NITROGEN FERTILIZER COMPOSITION

The invention relates to a solid fertilizer which contains at least 20% by weight of nitrogen, calculated as ammonium nitrate. The invention also relates to a method for the preparation of a fertilizer containing at least 20% by weight of nitrogen, calculated as ammonium nitrate.

When using solid nitrogen fertilizers, one problem is to improve the overall fertilizer uptake and thus the fertilizer's plant yield.

In CN 1463955, a solid fertilizer is described which contains 10 to 20% by weight of humic acid and other organic fertilizer components, 25 to 32% by weight of N, P, K and other inorganic fertilizer components, and 0.1 to 0.4% by weight of a selenium fertilizer component. The N component is a delayed release or long acting urea component rather than common urea. The fertilizer is prepared by one step granulation while controlling humidity and temperature to prevent agglomeration and biuret formation. Alternatively, an organic composite fertilizer containing Se, P and K is first prepared and then compounded with long-acting urea to form the final product.

In CN 1298849, a method for the preparation of a solid iodine-containing fertilizer is described. It contains 0.8 to 20% by weight of iodine and a balanced amount of a compound fertilizer containing nitrogen, phosphorus and potassium. The method includes mixing of the raw materials, atomization, dissolution, spray-drying, cooling and discharge to yield the product.

The problem lying behind the present invention compared to the above-mentioned references is to further increase the overall fertilizer uptake and plant yield. A factor which increases the plant yield is the reduction of the residence time of nitrogen and other nutrients in the soil. If nitrogen stays for a shorter time in the soil, it is not leached away, nor is it volatilized away as ammonia and or de-nitrified. This effect is pronounced with fertilizers containing much nitrogen such as over 20% by weight or over 50% by weight of nitrogen, calculated as ammonium nitrate. The above-mentioned situation has now been ameliorated by including into the solid fertilizer containing at least 20% by weight of nitrogen, calculated as ammonium nitrate, and both selenium and iodine.

The physiological mechanisms of selenium and iodine are not fully understood. They are both trace elements, i.e. they occur only in traces in the living organism

but are still essential. Trace elements are known to function in ionic dissolved or complex bound form. Selenium specifically is e.g. known to increase the UV- tolerance and drought resistance of plants. Without limiting the scope of protection, the combination of selenium and iodine is believed to shorten the residence time of nitrogen in the soil and thereby improve the fertilizer's plant yield. This effect is increased with fertilizers containing more nitrogen, preferably at least 50% by weight, calculated as ammonium nitrate.

By "calculated as ammonium nitrate" is meant that if e.g. ammonium sulphate is used, the amount calculated as ammonium nitrate is obtained by dividing the weight of the ammonium sulphate with the molecular weight of ammonium sulphate and multiplying the result with the molecular weight of ammonium nitrate.

The claimed solid fertilizer may be in any form. Preferably it is in the form of granules.

The first of the two trace elements to improve the plant yield is selenium. The selenium is preferably in the form of selenic acid or a selenate, preferably a selenate. Most preferably the selenium is in the form of sodium selenate and/or potassium selenate. According to an advantageous embodiment of the invention, the fertilizer according to the invention contains between 1 and 90 ppm by weight, preferably between 2 and 50 ppm by weight, most preferably between 3 and 8 ppm by weight, of selenium.

The second trace element used in the claimed fertilizer is iodine. According to one embodiment, the iodine is in the form of a salt, preferably sodium iodide and/or potassium iodide and/or potassium iodate and/or sodium iodate. Preferably, the fertilizer contains from 1 to 6000 ppm by weight, preferably from 10 to 3000 ppm by weight, most preferably from 30 to 150 ppm by weight, of iodine.

The above preferred amounts of selenium and iodine are used to avoid overdosing even in case high amounts of the claimed fertilizer are used per ha. The upper limit also depends on the parameters of the soil to be fertilized such as pH, as well as its chemical and physical interaction with the specific selenium and iodine salts used. Upper limit doses for increasing plant growth are about 500 μg/kg dm for selenium and about 10 mg/kg dm for iodine.

The main component of the claimed fertilizer is the nitrogen source. It may be selected from ammonium nitrate, calcium ammonium nitrate, ammonium sulpho- nitrate, ammonium sulphate, and complex fertilizers (NP, NK, NPK) in which the nitrogen comes from ammonium nitrate, ammonium sulphate and/or ammonium phosphate.

The amount of nitrogen in the solid fertilizer should be at minimum 10% N, preferably at least 20% N.

Advantageously, the nitrogen of the fertilizer is in the form of ammonium nitrate, ammonium sulphate or a mixture thereof. It may e.g. contain from 20 to 90% by weight of ammonium nitrate and from 0 to 70% by weight of ammonium sulphate, preferably from 44 to 80% by weight of ammonium nitrate and from 0 to 60% by weight of ammonium sulphate. Typically, it contains about 70% by weight of ammonium nitrate and about 3% by weight of ammonium sulphate.

The combination of selenium and iodine with mineral nitrogen leads to a higher assimilation of nutrients and thus to increased plant growth. With the claimed fertilizer, synergy exists between selenium and iodine. This effect is pronounced with fertilizers containing over 50% by weight of nitrogen, calculated as ammonium nitrate. Earlier, trace elements such as selenium or iodine were added merely to increase the nutrient value of the plant to livestock and human, but not to increase the yield of the plant itself.

Due to the low concentration of selenium and iodine needed, precise dosing and even distribution of the claimed fertilizer is of vital importance. A selenium concentration of 4 ppm and an iodine concentration of 50 ppm with an average use of 250 kg/ha lead to a distribution of 1 g selenium and 12.5 g iodine per ha and application (1 ha = 10 000 m ² ). If the fertilizer is used in granular form dosing and distribution are facilitated.

When using ammonium nitrate as nitrogen source and selenate as selenium source in the claimed fertilizer product, the plant absorption of selenium is improved. The high oxidation potential of the ammonium nitrate prevents the conversion of the selenate which is plant available into selenite which has low plant availability. When combined in the same granule, ammonium nitrate having a nitrogen availability of at least 10% N ensures a constant and reliable supply of selenium to the plant.

The combination of ammonium nitrate and iodine requires strict product safety considerations in order to avoid chemical composition of the ammonium nitrate. Without limiting the scope of protection, the improved plant yield is believed to be caused by a participation of selenium and iodine in the metabolism, especially the immune defence and stress resistance, of the plant.

The invention also relates to a process for the preparation of a fertilizer containing at least 20% by weight of nitrogen, calculated as ammonium nitrate. In the process, a selenium source and an iodine source, or a selenium plus iodine source, is

added to a nitrogen source. The nitrogen source is selected so that the fertilizer contains at least 20% by weight, preferably at least 50% by weight, of nitrogen, calculated as ammonium nitrate.

According to one embodiment of the invention, the fertilizer is prepared by the steps of forming a liquid phase containing the nitrogen source, adding to the liquid phase the selenium source and the iodine source, or the selenium plus iodine source, and solidifying the liquid phase. The liquid phase may be a solution, a melt, or an intermediate between a solution and a melt. Typically, the liquid phase comprises the nitrogen source in molten form. The liquid phase containing the selenium and iodine source is preferably solidified into the form of granules.

The preparation is typically started from the nitrogen source in liquid, preferably molten form. To this liquid, the selenium and iodine source/s is/are added. They are preferably added separately or together to the liquid phase as an aqueous solution. The selenium source is typically selenic acid or a selenate, preferably a selenate, most preferably sodium selenate and/or potassium selenate. The selenium content of the aqueous solution is preferably from 0.1 to 10% by weight, most preferably from 0.5 to 2% by weight. The amount of selenium source is advantageously selected so that the fertilizer will contain between 1 and 90 ppm by weight, preferably between 2 and 50 ppm by weight, most preferably between 3 and 8 ppm by weight of selenium.

The iodine source is typically a iodine-containing salt, preferably sodium iodide, potassium iodide, potassium iodate and/or sodium iodate. The iodine content of the aqueous solution is preferably from 5 to 30% by weight, most preferably from 8 to 16% by weight. The amount of iodine source is advantageously selected so that the fertilizer will contain from 1 to 6000 ppm by weight, preferably from 10 to 3000 ppm by weight, most preferably from 30 to 150 ppm by weight, of iodine.

The purpose of the above concentrations of selenium and iodine in the solution to be added is to ensure an even distribution if selenium and iodine in the final fertilizer. Therefore, it is important to check the achieved concentration and distribution of these elements in the product regularly during the process.

As was stated above in connection to the claimed product, the nitrogen source may be freely selected, but is preferably ammonium nitrate, ammonium sulphate or a mixture thereof. Then, the amount of ammonium nitrate, optionally together with ammonium sulphate, is according to one embodiment selected so that the fertilizer will contain from 20 to 90% by weight of ammonium nitrate and from 0 to

70% by weight of ammonium sulphate, preferably from 44 to 80% by weight of ammonium nitrate and from 0 to 60% by weight of ammonium sulphate.

Also other fertilizer components such as ammonium sulphate, gypsum, dolomite, and granulation additives may be added, whereby the liquid phase preferably is maintained.

Then, the liquid phase is formed into granules, cooled to normal temperature and preferably coated to prevent agglomeration. When preparing the above-mentioned complex fertilizers, further minerals may be added to the granules.

The preparation process according to the invention may be modified to enable blending into different fertilizer grades after the granulation process. Thus, according to one embodiment, the fertilizer product is prepared by using the building block concept. This means that first, granules are formed which contain concentrated amounts of selenium and iodine and then, these granules are mixed with granules containing little or no selenium and iodine. By regulating the ratio of loaded and unloaded granules, the right grades for different applications may easily be obtained. Typically, granules having five times more selenium and iodine than the final product average are first prepared and then blended with granules having little or no selenium and iodine to get a series of grades having contents under and above said average. When blending granules having more and less of selenium and iodine, it is important that the granules are compatible, i.e. have the same physical (e.g. density, diameter, form, surface, etc.) and chemical (e.g. pH, moisture, etc.) properties. This is to ensure safe product properties, avoid post reactions between the components and ensure homogeneous product properties. The fertilizer product according to the invention is either used for top dressing or local fertilizer application. The granular form allows standard distribution equipment. The amounts to be distributed are typically between 300 and 1 000 kg/ha depending on the intensity of crop production and the desired plant yield. The invention increases the nitrogen efficiency of a nitrogenous mineral fertilizers. The reduced dwelling time in the soil reduces i.e. the losses of nitrogen through leaching of nitrate, volatilization of ammonia and de-nitrification. This is especially the case with fertilizers having higher nitrogen content than normally. As such, the improved efficiency reduces negative environmental effects caused by intensive agricultural activity and makes it is easier to follow governmental rules and recommendation.

The combination of selenium and iodine with a nitrogen source also eliminates additional application steps when fertilizing crop. This releases the workload in professional farming.

The mere purpose of the following examples is to illuminate the claimed invention. EXAMPLES 1. Test fertilizers

The following solid fertilizer materials were prepared:

K42 without any Se or I (NS) K42 with Se (NS+Se 4 ppm) K42 with I (NS+I 50 ppm)

K42 with Se (NS+Se 4 ppm +l 50 ppm)

Preparation of K42:

The solid K42 fertilizer was prepared using ammonium nitrate, ammonium sulfate, dolomite and calcium sulfate as raw materials giving the final NPK formula 24-0-0 and 12% SO3. For the pot trial purposes the K42 was ground into powdery form.

Preparation of K42+Se

All the steps to prepare the fertilizer product were carried out like when preparing K42 but selenium was added as Na-selenate (10 mg Na-selenate per one kg final fertilizer product; Na-selenate contains 41 ,5% (w/w) Se). Preparation of K42+ 1

All the steps to prepare the fertilizer product were carried out like when preparing K42 but iodine was added as K-iodide (66 mg K-iodide per one kg final fertilizer product; K-iodide contains 76% (w/w) I).

Preparation of K42+Se+I All the steps to prepare the fertilizer product were carried out like when preparing K42 but selenium was added as Na-selenate and iodine as K-iodide in the same way and in same concentrations as described above.

2. Pot trial in the greenhouse

Ryegrass and oilseed rape cv. Hunter were used as test crops and mineral soil was used as growth substrate. All pots received similar NPK fertilizing, mg/kg dry soil: ryegrass N 150, P2O5 230, K 150; oilseed rape N225, P450, K2O 300. Phosphorus and potassium originated from monopotassium phosphate applied at sowing. Nitrogen, selenium and iodide originated from the test fertilizers K42,

K42+Se, K42+I and K42+Se+I. For oilseed rape 66% of the K42 fertilizer was mixed into soil at sowing and 34% was surface-applied at growth stage 31. For ryegrass 50% of the K42 fertilizer was mixed into soil at sowing but 50% was split applied after cuts 1 and 2.

Soil moisture of all ryegrass pots was kept at 20% but half of the oilseed rape trial was kept at 20% soil moisture and half at 16% soil moisture. Replicate number was five.

Treatments (5 replicates of each) were as follows: Ryegrass and oilseed rape

K42, 20% soil moisture

K42+Se, 20% soil moisture

K42+I, K42+Se+I, 20% soil moisture

Oilseed rape K42, 16% soil moisture

K42+Se, 16% soil moisture K42+I, 16% soil moisture K42+Se+I, 16% soil moisture

Ryegrass was cut in two weeks intervals, five cuts altogether. Oilseed rape phytomass was harvested forty days after sowing. The phytomass of each yield was dried and weighed.

3. Results

Results of the trial indicate that the addition of either selenium or iodine into K42 fertilizer enhanced the growth of ryegrass and oilseed rape (tablei .). However, the addition of both selenium and iodine into K42 fertilizer enhanced the phytomass production of both crops even more than either selenium containing K42 or iodine containing K42 alone. It is concluded that selenium and iodine combined together enhance the crop growth on a synergistic way.

Table 1. Phytomass results.

These tests show that I + Se gives considerably better plant yield compared to I or Se alone.