Optimizing an Organic Method of Sugar Beet Cultivation and Yield Gap Decrease in Northern Poland

Abstract

In the period of 2016–2018, two series of field studies on organic sugar beet growing (Beta vulgaris L.) were carried out in northern Poland on Luvisol loamy soil (medium–heavy) soil in Bałcyny and Płonne. The aim of this study was to decrease the yield gap between organic and conventional beets. Factors to increase the yield of organic beet were differentiated fertilization (cattle farmyard manure (FYM), compost, and Bioilsa) and choice of varieties (Eliska, Jampol, and Sobieski). The reference point was the conventional cultivation of the same sugar beet varieties, fertilized with manure and NPK mineral fertilizers, the prevailing standard of sugar beet cultivation in Poland. High sugar beet root yields exceeding the average yield in Poland by 25–30% were obtained in both studies, both in conventional and organic cultivation. Higher root and white sugar yields were obtained in the study conducted at Płonne (with similar soil conditions to those at Bałcyny), but they were characterized by higher temperatures during the growing season. The lowest root yields in both experiments were obtained by fertilizing the organic beet with compost (66.1 t per ha in Bałcyny and 78.13 t per ha in Płonne), which were 10.8% and 8.5% lower than the conventional crop, respectively. Higher root yields in organic cultivation were obtained by fertilizing the sugar beet with FYM, which reduced the differences from conventional beet to 7.7% in the study in Bałcyny and 2.1% in the study in Płonne. Thus, the results showed no need to convert cattle FYM to compost. The highest root yields in organic cultivation were obtained by fertilizing the sugar beet with Bioilsa N 12.5 supplemented with mineral fertilization of K, Mg, and S (Patentkali). This fertilization provided a yield of 78.1 t of roots per ha in Bałcyny, which is a reduction in the yield gap to 1.4%, a statistically insignificant value. Moreover, in the study at Płonne, organic sugar beet fertilized with Bioilsa and Patentkali yielded 86.7 t of roots per ha, compared to 85.6 t per ha of conventional beet, so a yield gap was not seen here. The choice of varieties was also of great importance for root and pure sugar yields in both farming systems. The lowest yields were obtained from the Eliska variety, and at Bałcyny, a change of beet cultivar to Jampol increased the organic root yield from 68.8 t per ha to 76.0 t per ha, while reducing the yield gap from 10.1% to 2.2%. At Płonne, replacing the Eliska variety with Jampol reduced the yield gap between organic and conventional roots from 6.6% to 0.3%.

1. Introduction

The productivity of most crops has increased significantly due to the development of mechanization, advances in breeding, and the use of synthetic plant protection products and fertilizers [1]. The side effects of increased agricultural productivity are difficult to reverse, with adverse changes to natural ecosystems and the emission of significant amounts of nitrogen, phosphorus, carbon dioxide, methane, and pesticides into the atmosphere and soil environment [2]. The introduction of intensive agriculture has also resulted in the breaking down of varietal resistance and a decline in the effectiveness of plant protection products, further increasing cultivation inputs, as well as increasing its chemistry. In order to mitigate the negative impact of the above-mentioned factors, attempts are being made to use more sustainable and environmentally and human-friendly farming systems, including organic farming.

Historically, it was in sugar beet cultivation that chemical methods for pathogen and pest control [3,4], as well as seed treatment and seed coating [5], began to be used earlier than in other plant species, and monogerm varieties were developed [6]. In addition, there have been successes in resistance breeding, especially against cercospora leaf spot [7] and rhizomania [8]. This contributed to a significant increase in sugar beet productivity, with the sucrose content of the roots increasing from 4% to more than 16% in the first 100 years of breeding, and the root yield has doubled in the last 50 years [9,10]. A period of extremely dynamic growth in sugar beet yields was followed by a phase of stabilization, but sugar yields in European countries are characterized by an annual increase of 0.6–1.4% [11] as a result of continuous breeding progress [12]. Sugar beet production has great potential to further increase its efficiency [13], especially within the framework of organic farming.

In organic sugar beet cultivation, the choice of varieties has an important influence [14], not least because organic beet is processed into sugar first—before the processing lines in the sugar factory are contaminated with conventional raw material. For this reason, beet varieties in organic cultivation should be characterized by rapid emergence and high growth dynamics in order to produce a high yield, despite an early harvest.

Among others, cercospora leaf spot, a common leaf disease in plantations grown in the organic system, is responsible for a significant reduction in sucrose content in the roots [15]. In this system, the use of most chemical plant protection products is prohibited, but treatments with preparations containing copper and sulfur, which have good efficacy, are allowed [16]. In the case of high pressure of cercospora leaf spot, it is advisable to use varieties with increased resistance [17]. Rhizoctonia has also been a major problem in organic beet cultivation recently, which can be counteracted by using resistant varieties and, above all, correct crop rotation [18]. Aphids, which are the vector for the yellow vector virus, are also a limiting factor for beet yields [19]. Their control in organic farming relies on the use of insects predatory to aphids, including ladybirds and wasps [20], as well as the use of neem oil from Azadirachta Indica and insecticidal soaps [21]. In the case of soil parasitic nematodes, such as the beet cyst nematode (Heterodera schachtii), anti-nematode measures are based on crop rotations involving intercropping using the so-called trapping mechanism, as well as the use of beet varieties tolerant to nematodes [22].

Balanced fertilization plays an important role in realizing the yield potential of sugar beet [23]. In organic farming, mainly animal manures, such as farmyard manure (FYM), are used. In the case of organic stockless farms, it is possible to use green manure, composts, and commercially offered organic nitrogen fertilizers, such as Bioilsa N 12.5, and mineral fertilizers, including potassium and phosphorus fertilizers of natural origin.

As a result of the increasing instability of weather conditions, abiotic factors are having an increasing impact on sugar beet yields [24]. They cause yield losses, both in organic and conventional cultivation, often constituting a so-called minimum factor. The effects of unfavorable abiotic factors can be counteracted by improving the physical properties of the soil, its structure, and the water and organic matter content.

If weed control measures are omitted, competition from weeds can result in root yield losses of 26% to nearly 100% [25]. For this reason, in heavily weedy fields, organic sugar beet cultivation is not recommended. Weed control is mainly based on the use of mechanical treatments, in which hoes equipped with optical sensors are highly effective [26].

As a species requiring balanced fertilization and careful weed control, sugar beet has been considered a vehicle for agricultural progress since its cultivation began [27]. However, whereas in the 19th century there were sufficient labor resources to carry out mechanical and manual weeding, this is very problematic today [28]. Only recently have high-end weeding machines, including the optical weeder and rotary harrow, become available that can replace human labor. This creates good conditions for increasing the area of organically cultivated beet in many European countries [29,30,31], including the organization of such cultivation in Poland, for the benefit of growers, organic food consumers, and biodiversity [32]. With the increasing demand for organic sugar, low cultivation costs, due to mechanical weeding, offer a real chance to reduce the price of organic sugar.

In the above context, the level of yield is also important, depending strongly on the amount of organic matter contained in the soil and its effect on the biological activity and productivity of the soil [33,34,35,36,37]. As a consequence of lower root yields in organic cultivation [38], sugar yields would also be much lower, so the prices could also not be significantly reduced. For the farmer, in addition to the income from the sale of roots [38,39], other positives also count [40], including the possibility to harvest the leaves as cattle feed or to buy back organic pulp from sugar factories. Environmental aspects, including climate, as well as physiological–biochemical and energy aspects of organic cultivation are also important. These issues have been the subject of a number of scientific studies [41,42,43]. In addition, there has been interest in organic fertilization [44,45,46,47,48], organic seed dressing [49], and biological control methods for sugar beet agrophages [50].

The aim of this study was to determine the possibility of increasing sugar beet root yields and sugar yields in organic farming, so that the difference with yields obtained in conventional farming would be as small as possible. The experimental factors considered in the study were differentiated fertilization (with manure, compost, and Bioilsa) and choice of cultivars (Eliska, Jampol, and Sobieski). The study was conducted in the northeastern part of Poland, with a lower pressure of sugar beet agrophages than in the southern part of the country.

2. Materials and Methods

2.1. Field Experiments

In the period 2016–2018, two series of field studies on organic sugar beet growing (Beta vulgaris L.) were carried out. The first was performed on medium–heavy soil in an Agricultural Experimental Station (belonging to the University of Warmia and Mazury in Olsztyn) and located in the village of Bałcyny (53°35′46″ N 19°51′19″ E), in the district of Ostróda, province of Warmia and Mazury, Poland. The second series of studies was performed on a medium–heavy soil on a certified organic farm located in the village of Płonne (53°07′27″ N 19°10′08″ E), near Golub Dobrzyń, province of Kuyavia-Pomerania, Poland.

The total rainfall during the sugar beet growing season (April–September) in 2016, 2017, and 2018 was 379.8, 426.2, and 431.6 mm in Bałcyny and 381.5, 401.2, and 332.7 mm in Płonne, respectively. Average temperatures during the experimental period ranged from 14.4 to 17.0 °C in Bałcyny and from 14.7 to 17.1 °C in Płonne. Little variation in weather conditions, especially precipitation, was recorded between the study years at both sites. Although in both field trials the same scheme was used, the field trials were carried out in two locations of northern Poland, which were located at a distance of ca. 90 km and, therefore, the results are presented separately.

Field and laboratory examinations were carried out to describe the soil type of the experimental fields. Soil pits were dug to determine soil morphology and systematic position. In both locations, the plots had Luvisol loamy soil (containing 28–29% particles ≤ 0.02 mm diameter)—in this paper, it is called medium–heavy soil. At both locations, the contents of individual soil fractions did not vary depending on the depth of the layer, which indicates its homogeneity (

Table 1. Physical properties of the soils in the experimental sites on organic farms in the villages of Bałcyny and Płonne.

Specification	Location of the Experiments
	Bałcyny	Płonne
Textural class	Silty loam	Silty loam
Soil layer 0–30 cm
Sand, %	38	42
Silt, %	33	30
Clay, %	29	28
Soil layer 30–60 cm
Sand, %	39	42
Silt, %	30	31
Clay, %	31	27

).

To determine the soil chemical properties, representative soil samples were obtained from the ploughing level (0–20 cm) using an Egner cane. The obtained material was dried to the state of air dry, grounded, and sieved. Such prepared samples of soil underwent a chemical analysis and were measured:

• − potentiometrically for pH in suspension of 1 mol KCl dm⁻³ solution,
• − for the content of the form of P and K, as determined by the method of Egner–Riehm,
• − for the content of assimilable Mg by Schachtschabel’s method,
• − for the content of assimilable S by the nephelometric method,
• − for the content of organic carbon by Turin’s method,
• − for content of nitrate–nitrogen by the ion-selective electrode method.

According to the chemical soil analysis, the soil pH in Bałcyny was neutral and in Płonne it was slightly alkaline, the content of K and Mg was low, and the content of S was medium (

Table 2. Selected chemical properties of medium–heavy soils.

Location and Soil Type	Organic C, g kg−1 of Soil	pH		Available Forms, mg kg −1 of Soil *
		1 mol KCl dm−3	H2O	N-NO3	P	K	Mg	S-SO4
Bałcyny, medium–heavy soil	9.84	6.05	6.33	24.3	65.4	59.5	48.8	26.5
Płonne, medium–heavy soil	9.91	6.42	6.89	37.7	64.6	71.4	64.2	28.6

* N-NO₃ was analyzed by the ion-selective electrode method, P and K were analyzed by the Egner–Riehm method, Mg by the Schachtschabel method, and S by the nephelometric method.

). The soils had 9.84–9.91 g of organic C per 1 kg of soil. Nitrate–nitrogen content in Bałcyny was medium and in Płonne it was high.

In both experiments, the sugar beet was fertilized using organic and mineral fertilizers. The crop was fertilized by cattle farmyard manure (FYM) at a rate of 30 t per ha (contains 105 kg N ha⁻¹), farmers’ compost at a rate of 30 t per ha, which corresponds to a rate of 103 kg of N per ha, and Bioilsa (12.5% of N) at a rate of 800 kg per ha, which corresponds to a rate of 100 kg of pure N per ha. Bioilsa is a commercially available organic fertilizer made of animal by-products obtained from slaughterhouses. The prevailing raw material is pig bristles from the slaughterhouse. That by-product undergoes enzymatic degradation to produce organic N fertilizer approved for organic agriculture, quite commonly used in many EU countries.

The content of basic macronutrients in the organic fertilizers is shown in

Table 3. Average content of dry matter and basic macronutrients in cattle FYM and compost used in the experiments.

Organic Fertilizer	Content %
	Dry Matter	N	P	K	Na	Ca	Mg
Cattle FYM	24.50	1.43	0.91	1.55	0.23	0.94	0.26
Compost	40.81	0.84	0.61	0.98	0.19	0.96	0.32

. The drying method was used to determine the dry mass of the organic fertilizers. The material was mineralized in concentrated sulfuric acid and a solution of 30% oxidized water, and the resulting solution was used to determine the content of basic macronutrients. A nitrogen distillation apparatus of the Büchi Distillation Unit B-324 (Büchi, Sankt Gallen, Switzerland) type was used to determine the total nitrogen content in the fertilizers. The solution obtained was titrated with hydrochloric acid at a concentration of 0.0169 molꞏdm⁻³. Phosphorus content was determined calorimetrically according to the molybdenum method, and potassium, calcium, magnesium, and sodium contents were determined by atomic absorption spectrometry using a Philips PU 9100X spectrometer (Philips, Amsterdam, The Netherlands).

Mineral K and Mg fertilization in both experiments in plots fertilized with Bioilsa was additionally applied in the form of kali magnesia (Patentkali) at a rate of 66.4 kg K and 16.1 kg Mg per ha. The fertilizer additionally contained sulfur, and 45 kg of S was applied using Patentkali. It should be noted that Patentkali fertilizer is allowed in organic farming. It is on the positive list as being acceptable for use on organic farms in Poland.

For conventional cultivation, FYM at a rate of 30 t per ha and ammonium nitrate (50 kg N per ha), potassium salt (80 kg K per ha), and superphosphate (40 kg P per ha) were applied, as this is a prevailing standard of sugar beet cultivation in Poland for the last two centuries, although in recent decades, less and less FYM is being applied, causing problems with organic matter content in soils.

For both series, a randomized block design (RBD) was used to arrange experimental plots (three replications) in the field. The plot size was 2.7 × 12 m, and at harvest only the central part of the plot was harvested (1.8 × 10 m).

As the second factor in the experiments, sugar beet cv. Eliska, Jampol, and Sobieski were grown:

• − The Eliska cultivar was bred by KWS (Germany). It is a diploid cultivar of normal-sugar type, with average sugar content and a very regular root shape, characterized by resistance to rhizomania, cercospora leaf spot, and tolerance to beet cyst nematodes.
• − The Jampol cultivar was bred by Kutno Sugar Beet Breeding Company (Poland). It is of normal-sugar type, with intense foliage, distinguished by its resistance to rhizomania and cercospora leaf spot.
• − The Sobieski cultivar was bred by Wielkopolska Sugar Beet Breeding Company (Poland). It is of normal-sugar type, characterized by resistance to rhizomania and cercospora leaf spot.

The beet was grown after winter wheat, in a crop rotation with a four-year return to the same field (1:5 cropping frequency). It was sown at both study sites in the first week of April. Each year, the beet was harvested in the first week of October. The roots were collected by hand from each central part of the plot (18 m²); then, after removing the leaves, they were cleaned and weighed. Qualitative parameters were analyzed for 20 sugar beet roots. Representative samples were collected according to the PN-R-74452 [51] standard to determine the technological quality. Root yield, sucrose content, K, Na, and N-amino molasses, and white sugar yield were assessed. The technological value of the raw material was measured using a Venema line by the Kutno Sugar Beet Breeding Company (KHBC) technology laboratory in Straszków (Poland). Sucrose content was polarimetrically determined in °Z degrees. The content of Na and K was determined using a flame photometer and the N-amino content using the fluorometric method. Molasses content was expressed in mmol per 1000 g of pulp. White sugar yield (WSY) was calculated using the Reinfeld formula [52]:

WSY = RY/100 [% sugar − 0.012(K + Na) − 0.024 N-α-NH2 − 1.08]

RY − root yield in t ha⁻¹; % sugar − biological sugar content

Melasotrophs: K, Na, and N-α-NH2, values in mmol 1000 g⁻¹ root pulp

2.2. Statistical Analysis

The results were worked out statistically using Statistica software (data analysis software system), version 12, StatSoft, Hamburg, Germany. The statistical ANOVA was carried out according to Tukey’s test at p < 0.05.

3. Results

3.1. Results Obtained in the Bałcyny Experiment

The significantly highest sucrose content (18.64%) in the series of studies in Bałcyny was recorded in the variants with conventional cultivation (FYM + NPK;

Table 4. Effect of organic and conventional cultivation variants and sugar beet varieties on sucrose content and white sugar yield (%). Bałcyny 2016–2018.

Parameters	Cultivars	Organic Growing				Conventional Growing	Mean—Cultivar
		FYM 30 t ha−1	Compost 30 t ha−1	Bioilsa 800 kg ha−1	Mean	FYM + NPK
Sucrose %	Eliska	18.14	17.90	18.09	18.04	18.40	17.38 b
	Jampol	18.60	18.41	18.61	18.54	18.85	18.62 a
	Sobieski	18.46	18.22	18.44	18.37	18.66	18.45 a
	Mean	18.40 B	18.18 C	18.38 BC	18.32 BC	18.64 A	18.15
White sugar %	Eliska	15.80	15.68	15.74	15.74	15.99	15.80 b
	Jampol	16.39	16.35	16.41	16.38	16.60	16.44 a
	Sobieski	16.27	16.16	16.29	16.24	16.45	16.29 a
	Mean	16.15 B	16.06 B	16.15 B	16.12 B	16.35 A	16.18

FYM, farmyard manure; A–C, significance of factor I (fertilization); a–b, significance of factor II (variety).

). Sugar beet roots grown in organic farming systems had an average sucrose content of 18.32%, with no statistically significant differences between variants with manure and Bioilsa fertilizer. The significantly lowest sucrose content was determined in beet fertilized with compost. There were no statistically significant differences in sucrose content between the Jampol and Sobieski varieties. The significantly lowest sucrose content was found in the roots of the Eliska cultivar.

The organic sugar beet cultivation variants did not result in statistically significant differences in white sugar expenditure (it averaged 16.12%). The significantly highest white sugar expenditure was found in the conventional cultivation. The varietal factor was shown to have a significant effect on white sugar expenditure. The highest white sugar expenditure was found in the roots of the Jampol variety and the lowest in the Eliska variety, at 16.44% and 15.80%, respectively.

The significantly lowest potassium content was determined in sugar beet roots fertilized with compost (45.0 mmol in 1000 g;

Table 5. Effect of organic and conventional cultivation variants and sugar beet varieties on the content of melasotrophs in roots: K, Na, and N-α-NH₂ (mmol 1000 g⁻¹). Bałcyny 2016–2018.

Parameters	Cultivars	Organic Growing				Conventional Growing	Mean—Cultivar
		FYM 30 t ha−1	Compost 30 t ha−1	Bioilsa 800 kg ha−1	Mean	FYM + NPK
K, mmol in 1000 g	Eliska	49.3	46.5	49.5	48.4	50.3	48.9 a
	Jampol	48.4	44.6	48.0	47.0	48.5	47.4 a
	Sobieski	46.9	44.0	45.9	45.6	46.7	45.9 a
	Mean	48.2 A	45.0 B	47.8 A	47.0 A	48.5 A	47.4
Na, mmol in 1000 g	Eliska	6.40	6.20	6.80	6.50	6.8	6.55 a
	Jampol	3.80	3.80	4.10	3.90	4.1	3.95 b
	Sobieski	4.60	4.30	4.50	4.50	4.7	4.53 b
	mean	4.90 A	4.80 A	5.10 A	5.00 A	5.2A	5.01
N-α-NH2, mmol in 1000 g	Eliska	14.7	12.8	13.9	13.8	17.2	14.7 a
	Jampol	14.0	11.8	13.5	13.1	16.5	14.0 a
	Sobieski	14.1	11.7	14.1	13.3	16.9	14.2 a
	Mean	14.3 B	12.1 D	13.8 BC	13.4 C	16.9A	14.3

FYM, farmyard manure; A–D, significance of factor I (fertilization); a–b, significance of factor II (variety).

). The other fertilizer variants did not differentiate the potassium content of beet roots. There was also no statistically significant effect of variety on potassium content.

Variety had a statistically significant effect on sodium content in the roots. The highest content of this element was determined in roots of the Eliska cultivar (6.55 mmol in 1000 g) and the lowest was in roots of the Jampol and Sobieski cultivars (3.95 and 4.53 mmol in 1000 g, respectively). The agricultural system did not cause statistically significant differences in sodium content.

The content of alpha-amino nitrogen in the roots did not depend on the cultivar and ranged from 14.0 to 14.7 mmol in 1000 g. However, the agricultural system was important—the significantly highest content of alpha-amino nitrogen was recorded in conventional cultivation (16.9 mmol in 1000 g), while the significantly lowest content of this melasotroph (12.1 mmol in 1000 g) was determined in roots from organic cultivation fertilized with compost. The content of the harmful nitrogen fraction in the other organic variants (FYM and Bioilsa fertilization) did not differ statistically significantly and was 14.3 and 13.8 mmol in 1000 g, respectively.

A significant interaction of experimental factors was found for the alpha-amino nitrogen content. The lowest statistically significant nitrogen content occurred in the roots of beet fertilized with compost and, in the case of cultivars, in the Sobieski and Jampol varieties.

The significantly highest root yield was obtained in conventional and organic cultivation fertilized with Bioilsa fertilizer (79.2 and 78.1 t ha⁻¹), respectively, while the significantly lowest yield was obtained in organic cultivation of beet fertilized with compost (66.1 t ha⁻¹; Figure 1). A statistically significant effect of the varietal factor was shown. The highest yield was characterized by the variant with the Jampol cultivar (77.7 t ha⁻¹), and significantly the lowest (70.8 t ha⁻¹) with the Eliska cultivar.

A significant interaction of experimental factors for root yield was determined. The highest statistically different root yields were obtained from the variant with conventional cultivation and the variant with organic cultivation using Bioilsa fertilization, in both cases with cultivation of the Jampol variety.

The lowest leaf yield was obtained by fertilizing the beet with compost (23.1 t ha⁻¹; Figure 2). There were no statistically significant differences in yields between the other organic fertilization options (FYM 30 t ha⁻¹ and Bioilsa 800 kg ha⁻¹). Indeed, the highest leaf yield (33.7 t ha⁻¹) was obtained from cultivation under the conventional system. The highest leaf yields were obtained from the Jampol and Sobieski cultivars (29.9 and 30.1 t ha⁻¹), while the lowest were obtained from the Eliska cultivar (25.8 t ha⁻¹).

Statistically significant differences in white sugar yield were recorded for all sugar beet varieties tested. The highest yield of white sugar was obtained from the Jampol cultivar (12.56 t ha⁻¹), while the lowest yield was obtained from the Eliska cultivar (11.19 t ha⁻¹; Figure 3). The highest yields were found in the conventional and organic systems in the variant fertilized with Bioilsa (12.94 and 12.62 t ha⁻¹), respectively, while the lowest sugar yield (10.62 t ha⁻¹) was found in the organic crop fertilized with compost.

3.2. Results Obtained in the Płonne Experiment

The agricultural system varied the sucrose content in the experiments in the village of Płonne, ranging from 17.63 (in organic beet fertilized with compost) to 18.06% (beet in conventional cultivation;

Table 6. Effect of organic and conventional cultivation variants and sugar beet varieties on the biological content of sugar and white sugar (%). Płonne 2016–2018.

Parameters	Cultivars	Organic Growing				Conventional Growing	Mean—Cultivar
		FYM 30 t ha−1	Compost 30 t ha−1	Bioilsa 800 kg ha−1	Mean	FYM + NPK
Sucrose %	Eliska	17.18	17.02	17.23	17.14	17.46	17.22 b
	Jampol	18.25	18.05	18.20	18.17	18.51	18.25 a
	Sobieski	17.98	17.82	17.92	17.91	18.21	17.98 a
	Mean	17.80 A	17.63 B	17.78 A	17.74 B	18.06 A	17.82
White sugar %	Eliska	14.89	14.87	14.95	14.90	15.14	14.96 b
	Jampol	16.01	15.86	15.88	15.89	16.14	15.97 a
	Sobieski	15.68	15.64	15.62	15.65	15.86	15.70 a
	Mean	15.53 B	15.46 B	15.48 B	15.48 B	15.71 A	15.54

FYM, farmyard manure; A–B, significance of factor I (fertilization); a–b, significance of factor II (variety).

). Taking into account the varietal factor, the lowest sucrose content (17.22%) was significantly determined in the Eliska variety.

The significantly lowest white sugar yield was found in all organic variants tested (15.48%), while the significantly highest was obtained in beet from conventional cultivation (15.71%). In terms of the varietal factor, the significantly lowest white sugar content (14.96%) was found in the Eliska variety. No significant differences were found for this parameter between the Polish cultivars Jampol and Sobieski (Table 6).

Cultivar selection did not significantly affect the potassium content of sugar beet roots. The significantly lowest K content (45.6 mmol in 1000 g) was determined in organic sugar beet roots fertilized with compost (

Table 7. Influence of organic and conventional cultivation variants and sugar beet varieties on the content of melasotrophs in roots: K, Na, and N-α-NH₂ (mmol 1000 g⁻¹). Płonne 2016–2018.

Parameters	Cultivars	Organic Growing				Conventional Growing	Mean—Cultivar
		FYM 30 t ha−1	Compost 30 t ha−1	Bioilsa 800 kg ha−1	Mean	FYM + NPK
K, mmol in 1000 g	Eliska	47.1	44.1	47.0	46.1	47.1	46.3 a
	Jampol	49.6	46.7	49.4	48.6	49.7	48.9 a
	Sobieski	48.8	45.9	48.6	47.8	49.1	48.1 a
	Mean	48.5 A	45.6 B	48.3 A	47.5 A	48.6 A	47.8
Na, mmol in 1000 g	Eliska	5.60	5.40	5.60	5.50	5.70	5.58 a
	Jampol	4.80	4.50	4.70	4.70	5.00	4.75 b
	Sobieski	5.00	4.90	5.30	5.10	5.50	5.18 a
	Mean	5.10 B	4.90 C	5.20 B	5.10 B	5.40 A	5.17
N-α-NH2, mmol in 1000 g	Eliska	20.2	17.4	20.2	19.3	23.7	20.4 a
	Jampol	18.5	15.5	18.2	17.4	21.5	18.4 b
	Sobieski	17.6	15.6	17.4	16.9	20.3	17.7 b
	Mean	18.8 B	16.2 C	18.6 B	17.9 BC	21.8 A	18.9

FYM, farmyard manure; A–C, significance of factor I (fertilization); a–b, significance of factor II (variety).

). The potassium content among the other variants did not differ significantly.

The highest sodium content (5.4 mmol in 1000 g) was recorded in the conventional cultivation, while the lowest was in the organic cultivation fertilized with compost. The content of this melasotroph in the cultivation of the Eliska variety was determined to be significantly higher than that for the Jampol and Sobieski varieties (Table 7).

Roots of organic beet fertilized with compost were significantly characterized by the lowest content of alpha-amino nitrogen (16.2 mmol in 1000 g), while the highest content of the molasses-forming fraction of this element (21.8 mmol in 1000 g) was determined in roots from conventional cultivation. There were no statistically significant differences in the content of alpha-amino nitrogen in roots from the other organic cultivation variants (FYM 30 t ha⁻¹ and Bioilsa 800 kg ha⁻¹). The cultivar factor also had a significant effect on the alpha-amino nitrogen content: in the Eliska cultivar, this content was 20.4 mmol in 1000 g, while in the other two cultivars (Jampol and Sobieski), it was 18.5 and 17.7 mmol in 1000 g, respectively.

A significant interaction of the experimental factors was shown for the content of alpha-amino nitrogen in the roots. Desirable for the sugar industry—the lowest content of this melasotroph occurred in organic beet roots fertilized with compost and in the Jampol and Sobieski cultivars (Table 7).

The highest root yield (94.6 t ha⁻¹) was produced by the Jampol variety and the lowest by the Eliska variety (74.8 t ha⁻¹; Figure 4). Considering the agricultural system, the lowest root yield was produced in the organic crop fertilized with compost. The other variants showed no statistically significant differences in root yield.

Significant interaction of experimental factors was shown for the root yield. The highest root yield, statistically different from the combination of the other two cultivation variants with the varieties Sobieski and Eliska, was obtained from beet of the variety Jampol fertilized with Bioilsa. The root yield produced in this combination did not differ from that of the conventionally grown beet—there was no yield gap.

The farming system had a significant effect on leaf yield, and each of the variants tested (fertilization and variety selection) showed statistically significant differences. The highest leaf yield was obtained in conventional cultivation (33.1 t ha⁻¹) and the lowest in organic cultivation fertilized with compost (21.4 t ha⁻¹; Figure 5). For the varietal factor, a statistically significant difference in yield was determined between the lowest yielding cultivar, Eliska (19.4 t ha⁻¹), and the Jampol and Sobieski cultivars (35.4 and 28.5 t ha⁻¹), respectively. There were no statistically significant differences between leaf yields in organic variants fertilized with manure, Bioilsa, and conventional cultivation fertilized with manure and NPK.

White sugar yield was the lowest in organic cultivation with compost fertilization (12.13 t ha⁻¹) and highest in conventional cultivation (13.48 t ha⁻¹; Figure 6). The choice of varieties significantly affected the sugar yield, and the lowest yield of technological sugar was obtained from the Eliska variety (11.19 t ha⁻¹).

4. Discussion

Sugar beet is grown successfully in many central and western European countries. In the scientific literature, there are numerous studies on its environmental impact, especially gas emissions deriving from conventional cultivation [43]. However, the subject of yield differences between these cultivation systems is extremely rarely addressed.

It is usually assumed that the organic cultivation of sugar beet results in a reduction in the yield of this crop of about 10–25% compared to conventional cultivation [53,54]. However, our own research has shown that with optimization of the fertilization method and the correct choice of variety in organic cultivation, it is possible to maintain key quantitative and qualitative parameters (root yield, sucrose content, and white sugar yield) at a level similar to that obtained from conventional cultivation. Sugar beet yields show variations depending on the growing region. The average root yield of sugar beet in Poland about 10 years ago exceeded 55 t ha⁻¹ [54] and shows a constant upward trend, exceeding 60 t ha⁻¹ [55]. Yields obtained in the experiments in Bałcyny and Płonne were about 25–30% higher than the national average. The reasons for this discrepancy can be attributed to the use of farmyard manure, which in Poland in conventional cultivation, is applied by a decreasing number of farmers (about 30%) [56]. The majority of sugar beet growers have no livestock on the farm and hence, no manure, and apply only NPK mineral fertilizers, thus worsening the soil organic matter balance and soil structure, which adversely affects the yields obtained. It is worth emphasizing that an organic farm applying natural fertilizer on a site with soils with average nutrient abundance may have a higher yield potential than a stockless conventional farm, i.e., using only mineral fertilizers and synthetic plant protection products.

The fertilization variants applied in organic cultivation resulted in high sugar beet yields. The beneficial effect of manure fertilization on sugar beet development has already been confirmed many times [57,58,59,60]. Manure fertilization in organic cultivation makes it possible to maintain a satisfactory yield level, little different from that in conventional cultivation. The available balanced nutrient pool covered the requirements of the sugar beet, while at the same time allowing the good processing value of the roots to be formed, by significantly reducing the content of melasotrophs, primarily alpha-amino nitrogen.

In the context of the above considerations, fertilization with Bioilsa has proven very beneficial. This is a fertilizer produced from slaughterhouse waste (mainly pig bristles), with a nitrogen content of 12.5%, which is released gradually during the growing season. Since sugar beet has a long growing season and organic cultivation is accompanied by considerable mechanical weeding (and at the same time, soil loosening), soil oxygenation is increased by accelerating the release of N. By fertilizing with Bioilsa, almost only N is supplied to the soil. Therefore, in organic cultivation, the mineral fertilizer Patentkali was additionally applied, with a composition of 30% K, 10% Mg, and 42.5% S. This was carried out to provide the beet plants with an adequate supply of K and Mg, which are present in large quantities in manure and compost, but which are basically absent in Bioilsa. To dispense with mineral fertilization of K and Mg, Bioilsa N, P, and K would have to be used.

Overall, the variant using the organic nitrogen fertilizer Bioilsa N 12.5 in organic sugar beet cultivation resulted in high yields, matching the yields obtained in conventional cultivation. In addition to ensuring high root yields, it is worth highlighting the beneficial effect of Bioilsa on the content of melasotrophs. Hence, Bioilsa 12.5, in combination with mineral K and Mg fertilization, is a good alternative for organic stockless farms.

In practice, fertilization with compost is used less frequently. The compost used in the experiments was made on the organic farm using cattle FYM as the substrate. The mature compost used in the experiment was a fertilizer with a fairly high concentration of nitrogen. In mature composts, however, it is more than 97% nitrogen in organic form, which requires mineralization for the plant to take it up. Nitrogen from composts is released over a very long period, up to 10 years, and hence beet plants may be deficient in nitrogen [61].

In our own research, compost fertilization proved to be the least effective fertilization method in organic farming. As mentioned above, the reason for this is the low availability and slow mineralization of organic compounds. The most obvious manifestation of nutrient deficiencies in cultivation with compost was the very low uptake of nitrogen. Although this resulted in a significantly lower content of melasotrophs, it also caused a significant reduction in root yield by 9.6% and 6.6%, as well as in tops yield by 15.7% and 20.7%, respectively, in the experiments at Bałcyny and Płonne, compared to the manure-fertilized variant. Poor leaf development is the primary cause of lower sucrose accumulation, which directly reduces sugar yield.

In a study by Łada [62], among others, the effectiveness of different fertilization rates of organic beet with manure and compost was compared. In that study, compost performed much worse than manure. Compost applied at 10 and 20 t ha⁻¹ increased root yield by 10.7% and 12.1%, respectively, compared to the unfertilized control, while fertilization with 30 t ha⁻¹ of FYM increased root yield by 33.9%.

In contrast to the results of our own study, a beneficial effect of compost fertilization on sugar beet yield in organic cultivation was found by Stępień and Adamiak [63]. However, it is worth noting that in their experiment, a very high dose of compost was used (40 t ha⁻¹), with high N content. According to contemporary restrictions on the use of N in manures in organic farming, the maximum is 170 kg N ha⁻¹, while in the above-cited study the dose was 219.7 kg N ha⁻¹, so the restriction was exceeded by 50 kg N ha⁻¹. It is worth noting that the manure used in this study, at a dose of 30 t ha⁻¹, contained only 118.3 kg of N, almost half as much as the compost.

An important factor influencing the yield of organically grown sugar beet proved to be the choice of cultivar. The lowest yield and less favorable yield quality parameters (including lower sucrose content) were found in the Eliska variety. This is surprising insofar as, in registered trials (conducted according to conventional farming principles), this variety was characterized by high root yields with high sugar content [64]. Thus, it seems that the reason for its poorer root and sugar yields in our own trials was the development of a low amount of foliage, which in turn led to late inter-row closure and weakened the possibility of environmental competition with weeds. Weed control after sugar beet has reached the two to four leaf stage proper (BBCH 14) is difficult in organic cultivation. Eliska was also characterized by a high content of melasotrophs in the roots, which further reduced the processing value of the harvested raw material.

5. Summary and Conclusions

Proper sugar beet cultivation methods applied in the field experiments allowed root yields 25–30% higher than the average for Poland to be obtained, which suggests the existence of a high potential for future widespread use. Higher root and white sugar yields were obtained in the study conducted at Płonne (with similar soil conditions to those at Bałcyny), but they were characterized by higher nitrogen content at the beginning of the growing season.

The organic farming cultivation method in the variant with compost fertilizer created the biggest root yield gap in comparison with conventional growing. A lower yield gap in organic growing was obtained by using farmyard manure, which indicated no need for conversion of FYM to compost in regard to sugar beet farming. The root yield gap in organic farming can be reduced to insignificant values or even exceed the level of conventional growing by fertilization using Bioilsa 12.5 supplemented with mineral fertilization of K, Mg, and S (Patenkali—approved for use in organic farming). Bioilsa 12.5 is successfully used in stockless organic farming, but its high cost negatively affects farm returns. The choice of sugar beet varieties suitable for organic farming has great importance in regard to root and white sugar yields, helping to significantly reduce the yield difference compared to conventional cultivation.