Cho-Rong Lee1, Nan-Hee An1, Young-Woong Byeon1, Yong-Ki Kim1 Sang-Min Lee1,
Gi- Chun Park1, and Byoung-Gu Ko1
1 Organic Agriculture Division, National Institute of Agricultural Sciences,
Rural Development Administration (RDA), Wanju-gun, Jeollabuk-do, Republic of Korea
Environmentally friendly agriculture in Korea is steadily increasing and organic fertilizers are becoming more important as a substitute for chemical fertilizers. The Rural Development Administration (RDA) developed the smart use of organic fertilizers for crop production, environmental sustainability, and soil conservation. First, we selected 57 green manures cultivated or wild grown in Korea and examined the seeding rate and timing of green manure according to weather conditions and environmental characteristics. We used intercropping to merge the benefits of legumes and non-legumes to increase crop productivity. Second, we increased organic matter in paddy soils to incorporate rice straw compost since 1954. Also, we made agricultural by-product composts (garlic, onion, and ginger) and investigated the effects of these composts on crop productivity and antibacterial activity. Third, we developed manuals that standardized the methods of producing organic liquid fertilizer using organic materials (bone meal, fish meal, and seaweed) and then distributed them to farmers to increase the uniformity of farm-made liquid fertilizers. Finally, we developed an organic fertilizer recommendation system (OFRS) that indicates the amount of organic materials that farmers should apply to their crops based on the nutrient contents and mineralization rate of organic materials. The OFRS is currently being conducted in fields on a national scale. In ongoing researches, we will extend the OFRS to upland crops for smart use of organic materials.
Keywords: Organic soil and nutrient management, organic fertilizer, organic material, environmentally friendly agriculture, organic fertilizer recommendation system, Korea
Environmentally friendly agricultural products (organic and non-pesticide) in Korea must be certified by the Government. Both types of certified products differ in their cultivation regulations:
Environmentally friendly agricultural production areas in Korea have been steadily decreasing since 2012 due to increased regulation of environmentally friendly agricultural products. However, compared to 2016, the cultivated area of certified environmentally friendly and organic products increased by 6.6% (80,114 ha) and 4% (20,673) in 2017 (Table 1). Thus, the area of environmentally friendly cultivation started rebounding in 2016 after a 4-year period of decline. The market for environmentally friendly agricultural products is expected to steadily increase in the future (Seong et al., 2017). Organic fertilizer as a substitute for chemical fertilizer should be used for soil and nutrient management in environmentally friendly agriculture. Recently, there has been an increasing interest in organic materials, such as compost and green manures, in conventional agriculture for soil conservation and environmental sustainability. Therefore, the use of organic fertilizer for environmentally friendly agriculture is becoming more important in Korea.
Table 1. Trends of environmentally friendly agriculture in Korea (2012–2017).
Organic agriculture in Korea uses a variety of organic materials, such as green manures, composts, and liquid fertilizers, for nutrient management. Organic fertilizers are mostly made from natural materials. They are different from conventional mineral fertilizers, which are synthesized using chemical processes to rapidly supply specific nutrients to plant. Organic fertilizers differ in nutrient supply depending on environmental conditions (e.g., soil temperature, moisture, and oxygen content) and the decomposition rate is lower because the ratio of degradable carbon compounds such as lignin is high (Lee et al., 2012). However, organic material has a complicated decomposition process and is not easy to use as a fertilizer.
The Rural Development Administration (RDA) developed various organic materials as components of technologies for sustaining crop production systems. First, RDA selected appropriate green manures for the Korean climate and determined appropriate seeding time and rate. Then, they developed the application technology to increase the crop yield. Second, RDA analyzed the nutrient contents of various organic materials and distributed standard manuals for liquid fertilizer or compost according based on the properties of each organic material to farmers. Third, RDA developed an organic fertilizer recommendation system (OFRS) that recommends the appropriate amount of organic material to be applied according to the mineralization characteristics of each organic material and soil nutrient conditions. Here, we describe the RDA study of the smart use of organic materials to increase crop production and environmental sustainability in Korea.
ORGANIC MATERIALS USED FOR TECHNOLOGIES
The cultivation of green manure helps to maintain and improve organic matter in soil, suppress crop pests, supply high quality plant nutrients, and prevent soil erosion. It especially increases the biological activity of soil microorganisms and nitrogen fixation, helping nutrient circulation from sub soils to surface soils, preventing nutrient loss and conserving nutrients.
RDA researchers selected seven kinds of barley as a green manure crop to supply nitrogen, phosphorous, and potassium for organic production of rice. To select the barley varieties, which are a substitute for rye that is imported from foreign countries, they tested several barley varieties as green manure at a national scale. The selection criteria for barley varieties were as follows: high wintering rate, less than 35% C/N ratio at mid-May due to the rice transit period (from the end of May to the beginning of June), rapid decomposition after incorporation into paddy soil, more than 15 Mega grams (Mg) of biomass production per ha. The results showed that seven barley varieties were suitable as a green manure crop in paddy fields: three varieties Youngyangbori, Sangnokbori, and Paldobori in Suwon-si, Gyeonggi province (central and northern regions), four varieties Youngyangbori, Geongangbori, Olbori, and Gwanganbori in Yesan-si, Chungnam province (central and southern regions), and three varieties Gwanganbori, Youngyangbori, and Keunalbori in Daegu Metropolitan city and Naju-si, Jeonnam province.
Other research showed that sowing 60–90 kg of hairy vetch seed per ha 10 days before rice harvesting replaced nitrogen fertilizer in rice paddy fields (Seo et al., 2002). Nutrient contents were analyzed for 57 types of green manures (12 legumes, 8 grasses, 18 wild weeds, and 19 others), and seeding time and seeding rate were determined according to weather conditions and environmental characteristics. For example, Optimal seeding time of hairy vetch is September to October in autumn and Seeding rate is 60 to 90 kg/ha in paddy soil and 30 to 40 kg/ha in upland soil. And optimal seeding time and rate of barley is February to March and 140 kg/ha (Kim, 2013).
Green manure was classified as a legume or non-legume (e.g., grass). Legumes with the ability to fix nitrogen from the atmosphere into soil via rhizobia can provide a large amount of nitrogen to soil, whereas legumes produce less biomass than grasses. Grass has a high biomass and C/N ratio when it is incorporated into soil, which can introduce organic matter into soil and may cause nitrogen starvation in soil. Green manure mixtures can utilize the advantages of each species. RDA researchers investigated legume-wheat mixtures to reduce chemical fertilizers for wheat production. The treatments consisted of five mixtures and two single crops: wheat-crimson clover (wheat 100 kg + crimson clover 10, 30, and 50 kg/ha), wheat-hairy vetch (wheat 100 kg + hairy vetch 20 kg/ha), wheat-crimson clover-hairy vetch (100, 20, and 30 kg/ha), wheat, and crimson clover. Wheat yield increased with increasing crimson clover seeding rate under the no fertilizer condition. The mixture of wheat-crimson clover (100 + 50 kg/ha) gave higher wheat yields than wheat alone (140 kg/ha). The results showed that the crimson clover mixture was good for reducing chemical fertilizer use in wheat production, conserving soil nutrients, and improving physical properties of the soil (Jeon et al., 2012).
In organic farming systems in Korea, fully decomposed composts are used to supply nutrients to plants, improve soil physical properties through soil aggregation, increase water- and nutrient-holding capacity, promote the activity of the microbial population, and suppress soil-borne plant diseases. Compost materials are classified by their nutrient components (Table 2).
Table 2. Compost materials classified by their nutrient components
RDA investigated the long-term effect of rice straw compost on soil organic matter in paddy since 1954. The results showed that rice straw compost treatment (7.5 Mg/ha/year) increased organic matter to 33 g/kg whereas chemical fertilizer (NPK, 110-70-80 kg/ha/year) increased organic matter to 18-20 g/kg under optimum range (25-30 g/kg). In conclusions, rice straw compost improved soil quality more than chemical fertilizer.
RDA investigated the effect of garlic, onion, and ginger by-product composts on crop production. They cultivated tomato using 0, 50, 75, or 100 g of garlic, onion, and ginger by-product composts per pot. Tomato shoot biomass increased in the 75 g of garlic by-product compost treatment and the 50, 75, and 100 g of onion by-product compost treatments. Also, onion and ginger by-product composts exhibited antibacterial activity against tomato wilt, and the ginger by-product compost exhibited antibacterial activity against lettuce stem rot.
It is difficult to supply nutrients at the late stage of growth using compost or green manure. Organic farmers in Korea use liquid fertilizers to overcome this problem that the basal application is insufficient for supply nutrient. Liquid fertilizers not only supply the nutrients needed by plants, but also activate beneficial microorganisms in the soil, and promote rooting (Kai et al., 1990; Elad and Shtienberg, 1994; Park et al., 2001). Since farmers produce organic liquid fertilizers by trial-and-error, they do not produce consistent effects and have some difficulties with consistency of application. Therefore, we developed standards manuals for organic liquid fertilizer production and distributed them to farmers.
Materials used as liquid fertilizers can be classified into organic or inorganic. Organic materials include animal by-products, such as blood meal, bone meal, and fish meal, and plant by-products, such as rice bran and oil cakes. Inorganic materials include mineral resources such as phyllite. In terms of nutrients, materials with high protein content, such as oil cakes, blood meal, and fish meal, are used to supply nitrogen, while materials such as bone meal and rice bran are used to supply phosphorus (An et al., 2012). Table 3 shows the materials used to produce liquid fertilizers by Korean organic farmers.
Table 3. Classification of materials used in farm-made liquid fertilizers
Bone meal liquid fertilizer (BMLF) for lettuce production
Bone meal has high nitrogen (1–3%) and phosphorus (22%) content. Liquid fertilizer made of bone meal shortens the crop node and improves the color and sugar content of fruits. To standardize the production method, we selected yogurt microorganism for fermentation from a choice of commercial microorganisms, yogurt, and rice wine, as the nutrient contents of BMLF with yogurt microorganisms were similar to those in BMLF with commercial microorganisms. We also determined that nitrogen content of BMLF was stable at a ratio of 30% bone meal and 5% molasses. Lettuce productivity increased in both the 500- and 1000-fold diluted BMLF (Table 4).
Table 4. Lettuce yields at 500- and 1000-fold dilution of BMLF with different ratios of molasses.
*BM is bone meal and M is molasses
Fish meal liquid fertilizer (FMLF) for cucumber production
Fish meal with high nitrogen (7–10%), phosphorus (4–9%), and potassium (about 1%) contents were used as feed or fertilizer. In order to standardize the production method, we selected the fermenting microorganism and determined the ratio of fish meal to molasses and investigated the effect of FMLF on cucumber productivity.
Figure 1 shows standardized method of FMLF.
Fig. 1. Standardized production process of fish meal liquid fertilizer (FMLF).
We analyzed the nutrient content of liquid fertilizers that were fermented using dried yeast, yogurt, rice wine, and leaf mold. Dried yeast, which rapidly mineralizes organic nitrogen to inorganic nitrogen, was suitable as a fermenting microorganism and liquid fertilizer was mainly used as an additional fertilizer (Fig. 2). The results showed that FMLF with 20% fish meal was the most effective at supplying nutrients (Fig. 3). We then investigated the effect of 100-fold dilution of 20% FMLF on cucumber growth at 90 days after transplanting. The results showed that FMLF is a good substitute for chemical fertilizer for cucumber production, as growth parameters (Table 5) after application of FMLF were not significantly different from those produced under chemical fertilizer (except total yield), despite the low nitrogen supply (An et al., 2016).
Fig. 2. Change in pH, EC, NH4-N, and P2O5 contents of FMLF fermented using different microorganisms.
Fig. 3. Change in pH, EC, NH4-N, and P2O5 contents of FMLF as a function of the ratio of fish meal to water.
Table 5. Effect of FMLF and chemical fertilizer on cucumber growth and yield at 90 days after transplanting
*FMLF is 100-fold dilution of fish meal liquid fertilizer.
** Same letters were not significantly different in a t-test at the 5% significance level.
Seaweed liquid fertilizer (SLF) for Chinese cabbage production
Seaweed contains a variety of plant hormones, such as auxins and cytokinins, and has beneficial components, such as colloids, amino acids, and mineral components. Plant hormones are known to promote crop growth and beneficial components are known to increase crop yield and improve crop quality.
We composed the standards manual of SLF for organic farmers in Korea and examined the effect of SLF on crop growth (Fig. 4). Among the fermenting microorganisms of dried yeast, yogurt, rice wine, and leaf mold, dried yeast was the most effective for making SLF as it promoted nitrogen mineralization (Fig. 5). Table 6 shows that a combination of 100, 500, or 1000-fold diluted SLF with dried yeast promoted Chinese cabbage growth compared to no fertilizer (An et al., 2015).
Fig. 4. Production process of seaweed liquid fertilizer (SLF).
Fig. 5. Change in pH, EC, NH4-N, and P2O5 contents of SLF fermented using different microorganisms.
Table 6. Effects of SLF on plant weight, leaf length, and number of leaves of Chinese cabbage.
*SLF 100, SLF 500, and SLF 1000 are 100-, 500-, and 1000-fold dilution of SLF, respectively.
** Same letters in a column are not significantly different with duncan’s multiple range test (DMRT) at the 95% significance level.
In addition, we developed technologies for other materials, such as seawater, coffee grounds, chlorella, and compost tea to further develop environmentally friendly agriculture.
ORGANIC FERTILIZER RECOMMENDATION SYSTEM
Various organic materials are used for organic agriculture in Korea. Information on the nutrient content and mineralization rate of each organic material is essential for appropriate nutrient supply from these organic materials. Unlike chemical fertilizers, mineralization of organic materials depends on soil properties, such as temperature and moisture, and on the ratio of degradable carbon compounds, such as lignin. We investigated the nutrient content (Table 7) and mineralization rate of organic materials used for organic farming in Korea considering C/N ratio (Fig. 6) and incubation temperature (Fig. 7) using a laboratory experiment. We then verified the actual mineralization rate and nutrient use efficiency of crops in the field. Finally, we developed the organic fertilizer recommendation system (OFRS) for organic rice. We are currently implementing this system at a national scale.
Table 7. Total nitrogen and carbon content and C/N ratio of organic materials.
Fig. 6. Nitrogen mineralization of organic materials as a function of C/N ratio.
Fig. 7. Nitrogen mineralization of organic materials depending on temperature (20, 25, or 30 °C).
The OFRS recommends the amounts of organic materials that farmers should apply taking account of nutrient content and mineralization of organic materials depending on soil analysis values. The systematic diagram of the OFRS is shown in Figure 8. The OFRS increased rice yields by 96–111% compared to yield before the application of the OFRS, which was 91–98%. Overall, the OFRS increased rice productivity (Fig. 9). The OFRS is serviced in our website, Heug-Toram (http://soil.rda.go.kr) for farmers (Fig. 10).
Fig. 8. Systematic diagram for organic fertilizer recommendation system (OFRS).
Fig. 9. Rice yield index before and after the application of the OFRS. Left bars indicate before application of OFRS and right bars indicate after application of OFRS.
Fig. 10. Example of OFRS in Heug-Toram.
Environmentally friendly agriculture including organic agriculture is increasing in Korea. With politic support, organic fertilizers are becoming more important for crop production, environmental sustainability, and soil conservation. The RDA researched and developed technologies for the smart use of organic materials. This paper introduces some typical organic materials: green manure, compost, liquid fertilizer, and the organic fertilizer recommendation system. Using green manure, it is possible to reduce the use of chemical fertilizers on crops. Also, by intercropping legumes with non-legumes, which merge the benefits of each species, we can achieve a positive effect on crop production, environmental sustainability, and soil conservation. Compost made of agricultural by-products increases crop yields and antibacterial activity and would be useful for agricultural fields. Liquid fertilizers can supply nutrients to growing crops with a long growing period in which the application of green manure or compost is difficult. Our standards manual can be used to improve the quality of both soils and crops by increasing soil beneficial microbial populations. The OFRS is expected to be more convenient for farmers who want to use organic materials, but which are difficult to use effectively because of their characteristics. This will provide a service to farmers nationwide after on-going field demonstrations. RDA will continue to develop environmentally friendly agriculture through studies of the efficient use of organic materials.
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