STUDIES ON RECYCLING USE OF ORGANIC WASTES FOR SUSTAINABLE AGRICULTURE IN VIETNAM ベトナム農業の持続的発展のための有機性廃棄物リサイク ル利用に関する研究 2018, September HOANG THI QUYNH Graduate School of Environmental and Life Science (Doctor’s Course) OKAYAMA UNIVERSITY CONTENTS ACKNOWLEDGEMENTS. ii LIST OF TABLES. vi LIST OF FIGURES. EFFICACY OF COMPOSTED ORGANIC WASTES WHEN APPLIED IN CONCERT WITH CHEMICAL FERTILIZER .2 Materials and Methods .3 Sampling and analysis .3 Results and Discussion .1 Effect of compost on crop productivity.2 Dynamics of compost-N amended soil.
“ORGANIC FERTILIZERS” IN VIETNAM .2 Materials and Methods .1 Sampling and chemical analysis .2 Investigation of the flow of raw materials and manufacturing process of an “organic fertilizer” .3 Results and Discussion .1 Characteristics of “organic fertilizers” .2 Production method of an “organic fertilizer” from coffee by-products .3 Effects of “organic fertilizers” on plant growth and N leaching .4 Conclusions and Implications. RAPID ON-FARM COMPOSTING OF COFFEE BY-PRODUCTS AND ITS USE AS A FERTILIZER .2 Materials and Methods .1 Coffee by-products and bulking agent .3 Sampling and analysis .1 Physicochemical properties of finished composts .2 Effects of the composts application on plant growth .1 Quality of finished composts .2 Applicability in Vietnam. IMPLICATIONS AND FURTHER WORK. 71 ACKNOWLEDGEMENTS First and foremost, I would like to express my sincere gratitude to my supervisor Professor Shima Kazuto for his guidance and support.
My sincere thanks also goes to my co-supervisor, Professor Keiji Sakamoto and Professor Muneto Hirobe. In addition, I am very grateful to the Japanese Ministry of Education, Culture, Sports, Science, and Technology (MEXT) for giving a scholarship to conduct the study. I am also grateful the Research Grant for Encouragement of Students, Graduate School of Environmental and Life Science, Okayama University, Japan for supporting in my publications. I would like to thank the anonymous reviewers, the editors and colleagues for their valuable comments on my manuscripts.
Thanks all lab-mates of the Laboratory of Environmental Soil Science, Okayama University for their help in doing experiments and emotional support. Special thanks go to Mr. Vo Trung Tin, the director of Hope Land Vietnam Co., ltd for his strongly support in the consultation and survey in Lam Dong provice, Vietnam. Thanks to all those who have helped me directly and indirectly in the successful completion of my study.
Last but not least, I would like to thank my beloved family for their immeasurable support and love. Thank you very much! Okayama, 2018 Hoang Thi Quynh. I ABSTRACT The use of recycled organic wastes as fertilizer has gained attention because of a variety of reasons. Among others, the need to find a sink for the growing amount of wastes and the necessity to reduce soil exposure to degradation and other negative effects of the use of conventional chemical fertilizers, are the factors that are most crucial.
In Vietnam, different kinds of fertilizers that are labeled as “organic fertilizer” are available; however, as the raw material and manufacturing process are poorly regulated, their quality has yet not been fully explored. Organic fertilizer has the potential to improve the physico-chemical properties of the soil and minimize groundwater contamination by nutrient leaching. Under the Asian monsoon climate, loss of applied N due to leaching is excessive due to the high frequency of heavy rainfall. In order to promote the use of recycled organic wastes as fertilizer in Vietnam, the objectives of this dissertation are three-fold: (1) to evaluate organic waste-based fertilizers with an emphasis on the nitrogen dynamics of the plant-soil system, (2) to demonstrate an on-farm rapid composting method, and (3) to make suggestions regarding the recycling of organic waste and the utilization of organic fertilizers under humid tropical climates.
To clarify the efficacy of composted organic wastes as fertilizer, a cultivation experiment using the technique of 15N labeling was conducted in sandy loam-textured soil in a greenhouse. Composted municipal solid waste (MSW), sewage sludge (SS), and cow dung (CD) were applied as the basal fertilizer, while 15N labeled urea was applied 4 weeks after planting, as an additional fertilizer. There were no significant differences in the shoot dry weight among the MSW, SS, and chemical fertilizer treatments. The uptake of N from the compost by the plants was as follows: MSW (39.0% of the N derived from the urea-N fertilizer was assimilated by the plants.
Approximately two-thirds of the urea-N II fertilizer was lost by leaching while half of the N derived from the compost remained in the soil after 14 weeks of cultivation. As the efficacy of the compost might depend on the type of raw material and composting technique, the following investigations were carried out to verify the effects of these factors on the quality of the finished compost. To investigate the quality of the “organic fertilizers” which are being sold in Vietnam’s markets, 16 products (12 domestic and 4 imported) were acquired from 4 provinces of Vietnam. On these fertilizers, the nutrient contents were analyzed and experiments were conducted.
A 20-day incubation experiment involving 80 g sandy-textured soil mixed with the fertilizer at a rate of 109.4 mg N kg−1 soil was performed in 150 cm3 glass bottles at 25°C in the dark. In addition, komatsuna (Brassica rapa var. perviridis) was cultured in sandy-textured soil using some typical “organic fertilizers” applied at a rate of 200 mg N kg−1 soil in a greenhouse. The nutrient content greatly varied among the domestic products, whereas there were some similarities observed between the imported products.
Two-thirds of the domestic products contained over 30% of the total N in the inorganic form, implying that the concentration of the inorganic N dramatically increased in some products rather than in their supposed raw materials. The remarkably high ratio of the inorganic N to the total N was attributed to the excessive N leaching from the soil by the application of domestic fertilizers. As the product label contained insufficient information and therefore, the comparison could not be drawn between the commercial products and the raw materials. To clearly explain the characteristics of domestic “organic fertilizers,” we further studied the production of one such “organic fertilizer” made from coffee by-products (the discarded shells of the cherries in the coffee processing industry).
The stages involved in the production were composting, the addition of extra soil as a bulking agent and the mixing-in of chemical substances to increase the nutrient content. The analysis of the nutrient levels of the collected samples at each stage indicated that III the coffee by-products were nutrient-rich organic material. The total C content was high, up to 423.2 g kg−1, and the N and K contents were 32. After composting, a slight decrease was observed in the C content but the concentration of the total N and K showed an increase.
The compost was found to contain 34.8 g kg−1 of N and 12. After increasing the bulk of the compost with extra soil, the total C, N, and K contents reduced to 83. However, at the time of shipment, it was observed that the total N content nearly doubled from 6.20 g kg−1, while the total P content tripled from 0. These observations provide evidence to confirm that the addition of chemical material is typically the final step in the production of organic waste-based fertilizers in Vietnam.
Moreover, being the second largest coffee-producing country worldwide, Vietnam is estimated to generate approximately 1 million m3 of coffee pulp (coffee by-products of wet processing) annually. Instead of being effectively utilized in the form of recycling resources, most of the waste is discarded, causing serious environmental pollution even though it contains essential macronutrients in high concentrations. This large volume of organic waste is mainly generated during the months of the harvesting season. Additionally, it is difficult to store this material because of its high moisture content.
On the other hand, for a long time, farmers have mainly used chemical fertilizers instead of organic fertilizers, resulting in soil degradation. Therefore, a simple method of rapid on-farm composting is the need of the hour to establish a system for recycling organic waste for sustainable agriculture. Five on-farm small-scale composting trials of coffee pulp were performed to examine the feasibility of the composting process with bulking agents under different aerobic conditions. After 2 months of composting, samples were collected for analysis and a cultivation experiment was conducted to clarify the effectiveness of the composts.
The total C, N, and K contents of the composts were in the range of 340. In the compost where wood chips were used as the bulking agent under air flow, exhibited a concentration of inorganic N that was significantly higher than that of the other composts. This indicates that the most important factor influencing the composting process is the control of aeration with wood chips and air flow. The plant biomass corresponding to the composts showed similarity with chemical fertilizers.
Additionally, the fertilizer effect depended on the type of soil. Furthermore, the P content and the plants produced by the compost in which chicken manure was added, were investigated. The results obtained clearly indicate that the addition of P-sources as manure in the manufacturing process enhanced the fertilizing efficiency of the compost. However, replications were not included in separate composting trials; thus, further work is required to understand the optimum conditions of composting.
These results suggest the need for quality criteria and guidelines for organic fertilizers in Vietnam that not only specify the nutrient levels, but also control the raw materials used and the manufacturing process. Production of coffee pulp composting within 2months might be a feasible method to recycle coffee pulp into good-quality organic fertilizer. The majority of N in the self- make compost was in the organic form, requiring an enhancement to make it available to plants. In this regard, urea might have a role to play in enhancing the N mineralization of organic-N in compost when applied together.
Under humid tropical climates, a combined application of compost and urea with lower amount of applied urea might extend the benefits. Further field experiment is required to evaluate the effectiveness of this suggestion. V LIST OF TABLES Table 2.1 Chemical properties of the materials.1 pH and nutrient contents (g kg-1) of soil used in the cultivation experiment.2 pH, C: N ratio and concentration of other nutrients in the so-called organic fertilizers in Vietnam's markets.3 General available information on collected samples.4 Changes in the nutrient levels during the production of the “organic fertilizer”.5 Two-way analysis of variance (ANOVA) testing the effects of fertilizer type and nutritional supplementation on dry weight of plants.6 Two-way analysis of variance (ANOVA) testing the effects of fertilizer type and nutritional supplementation on N uptake.7 Two-way analysis of variance (ANOVA) testing the effects of fertilizer type and nutritional supplementation on P uptake.8 Dry weight and nutrients uptake of treatments.1 Moisture content (%) and nutrient content (g kg-1) of the materials.2 Materials and condition of composting trials.3 pH and nutrient content of soils used in the cultivation experiment.4 pH and nutrient content of finished composts influenced by composting trials.5 Two-way analysis of variance testing the effects of soil types and applied fertilizers on dry weight of plants. VI LIST OF FIGURES Fig.1 The nitrogen cycle and human management of soils Fig.2 An outline of the thesis Fig.1 A diagram of the experimental setup.2 A picture of the cultivation system.3 Changes in shoot length at the first harvest as influenced by different treatments.4 Shoot dry weight as influenced by different treatments.5 N dynamics of basal fertilizer (Basal) and additional fertilizer (Add.) as influenced by different treatments.1 N content of “organic fertilizers” in Vietnam's markets.2 P content of the “organic fertilizers” in Vietnam's markets.3 K content of the “organic fertilizers” in Vietnam's markets.4 Relationship between total N and P of the “organic fertilizers”.5 Flow of raw materials and production method of an “organic fertilizer” from coffee by- products.6 Correlation between N leaching and ratio of inorganic N to total N in the fertilizers.7 Relationship between dry weight of plants and N leaching Fig.1 Schematic diagram of the composting system.