Sumary of agricultural doctoral thesis: Studying on potassium nutrient balance for sugarcane in Lam Son sugarcane belt Thanh Hoa province

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Aims of the research: Setting an equation to determine the amount of K fertilizers apllied for sugarcane based on a nutrient balance, creating background knowledges for a sustainable management of K for each specific area, contributing to improve productivity, quality and efficiency of cane production in Lam Son hilly regions of Thanh Hoa.

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Nội dung Text: Sumary of agricultural doctoral thesis: Studying on potassium nutrient balance for sugarcane in Lam Son sugarcane belt Thanh Hoa province

MINISTRY OF EDUCATION AND TRAINING – MINISTRY OF AGRICULTURE AND RURAL DEVELOPMENT VIETNAM ACADEMY OF AGRICULTURAL SCIENCES PHAM THI THANH HUONG STUDYING ON POTASSIUM NUTRIENT BALANCE FOR SUGARCANE IN LAM SON SUGARCANE BELT THANH HOA PROVINCE Major: Soil Science Code : 62.62.01.03 SUMARY OF AGRICULTURAL DOCTORA L THESIS HA NOI, 2014
STUDIES RELATED TO THE RESEARCH 1. Pham Thi Thanh Huong, Đang The Giang (2009), “The sugarcane production at Lam Son sugarcane belt Thanh Hoa province” Journal of soil sciences No.31 in 2009. 2. Pham Thi Thanh Huong, Tran Cong Hanh, Nguyen Van Bo, (2013), “Potassium supply capacity of grey soil (Haplic Ferralic Acrisols) to sugarcane in Lam Son sugarcane area Thanh Hoa Province", Journal of Agriculture and Rural Development, No. 20 in 2013. 3. Pham Thi Thanh Huong, Tran Cong Hanh, Nguyen Van Bo (2013), “Efficiencies of potassium application to sugarcane on gray soil (Haplic Ferralic Acrisols) in Lam Son sugarcane area Thanh Hoa Province", Journal of Agriculture and Rural Development, No. 21 in 2013.
Thesis completed at: VIETNAM ACADEMY OF AGRICULTURAL SCIENCE Advisor: 1. Associated Prof. Dr. Nguyen Van Bo 2. Dr. Tran Cong Hanh Examinant 1: Examinant 2: Examinant 3: The thesis was defended at the council of institute level: Vietnam Academy of Agricultural science At h date month year Thesis can be found at library: National library of Vietnam Library of Vietnam Academy of Agricultural science
1 INTRODUCTION 1. Rationale of the research Sugarcane (Saccharum officinarum L.) originated from tropical region, has a high yield potential, a wide adaptation range, and has been identified as a crop that has competitive advantages over the drought condition of upland region Among factors that contribute to increases in yield and quality of sugarcane, macro nutrients like nitrogen (N), phosphorus (P), potassium (K) play an important role. K is an element that sugarcane absorbs the most and has an active influence to most physiological and biochemical processes occur in cells especially in the synthesis, transport and sugar accumulation processes. However, the level of response to K fertilizer of sugarcane has large fluctuations depending on climate, soil, sugarcane varieties, farming techniques and the interactive relationship between K with other nutrients. Unlike N and P, sugarcane has a lavish spending phenomenon on K. On the other hand, K deficiency symptoms are often not immediately evident in case of K loss by erosion, leaching or fixation. The needs to supply K are often only apparent after a few no-fertilized crops or the K supply is not ecnough to compensate the K loss by crop harvesting, as K reserves in the soil are reduced to the "impoverishment" level. Thus, excess or deficiency of fertilizer or fertilizer K will result in a decrease in the production efficiency of sugarcane. Sugarcane area Lam Son (Thanh Hoa province) is planned to have a total area of sugarcane 54. 314 ha by 2020, located in 10 districts in the west midland and moutainous regions of the province. Yearly sugarcane-planted area (in the period 2005-2013) on average is 15,000 ha, of which over 70% are grown in gray ferralit soil in hilly regions. In tropical climate zones, mineralization, erosion, and leaching occur drastically, together with a low organic matter content as well as low K-rich clay minerals ratio and composition in the soils are the reasons for not only poor K soils but also low K holding capcity. As a result, K fertilizer efficiency is also affected. The research "Study of potassium balance for sugarcane in sugarcane area Lam Son in Thanh Hoa province" was conducted to: - evaluate the capacity of gray ferralit soils to sypply K supply for sugarcane; - evaluate the relationship between the amount of K fertilizers applied and yields and quality of sugarcane; - investigate the amount of nutrient inputs and outputs in K balance in current sugarcane productions - assess amounts of K reserves in the soil and the causes for the K imbalance We thereby proposed solutions for a sustainable management of K and to enhance production efficiency and maintain reserve levels K of land for sustainable development of sugarcane production on hilly lands. 2. Aims and requirements 2.1. Aims of the research Setting an equation to determine the amount of K fertilizers apllied for sugarcane based on a nutrient balance, creating background knowledges for a sustainable management of K for each specific area, contributing to improve productivity, quality and efficiency of cane production in Lam Son hilly regions of Thanh Hoa. 2.2. Requirements - Evaluate the basic conditions of Lam Son sugarcane region in relationship with K balance for sugarcane. - Determine the capacity to provide K for sugarcane of gray soil ferralit and amount of K inputs and outputs in K balance for sugarcane.
2 - Determine the relationship between the amount of K fertilizers appiled to yield and quality of sugar cane, sugar yield and amount of K removed at harvesting. - Determine a K balance at different levels of K fertilization and in current sugarcane production. - Set up an equation determining the amount of K fertilizer for sugarcane through nutrient balance. - Determine the efficiency of an empirical model for a sustainable management of K for sugarcane based on the nutrient balance. 3. Scope of the research Research on K nutrient balance for the sugarcane area Lam Son, Thanh Hoa was done at the small scale (size fields) on typical gray ferralit (Hapli Ferralic Acrisols: ACfa - h) using the sugarcane variety MY 55 - 14 and the cultivation techniques that are commonly used in the area. 4. The scientific and practical significance The results of the research thesis contribute additional scientific data to serve nutriently balanced assessment and determine the amount of K fertilizer for sugarcane through appropriate nutrient balance. At the same time, the results will be basic bckgrounds to recommend a sustainable management strategy of K for each specialist region in the production of sugarcane in Lamson hill in particular, the hill cane area in Thanh Hoa province and in Vietnam. 5. New findings of the research The research has identified the K supplying capacity of soil; amount and the relationship between the nutrient inputs and outputs in K balance. An equation to determine the proper amount of K fertilizer needed for sugarcane through nutrient balance was set up and a model for sustainable management of K nutrition for sugarcane on the typical grey ferralit soil in hilly regions at Lam Son, Thanh Hoa was established to achieve high yields, high cane quality and production efficiency, at the same time to maintain soil K reserves. Chapter 1 LITERATURE REVIEW Nutrient balance in cropping systems is the determination of the amount of all nutrients input, output per unit area of arable land in the specific production conditions, thereby assessing the situation nutrient reserves in the soil and the degree of land degradation. The results from studies on nutrient balance are an important basis to build and implement strategies for sustainable management of nutrients, to meet the demands of increasing productivity, quality and efficiency of crop production, while improve, maintain and enhance soil fertility. In the world and in Vietnam in particular, there has been many researches on plant nutrient balance. Depending on the spatial scopes and objectives of a research, nutrient balance study is done at different scales: large scale ( global , regional or national ) with the main objective is to quantify the input and output sources for the three macro nutrients N, P, K; medium scale (districts, ecological zones) in order to create a basis for policy making, production and business planing in the region; small scale (fields, farms) primarily serve the nutrient management of site-specific crops. Accordingly, the content, methodology, accuracy, relicapacity of the quantitative measurements of nutrient inputs and outputs as well as the feasibility of the study results on nutrient balance are different between the scales of studies (FAO, 1998; Roy. R. N et al, 2003; Sheldrick et al, With. C et al, 2009; Buresh et al , 2010 ... ). For sugarcane, K plays an important role in the physiological and biochemical activities occuring in cells, especially sugar metabolism between hexoza and saccaroza. Kali participates in catalytic activity of the invertaza enzyme in the sugar synthesis and in protein synthesis and transport leading to increasing soluble solids (Brix), relatively sugar levels (Pol), the level of purity of pressed sugar cane juice (AP), reducing the amount of reducing sugars (RS), increase of commercial sugar (CCS). In soil, K exists in the form of structural K, non-exchangable K, exchangable K and K in solution. There are equilibrium and kinetic reactions between these four forms of soil K with the two proccesses, fixation
3 and release. The K kinetic reactions in soil and K fertilizer use efficiency of sugarcane have a large fluctuation, are site-specific and depend on climatic conditions, soils, sugarcane varieties, farming techniques and interactive relationship with other nutrients (Van Dillewijn , 1952 ; Gururaj Hunsigi , 2011 ; Alex Alexander Gerchell , 1973 ... ). Chapter 2 MATERIALS, CONTENTS AND METHODOLOGY 2.1. The research materials The research were conducted on typical gray ferralit soil; MY 55-14 was used as a main sugarcane variety (accounting for over 60% of the sugarcane varieties throughout the region); NPK fertilizer specialized for sugarcane in Lam Son (NPK - HC 6.4 - 3.2 to 6.6 - HC 9.5); commonly used mineral fertilizers on the market (46% N urea, superphosphate - SSP 16% P2O5, 60% K2O potassium chloride) and sugarcane residues after harvesting. 2.2. The research contents To achieve the aims and requirements of the study, we focused on the following: 1) Basic conditions in Lam Son region of Thanh Hoa in relation to balance K for sugarcane. 2) The K supplying capacity of the soil; the amount of K provided by rain water; the amount of K loss by erosion and leaching. 3) The relationship between the amount of K fertilizer to yield and quality of sugar cane, sugar yield and qualitative K loss per harvested product. 4) K nutrient balance for sugarcane at different K fertilizer application levels and different sugarcane production conditions. 5) Set up equations determining the optimum amount of K fertilizer for sugarcane based on nutrient balance. 6) The efficiency of a sustainable K management model for sugarcane based on the nutrient balance. 2.3. Methodology 2.3.1. The research process The research was done in the period from 1/2010 to 2/2013 in three steps: (1) investigating and evaluating the basic situation in Lam Son region of Thanh Hoa; (2) experiments set up according to research content; (3) empirical model building for a sustainable nutrient management of K for sugarcane on the basic results of the nutrient balance study. 2.3.2. Method of secondary data collection Investigate, collect resources, statistical data, maps, technical processes, research findings related to climatic conditions, land of Lamson area. 2.3.3. Method of data collection Investigation and collection of information related to the production, sugarcane cultivation techniques in the region through the household survey using pre-printed questionnaires. Number of investigated households were 200 households in 4 major sugarcane growing districts (Tho Xuan, Ngoc Lac, Lang Chanh, Thuong Xuan), 50 households per district. Sumarizing and analyzing the obtained data by the descriptive statistic method by group of criteria. 2.3.4. Experimental layout method in jars The experiment was conducted in jars following a batch method (no K fertilizer). The jars were put naturally outdoors to investigate the K supplying capacity of the typical gray ferralit (Hapli Ferralic Acrisols) in irrigated condition and with different N, P fertilizers. The experiment consisted of 4 treatments and was set up following a RCB layout style with three replicates: (1) No irrigation - no fertilizers N, P; (2) No irrigation - fertilizer N, P; (3) With irrigation - no fertilizer N, P; (4) With irrigation - fertilizers N, P.
4 The soils used in this experiment was collected from a ratoon farm at depth from 0-40cm. Each jar was filled with 30 kg soil, three cuttings per jar with 1 bud per cutting. Fertilizers N, P were applied at rates of 200 N + 100 P2O5 (kg/ha) (3.32 g urea / jar; 4.46 g superphosphate / jar) for fertilized treatments (treatments 2, 4). Regular checking and irigation were done (using distilled water to avoid K contamination) to maintain soil moisture around 70-80 % of field capacity in the irrigated treatments ( 1, 3). to the growth indicators, elements biomass and biomass of all parts of sugarcane (above and below ground) when the plants stop growing. Determination of dry matter content, content of K2O, K2O accumulated in parts of sugarcane. Then the amount of K2O the soil is capable of supplying was calculated. Time and location of study: planting date 10/2/2010, harvest date 15/9/2010. The experiment was located at Hong Duc University. 2.3.5. The method of field trial layout A field experiment was established to study the effect of the amount of K fertilizer on growth, yield and quality of sugar cane, sugar yield, the amount of K loss by harvested products and the relationship among them. The experiment included 6 treatments, corresponding to 6 rates of K fertilizer levels (0, 50, 100, 150, 200, 250 and 300 kg K2O/ha) on the basic fertilization 200 N + 100 P2O5. Area of the experiment was 90 m2 (with 5 sugarcane rows, 15 m long each, 1.20 m spacing), RCB -style layout, 3 replicates. Cultivation techniques: using cuttings with 2 buds (8 -month-old cane). The amount of cuttings planted were 32,000 cuttings / ha (4 cuttings/m long). Basal fertilizing (when planting or when treating the canes for the next seasons) 100 % P + 30 % N+ 30 % K. Apply additional fertilizer at tillering 30 %N + 30 % K. Apply additional fertilizer at cane elongation 40 % N + 40 % K (the amount of fertilizer followed to each treatment). The cultivation techniques were done similarly using the currently used techniques in the region. Keeping records on indicators of growth, yield and quality of sugar cane, sugar yield, cane foliage mass, dry matter content, K2O content in cane stalks and leaves at harvesting. Determining the technically maximum amount of K, optimum economics for cane yield, sugar yield; reciprocal internal efficiency of K (RIEK), harvest index of K (HIK); K –recovery efficiency of K (REK). The experiment was repeated in 1 sugarcane cycle (1 planting cane, 2 ratoons): 11/1/2010 planting date, harvest date 01/29/2011 (planting cane); 02/10/2012 (ratoon 1); 02/25/2013 (ratoon 2). It was located in Tho Xuan – Sao Vang, Lam Tho commune, Tho Xuan District. 2.3.6. Method of determining the amount of K due to rainwater Keeping records on monthly precipitation over the year by Pluviometer in the Hydrometeorology station - Bai Thuong Thuong Xuan district, Thanh Hoa province. Rainwater samples were analyzed at outdoor vessels in field trial areas. Water samples (sample mixture of rain in the month) were taken on the last day of the month. The amount of K provided by rainwater (kg K2O /ha/year) was determined by rainfall and K2O content in the rainwater in months. Study period: 3 years (2010, 2011, 2012). 2.3.7. Method of determining the amount of K loss by erosion The plots to measure erosion were followed the same layout to field trial plots, corresponding to the amount of K fertilizer (0-300 kg K2O /ha). Area of the erosion measure plot was 90 m2 (6 x 15 m). 5 rows of sugarcane were planted, the distance between rows was 1.2 m. Containers to collect washed soil were placed at the end of the plot (size: 1.5 m length x 1.0 m width x 1.0 m height). Nylon cloths were put at the bottom of the containers. After raining, the amount of water, soil suspension and soil sediment were sampled and analyzed to determine K2O content. The amount of K loss by erosion (kg K2O /ha/year) is the total amount of K2O loss due to runoff water, washed out soil suspension and sediments in all months of the year.
5 Time and location of study: 3 years (2010, 2011, 2012) at Raw Materials Station Tho Xuan – Sao Vang, Lam Tho commune, Tho Xuan District. 2.3.8. Method of determining the amount of K loss by leaching Several Lizimet to measure leaching was set according to the field trial plots, corresponding to the amount of K fertilizer (0-300 kg K2O/ha). Leached water were collected using funnels with size 40 x 40 cm, placed at a depth 40cm (from the surface, within 80% of rhizospheres). After raining, leached water was taken and measured for vollume, leached soilspension soil. Leached soils were sampled and analyzed for K content. The amount of K loss by leaching (kg K2O/ha/year) is the total amount of K2O loss due to runoff water, leached suspension of all the months of the year. Time and location of study: 3 years (2010, 2011, 2012), at Tho Xuan raw material station – Sao Van, Lam Tho commune, Tho Xuan District. 2.3.9. Methods of empirical model building for a sustainable nutrient management of K for sugarcane on the basic results of the nutrient balance The results of studies on nutrient balance were used to construct an empirical model for sustainable K management for sugarcane hilly areas of Lamson with 2 treatments: Control treatment (5 ha): fertilizer application according to the currently common technique in the area: 2 tons / ha NPK Lamson. No cane foliage return. Investigated treament (5 ha): fertilizer application based on the research results of nutrient balance: 2 tons / ha NPK Lamson; 100 % cane foliage incorporated in soils while adding N, P mineral fertilizers at dose of 200 N, 100 P2O5. K fertilizer was determined depending on target yields, the inputs and outputs of K balance and requirements of K reserve levels in soils. The model was carried out on Hapli Ferralic Acrisols, previous crop was ratoon cane, and then was prepared for a new planting. Other farming techniques are implemented the same for all treaments following to the techniques that were commonly used in the area. Record on growth indicators, yield and quality of sugar cane, sugar yield, and sugarcane production efficiency, soil properties before and after the construction of the model. Time and location: 3/12/2011 planing date, harvesting date 12/28/2012. At Tho Xuan raw material station - Sao Vang, Lam Tho commune, Tho Xuan District. 2.3.10. Methods of recording and identifying research targets for sugarcane Record on growth indicators, components of yield and yield of sugarcane by means of weighing, measuring, and counting directly on the field. Keep checking on sugarcane pests (borers, aphids and white wooly aphids) according to the National Technical Regulation on methods of plant pest detection (QCVN 0138/BNN- PTNT - 2010). Determine the amount of K fertilizers that is technically maximum, economically optimum based on the intereacitve equation between cane yields, sugar yield with the amount of K fertilizer proposed by Lecompt Michel (1965). Reciprocal internal efficiency of K (Riek %) was determined by the ratio between the amount of K2O in cane stalks and leaves at harvesting compared to sugarcane yield. K harvest index (HIK) was determined through the ratio between the amount of K2O in cane stalks in relation with the total amount K2O foliage and stalks. K – recovery efficiency of mineral fertilizer K (REK %) was determined by the ratio between the amount of K2O in cane stalks and leaves in relation to the amount of fertilizer K2O provided by mineral fertilizers. Marinal benefit cost ratio (MBCR) was determined by the ratio between the value of the products increased as compared to the cost of production increased from applying advanced techniques
6 2.3.11. Methods for soil, wáter, fertilizer, and crop analysis Analysis of soil, water, fertilizers, and plant following to Vietnam standards was done at the laboratory at Hong Duc University: the soil texture according toVietnam standards 8567 : 2010; pH (KCl) TCVN 5979;2007; total organic matter TCVN 7376-2004; total N TCVN 7373: 2004; total P2O5 TCVN 7374: 2004; available P2O5 TCVN 5256: 2009; total K2O TCVN 7375: 2004; exchangable K2O TCVN 8569: 2010; CEC TCVN 6646: 2000 . Sewage sludge from sugar production: total N: TCVN 8557: 2010; effective P2O5 8563: 2010; effective K2O TCVN 8560: 2010; the amount of K in water QCVN 39: 2011; K content in cane stalks and foliage TCN - 454: 2001. Analysis of cane juice quality criterias: soluble solids (Brix); apparen sucrose content (Pol); purity of pressed sugar cane juice (AP); reducing sugar (RS); commercial cane sugar (CCS) according to the methods currently applied in cane quality assurance department, Joint-Stock Company Sugar Lam Son. 2.3.12. Methods of data processing Equations and correlation graphs using EXCEL - 2007. Data analysis by IRIRSTAT 5.0 program. Chapter 3 RESEARCH RESULTS 3.1. Basic conditions of LamSon region in relation to K balance for sugarcane 3.1.1. Climate Sugarcane area Lam Son - Thanh Hoa located in the west of Thanh Hoa Province, has a tropical climate influenced by the dry and hot southwest monsoon, and dry and cold northeast monsoon. The total area of land under cane cultivation is planned to achieve 54.314 ha by 2020, distributed over 10 geographical districts, three sub-regions of terrain: plains sub-regions (Yen Dinh and Thieu Hoa, Trieu Son), mid-land sub-regions (Cam Thuy district, Tho Xuan, Nhu Thanh, Nhu Xuan, Ngoc Lac), mountainous sub-regions (Thuong Xuan district, Lang Chanh). Changing in climate over the months of the year (average data for 20 years, from 1993 to 2012) are shown in Figure 3.1 Figure 3.1. Evolution of climatic factors in Lam Son - Thanh Hoa (1993 – 2012) Figure 3.1 shows that climate in Lamson region has many advantages, which allow effectively exploiting the potential yield and high sugar content of sugarcane: total temperature (annual average ) is 8.9600, temperature 23.80C, rainfall 1,659 mm / year, 84.8% air humidity, evaporation 897mm, 1,542 hours of sunlight (average 4.2 hours / day). In particular, from May to October it has high temperature, air humidity, light and high rainfall (May to October) coincides with the period of strong growth of sugarcane plants, zoos and create economic productivity. From November to April next year, temperature, air humidity, light and rainfall are low; temperature difference between day and night is highly, which is favorable conditions for the accumulation of sugar cane as well as the process of harvesting, transporting and processing of sugar . The main drawbacks of this climate condition are low temperature, air humidity and rainfall during the planting season, and ratoon cane treatment (on December, January, Febuary), which cause bad affects on germination and regeneration of sugarcane. High precitaion on August, September, October causes erosion and nutrient leaching.
7 3.1.2. Sugarcane planted areas Table 3.1. Area of planted cane in Lam Son region Thanh Hoa (Planning to 2020) No Soil group Symbol Area % compare % compare (ha) with whole with soil reigion group Whole region 54.314 100 1 Gray ferralit AC 48.064 88,5 100 1.1 Typical gray ferralit Acfa - h 40.225 74,1 83,7 1.2 Gray ferralit with stone and farm Acfe 7.839 14,4 16,3 2 Alluvia FL 6.250 11,5 100 2.1 Neutral less acidic alluvia P–h 3.408 6,3 54,5 2.2 Acidic alluvia Pgc 2.842 5,2 45,5 (Source: Lam Son sugarcane Joint-Stock Company, 2008) The results in Table 3.1 show that the total sugarcane area of region is 54.314 ha, including ferralit (AC) accounted for 88.5% (48.064 ha), the remaining is alluvial soil (FL) 6,250 ha. In ferralit gray soil, area of typical gray ferralit (Acfa - h) is 40.225 ha, accounting for 83.7% and 74.1% of the total gray ferralit soil areas and of the whole region, respectively. 3.1.3. Sugarcane varieties Table 3.2. The structure of the sugarcane varieties in Lam Son region of Thanh Hoa (season 2007-2008) No Group of sugarcane varieties Area Yeild % compare % compare (ha) (tấn/ha) with total with group Whole region 15.571 61,15 1 Early maturity group 2.180 62,46 14,0 - Main variety: QĐ 93 - 159 2.107 62,80 13,5 96,7 Other varieties 73 49,80 0,5 3,3 2 Early maturity group – average 2.893 66,61 18,6 - Main varieties: QĐ 94 -119; ROC 10; ROC 23 1.684 67,89 10,8 58,2 Other varieties 1.209 64,82 7,8 41,7 3 Average maturity group – late 10.498 59,38 67,4 - Main variety: MY 55 – 14 9.589 58,30 61,6 91,3 Other varieties 909 70,77 5,8 8,7 (Source: Lam Son sugarcane Joint-Stock Company, 2009) Table 3.2 shows that the varieties structure of whole region includes early maturity varieties acounting for 14%, yield of 62.46 t / ha on average, the main varieties is QD 93-159. Mid-early maturity group accounts for 18.6%, with an average yield of 66.61 t / ha, the main variety is QD 94- 119, ROC 10 and ROC 23. Group of Mid-late maturity varieties accounts for 67.4%, with an average yield of 59.38 t / ha, the main variety is MY 55-14. Planted area of MY 55-14 is 9,589 ha, yield 58.3 tons / ha, accounts for 91.3% and 61.6% of the Mid-late varieties and of the whole region, respectively, and is identified as a key variety in the current structure of the Lamson region. 3.1.4. Sugarcane areas and yield Results from a survey of cane areas and cane yield of 200 farmers of four major sugarcane growing districts in Lam Son area, categorized by land groups: hilly land, farm land (land has been shifted from rice cultivation to sugarcane) and alluvial land (alluvial soil beyond dikes)presented in Table 3.3 shows that: In the Lam Son region, sugarcane is grown mostly on hilly land, accounting for 77.1% of the total area, the average yield of 58.8 tons / ha. In particular, newly planted cane yield of
8 61.9 tonnes / ha, higher than the ratoon canes of 10%. Ratio between the area of newly planted sugarcane and ratoon cane is 44.8% and 55.2%. Compared to sugarcane grown on farmland and alluvia land, planted sugarcane yields on hilly land is lower than 22.2% (16.8 tonnes / ha) and 26.1 (20.8 tons / ha), respectively. Table 3.3. Sugarcane area and yield via household survey in Lam Son region of Thanh Hoa No Land for Survey area (ha) Yield (ton/ha) % compare planting Newly Ratoon Total Newly Ratoon Average with survey sugarcane cane cane cane cane area Total 244,5 326,9 571,4 61,5 60,8 62,7 100 1 Hilly land 197,3 243,1 440,4 61,9 56,2 58,8 77,1 2 Farm land 40,4 59,4 99,8 78,0 73,2 75,1 17,5 3 Alluvial land 6,8 24,4 31,2 82,5 76,7 78,0 2,75 3.1.5. Fertilizers for sugarcane Results of the farmer survey about fertilizer using situation for sugarcane in the Lam Son area are shown in Table 3.4 and Table 3.5. Table 3.4. Situation of fertilizer using for sugarcane in the Lam Son region of Thanh Hoa No Type of fertilizers Survey Area divided to groups (ha) area (ha) Hilly land Farm land Alluvia land 1 Organic fertilizers 43,5 16,7 19,2 7,6 2 Mineral fertilizers 571,4 440,4 99,8 31,2 2.1 Using only NPK Lam Son 542,3 424,6 89,5 28,2 2.2 Using only N, P, K 3,7 - 2,6 1,1 2.3 Using NPK Lam Son, addition of N 17,4 11,0 5,4 1,0 fertilizer 2.4 Using other mixed NPK 8,0 4,8 2,3 0,9 Table 3.5. The utilization of NPK Lam Son for sugarcane in Lam Son region of Thanh Hoa No Land for planting Survey area (ha) Area classification according to sugarcane fertilizing level (ha) Newly cane Ratoon Total Level 1 Level 2 Level 3 cane Total 243,9 302,1 546,0 91,3 397,2 59,0 1 Hilly land 197,3 219,1 416,4 63,0 307,6 45,8 2 Farm land 39,8 58,6 98,4 21,5 67,4 11,0 3 Alluvia land 6,8 24,4 31,2 6,8 22,2 2,2 Note:level 1: 1500 - < 2000; level 2: 2000 -< 2500; level 3: 2500 - < 3000. - For organic fertilizers: there are 43.5 ha out of 571.4 ha of the survey (7.6%) are organic fertilizers. Proportion of cane planted area on hills is used only organic fertilizers 3.8%; farmland 19.2%, 24.4% alluvia land compared to the area covered by each group. - For Mineral: 571.4 ha of investigation has 542.3 (94.9%) of cane area that is entirely used NPK Lamson (NPK - HC 6.4 - 3.2 to 6,6 HC 9.5) by the Fertilizer Corporation Lamson production and invest for farmers through sugarcane purchase contracts sugarcane; 3.1% NPK fertilizers by the Lam Son and additional inorganic N. In addition, a small proportion of the area ( 2 % ) with inorganic fertilizer or other NPK fertilizers on the market . The amount of fertilizer NPK Lamson average 2000-2200 kg / ha. Organic materials for NPK fertilizer production Lam Son is sugar refinery sludge.
9 3.1.6. Irrigation Forms for sugarcane irigation is applying in Lam Son area include: (1) craft irigation (mainly for sugarcane growing area in the garden, garden hills, use of the pressure pump capacity small irrigational system with pipes directly into the trench cane; (2) furrow irrigation (applied to the area of land planted in sugar cane fields, flat terrain, there are proactive system of canals for irrigation, drainage) and (3 ) drip - drip irrigation (under construction project model test irrigate sugarcane hills of Israeli technology, size of 1,000 ha, mainly in Tho Xuan district). Table 3.6. The situation of sugarcan irrigation in the Lam Son region of Thanh Hoa No Land of Area survey (ha) Irrigated area (ha) sugarcane Newly Root cane Total Level 1 Level 2 Level 3 planting cane Total 244,5 326,9 571,4 3,2 20,0 9,0 1 Hilly land 197,3 243,1 440,4 1,3 - 11,0 2 Farm land 40,4 59,4 99,8 20,0 5,1 3 Alluvia land 6,8 24,4 31,2 1,3 - - Note: Level 1: irrigation 1 time; Level 2: irrigation 2 - 3 times; Level 3: usually irrigation The survey results for situation of sugarcane irrigation presented in Table 3.6 shows that except for area in which constructs a trial model for sugarcane drip irrigation; areas were used both two forms including scraft and furrow irrigation, which are limited. In total 571.4 ha survey, only 32.2 ha (5.6%) of sugarcane is irrigated from one or more times. In group of hilly land, only 6.2% of irrigated area under irrigation shaped craft, irigation one times when planting. Thus, the production of sugarcane in the hills Lamson primarily based on rainfed. 3.1.7. Using the top and foliage of sugarcane after harvesting The household survey on the using of sugarcane foliage showed management of sugarcane foliage post-harvest have not been given due attention by growers. In the period, they burned or buried and cornered, returned to the land. However, now part of poor management and part of high labor cost of sugarcane, growers applied forms a part of the rent paid workers harvest sugar cane by sugar cane leaves them taken tops carry on. Thus, almost the entire sugarcane tops were removed from the field immediately after the end of sugar cane harvesting. 3.2. The capacity of K Supply of soil; amount of K by rainwater supply; amount of K loss by erosion and leaching 3.2.1. The capacity of K supply of soil 3.2.1.1. Experimental soil properties The results of analysis of soil agrochemical targets of typical gray ferralit in Lam Son hilly region, used in experiment about the K supply capacity of soil for cane showed that soils with light mechanical composition 1,05 g/cm3; acidic soil (pH 4.64); poor organic matter content (1.22% OM); N, P, K compound are poor level (0.11% N, P2O5 0,05% K2O: 0.08%); phosphorus, exchange potassium are poor (P2O5 4,15 mg/100 g soil, K2O 5,75 mg/100 g soil exchange); low cation exchange capacity (CEC 11,31 mg/100 g soil). 3.2.1.2. The situation of sugarcane growth Results of monitoring the sugarcane growing criteria presented in Table 3.7 show that: In irrigated condition, the growing indicators of sugarcane increased compared with no irrigation in both cases, no fertilizing and N, P fertilizing. As N, P fertilizing, growing indicators increased compared with no N, P fertilizin in both no irigation and irigation cases, but the increasing level was lower than in irrigated conditions.
10 Table 3.7. Effect of irigation and N, P fertilizing on the sugarcane growth N Formulas Germinat Tillering Plant Stem Plant Number o ive time ratio height diameter volume of plant (date) (time) (cm) (mm) (g/plant) (plant/jar) 1 No irigation – no N, P 15 1,33 145,1 16,4 103,0 4,0 2 No irigation- N, P fertilizing 15 1,47 159,8 17,8 115,5 4,3 3 Irigation-no N, P fertilizing 10 1,63 186,5 20,7 116,7 4,5 4 Irigation - N, P fertilizing 10 1,90 225,5 24,6 153,3 5,4 LSD0,05 - 0,06 10,2 1,4 7,14 0,3 Irigation combined with N, P fertilizing, growing indicators of sugarcane increased compared with the cases that are irigation - no N, P fertilizing and no irigation – N, P fertilizing. Compared N, P fertilizing - no irigation formula with irigation - no N, P fertilizing, tillering ratio of sugarcane in the formula of N, P fertilizing increased 29.3 % and 16.6 %; plant height increased 41.1 % and 20.9 %; sten diameter increased 38.2 % and 18.8 %; plant volume increased 32.7 % and 31.4 %; plant density increased by 25.6 % and 20 % , respectively . 3.2.1.3. Amount of K2O accumulated in the plant Table.3.8. Effect of irigation and N, P fertilizing on amount of K accumulated in the plant No Formulas Fresh Dry matter Dry Content Amount of K2O volume content volume K2O accumulated (g/jar) (%) (g/jar) (%) (g/jar) 1 No irigation – no N, P fertilizing 568,0 27,4 153,5 0,19 0,34 2 No irigation - N, P fertilizing 684,3 28,7 197,5 0,22 0,51 3 Irigation - no N, P fertilizing 766,3 22,9 171,1 0,22 0,45 4 Irigation - N, P fertilizing 1059,9 25,3 264,4 0,280 0,870 The results in Table 3.8 show that compared with no irigation, irigation formulas have reduced dry matter content in all parts of the tree in both cases, no fertilizing and N, P fertilizing. However, due to living mass , dry mass and K2O content increased high result in that mass of K2O accumulated in tree increased high: 32.4 % and 70.6 % compared with no irigation, in the cases both fertilizing and N, P fertilizing respectively. N, P fertilizing increased living mass, dry matter content and K2O content result in that K2O cumulative volume in plant increased 50 % and 93.3 % compared to no N, P fertilizing in the cases of irigation and no irigation respectively . Irigation combined with fertilizer N , P , K2O cumulative volume reached the highest value (0.87 g / jar), up 93.3 % compared with the case of only irigation, no N, P fertilizing and 70,6 % compared with the case of only N, P fertilizing, no irigation. 3.2.1.4. Effect of irigation and N, P fertilizing on K supply capacity of land for plant K supply capacity of land for plant in conditions of irigation and N, P fertilizing differently is determined by the total K2O cumulative volume in all of the sugarcane after deducting the amount of K2O in cutting when planting. K2O volume in land able to provide for plant (kg K2O /ha) are converted from the land mass in the jar and the land mass in the range of 90% active sugarcane roots (depth of 0- 40 cm, natural weight of land 1.05 g/cm3). The research results are presented in Table 3.9; 3.10. Table 3.9. K2O volume in the cuttings when planting Number of cuttings Cutting volume Dry content K2O content K2O volume (cutting) (g/cutting) (%) (%) (g/jar) 3 11,5 31,2 0,47 0,05
11 Table 3.10. K2O supply capacity of land for sugarcane No Formulas K2O K2O plants take K2O soil ables accumulation from the soil to supply (kg in plant (g/jar) (g/jar) K2O/ha) 1 No irigation – no N, P fertilizing 0,34 0,29 40,6 2 No irigation - N, P fertilizing 0,51 0,46 64,4 3 Irigation - no N, P fertilizing 0,45 0,40 56,0 4 Irigation - N, P fertilizing 0,87 0,82 114,8 LSD0,05 0,03 0,05 6,9 The results in Table 3.9; 3.10 showed: Sugarcane in irrigated conditions, the K2O volume that soil ables to provide for plant increased 37.9 % and 78.3 % compared with no irigation condition in cases of no fertilizing and N, P fertilizing respectively. Sugarcane in conditions of N, P fertilizing, K2O volume that soil ables to provide for plant increased 58.6 % and 105 % compared with N, P fertilizing in cases of irigation and no irigation respectively. Sugarcane in irrigated conditions combine with N, P fertilizing, the soil ables to provide the highest K2O volume for sugarcane: reach 0.82 g / jar (kg / ha), an increase of 105 % (0.42 g / jar) higher than in the case of irigation - no N, P fertilizing, and 78.3 % ( 0.36 g / jar ) higher than in the case of N, P fertilizing - no irigation. From the above results showed, irigation and N, P fertilizing have a significant impact on the K supply capacity of typical gray ferralit soil. Irigation combined with N, P fertilizing, soil has able to provide the highest level of K2O volume (114.8 kg K2O /ha). In the case of only irigation - no N, P fertilizing or N, P fertilizing - no irigation, K2O volume, that is provided by soil, is reduced to 56 kg K2O /ha (down 48.8 %) and 64, 4 kg K2O /ha (down 56.1 % ) compared with the case of irigation combination fertilizer N, P. 3.2.2. K due to rainwater From the hypothesis that, in the area of sugar mills, K content in rainwater is higher than other areas due to the manufacturing process, the sugar mills use bagasse as a feedstock for boiler and emit into the atmosphere a considerable amount of furnace ash dust. Besides, sugarcane leaf tip burn practices after each harvest also contributes to increased levels of ash in the air. When it rains, dust rainwater enters the soil, thereby returning to land a certain amount of K. Rainfall (mm) K2O content (mg/lít ) K2O volume (kg/ha) Month Month Month Rainfall K2O Content K2O volume Hình 3.2: K due to rainwater supply for soil in the Lam Son region of Thanh Hoa (2010 - 2013) K2O amount due to rainwater supply for soil (kg K2O /ha/year) are determined through rainfall and K2O concentrations in rainwater over the months of the year. Results monitoring of precipitation, and the amount of K2O, K2O content in rainwater over the month in 3 years (2010-2012) in the Lam Son presented in Figure 2 show that the climatic conditions of the Lam Son, the June, July, August, September, October, November have the highest total rainfall (average 1684.3 mm, accounting for 87.5 % of the total rainfall for the year). K content in rainfall is low (average 0.38 mg/l). The amount of K2O give land 5.81 kg K2O /ha/year, accounting for 70.8 % of K2O by rainwater supply in years. In contrast, December , January, Febuary, March, April, May K content in rainfall is high (1.18 mg / l), 3.1 times higher than the average of
12 June , July, August, September, October, November. However, due to low rainfall (only 12.47 % of the total rainfall in the year) K content provides for soil only 2.4 kg K2O /ha/year. 3.2.3. K loss by erosion Table 3.11. K loss by erosion in Lam Son region of Thanh Hoa (2010 - 2012) No Monitoring criteria Basis Basis + Basis + Basis + Basis + Basis + 100 150 200 250 300 K2O K2O K2O K2O K2O 1 K loss due to erosion Erosive water (m3/ha) 713,45 535,09 442,34 385,26 299,65 278,24 K2O content (mg/l) 2,91 3,32 3,46 3,40 3,49 3,48 K2O loss due to erosive water (kg/ha) 2,08 1,78 1,53 1,31 1,05 0,97 2 K loss by suspension soil Erosive suspension soil (kg/ha) 1.555 1.211 1050 926 846 1.123 K2O content (mg/l) 1,38 1,48 1,51 1,52 1,55 1,30 K2O loss by soil suspension (kg/ha) 21,46 17,92 15,86 14,08 13,11 14,60 3 K loss by sediment Soil sediment erosion (m3/ha) 773,16 602,43 543,94 472,45 408,01 520,43 K2O content (mg/l) 0,58 0,61 0,61 0,62 0,63 0,50 K2O loss by soil sediment (kg/ha) 4,48 3,67 3,32 2,93 2,57 2,60 4 Total K2O loss by erosion (kg/ha) 28,02 23,37 20,71 18,32 16,73 18,17 Research results K2O amount loss due to erosion (3-year average 2010-2012) presented in Table 3.11 shows that: K fertilizing had a positive influence to limit the amount of K loss by erosion. Water, soil suspension and erosive sediment soil tends to decrease when increasing the amount of K fertilizing, in contrast, K2O content in them tends to increase. However, due to the decline in water quality, suspension soil and erosive sediment soil is faster than the rate of K2O content in them, leading to loss of K according to the amount of ingredients as well as the total amount of K loss by erosion reduces gradually. However, the difference is only evident when comparing the formula of K fertilizing with formula of no K fertiling, even among the formulas of K fertilizing, the difference only shows unclear. The total amount of K loss due to erosion of volumes average from 100 to 300 kg K2O /ha/year is 19.5 kg K2O /ha, in which 77.7% (15.1 kg K2O /ha) loss by erosive suspension soil. The amount of K loss by erosive sediment accounted for only 15.5% (3.0 kg K2O /ha). The amount of K loss under erosive water accounted for only a small fraction (6.8%, 1.3 kg K2O /ha respectively). In the case of no K fertilizing, the amount of K loss by erosion is 28.0 kg higher 8.56 kg K2O /ha (44.0%), compared with average of fertilizing formulas from 100 to 300 kg K2O /ha. The amount of K loss due to erosion of the average three fertilizer formulas 200, 250 and 300 kg K2O /ha is 17.7 kg decrease 5.6 kg K2O /ha (down 23.4%), compared with the amount of fertilizer 100 kg K2O /ha. From the above results, the amount of K loss by erosion suggest to use in evaluating nutrient balance and determine the amount of K fertilizer suit for sugarcane cultivation on typical gray ferralit soil, no irigation, MY 55-14 variety, base fertilizer 200 kg N + 100 kg P2O5 in the Lam Son rgion is 17.7 kg K2O/ha. 3.2.4. K loss by leaching Research results K2O amount loss by leaching (average 3-year 2010-2012) presented in Table 3.12 show that changes in water, leaching suspension soil, K2O content in them and the amount of K2O loss by leaching at different levels of K fertilizing also occur similar to the case of erosion. The total amount of K loss by average leaching of the fertilizing levels from 100-300 kg K2O /ha/year is 29.5 kg K2O /ha, in which loss 99.2 % according to leaching water. The amount of K loss by leaching
13 suspension soil comprised up only 0.8 %. In the case of no K fertilizing, the amount of K loss by leaching is 36.25 kg K2O /ha higher 6.71 kg K2O /ha (22.7 %) compared with the average of the fertilizing formulas from 100-300 kg K2O /ha. The amount of K loss by average leaching of three formulas 200, 250, 300 kg K2O /ha is 26.7 kg K2O /ha, 8.54 kg K2O/ha decrease (down 24.3 %), compared with the amount of fertilizer 100 kg K2O /ha. Table 3.12. K loss by leaching in the Lam Son region of Thanh Hoa (2010 - 2012) No Monitoring criteria Basis Basis + Basis + Basis + Basis + Basis + 100 150 200 250 300 K2O K2O K2O K2O K2O 1 K loss by leaching water Leaching water (m3/ha) 9.186 7.257 6.522 6.063 4.961 4.593 K2O content (mg/l) 3,92 4,82 4,94 5,02 5,06 5,18 K2O loss by leaching water (kg/ha) 36,01 34,98 32,22 30,44 25,10 23,79 2 K loss by suspension soil Leaching suspension soil (kg/ha) 10,67 8,43 8,11 7,79 7,90 7,36 K2O content (mg/l) 2,23 2,76 2,83 2,89 2,92 2,96 K2O loss by suspension soil (kg/ha) 0,24 0,23 0,23 0,23 0,23 0,22 Total K loss by leaching (kg/ha) 36,25 35,21 32,45 30,67 25,33 24,01 From the above results, the amount of K loss by leaching annually proposed to use to assess nutrient balance and determine the appropriate amount of K fertilizing for sugarcane on typical gray ferralit soil, no irigation, MY 55 -14 variety, fertilizing 200 kg N + 100 kg P2O5/ha in the Lam Son region is 26.7 kg K2O/ha. 3.3. Relationship between the amount of K fertilizer with yield, quality of sugarcane, sugar yield, and K loss per harvedted products 3.3.1. Effect of K fertilizing volume on growth, yield, and quality of sugarcane, sugar yeild Results of the study affect the amount of K fertilizing on growth, yield, and quality of sugar cane, cane sugar yield of MY 55-14 variety on typical gray ferralit soil, no irigation, basic fertilizing 200 kg N + 100 kg P2O5 /ha in the Lam Son region presented in Table 3.13 show: - For the growth of sugarcane: K fertilizing had a positive influence tillering situation, rising and spending diameter of plant, plant weight, plant density at harvest. However, the increase in the growth indicators is evident only in low amount of fertilizing (100-150 kg K2O/ha) and stopped in the amount of fertilizing 200 kg K2O /ha. Comparison between the K fertilizing formula with no K fertilizing formula showed a significant difference in the growth indicators of sugarcane: tillering average coefficient of the fertilizing volume from100 kg K2O /ha to 300 kg K2O /ha increased 0.31 times; plant height increased 14.3 % (33.3 cm); stem diameter increased 12.4 % (0.30 cm); plant volume 16.5 % (0.17 kg/tree); effective plant density at harvest increased 13.2 % (0.70 plant/m2). Between the amounts of K fertilizing, the growth indicators increase in the amount of fertilizing 100 kg K2O /ha to 150 kg K2O /ha, then stopped at 200 kg K2O. - For cane yield: K fertilizing increased the growth indicators lead to increasing cane yield, but the difference is only evident when comparing the K fertilizing formula with no K fertilizing formula. Among the fertilizing levels, cane yield increased only in the amount of fertilizing 100 kg/ha and stopped in the amount of fertilizing 150 kg K2O /ha. No K fertilizing, cane yield reached 57.85 tons/ha. Fertilizing 100kg K2O/ha, yield was 66.37 increase of 14.7%, (8.52 tonnes / ha), exceeding the limit significant differecnces at 95% probcapacity (LSD0, 05 = 7, 17 tons/ha). The amount of fertilizing 150 kg K2O/ha, sugarcane yields continue rising, compared to fertilizing 100 kg K2O /ha, but increasing rate is low (3.76 tons / ha) and lies within the experimental error. Thus, although the growth indicators increase the amount of fertilizing to 150 kg K2O /ha, the increase is not large enough to be able to increase productivity with certainty at this fertilizing level.
14 Table 3.13. growth, yeild, quality of sugarcane, sugar yeild No Monitoring criteria Basis Basis + Basis + Basis + Basis + Basis + LSD0.05 100 150 200 250 300 K2O K2O K2O K2O K2O 1 Growth Tillering ratio (time) 0,97 1,17 1,27 1,31 1,30 1,31 0,13 Plant height (cm) 232,75 253,66 264,09 268,87 270,45 273,15 28,73 Stem diameter (cm) 2,45 2,67 2,76 2,77 2,77 2,80 0,26 Plant volume (kg/plant) 1,02 1,13 1,18 1,2 1,21 1,22 0,14 2 Plant density (plant/m ) 5,34 5,68 5,99 6,17 6,16 6,21 6,62 2 Sugarcane yield (ton/ha) 57,85 66,37 70,13 71,77 71,08 71,83 7,17 3 Sugarcane quality Bix (0) 18,40 19,16 19,43 19,97 20,23 20,63 - The rich sugar (Pol %) 13,39 15,95 16,39 17,15 17,32 17,67 - Purity (AP %) 81,62 84,44 86,76 88,22 88,14 89,90 - Reducing sugar content (RS %) 2,59 1,44 1,23 1,10 0,97 1,00 - 4 Commercial Cane Sugar (CCS) 8,98 10,12 10,70 11,11 11,13 11,39 0,27 5 Sugarcane yield (ton/ha) 5,19 6,71 7,49 7,97 8,16 8,18 0,73 - For cane quality: K fertilizing affects significantly to improve the sugarcane juice quality and sugar content in plants. Indicators: Brix, Polarization (Pol), the purity of sugarcane juice (AP) increase continuously in the amounts of fertilizing from 100 kg K2O /ha to 300 kg K2O /ha, while reducing sugar content (RS) decreases. Compared with the no K fertilizing, Brix (average of the amount of fertilizer 100-300 kg K2O/ha) increased 1.48 degrees; Pol increased 3.51 degrees; AP increased by 5.87%; RS decreased 1.44 %. - For commercial cane sugar: sugar content of commercial sugarcane increased continuously in the amount of fertilizing from 100 kg to 250 kg K2O/ha and stop fertilizing at 300 kg K2O/ha. Compared with no K fertilizing, the average sugar content in the fertilizing formulas from 100 kg to 300 kg K2O/ha up 21.7%, corresponding to 1.95 CCS. Comparison between K fertilizin levels showed: increasing level of sugar content between 150 kg K2O /ha compared with 100 kg K2O /ha is 0.58 CCS and between 200 kg K2O /ha compared with 150 kg K2O /ha is 0,41 CCS. The difference is very reliable, exceeding the limit significant differences at 95% probcapacity (LSD0, 05 = 0.35 CCS). The difference in sugar content between the amount of fertilizer 250 kg K2O /ha compared with 200 kg K2O /ha, although it is not beyond the scope of laboratory data, it is still at high levels (up 0.22 CCS). - For sugar yield: K fertilizing causes increasing sugarcane yields, especially sugar content lead to increasing sugar yield. Compared with the control no K fertilizing, yield averages of the amount of fertilizing from 100 kg K2O/ha to 300 kg K2O/ha reached 7.7 tonnes/ha, increased of 48.4% (2.51 tonnes/ha). Among the levels of K fertilizing, sugar yield gap between the amount of fertilizing 150 kg K2O /ha compared with 100 kg K2O /ha (0.78 tonnes / ha) was reliable (LSD0, 05 = 0.73 tons/ha ). The difference between the amount of fertilizing 200 kg K2O /ha compared with 150 kg K2O /ha is 0.48 tons/ha, although it is not beyond the scope of experimental error, it is high increasing rates (0.48 tonnes / ha). In a word, the K fertilizing level, that brings benefits for growth and cane yield, is 150 kg K2O /ha. However, due to increased levels of sugarcane fertilizing continuously from 100 kg K2O /ha to 200 kg K2O /ha and only stopped when applied to K2O /ha, so the amount of K fertilizing for sugar yield the best was determined at 200 kg K2O /ha.
15 3.3.2. Effect of the amount of K fertilizing to sugarcane pest situation Table 3.14. Effect of the amount of K fertilizing to sugarcane pest situation No Formulas Ostrinia nubilalis Ceratovacum lanigera Rate (%) Levels Rate (%) Levels 1 Basis 26,2 4 47,6 4 2 Basis + 100 K2O 19,7 3 34,5 3 3 Basis + 150 K2O 18,4 2 25,2 2 4 Basis + 200 K2O 16,6 2 23,3 2 5 Basis + 250 K2O 13,8 2 22,7 2 6 Basis + 300 K2O 13,4 2 22,8 2 Monitoring results of Ostrinia nubilalis and Ceratovacum lanigera situation at K fertilizing volumes presented in Table 3.24 showed that: K fertilizing could decrease damaged rate of Ostrinia nubilalis and Ceratovacum. If K fertilizing volume increases, damaged rate decreases. On the 200 N + 100 P2O5 fertilizing and no K fertilizing, Ostrinia nubilalis ratio on the sapling period period is at 26.2 % (level 4), the rate of Ceratovacum lanigera in ripening period - harvest (September in last year to April in next year ) is 47.6 % (level 4), up 9.82 % and 21.9 % (up1 level) compared with the average of fertilizing volumes from 100 kg K2O/ha to 300 kg K2O/ha for Ostrinia nubilalis and Ceratovacum lanigera rate respectively. Between the level of K fertilizing, Ostrinia nubilalis rate decreased from 19.7 % to 13.4 % , Ceratovacum lanigera rate decreased from 35.5 % to 22.8 % (down from level 3 to level 2) in the amount of fertilizing 100 kg K2O/ha and 300 kg K2O/ha respectively. This is also one of the reasons for increasing quality while increasing cane quantity as K fertilizing 3.3.3. K productivity at different fertilizing levels Table 3.15. K productivity at different fertilizing levels No Formulas Yield Difference with basis K productivity Sugarcane Sugar Sugarcane Sugar Kg sugarcane/ Kg sugar/ (ton/ha) (ton/ha) (ton/ha) (tấn/ha) kg K2O kg K2O 1 Basis 57,85 5,19 - - - - 2 Basis + 100 K2O 66,37 6,71 8,52 1,52 85,20 15,20 3 Basis + 150 K2O 70,13 7,49 12,28 2,30 81,87 15,33 4 Basis + 200 K2O 71,77 7,97 13,92 2,78 69,60 13,90 5 Basis + 250 K2O 71,98 8,16 14,13 2,97 56,52 11,88 6 Basis + 300 K2O 71,83 8,18 13,98 2,99 46,60 9,97 Table 3.25 show: K productivity reaches the highest at fertilizing volume 100 kg K2O/ha (85.2 kg cane/kg K2O) and fertilizing volume 150 kg K2O /ha for sugar volume (reaching 15, 33 kg sugar /kg K2O), and then gradually reduce the amount of fertilizing at higher (from 150 K2O/ha for sugarcane and 200 K2O/ha or more for sugar). Compared to 100 kg K2O/ha fertilizer, fertilizing amount 100 kg K2O/ha in which performance begins to decline, for cane is 250 kg K2O/ha (33.7% reduction, respectively 28.68 kg cane/kg K2O), and for sugar is 300 kg K2O/ha (34.9% reduction, respectively, 5.36 kg of sugar/kg K2O). 3.3. 4. The relationship between K fertilizing volume and sugarcane yield, cane yield Based on the basis of 200N + 100 P2O5 fertilizing, MY 55-14 variety grows in typical gray ferralit soil, no irigation in the Lam Son region, among cane yield, sugar yield and K fertilizing volume (0-300 kg K2O/ha) correlated quadratic as follows (Figure 3.3)