element absorbed the most by sugarcane. K has a positive effect on most physiological and biochemical processes occurring in cells, especially the synthesis, transport and accumulation of sugar. However, the response of sugarcane to K fertilization is highly variable, showing high locality, depending on climatic conditions, soil, sugarcane varieties, cultivation techniques and interactions with other essential nutrients [53], [40].
Unlike N and P, sugarcane has a “luxury” consumption of K [106]. In addition, K deficiency symptoms are often not immediately apparent in cases where K is lost due to erosion, leaching or fixation. The need for K fertilizer only becomes apparent after a few sugarcane growing seasons with no or insufficient K compared to the amount of K lost after each harvest. Therefore, in both cases, excess or lack of K fertilizer leads to a reduction in sugarcane production efficiency [78].
Lam Son Thanh Hoa sugarcane area is planned in 10 districts in the midland and mountainous areas of the West of Thanh Hoa province with a total sugarcane growing area of 54,314 hectares, of which over 80% is of the Ferralit gray soil group [37]. In tropical climate conditions, mineralization, erosion, and leaching occur strongly, the organic matter content, the ratio and composition of K-rich clay minerals in the soil are low, which make sugarcane growing soil not only poor in K but also has low K retention capacity, leading to reduced K fertilization efficiency, reduced yield, quality and sugarcane production efficiency.
Studying the soil's K supply capacity and the relationship between input and output K nutrient sources with sugarcane yield and quality under specific production conditions, as a basis for assessing the current status of K reserves in the soil, detecting the causes of imbalance. At the same time, thereby determining the amount of K fertilizer and appropriate cultivation techniques in the direction of "Site specific nutrient management - SSNM" to ensure the requirements of both improving productivity and quality,
Effective sugarcane production, maintaining K reserves in the soil, and preventing soil degradation for sustainable production development are issues of scientific, practical, and urgent significance for sugarcane growing areas in our country today.
Based on the above issues, we conducted the topic " Research on potassium nutritional balance for sugarcane in Lam Son Thanh Hoa ".
2. Purpose and requirements of the topic
2.1. Purpose
Establishing an equation to determine the appropriate amount of K fertilizer for sugarcane through nutritional balance, creating a basis for sustainable management of K nutrition in specialized areas, contributing to improving productivity, quality and efficiency of sugarcane production in Lam Son Thanh Hoa hill region.
2.2. Requirements
- Evaluate the basic conditions of Lam Son sugarcane area in relation to K balance for sugarcane.
- Determine the ability to supply K to sugarcane of ferralit gray soil and the amount of input and output nutrients of the K balance for sugarcane.
- Determine the relationship between the amount of K fertilizer and the yield, quality of sugarcane, sugar yield and the amount of K lost according to the harvested product.
- Determine K balance at different K fertilization levels and under current sugarcane production conditions.
- Establish an equation to determine the appropriate amount of K fertilizer for sugarcane through nutrient balance.
- Determine the effectiveness of the experimental model for sustainable management of K nutrition for sugarcane based on the results of nutritional balance.
3. Research limitations
Research on K nutrient balance for sugarcane in Lam Son Thanh Hoa region was conducted at small scale (field scale) under the following specific conditions:
- Soil type: typical ferralit gray soil
- Sugarcane variety MY 55 - 14: main variety, accounting for over 60% of the current sugarcane variety structure of Lam Son region.
- Sugarcane growing cycle: 3 crops (1 crop of newly planted sugarcane, 2 crops of sugarcane to keep the roots).
- Sugarcane intensive cultivation techniques: except for the amount of K fertilizer as a research factor, sugarcane intensive cultivation techniques in the experiment were carried out according to the sugarcane intensive cultivation technique process of Lam Son Sugarcane Joint Stock Company which is currently widely applied in the region [13].
4. Scientific and practical significance of the topic
4.1. Scientific significance
The research results of the thesis contribute to supplementing scientific data for assessing nutritional balance and determining the appropriate amount of K fertilizer for sugarcane through nutritional balance on Ferralit gray soil, Lam Son hill area, Thanh Hoa.
4.2. Practical significance
The research results of the project are the basis for disseminating and recommending sustainable management of K nutrition in specialized areas in hill sugarcane production in Lam Son in particular, hill sugarcane areas in Thanh Hoa province and in the whole country in general.
5. New points of the thesis
The thesis topic has determined the soil's ability to supply K; the quantity and relationship between input and output nutrient sources of K balance. Thereby, establishing an equation to determine the appropriate amount of K fertilizer for sugarcane through nutrient balance and building a sustainable management model of K nutrition for sugarcane on typical ferralit gray soil in Lam Son Thanh Hoa hill area, achieving high productivity, quality, efficiency, and maintaining the K reserve content in the soil.
CHAPTER 1
OVERVIEW OF RESEARCH MATERIALS
1.1. General theory of nutritional balance
1.1.1. Nutritional balance in cropping systems
According to FAO (1998) [71], nutrient balance in a cropping system is the determination of the quantity of all nutrient inputs and outputs per unit area of cultivated land under specific conditions. Nutrient balance in a cropping system is established when the total value of nutrient outputs is equal to the total value of nutrient inputs.
The main purpose of nutrient balance in cropping systems is to assess the status of nutrient reserves in the soil, through determining the quantity of input and output nutrients in the entire cropping system, thereby assessing the level of soil degradation. The results of nutrient balance research are an important basis for developing a sustainable crop nutrition management strategy to provide adequate and balanced nutrients for plants, while improving, maintaining and enhancing soil fertility, ensuring the sustainable development of the cropping system.
In natural ecosystems, the biological components themselves are capable of compensating for the minimum amount of nutrients lost due to erosion and leaching. Even under suitable conditions, biological components not only compensate for the lost nutrients but also accumulate a certain amount in the topsoil. Unlike natural ecosystems, in crop systems, a certain amount of nutrients is removed from the ecosystem every year and a certain amount of nutrients from outside is added to ensure the maintenance and improvement of productivity and quality of crop products. Human intervention at different stages in the crop growth cycle with the aim of obtaining maximum crop products means taking out
from the system an amount of nutrients corresponding to the harvested product (Iftikar W, 2010) [82].
In cropping systems, the ability of soil to supply nutrients to plants is considered as “Immobilized Capital” because nutrients in the soil cannot move from one field or area to another. Nutrient reserves in the soil are limited. Excessive reduction of nutrient reserves in the soil will lead to reduced fertility and soil degradation. Nutrients in crop residues, organic fertilizers, green manures and agricultural and food industry by-products constitute “Working Capital” because they can be moved and distributed to each crop in the crop rotation system according to the purpose and requirements of the producer (Buresh R. J, 2010 (a); 2010 (b) [59], [60]).
In the plant nutrition system, the deficiency of a certain nutrient element will lead to limited effectiveness of other nutrients, thereby reducing productivity and quality of agricultural products (Chu Van Hach, 2012; Tran Minh Tien et al. (cs), 2013; FAO STAT, 2012 [23], [39], [70]). The imbalance of easily available nutrients can lead to overexploitation of nutrient reserves in the soil, while promoting plants to absorb excess nutrients, leading to reduced fertilizer efficiency and waste of land resources (Nguyen Trong Thi et al., 1999; FAO, 2010; IFA, 2011; 2012 [49],
[72], [80], [81])
In actual production, the amount of easily digestible nutrients for reuse through crop residues and animal waste products is difficult to compensate for the amount of nutrients lost in the harvested products, even for well-managed crop systems. Therefore, mineral fertilization is identified as a mandatory requirement to increase crop productivity (Nguyen Van Bo, 2013 [2]).
In theory, fertilizing crops must follow the laws of fertilizer use: the law of return, the law of limited nutrients, the law of decreasing fertilizer efficiency, the law of prioritizing product quality, and the law of balanced fertilization (cited in (dt.) Vu Huu Yem, 1998 [52]). A balanced and reasonable fertilization regime is the basis for ensuring high productivity, quality of agricultural products and fertilizer efficiency, while maintaining and improving soil fertility, limiting factors that pollute groundwater, surface water and greenhouse gas emissions (Ministry of Natural Resources and Environment, 2010; Pham Quang Ha et al., 2013; IPCC, 2010; Cao Ky Son, 2013 [12], [22], [25], [35]).
In fact, the input and output sources of nutritional balance have great changes, depending on the farming system, spatial scope, and time under specific conditions. The assessment of nutritional balance can be carried out on one or more types of soil with different farming regimes and management levels. Therefore, the input and output sources of nutrients in the cropping system are also linked to the characteristics of natural conditions and farming techniques within the research area.
According to Roy R. N et al (2003) [97], to evaluate the nutrient balance in the cropping system, it is necessary to first review all factors related to the input and output sources of nutrients in the research area to accurately determine the input and output sources of the nutrient balance, and then determine their quantities. Determining the quantity of input and output factors is done by direct or indirect methods. Nutrient balance achieves high accuracy and feasibility when the input and output sources of nutrients are determined through experimental design. In conditions where experiments cannot be arranged or some survey data are not available, extrapolation or estimation methods based on standard formulas can be used to determine and calculate the balance.
1.1.2. Levels of nutritional balance research
Depending on the scope of the research space, there are three levels of research on nutrient balance in cropping systems: macro level, meso level and micro level. The macro level applies to research at national, continental and global scales. The meso level applies to research at provincial, district, ecological region or specialized production area scales. The micro level applies to research at farm and household group scales.
For macro-level studies, nutrient balance focuses mainly on quantifying the input and output of three macronutrients N, P, and K in cultivated soils at national or continental levels. These elements are present in soils in easily digestible or fixed forms for crops and fluctuate after each harvest due to changes in input and output nutrient sources.
In the Saharan Africa region, during the period from 1983 to 2000, nutrient balance assessments were conducted on the basis of FAO data linked to land use types to assess the status of N, P, K depletion in soils. The results of nutrient balance studies in Ghana, Kenya and Mali conducted by Wageningen University, the Netherlands were further improved by clearly defining the space combined with the use of FAO databases and geographic information systems (GIS), so that calculations were faster and easier, with higher reliability than using only FAO data linked to land use types (Roy. R. N et al, 2003 [97]).
In China, the innovation in nutritional balance assessment, period 1961 - 1997, is to build a model of input and output values of nutrient circulation for national nutrition control. This method allows to perform balance assessment quickly, ensuring high accuracy (Sheldrick et al, 2003 [100]).
For studies at the medium level, district level, ecological region or specialized production areas, the goal of nutrient balance is to create a basis for planning policies and production and business plans in the area. Therefore, the amount of input and output factors needs to be calculated in detail to ensure the accuracy and high feasibility of the balance results.
For micro-level studies, the goal of nutrient balance is to serve the on-site approach to nutrient management within the field, farm or household production. At this level, the identification of sources and quantities of input and output nutrients is often carried out using a participatory approach with stakeholders, to analyze and evaluate specific conditions, nutritional status, and economic efficiency. Thereby providing a reliable database for calculating nutrient balances, while also linking to SSNM strategies for each crop (FAO, 1998) [71].
1.1.3. Input and output sources of nutritional balance
Correctly determining the input and output sources of nutrient balance suitable for the spatial scope and specific conditions of the research area is the content that determines the accuracy of the nutrient balance. According to Roy R. N et al (2003) [97], there are 5 input sources of nutrients and 5 output sources of nutrient balance for cropping systems, specifically as follows:
Table 1.1. Input and output sources of nutritional balance
Input nutrition
Symbol | Output nutrition | Symbol | |
Mineral fertilizer | IN 1 | Harvest products | OUT 1 |
Organic fertilizer | IN 2 | Plant residues | OUT 2 |
Settling (dust/rain) | IN 3 | Wash away | OUT 3 |
N-fixing microorganisms | IN 4 | Evaporation | OUT 4 |
Sediment, sedimentation (irrigation/silt) | IN 5 | Erosion | OUT 5 |
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(Source: Roy. R. N et al 2003 [97])