JP5787828B2 - Soil improvement method - Google Patents

Description

  The present invention relates to a soil improvement method for farmland from which topsoil contaminated with radioactive cesium has been removed.

In the accident at TEPCO's Fukushima Daiichi NPS in March 2011, a large amount of radioactive isotopes were released into the sea and land. For radioactive cesium, there are ¹³⁴ Cs and ¹³⁷ Cs, and these were released in large quantities. It has been reported that the total amount of radioactive cesium emissions reaches 1.5 × 10 ¹⁶ becquerel even for ¹³⁷ Cs alone (Non-patent Document 1).

  Not only the ocean, but also vast soil was contaminated with radioactive cesium, and farmland was also contaminated.

In an accident at the Chernobyl nuclear power plant in the former Soviet Union in 1986, 8.5 × 10 ¹³ becquerel of radioactive cesium was reported to be released. After the Chernobyl nuclear power plant accident, detailed analysis of soil contamination by radioactive cesium has been made, and it has been reported that in many soils, radioactive cesium has accumulated in the top soil of about 10 cm from the surface (non-patent literature). 2).

  In the accident at the Fukushima Daiichi NPS, as in the case of the Chernobyl NPS, it was reported that radioactive cesium remained on the topsoil about 10 cm from the ground surface, and the topsoil was contaminated with radioactive cesium. By removing about 4 cm from the surface of the earth, it is possible to efficiently remove radioactive cesium, so it is recommended for decontamination of soil contaminated with radioactive cesium, and is actually implemented (Non-Patent Document 3) ).

Nature Vol. 478 p. 435-P. 436 (2011) Environmental Consequences of the Chernobyl Accident and the Remediation: Twenty Years of Experience, p. 33, INTERNATIONAL ATOMIC ENERGY AGENCY (2006) About Ministry of Agriculture, Forestry and Fisheries Agricultural, Forestry and Fisheries Technology Conference Home Page, Radioactive Substance Removal Technology (Decontamination Technology) of Farmland Soil [Appendix 2] Summary of Proven Decontamination Technology Results (http: //www.s.affrc.go. jp / docs / press / 110914.htm)

  However, it is considered that there are the following problems for farmland contaminated with radioactive cesium.

  Topsoil contaminated with radioactive cesium is soil from the surface to a depth of 10 cm. This topsoil contains mineral components such as silicic acid, lime, magnesium, manganese, and iron. In addition, organic matter derived from humus is included, and many microorganisms are inhabited. In addition, the topsoil has a nodule structure so that oxygen and water can be appropriately supplied to the roots of microorganisms and cultivated crops.

  In order to remove radioactive cesium, mineral components such as silicic acid, lime, magnesium, manganese, and iron contained in the topsoil are lost by removing the topsoil from the ground surface to a depth of about 10 cm. In addition, the aggregate structure, microorganisms and organic matter will be lost.

  As a result, there is a concern that agricultural crops are difficult to grow on farmland excluding topsoil in order to remove radioactive cesium.

  Therefore, in the present invention, a soil improvement method capable of imparting silicic acid, lime, magnesium, manganese, iron, and organic matter economically and efficiently to agricultural land excluding topsoil contaminated with radioactive cesium. The purpose is to provide.

  As a result of intensive studies to solve the above-mentioned problems, the inventor of the present invention economically and efficiently, silicic acid, lime, and agricultural land excluding topsoil contaminated with radioactive cesium as follows. The present invention was completed by successfully establishing a soil improvement method for providing magnesium, manganese, iron and organic matter.

The gist of the present invention is as follows.
(1) to land except topsoil containing radioactive cesium, by applying the topsoil was removed by heating the radioactive cesium, and a mixture of manure and steel slag, and silicate on the farmland, lime, magnesium, A method for improving soil, comprising adding manganese, iron and organic matter.
(2) The soil improvement method according to (1), wherein a mass ratio of the steelmaking slag to the livestock waste of the mixture of the livestock excrement and the steelmaking slag is 10% or more and 30% or less.
(3) The soil improvement method according to (1) or (2), wherein a moisture content of the mixture of the livestock excrement and the steelmaking slag is 30% or more and 50% or less.
(4) The mixture of the livestock excrement and the steelmaking slag is compost produced by mixing the steelmaking slag with the livestock excrement, according to any one of (1) to (3). Soil improvement method.
(5) The composition of the steelmaking slag is mass%,
CaO: 20% to 50%,
SiO ₂ : 10% to 30%,
MgO: 1% or more and 20% or less,
MnO: 2% or more and 10% or less,
Total iron: 10% or more and 30% or less, The soil improvement method according to any one of (1) to (4).
(6) The soil improvement method according to any one of (1) to (5), wherein a particle diameter of the steelmaking slag is 3 mm or less.
(7) The livestock excrement is at least one of cow dung, chicken dung, and pork puff that is not contaminated with radioactive cesium. (1)-(6) Soil improvement method.
How to use (8) before Ki施 is, the surface soil was removed by heating the radioactive cesium, and a mixture of manure and steel slag, a superimposed thickness 5cm 20cm or more below the surface of the land except for the topsoil It is a method, The soil improvement method as described in any one of (1)-(7) characterized by the above-mentioned.
(9) The topsoil from which the radioactive cesium has been removed by heating is a topsoil obtained by heating the topsoil containing the radioactive cesium removed from the farmland, according to any one of (1) to (8). Soil improvement method.
(10) The soil according to (9), wherein the topsoil from which the radioactive cesium has been removed by heating is a topsoil obtained by heating the topsoil containing the radioactive cesium removed from the farmland to a temperature equal to or higher than the boiling point of cesium. Improvement method.

  By applying a mixture of livestock excrement and steelmaking slag to farmland excluding topsoil contaminated with radioactive cesium according to the present invention, by applying silicic acid, lime, magnesium, manganese, iron and organic matter, farmland at an early stage As a result, it becomes possible to grow crops.

  Hereinafter, preferred embodiments of the present invention will be described in detail.

The farmland excluding topsoil contaminated with radioactive cesium targeted by the present invention is the following farmland. The radioactive cesium is ¹³⁴ Cs and ¹³⁷ Cs, and in many cases, these are only in the surface layer of the farmland soil and a depth of about 10 cm from the ground surface. Called topsoil contaminated with cesium.

  There are various methods for removing topsoil contaminated with radioactive cesium. For example, if you use a shovel to remove it manually, use a dozer excavator, backhoe, yumbo, power shovel, or other machine. If the topsoil is soft and difficult to remove, use a solidifying agent to harden the topsoil. There is also a way to remove it. The farmland excluding the topsoil contaminated with radioactive cesium targeted by the present invention may be any method that removes the topsoil.

  Next, the livestock excrement targeted by the present invention will be described.

  In the present invention, livestock excrement is used as a source of organic matter (substance containing carbon derived from living organisms) to agricultural land excluding topsoil.

  The livestock excrement targeted by the present invention means beef dung, pork duck, chicken dung that is not contaminated with radioactive cesium, among cow dung, pork dung, chicken dung, etc. that are generated by livestock breeding such as livestock industry and dairy farming. In particular, as for cow dung, cow cow dung that was fed by rice straw contaminated with radioactive cesium caused by the accident at TEPCO's Fukushima Daiichi nuclear power plant and that was contaminated with radioactive cesium was detected. Therefore, it is preferable to confirm beforehand that the livestock excrement targeted by the present invention is not contaminated with radioactive cesium.

  Next, regarding the steelmaking slag targeted by the present invention, the steelmaking slag targeted by the present invention is obtained as a converter slag, hot metal pretreatment slag, dephosphorization slag, etc. from the steelmaking process of the steel industry. is there. In the present invention, these can be used alone or in combination as appropriate as steelmaking slag.

  Next, the mixture of livestock excrement and steelmaking slag according to the present invention will be described.

  First, regarding the mixing ratio of the steelmaking slag to the livestock excrement, the mixing ratio of the steelmaking slag to the livestock excrement is preferably 10% or more and 30% or less by mass ratio. When the mixing ratio of steelmaking slag with respect to livestock excrement is less than 10% by mass, components such as Ca, Si, Mg, etc. derived from steelmaking slag decrease, and the effect of promoting cultivation of agricultural products may not be seen There is sex. On the other hand, when the mixing ratio of the steelmaking slag with respect to the livestock excrement exceeds 30% by mass, the amount of the steelmaking slag is so large that the pH of the mixture of the livestock excrement and the steelmaking slag becomes pH 9 by CaO or MgO derived from the steelmaking slag. There is a possibility that it may become alkalinized, and it may become unsuitable for cultivation of crops. Therefore, it is preferable that the mixing ratio of the steelmaking slag to the livestock excrement is 10% or more and 30% or less in terms of mass ratio.

  In addition, since the mineral supply effect by steelmaking slag and the pH of the mixture of livestock excrement and steelmaking slag are about 6 to 7 suitable for cultivation of agricultural crops, the mixing ratio of steelmaking slag to livestock excrement is about 15% by mass ratio. It is more preferable that

  Moreover, although it is about the moisture content of the mixture of livestock excrement and steelmaking slag, it is preferable that they are 30% or more and 50% or less. If the water content of the mixture of livestock excrement and steelmaking slag exceeds 50%, there is too much moisture, so the mixture of livestock excrement and steelmaking slag may not be able to form a good aggregate structure or is contained in livestock excrement. There is a possibility that reaction products generated by microbial decomposition of the components that act on the cultivation of agricultural crops may have an inhibitory effect. On the other hand, when the water content of the mixture of livestock excrement and steelmaking slag is less than 30%, there is a possibility that the water content is too small and the mixture of livestock excrement and steelmaking slag cannot form a good aggregate structure. Therefore, the water content of the mixture of livestock excrement and steelmaking slag is preferably 30% or more and 50% or less.

  The mixture of livestock excrement and steelmaking slag of the present invention is preferably compost produced by mixing livestock excrement and steelmaking slag and applying a treatment such as turning over. Examples of the compost making method include a deposition method, an open stirring method, and a closed stirring method, and any method may be used. What is important in compost production is the supply of oxygen. In the deposition method, it is possible to supply oxygen necessary for composting to the inside of the deposit by turning over the mixture of livestock excrement and steelmaking slag at least once a week. In the open type stirring system, oxygen can be supplied by stirring a mixture of livestock excrement and steelmaking slag using a rotary scoop or the like. In the closed stirring method, oxygen can be supplied by stirring with a stirring propeller or the like. Composting can be expected to decompose and remove components harmful to the cultivation of crops caused by organic matter contained in livestock excrement being decomposed by microorganisms, and the water content of the mixture of livestock excrement and steelmaking slag can be composted. This is because it is possible to voluntarily achieve 30% or more and 50% or less as desired by the present invention using the heat generated during the conversion. Moreover, the mixture of the livestock excrement and steelmaking slag which became compost can also expect the fertilizer effect to agricultural crops. Therefore, it is preferable that the mixture of livestock excrement and steelmaking slag is compost produced by mixing livestock excrement and steelmaking slag.

Then, although the composition of the steel slag to be used in the present invention, the composition of the steel slag to be used in the present invention, in mass%, CaO: 20% to 50%, _SiO 2: 10% or more than 30% MgO: 1% or more and 20% or less, MnO: 2% or more and 10% or less, Steel: Slag having a composition of 10% or more and 30% or less is preferable.

  First, Ca contained in steelmaking slag will be described.

Ca contained in the steelmaking slag exists in a chemical form such as quick lime CaO, dicalcium silicate (2CaOSiO ₂ ), tricalcium silicate (3CaOSiO ₂ ). Usually, when expressing the composition of steelmaking slag, all Ca is displayed as CaO content.

  In steelmaking slag with a CaO content of less than 20% by mass, organic matter contained in livestock excreta undergoes microbial decomposition to become organic acids, or ammonia nitrogen is converted to nitrite nitrogen and nitrate by the action of ammonia oxidizing bacteria and nitrifying bacteria. There is a possibility of acidification by generating nitrogen. Since CaO contained in steelmaking slag is alkaline, it is expected to keep the mixture of livestock excrement and steelmaking slag in a neutral environment advantageous for the growth of crops by suppressing acidification due to microbial degradation of such livestock excrement. it can.

  In steelmaking slag having a CaO content of less than 20% by mass, the alkaline effect of this CaO is reduced, so that the pH of the mixture of livestock excrement and steelmaking slag is acidified, which may hinder the cultivation of crops. is there. Moreover, in the steelmaking slag whose CaO content exceeds 50% by mass, the alkaline effect of CaO may cause the pH of the mixture of livestock excrement and steelmaking slag to become alkaline with a pH of 9 or higher, which is not suitable for crop cultivation. Therefore, the CaO content of the steelmaking slag used in the present invention is preferably 20% by mass or more and 50% by mass or less.

  Note that the CaO content of the steelmaking slag can be measured, for example, by fluorescent X-ray analysis.

  Next, Si contained in the steelmaking slag will be described.

Si is a representative component together with Ca, among the fertilizer-effect components for farm products derived from steelmaking slag, which are contained in the mixture of livestock excrement and steelmaking slag of the present invention. Si in steel slag is dicalcium silicate (2CaOSiO _2), is believed to be present in chemical forms such as tricalcium silicate (3CaOSiO _2). Usually, to represent the composition of the steelmaking slag, to display all Si as SiO ₂ content.

Steelmaking slag having a SiO ₂ content of less than 10% by mass has a low Si content in the mixture of livestock excrement and steelmaking slag used in the present invention, and therefore there is a possibility that a fertilizer effect on agricultural crops cannot be expected. Moreover, since it hardly occurs in the iron making process, it is not easy to obtain. On the other hand, steelmaking slag whose SiO ₂ content exceeds 30% by mass is hardly generated in the ironmaking process, and thus is not easy to obtain. Therefore, the SiO ₂ content of the steelmaking slag used in the present invention is preferably 10% by mass or more and 30% by mass or less.

The content of SiO ₂ contained in the steelmaking slag, for example, can be measured by X-ray fluorescence analysis.

  Next, Mg contained in the steelmaking slag will be described.

  Steelmaking slag contains Mg as magnesium oxide MgO. MgO is an alkaline causative substance like CaO. Mg is also a fertilizer effect element for crops that are only contained in livestock excreta at low content. When the steelmaking slag has an MgO content of less than 1% by mass, the effect of supplying Mg to crops may be insufficient. Moreover, since the steelmaking slag whose MgO content exceeds 20 mass% hardly occurs in the iron making process, it is difficult to obtain. Therefore, the MgO content is preferably 1% by mass or more and 20% by mass or less.

  Note that the MgO content of the steelmaking slag can be measured, for example, by fluorescent X-ray analysis.

  Next, Mn contained in the steelmaking slag will be described.

  Mn exists mainly as MnO in steelmaking slag. Steelmaking slag having a MnO content of less than 2% by mass or more than 10% by mass hardly occurs in the iron making process, and is difficult to obtain. Therefore, the MnO content is preferably 2% by mass or more and 10% by mass or less.

  Note that the MnO content of the steelmaking slag can be measured, for example, by fluorescent X-ray analysis.

  Next, iron contained in the steelmaking slag will be described.

Steelmaking slag including _iron, Fe ₂ O 3, FeO, as metallic iron. Steelmaking slag having a total iron content of steelmaking slag of less than 10% by mass or exceeding 30% by mass hardly occurs in the ironmaking process and is difficult to obtain. Therefore, it is preferable to use a steelmaking slag having a total iron content of 10% by mass to 30% by mass.

  In addition, the total iron content of steelmaking slag can be measured by, for example, titanium chloride (III) reduction potassium dichromate titration method.

Here, although it is about the particle size of the steelmaking slag used by this invention, it is preferable that the particle size of the steelmaking slag used by this invention is 3 mm or less. When the steelmaking slag particle size exceeds 3 mm, the specific surface area of the steelmaking slag is smaller than when the particle size is 3 mm or less, so fertilizer effect components such as CaO, SiO ₂ and MgO contained in the steelmaking slag. The elution efficiency of becomes low. Moreover, since not only the elution efficiency of a fertilizer effect component but mixing with a livestock excrement is good, since a small particle size is preferable, it is desirable that the particle size of a steelmaking slag particle is 3 mm or less.

  In addition, the particle size of steelmaking slag can be specified by measuring which particle size range the steelmaking slag is in, for example, using sieves having different mesh intervals.

  Moreover, although it is about the form of the steelmaking slag used in the present invention, the steelmaking slag may remain as it is, but the powder obtained by crushing the steelmaking slag has a larger specific surface area and higher elution efficiency. More preferable. The steelmaking slag used in the present invention may be a granulated powdery product.

  Next, a method of mixing steelmaking slag with livestock excrement will be described.

  As a method of mixing the livestock excrement and the steelmaking slag, any method may be used as long as the livestock excrement and the steelmaking slag can be mixed. For example, a method of mixing livestock excrement and steelmaking slag using a manual spreader, a method of mixing livestock excrement and steelmaking slag using a backhoe, a wheel loader, or the like is also possible.

  Next, a method for applying a mixture of livestock excrement and steelmaking slag to farmland excluding topsoil contaminated with radioactive cesium will be described.

  The simplest method is to place a mixture of livestock excrement and steelmaking slag on the surface of the farmland excluding the topsoil contaminated with radioactive cesium. The topsoil contaminated with radioactive cesium is mostly from the surface to a depth of about 10 cm, so apply a mixture of livestock excrement and steelmaking slag of a considerable thickness on the farmland where this topsoil has been removed. Therefore, it is preferable to stack a mixture of livestock excrement and steelmaking slag on the surface of farmland excluding the topsoil contaminated with radioactive cesium with a thickness of 5 cm to 20 cm. And in order to accelerate | stimulate the proliferation of the soil microorganism originally in the farmland, it is preferable to mix the mixture of livestock excrement and steelmaking slag with the farmland soil under it.

  If the thickness of the mixture of livestock excrement and steelmaking slag is less than 5 cm, the application effect of the mixture of livestock excrement and steelmaking slag will reduce the effect of applying silicic acid, lime, magnesium, manganese, iron and organic matter. There is a possibility that the effect of promoting the cultivation will not be seen.

  On the other hand, if the thickness of the mixture of livestock excrement and steelmaking slag exceeds 20 cm, it will be necessary to apply a mixture of livestock excrement and steelmaking slag that is more than necessary for soil improvement to promote the cultivation of agricultural products. Can be disadvantageous both efficiently and efficiently. In order to decontaminate the farmland contaminated with radioactive cesium in a shorter period of time and to enable the cultivation of crops that are free of contamination by radioactive cesium, it is necessary to reduce the amount of animal waste and steelmaking slag more than necessary. It is believed that application of the mixture should be avoided.

  Therefore, it is preferable to stack a mixture of livestock excrement and steelmaking slag on the surface of farmland excluding topsoil contaminated with radioactive cesium with a thickness of 5 cm to 20 cm.

  For example, since the boiling point of cesium is 641 ° C., the topsoil contaminated with radioactive cesium vaporizes cesium when heated, and the topsoil excluding the radioactive cesium can be recovered. In addition, for example, by using a soil washing or a zeolite having a high affinity for cesium, it is possible to recover the topsoil excluding radioactive cesium. In such a case, it is preferable to return the topsoil after removing radioactive cesium to the original farmland. By doing so, there is a possibility that the volume of farmland soil stored in the radioactive waste storage facility can be reduced. For example, it is also preferable to apply the mixture of livestock excrement and steelmaking slag by mixing the topsoil from which radioactive cesium has been removed with a mixture of livestock excrement and steelmaking slag, and then stacking the surface of the farmland with a thickness of 5 cm or more and 20 cm or less. . Due to treatment such as heating and washing to remove radioactive cesium, the topsoil may have lost components, organic matter, and microorganisms that are effective for fertilizer effects in the cultivation of crops. By mixing a mixture of livestock excrement and steelmaking slag and topsoil excluding radioactive cesium, it becomes possible to supply fertilizer effect components, organic matter, and microorganisms necessary for cultivation of crops.

  If the thickness of the mixture of topsoil from which radioactive cesium has been removed and livestock excrement and steelmaking slag is less than 5 cm, the mixture of the topsoil from which radioactive cesium has been removed and the mixture of livestock excrement and steelmaking slag is applied. Since the effect of imparting acid, lime, magnesium, manganese, iron and organic matter is reduced, there is a possibility that a sufficient effect for promoting the cultivation of agricultural products may not be observed.

  On the other hand, if the thickness of the mixture of topsoil from which radioactive cesium has been removed and the mixture of livestock excrement and steelmaking slag exceeds 20 cm, the amount of livestock excrement and steelmaking slag more than necessary for soil improvement to promote the cultivation of crops Would be disadvantageous both economically and efficiently. In order to decontaminate the farmland contaminated with radioactive cesium in a shorter period of time and to enable the cultivation of crops that are free of contamination by radioactive cesium, it is necessary to reduce the amount of animal waste and steelmaking slag more than necessary. It is believed that application of the mixture should be avoided.

  Therefore, it is preferable that the thickness of the mixture of the topsoil from which the radioactive cesium has been removed and the mixture of the livestock excrement and the steelmaking slag is stacked on the surface of the farmland excluding the topsoil contaminated with radioactive cesium by a thickness of 5 cm to 20 cm.

  By applying a mixture of livestock excrement and steelmaking slag to farmland excluding topsoil contaminated with radioactive cesium as described above, silicic acid, lime, magnesium, manganese, iron, and organic matter can be given. it can. Furthermore, the organic substance containing a aggregate structure and microorganisms can be provided.

  As described above, it can be expected that the farmland contaminated with radioactive cesium will be able to grow crops at an early stage.

Hereinafter, the present invention will be described more specifically with reference to examples. However, the technical scope of the present invention is not limited to the following examples.

{Example 1} Compost For three rectangular farmland contaminated with radioactive cesium, farmland A, farmland B, and farmland C (all 5m long x 2m wide rectangular), the radioactivity of the topsoil from the surface to a depth of 10cm The radioactivity resulting from cesium was ¹³⁴ Cs and ¹³⁷ Cs, and was 32500 becquerels / kg soil in farmland A, 34700 becquerels / kg soil in farmland B, and 33600 becquerels / kg soil in farmland C. For farmland A and farmland B, the topsoil was removed from the ground to a depth of about 10 cm using a shovel. Radioactivity caused by radioactive cesium in the soils of farmland A and farmland B after removing the topsoil is the sum of ¹³⁴ Cs and ¹³⁷ Cs, with 76 becquerels / kg soil in farmland A and 85 becquerels / kg soil in farmland B Met.

  In order to apply the mixture of cow dung and steel slag to the farmland A, this cow dung and steel slag mixture was prepared as follows.

  1.5 t of steelmaking slag having a particle size of 3 mm or less whose composition is shown in Table 1 was added to 10 t of cow dung with a moisture content of 80% and mixed using a manuscript spreader. Then, every 10 days, the mixture was turned back and mixed, matured for 60 days, and composted.

  The composition of the composted cow dung and steel slag mixture is shown in Table 2 below. In Table 2 below, the organic carbon content was measured by a dry combustion method as the organic matter content.

  After applying this mixture of beef dung and steelmaking slag so as to overlap the surface of the farmland A after removing the topsoil by about 10 cm, it was cultivated about 20 cm deep and mixed with the soil of the original farmland A at the bottom. .

  On the other hand, the farmland B excluding the topsoil and the farmland C from which the topsoil was not removed were cultivated in the same manner as the farmland A at a depth of about 20 cm from the ground surface without applying a mixture of cow dung and steel slag.

Next, in order to supply nitrogen N, phosphorus P, and potassium K, 100 g / m ^{2 of} chemical fertilizer (8-8-8) was applied to farmland A, farmland B, and farmland C. Komatsuna seeds were sown in each of farmland A, farmland B, and farmland C, cultivated under the same conditions, and the yields were compared. The results obtained are shown in Table 3 below.

  As is apparent from Table 3 above, in the farmland A where the mixture of cow dung and steel slag was applied, the yield of Komatsuna was approximately doubled compared to the farmland B where the mixture of cow dung and steel slag was not applied. . Moreover, in the farmland A which applied the mixture of cow dung and steelmaking slag, the yield increased about 20% compared with the farmland C which did not remove topsoil while being contaminated with radioactive cesium.

Table 4 below shows the results of measuring the radioactivity of radioactive cesium (total value of ¹³⁴ Cs and ¹³⁷ Cs) contained in the harvested Komatsuna.

  As is clear from Table 4 above, in farmland A and farmland B excluding the topsoil contaminated with radioactive cesium, compared to farmland C that did not remove the topsoil contaminated with radioactive cesium, the radioactive cesium produced by Komatsuna Uptake could be suppressed.

  Therefore, it was confirmed that by applying a mixture of cow dung and steelmaking slag to the farmland from which the topsoil was removed, the growth of Komatsuna was promoted and the farmland was suitable for the cultivation of crops.

{Example 2}
Radioactivity caused by radioactive cesium in the topsoil from the ground surface to a depth of 10 cm for three rectangular farmland, farmland A, farmland B, and farmland C (all 5m long x 2m wide rectangular) contaminated with radioactive cesium The total of ¹³⁴ Cs and ¹³⁷ Cs was 21300 becquerels / kg soil in farmland A, 18600 becquerels / kg soil in farmland B, and 20700 becquerels / kg soil in farmland C. For farmland A and farmland B, the topsoil was removed from the ground to a depth of about 10 cm using a shovel. Radioactivity caused by radioactive cesium in the soils of farmland A and farmland B after removing the topsoil is the sum of ¹³⁴ Cs and ¹³⁷ Cs, 56 becquerels / kg soil in farmland A, 48 becquerels / kg soil in farmland B Met.

  In order to apply the mixture of cow dung and steel slag to the farmland A, this cow dung and steel slag mixture was prepared as follows.

  1.5 t of steelmaking slag having a particle size of 3 mm or less whose composition is shown in Table 5 was added to 10 t of cow dung with a moisture content of 60%, and the mixture was mixed using a manual spreader. The composition of the mixture of beef dung and steelmaking slag is shown in Table 6 below. In Table 6 below, the organic carbon content was measured by the dry combustion method as the organic matter content.

  After applying this mixture of beef dung and steelmaking slag so as to overlap the surface of the farmland A after removing the topsoil by about 10 cm, it was cultivated about 20 cm deep and mixed with the soil of the original farmland A at the bottom. .

  On the other hand, the farmland B excluding the topsoil and the farmland C from which the topsoil was not removed were cultivated in the same manner as the farmland A at a depth of about 20 cm from the ground surface without applying a mixture of cow dung and steel slag.

Two weeks later, in order to supply nitrogen N, phosphorus P, and potassium K, 100 g / m ^{2 of} chemical fertilizer (8-8-8) was applied to farmland A, farmland B, and farmland C and applied to each farmland. Komatsuna seeds were sown and cultivated under the same conditions, and the yields were compared. The results obtained are shown in Table 7 below.

  As apparent from Table 7 above, in the farmland A where the mixture of cow dung and steelmaking slag was applied, the yield of Komatsuna was approximately doubled compared to the farmland B where the mixture of cow dung and steelmaking slag was not applied. . Moreover, in the farmland A which applied the mixture of cow dung and steelmaking slag, the yield increased about 10% compared with the farmland C which did not remove topsoil while being contaminated with radioactive cesium.

Table 8 below shows the results of measuring the radioactivity of radioactive cesium (total value of ¹³⁴ Cs and ¹³⁷ Cs) contained in the harvested Komatsuna.

  As is clear from Table 8 above, in farmland A and farmland B excluding the topsoil contaminated with radioactive cesium, compared to farmland C that did not remove the topsoil contaminated with radioactive cesium, the radioactive cesium produced by Komatsuna Uptake could be suppressed.

  Therefore, even if it is not compost made by mixing steelmaking slag with cow dung as shown in Example 1, the mixture of cow dung and steelmaking slag is applied as it is to farmland from which topsoil has been removed, so that the growth of Komatsuna can be improved. It was confirmed that it was promoted and suitable for crop cultivation.

{Example 3} Mixing with topsoil excluding radioactive cesium Three rectangular farmland contaminated with radioactive cesium, farmland A, farmland B, and farmland C (all 5m long by 2m wide) deep from the ground The radioactivity caused by radioactive cesium in the topsoil up to 10 cm in length is the sum of ¹³⁴ Cs and ¹³⁷ Cs. It was soil. For farmland A and farmland B, the topsoil was removed from the ground to a depth of about 10 cm using a shovel. The radioactivity caused by radioactive cesium in the soil of the farmland after removing the topsoil was a total of ¹³⁴ Cs and ¹³⁷ Cs, and was 26 becquerels / kg soil in the farmland A and 22 becquerels / kg soil in the farmland B.

  In order to apply the mixture of cow dung and steel slag to the farmland A, this cow dung and steel slag mixture was prepared as follows.

  1.5 t of steelmaking slag having a particle size of 3 mm or less whose composition is shown in Table 9 was added to 10 t of cow dung with a moisture content of 80% and mixed using a manual spreader.

  Every 10 days, the mixture was turned over and mixed for 60 days to compost.

  The composition of the composted cow dung and steelmaking slag mixture is shown in Table 10 below. In Table 10 below, the organic carbon content was measured by the dry combustion method as the organic matter content.

  On the other hand, the topsoil contaminated with the radioactive cesium removed from the farmland A was heated for 30 minutes while stirring with a kiln at 1100 ° C. to vaporize and remove the radioactive cesium, and then returned to room temperature. When radioactive cesium contained in the topsoil was measured, it was reduced to 55 becquerel / kg soil. Moreover, the organic carbon was 0% and no organic matter was contained.

  Agricultural land A excluding topsoil was divided into two equal parts, which were defined as agricultural land AI and agricultural land AII (both 2.5 m long and 2 m wide rectangle).

  For the farmland AI, a mixture obtained by mixing 1 t of the topsoil from which the radioactive cesium was removed by heating and 0.5 t of the mixture of the composted beef dung and steel slag was applied to the surface of the farmland AI so as to have a thickness of about 15 cm. .

  Only the topsoil from which this radioactive cesium was removed by heating was applied to the farmland AII so as to overlap the surface of the farmland AII by about 15 cm.

  On the other hand, for the farmland B excluding the topsoil and the farmland C from which the topsoil was not removed, the mixture of the topsoil with the radioactive cesium removed by heating and composted cow dung and steelmaking slag, or the radioactive cesium by heating. The topsoil was removed and plowed about 15 cm deep from the surface.

Subsequently, in order to supply nitrogen N, phosphorus P, and potassium K, 100 g / m ^{2 of} chemical fertilizer (8-8-8) was applied to farmland AI, farmland AII, farmland B, and farmland C.

  Komatsuna seeds were sown in each of farmland AI, farmland AII, farmland B, and farmland C, cultivated under the same conditions, and yields were compared. The results are shown in Table 11.

  As is apparent from Table 11 above, in the farmland AI where the mixture of topsoil from which radioactive cesium has been removed by heating and composted cow dung and steelmaking slag has been applied, the topsoil from which radioactive cesium has been removed by heating and composted cow dung and The yield of Komatsuna was approximately doubled compared to Farmland B where the steelmaking slag mixture was not applied. Furthermore, in the farmland AI applied with a mixture of topsoil from which radioactive cesium has been removed by heating and composted cow dung and steelmaking slag, the yield is about 15% that of farmland C in which the topsoil has not been removed while being contaminated with radioactive cesium. It was confirmed that it increased.

  On the other hand, in the farmland AII where only the topsoil from which radioactive cesium was removed by heating was applied, the yield of Komatsuna was significantly reduced compared to the farmland B and farmland C, probably because of the effects of the removal of organic substances and the death of microorganisms. did.

Table 12 below shows the results of measuring the radioactivity of radioactive cesium (total value of ¹³⁴ Cs and ¹³⁷ Cs) contained in the harvested Komatsuna.

  As is clear from Table 12 above, in the farmland AI, farmland AII, and farmland B excluding the topsoil contaminated with radioactive cesium, compared to the farmland C that did not remove the topsoil contaminated with radioactive cesium, Incorporation of radioactive cesium could be suppressed.

  Therefore, it was confirmed that the growth of Komatsuna was promoted by applying a mixture of the topsoil from which radioactive cesium had been removed by heating to the farmland from which topsoil had been removed, and composted cow dung and steelmaking slag, which was suitable for the cultivation of crops. . Moreover, it has confirmed that the cesium absorption to a plant was also suppressed.

As mentioned above, although preferred embodiment of this invention was described in detail, this invention is not limited to this example. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

Claims (10)

To farmland excluding topsoil containing radioactive cesium, by applying the topsoil was removed by heating the radioactive cesium, and a mixture of manure and steel slag, and silicate on the farmland, lime, magnesium, manganese, iron The soil improvement method characterized by providing organic substance. The soil improvement method according to claim 1, wherein a mass ratio of the steelmaking slag to the livestock waste of the mixture of the livestock waste and the steelmaking slag is 10% or more and 30% or less. 3. The soil improvement method according to claim 1, wherein a moisture content of the mixture of the livestock excrement and the steelmaking slag is 30% or more and 50% or less. The soil improvement method according to any one of claims 1 to 3, wherein the mixture of the livestock excrement and the steel slag is compost produced by mixing the steel slag with the livestock excrement. The composition of the steel slag is mass%,
CaO: 20% to 50%,
SiO ₂ : 10% to 30%,
MgO: 1% or more and 20% or less,
MnO: 2% or more and 10% or less,
Total iron: 10% or more and 30% or less, The soil improvement method according to any one of claims 1 to 4 characterized by things. The soil improvement method according to any one of claims 1 to 5, wherein a particle diameter of the steelmaking slag is 3 mm or less. The soil improvement method according to any one of claims 1 to 6, wherein the livestock excrement is at least one of cow dung, chicken dung, and pork dung not contaminated with radioactive cesium. How to use before Ki施 is,
And topsoil the radioactive cesium was removed by heating, a mixture of manure and steel slag, and wherein the topsoil is thick 5cm method overlaying least 20cm below the surface of the land except a claim The soil improvement method as described in any one of 1-7. The soil improvement method according to any one of claims 1 to 8, wherein the topsoil from which the radioactive cesium has been removed by heating is a topsoil obtained by heating the topsoil containing the radioactive cesium removed from the farmland. The soil improvement method according to claim 9, wherein the topsoil from which the radioactive cesium has been removed by heating is a topsoil obtained by heating the topsoil containing the radioactive cesium removed from the farmland to a temperature equal to or higher than the boiling point of cesium.