Agriculture and Science 2022/10

Ecological risk and emissions of microplastics from coated fertilizers

National Institute of Agro-Environmental Sciences
　Senior Research Fellow Takashi Nagai

Introduction

　Microplastics are defined as plastics (including synthetic fibers and rubbers) of 5 mm or less in diameter, and are broadly classified into primary microplastics (manufactured as particles of 5 mm or less from the beginning) and secondary microplastics (crushed and fragmented in the environment after manufacture). The presence of microplastics in the world's oceans has been confirmed, and they have been detected in the digestive organs of various organisms such as whales, sea turtles, seabirds, and fish that inhabit the oceans. For this reason, the effects of microplastics on human health and ecosystems are currently the focus of much attention1).

　Starting with the regulation of microplastic beads such as facial cleansing scrubs in cosmetics in the United States in 2015, other countries have begun to regulate microplastic beads. The main reason for this is that they cannot be degraded in the environment and are difficult to recover, not because they have been proven to have adverse effects in the actual environment2). In Japan, efforts have also been made, such as the introduction of a charge for plastic bags in July 2020.

　Coated fertilizers used in agricultural applications contain fertilizer components in capsules of a few millimeters in diameter, and the fertilizer components gradually dissolve out of the capsule. They are effective over a long period of time, and are said to be effective in saving labor for fertilizer application, reducing the amount of fertilizer applied, and preventing runoff of fertilizer components into the water system. However, the small size of the capsules makes it difficult to recover the capsules as primary microplastics, and many have been found to have leaked into the water system3).

　Therefore, the purpose of this article is to summarize the problem of runoff of plastic capsules of coated fertilizers into water systems in terms of ecological risk and emissions.

2. ecological risk from microplastics

　Ecological risks from microplastics can be divided into three types
(1) Hazardousness of plastic particles themselves
(2) Toxicity due to various chemicals added to plastics
(iii) Persistent in the environment adsorbed on plastic particles

　(2018) comprehensively reviewed reports on toxicity assessments and environmental concentrations up to 2018, and reported that current microplastics are not at concentration levels that would have an impact on aquatic ecosystems4). In this paper, the predicted no-effect concentrations for each particle size were estimated for each ecosystem using a method called species sensitivity distribution (a probability distribution of the relationship between concentration and the proportion of species affected)5) using no-effect concentrations for many aquatic organisms collected from the literature. The actual concentration distribution of microplastics in the environment is several orders of magnitude lower than the predicted no-effect concentration, indicating that the ecological risk is currently at a level of concern.
No, it was rated as no.

　Plastic products contain various additives such as plasticizers, UV absorbers, antioxidants, release agents, and flame retardants. Plastic itself is not absorbed into the body through the digestive tract and is mostly excreted outside the body, but the chemical substances added to or absorbed by the plastic are absorbed into the body. When fish and other aquatic organisms were exposed to microplastics containing such chemicals, effects such as liver dysfunction and the development of tumors were observed. However, these effects were observed at concentrations that were an order of magnitude higher than actual environmental concentrations1). Furthermore, the percentage of hydrophobic organic chemicals that adsorb onto microplastics in the ocean is extremely low and is unlikely to pose any real ecological risk concern at this time6).

　The European Commission's Consortium for Scientific Advice for Policy also reported that the ecological risk is not currently at a level of concern7) . However, it also stated that if microplastic emissions into the environment continue in the future, the ecological risk of microplastics may become apparent over a wide area within 100 years.

　From the above, it can be summarized that the ecological risk of microplastics is currently below the level of concern, but that they should not be continuously discharged any more. However, while it is true that "harmful effects were observed when organisms were exposed to microplastics (at concentrations much higher than the actual environmental concentration)" and "microplastics were detected in the environment or in the bodies of organisms (but at concentrations much lower than the no-effect concentration)," the image of microplastics would change greatly if this information were spread in a form that omits the parentheses. However, if this information is spread in a form that omits the parentheses, the image will change significantly.

　In addition, the following points have been pointed out as remaining issues for ecological risk assessment of microplastics6) .
Size, shape (sphere, fiber, fragment), polymer type (polystyrene, polyethylene)
(e.g., len, etc.), and the effect on toxicity due to age-related deterioration.
Should the unit of concentration be weight or number of particles?
No. of uptake into the body
Comparison with natural particulates

3. sources and emissions of microplastics

　Although plastic bottles, plastic bags, coated fertilizer capsules, and artificial turf tend to attract attention as sources of microplastics, the overall picture of the sources is not well known. A report by the Fraunhofer Institute in Germany lists the top 30 sources (Table 1 shows the top 12). The overall emission amount is about 2,500 g/year/person. Of these, the largest amount is secondary microplastics generated by abrasion and other processes, while primary microplastics are a minor source.

　Furthermore, among secondary microplastics, wear on tires, asphalt, shoes, and artificial turf is very common. Also in 12th place is the category "Wear of agricultural plastics," which includes all agricultural applications.
In Europe, although coated fertilizers are used, the amount of runoff into the water system is considered to be much lower than in Japan because of the small number of paddy fields. Although coated fertilizers are also used in Europe, the discharge into the water system is considered to be much lower than in Japan because there are fewer paddy fields in Europe. Therefore, it is assumed that this category of emissions is caused by the wear of large materials such as plastic greenhouses and mulch.

　Next, plastic emissions from agriculture are summarized. Plastic emissions from the agricultural sector include covering materials for agricultural greenhouses and tunnels, mulch, and pots for seedlings and flowers, as well as capsules for coated fertilizers. According to data from the Ministry of Agriculture, Forestry and Fisheries9) , a total of 106,501 tons of plastic was discharged on a 2018 basis. Not all of these emissions go out into the environment; most are disposed of as waste. Of the recycled, landfilled, and incinerated waste, more than 70% is recycled.

　Looking at the emissions of agriculture-derived plastics by material, vinyl chloride used for plastic greenhouses and polyolefins (e.g., polyethylene) used for tunnels, mulch, and solid coverings account for the majority. The amount of covered fertilizers, along with seedling trays and pots, is classified as "other plastics," and accounts for 171 TP3T (17,928 tons) of the total. The overall amount of emissions has been on a decreasing trend.

　Since there is no information on the amount of coated fertilizers in the breakdown of "other plastics," a simple estimation is attempted here. First, dividing the 17,928 tons of "other plastics" by the Japanese population, we arrive at 140 g/person/year. If we divide this amount roughly into three equal parts (seedling trays, pots, and fertilizer capsules), we arrive at a figure of 47 g/person/year. Furthermore, assuming that 10% of the fertilizer capsules used would runoff into the water system, the amount would be about 5g/year/person. Another study9) by the Ministry of Agriculture, Forestry and Fisheries (MAFF) indicates that 2-91 TP3T of the fertilizer-derived capsules applied were discharged out of the system, and that most of them were discharged after the replacement of fertilizer. Therefore, the runoff rate of 101 TP3T to the environment is a slightly larger estimate.

　In addition, estimates from measured surveys of microplastics can be referenced. PIRICA has been continuously conducting large-scale surveys of microplastics, and the data are publicly available11) . Dividing this figure by the population, it is calculated to be 0.2 g/person/year. The total of 157 tons is a rather small figure, but it is thought that particles too small to be counted, such as tire-wear dust, are not included.

　From the above, it is estimated that the actual emissions are between 0.2 and 5 g/person/year. Assuming that the total emission of microplastics in Germany is 2,500 g/person/year and the same in Japan, the emission from coated fertilizers is estimated to be less than 11 TP3T of the total. Even if the emissions are limited to agricultural plastics (Table 1), the emissions from other sources than coated fertilizers are higher.

4. the nature of the problem with coated fertilizer capsules is not so much a risk issue as it is a garbage issue

　Considering that the current ecological risk is below the level of concern and that coated fertilizers are a minor source of microplastic emissions, as we have summarized, discontinuing the use of coated fertilizers as a microplastic risk reduction measure would be very inefficient. If the use of coated fertilizer is discontinued and repeated fertilizer application is considered, it is necessary to consider that fertilizer efficiency will be reduced and the amount of fertilizer dropped will increase, and that repeated field trips for fertilizer application will increase other risks due to vehicle use (tire wear is a top source of microplastic emissions). . Increased fertilizer drops can also cause other environmental problems, such as eutrophication of water systems and greenhouse gas emissions from denitrification. Thus, discontinuing the use of plastics alone will not solve the problem.

　So, can we continue to use coated fertilizers without any problems? This question must be considered separately from the issue of risk. Just as it is very unpleasant to see a lot of plastic trash washed up on the beach, capsules derived from coated fertilizers found in large numbers in water systems have an intuitively negative image (they are identified as bad). Then comes the perception that if something is bad, it must have high risk and low benefit. When information such as the negative effects of microplastics comes in, it reinforces their intuitive negative image and they strongly recognize that their intuition was not wrong. In other words, we should not consider that we have a negative image because of the risk, but rather that our intuitive negative image, which has existed from the beginning, is amplified by the risk information.

　Therefore, simply providing information that the current ecological risk is below the level of concern may not be very effective in dispelling the negative image. Thus, the thought process of first making judgments based on feelings, such as whether a subject is good or bad (like or dislike), and then secondly judging the risks and benefits of the subject, is called the (emotional) heuristic12) . Such feelings and values of citizens should never be ignored.

　Therefore, the users should take full responsibility for their use, for example, by thorough water management to prevent runoff outside the field system, and by making efforts to collect as much as possible at the drainage outlets. In other words, it is necessary to consider this as a plastic waste problem rather than a risk problem. Measures to prevent runoff through water management can prevent not only plastic but also pesticides and fertilizers from leaking out of the system, thus reducing the overall environmental burden. Although the amount of runoff after paddy field plowing is high, it has been reported that collection at the drainage outlet is effective9) .

　In 2022, JA Zen-Noh and industry associations released a "Policy for Efforts to Prevent Marine Discharge of Plastic Coated Shells of Slow-release Fertilizers". The policy outlines the following three initiatives to be achieved by 2030:
(1) Publicize the presence of plastic in coated fertilizers
(2) Implementation of measures to control runoff of plastic-coated shells from agricultural land
(iii) Realization of agriculture that does not rely on plastic coating through the development and diffusion of new technologies

　In addition to the above efforts, risk communication will be required to build mutual understanding and trust through information sharing, dialogue, and exchange of opinions among the parties involved. This is not a one-way provision of information, but interactive communication is important, and care must be taken to avoid the perception that it is a technique for persuasion12).

References

(1) Science Council of Japan. Recommendation "Necessity of Research on Ecological and Health Effects of Water Pollution by Microplastics.
　Governance of Sex and Plastics" (2020)
(2) Environment and Energy Unit, Center for Research and Development Strategy, Japan Science and Technology Agency.
　Overhead Workshop Report "Environmental Risk Assessment Research as a Foundation for Social and Industrial Competitiveness
　Research" (2020)
3) Ikegai, T., Mishima, S., Kikuchi, H., Namba, A., and Kobayashi, K. (2004). Microplastics in the Coastal Zone of Sagami Bay, Japan.
　Ku Drifting Characteristics. Kanagawa Environmental Science Center Research Report. 41, p. 1-10 (2018).
4) Burns EE, Boxall ABA. Microplastics in the aquatic environment: Evidence for or against
Adverse impacts and major knowledge gaps. Environmental Toxicology and Chemistry.
　37, p. 2776-2796 (2018)
5) National Institute of Agro-Environmental Sciences. Technical Manual] Species for Ecological Risk Assessment of Pesticides.
　Susceptibility distribution analysis of Ver. 1.0 (2016)
(6) Yuichi Iwasaki, Hiroyuki Mano, Bin-Le Lin, and Wataru Naito. Particle Effects of Microplastics on Aquatic Organisms.
　Current Status and Issues of Toxicity Assessment with an Eye on the Environmental Toxicology. Journal of Environmental Toxicology. 24, p.53-61 (2021)
7) Science Advice for Policy by European Academies. A scientific perspective on
　microplastics in nature and society (2019)
(8) Fraunhofer Institute for Environmental, Safety and Energy Technology UMSICHT.
Kunststoffe in der umwelt: mikro- und makroplastik (2018)
(9) Horticultural Crops Division, Agricultural Produce Bureau, Ministry of Agriculture, Forestry and Fisheries. Situation concerning plastics discharged from the agricultural sector (2022).
(10) Ministry of Agriculture, Forestry and Fisheries. Survey on plastic-coated fertilizers in FY2020 (2021).
(11) PIRICA. Microplastic Runoff Status Database.
(12) Kinoshita, Tomio. Philosophy and Technology of Risk Communication. Nakanishiya Publishing (2016)

In "Ra-mugi" wheat for Chinese noodles
　Labor-saving fertilization method that can ensure high seedling protein content

Fukuoka Prefecture Iizuka Agriculture and Forestry Office
Iizuka Extension Guidance Center
Tomomichi Ishimaru

Introduction

　The area of Chinese wheat "Ra-mugi" (variety name: Chikushi W2) bred in Fukuoka Prefecture for Chinese noodles is 1,890 ha in the 2020 sowing, accounting for 121 TP3T of the wheat crop area in Fukuoka Prefecture. In order to maintain good suitability for ramen noodle making, the customers demand a seedling protein content of 12% or higher for the planting of "Ra-mugi" (Furusho et al. 2013). In order to secure a seedling protein content of 121 TP3T or higher, Fukuoka Prefecture has adopted a three-fertilizer system, consisting of a bimetallic fertilizer, an ear fertilizer, and an additional fertilizer at the time of ear-justification.

　However, since fertilizer application during the ear-justification period is a heavy workload for growers, a labor-saving system was desired (Tanaka 2013). Therefore, we investigated a one-time fertilizer application system in which a combination of a fast-acting fertilizer and a controlled-release fertilizer is applied at the same time of the full-season fertilizer application, thereby eliminating both the ear fertilizer application and the full-season fertilizer application. The controlled-release fertilizers were a 20-day type, which has the shortest leaching period for early nitrogen leaching, and a sigmoid type, which suppresses nitrogen leaching until the stem-planting stage and leaches nitrogen from around the stem-planting stage to the ear-planting stage. S20) was selected. Since nitrogen leaching of coated fertilizers depends on temperature, the leaching pattern may vary from year to year, so the hydrolysis type Kumiai Good IB Granules 33 (J-Cam Agri Co., Ltd., hereafter IB) was also considered. Here, a brief outline of the study is presented.

2. Methods

1. Nitrogen leaching by period for S20

　To estimate the nitrogen leaching rate of S20 over a period of three years from 2012 to 2014 (sowing years), a burial test was conducted in a paddy field (clay loam soil, post cropped with rice) at the Buzen Branch of the Fukuoka Agricultural Experiment Station (Yukuhashi City, Fukuoka Prefecture, Japan). The S20 was placed on the ground surface at the time of application of manure, and then covered with soil to replicate local practices, and collected approximately every 15 days. The amount of residual nitrogen in the collected S20 was determined by the absorbance spectrophotometric method of the PDAB chromogenic method. The nitrogen leaching rate was calculated from each residual nitrogen amount and converted to the nitrogen leaching amount when the fertilizer nitrogen amount was 8 kg/10a. The amount of nitrogen leached was then subtracted from the amount of nitrogen leached during the previous survey to obtain the amount of nitrogen leached during the period
The nitrogen leaching rate was calculated for each interval.

2. growth and yield of "Ra wheat" by labor-saving fertilization

　The seeding method was four-row sowing with a foot width of 150 cm, and the target number of germinated plants was 150 plants/m2. The target number of germinated plants was set at 150 plants/m2. The trial was conducted in three replications of 8.3 m2 per plot, sown on November 21-22. The composition of the test plots is shown in Table 1. The base fertilizer was a fast-acting chemical fertilizer with nitrogen, phosphate, and potash components of 5, 5, and 5 kg/10a, respectively, for all plots. Labor-saving fertilizer was applied at the time of fertilizer application (in late January) at 3,0,3 kg/10a of fast-acting fertilizer and 9,0,0 kg/10a of S20, or at 3,0,3 kg/10a of fast-acting fertilizer, 8,0,0 kg/10a of S20, and 1,0,0 kg/10a of IB (33-0-0). 0-0) and 1,0,0 kg/10a of compound fertilizer were applied.

　The amount of nitrogen in the fertilizer blends was increased by 2 kg/10a to a total of 7 kg/10a of nitrogen fertilizer, which was the combined amount of the divided application of ear fertilizer and the full-rotation fertilizer, and the amount of fast-acting fertilizer in the divided application was reduced by 1 kg/10a. In the divided application area, fast-acting fertilizers were applied at 4,0,4 kg/10a as additional fertilizer, 2,0,2 kg/10a as ear fertilizer (applied in early March at the stem-rotation stage), and 5,0,0 kg/10a of ammonium sulfate as additional fertilizer at the ear-rotation stage, based on Fukuoka Prefecture's fertilization standards.

3. results

1. Nitrogen leaching by period for S20

　Figure 1 shows the nitrogen leaching rate of S20 buried in late January (at the time of fertilizer application). After 45 days after burial, the total nitrogen leaching rate of S20 was 0.92-1.51 kg/10a from 45 to 60 days after burial (internode elongation stage to leaf stop extraction stage), 2.09-2.17 kg/10a from 60 to 75 days after burial (leaf stop extraction stage to flowering stage), and 0.4 kg/10a from 75 to 90 days after burial (flowering stage to ear emergence stage) for the 2012 and 2013 seedings, and 0.92-1.51 kg/10a from 75 to 75 days after burial for the 2013 seeding. Nitrogen leaching increased after the internode elongation stage, ranging from 1.90 to 1.93 kg/10a from 75 to 90 days after burial (around the flowering stage to 17 to 21 days after ear emergence).

　In 2014, the amount of nitrogen leaching increased after the leaf stop extraction stage.

2. growth, yield, and quality of "rah-rah barley" by labor-saving fertilization

　Growth, yield, and quality by fertilizer application method are shown in Table 2. Compared to the partial application, the number of stems and ears tended to be lower in the fast-acting fertilizer and S20 blends, especially in the 2014 seeding, and the ear emergence and maturity stages were almost on the same day. Stem and ear numbers were similar for the fast-acting fertilizer and S20 and IB blends, with the same ear emergence date and maturity date delayed by about 1 day. There was no difference in the degree of downfall between the test sites. The yields of the two fertilizer-saving treatments were similar in 2012 and 2014 sowing and higher in 2013 sowing, and there was no difference in quality. Seedling protein content was above 121 TP3T in the labor-saving fertilizer treatments in all three years tested, including the 2014 sowing, when the protein content was below 121 TP3T in the partial fertilizer treatment (Figure 2).

Consideration

　A labor-saving fertilizer application system for Chinese noodle wheat "Ra-mugi" was studied, in which a combination of a fast-acting fertilizer and a controlled-release fertilizer is applied during the off-planting period, and ear fertilizer and fertilizer application at the ear-planting period are omitted.

　First, we investigated the nitrogen leaching rate of S20 fertilizer by time period. The nitrogen leaching rate of S20 varied from 0.37 to 1.51 kg/10a and from 1.39 to 2.17 kg/10a (Fig. 1) for the period from 45 to 60 days after burial (during the internode elongation period to leaf stop extraction) and from 60 to 75 days after burial (during the leaf stop extraction period to flowering period), respectively, and the leaching rate for the period from 1.39 to 2.17 kg/10a (Fig. 1) for each of the three years. The amount of nitrogen leached from the leaf-extraction stage to the flowering stage was lower in the 2014 seeding than in the other two years.

　Since nitrogen leaching of S20 is temperature-dependent, the average temperatures after mid-March, when differences in leaching occurred, were 1.2-1.4°C higher than normal for the 2012 sowing, 1.2-2.2°C higher for the 2013 sowing, and 0.4-1.7°C higher for the 2014 sowing in mid- and late March, respectively, and 2.2°C higher for the 2012 sowing and 0.4°C lower for the 2013 and 2014 sowing in early April. In early April, the 2012 seeding was 2.2°C higher and the 2013 and 2014 seedings were 0.4°C lower than the 2012 seeding (Yukibashi AMeDAS). Therefore, factors other than the average temperature may have contributed to the delayed nitrogen leaching in the 2014 seeding.

　Kobayashi et al. (1997) reported that a certain amount of water penetration into the coating membrane is necessary for nitrogen leaching of coated fertilizer to start. The delay in nitrogen leaching in the 2014 seeding may be due to low precipitation in February, which resulted in insufficient water penetration into the coating and delayed leaching.

　According to Fukuoka Prefecture's fertilizer standard, the timing of ear fertilizer application in a divided application is the stalk-planting period, and the amount of nitrogen applied is 2 kg/10 a. The cumulative nitrogen leaching of S20 reaches 2 kg/10 a, which is equivalent to the amount of nitrogen in the divided application of ear fertilizer, from the leaf-extraction period to the blooming period, which is later than the stalk-planting period. Therefore, it was necessary to clarify the effects of nitrogen fertilization around the leaf-extraction stage on nitrogen content, yield, and quality of wheat in order to examine the effects of S20 as an ear fertilizer. Although data are omitted due to space limitation, when the ear fertilizer was applied at the stem-rotation stage or at the leaf-extraction stage, the nitrogen utilization rate was about 701 TP3T at both stages, and no significant differences were observed in the number of ears, seedling weight, and protein content of the seedlings.

　Ishimaru et al. (2016) reported that when ear fertilizer was applied at the stem-standing stage, fertilizer nitrogen utilization was as high as about 701 TP3T, similar to that of fertilizer applied at the ear-justification stage. Therefore, it was considered that the nitrogen absorption capacity of wheat was as high when the ear fertilizer was applied at the stop-leaf extraction stage as it was at the stem-standing and ear-planting stages, and no difference was observed. Therefore, S20, which is applied during the tillering stage and nitrogen is leached from around the leaf extraction stage, seems to be as effective as a fast-acting nitrogen fertilizer for ear fertilization during the stem-rotation stage.

　Next, to examine the type and amount of fertilizer with regulated fertilizer efficacy that should be added in the labor-saving fertilization method, two types of fertilizers were applied: a combination of 3 kg/10a of fast-acting nitrogen fertilizer and 9 kg/10a of S20 or a combination of 3 kg/10a of fast-acting nitrogen fertilizer, 8 kg/10a of S20, and 1 kg/10a of IB, and the effects on growth, yield, and fruit and protein The effects on growth, yield, and seedling protein content were compared with those of conventional fertilizer application (Table 2, Figure 1). Generally, the nitrogen leaching rate of controlled-release fertilizers is 80-901 TP3T of the fertilizer applied. The amount of nitrogen fertilizer was increased by 2 kg/10a to 7 kg/10a.

　The results showed that the number of stems and ears of fast-acting fertilizer and S20 tended to be lower than those of the fractional application, suggesting that S20 does not leach nitrogen until the stem-planting stage after application, resulting in insufficient nitrogen supply. On the other hand, there was no difference in the number of stems and ears among the fast-acting fertilizer, S20, and IB (Fujiwara et al. 1998), because IB is a fertilizer that changes to urea through hydrolysis (Fujiwara et al. 1998), and rainfall after application causes hydrolysis of the nitrogen from IB and provides a continuous nitrogen supply. In all three years tested, rainfall occurred immediately after fertilizer application, and this may have initiated the supply of nitrogen from IB, compensating for the reduced nitrogen from the fast-acting fertilizer and ensuring the same number of stems and ears as with a partial fertilizer application.

　Therefore, fast-acting fertilizers and S20 and IB blends are preferable to ensure a stable nitrogen supply, stem number, and ear number. The thousand-grain weight, volume weight, yield, and test grade did not differ from the conventional application of any of the compound fertilizers (Table 2). Seedling protein content was above 121 TP3T in all three years tested (Figure 2).

　The above results indicate that when Chinese noodle wheat "Ra-Mugi" was sown at the right time and fertilized with a combination of 3 kg/10 a of fast-acting nitrogen fertilizer, 8 kg/10 a of S20, and 1 kg/10 a of IB during the seedling stage, the growth, yield, and seedling protein content were equivalent to those of conventional fertilizer application, and that labor-saving fertilizer application was possible without using ear fertilizer or fertilizer at the ear-planting stage. Labor-saving fertilizer application was possible by omitting the application of ear fertilizer and early-season fertilizer.

References

Shunrokuro Fujiwara, Tetsuro Anzai, Yoshio Ogawa, Tetsuro Kato, eds.
1998. Soil and Fertilizer Encyclopedia. Noubunkyo. Tokyo. 216-217.
Furusho, M., Baba, T., Miyazaki, M., Ishimaru, T., Ohno, R., Takada, E., and Hamachi, Y. 2013. Japan's first
　Development of a Ramen Wheat Breed "Chikushi W2" and Establishment of High-Quality Production Technology. Nissaku Ki 81 (Supplement No.1):
　518-521.
Tomomichi Ishimaru, Masato Araki, Takuya Araki, and Tomizo Yamamoto 2016.
　Utilization rate of fertilizer nitrogen and soil in seedling protein content of Chikushi W2, a wheat variety for Chinese noodles.
　Contribution of Force-Nitrogen. Nissaku Ki 85: 385-390.
KOBAYASHI, Arata; FUJISAWA, Eiji; HANYU, Tomoharu 1997. leaching of coated fertilizer and behavior of water content inside and outside the coated film. Dohi Journal 68:
　14-22.
Tanaka, Kohei 2013. "Technical Development Required by the Field - Hardness
　From the Efforts to Popularize the Wheat "Chikushi W2" (Ra Wheat) -. Nissaku Kyu Shiho 79: 65-68.

No Soil - No. 15
　　Wheat growth in a field where only chemical fertilizers are used
　　-Compared to a compost-only field...

Hokkaido Branch Office, JCM Agri Co.
　Teruo Matsunaka Technical Advisor

　The first chemical fertilizer to be marketed commercially in the world was Rhodes in England, on July 1, 1843.
Until then, the source of nutrients for crops was exclusively compost. The German Thea pointed out that plant nutrients were found in the soil
This is because it was a time when the prevailing belief was that it was some organic material (humus = humus).

1. an era in which plant nutrients are changing from organic to inorganic

　In 1828, Sprengel of Germany was the first to question this common theory and point out that plant nutrients are not organic but inorganic (minerals). It was Liebig, also of Germany, who further supported his point of view and popularized the theory in 1840. It was during this period that Rose marketed an inorganic chemical fertilizer (a patented fertilizer composed of lime superphosphate, ammonium phosphate, and potassium silicate) as a nutrient for crops.

　Rose attempted several trials in his hometown of Rothamsted, Harpenden, to verify the efficacy of the chemical fertilizers he intended to sell. He conducted pot trials in 1837-39 and small field trials in 1840-41. From these trials, he recognized the importance of phosphorus as a nutrient for cabbage, since the highest yields were obtained when cabbage was treated with ammonium phosphate, which contained phosphorus as well as nitrogen.

2. overview of broadbore wheat field trials

　Rose brought in Gilbert, who had studied chemistry at Liebig's, as a scientific collaborator and began comparing the nutrient effects of chemical fertilizers and compost. It was in the fall of 1843, the very same year that chemical fertilizers were introduced to the world, that he sowed wheat (fall-sown wheat) as a crop for testing. This is the Broadbark wheat test plot introduced this month. The year 1843 was the founding year of the Rothamsted Agricultural Experiment Station.

　This field trial has continued uninterruptedly since then until now, 179 years later. In addition to the no-fertilizer treatment, the chemical fertilizer-treated area was given a certain amount of phosphorus, potassium, magnesium, and other nutrients in addition to nitrogen at four levels: 0, 48, 96, and 144 kg/ha of nitrogen. Currently, in addition to these four levels, trials are continuing at seven levels, including treatments of 192, 240, and 288 kg/ha. Of course, since the trials were started in the same year that chemical fertilizers were introduced to the market, there is no field on earth that has been grown with chemical fertilizers alone for a longer period of time than the Broadbork field.

　In 1968, a high-yielding wheat variety (with shorter culms and less susceptibility to collapse under high-fertilizer conditions) was selected for testing.
In 1968, the crop was switched to a new variety of the same name (a variety with improved light-receiving posture by making the leaves erect). In 1968, the same year, in addition to the conventional row-crop treatment, a five-year crop rotation was added, and 35 t/ha of compost and 96 kg/ha of nitrogen (increased to 144 kg/ha in 2005) were added to the compost.

3. results of broadbark wheat field trials

　1) Yield equivalent to composted area with appropriate amount of chemical fertilizer

　Figure 1 shows the results of this trial. The yield of wheat seedlings in the chemical fertilizer (N144 kg/ha) area of the continuous wheat test was not much different from that in the compost area. It was confirmed that the production of wheat seedlings with chemical fertilizer alone was almost equal to that with 35 t/ha of compost, if the amount of fertilizer applied was appropriate.

　Interestingly, after 60 years of continuous cropping, in 1902, both treatments showed continuous crop failure and yield decreased. When the fallow treatment was introduced (one-year fallow followed by four-year row cropping), yields recovered again. This indicates that the continuous cropping failure of wheat occurs not only in the chemical fertilizer area but also in the compost area, and that the fallow treatment is more effective for recovery than the nutrient treatments such as compost or chemical fertilizer.

(2) Dramatic increase in yields with the introduction of high-yielding varieties

　Since 1968, when high-yielding varieties were introduced, the yield of row crops of wheat has nearly doubled, despite no change in compost or chemical fertilizer application treatments. This confirms the high seed production capacity of high-yielding varieties.

　Furthermore, in the five-year crop rotation established after 1968, when the nitrogen content of chemical fertilizers was added to the compost to increase the total nitrogen application, the yield was nearly 10 t/ha. This is not only about three times the yield of the composted area in the old variety era until 1967, but also about twice the average yield in Japan. The effect of the addition of chemical fertilizer nutrients to the compost is clear, and the high-yielding variety's response to fertilizer nutrients is understandable.

3) Soil organisms in fields where only chemical fertilizers are used.

　Some people worry that continued use of chemical fertilizers will kill off the organisms in the soil and "kill the soil. If the continued use of chemical fertilizers were causing the extinction of soil organisms, it would, of course, affect the yield and growth of the wheat crop in this trial. However, such a phenomenon has not been observed at all, even in this Broadbark wheat test plot, which is the longest in the world where only chemical fertilizers have been used (Figure 1). Soil in the chemical fertilizer and composted manure plots
According to the results of the biological counts, there is no evidence that the continuous application of chemical fertilizers alone has resulted in the loss of soil organisms (Table 1).

　Russell, who was the head of the Rothamsted Farm Experiment Station for many years, clearly pointed out that "there is some concern that chemical fertilizers are harmful to earthworms and should not be used. However, Russell clearly pointed out that "there is no indication that this is the case in the Broadbark wheat test plots after more than 100 years of continuous application of chemical fertilizers in amounts greater than customary" (Russell, 1957).
　These test results indicate that, as long as chemical fertilizers are used appropriately, there is no need to worry about their negative effects on crops.