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 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 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 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: Associated Prof Dr Nguyen Van Bo 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 INTRODUCTION 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 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 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 - 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 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 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 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 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 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 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 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 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 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 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 treatments, corresponding to 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 sugarcane rows, 15 m long each, 1.20 m spacing), RCB -style layout, replicates Cultivation techniques: using cuttings with buds (8 -month-old cane) The amount of cuttings planted were 32,000 cuttings / (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 sugarcane cycle (1 planting cane, 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: 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) 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 Time and location of study: 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: 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 treatments: Control treatment (5 ha): fertilizer application according to the currently common technique in the area: tons / NPK Lamson No cane foliage return Investigated treament (5 ha): fertilizer application based on the research results of nutrient balance: tons / 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 10 Table 3.7 Effect of irigation and N, P fertilizing on the sugarcane growth N o Formulas Germinat Tillering Plant Stem Plant Number ive time ratio height diameter volume of plant (date) (time) (cm) (mm) (g/plant) (plant/jar) No irigation – no N, P 15 1,33 145,1 16,4 103,0 4,0 No irigation- N, P fertilizing 15 1,47 159,8 17,8 115,5 4,3 Irigation-no N, P fertilizing 10 1,63 186,5 20,7 116,7 4,5 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 volume (g/jar) 568,0 Dry matter content (%) 27,4 Dry volume (g/jar) 153,5 Content K2O (%) 0,19 Amount of K2O accumulated (g/jar) 0,34 No irigation – no N, P fertilizing No irigation - N, P fertilizing 684,3 28,7 197,5 0,22 0,51 Irigation - no N, P fertilizing 766,3 22,9 171,1 0,22 0,45 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 040 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) Cutting volume (g/cutting) 11,5 Dry content (%) 31,2 K2O content (%) 0,47 K2O volume (g/jar) 0,05 11 Table 3.10 K2O supply capacity of land for sugarcane No Formulas K2O accumulation in plant (g/jar) 0,34 0,51 0,45 0,87 0,03 K2O plants take from the soil (g/jar) 0,29 0,46 0,40 0,82 0,05 K2O soil ables to supply (kg K2O/ha) 40,6 64,4 56,0 114,8 6,9 No irigation – no N, P fertilizing No irigation - N, P fertilizing Irigation - no N, P fertilizing Irigation - N, P fertilizing LSD0,05 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, 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) Month Rainfall K2O volume (kg/ha) K2O content (mg/lít ) Month Month 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 years (2010-2012) in the Lam Son presented in Figure 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 K loss due to erosion Erosive water (m3/ha) K2O content (mg/l) K2O loss due to erosive water (kg/ha) K loss by suspension soil Erosive suspension soil (kg/ha) K2O content (mg/l) K2O loss by soil suspension (kg/ha) K loss by sediment Soil sediment erosion (m3/ha) K2O content (mg/l) K2O loss by soil sediment (kg/ha) Total K2O loss by erosion (kg/ha) Basis Basis + Basis + 100 150 K2O K2O Basis + 200 K2O Basis + 250 K2O Basis + 300 K2O 713,45 2,91 2,08 535,09 3,32 1,78 442,34 3,46 1,53 385,26 3,40 1,31 299,65 3,49 1,05 278,24 3,48 0,97 1.555 1,38 21,46 1.211 1,48 17,92 1050 1,51 15,86 926 1,52 14,08 846 1,55 13,11 1.123 1,30 14,60 773,16 0,58 4,48 28,02 602,43 0,61 3,67 23,37 543,94 0,61 3,32 20,71 472,45 0,62 2,93 18,32 408,01 0,63 2,57 16,73 520,43 0,50 2,60 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 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 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 + 100 K2O Basis + 150 K2O Basis + 200 K2O Basis + 250 K2O Basis + LSD0.05 300 K2O 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 Plant density (plant/m ) 5,34 5,68 5,99 6,17 6,16 6,21 6,62 Sugarcane yield (ton/ha) 57,85 66,37 70,13 71,77 71,08 71,83 7,17 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 Commercial Cane Sugar (CCS) 8,98 10,12 10,70 11,11 11,13 11,39 0,27 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 Basis 26,2 47,6 Basis + 100 K2O 19,7 34,5 3 Basis + 150 K2O 18,4 25,2 Basis + 200 K2O 16,6 23,3 Basis + 250 K2O 13,8 22,7 Basis + 300 K2O 13,4 22,8 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 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 Basis 57,85 5,19 Basis + 100 K2O 66,37 6,71 8,52 1,52 85,20 15,20 Basis + 150 K2O 70,13 7,49 12,28 2,30 81,87 15,33 Basis + 200 K2O 71,77 7,97 13,92 2,78 69,60 13,90 Basis + 250 K2O 71,98 8,16 14,13 2,97 56,52 11,88 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 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) 16 NS đường (kg/ha) NS mía (kg/ha) Lượng bón K2O (kg/ha) Cane yield – planting cane ƯNS mía (kg/ha) Lượng bón K2O (kg/ha) Sugar yield – planting cane NS đường (kg/ha) Lượng bón K2O (kg/ha) Cane yield – ratoon cane1 Lượng bón K2O (kg/ha) Sugar yield – ratoon cane NS mía (kg/ha) NS đường (kg/ha) Lượng bón K2O (kg/ha) Lượng bón K2O (kg/ha) Cane yield – ratoon Sugar yield – ratoon Figure 3.3 The correlation between the K fertilizing volume and cane yield, sugar yield On the basis of the correlation equation, the K fertilizing volume maximum about techical and optimum about economics for sugarcane yield, sugar yield is determined and presented in Table 3:16 Table 3.16 K fertilizing volume maximum technique and optimum economics Cane types K fertilizing volume maximum K fertilizing volume optimum technique (kg K2O/ha) economics (kg K2O/ha) Cane Sugar Cane Sugar Newly cane 252,14 299,27 209,70 269,19 Root cane 254,82 316,15 213,14 286,91 Root cane 261,75 285,26 198,29 251,30 Average 255,70 301,00 204,80 267,90 Note: cost of fertilizer KCl (60% K2O): 12.000đ/kg; cost of sugarcane 10 CCS: 950đ/kg) From the results in Table 3.16 show: the purchase price of sugarcane 10 CCS is 950 VND / kg; price of KCl (60% K2O) is 12,000 VND / kg, fertilizing volume optimum economics for sugarcane yield was 204.8 kg K2O /ha lower than 50.9 kg K2O /ha compared to the amount of fertilizer maximum techniques The fertilizing volume optimum economics for sugar yield was 267.9 kg K2O /ha less than 33.1 kg K2O /ha compared to the amount of fertilizing maximum techniques Theoretically, K fertilizers can moderate K2O /ha 255.7 kg to a maximum cane yield and 301 kg K2O /ha to achieve maximum sugar yields 17 3.3.5 Relationship between K fertilizing volume and K loss according to harvested product Table 3.17 Effect of K on K2O volume in harvest products No Content Basis Basis +100 K2O Basis +150 K2O Basis +200 K2O Basis +250 K2O Basis +300 K2O LSD0.05 Stem of cane Fresh volume 57,85 66,37 70,13 71,77 71,98 71,83 7,17 Dry matter content (%) 22,58 23,69 24,08 24,35 24,42 24,38 2,28 K2O content (%) 0,38 0,52 0,57 0,63 0,67 0,68 0,046 Cummulative K2O volume (kg/ha) 49,49 81,78 96,06 109,31 116,07 118,35 5,26 Cane foliage Fresh volume 21,33 24,56 25,98 26,69 27,72 26,66 2,72 Dry matter content (%) 22,35 24,37 24,49 24,51 24,57 24,55 2,43 K2O content (%) 0,45 0,71 0,74 0,77 0,81 0,83 0,054 Cummulative K2O volume (kg/ha) 21,39 42,40 47,13 50,32 52,57 54,08 3,54 The research results about effect of the amount of K fertilizing on K2O amount loss follow harvested products (plant cane, cane foliage) presented in Table 3.17 shows: - For the amount of K loss by product of sugarcane: K fertilizing increases the volume of sugarcane, dry matter content and K2O content lead to an increased amount of K2O accumulation Compared with no K fertilizing, the average amount of sugarcane in the fertilizing formula from 100 kg K2O /ha to 300 kg K2O /ha is 21.7% (12.57 tonnes / ha); dry matter content is higher than 1,6%; K2O content is higher than 0.23%, result in that the volume of K2O increases 110.9% (54.82 kg K2O /ha) Among the levels of K fertilizing, the accumulative K2O volume in sugarcane increased continuously at the amount of fertilizing from 100 kg K2O /ha to 250 kg K2O /ha and stopped at 300 kg K2O /ha Compared with 100 kg K2O /ha, cumulative K2O volume in sugarcane at the amount of fertilizing 150 kg K2O /ha, 200 kg K2O /ha and 250 kg K2O /ha increase respectively: 17.5% (14.28 kg K2O/ha), 13.8% (13.25 kg K2O/ha) and 6.2% (6.76 kg K2O/ha) The difference in K2O volume is very reliable, exceeding the limit significant differences at 95% probcapacity (LSD0, 05 = 5.26 kg K2O /ha) - For the amount of K loss under sugarcane foliage after harvest: similar to sugarcane, foliage mass, dry matter content, K2O content in foliage increased with increasing the amount of K fertilizing Compared with no K fertilizing, the average amount of sugar cane foliage of the formulas 100-300 kg K2O/ha increases 22.5% (higher than 4.79 tons/ha); dry matter content is higher than 2.5%; K2O content is higher than 0.32% result in that a K2O volume increases 30.5% ( higher than 27.91 kg K2O/ha) The increase of the targets tracked is very reliable, exceeding limits LDS0.05 (fresh sugarcane foliage mass = 2.72 tons/ha, dry matter content = 2.43%, K2O content = 0.054 %, cumulative K2O volume = 3.54 kg/ha) Compare among the different levels of K fertilizing shows the volume of sugarcane foliage and dry matter content tends to increase continuously in the amount of fertilizing from 100 kg to 250 kg K2O /ha K2O content and accumulative K2O volume increased continuously for up to 300 kg K2O/ha However, only the difference in quality is evident K2O fertilizer at 150 kg compared with 100 kg K2O/ha K2O /ha (K2O /ha increased 4.73 kg), 200 kg K2O /ha or more, the difference between the K fertilizer rates have not exceeded the scope of experimental error (LSD0,05 = 3.54 kg K2O/ha) Reciprocal internal efficiency of K (Riek), harvest index K (HIK) and K recovery efficiency of mineral fertilizer (REK) in different levels of K fertilizer are presented in Table 3:18 18 Table 3.18 Effect of K on agronomic performance, harvest index, and K use efficiency No Formulas Basis Basis+100K2O Basis+ 150K2O Basis+ 200K2O Basis+ 250K2O Basis+ 300K2O Thedifference Acumulative K compared (kg K2O /ha) with basis Plant Foliage Total (kg K2O/ha) cane 49,49 21,39 70,88 81,78 42,40 124,18 53,30 96,06 47,13 143,19 72,31 109,31 50,32 159,63 88,75 116,07 52,57 168,64 97,76 118,35 54,08 172,43 101,55 RIEK HIK REK (%) 0,12 0,19 0,21 0,22 0,24 0,24 0,70 0,66 0,67 0,68 0,69 0,69 45,09 42,73 40,27 35,82 31,11 For RIEK: K fertilizing increases the volume of sugarcane, cane foliage volume after harvest as well as dry matter content, content of K2O and accumulative K2O amount in them, leading to increased RIEK RIEK average fertilizing level of 100 -300 kg K2O/ha is 0.22% higher than 0.83 times the formula that does not fertilizer K Among K fertilizing levels, RIEK continuous increase in levels from 100 kg K2O /ha to 250 kg K2O /ha (up from 0.19% in the amount of 100 kg K2O /ha, up 0.24% in the amount of 250 kg K2O /ha) and stop fertilizer at 300 kg K2O/ha From the above results, the linear correlation between the amount of K fertilizer and Riek in different sugarcane crop is determined and presented in Figure 3.4 RIEK(% ) RIEK(% ) Cane yield (ton/ha) Planting Cane yield (ton/ha) Ratoon RIEK(% ) RIEK(% ) Cane yield (ton/ha) Cane yield (ton/ha) Ratoon Average of crops Figure 3.4 Relationship between cane yield and reciprocal internal efficiency of K (RIEK) For HIK: K fertilizing affects simultaneously increase in K2O volume both product of sugarcane and leaves of sugarcane as harvest However, due to the increase in the amount of K2O in sugarcane higher than the increase in the amount of K2O in foliage, resulting in that HIK in the K fertilizing formulas decreased compared with no K fertilizing HIK average of the amount of fertilizing from 100 kg K2O /ha to 300 kg K2O /ha is 0.68 while HIK in fertilizing formula K is 0.70 However, when comparing the level of K fertilizing noticed, HIK have tended to increase with increasing the K fertilizing volume: increase from 0.66 at 100 kg K2O /ha up 0.70 at 300 kg K2O/ha From the results showed no significant variation about HIK between the K fertilizing volumes Thus, it can use average data (HIK = 0.68) to calculate the equilibrium and set equatation to determine K fertilizing suit for sugarcane on the basis of nutrient balance - For REK: fertilizing at 100-300 kg K2O /ha, REK ranged 31-47% and in the direction of decreasing with increasing amount of fertilizer applied at 100 kg K2O /ha is 45.9% Increase the amount 19 of fertilizer to 250 kg K2O /ha and 300 kg K2O /ha, REK fell to 35.82% (down 9.27%) and 31.11% (down 13.98%), respectively To simplify and facilitate the application of research results in practical production, REK introduced to use in balanced calculation and determine the amount of K fertilizing on the basis of nutrient balance is 40% 3.4 K balance and determination of suitable K fertilizing volume for cane base on nutrional balance in the Lam Son sugarcane area 3.4.1 K balance for cane at different K fertilizing levels On the basis of the research results about quantity and the relationship between nutrient input and nutrient outputs, K balance for sugarcane at different K fertilizing levels, base 200N + 100 P2O5 fertilizing, MY 55-14 sugarcane varieties grown on typical gray ferralit soil, no irigation in the Lam Son region is determined and presented in Table 3.19 Table 3.19 K balance for cane in the different K fertilizing volume No Nutrient source Basis Basis + 100 K2O Basis + 150 K2O Basis + 200 K2O Basis + 250 K2O Basis + 300 K2O 108,21 100 158,21 150 208,21 200 258,21 250 308,21 300 8,21 8,21 8,21 8,21 8,21 8,21 Output 135,2 182,86 196,34 208,63 210,65 214,56 Loss by stem removal 49,49 81,78 96,06 109,31 116,07 118,35 Loss by foliage removal 21,39 42,4 47,13 50,32 52,57 54,08 Loss by erosion 28,07 23,45 20,7 18,35 16,69 18,14 Loss by leaching 8,21 - Rain water Input Mineral fertilizers 36,25 35,23 32,45 30,65 25,32 23,99 Balance -126,99 -74,65 -38,13 -0,42 47,56 93,65 The results in Table 3:19 shows that no K fertilizing, not buried back cane foliage, negative K balance at the average 127 K2O/ha/vụ Mineral K fertilizing, K balance decreased from 74.6 kg K2O/ha at fertilizing level 100 kg K2O/ha to 0.4 kg K2O/ha at fertilizing level 200 kg K2O/ha K balance achieved at fertilizing level 250 kg K2O/ha upwards, so to ensure K reserves in the soil is not decline, the K fertilizing volume needs a minimum of 200 K2O/ha/vụ 3.4.2 K balance for cane in exist productional condition Đầu vào Kali cung cấp từ phân khoáng (IN1) Cân Kali cung cấp từ nước mưa (IN 3) Dinh dưỡng kali dự trữ Trung gian Đầu Kali cung cấp từ phân hữu (IN2) đất Kali rửa trôi chiều sâu (OUT 4) Kali xói mịn bề mặt (OUT 3) Cân kali hoàn toàn (IN1 + IN2 + IN 3) – (OUT1 + OUT + OUT + OUT 4) Kali theo sản phẩm mía nguyên liệu (OUT1) Kali theo mía sau thu hoạch (OUT 2) Cân kali theo sản phẩm (IN1 + IN2 + IN 3) – (OUT1 + OUT 2) Figure 3.5 Diagram of K balance for cane in exist productional conditions in the Lam Son sugarcane area 20 - K nutrient input from fertilizer: analyzing results in chemical compostions, organic material and determine K due to NPK presented in Table 3.20; 3.21 Table 3.20 Chemical composition, organic materials produce NPK Lam Son N P O5 Dry (%) (% dry weight) Sludge of sugar mill 7,1 31,5 1,76 1,91 Table 3.21 Nutrient volume N, P2O5, K2O is provided by NPK Lam Son Materials pH(KCl) K2O 1,28 P O5 K2O (kg/ha) NPK Lam Son 2.000 5,8 6,3 4,2 - K nutrient source was lost by harvested products: the average cane yield 62 tonnes/ha, K2O volume loss by product of sugarcane and cane foliage when harvest determined through reciprocal internal efficiencyof K (RIEK GY = 0.007 - 0.327) is 107 Kg K2O/ha - Balance: K balanced calculation results presented in Table 3:22 show, in the current sugarcane production, the amount of fertilizer to 2,000 kg / NPK Lamson, average cane yield 62 tonnes / ha, no buried cane foliage returns, K balance is Kg K2O/ha/vu Table 3.22 Cân K cho mía điều kiện sản xuất mía Supplying source Nutrient source K Input Output Balance Symbol IN IN IN Total OUT OUT OUT OUT Total Volume (kg/ha) N Describe K mineral in NPK Lam Son K organic in NPK Lam Son K from rain water K loss by cane stem removal K loss by residue removal afer harvesting K loss due to erosion K loss due to leaching Volume (kg K2O/ha) 132,0 4,2 8,2 144,4 107,0 17,7 26,7 154,4 - 7,0 3.4.2 The equation determines the suitable K fertilizing volume for sugarcane on the basis of nutrional balance - General equation: on the basis of research results the relationship between the amount of K fertilizing to yield and quality of sugar cane, the amount of K loss by harvested product and the amount of K nutrient elements inputs and outputs in the Lam Son condition, the suitable K fertilizing volume for sugarcane varieties MY 55-14 on typical gray soil, no irigation, fertilizing base 200N + 100P2O5, has the form: FK= [(GY x RIEK - KCR - KR + KE + KL) x FM] + (GY - GY0K) x RIEK/REK) where: FK: mineral K needs to fertilizer to achieve targets of yield (kg K2O/ha) GY: expected cane yield (ton/ha) GY0K: cane yield in condition of no K fertilizing (ton/ha) RIEK: K reciprocal internal efficiency(%) KR: K supply due to rain water (kg K2O/ha/year) KE: Amount of K loss by erosion (kg K2O/ha/year) KL: Amoun of K loss by leaching (kg K2O/ha/year) 21 KCR: Amount of K returns to soil via returning cane foliage (kg K2O/ha) KCR = GY x RIEK x (1 - HIK) x CRR, where: HIK harvested index of K; CRR: crop residue retained (%); REK: Recovery efficiency of K mineral fertilizer FM: maintain coefficient K reserves in the soil compared to the first crop (FM> potassium reserves in the soil are enhanced, FM