The effect of ammonium nitrate and humic acid fertilizers on the quantitative and qualitative traits of sugar beet cultivars

Extended Abstract
Introduction
Sugar beet (Beta vulgaris L.) is a major industrial crop with significant economic importance, particularly in regions such as Iran, where it contributes to both agricultural output and sugar production industry. Despite its potential, average sugar beet yield remains suboptimal, emphasizing the need for improved crop management strategies. Nitrogen is a critical nutrient that enhances vegetative growth, root development, and sugar accumulation, and its efficient uptake and utilization are strongly influenced by cultivar-specific characteristics. Humic acid, as an organic amendment, has been shown to stimulate enzymatic activity, enhance nutrient absorption, and improve root architecture, thereby increasing both yield and quality. The integration of mineral nitrogen and humic substances not only boosts biomass and sugar yield but also improves nitrogen use efficiency, offering agronomic and environmental benefits. Considering these factors, the present study aimed to investigate the combined effects of ammonium nitrate and foliar-applied humic acid on the quantitative and qualitative traits of three sugar beet cultivars.
 
Materials and Methods
This study was conducted to evaluate the effects of foliar-applied humic acid and ammonium nitrate fertilizer on the quantitative and qualitative performance of three sugar beet  cultivars in Farooj, Iran, during the 2021 growing season. The experiment was arranged in a split-split plot design based on a randomized complete block design with three replications. The main factor was cultivar, including Aria, Marinia, and Ernstina. The sub-factor was nitrogen fertilizer (ammonium nitrate) applied at three levels: 0, 100, and 150 kg ha⁻¹. The sub-sub-factor was foliar application of humic acid at three levels: 0, 2.5, and 5 L ha⁻¹. Planting was carried out in early April using a six-row pneumatic planter, with 50 cm row spacing and 7 cm between plants within each row. Buffer zones were established between plots and replications to minimize edge effects. Irrigation was applied using a sprinkler system immediately after planting, repeated every four days until emergence, and subsequently every 10 days. During the growing season and at harvest, root length and diameter, as well as fresh and dry biomass of roots and above-ground parts, were measured. For qualitative analysis, root pulp extracts were prepared, and sodium and potassium concentrations were determined using flame photometry, while alpha-amino nitrogen was measured with a Betalizer. White sugar yield was calculated by multiplying recoverable sugar by root weight. Data were checked for normality using XLSTAT 2016, analyzed via ANOVA in SAS 9.1, and mean comparisons were performed using LSD at P ≤ 0.05.
 
Results and discussion
Results of the variance analysis indicated that the interaction of cultivar × ammonium nitrate × humic acid was significant (P < 0.01) for shoot dry weight. Mean comparisons showed that, in all three cultivars, shoot dry weight increased with higher humic acid application under ammonium nitrate treatments. The highest shoot dry weight was recorded in Ernestina with 150 kg ha⁻¹ ammonium nitrate combined with 5 L ha⁻¹ humic acid (48.2 t ha⁻¹), whereas the lowest was observed in the control treatment (N0H0) at 25.1 t ha⁻¹. The interaction of cultivar× ammonium nitrate and humic acid× ammonium nitrate was sig nificant (P< 0.01) for root yield. Low ammonium nitrate levels resulted in the lowest root yield, and higher levels enhanced it. Ernestina exhibited superior performance across all nitrogen levels, reaching 74.61 t ha⁻¹ at N150, with the highest nitrogen use efficiency, whereas Aria required higher nitrogen levels to achieve optimal yield. The interaction of cultivar× ammonium nitrate × humic acid was also significant for root sodium and potassium contents. Increasing ammonium nitrate and decreasing humic acid led to higher accumulation, with maximum sodium and potassium contents of 2.94 and 41.7 meq per 100 g fresh weight in Ernestina under N150H0, and minimum values of 1.46 and 3.7 meq per 100 g in Aria under N0H5. The interaction of cultivar× ammonium nitrate× humic acid was significant for sugar yield, while interactions of cultivar× humic acid, cultivar× ammonium nitrate, and ammonium nitrate× humic acid significantly affected white sugar yield. Sugar yield decreased with increasing ammonium nitrate but increased with humic acid, with the lowest value of 8.43 t ha⁻¹ in Aria under N150H0 and the highest of 21.41 t ha⁻¹ in Ernestina under N0H5. White sugar yield consistently increased with humic acid across all nitrogen levels, reaching a maximum of 12.44 t ha⁻¹ in Ernestina. These findings indicate that the combination of 150 kg ha⁻¹ ammonium nitrate and 5 L ha⁻¹ humic acid produced the greatest improvements in both quantitative and qualitative traits. Integrated management of nitrogen and humic acid, considering the genetic characteristics of cultivars, plays a critical role in enhancing growth and increasing sugar beet performance.
 
Conclusion
The results of this study demonstrate that the combined application of ammonium nitrate and humic acid significantly influenced vegetative growth, root yield, and sugar quality of sugar beet. Increasing ammonium nitrate up to 150 kg ha⁻¹ enhanced shoot dry weight, root yield, and sugar production, while excessive nitrogen could reduce sugar quality. Humic acid, particularly when applied with high nitrogen levels, improved vegetative growth, sugar content, and the uptake of beneficial nutrients while reducing the accumulation of harmful compounds. Among the cultivars, Ernstina showed the highest nitrogen use efficiency, highlighting the importance of integrated management of these inputs to maximize yield.
 References
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The results indicated that the application of humic acid and ammonium nitrate had significant effects on all studied traits. The highest root yield (63.5 t ha⁻¹), fresh shoot weight (13.5 t ha⁻¹), shoot dry weight (2.48 t ha⁻¹), root dry weight (10.89 t ha⁻¹), root diameter (14.86 cm), and leaf area index (5.24) were obtained from the application of 150 kg ha⁻¹ ammonium nitrate combined with 5 L ha⁻¹ humic acid. In addition, the highest sugar content (23.54%) was achieved from the treatment of 5 L ha⁻¹ humic acid in the Ernestina cultivar.


The alkalinity coefficient and extractable sugar percentage increased with humic acid application, whereas root sodium and potassium contents decreased. Overall, the Ernestina cultivar outperformed the other two cultivars in terms of root and shoot growth characteristics in response to the applied treatments. Therefore, under conditions similar to those of the present experiment, the use of the Ernestina cultivar in combination with 150 kg ha⁻¹ ammonium nitrate and 5 L ha⁻¹ humic acid is recommended to achieve the highest pure sugar yield along with the highest sugar content.