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Seok-Cheol Kim, Rog-Young Kim, Yong Bok Lee,
Hong Bae Yun, Ye Jin Lee, and Byoung Choon Jang
Division Soil & Fertilizer Management,
National Academy of Agricultural Science (NAAS), RDA

ABSTRACT

In recent years, agriculture in South Korea, which is highly dependent on imported agricultural materials, has been heavily burdened by the liberalization of agricultural imports and the increasing costs of agricultural materials. Hence, to alleviate the problem, South Korea has continuously struggled to develop agricultural technologies for better and improved plant nutrition diagnosis, soil fertility management, fertilization efficiency, and conservation of the agricultural environment. The country's agricultural policy aims to support the practice of the eco-friendly sustainable agriculture and produce high-quality and safe agro-products.

Because of the high dependence on imported agricultural materials, the fertilizer supply in South Korea is greatly affected by the international price. Therefore, there is an urgent need to stabilize the supply and price of fertilizer by securing raw materials and be more self-sufficient in fertilizer production. To manage eco-friendly soil fertilization schemes and produce high-quality and safe agricultural products, the input-output analysis of the agro-ecosystem which includes nutrient uptake of crops, remaining amounts of soil nutrients, and the outflow to the environment should be conducted. Essentially, we have to focus on the establishment of a fertilization system that will ensure for the improvement of nutrient balance on a national scale.

Keywords: soil information system, soil fertility research, chemical fertilizers

INTRODUCTION

Korean Soil Information System

History of Korean Soil Information System

The importance of soils as the basis of Korean farming was recognized long time ago. A book titled "Nong-Sa-Jik-Seol" (meaning Instruction for Agriculture), which was published in 1429 during the reign of Great King Sejong, presents in much detail the quality of soils, touching on how and when to plow the lands, how to improve the fertility of barren soils, and even how to test soil quality by tasting it. Many books about agriculture were published during the Choson Dynasty, following the example of "Nong-Sa-Jik-Seol".

The first modern soil survey was initiated in 1964, when the Korean Government and UNDP/FAO of United Nations jointly established the Korea Soil Survey Organization in the Office of Rural Development (now Rural Development Administration, RDA) in Suwon. From 1964 to 1967 a reconnaissance survey was carried out which generated the publication of the 1:250,000 and 1:50,000 scales Korean soil maps (Table 1). Thereafter, the substantial progress of soil survey has been made as follows: the Detailed Soil Survey (1:25,000) from 1968 to 1990; the Highly Detailed Soil Survey (1:5,000) from 1995 to 1999; the Soil Testing Survey from 1998 until present; and the Agro-Environmental Change Monitoring Project from 1999 to 2008. Now, based on the results of all the soil survey projects carried out by RDA for about 40 years, an internet-based Soil Information System was developed for managing soil resources rationally and for providing soil information promptly to the public. Table 1 shows the summary of the Korean soil survey history and its applications.

Use of Korean Soil Information System

Based on the national soil survey projects, two different kinds of soil databases were constructed that serve as the concrete bases for Korea's Soil Information System. One is the spatial database soil map (morphological and physical properties) at a variety of scales (1:250,000, 1:50,000, 1:25,000, and 1:5,000) established between 1998 and 2005 as shown in Table 1. All the soil maps were digitized and in a GIS file format. The soil map database can be used to make a recommendation for the land use, crop suitability, and land suitability.

The other is the parcel-based soil fertility database (chemical properties) established using an oracle relational database management system through the soil testing done from 1998 until present. Soil testing determines both the amount of essential nutrients for plants and the presence of any harmful elements in the soils. RDA is in charge of the national soil survey projects and updating of soil information. With regards to the soil testing project, RDA prepares the plan and the Agricultural Technical Center (ATC) of each city or county takes charge of the implementation of the plan. RDA provides the standard of fertilization scheme for 104 crops, checks samples for laboratory analyses, and initiates the web-based operating program to print out fertilizer recommendation. Each local ATC collects and analyzes soil samples for its area. They also upload the soil fertility data analyzed from the RDA database. The Web-based fertilizer recommendation program developed in 2007 facilitates the uploading of the soil testing data from local ATCs automatically to the RDA soil fertility database while they input the soil test data for printing a fertilizer prescription. The web-based fertilizer prescription contributes a lot to make recommendations for optimum plant growth via amount and type of fertilizer, timing and exact location of fertilizer application.

RDA has also carried out the Agro-Environmental Change Monitoring Project, which investigates the soil chemical properties and heavy metal concentrations as well as soil microbes in agricultural soils including vulnerable agricultural soils at fixed sampling sites. Since 1999 until today, soil samples for each cropland type are designed to be collected every other four years from the paddy (sampling point ca. 2,000), upland (sampling point 1,600), plastic film houses (sampling point 1,200), and orchards (sampling point 1,300). Heavy metals concentration which include As, Cd, Cr, Cu, Ni, and Zn are examined each year since 1999 using 600 samples collected from vulnerable agricultural fields near or adjacent to metal mines, industry complex areas, highway, and municipal wastewater.

On the other hand, the web-based Agro-Environmental Resources System which just started in NAAS, RDA was developed based on the agro-environmental resources inventory. This system primarily aims to establish a national agro-environmental resources inventory and facilitate for its rational use. Since early 2009, the Web-GIS system for agro-environmental resources information had already provided a spatial database on natural resources, 3-D soil maps, an image database, statistics, and cyber forum.

It is worth to mention that these soil Information can be applied to map soil functional properties, soil carbon storage and available water capacity which are critically important for land management, plant production and ecosystem management. Hydrologic soil group, soil erodibility, and potential runoff are based on the soil map which represents different kinds of soil characteristics. Soil chemical properties statistics can also be calculated using the soil testing data (Hong et al. 2008).

Soil fertility research in Korea

Paradigm change on soil fertility research

Soil fertility, in a narrow sense, can be defined as soil capacity to produce crops via chemical fertilizers, soil amendments, deep tillage, or soil replacement. The paradigms underlying soil fertility research in Korea have undergone considerable reforms over time because of experiences gained in the field and the changing economic conditions, as well as changing social and political demands. A considerable number of long-term projects have been accomplished in Korea since the 1900s, and have given valuable insights in soil fertility management. The modern soil fertility management research was started in 1964 by RDA parallel to the Reconnaissance Soil Survey as mentioned above and which was supported also by UNDP/FAO of United Nations (Table 2). Until the late 1980s, the soil fertility research focused on improving crop yield to ensure a sufficient food supply via massive applications of agricultural materials and variety breeding. From the late 1980s, the paradigms shifted towards environment-friendly agriculture due to the growing awareness on increasing environmental problems. In 1997, the Environment-friendly Agriculture Promotion Act was enacted in order to protect and conserve the natural soil productivity and produce high quality agricultural products using minimal chemical fertilizers and chemicals and a special cultivation method. In the 2000s, Organic Farming and Good Agricultural Practices (GAP) have been developed to contribute to environmental, economic and social sustainability of agricultural production including safe and healthy food and non-food agricultural products.

Soil fertility research: An overview

Simultaneous to the Reconnaissance Soil Survey mentioned above, a six-year soil fertility project was accomplished from 1964 to 1969 in 25,200 sites over the entire country, mainly on land areas with low-productivity. During this project, the effects of NPK management and soil improvement methods on plant growth were investigated. This resulted to the development of methods on adequate fertilization for each crop and soil improvement for each soil type. Furthermore, the balance between supply and demand for each chemical fertilizer was analyzed. Cation exchange capacity, anion exchange capacity, and organic matter were considered as main factors effecting soil fertility, whereas cation exchange capacity, organic matter, and clay contents were determined to be of great importance for phosphate availability. Thus, the amounts of available silicic acid in 365 paddy soils and available boron in 262 upland soils were analyzed. Based on the results analyzed, the supply of silica fertilizer and boron was increased. The chemical properties determined such as pH, OM, available P2O5, exchangeable K, Ca, Mg, and available SiO2 from 5,130 paddy soils and 3,661 uplands soils from the 1970s until present are summarized in Table 3 and Table 4. The relationships between the soil test results and crop growth responses were analyzed to determine the adequate fertilization rate. However, due to the huge amounts of analyses in the 1960s, we were not able to obtain a comprehensive evaluation of soil fertility. But, there were a lot of progress in the statistical systems and the skills for soil and plant analysis.

In the early 1970s a reclamation project for the development of hilly and abandoned land was carried out by RDA using barley, bean, sorghum, sweet potato, perilla, hemp, legume, horticultural crop, oak, and pasture plant as test crops. The tested soil improvement methods such as liming, deep tillage (20 cm), and application of fused magnesium phosphate and organic matter increased the crop yield 1.7 - 2.9 fold as compared with the application of NPK only in degraded lands.

From 1975 to 1979, a five-year soil fertility project was carried out to determine adequate fertilization rate for rice and improve the land use for each of the eight climate zones within the entire country consisting of 56 regions, 74 soil series, and 13 crop breeds. The soil improvement methods conducted for the paddy soil type are summarized in Table 5.

From 1980 to 1989, a ten-year arable lands development project was carried out to raise food self-sufficiency rate and produce the maximum possible crop yield. For this purpose, 647,000 paddy soils and 65,000 upland soils were analyzed which resulted to the issuance of the computerized prescription for improving soil fertility to the farmers. The recommended Nitrogen fertilization was established basedon the available amounts of silicic acid, organic matter and exchangeable bases. The change in the recommendation rate of NPK fertilizer from 1950s until the 2000s is listed in Table 6. The determined chemical properties (pH, OM, Av. P2O5, Ex. K, Ca, Mg, and Av. SiO2) from the investigated soils which include paddy, uplands, and plastic film house are also summarized in Table 3, Table 4, and Table 7.

In the 1990s the soil fertility paradigm shifted towards environment-friendly agriculture aiming at low input of resources. Thus, to improve the fertilizer recommendation rate, 137 test objects were analysed from where a recommendation formula for NPK fertilizer was drawn on the parcel basis. Using this recommendation formula, the amounts of fertilizer application could be reduced, while the crop yields remained at the same level. Furthermore, a bulk blend fertilizer (BB fertilizer) was produced in 1996 and its production amounted to 50,000 tons in 1998. To produce 5,000-5,500 kg ha-1 tons of rice, the recommendation rates for nitrogen fertilizer were 150-180 kg ha-1 under direct seeding on dry paddy soils and 110-130 kg ha-1 under seeding on flooded paddy soils. In addition, standard values for soil physical and chemical properties, the NPK fertilization rate, organic matter content, and the liming method for 21 crops including vegetables were proposed, modified several times, and are used until today.

The 2000s is the maturity stage for soil fertilization management in Korea. The change in the NPK fertilizer recommendation rate from the 1950s until the 2000s is listed in Table 6. The determined chemical properties (pH, OM, Av. P2O5, Ex. K, Ca, Mg, and Av. SiO2) of the investigated paddy soils, uplands soils, orchard soils, and plastic film house soils are shown on Table 3, Table 4, and Table 7, and Table 8. The differences in soil chemical properties between soil use types are reflected in Table 9.

Development and use of chemical fertilizers in Korea

NPK fertilizer

Most of the arable lands in Korea have low soil fertility which is one of the main constraints for crop production. In particular, soil pH and organic matter content were insufficient to maintain sustainable crops production. To increase pH, these lands were amended with ground limestone, which started in 1940, until the present time. Since application of limestone to arable soils could not raise the desired pH level at one-time application, lime was continuously applied once after every three years from 1971 to 1990 and then every five years since 1991 until now with subsidy from the Korean government. Likewise, since rice is the most important staple food in Korea, serious pursuits on rice intensive research were conducted over the last four decades. From the 1970s, studies on rice mainly focused on determining the appropriate fertilizer application rate, improvement of varieties, and disease control to achieve desired rice yields. Thus, most of the chemical fertilizers developed were also used for rice cultivation. In Korea, the modern chemical fertilizer, which was introduced in the 1930s, was ammonium sulfate. The use and development of chemical fertilizer begun along with the construction of large fertilizer factories in 1960s.

Chemical fertilizer was firstly used as single nutrient forms such as ammonium sulfate, urea, phosphate, and potassium chloride. The use of these fertilizers caused more N fertilization than standard N fertilization. The first NPK fertilizer was 22-22-11 (N-P2O5-K2O), 18-18-18, and 14-37-14 for rice field, rice seedling, and wheat field, respectively. The introduction of NPK fertilizer had contributed to balance for NPK fertilization rate and farmers' participation.

The optimal mix of N, P, and K depended on the variety of crops and the soil quality. Before the 1st half of 1970s, the target of rice breeding in Korea was to attain high yield and develop resistance to lodging, plant diseases and various environmental stress rather than grain quality. In the 1980s, the major rice breeding objective focused on improvement of grain quality since self-sufficiency in rice production was already achieved in 1975. The interest on improving grain quality was directly affected by N application rate. Most of the high-quality variety that were developed required lower N fertilization rate than that of the high- yielding variety, and was considered to be one of the main reasons for the introduction of a standard N application rate for rice cultivation from 137 kg N ha-1 in 1970s to 90 kg N ha-1 in 2000 (Table 4).

The NPK mixed fertilization significantly improved crop production, but it also contributed to the increased accumulation of P and K in arable lands (Table 5, 6, 7, and 8). The rapid growth and intensification of livestock farming, which provided vast supply of livestock manure containing high amounts of P also increased the P accumulation in Korean soils. After 1980, the livestock industry in Korea increased 3-4 times for over two decades. As a consequence, livestock manure disposal and re-cycling posed a serious problem in terms of its proper disposal and utilization. The Ministry of Agriculture estimated that about 44 million tons of animals produced in 2006 and the National Survey reported that more than 80% of livestock manure production in Korea is processed as compost. Because of handling and sanitary problems, farmers prefer to use compost rather than raw manure for land application. The compost from animal manure was normally applied at rates designed to meet crop N requirement but P. This often resulted in a buildup of available soil P above the required amount of P to obtain a desired crop yield since plants need a lower N/P ratio. More than 60% of agricultural lands in Korea is estimated to have P surplus, mainly caused by the excessive amount in the use of livestock manure compost. There are serious concerns that agricultural runoff and erosion from high P soil may be the major contributing factors to surface water eutrophication. Phosphorus loss in agricultural runoff is not of economic importance to farms because it generally accounts for only 1% or 2% the P applied. However, P loss can lead to significant off-site economic impacts because improvement in water quality or water treatment is difficult, expensive and requires a length of time. To mitigate phosphorus accumulation in arable land, low P containing NPK fertilizer such as 21-11-21, 21-9-17 and 17-0-17 were developed and supplied to farms in 1991.

Another approach that was tried by the National Research Institute in 1996 to improve the nutrient balance in soil was the use of the Bulk Blending (BB) fertilizer. The BB fertilizer contained 976 kinds of N, P, and K mixture ratio. The NPK mixture ratio in the BB fertilizer was determined based on soil test and crops. However, the BB fertilizer did not effectively contribute to the improvementf nutrient soil balance due to the limitation of its supply and use.

To overcome the limitations of BB fertilizer, the "customized fertilizer" was recently developed for rice cultivation. The choice of the customized fertilizer was determined by using the fertilization prescription which is very similar system with BB fertilizer. However, customized fertilizer consisted of 25 kinds of basal fertilizer and 6 kinds of additional fertilizer for rice cultivation. As a result of the experiment done in 2009, the application of customized fertilizer reduced the lodging rate of rice as compared to conventional fertilization, and had the same level of rice yield and quality with conventional fertilization. The customized fertilizer for upland crop and vegetable will soon be supplied to farmer.

Slow-release fertilizer

Slow-release fertilizer provides an attractive alternative to granular fertilizer. It is more expensive than common chemical fertilizer but they have several advantages: 1) the danger of over-fertilizing is reduced as the release of fertilizers occurs gradually, 2) fertilization is necessary only occasionally, sometimes only once in a season, 3) nutrients do not leach from the soil so the plants receive all the nutrients applied. In Korea the first slow-release fertilizer introduced was sulphur coated urea (SCU) which was imported from USA in 1970. The SCU is a urea coated by sulphur, waxes, and clay and the nutrient release rate is controlled by thickness of sulphur coating. Many experiments were conducted to ascertain the effect of SCU on crop yield and reduction of fertilizer application rate. The experiment results revealed that the SCU-fertilized rice had 8% increased in yield compared to common chemical fertilizer. The SCU was more effective in reclaimed rice field, which improved rice yield to about 27%. Although SCU had several benefits for increasing rice yield and reducing fertilizer application rate, it was not used in the field at that time due to high cost and limitation of manufacturing facilities.

Up to now, several slow-released fertilizers were developed in Korea. The representative slow-released fertilizer developed in Korea was latex coated urea (LCU) (), wherein urea was coated by sodium silicate and then coated by 5% to 20% latex to control release rate. The LCU did not show an increase in rice yield compared to common fertilizer, but it had significantly reduced fertilizer application rate and achieved same rice yield with that applied with common fertilizer (Table 10).

The nutrient release in slow-released fertilizer is affected or can be controlled by soil temperature or moisture, but it is not affected by soil factors such as pH, texture, oxidation-reduction potential, and nutrient concentration. Recent advances in slow-release fertilizer technology allows predictable nutrient release and the agricultural markets in Korea are still in its infancy stage.

Silicate fertilizer

Rice requires large amount of silicon for vigorous growth, tolerance to lodging, and resistance to pests and diseases. Korea has a long history of research on the effects of silicon on rice growth and yield, which started since the 1960s. Korean paddy soils are generally characterized by low pH value and level of available Si content. In the 2000s, the national average values for the pH and available Si were 5.6 and 72 mg SiO2 kg-1, respectively, which were lower than the optimum ranges of pH (6.0-6.5) and available Si (130-180 mg SiO2 kg-1).

The first silicate fertilizer in Korea that was supplied to farm from 1963 to 1990 was the grounded wollastonite. Another source of silicate fertilizer is the furnace slag produced by the iron industry. This silicate fertilizer is provided to farm every 4 year and is subsidized by the government since 1996 until now. With silicate fertilizer application, the average silicon content in soil was increased from 75 mg SiO2 kg-1 in 1970s to 118 mg SiO2 kg-1 in 2003.

Although Si is not an essential element for plant nutrition, the beneficial effect of Si on rice yield has been intensively studied in Korea. For instance, a 26 years field experiment was done from 1975 to 2000 on the silicate fertilization of of 1.5 Mg ha-1 to the clay loam paddy fields. The changes in the average rice yield for 5 years interval was observed to continually increase with the treatment of silicate fertilizer at 1.5 Mg ha-1 as compared to NPK treatment (Table 11).

Nowadays, rice productivity is no longer a major concern in Korea as it was over the last three decades. Today, grain quality is becoming the major research topic for rice. Many researchers have shown that grain quality was directly affected by nitrogen application rate. Improvement of nitrogen efficiency contributes to enhancing grain quality and reducing nitrogen application levels. It is a well-known fact that Si fertilizer increases nitrogen uptake. According to Lee et al. (2005), silicate fertilizer applied one and two times more than the recommended level decreased approximately ca. 51 and 66 % of the amount of nitrogen applied to get the maximum rice yield as compared with the non-Si treatment. Therefore, Si fertilizer could be a good alternative source to decrease nitrogen fertilizer application rate yet increasing nitrogen efficiency.

Nitrogen and phosphorus balance as agri-environmental indicators in Korea

Beginning from the 1960s up to the present, our government has been steadfast in its endeavor to raise food self-sufficiency rate by specifically increasing rice and meat production.

These efforts led to intensive farming systems, high-yielding agriculture and animal breeding, but all these resulted to serious major nutrient imbalance in our environment. Since then, the government started its advocacy to minimize the use of excessive amount of fertilizers in most farming systems.

Nitrogen balance

oNitrogen fertilizers made significant contribution to the increase in crop production in Korea for the past 40 years but has also been considered the main nitrogen (N) source of pollution in water bodies and air. Surface N balance is used as an indicator of the environmental impact of agricultural production both at the national and global scales (Bouwman et al., 2005).

The changes of N balance in Korea, which is calculated according to the surface balance method of the PARCOM guidelines (PARCOM, 1995), is shown in Fig. 1. The N balance increased tremendously from 1991 to 1998 and decreased rapidly from 2003 to 2006. The highest N balance was recorded in 1998 with about 270 kg N ha-1 during the investigation period. However, N balance of other OECD countries steadily decreased over the past years. Several reasons could be considered with this trend in N balance in Korea. In the early 1990s, the Korean government, through its natural recycling policy, actively encouraged farmer to use livestock manure instead of chemical fertilizer. This situation, however also resulted in the significant increase of N supply in soils. In addition, farmers were strongly required to reduce the use of chemical fertilizer for agro-environmental conservation and sustainable productivity.

The N input at the national scale was 643,320 Mg in 1985 and has reached its highest levels at 812,213Mg in 1990 but steadily decreased after the following years. The decrease of N input from 1995 was mainly due to the decrease of chemical fertilizer inputs, but not in N input from livestock manure, which slightly increased during this period.

The arable land area in Korea was 2.225 million ha and has been reduced to 1.967 million ha in 1998 due to rapid urbanization and industrialization. Therefore, significant decrease of the N input by chemical fertilizer was not mainly affected by the changes in N balance, but due to the decrease in the arable land area and increase in the application of livestock manure.

Phosphorus balance

The phosphorus load originating from arable land and livestock industry is a major contributor to the eutrophication of lakes and rivers. The P input in the arable lands from chemical fertilizer and livestock manure were taken up by plant after harvest, but P surplus at large quantity are still accumulated in the soil. The range of P balance depended on farming system management. In particular, application of livestock manure, which had high P content, led to higher P accumulation in the soil as lower N/P ratio was only required for plant growth.

Phosphorus balance at the national scale had the same trend with N balance as shown in Fig. 1. In 1985, P balance was 36 kg P ha-1, which reached to the maximum level at 57 kg P ha-1 in 1995 and decreased sharply at about 41 kg P ha-1 in 2006. Until 1995, the P surplus was mainly due to chemical fertilization. After 1995, P input by chemical fertilization significantly decreased for various reasons: specifically, reduction in standard fertilizer application rate in rice cultivation and abolition of government subsidy for chemical fertilizers of the farmers. However, the P input from livestock manuring still gradually increased from 1990 to 2006 (Fig. 2).

Among the OECD countries, Japan has the highest P balance. The arable lands of Japan, which mainly consist of volcanic ash soil, are characterized to have high P fixation capacity. Therefore, Japan needed to apply large amount P fertilizer to increase crop production. However, the P balance of Japan was significantly decreased to 50 kg P ha-1 from 1993 to 2004 through the implementation of strong policies on reducing the usage of chemical fertilizers. Their P balance level was similar to that of Korea. Meanwhile, the P balances of the Netherlands (1986) and Belgium (1989) were also higher than that of Korea (1985) since their livestock population per hectare were very high compared to Korea. Because Belgium and Netherlands governments controlled their livestock production and livestock manuring, their P balance gradually decreased to 21 and 16 kg P ha-1, respectively in 2004 which were comparably lower than Korea (50 kg P ha-1). Presently, Korea may have the highest P balance among the OECD countries. To reduce P balance like other OECD countries, it is highly recommended that the Korean government must introduce stronger policies to reduce P inputs from livestock manuring and chemical P fertilization.

CONCLUSION

Future directions

Internet-based Soil Information System of Korea was developed in 2006 that consists of five main parts: 1) digital soil map service such as soil theme maps and crop suitability maps, 2) fertilizer recommendation, 3) soil statistics for selected soil themes, 4) Korean soils, and 5) `soil love' for kids. Based on the agro-environmental resources inventory, development of Agro-Environmental Resources System also just started in NAAS, RDA, to establish national agro-environmental resources inventory and its rational use. The soil database needs further applications to estimate soil carbon storage, water capacity, and soil loss. Digital mapping of soil and environment using state-of-the-art and emerging technologies with soil mapping pedometrics concept and predicting soil and environment properties will lead the country's future directions. A paradigm shift in soil fertility management is necessary to anticipate future soil contamination, develop labor-saving fertilization, and utilize the accumulated nutrients in soils. A recommended technology system for livestock manure compost utilization and management still needs a more thorough assessment to improve the national phosphate balance and phosphate accumulation in the arable lands.

REFERENCES

  • Bouwman, A.F., G. Van Drecht, and K.W. Van der Hoek. 2005. Surface nitrogen balances and reactive N loss to the environment from global intensive agricultural production systems for the period 1970-2030. Sci. Chi. Ser. G. 48(special issue): 767-779.
  • Hong, S.-Y., Y.-S. Zhang, B.-K. Hyun, Y.-K. Sonn, Y.-H. Kim, S.-J. Jung, C.-W. Park, K.-C. Song, B.-C. Jang, E.-Y. Choe, Y.-J. Lee, S.- K. Ha, M.-S. Kim, J.-S. Lee, G.-B. Jung, B.-G. Ko, and G.-Y. Kim. 2009a. An introduction of Koran soil information system. Korean J. Soil Sci. Fert. 42(1): 21-28.
  • Hong, S.-D., C.-S. Lee, and S.-W. Hwang. 2009b. Soil fertility. Korean. J. Soil Sci. Fert. 42(special edition):178-194.
  • Kim, C-B. and J. Choi. 2002. Changes in rice yield, nutrients use efficiency and soil chemical properties as affected by annul application of slag silicate fertilizer. Korean J. Soil Sci. Fert. 35(5):280-289.
  • Kim, M.-S. and S.-S. Kang. 2010. Soil fertility management to conserve soil environments. p. 93-135. In: RDA. Utilization of Agro-Environment Information system for rational soil management.
  • Kim, P-J., Y-B. Lee, Y. Lee, H-B. Yun. and K-D. Lee.2008. Evaluation of livestock manure utilization rates as agricultural purpose in developed OECD countries by using nutrient balances. Korea J. Evniron. Agricul. 27(4):337-342.
  • Lee, C-H., M-S. Yang, K-W. Chang, Y-B. Lee, K-Y. Chung, and P-J. Kim. 2005. Reducing nitrogen fertilization level of rice (Oryza sativa L.) by silicate application in Korean paddy soil. Korean J. Soil Sci. Fert. 38(4):194-201.
  • NIAST (National Institute of Agricultural Science and Technology). 2001. Korean soil and environmental information system.
  • PARCOM, 1995. PARCOM guidelines for calculating mineral balances. Oslo and Paris conventions for the prevention of marine pollution programs and measures committee (PRAM), Oviedo, 20-24, February.
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Index of Images

  • Fig. 1 Changes in nitrogen and phosphorus balance of OECD countries. (Kim et al., 2008)

    Fig. 1 Changes in nitrogen and phosphorus balance of OECD countries. (Kim et al., 2008)

  • Fig. 2 Changes in nitrogen and phosphorus input by chemical fertilizer and livestock manure in OECD nutrient balance in Korea. (Kim et al., 2008)

    Fig. 2 Changes in nitrogen and phosphorus input by chemical fertilizer and livestock manure in OECD nutrient balance in Korea. (Kim et al., 2008)

  • Table 1 History of Korean soil survey and its applications

    Table 1 History of Korean soil survey and its applications

  • Table 2 An overview of Korea's soil fertility management researches.

    Table 2 An overview of Korea's soil fertility management researches.

  • Table 3 Change in soil chemical properties in paddy soils.

    Table 3 Change in soil chemical properties in paddy soils.

  • Table 4 Change in soil chemical properties in uplands soils.

    Table 4 Change in soil chemical properties in uplands soils.

  • Table 5 Soil improvement methods for the paddy soil type in the 1970s.

    Table 5 Soil improvement methods for the paddy soil type in the 1970s.

  • Table 6 Change in recommendation rate of NPK fertilizer (units: kg 10a-1).

    Table 6 Change in recommendation rate of NPK fertilizer (units: kg 10a-1).

  • Table 7 Change in soil chemical properties in plastic film house soils.

    Table 7 Change in soil chemical properties in plastic film house soils.

  • Table 8 Change in soil chemical properties in orchard soils.

    Table 8 Change in soil chemical properties in orchard soils.

  • Table 9 Soil chemical properties under different soil use types.

    Table 9 Soil chemical properties under different soil use types.

  • Table 10 Rice yield with different LCU fertilization levels (unit: Mg ha<SUP>-1</SUP>).

    Table 10 Rice yield with different LCU fertilization levels (unit: Mg ha-1).

  • Table 11 Changes in average rice yield every 5 year period (unit : Mg ha-1).

    Table 11 Changes in average rice yield every 5 year period (unit : Mg ha-1).

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