1 The PhD study was completed at College of Agriculture and Applied Biology, Can Tho University. Scientific supervisor: Prof. Dr. Vo Thi Guong. Reviewer 1:……………………………… Reviewer 2: ……………………………… Reviewer 3: ……………………………… The Doctoral thesis is defensed in front of the Examination Council at University level held in Can Tho University Time:…………………… Date:…………………… This thesis can be found at: 1. Learning Resource Centre of Can Tho University 2. National Library of Vietnam 2 GENERAL INFORMATION 1. Introduction Rambutan and mangosteen orchards are the major fruit orchards with about 2.350 ha at Cho Lach district. Theses fruit are high economic value and high export potential. However the average yield of rambutan and mangosteen was very low which was only about 2.1 and 0.8 tons per ha, respectively. Currently, surface area of these fruit orchards has been reduced dramaticaly due to low yield and low fruit quality. The leaf blight of the rambutant trees and the gamboge disorder of mangosteen fruit is a severely problem which lead to loose remarkable income of farmers. Consequently, farmers have to destroy these fruit orchards and replace by other plants. Finding the solution to improve mangosteen and rambutant fruit yield, better quality, higher benefit return and sustainability production are very essential study to contribution to the social-economic development of the area. 2. Aims of research - To survey and to evaluate soil fertility in terms of chemical and physical and biologicalsoil properties of mangosteen orchard in various age range of raised beds - To evaluate the effect of different organic manure in improvement of soil fertility, fruit yield and and fruit quality of rambutant and mangosteen orchards. - To find the solution for mitigating gamboge disorder of mangosteen fruit and leaf blight of rambutant through water management, balanced inorganic fertilization in combination with organic amendment. 3. Meaning in science and practice 3.1 Meaning in science - Providing scientific data on using compost in combined with balanced inorganic fertilizer in a relatively longterm to improve soil chemical-physical and biological fertility, significantly increasing fruit yield and fruit quality of mangosteen and rambutant orchards. - Organic amendment in combined with covering the soil surface with plastic sheet resulted in significantly decrease gamboge disorder ratio on mangosteen fruits. - Providing scientific data on improvement of leaf blight of rambutant. A combination of balanced N and K fertilizer and compost led to reduce remarkly leaf blight ratio on rambutan orchards in comparision with farmers’ practice with a low K/N ratio. 3.2 Meaning in practice Providing scientific information on the soil degradation in terms of physical, chemical and biological aspects of mangosteen and rambutan orchards with the ages of raised beds over 20 years,. The research results indicated the important role of organic amendment in improvement of soil constraints, enhancement of productivity, fruit quality and economic return of mangosteen and rambutan orchards. A combination of organic amendment and proper soil moisture management led to mitigating of gamboge disorder of mangosteen fruits. 3 Whilst, an application of organic fertilization combined with balanced K and N fertilizers resulted in significantly reduce rambutants’ leaf blight. This management practices have contributed to significant increase in fruit yield, economic value and farmers’ income. These results need to be recommended to farmers for improving the cultivation technique to obtain sustainable and higher economic efficiency of mangosteen and rambutan cultivation. 4. New findings of the research The degradation of raised bed soils of mangosteen orchards with the age of over 20 years. The soil was very acidic with the mean pH value of 3.5. Soil chemical properties such as soil organic matter, exchangeable cations (Ca, Mg and K), avalible N and P were very poor. Soil micro-organism activities were very low. Also, soil physical properties such as water capacity and structural stability were low. For mangosteen soil, an application of 22.5 kg of organic fertilizer per plant in combination with balanced inorganic fertilizers resulted in improving of soil degradation and increase fruit yield significantly. The practice for mitigation of gamboge disorder of mangosteen was highly effective. It led to decrease about 45% of gamboge disorder of mangosteen through applying organic and balanced inorganic fertilizers and covering the soil surface with plastic in rainy season (the rate of gamboge disorder decreased from 64% to 19%) and consequently increase fruit yield significantly. With respect to rambutant orchards, application of 18kg of organic fertilizers in the form of sugarcane filter mud, biogas sludge, Ox-eyes daisy compost resulted in improving of soil fertility in terms of physical, chemical and biological aspects. Soil chemical properties such as pH, organic matter, percentage of base saturation increased significantly. Soil physical properties such as structural stability, water holding capacity and hydraulic conductivity also increased significantly. Biological activity remarkably increased though increase in enzyme catalase content in the soil. Application of organic fertilizer provided a significant increase in rambutan yield compared with farmer’s fertilization or only application of inorganic fertilizers. Application of inorganic fertilizers with a K/N rate between 0.9 and 1.3 combined with 18 kg of organic fertilizer per plant helped reduce 60% of leaf blight rate of rambutan. The benefit return obtained from cultivation of magosteen and rambutan was highest when applying sugarcane press mud, biogas sludge in combination with balanced inorganic fertilizers. 4 CHAPTER 3: METHODOLOGY The research was carried out since March 2009 to August 2012 on four experimental orchards. The contents of the research are presented generally through a diagram in Fig. 3.1. Figure 3.1: Schematic prepresentation of the research contents Object and scrope of the research Object of the research: The research focused on mangosteen and rambutan orchards at Long Thoi, Son Dinh, and Phu Phung Commune, Cho Lach District, Ben Tre Province, and the soil properties of these orchards. Scope of the research: - Survey and evaluate farming practices of local farmers and factors that cause gamboge disorder of magosteen and leaf blight of rambutan. - Analyse and evaluate soil quality of orchards with different age of raised beds. - Evaluate the effects of the improvement of magosteen and rambutan soil fertility in terms of chemical, physical and biological aspects - Applying balanced inorganic fertilizer in combination with organic fertilizer types in the form of biogas sludge, sugarcane press mud, Perionyx excavatus’ manure, and Sphagneticola trilobata compost in order to improve soil fertility, enhance fruit yield and quality. Applying organic fertilizer, together with coverage of the tree foots with plastic aimed to reduce gamboge disorder of mangosteen and leaf blight of rambutan. Trial (1): Applying organic fertilizer to improve soil fertility and fruit yield Surveying orchard soil properties and gamboge disorder in mangosteen MANGOSTEEN Improving soil quality and enhancing fruit yield and quality in mangosteen and rambutan orchards RAMBUTAN Trial (2): Reducing gamboge disorder and enhancing fruit yield Surveying leaf blight desease of rambutan Trial (4): Applying organic fertilizer to improve soil fertility, fruit yield and qualtity Trial (3): Applying organic fertilizer and K fertilizer to prevent rambutan leaf blight and improve fruit yield 5 A. RESEARCH ON MANGOSTEEN 3.1.1 Methodology The surveyed households had cultivated land area of 0.3 ha or more. Mangosteen tree was in the age of giving fruits. Studied orchards were divided into four types based on the age of raised beds: (i) below 20 years; (ii) between 20 and 40 years; (iii) orchards with the cultivated duration between 40 and 60 years; and (iv) above 60 years. 3.2 Estimation of the effects of organic amendent on the improvement of soil fertility and magosteen fruit yield. Aim of experiment: Based on the survey and estimation of soil quality of mangosteen orchard, experiment was carried out to aim at improving soil fertility and fruit yield of mangosteen. Experimental design: The experiment was laid out in a randomized complete block design (RCB) with 5 fertilizer treatments and 4 replications per treatment. The mangosteen orchard which was experimented had been cultivated over 50 years and had the age of raised beds of 65 years. This orchard had low productivity. The experimented soil belonged to developing alluvial soils and was categorized as Endo Protho Thionic Gleysols according to the soil classification system of FAO-UNESCO. The potential acidity of the soil was medium. The treatments of the experiment are the followings: Treatment 1 (control treatment): Farmer’s inorganic fertilizer dose (1.8 kgN + 1.8 kgN + 2.0 kgP 2 O 5 + 0,02 kg K 2 O.plant -1 ) Treatment 2: Recommended balanced inorganic fertilizer dose (1.6 kgN + 1.5 kgP 2 O 5 + 2.2 kg K 2 O.plant -1 ). Treatment 3: 22.5 kg of Sphagneticola trilobata compost/plant + recommended dose in treatment 2 Treatment 4: 22.5 kg of Perionyx excavatus’ manure/plant + recommended dose. Treatment 5: 22.5 kg of sugarcane press mud/plant + recommended dose Treatment 6: 22.5 kg of biogas sludge/plant + recommended dose The improvement of soil fertility and fruit yield and economic efficiency were analysed and evaluated in the third crop after 3-year application of organic fertilizers. 3.3 Effect of organic amendment and plastic coverage on soil fertility, yield and gamboge disorder of mangosteen fruits. Aim of experiment: The experiment was done to aim at (i) evaluating properties of mangosteen orchard soil and gamboge disorder status of mangosteen fruits, and (ii) studying methods for mitigating gamboge disorder of mangosteen fruits and improving fruit yield through supplying nutrients and adjusting soil moisture. Experimental design: The experiment was laid out in a randomized complete block design (RCB) with 5 treatments which one included two plants and 3 replications per treatment. The treatments of the experiment are the followings: 6 Treatment 1 (control treatment): Farmer’s dose (0.4 kgN + 0.22 kgP 2 O 5 + 0.02 kgK 2 O/plant); without covering the soil surface with plastic. Treatment 2: Inorganic fertilizer dose (1.5 kgN + 1.0 kgP 2 O 5 + 2.2 kgK 2 O./plant) + 14,4 kg/plant of biogas sludge; without covering the soil surface with plastic Treatment 3: 28.8 kg of biogas sludge/plant; without covering the soil surface with plastic. Treatment 4: Farmer’s dose + covering the soil surface with plastic at the onset of rains Treatment 5: Inorganic fertilizer dose (1.5 kgN + 1.0 kgP 2 O 5 + 2.2 kgK 2 O./plant) + 14,4 kg of biogas sludge/plant; without covering the soil surface with plastic Observed parameters - Initial samples: Before fertilization, soil samples were collected to analyse some of soil physical and chemical properties, such as soil pH - Mid-cropping samples: After applying organic fertilization for three months, soil samples were taken to analyze the following properties: pH, organic matter, available nitrogen, phosphorus and potassium and exchangeable Ca, Mg, bulk density and soil structural stability. - Fruit yield: Fruits were weighted to determine fruit yield at every harvet. - Economic efficiency from application of organic fertilizer and balanced inorganic fertilizer was analyzed. - Soil water content was determined once a week since the soil surface was covered with plastic. - For calculation of gamboge disorder percentage, on each tree 20 fruits were uniformly randomly harvested in four directions of the canopy. Then the number of fruits with gamboge disorder was counted. The percentage of gamboge disorder of mangosteen is calculated as the following: B. RESEARH ON RAMBUTAN 3.4. Experiment on evaluation of effects of organic and K fertilizer on the mitigation of leaf blight of rambutan and improvement of fruit yield. 3.4.1 Suveying leaf blight status of rambutan Eighteen orchards from two different land regions (riverine land and mound) were involved in the survey. Parameters relevant to cultivation were observed including the rate of inorganic and organic fertilizer, K/N ratio of the fertilizer which farmers used. The relationship between K/N ratio and the degree of leaf blight of rambutan was also evaluated. In order to evaluate the degree of leaf blight, three orchards per each commune were chosen and in each orchard choosing randomly three plants and on each plant collecting 120 leaves contributed uniformly in four directions. The number of leaves getting leaf blight was counted relying on visual 7 obersivation. The degree of leaf blight is divided into three levels consisting of strong, moderate and light level accoding to Le Van Be (2006). Table 3.1 represents different degrees of leaf blight. Table 3.1 Assessment of leaf blight degree of rambutan Level The number of leaves getting leaf blight in percentage 0 < 10% of total leaves 1 10 - 30% of total leaves 2 > 30 - 50% of total leaves 3 > 50% of total leaves 3.4.3 Evaluation of the practice for the improvement of leaf blight of rambutan Aim of experiment: The field experiment of application of organic and K fertilizer with various K/N ratios was carried out to aim at mitigating leaf blight status of rambutan, improving soil quality and rambutan fruit yield. Experimental design: The experiment was established at Son Dinh Commune, Cho Lach District on a rambutan orchard with the garden’s age of 12 years and the raised beds’s age of 20 years. Rambutan trees did not grow well which provided low yield and low fruit qualtity. The leaf blight percentage was high. The research soil lies on high landscape and belonged to developing alluvial soil types with medium potential acidity. The soil was categorized as Endo Protho Thionic Gleysols according to FAO-UNESCO (2006). The experiment was laid out in a randomized complete block design (RCB) with 5 treatments which one included two plants and 3 replications per treatment. Treatment 1 (Control treatment): Farmer’s dose with the K/N of 0.1 (2.0kgN + 3.0kgP 2 O 5 + 0,2 kgK 2 O per plant) Treatment 2: Farmer’s dose with the K/N of 0.1 (2.0kgN + 3.0kgP 2 O 5 + 0.2kgK 2 O per plant ) + 18 kg of biogas sludge per plant Treatment 3: Farmer’s dose with the K/N of 0.9 (1.4kgN + 1.0kgP 2 O 5 + 1.3kgK 2 O per plant) + 18 kg of biogas sludge per plant Treatment 4: Farmer’s dose with the K/N of 1.2 (1.4kgN + 1.0kgP 2 O 5 + 1.7kgK 2 O per plant) + 18 kg of biogas sludge per plant Treatment 5: Farmer’s dose with the K/N of 1.3 (1.4kgN + 1.0kgP 2 O 5 + 1.8kgK 2 O per plant) + 18 kg of biogas sludge per plant Observed parameters Potassium content in leaves and soil was analysed. The leaf samples were taken according to four degrees of leaf blight on different orchards which was gotten leaf blight. On each tree, four branches were taken to determine green leaf area and count the number of leaves getting leaf blight to evaluate the degree of leaf blight. 8 At the harvest, fruit yield was recorded and economic return was calculated. 3.5. Effect of organic fertilization on the improvement of soil fertility and yield and quality of rambutan fruits. Experiment was established to evaluate the improvement of soil fertility and fruit yield and quality. Plants of the experimented orchard were grown for 17 years and the raised beds were established for 20 years. Under the SANSED project which experiments were carried out for tree crops before, the experiment was continued from the fouth and fifth crop. Aim of research The experiment was done to aim at evaluating the effects of organic amendment on the improvement of soil quality and yield and quality of rambutan fruits. Experimental design The experiment was designed in a randomized complete block design (RCB) with five treatments of fertilizer and three replications per treatment. Each treatment had an area of 30 m 2 and consisted of two plants. The studied soil was categorized as Endo Protho Thionic Gleysols according to FAO- UNESCO (2006). Organic fertilizer amount used for the experiment was 18 kg per plant equivalent to 3.6 tons per ha. The treatments of the experiment are the followings: Treatment 1: Farmer’s dose (2.2 kgN +1.5 kgP 2 O 5 + 0,3 kgK 2 O per plant). Treatment 2: 18 kg of sugarcane press mud per plant + (1.5 kgN + 1.0 kgP 2 O 5 + 1.7K 2 O per plant). Treatment 3: 18 kg of biogas sludge per plant + (1.5 kgN + 1.0 kgP 2 O 5 + 1.7 kgK 2 O per plant). Treatment 4: 18 kg of Perionyx excavatus’ manure per plant+ (1.5 kgN + 1.0 kgP 2 O 5 + 1.7 kgK 2 O per plant). Treatment 5: 18 kg of Sphagneticola trilobata + (1.5 kgN + 1.0 kgP 2 O 5 + 1.7 kgK 2 O per plant). Observed parameters Soil samples were taken at harvest of the fifth crop to analyze physical, chemical and biological properties. At harvest, about 4 kg of fruits were collected per each plant. Fruits were equally harvested in four different directions of the canopy. Then the number of fruits per kg unit was counted. Assessment of fruit quality: 30 fruits per plant were collected to assess the brix (sugar content) of pulp, and weight of pulp. Nutrients in pulp such as Pb, Zn and K were also analysed. Economic return or efficiency was calculated. 3.7. Method of soil analysis Chemical properties: pH, NH 4 + and NO 3 - , easily decomposed organic N, available P, organic matter, exchangeable cations (Ca, Mg and Na), Zn, CEC and base saturation. Physcial properties: Bulk density, structural stability and available water content. 9 Biological properties: Microbiological population was determined by counting the number of colonies grown in the environment of agar. The intergated environment TSA (Trypon Soya Agar) was used to qualtify the total population of microorganisms in the soil. The Hutchinsion-Clayton environment supplied with 1% CMC (Carboxyl Methy Cellulose) was used to grow and quantify the population of microorganisms which are capable of decomposing cellulose (Subba Rao, 1984 và Ulrich và ctv., 2008). Activity of enzym catalase in the soil was determined by standardized method of Drawgan- Bularda (2000), while enzyme β-Glucosidase was determined by the color testing method of Eivazi and Tabalabai (1988) with the substratum p-nitrophenyl- β glucopyranoside (PNG 0,05 M). 3.10. Content of nutrients in organic fertilizer Nutrient content of various types of organic materials are presented in Table 3.2 Table 3.2 : Content of nutrients in organic materials Organic material Nutrient content (%) N P 2 O 5 K 2 O CaO MgO C Biogas sludge 1.45 0.55 0.36 0.06 0.27 37.0 Sugarcane press mud 1.90 2.50 0.34 0.35 0.27 29.8 Perionyx excavatus’ manure 0.60 0.21 0.81 0.003 0.34 5.4 Sphagneticola trilobata (3-day compost) 0.76 0.36 0.11 0.025 0.22 13.9 3.11. Data analysis Experimental and surveyed data were arranged by using Microsoft Excel programme and analyzed using statistical programme SPPSS version 11.5. The ANOVA was used to compare the diference among treatments. Grapths and tables were made in Excel. 10 CHAPTER 4: RESULTS AND DISCUSSION A. STUDIED RESULTS ON THE MANGOSTEEN ORCHARD 4.1 The general information on mangosteen orchards In Cho Lach district, the mangosteen orchards that were between twenty and forty years old accounted for 40%, whilst the younger orchards (below twenty years old) accounted for 9% of the total orchards in the region. It was about 60% of fruit orchards that were grown between 20 and 60 years. However, there were orchards that have been grown between twenty and seventy years. The cultivation technique that used excessive and unbalanced inorganic fertilizers resulted in low yield and gamboge disorder of mangosteen which occurred mainly on the younger ones (below 20 years old) and between June and August of the year.The soil quality was low which was indicated through low pH, poor in organic matter and nutrients, low in activities of microorganisms as well as water holding capacity and structural stability. Based on the surveyed results above, the experiment was carried out to aim to aim at investigating the effects of organic fertilizer on the improvement of soil properties, mangosteen yield and mitigation of gamboge disorder of mangosteen 4.2. The efficiency of organic amendment on soil properties and mangosteen yield. The research results showed that the obvious effect of organic fertilization on the improvement of soil fertility was indicated in the fourth crop. Also, the research results suggested that application of organic fertilizer helped in improving soil pH, increase organic matter, promoting the supply of available nutrients such as available N, exchangeable K and Ca (Figure 4.4; 4.5; 4.6; 4.7; 4.8 and 4.9), and increasing cation absorption capacity and base saturation (Figure 4.11 and 4.12). The most effective of organic amendment was found in the treatment applied with sugarcane press mud and biogas sludge. Figure 4.4: Effect of organic fertilizer on soil pH [...]... (levels of disease) Treatments Exchangeable K (cmol/kg) The scorched leaf area (%) Levels of disease Treatment 1 1,00b 79,58a Level 3 Treatment 2 0,99b 46,24b Level 2 Treatment 3 1,43a 22,33c Level 1 Treatment 4 1,47a 22,16c Level 1 Treatment 5 1,77a 18,95c Level 1 CV (%) 16,21 11,80 Treatment 1 (Control): Farmer’s dose 1 (K/N = 0.1) (2.0 kg N + 3.0 kg P2O5 + 0.2 kg K2O) per plant; Treatment 2: Farmer’s... fertilizers treatment on rambutan orchards (Unit:1,000 VND) Treatment Content Treat 1 Treat 2 Treat 3 Treat 4 Treat 5 Total expenses (ha/year) 24,714 34,448 30,263 31,863 32,263 Yield (kg/plant) 40.67 54.5 73.33 78.33 78.33 21 Price 8 8 8 8 8 200 200 200 200 200 Goss value (ha/year) 65,072 87,200 117,328 125,328 125,328 Profit (ha/year) 40,358 52,753 87,065 93,065 Plant number/ha 93,465 Treatment 1... efficiency for treatments are presented in Table 4.7 Calculated resuts showed that a combied application of organic fertilzier and balanced inorganic fertilizer, together with covering the soil surface with plastic resulted in very high benefit for gardeners 18 Table 4.7: The economic efficiency for each treatment in mangosteen orchard (Unit: 1,000 VND) Contents Treat 1 Treat 2 Treat 3 Treat 4 Treat 5 Total... (ha/year) 2,186 Notes: Number of trees: 250 trees/ha; Fruit yield = Fruit weight per tree x number of trees per ha Treatment 1: Farmer's dose (0.4kgN + 0.22kg P2O5 + 0.02kg K2O/plant, without mulching of the soil surface by plastic cover; Treatment 2: 14.4kg of biogas sludge + (1.5kgN + 1.0kg P2O5 + 2.2kg K2O/plant), without mulching of the soil surface by plastic cover; Treatment 3: 28.8kg of biogas,... yield compared with the control treatment Figure 4.13: Efficiency of organic fertilizers on mangosteen yield improvement Treatment 1 (Control treatment): Farmer’s dose (1.8 kg N + 2.0 kg P2O5 + 0.02 kg K2O/plant); Treatment 2: Recommended dose (1.6 kg N + 1.5 kg P2O5 + 2.2 kg K2O/plant); Treatment 3: 22.5kg of Sphagneticola trilobata compost/plant + recommended dose; Treatment 4: 22.5kg of Perionyx... farmer’s fertilization (Treatment 1), recommended fertilization (Treatment 2) provided higher profit and increased by 134% Whilst, the profit of the biogas sludge amendment (Treatment 6) increased by 162% in comparison with the recommended fertilization (Treatment 2) Especially, biogas slude amendment (Treatment 6) could result in an increase in profit by 218% compared with the control (Treatment 1) or without... long-term (Revees và ctv., 1997; Anne và ctv., 2006) 26 Figure 4.40: Effectiveness of organic fertilizer on the fruit yield Treatment 1: Farmer’s dose (2.2 kg N +1.5 kg P2O5 + 0.3 kg K2O) per plant; Treatment 2: 18kg of sugarcane press mud per plant + (1.5 kg N + 1.0 kg P2O5 + 1.7kg K2O) per plant; Treatment 3: 18kg of biogas sludge per plant + (1.5 kg N + 1.0 kg P2O5 + 1.7 kg K2O) per plant; Treatment 4:... (Control): Farmer dose 1.8 kg N + 2.0 kg P2O5 + 0.02 kg K2O/plant); Treatment 2: Recommended dose (1.6 kg N + 1.5 kg P2O5 + 2.2 kg K2O/plant); Treatment 3: 22.5kg of Sphagneticola trilobata compost + Recommended dose Treatment 4: 22.5kg of Perionyx excavatus’ manure + Recommended dose; Treatment 5: 22.5kg of sugarcane press mud + Recommended dose; Treatment 6: 22.5kg of biogas sludge +Recommended dose Urea... soil CEC Treatment 1(Control): Farmer’s dose (2.2 kg N +1.5 kg P2O5 + 0.3 kg K2O) per plant; Treatment 2: 18kg of sugarcane press mud per plant + (1.5 kg N + 1.0 kg P2O5 + 1.7 K2O) per plant; Treatment 3: 18kg of biogas sludge per plant+ (1.5 kg N + 1.0 kg P2O5 + 1.7 kg K2O) per plant; Treatment 4: 18kg of Perionyx excavatus’ manure per plant + (1,5 kg N + 1,0 kg P2O5 + 1,7 kg K2O) per plant; 24 Treatment... year showed that among treatments, the biogas slude treatment had the highest yield which was significantly different from that of the other treatments and increased by 35 to 40% compared to that of the control treatment (Fig 4.40) Besides, application of sugarcane press mud and Perionyx excavatus’ manure resulted in a significant increase in fruit yield compared to the control treatment At the harvest . Table 4.7: The economic efficiency for each treatment in mangosteen orchard (Unit: 1,000 VND). Contents Treat 1 Treat 2 Treat 3 Treat 4 Treat 5 Total expenses (ha/year) 9,100 36,040. design (RCB) with 5 treatments which one included two plants and 3 replications per treatment. The treatments of the experiment are the followings: 6 Treatment 1 (control treatment): Farmer’s. 2,186 26,657 13,162 16,275 57,071 Notes: Number of trees: 250 trees/ha; Fruit yield = Fruit weight per tree x number of trees per ha Treatment 1: Farmer's dose (0.4kgN + 0.22kg P2O5