture is the foundation of national economy, and under the pressure of this current situation, the development of modern agriculture characterized by low input, high output, high efficiency and sustainable development must be accelerated. Wherein the fertilizer industry and the water resource utilization are the traditional Chinese medicine material basis for the production and development of modern agriculture.

The water resource is relatively poor and unevenly distributed in China, the water is wasted greatly, the utilization rate of irrigation water is only about 40% taking agriculture as an example, China is a big agricultural country, and the agricultural water consumption accounts for nearly 80% of the total water consumption. With the rapid development of cities and agriculture and industry, the contradiction between water supply and demand becomes more and more prominent, the contradiction between water contention between agriculture and industry is more acute, and the shortage of water resources becomes an important factor for limiting the sustainable development of agriculture and industry production in China. The implementation of high-efficiency water-saving agriculture is a necessary way for sustainable development of agriculture in China.

It is well known that the application of fertilizers plays a considerable role in agricultural production. The chemical fertilizer mainly comprises nitrogenous fertilizer, phosphate fertilizer and potash fertilizer. The conventional fertilizers have simple components, high nutrient content and quick fertilizer efficiency, and can greatly improve the quality of crops and increase the yield. The application amount of the fertilizer in China is extremely remarkable every year. While the yield increasing effect is achieved, some problems need to be solved. The most outstanding problems are that water resources in China are short, the agricultural water demand is high, and water shortage in dry seasons is one of important factors which hinder agricultural development in China. Therefore, the problems of fertilizer utilization rate, soil pollution and agricultural water conservation become important objects for researching fertilizers, and the novel fertilizer is one of important means for solving the three problems.

The slow release fertilizer can reduce nutrient loss, reduce the fertilization times, avoid the damage to seeds or seedlings caused by excessive fertilization, reduce the pollution to the environment and be beneficial to improving the quality of agricultural products and the food safety; the water-retaining slow-release controlled-release fertilizer is an important means for solving the problem. According to the requirements of plants on fertilizers in different periods, the release rate and the release amount of the fertilizers are controlled within preset time, so that the utilization rate of the fertilizers can be improved, the loss of the fertilizers is reduced, the moisture in soil is kept, the growth of crops is promoted, and time and labor are saved.

Coated fertilizers are a major class of slow release fertilizers, and both inorganic (mineral) materials and organic high molecular polymers are generally used as coating materials. The inorganic (mineral) substances are mainly sulfur, zeolite, diatomite, bentonite, phosphate, etc. The organic polymer mainly includes synthetic polymer, natural polymer and semisynthetic polymer. The development and development of new polymer coating materials are important directions of current research.

However, the existing water-retaining slow-release controlled-release fertilizer has the defects of unstable water-retaining property, poor slow-release effect, poor quality stability and the like, and is not beneficial to popularization.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides a double-envelope slow-release water-retention urea fertilizer and a preparation method thereof, wherein a fertilizer inner core with specific composition, sodium alginate and chitosan with specific weight ratio are used as inner envelope, treated bletilla striata gum and polyethylene glycol ester are used as bonding agents, starch graft acrylate copolymer cross-linked polymer with specific weight ratio and acrylamide-acrylate copolymer cross-linked polymer are used as outer envelope; the slow release performance and the water retention performance of the urea in the fertilizer core are ensured by the synergistic effect.

In order to achieve the above purpose, the invention adopts the following technical scheme: a double-coated slow-release water-retaining urea fertilizer comprises a fertilizer core, an inner-layer coated film, a binder and an outer-layer coated film, wherein the fertilizer core comprises talcum powder, urea, orange peel, tea and a slow-release aid, the inner-layer coated film comprises sodium alginate and chitosan, the binder comprises processed bletilla hyacinthine gum and polyethylene glycol, and the outer-layer coated film comprises a water-retaining agent.

Further, the fertilizer inner core comprises the following components in parts by weight: urea: 50-58 parts of citrus peel: 12-20 parts of tea leaves: 5-10 parts of talcum powder: 10-20 parts of a slow release auxiliary agent: 4-7 parts of slow release auxiliary agent, wherein the slow release auxiliary agent is hydroxyethyl cellulose.

The inner envelope is a mixture of sodium alginate and chitosan, and preferably a composition with the weight ratio of 1.2-1.6: 1.

The processing method of the processed bletilla striata gum comprises the following steps: pulverizing rhizoma bletilla gum, and sieving with 20 mesh sieve; 95% of ethanol, sodium hydroxide and the sieved and crushed materials in a weight ratio of 10: 0.8: stirring for 3 hours to obtain reaction liquid; neutralizing the reaction solution with 732 type strong acid ion exchange resin until the pH is 7.5; filtering to remove resin, and freeze drying the filtrate to obtain treated bletilla hyacinthine gum.

The outer coating film is a water-retaining agent which is a mixture of a starch graft acrylate copolymerization crosslinking product and an acrylamide-acrylate copolymerization crosslinking product, and the weight ratio is 2.5-3.2: 1. Preferably 2.6-3.0: 1.

The polyethylene glycol is polyethylene glycol 400.

The weight ratio of the treated bletilla striata gum to the polyethylene glycol 400 is 0.6-0.7:0.3-0.4, preferably 0.65: 0.35.

The invention relates to a preparation method of a double-coated slow-release water-retention urea fertilizer, which comprises the following steps:

1) preparing a slow-release water-retention urea fertilizer kernel: adding urea particles into a granulator, spraying atomized water to wet the surfaces of the urea particles, adding 5-10 parts of talcum powder, after the talcum powder is uniformly coated on the surfaces of the urea particles, adding powder formed by mixing orange peels and tea leaves, continuously rotating the disc until the urea particles are completely coated, repeating the above operations, spraying atomized water, adding the rest talcum powder and the water-retaining agent, rotating the disc until the urea particles are completely coated, taking out the prepared particles, and drying to obtain the water-retaining slow-release fertilizer core;

2) preparing the inner envelope slow-release water-retention urea fertilizer: and putting the prepared fertilizer core particles into a granulator, rotating a disc, spraying sodium alginate and chitosan solution, taking out, and drying to obtain the inner-coating water-retention slow-release fertilizer.

3) Preparing a double-coated slow-release water-retention urea fertilizer: putting the dried fertilizer granules into a granulator, spraying the treated bletilla striata gum and polyethylene glycol solution, adding a mixture of a starch grafted acrylate copolymerization cross-linked substance and an acrylamide-acrylate copolymerization cross-linked substance, coating until the surfaces of the fertilizer granules are uniformly coated, and drying the coated granules to obtain the double-coated water-retaining slow-release fertilizer granules.

In the preparation method, in the step 1), the particle diameters of the talcum powder and the water-retaining agent are 50-100 μm.

In the preparation method, in the step 1), the average particle size of the orange peel and the tea is 100-150 μm.

In the preparation method, in the step 2), the sodium alginate and chitosan solution is prepared by dissolving sodium alginate and chitosan in 70-80% ethanol solution, preferably 75% ethanol solution.

In the preparation method, in the step 2), the sodium alginate: and (3) chitosan: the weight ratio of the ethanol solution is (1.2-1.6):1 (47-52), preferably (1.2-1.6):1: 50.

In the preparation method, in the step 3), the bletilla hyacinthine gum and polyethylene glycol solution is prepared by dissolving bletilla hyacinthine gum and polyethylene glycol in 70% -80% ethanol solution, preferably 75% ethanol solution.

In the preparation method, in the step 3), the bletilla striata gum: polyethylene glycol: the weight ratio of the ethanol solution is (0.6-0.7:) (0.3-0.4): (29-31), preferably 0.65:0.35: 30.

The invention has the following advantages:

1. the fertilizer core with specific composition, sodium alginate and chitosan with specific weight ratio as inner coating, and treated bletilla hyacinthine gum and polyethylene glycol ester as adhesive are adopted, and the slow release performance of the fertilizer core urea is ensured by synergistic effect, wherein the release rate in 90 days is not higher than 70%, preferably not higher than 65%; the release rate in 180 days is 80-90%.

2. The starch graft acrylate copolymer cross-linked polymer and the acrylamide-acrylate copolymer cross-linked polymer in a specific weight ratio are adopted as outer coating films, so that the fertilizer has high water retention performance, the slow release performance of the fertilizer can be further adjusted, the soil moisture can be maintained, the water evaporation is slowed down, the fertilizer is fully absorbed by crops, and the soil moisture retention of 30 days is not less than 30%, preferably not less than 40%, and more preferably not less than 50%.

3. The double-coated slow-release water-retention urea fertilizer prepared by the invention has stable quality, and the slow-release performance and the water-retention performance are kept unchanged after the fertilizer is placed for 12 months at normal temperature.

Detailed Description

The invention discloses a double-coated slow-release water-retaining urea fertilizer and a preparation method thereof, and the method can be realized by combining the relevant principles of agricultural fertilizer technology and properly improving process parameters by taking the contents of the invention as reference by the technical personnel in the field. It is expressly intended that all such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the scope of the invention. While the invention has been described in terms of preferred embodiments, it will be apparent to those skilled in the art that variations may be applied, or changes and combinations may be made, in the methods and applications described herein to achieve and use the inventive techniques without departing from the spirit, scope, and content of the invention.

For a better understanding of the invention, and not as a limitation on the scope thereof, all numbers expressing quantities, percentages, and other numerical values used in this application are to be understood as being modified in all instances by the term "about". At the very least, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

The present invention is further illustrated by the following examples, which are not intended to limit the invention in any way.

In the following examples, the particle size of talc powder and water-retaining agent is 50-100 μm, and the average particle size of orange peel and tea is 100-150 μm.

Example 1: double-coated slow-release water-retaining urea fertilizer

The preparation method comprises the following steps:

1) preparing a slow-release water-retention urea fertilizer kernel: adding urea particles into a granulator, spraying atomized water to wet the surfaces of the urea particles, adding 8 parts of talcum powder, after the talcum powder is uniformly coated on the surfaces of the urea particles, adding powder formed by mixing orange peels and tea leaves, continuously rotating the disc until the urea particles are completely coated, repeating the above operations, spraying atomized water, adding the rest talcum powder and the water-retaining agent hydroxyethyl cellulose, rotating the disc until the urea particles are completely coated, taking out the prepared particles, and drying to obtain a water-retaining slow-release fertilizer core;

2) preparing the inner envelope slow-release water-retention urea fertilizer: and putting the prepared fertilizer core particles into a granulator, rotating a disc, spraying sodium alginate and chitosan solution, taking out, and drying to obtain the inner-coating slow-release water-retention fertilizer.

3) Preparing a double-coated slow-release water-retention urea fertilizer: putting the dried fertilizer granules into a granulator, spraying the treated bletilla striata gum and polyethylene glycol solution, adding a mixture of a starch grafted acrylate copolymerization cross-linked substance and an acrylamide-acrylate copolymerization cross-linked substance, coating until the surfaces of the fertilizer granules are uniformly coated, and drying the coated granules to obtain the double-coated slow-release water-retaining fertilizer granules.

Example 2: double-coated slow-release water-retaining urea fertilizer

The preparation method comprises the following steps: the same as in example 1.

Example 3: double-coated slow-release water-retaining urea fertilizer

The fertilizer comprises the following components:

the preparation method comprises the following steps: the same as in example 1.

Example 4: double-coated slow-release water-retaining urea fertilizer

The preparation method comprises the following steps: the same as in example 1.

Example 5: double-coated slow-release water-retaining urea fertilizer

The preparation method comprises the following steps: the same as in example 1.

Example 6: double-coated slow-release water-retaining urea fertilizer

The preparation method comprises the following steps: the same as in example 1.

Example 7: double-coated slow-release water-retaining urea fertilizer

The preparation method comprises the following steps: the same as in example 1.

Comparative example 1: double-coated slow-release water-retaining urea fertilizer

The fertilizer comprises the following components: the same procedure as in example 1 was repeated except that untreated bletilla gum was used instead of treated bletilla gum.

The preparation method comprises the following steps: the same as in example 1.

Comparative example 2: double-coated slow-release water-retaining urea fertilizer

The fertilizer comprises the following components: the fertilizer core comprises the following components; the inner envelope, adhesive and outer envelope were the same as in example 1.

The preparation method comprises the following steps: the same as in example 1.

Comparative example 3: double-coated slow-release water-retaining urea fertilizer

The fertilizer core comprises the following components; the inner envelope, adhesive and outer envelope were the same as in example 1.

The preparation method comprises the following steps: the same as in example 1.

Comparative example 4: double-coated slow-release water-retaining urea fertilizer

The fertilizer core comprises the following components; the inner envelope, adhesive and outer envelope were the same as in example 1.

The preparation method comprises the following steps: the same as in example 1.

Comparative example 5: double-coated slow-release water-retaining urea fertilizer

The inner wrapping film comprises the following components; the fertilizer inner core, the adhesive and the outer coating film are the same as the embodiment 1.

The preparation method comprises the following steps: the same as in example 1.

Comparative example 6: double-coated slow-release water-retaining urea fertilizer

The inner wrapping film comprises the following components; the fertilizer inner core, the adhesive and the outer coating film are the same as the embodiment 1.

The preparation method comprises the following steps: the same as in example 1.

Comparative example 7: double-coated slow-release water-retaining urea fertilizer

The outer wrapping film comprises the following components; the fertilizer core, the inner wrapping film and the adhesive are the same as those in the embodiment 1.

The preparation method comprises the following steps: the same as in example 1.

Comparative example 8: double-coated slow-release water-retaining urea fertilizer

The outer wrapping film comprises the following components; the fertilizer core, the inner wrapping film and the adhesive are the same as those in the embodiment 1.

The preparation method comprises the following steps: the same as in example 1.

Comparative example 9: double-coated slow-release water-retaining urea fertilizer

The binder is composed as follows; the fertilizer inner core, the inner wrapping film and the outer wrapping film are the same as those in the embodiment 1.

The preparation method comprises the following steps: the same as in example 1.

Example 8: test of sustained Release Performance

The release rates of the double-coated slow-release water-retaining urea fertilizers prepared in examples 1-7 and comparative examples 1-9 are measured for 24h, 14d, 56d, 90d and 180d, the measurement method is as shown in GB/T23348-2009, and the experimental results are shown in Table 1. The measurement temperature was 25 ℃.

TABLE 1 Release Rate results for Dual-coated Slow Release Water-holding Urea fertilizers

As can be seen from table 1: according to the double-coated slow-release water-retention urea fertilizer provided by the invention, the fertilizer inner core, the sodium alginate and the chitosan with specific weight ratio are used as inner-layer coatings, the treated bletilla striata gum and the polyethylene glycol ester are used as binders, and the slow-release performance and the water-retention performance of the double-coated slow-release water-retention urea fertilizer are ensured under the synergistic effect.

Comparing examples 1-7 with comparative examples 2-3, it can be seen that: the slow release performance of the double-coated slow-release water-retention urea fertilizer is influenced by the composition of the fertilizer inner core, when urea is used as the fertilizer inner core (comparative example 2) or urea, talcum powder and hydroxyethyl cellulose are used as the fertilizer inner core (comparative example 3), the prepared double-coated slow-release water-retention urea fertilizer releases not less than 80% in 90 days, has high release speed and cannot meet the requirements of the slow-release fertilizer.

Comparing and analyzing examples 1-7 and comparative examples 5-6, the composition of the inner coating film influences the slow release performance of the double-coating film slow-release water-retention urea fertilizer, when the inner coating film with different compositions (0.8 part of sodium alginate and 1.7 parts of chitosan in comparative example 5) or only chitosan is used as the inner coating film (comparative example 6), the prepared double-coating film slow-release water-retention urea fertilizer releases not less than 80% in 90 days, has high release speed, and cannot meet the requirements of slow-release fertilizers.

Comparing and analyzing examples 1-7 and comparative example 9, the composition of the binder influences the slow release performance of the double-coated slow-release water-retention urea fertilizer, and when only the treated bletilla striata gum is used as the binder (comparative example 9), the prepared double-coated slow-release water-retention urea fertilizer releases no less than 80% in 90 days, has high release speed and cannot meet the requirements of the slow-release fertilizer.

Example 9: testing of Water Retention

The test method comprises the following steps: 2.0g of fertilizer granules and 400g of dry soil (sieved by a 20-mesh sieve) are fully and uniformly mixed, then the mixture is placed into a 500mL beaker, weighed and recorded as A, and placed at room temperature. A quantity of tap water was then added to each beaker to saturate the soil sample and weighed every 2 days as B. Other conditions are the same. And evaluating the water retention performance of the fertilizer on soil by using the ratio of B to A. The results of the experiment are shown in table 2.

TABLE 2 Water retention results of double-coated slow-release water retention urea fertilizer

As can be seen from table 2: the double-coated slow-release water-retention urea fertilizer provided by the invention adopts the fertilizer inner core with specific composition, and adopts the starch graft acrylate copolymer cross-linked polymer and the acrylamide-acrylate copolymer cross-linked polymer with specific weight ratio as the outer coating, and the water retention performance of the double-coated slow-release water-retention urea fertilizer is ensured by the synergistic effect.

Comparing examples 1-7 with comparative example 4, it can be seen that: the water retention performance of the double-coated slow-release water-retention urea fertilizer is influenced by the composition of the fertilizer kernel, and when hydroxyethyl cellulose is not added into the fertilizer kernel (comparative example 4), the soil water retention of the prepared double-coated slow-release water-retention urea fertilizer is lower than 50% in 30 days, the water retention performance is poor, and the requirements of the slow-release fertilizer cannot be met.

Comparing and analyzing examples 1-7 and comparative example 7, the water retention performance of the double-coated slow-release water-retention urea fertilizer is influenced by the composition of the outer coating, and when only the starch grafted acrylate copolymer cross-linked polymer is used as the outer coating (comparative example 7), the soil water retention of the prepared double-coated slow-release water-retention urea fertilizer is lower than 50% in 30 days, the water retention performance is poor, and the requirement of the slow-release fertilizer cannot be met.

Example 10: test of slow release performance of double-coated slow release water-retaining urea fertilizer after 12 months of placement

The release rates of the double-coated slow-release water-retaining urea fertilizers prepared in the example 1, the comparative example 1 and the comparative example 8 after being placed for 12 months are measured for 24h, 14d, 56d, 90d and 180d, the measurement method refers to GB/T23348-. The measurement temperature was 25 ℃.

Table 3: release rate results of double-coated slow-release water-retention urea fertilizer after 12 months of storage

Comparing and analyzing the example 1 and the comparative example 1, the composition of the binder influences the slow release performance of the double-coated slow-release water-retaining urea fertilizer, when untreated bletilla hyacinthine gum is used to replace the treated bletilla hyacinthine gum (comparative example 1), the prepared double-coated slow-release water-retaining urea fertilizer releases not less than 80% in 90 days after being placed for 12 months, the release speed is high, and the requirement of the slow-release fertilizer cannot be met.

Example 11: testing of Water Retention

The double-coated slow-release water-retention urea fertilizer prepared in example 1 and comparative example 8 after being left for 12 months was subjected to a soil water-retention test.

The test method comprises the following steps: 2.0g of fertilizer granules and 400g of dry soil (sieved by a 20-mesh sieve) are fully and uniformly mixed, then the mixture is placed into a 500mL beaker, weighed and recorded as A, and placed at room temperature. A quantity of tap water was then added to each beaker to saturate the soil sample and weighed every 2 days as B. Other conditions are the same. And evaluating the water retention performance of the fertilizer on soil by using the ratio of B to A. The results of the experiment are shown in table 4.

Table 4: water retention result of double-coated slow-release water retention urea fertilizer after being placed for 12 months

Comparing and analyzing the example 1 and the comparative example 8, the composition of the outer coating film influences the water retention performance of the double-coating film slow-release water-retention urea fertilizer, when starch graft acrylate copolymer cross-linked polymer and acrylamide-acrylate copolymer cross-linked polymer with different compositions are used as the outer coating film (the comparative example 8), the soil water retention is lower than 50% in 30 days after the prepared double-coating film slow-release water-retention urea fertilizer is placed for 12 months, the water retention performance is poor, and the requirement of the slow-release fertilizer cannot be met. .