Effect of planting density, irrigation method, and nitrogen fertilizer on the quantitative and qualitative performance of sugar beet under transplanting system

Extended Abstract
 
Introduction
Materials and Methods
A two-year field experiment (2022 and 2023) was conducted in Abyek, Qazvin Province. The experiment was arranged as a split-split plot design within a randomized complete block design (RCBD) with three replications.
The treatments included two planting densities (83,000 and 100,000 plants per hectare) as the main plots (C₁ and C₂), three irrigation methods (furrow, drip tape, and alternate furrow) as the subplots (I₁, I₂, and I₃), and three nitrogen fertilizer levels (50, 100, and 150 kg N ha^-1) as the sub–subplots (N₁, N₂, and N₃). The distance between emitters in the drip lines was 20 cm. The German monogerm sugar beet cultivar 'Puma' was used. Seedlings were raised in a nursery and transplanted at the 8-10 leaf stage, approximately 60 days after sowing. Irrigation scheduling was managed using the CROPWAT 8.0 software based on daily meteorological data from the local station,  with application efficiencies of 95% for drip and 60% for furrow irrigation. Morphological traits including leaf length and width, root length and diameter, plant height, and number of leaves, as well as root yield and quality parameters (sugar content, extractable sugar, molasses percentage, sodium, potassium, and alpha-amino nitrogen) were measured at harvest. Data were analyzed using SAS 9.4 software, and mean comparisons were performed using Tukey's test at a 5% significance level.
 
Results
The combined analysis of variance revealed that planting density, irrigation method, and nitrogen fertilization significantly influenced most measured traits.
Morphological Traits and Yield: Drip irrigation (I2) combined with the lower planting density of 83,000 plants ha⁻¹ (C1) produced the highest values for leaf length (46.86 cm), leaf width (18.75 cm), root diameter, plant height (105.88 cm), and dry matter weight (1319.94 g). In contrast, alternate furrow irrigation (I3) at the higher density (C2) resulted in the lowest values. Root yield was highest (113.61 T ha⁻¹) under drip irrigation at the C1 density.
Quality Parameters: Sugar content (20.24%) and extractable sugar coefficient were maximized under drip irrigation (I2) at C1 density. The lowest molasses percentage and alpha-amino nitrogen content (3.04 mmol/100g pulp) were also recorded under this treatment. Conversely, higher planting density (C2) combined iwth furrow irrigation increased sodium content and root alkalinity. Nitrogen application up to 150 kg ha⁻¹ increased root length but occasionally reduced the extractable sugar coefficient, indicating a potential negative impact on processing quality at very high rates.
 
Discussion
The superior performance under drip irrigation is attributed to the uniform and efficient application of water and nutrients directly to the root zone, which reduces stress and optimizes growth conditions. Lower planting density (83,000 plants ha⁻¹) minimized inter-plant competition for resources such as light, water, and nutrients, allowing for better individual plant development and larger root size, thereby contributing to higher yield and quality. The response to nitrogen was complex. While increasing nitrogen up to 150 kg ha⁻¹ improved vegetative growth and root yield, the optimal rate for balancing yield with high sugar quality (extractable sugar) was 100 kg N ha⁻¹. This aligns with previous studies indicaing that excessive nitrogen promotes vegetative growth at the expense of sucrose accumulation and increases impurities like alpha-amino nitrogen. The significant interaction between year and other factors highlights the influence of climatic variations between the two growing seasons, highlighting the importance of adaptable management practices.
Conclusion
This study demonstrates that the interaction of planting density, irrigation method, and nitrogen fertilization is crucial for optimizing sugar beet production. The combination of lower planting density (83,000 plants ha⁻¹), drip irrigation, and moderate nitrogen application rate (100 kg N ha⁻¹) provided the best results for both quantitative yield and qualitative traits (sugar content and purity) in transplanted sugar beet in the Abyek region. This management strategy efficiently utilizes resources, improves water productivity, and maximizes economic returns, providing valuable guidance for farmers in similar semi-arid environments.
 
Keywords: Molasses percentage, Morphological traits, Sugar beet root yield, Sugar content.
 
References
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