Agriculture and Science 8/9/2023

High-density seeding in paddy rice and
　Labor-saving technology combined with whole seedling box fertilization

Kumamoto Prefectural Agricultural Research Center, Production Environment Research Institute
Soil Environment Laboratory
　　 Kazunari Tanaka

Introduction

　Rice cultivation in Kumamoto Prefecture is no exception to the recent severe situation, with stagnant rice prices and a growing shortage of rice farmers. One of the agricultural policies to solve these problems is the development and practical application of technology that contributes to the consolidation of farmland through the expansion of management scale and the accompanying reduction of production costs and labor hours, which is expected to lead to improved rice farming management.

　Currently, high-density seeding technology and whole seedling box fertilization technology are attracting attention as low-cost and labor-saving cultivation technologies for paddy rice that have been put into practical use. The former is a technology that significantly reduces the number of seedling boxes required by increasing the amount of seeding per seedling box and removing a small amount of fertilizer. The latter is a fertilization method in which the amount of nitrogen necessary for growth is applied in the seedling box at the time of sowing, and the fertilizer is held by the paddy rice seedlings before transplanting. Both of these techniques have already been adopted as low-cost and labor-saving cultivation techniques for paddy rice by some large-scale farmers in the prefecture.

　This paper describes the results of research conducted to clarify the effects of the combination of high-density seeding and whole seedling box fertilization on seedling quality, growth, and yield of paddy rice, with the aim of further reducing costs and saving labor by combining these two technologies, which have been separately practiced.

2. Testing Method

(1) Seedling quality test

　Seedling transplanting tests were conducted under the assumption that the seedlings would be transplanted by machine in the middle of June, which is the standard transplanting time for normal-season cultivation in Kumamoto Prefecture. Two levels of seedling production were used: conventional seedling production (hereinafter referred to as "conventional") and a combination of high-density seeding and full fertilizer application to seedling boxes (hereinafter referred to as "high-density seeding with box fertilizer"). The rice variety was Hinohikariʼ, and the trial was conducted for two years from 2020 to 2021. The seeding rate was 100 g (dry matter equivalent) per box in the conventional level, and 250 g (dry matter equivalent) per box in the high-density seedling box fertilization level. In the conventional area, commonly used 30-mm-deep medium seedling boxes were used.

　In the high-density seedling box fertilization zone, seedling boxes with a depth of 40 mm (manufactured by Sanko Co., Ltd.) were used, and 2,250 g of "Seedling Box Makase® N400-120" per box was applied to the bottom of the box. During the seedling growth period, the seedlings were irrigated by hand with top irrigation. As a common practice, commercially available artificial granulated soil (Hinokuni soil manufactured by Ryoto Fertilizer Co.
Seedling height, stem, leaf and root dry matter weights, seedling weight per box, and root mat strength were examined immediately prior to transplanting in both locations.

(2) Measurement of seedling weight per box at sowing and transplanting

　The weight of seedlings (including the weight of the seedling box) per box at sowing was measured after filling the seedling box with bedding soil or seedling box material, irrigating, sowing, covering with soil, irrigating again, and allowing the seedlings to rest until gravity water had sufficiently drained out. The weight of seedlings per box at the time of transplanting was measured after irrigating the seedlings before measuring the weight and allowing the seedlings to rest until the gravity water had completely drained out.

(3) Seedling root mat strength survey method

　The center of the seedling was cut at right angles to the cross section (28 cm) with a width of 10 cm, and clips (at least 10 cm wide) were fixed to both short sides.

　The standard root mat strength that does not interfere with machine transplanting operations is 1.8 N/cm or higher in a normal seedling box with a depth of 30 mm, but this strength varies depending on the weight of the seedlings. However, this strength varies depending on the weight of the seedlings. Since a seedling box with a depth of 40 mm is used here, the weight of the seedlings is heavier, and the root mat strength is considered to be affected. Therefore, it is necessary to check whether the root mat has sufficient strength when transferring seedlings grown in a 40 mm-deep seedling box to the seedling bed of a rice transplanter.

　Therefore, we determined the required strength of a seedling per cm of seedling width, which is equivalent to holding the seedling in one hand, using the formula: required strength (N/cm) = weight of seedling after seedling growth (kg) / length of seedling cross section (28 cm) x moment of force (9.8 m/s²), and compared this to actual measured values.

(4) Cultivation test

　Cultivation trials were conducted to determine the effects of the technology combining high-density seeding and full seedling box fertilization on the growth and yield of paddy rice in the rice paddies.

　Table 1 shows the details of the in-house trials. The test area consisted of two levels: a high-density seedling box fertilization area in which 2,250 g of "Seedling Box Makase® N400-120" was applied to the bottom of the box at a seeding rate of 250 g (dry matter equivalent) per box, and a conventional area in which seedlings were raised at a seeding rate of 100 g (dry matter equivalent) per box. In the former, fertilizer was applied to the rice paddies. In the former, no fertilizer was applied to the seedlings and they were transplanted directly, while in the latter, all the base fertilizer was applied with LP-coated compound fertilizer, and then the seedlings were transplanted in the middle. The amount of nitrogen fertilizer applied was 7.2 kg/10a in the high-dense seedling box fertilization area, assuming the number of seedling boxes used was 8, and 8 kg/10a in the conventional area, respectively.

　To confirm its applicability in the field, we conducted a cultivation test similar to the in-field test. The test site was a paddy field in Taragi Nobiru (Taragi Town, Kuma County, Kumamoto Prefecture), and the variety was 'Hinohikari'. The seedlings were sown on May 25, 2021 and transplanted on June 10, 2021. In the high-density seedling box fertilization area, 2,025 g of "Seedling Box Makase® N400-120" was applied to the bottom of each box at a seeding rate of 300 g (wet weight) per box. In the conventional method, seedlings were grown at a rate of 100 g (dry matter equivalent) per box of seeding, and all fertilizer was applied as basal fertilizer. Nitrogen fertilizer was applied at a rate of 8.1 kg/10a in the high-density seedling box fertilization area and 9 kg/10a in the conventional area.

Results and Discussion

(1) In-situ testing

(1) Seedling length and fullness

　Seedlings were grown for 17 days in the high-density box-fertilized area and for 28 days in the conventional area, and seedlings with no problems in terms of appearance were successfully grown (Photo 1). The most important factors in determining whether paddy rice seedlings are suitable for transplanting by machine are seedling length and rootmat strength.

　The seedling height range of 10 to 25 cm is considered suitable for machine transplanting, considering that the transplanter can transplant without difficulty and the transplanted seedlings are not submerged in water. As shown in Figure 1, seedling height in the high seeding box fertilized area was lower than that in the conventional area in both years, but seedling height in the high seeding box fertilized area was in the range of 13 to 19 cm, which was sufficient for machine transplanting.

　On the other hand, the seedling enrichment (stem and leaf dry matter weight/seedling height) was lower in the high seedling density box-fertilized area than in the conventional area in both years (Figure 2), presumably because the seedlings were grown for 10 days shorter than in the conventional area.

(2) Seedling weight per box and root mat strength

　Seedling weight per box was approximately 1 kg heavier in the high-density seedling box-fertilized area at sowing and approximately 2 kg heavier at transplanting than in the conventional area (Figure 3). This was considered to be due to the fact that the seedling boxes used in the high-density seedling box fertilization area were deeper than those used in the conventional area, which increased the amount of soil and moisture retention.

　The strength of the root mats was sufficient for the conventional area, but less than the required strength for the area with the high density seedling box fertilizer (Figure 4). In fact, in the conventional area, it was possible to hold a seedling removed from the seedling box with one hand, but in the high-density seedling box fertilization area, it was not possible to hold the seedling even with both hands. This may be because the root mat was not strong enough to withstand the weight of the seedlings themselves due to the increased overall weight of the seedlings in the high-density seedling box fertilization area, where 40 mm-deep seedling boxes were used. However, it was confirmed that the seedlings could be moved to the rice transplanter by using the seedling pick-up board, and there was no problem in transplanting work in the rice field.

(3) Growth and yield in the main field

　In the 2021 trial, grass height was similar and the number of stems was slightly higher in the conventional treatment than in the high-density seedling box fertilization treatment. Culm length, ear length, and ear number at maturity were similar in both years.

　Yield (milled brown rice weight) was higher in the high-density seedling box-fertilized area than in the conventional area in both years. In terms of appearance quality (inspection grade), the high-density seedling box fertilizer application area showed superior quality compared to the conventional area in both years (Table 2).

(2) On-site testing

　In the field (Taraki Town), grass height was lower in the conventional plot at the highest stage of the maximum height stage, but the number of stems was higher.
At the ear-planting stage, the color of standing hairs in the high-density seedling box-fertilized area was darker green than that in the conventional area (Photo 2). At maturity, ear length was longer in the high-density seedling box-fertilized area, but the number of ears was higher in the conventional area. Yield (weight of polished brown rice) was higher in the high-density seedling box-fertilized area than in the conventional area, and there was no difference in appearance quality (inspection grade) (Table 3).

Summary

　As described above, using seedling boxes with a depth of 40 mm and combining high-density seeding with total fertilizer application to the seedling boxes (box-bottom fertilization), it was possible to produce seedlings of good quality that would not interfere with transplanting operations. This reduced the number of seedling boxes used per 10a to eight, eliminating the need to apply fertilizer to the rice paddies and suggesting that labor-saving cultivation is possible with a 10% reduction in nitrogen fertilizer compared to the conventional fertilizer application.

　The following points should be kept in mind when utilizing the labor-saving technology combining high-density sowing and whole seedling box fertilization introduced in this paper.
(1) It is necessary to confirm that the sowing machine is adaptable to seedling boxes 40 mm deeper than normal.
(2) In order to improve the supply of water and oxygen to the roots of paddy rice seedlings, field raising is recommended. However, it is recommended to use a field method of seedling cultivation that is more efficient than conventional seedling cultivation.
　Therefore, it is necessary to increase the irrigation frequency per day to prevent the seedlings from wilting.
　The following is a summary of the results of the survey.
Remove the sheet after seedling emergence when seedlings are about 1 cm in length to prevent seedlings from becoming less full.
　(2) Manage the seedlings to produce seedlings that are well grown and well adapted to the conditions in the field. In addition, basic seedling management for full fertilizer application to the seedling box should be observed.
　In addition, it is desirable to make a small-scale prototype in advance when working on the project for the first time.
(4) In high-density seedling box fertilization, it is expected that sufficient root mat strength may not be obtained due to the heavy weight of seedlings.
　However, the transplanting operation can be carried out without any problems if a seedling pick-up board is used.
(5) When transplanting, rice transplanters that can handle high-density seeding are used, and the number of boxes used per area is less than the amount of fertilizer applied to the rice field.
　The number of boxes used per area is accurately set by the number of horizontal feeds and the amount of raking (height), since these factors are related to the
　Necessary.

Labor-saving fertilization method for strawberry "Amao" in seedling stage

Fukuoka Prefectural Agriculture and Forestry Experiment Station, Chikugo Branch
Katsutoshi Ryu

Introduction

　The strawberry "Amao" (variety name: Fukuoka S6), bred at the Fukuoka Prefectural Agriculture and Forestry Experiment Station, is produced only in Fukuoka Prefecture, with a planted area of approximately 300 ha (in 2022), and 100% of the strawberries sold through the joint marketing of the strain are "Amao". As the name "Amaou" (meaning "big, round, large, and delicious") implies, the fruit is characterized by its red, glossy, large size, and well-balanced sweetness and acidity. For this reason, it is extremely popular not only among consumers nationwide, but also among professional chefs, and the market demands a stable production and supply.

　Compared to other fruits and vegetables, strawberries require more seedlings to be planted and more labor for seedling production due to their nutritional reproduction. In addition, it is necessary to control the growth and flowering of seedlings during the seedling growth period through fertilizer management. Specifically, it is necessary to supply sufficient nitrogen for growth during the first half of the seedling training period, while in the second half of the seedling growth period after late August, nitrogen supply should be stopped to promote flower bud differentiation and reduce the nitrogen concentration in the body of the seedlings (Uematsu, 1998).

　In the case of "Amao", solid fertilizer containing about 70 mg of nitrogen is applied about three times, and if nitrogen is insufficient, it is generally supplemented with liquid fertilizer (Management Technology Support Division, Department of Agriculture, Forestry and Fisheries, Fukuoka Prefecture, 2020). However, fertilizer application during seedling growth is not performed until July
The fertilizer application takes place during the high-temperature season from April to August, when approximately 8,000 seedlings per 10a must be fertilized multiple times, which is hard work for the growers, and labor saving has been desired.

　In order to reduce the labor-intensive burden of fertilizer application, we investigated a system in which all fertilizer is applied at once using a slow-release coated fertilizer with adjustable leaching rate and duration of fertilizer components. Here, we introduce the outline of the system.

2. Methods

(1) Fertilization method

　A two-year trial was conducted in 2019 and 2020 comparing a single application of slow-release coated fertilizer (hereafter referred to as "total fertilizer") and four applications of solid fertilizer (hereafter referred to as "conventional").

　Based on the leaching simulation of coated fertilizers (Figure 1), Ecolong Total 391-70 type, a linear coated phosphorus nitrate-alkali (N:P₂O₅, K₂O=13:9:11%, Jaycam Agri Co: K₂O=13:9:11%, Jaycam Agri Co. For the total fertilizer application, a potting fertilizer (Shot-kun, Matsumoto Co., Ltd.) was used (Fig. 2). Fertilizer application for the total fertilizer application was conducted on June 24, 2019 and June 25, 2020, at a rate of 2 g/pot (260 mg nitrogen/pot).

　IB Kasei S No. 1 (N: P₂O₅: K₂O = 10:10:10%, Jaycam Agri Co.) was used as fertilizer in the conventional plot. Fertilizer applications in the conventional zone were made on June 24, July 8, July 22, and August 5 in 2019 and on June 25, July 8, July 22, and August 5 in 2020, with one grain per application, for a total fertilizer rate of approximately 2.8 g/pot (280 mg nitrogen/pot).

(2) Seedling raising method

　Seedlings were collected by the potting method, and seedling culture medium was strawberry medium No. 2 (N: P₂O₅: K₂O = 100: 400: 50 mg/L, Seishin Sangyo Co., Ltd.) containing palm peat and charcoal. Seedlings were managed under rain-shielded conditions. No liquid fertilizer was applied to the seedlings during seedling growth. Seedlings were irrigated 1 to 3 times/day during seedling growth, depending on weather conditions. Leaves were harvested every two weeks from the beginning of July to obtain 3.0 to 3.5 leaves remaining in the seedlings.

(3) Cultivation method after seedling planting

　A single greenhouse (6 m wide and 20 m deep) was used for growing strawberries. The planting style was 120 cm wide rows with
The soil was cultivated with 50 cm between rows and 25 cm between plants, with two rows inside each row. Planting was done on September 24 in 2019 and September 23 in 2020.

　For the base fertilizer, 10 kg/10 a of nitrogen was applied with a special Amao fertilizer (N:P₂O₅:K₂O=8:6:3%, Dainippon Sangyo K.K.), which contains organic matter and coating nitrogen. In late October, 5 kg/10 a of nitrogen was applied as additional fertilizer to the seedlings, respectively, with a special fertilizer for Amao and Super Ecolong 413-140 (N:P₂O₅:K₂O=14:11:13%, JCAM Agri Co.

　Mulch cover was applied on October 18 in 2019 and October 26 in 2020. Overhead vinyl cover was applied on October 29 in both years, and the plants were heated with a hot-air heater to prevent the minimum nighttime temperature from falling below 5°C. The irradiation was interrupted during the dark period. Electricity was applied from November 15 to February 28 in 2019 and from November 15 to February 18 in 2020, for 2 to 4.5 hours, depending on the vigor of the grass.

3. results

(1) Nitrate nitrogen content in the medium

　The nitrate nitrogen content in the medium during the seedling growth period is shown in Figure 3, and in both years, the nitrate nitrogen content in the medium was 13-25 mg/100 g dry soil in early July in the total fertilizer application area, 1-3 mg/100 g dry soil in mid-August, and no difference was observed after late August and remained below 3 mg/100 After the end of August, no difference was observed, and the dry soil content remained below 3 mg/100 g dry soil.

(2) Nitrate ion concentration in petioles and flower bud differentiation

　Figure 4 shows the trends of nitrate ion concentrations in petioles during the seedling growth period. Nitrate ion concentrations in petioles in the total fertilizer-applied area were higher than those in the conventional area, exceeding 1,000 ppm in mid-July, and were generally 40 to 50 ppm from mid-August onward, remaining at the same level or lower than those in the conventional area. The flower bud differentiation index in the total fertilizer-applied area did not differ from that in the conventional area in both years (data omitted).

(3) Growth during seedling stage

　Trends in crown diameter are shown in Figure 5. In 2020, the crown diameter was larger on August 17 in the total fertilizer application area than in the conventional area, but there was no difference at other times. Thus, there was no consistent trend between the two years when differences in crown diameter occurred, and no difference was observed at the end of September during the planting period, when both areas were about 10 mm in diameter. Petiole length and leaf width of the third leaf were 6 to 7 cm and 5 cm, respectively, at the end of September when the plants were planted, and there was no difference between the two test sections (data not shown).

(4) Effect on fruit yield and flower cluster

　Product yields at different times of the year are shown in Table 1. There were no differences in the commercial fruit yields among the test sections at any time of the year. Flowering date, days to maturity, one-fruit weight, number of early budding plants of the first axillary flower, and number of heart stopping plants of the first flower of the apical bunch are shown in Table 2. No differences were observed between the two test sections. In both years, no early budding or dead center plants of the first axillary flower cluster were observed in both locations.

(5) Cost estimates for different fertilization methods during seedling growth

　The cost of materials in the total fertilizer application area was 7,200 yen, which was the sum of the fertilizer cost of 5,100 yen and the annual depreciation cost of 2,100 yen for the potted plant metering device (calculated with a product price of 15,000 yen and a useful life of 7 years). The cost of materials in the conventional zone was 4,400 yen for fertilizer (data omitted). The material cost of the total fertilizer application area was 2,800 yen higher than that of the conventional area. On the other hand, the total fertilizer application time per 10a was 4.7 hours (one application) in the fully fertilized area, which was 14 hours less than the 18.7 hours (four applications) in the conventional area (data not shown). The labor wage calculated from this fertilizer application time (1,460 yen per hour of own labor value; Fukui
The total fertilizer application rate (surveyed by the Agriculture, Forestry and Fisheries Department of Oka Prefecture) was 6,900 yen for the total fertilizer application area and 27,300 yen for the conventional area, with the total fertilizer application area being 20,400 yen cheaper than the conventional area.

　The total cost of materials plus labor was estimated to be 14,100 yen for the total fertilizer application area and 31,700 yen for the conventional area, a reduction of 17,600 yen for the total fertilizer application area compared to the conventional area.

Consideration

　When the average temperature of strawberry plants drops to around 25°C from late summer to early autumn, flower bud differentiation occurs in response to the shortened day length (Honda 1977). However, if the nitrogen content in the seedling medium is high, flower bud differentiation will be delayed even under short day length conditions (Yasumatsu and Kimura 1981). Therefore, different fertilizer management is needed for the first half of seedling growth, in which an appropriate amount of nitrogen is provided to produce fuller seedlings, and for the second half, in which flower bud differentiation is induced by nitrogen interruption.

　In this test, the nitrate nitrogen content in the seedling medium of the fully fertilized area was 13-25 mg/100 g dry soil in early July compared with the conventional area, but no difference was observed after late August, and the nitrate nitrogen content remained below 3 mg/100 g dry soil. These results suggest that more nitrogen was supplied to seedlings in the total fertilizer application area in the first half of seedling growth in early July than in the conventional area, and the same level of nitrogen was supplied to seedlings in the latter half of seedling growth from late August onward as in the conventional area. In fertilization management in the latter half of seedling growth, it is important to interrupt nitrogen supply from mid-August to induce flower bud differentiation smoothly, and to keep the nitrate ion concentration in petioles below 100 ppm, which is a standard for nitrogen concentration in the body (Morishita 2014).

　On the other hand, it has been reported that flower bud differentiation and development are rather suppressed when extremely low nitrogen conditions are applied from around early September (Yoshida et al. 2002). In addition, when the nitrate ion concentration in petioles at the planting stage falls below 10 ppm, early budding of the first axillary flower cluster and heart-stopping plants are likely to occur (Takeuchi and Sasaki 2008). Therefore, it is considered necessary to maintain the nitrate ion concentration in petioles in the range of 10 to 100 ppm from mid-August to late September to avoid reducing the nitrogen concentration in the body too much in the latter half of seedling growth.

　In this test, the nitrate ion concentration in petioles of the total fertilizer-applied area was above 1,000 ppm in late July in both years, but after mid-August, the concentration remained at 40 to 50 ppm, similar to or lower than that of the conventional area. In the total fertilizer-applied area, no delay in flower bud differentiation was observed at planting time, and no early budding or heart-stopping plants were observed after planting. These results suggest that even if the nitrate concentration in petioles of "Amao" was 1,000 to 1,300 ppm in late July, flower bud differentiation was not delayed and flower bud differentiation could be induced around September 20 to 25 if the nitrate concentration was controlled at 40 to 50 ppm from mid-August onward.

　However, the coated fertilizer used in the total fertilizer application is designed to accelerate nitrogen leaching under high temperature conditions (Gunjikake 2020); therefore, when temperatures in June to August are higher than normal, nitrogen leaching is accelerated in the total fertilizer application method, and there is concern that nitrogen may become insufficient in the latter half of seedling growth. In such cases, it is necessary to pay attention to prevent the nitrate ion concentration in petioles from decreasing too much in the latter half of seedling growth, for example, by using liquid fertilizer to add fertilizer.

　Because seedling size and nutritional status at the time of planting affect yield after planting, the goal for "Amaou" is to grow seedlings with crown diameters of 8.5 to 10 mm and short petioles that do not grow long (Fukuoka Prefecture Horticultural Promotion Council 2006). Seedlings in the total fertilizer application area in this study had seedling quality comparable to that of the conventional area at planting time in late September, with crown diameters of 10 to 11 mm. In the post-planting survey, no difference was observed in the flowering date of the first flower of the apical flower cluster or in the yield after planting in the total fertilizer-applied area compared to the conventional area. These results indicate that seedling quality, flowering date of the first flower of the apical flower cluster, and yield after planting are equivalent to those of the conventional method in late September when "Amao" seedlings are grown by the total fertilizer application method using coated fertilizer.

　We estimated the cost of different fertilizer application methods during the seedling stage, taking into account the cost of materials and labor. As a result, the total cost per 10a was estimated to be 17,600 yen lower than that of the conventional method, because the total cost per 10a was reduced by the labor-saving fertilizer application, although the cost of materials increased with the introduction of the fertilizer applicator in the total fertilizer application area. In other words, in the total fertilizer application method, the increase in material costs was more than offset by the decrease in labor costs due to labor-saving fertilizer application.

　In conclusion, it is clear that the total application method of coated fertilizer using a metered-quantity fertilizer applicator for potted plants in raising strawberry "Amao" seedlings can produce seedling quality and yield comparable to those of conventional cultivation, and can save labor for fertilizer application.

References

Gunjikake Noriaki (2020) Labor-saving fertilization with slow-release fertilizers in the cultivation of potted flowering plants. Agriculture and Science 726: 9-11
Honda, F. (1977) Strawberry cultivation from the viewpoint of physiology and ecology.
Culture Technology. Seibundo Shinkosha. Tokyo. p136-140
Fukuoka Prefecture Horticulture Promotion Council (2006) Heisei 18 nendo "Amaou Cultivation Guide. 3. Seedling Management. Fukuoka Prefecture, Japan.
　p13-27
Management Technology Support Division, Agriculture, Forestry and Fisheries Department, Fukuoka Prefecture (2020) Cultivation Technology Guidelines for Major Vegetables (11th Edition). p17-22
Morishita, M. (2014) Basic knowledge of strawberries: Ecology and cultivation techniques. Seibundo Shinkosha. Tokyo. p157-162
Yasumatsu, T. and Kimura, M. (1981) Seedling quality, flowering and harvesting patterns of strawberry Hohkoh-early cultivars in accelerated cultivation.
　In: Nara Prefectural Agricultural Experiment Station Bulletin 12: 30-42. Nara Prefectural Agricultural Experiment Station Bulletin 12: 30-42
Takeuchi T, Sasaki M (2008) Effect of seedling growth method on growth and yield of strawberry 'Benihoppe'. Shizuoka Agricultural
　TESTIMONIALS 1: 1-10
Uematsu, N. (1998) Theory and practice of strawberry cultivation. Seibun
　Do-shinko-sha. Tokyo. p40-44
Yoshida Y., Morimoto Y., Oi M. (2002) Temperature effect on flower bud differentiation of tray-grown strawberry varieties.
　and Effects of Nitrogen Nutrition. Zoological Miscellany 71, no. 2: 372

No Soil - No. 24 Soil is a Product of the Environment
　　　-Weathering and biological action create soil from rock.

Former Technical Advisor, Hokkaido Branch, Jcam Agri Co.
Teruo Matsunaka

　About 600 million years ago, 4 billion years after the birth of the earth 4.6 billion years ago, something like soil (early soil) was formed, and about 300 million years ago, the soil we imagine was formed on the earth. In the last issue, I told you the story of the formation of soil. This time, I would like to talk about how soil is created by the environment.

1. change in perception of soil

　Until the 19th century, soil was considered to be nothing more than a soft, weathered rocky surface layer of the earth's crust. Dokuchaev (1846-1903), a young Russian geologist who later became known as the founder of soil science, changed this view to one in which soil is created by the environment.

　He believed that soil is formed by the interaction of various factors such as rocks, which are the raw materials of soil, climate, plants and animals, and topography, and that the formed soil changes with time. He also argued that soil, like animals and plants, is one of the components of nature and that soil is a product of the environment. Let us look at this idea in detail below.

2. two factors that create soil - weathering and biological action

　In Japan, soil made from volcanic ash (black soil) is widely distributed. However, from a global perspective, black soil is an exceptional soil, and the raw material for soil in general is rock. The rock used as the raw material is called the host rock. Soil is formed from the parent rock by two processes: the breaking of the rock into small pieces (weathering) and the formation of soil by the action of organisms on the broken rock (Fig. 1).

　The first step in the formation of soil is for lichens and microorganisms, as described in last month's issue, to attach themselves to the surface of a material that has been broken into small pieces by weathering (this is called the parent material of soil). When they die after completing their lives, their remains are decomposed by other microorganisms. The decomposition products become plant nutrients. As these nutrients accumulate, an environment is created in which plants can live, and higher plants, such as mosses and grasses, invade. When mosses and grasses enter, their remains are decomposed by microorganisms and nutrients increase further. Then, soil animals (earthworms, etc.) can live there.

　Soil animals live and die by feeding on the organic matter that has accumulated in the matrix as decomposition products of plant remains. As a result, the surface of the parent material becomes richer in nutrients. In this way, higher plants are able to live. As the higher plants die and are replaced by dead bodies, a black-colored layer of soil with a mixture of organic matter and the parent material gradually forms on the surface of the parent material.

　The action that creates soil in this way is the result of the action of living organisms on the parent material. No matter how much a rock is weathered and crushed into small pieces, soil cannot be created without the presence and action of living organisms.

3. the function of soil-building organisms is affected by the environment

　The workings of the organisms that make up the soil are closely linked to the environment. This is because the types of organisms and their activity are greatly influenced by the climate.

　In cold regions at high latitudes, the amount of organic matter added to the soil is low because plant growth is poor. However, because of the cold weather, decomposition of organic matter by microorganisms does not progress, and organic matter accumulates, resulting in dark soil with a darker color, as indicated by the organic matter. On the other hand, in low-latitude tropical rainforest areas, the amount of organic matter added to the soil is much higher than in colder regions because of vigorous plant growth. However, because of the higher temperatures, the decomposition of organic matter by microorganisms is faster, and organic matter is less likely to accumulate in the soil. Therefore, the soil in this region does not darken, and a reddish-brown color is produced.

　Soil is formed and changes within the limits of given environmental conditions, not at will. This is why Dochkiaev describes soil as "a product of the environment," and asserts that "soil is not some mechanical, accidental, lifeless mixture; on the contrary, it is a natural history formation (a historical natural body) determined and governed by independent and fixed laws. In other words, given certain environmental conditions, the same soil will be produced if the base material is the same. However, even if the base material is the same, if the environmental conditions are different, the resulting soil will be different. The environment creates the soil.

　Looking at the world's soil again (Figure 2), it appears that soil is distributed in a band along the latitude of the earth.
This is because the climate varies greatly with latitude, and the soil is formed by the different actions of organisms in response to these changes.
From a macroscopic viewpoint, we can realize that "soil is a product of the environment," as Dokuchaev pointed out.

　The moon is devoid of life. Therefore, the biological processes necessary to create soil do not work. Therefore, there are rocks on the moon, but no soil. Because the earth is at a perfect distance from the sun, the atmosphere and water can exist, and organisms were born. Thanks to the work of these organisms, soil was created and agriculture began.