Method for Determining the Amount of K Provided by Rainwater, the Amount of K Lost by Erosion and the Amount of K Lost by Leaching

K 2 O/ha/year. In the case of burying and returning all the straw to the soil, the negative K balance decreases sharply, from negative 19 kg K 2 O/ha/year to positive 10 kg K 2 O/ha/year.

On the alluvial soil with little sedimentation and two rice crops per year in the Mekong Delta, under the condition of no K fertilizer application and complete removal of straw, the negative K balance is at 70 kg K 2 O/year to 45 kg K 2 O/year. For other two-crop soils, when 70 kg K 2 O/ha/year is applied and a part of the straw is removed, the K balance reaches equilibrium (0). On the three-crop soil, when K fertilizer is applied at 40 kg K 2 O/ha/year and a part of the straw is removed, the negative K balance is at 80 kg K 2 O/ha/year (Nguyen My Hoa, 2003 [93]).

In summary: Up to now, in the world and in the country, there have been many research projects on nutritional balance at both macro, medium and micro levels. The general goal of the studies is to evaluate the balance of the three macronutrients N, P, K in the current production conditions of the research area, as a basis for evaluating nutrient reserves in the soil, determining the need and plan for fertilizer supply as well as solutions to overcome nutritional imbalance in the cropping system.

In order to supplement scientific data on input and output nutrient sources to serve the assessment of nutritional balance and determine the appropriate amount of K fertilizer for sugarcane on ferralit gray soil, at the same time, create a basis for dissemination, recommendation, and application in production, contributing to improving productivity, quality, and production efficiency in sugarcane growing areas in Thanh Hoa province and the whole country, we carry out the topic "Research on potassium nutritional balance for hill sugarcane in Lam Son Thanh Hoa area".

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CHAPTER 2

MATERIALS, CONTENT, RESEARCH METHODS

2.1. Research materials

2.1.1. Experimental soil

The experiments were arranged on typical ferralit gray soil with a slope of less than 8 - 10 o , no lumps at a depth of 0 - 50 cm. The soil has light - medium mechanical composition, low cation exchange capacity, acidic soil, poor organic matter, the content of nutrients N, P 2 O 5 , total K 2 O and easily available are all at poor to medium levels, limited irrigation conditions, sugarcane cultivation depends entirely on rainwater.

2.1.2. Experimental sugarcane varieties

Experiments were arranged with sugarcane variety MY 55 - 14.

Sugarcane variety MY 55 - 14 is a hybrid of the parent pair CP 3479 x B 45181, bred by the Cuban Sugarcane Research Institute. MY 55 - 14 was imported into Northern Vietnam in the early 1970s. After being propagated, tested and selected by the Institute of Industry, Ben Cat Sugarcane Research Institute, MY 55 - 14 was recognized as a national good variety and put into mass production. Characteristics: medium - late ripening (12 - 14 months old). Good drought tolerance, good germination and tillering. Sugarcane is large, straight, strong growth, good ability to retain roots, wide adaptability, does not flower in the climate conditions of the North Central region. High yield potential (80 - 100 tons/ha), suitable for planting on dry hills. The main disadvantage of the variety is sensitivity to white fiber aphids, high rate of hollow plants. Currently, MY 55 - 14 is identified as one of the main varieties in Lam Son Thanh Hoa region (accounting for over 60% of the variety structure), sugarcane growing areas nationwide and is considered a variety with high adaptability to climate change conditions [19].

2.1.3. Fertilizer

Fertilizers used in the experiment included: urea (46% N), superphosphate - SSP (16% P 2 O 5 ), potassium chloride (60% K 2 O), NPK fertilizer with organic additions: 6.4 - 3.2 - 6.6 - HC 9.5 (specialized for sugarcane) produced by Lam Son Fertilizer Joint Stock Company, sugarcane tops after harvest.

2.2. Research content

To meet the proposed purpose and requirements, the thesis focuses on researching the following contents:

1) Evaluation of basic conditions in Lam Son Thanh Hoa region in relation to input and output nutrient sources of K balance for sugarcane.

2) Study the ability to supply K to sugarcane of typical ferralit gray soil; the amount of K supplied to the soil annually by rainwater; the amount of K lost due to erosion and leaching after each sugarcane crop.

3) Study the relationship between K fertilizer application and yield, sugarcane quality, sugar yield and K loss according to harvested products.

4) Evaluation of K nutrient balance under current sugarcane production conditions.

5) Establish an equation to determine the appropriate amount of K fertilizer based on the input and output nutrient sources of the K balance for sugarcane.

6) Study the effectiveness of the model for sustainable management of K nutrition in sugarcane production based on the results of nutritional balance research.

2.3. Research method

2.3.1. Research process

The entire research work of the thesis was carried out from January 2010 to February 2013 (1 sugarcane cycle of 3 crops: 1 crop of newly planted sugarcane, 2 crops of sugarcane to keep the stump) through three steps as follows:

- Step 1: Investigate and evaluate the basic situation of Lam Son Thanh Hoa region in relation to sugarcane production through the method of resource research.

Secondary data and household surveys were used to determine the input and output sources of K balance under current sugarcane production conditions.

- Step 2: Based on the results of the basic situation investigation, conduct experiments to evaluate the soil's ability to supply K, determine the quantity of input and output nutrients and their relationship with sugarcane yield and quality. Thereby, evaluate the K balance under current production conditions and establish a method to determine the appropriate amount of K fertilizer for sugarcane through nutrient balance.

- Step 3: Build and evaluate the effectiveness of an experimental model for sustainable management of K nutrition in sugarcane production based on the application of the results of determining the input and output factors of the K balance and the equation for determining the amount of K fertilizer for sugarcane through the nutritional balance.

2.3.2. Basic situation investigation method

2.3.2.1. Collect secondary information

Collect all sources of documents, statistics, maps, technical processes, scientific reports, production reports... related to climate conditions, soil, production situation and technical measures for intensive sugarcane cultivation in Lam Son Thanh Hoa area, as a basis for synthesizing, analyzing and evaluating basic conditions in relation to input and output nutrient sources of K balance for sugarcane.

2.3.2.2. Primary information collection

Investigate and collect information related to sugarcane production and intensive farming techniques of farmers through household survey methods, specifically:

- Selecting points and households for investigation: select 4 out of 10 districts with the highest annual sugarcane growing area in the raw material area as investigation points, including the districts: Tho Xuan, Ngoc Lac, Lang Chanh, Thuong Xuan. In each district, randomly select 50 sugarcane growing households in the localities in the district as investigation households. Total number of households for investigation: 4 districts x 50 households/district = 200 households.

- Investigation method: Investigate and collect information according to a survey form with pre-printed questions, including both closed and open questions (sample form is included in the appendix) .

- Survey content: includes general information about the household, the sugarcane production situation of the household in the last 3 years (area, yield, sugarcane quality), the implementation of technical measures for sugarcane cultivation (sugarcane varieties, soil preparation techniques, planting, care, watering, fertilization, care, harvesting), investment costs, production efficiency and existing problems and limitations in current sugarcane production, recommendations and proposed solutions.

- Synthesize and process survey information: use statistical grouping method according to survey criteria to analyze and describe information collected through survey forms.

2.3.3. Experimental layout method

2.3.3.1. Experiment in jar

The experiment was arranged in a jar using the defected plot method (no K fertilization), left naturally outdoors, to study the ability to provide K nutrition for sugarcane of typical ferralit gray soil under different conditions of water regime and N, P fertilization. The ability to provide K of the soil was determined through the amount of K 2 O absorbed and accumulated by the plant in all above-ground parts (stems, dry leaves that fall from the stem during the growth process, leaf tips when harvested) and below-ground (roots, roots) at the time when the sugarcane stopped growing. The experiment consisted of 4 formulas, arranged in a completely randomized block design (Randomized Complete Block - RCB), repeated 3 times.

- Experimental formula:

1. No watering - no N, P fertilization

2. Do not water - fertilize with N, P

3. With irrigation - no N, P fertilization

4. With irrigation - N, P fertilization

- Experimental soil: typical ferralit grey soil. Soil was taken from the second crop of sugarcane (destroyed to plant new) at a depth of 0 - 40 cm (range of activity of over 90% of sugarcane roots) [Mohan Naidu. K et al, 1987 [92]. Each jar contained 30 kg of soil.

- Cultivation techniques applied in the experiment:

+ Plant sugarcane with single-bud cuttings, plant 3 cuttings per pot.

+ Fertilizer: apply N, P at the rate of 200 kg N/ha; 100 kg P 2 O 5 /ha (3.32 g urea/jar; 4.46 g superphosphate/jar) in the formulas with fertilizer (formulas 2; 4). Fertilization method: P is 100% basal fertilizer when planting; N is divided into 3 fertilizations: 30% basal fertilizer, 30% tillering stimulation, 40% height stimulation.

+ Watering: for formulas with irrigation (formulas 1, 3), regularly check and water to maintain soil moisture in the pot within the range of 70 - 80% of the maximum field humidity. Use distilled water once for watering to eliminate the possibility of supplying K from irrigation water.

- Monitoring indicators:

+ Monitor growth indicators, biomass constituents and biomass of all sugarcane parts when the plant stops growing.

+ Determine dry matter content, K2O content , K2O mass accumulated in plant parts and K2O supply capacity of soil under different watering and N, P fertilization conditions.

- Time and place of research:

+ Time: Planting date: February 10, 2010, harvest date: September 15, 2010.

+ Location: the experiment is located at Hong Duc University.

2.3.3.2. Field experiment

Field experiments were conducted to study the effects of different amounts of K fertilizer on growth, yield, sugarcane quality, sugar yield, K loss in harvested products and the relationship between them. The experiment consisted of 7 treatments, arranged in a randomized complete block design (RCB), repeated 3 times:

- Experimental formula:

1. Base (200 kg N/ha + 100 kg P 2 O 5 /ha)

2. Base + 100 kg K 2 O/ha

3. Base + 150 kg K 2 O/ha

4. Base + 200 kg K 2 O/ha

5. Base + 250 kg K 2 O/ha

6. Base + 300 kg K 2 O/ha

- Experimental plot area: 90 m 2 , planted with 5 rows of sugarcane 15 m long, row spacing 1.20 m.

- Experimental soil: the experiment was arranged on typical ferralit gray soil, sugarcane was grown in the previous crop, and the roots were destroyed for new planting.

- Cultivation techniques applied in the experiment:

+ Plant sugarcane with 2-bud cuttings taken from the autumn propagation field (8-month-old sugarcane). The number of cuttings planted is 32,000 cuttings/ha (4 cuttings/m long).

+ Fertilization: basal fertilizer 100% P, 30% N, 30% K (when planting sugarcane or when treating the roots of sugarcane with roots left). Top dressing for tillering 30% N, 30% K. Top dressing for growing 40% N, 40% K (calculated according to the amount of fertilizer of each experimental formula).

+ Other cultivation techniques applied in the experiment (soil preparation, planting, weeding, care, pest control, harvesting) are carried out consistently according to the sugarcane growing technical process of Lam Son Thanh Hoa Sugarcane Joint Stock Company, currently widely applied in the region [13].

- Research criteria:

+ Growth indicators, productivity, sugarcane quality, sugar yield.

+ Weight of sugarcane leaves after each harvest.

+ Dry matter content, K2O content , K2O mass accumulated in above-ground parts of sugarcane when harvested (sugarcane stalks, sugarcane leaves).

+ Maximum technical and economic K fertilizer amount for sugarcane yield and sugar yield.

+ Agronomic efficiency of K (Reciprocal Internal Efficiencies of Potassium - RIE K ).

+ Harvest Index of Potassium (HI K ).

+ Recovery Efficiency of Potassium (RE K ).

- Time and place of research:

+ Time: the experiment was arranged to be repeated continuously in 3 sugarcane crops (1 new sugarcane crop, 2 sugarcane crops to keep the stump), starting in 2010 and ending in 2013:

SugarcaneSugarcane root 1Sugarcane root 2

Planting date 11/1/2010 - -

Harvest date 1/29/2011 2/10/2012 2/25/2013

+ Location: Tho Xuan - Sao Vang raw material station belongs to Lam Son Sugarcane Joint Stock Company, Tho Lam commune, Tho Xuan district.

2.3.4. Method for determining the amount of K supplied by rainwater, the amount of K lost due to erosion and the amount of K lost due to leaching

2.3.4.1. Amount of K provided by rainwater

The amount of K supplied by rainwater is determined through the amount of rainfall and the K2O content in rainwater over the months of the year.

- Monitor rainfall through the months of the year using a rain gauge at the station.

Bai Thuong Hydrometeorology - Thuong Xuan District, Thanh Hoa Province

- Collect rainwater samples to analyze K2O content : arrange an outdoor rainwater tank in the field experiment area at Tho Xuan - Sao Vang Raw Material Station of Lam Son Sugarcane Joint Stock Company, Tho Lam Commune, Tho Xuan District. The rainwater tank has a diameter of 50 cm and a height of 70 cm, ensuring that it can collect rainwater from all rainstorms at the intensity.

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