The Effect of Harvest Date on the Chemical Composition and Fodder Yield of Guizotia abyssinica (Guizotia abyssinica (L.f.) Cass.) under the Climatic Conditions of South-West Poland

Abstract

Guizotia abyssinica (Guizotia abyssinica (L.f.) Cass.) is regarded as a minor oilseed crop, which is important in terms of its nutritional value and potential uses. An important benefit of this crop is its cultivation for green matter and seed yield even under the difficult conditions of marginal cultivation. Guizotia abyssinica has not yet gained popularity in Europe. However, in a changing climate and taking into account its feeding value, it could gain in importance for ruminant nutrition in the near future. A field experiment was conducted in 2018 and 2019 in the west part of Poland on a farm in Opolskie voivodship (commune Prudnik). The objective of the field study was to assess the effect of three harvest dates on the yield and the chemical composition of fodder in a 90-day cultivation cycle in each year of the study. Stage of growth seems to be the most important factor affecting yield and the chemical composition of Guizotia abyssinica. In both years of the research, the green fodder yield reached the highest value after 90 days from sowing—32.5 and 36.9 t ha⁻¹—while dry matter was 6.85 and 7.99 t ha⁻¹, respectively. Chemical composition was also significantly dependent on harvesting date. Crude protein (in 2018 from 154.5 to 100.7 g kg⁻¹ and in 2019 from 148.3 to 78.2 g kg⁻¹) and crude ash (in 2018 from 165.8 to 98.7 and in 2019 from 155.2 to 89.9 g kg⁻¹) content decreased with progressive harvest date while nitrogen-free extracts (in 2018 from 500.5 to 562.0 g kg⁻¹ and in 2019 from 582.2 to 605.2 g kg⁻¹) and gross energy increased (in 2018 from 19.4 to 21.17 MJ kg⁻¹ and in 2019 from 18.63 to 19.73 MJ kg⁻¹.). The most favorable date for harvesting green forage is 90 days after sowing, due to the significantly highest yield of fresh and dry matter of green forage and with potential as a forage for animals.

1. Introduction

Guizotia abyssinica (Guizotia abyssinica (L.f.) Cass.) is regarded as an annual high-yielding plant classified to the Asteracea family constituting a minor oilseed crop on less fertile soil. Its use is connected to culinary purposes, production of paints, soft soaps, lighting, and the lubrication and perfume industries [1,2,3,4]. In the USA, seeds of this crop are commonly used as thistle seed and used as bird food. Guizotia abyssinica seeds are characterized by a high content of edible oil (38 to 43%), protein (20%), sugar (12%), and other minerals needed by animals and people [5]. As an oilseed source, this crop has been cultivated for a long time on a larger scale in Ethiopia, where it satisfies about 50% of oil demand [6,7]. In turn, in India, this crop constitutes 3% of the supply of national oil production [8]. The crop is regarded as the most resistant to drought, occupying soils where moisture is the limiting factor and sub-marginal to marginal soils as well as high soil moisture levels with waterlogging [9]. The advantage of its cultivation is the minimum agro inputs; however, nutrient stress seems to be an important factor responsible for its low quality and productivity [10]. Additionally, this crop is used in intercropping systems cultivated on wet soils, contributing to soil conservation [11].

The cultivation and consumption of Guizotia abyssinica is strongly related to Ethiopian culture where the value of the plant is highly recommended as the most popular oilseed crop for local consumption. This crop is also cultivated on a small scale in several other African countries (Sudan, Uganda, Congo, Tanzania, Malawi, and Zimbabwe) and in Asia (Bangladesh, Nepal, and Bhutan), where it is a significant edible-oil-producing plant [2].

Optimal conditions for Guizotia abyssinica growth comprise an appropriate amount of rainfall that ranges from 66 to 179 cm per month, and temperature in a range of 13.6–27.5 °C. The optimum pH for cultivation of this plant is 5.5–7.5 [12]. The growing season of Guizotia abyssinica in the Aral Sea region is around 170–190 days [13]. This crop has started to be cultivated as an intercrop in Germany, Austria, Czech Republic, Croatia, Brazil, and Italy [14,15]. Due to its fast growth rate, it can be used as a fodder for ruminant animals or in biofuel production [6,16,17]. Seed can also reduce methane emissions in rumen [18].

In Poland, this crop has not yet been widely cultivated. In connection with climate changes related to frequent periods of drought, the possibility of its cultivation under local conditions is promising. The antioxidant system employed by Guizotia abbysinica effectively protects plants during drought periods (even up to 48 h). Heat under 72 h can lead to decreased growth of plants [19]. Thus, the effect of increasing temperatures is to lengthen the vegetation period and the possibility of cultivating thermophilous plants in Poland. Attempts to pre-sow Guizotia abyssinica indicate that it can grow very intensively under the conditions of our country. However, there is still a lack of detailed data/information in the available literature on the agrotechnics, technology of cultivation, yield, and chemical composition of green fodder obtained at different dates of harvest under Polish climate conditions. Guizotia abyssinica is sensitive to a long photoperiod, and flowering is delayed or absent for photoperiods longer than 12 h. Sensitivity to photoperiod also limits crop expansion to regions characterized by long summers; however, there are genotypes less sensitive to long photoperiod as part of a multidirectional study of this at the Swedish University of Agricultural Science (these genotypes are able to flower even under 16 h of light) [20].

Lodging and self-compatibility are identified as the main factors leading to the low yield of Guizotia abyssinica. Little attention has been given to it to improve yields. This situation, however, has changed in both industrialized and developing countries by breeding methods [21]. However, more publications concerned seed yield. Research has shown that yield of Guizotia abyssinica increases, depending on adoption, can be improved by manipulating agronomic practices to ensure optimal environmental conditions [22].

It is difficult to find, in either international or Polish literature, information on the cultivation of Guizotia abyssinica. There is not much work on the usefulness of the forage in animal nutrition. Chemical composition in the available literature mainly concerns seeds in terms of total liquid content and fatty acid profiles [7,23,24]. In the literature, intensive research has been conducted on this crop on the chemical composition of seeds with regard to its nutritional value, biological activities, and antioxidative properties. Therefore, an attempt at Guizotia abyssinica cultivation has been carried out in Poland for green fodder production. Agronomic treatments play a pivotal role in forage yields that can be achieved during field experiments developed in specific regions. Seeds of Guizotia abyssinica used fertilizers or herbicides [25], which is similar to what was done in the present experiment.

Due to limited knowledge about agrotechnical treatments to increase the yield of Guizotia abyssinica, Poland, as well as other European countries, face several challenges, mainly because there is little experience cultivating this crop. Seed varieties, fertilizer rate, seeding rate, soil, and weather/climate are some of the factors that affect crop productivity. The research hypothesis was that the yield as well as the chemical composition of the green fodder will vary depending on the harvest date. The aim of the field study was to identify the cultivation potential of Guizotia abyssinica as a part of a two-year study (in a 90-day cultivation cycle) in the south-west of Poland by determining the yield and chemical composition of green fodder at various harvest dates.

2. Materials and Methods

2.1. Site Description and Materials

The field experiment was conducted at a farm in Czyżowice, Prudnik commune, Opolskie voivodship (50°19′11″ N 17°34′45″ E, elevation 265 m above mean sea level) (Figure 1), during a 90-day vegetation period in 2018 and 2019. The climate conditions are affected by its proximity to the Opawskie Mountains. The average temperature is +8 °C (average for the whole year). The area was characterized by a growing season lasting 223–230 days, with an average temperature during the growing season of 14.5 °C. Annual precipitation varies from 500 to 600 mm and rainfall is approximately 350 mm during the growing season (IV–XI). Snow cover often occurs from December to April, with prevailing westerly winds.

The total (each of the fields combined) area under Guizotia abyssinica cultivation amounted to ca. 1 ha in both years of the research. The experiment was conducted on soil belonging to class III of bonitation (Polish classification of soil quality) [26]. The average pH of the soil was 6.0 in the years of the study, with the following average content of macroelements: low content of phosphorus (10.45 mg P₂O₅ per 100 g of the soil), medium potassium content (15.0 mg K₂O per 100 g of the soil), and medium content of magnesium (48.9 mg Mg₂O per 100 g of the soil). The assessment of the soil’s nutrient content was determined by limit numbers to assess the content of elements developed by the Polish Institute of Soil and Plant Cultivation in Puławy [27].

In both years of the research, the fore crop for Guizotia abyssinica was winter rape (Brassica napus var napus). Before the experiment, the soil was cultivated using disc harrow cultivation to reduce the amount of emergence from oilseed rape seeds remaining in the field (spilled from the siliques during harvesting). The agrotechnical treatments were identical for each year of the field experiments. Guizotia abyssinica was sown in the third decade of July in 2018 (i.e., 21 VI 2018) and in the first decade of August in 2019 (i.e., 2 VIII 2019) using the same treatments as on the first field cultivated in 2018. Guizotia abyssinica seeds were sourced from Saatbau Polska Sp. z o.o. [28] and before sowing, the seeds were mixed with urea fertilizer (46% N, Pulrea^®, Grupa Azoty Zakłady Azotowe Puławy S.A., Poland) at a rate of 9 kg ha⁻¹ of Guizotia abyssinica and 100 kg ha⁻¹ of fertilizer (ratio 1:11). Seeds were sown using an Amazone seeder (Amazonen-Werke H. Dreyer SE and Co. KG, Hasbergen, Germany). No phosphorus, potassium fertilizers, or plant protection products were applied during the experiment. Guizotia abyssinica is drought and disease resistant and, in addition, is not attacked by pests. In the present study, no pests or diseases were observed, and weeds were only occasionally noted at the beginning of the vegetation period. Therefore, no herbicides or insecticides were applied.

After sowing, a harrowing treatment with light harrows was also applied to cover the sown seeds with soil and prevent them from being eaten by birds or other animals.

The green matter yield of Guizotia abyssinica was harvested on three dates: 17 IX 2018, 27 IX 2018, and 19 X 2018 (that is, 58, 68, and 90 days from the date of sowing, respectively) from the determined area of the first field (in 2018) and from the determined area of the second field (in 2019) on: 29 IX 2019, 9 X 2019, and 31 X 2019.

2.2. Weather Conditions

During the field observations, the amount of precipitation, air temperature, and humidity in each year of the experiment was recorded. The amount of precipitation was measured using a rain gauge (Mizar: 53784—Mizar Zaręba sp. j., Trzydnik Duży, Poland). Based on the measurements, figures were prepared presenting the cumulative distribution of precipitation and changes in humidity and temperature during the experiment (data not shown).

Monthly data from the experiment related to the temperature and precipitation in 2018 and 2019 are presented in

Table 1. Weather conditions during the experiment conducted in 2018 and 2019 (Prudnik, Poland).

Item	Months (Vegetation Period)					Sum	Average
2018
	VII	VIII	IX	X	XI	VII–X	VII–X
Average temperature (°C)	22.6	20.5	17.2	14.2	-	-	18.3
Precipitation (mm)	1	52	61	9	-	123	-
2019
	VII	VIII	IX	X	XI	IX–XI	IX–XI
Average temperature (°C)	-	-	16.2	12.8	7.6	-	12.2
Precipitation (mm)	-	-	30	23	25	78	26.0
Average (1981–2010)
Average temperature	19.3	18.3	13.6	9.1	3.9	-	12.84
Average precipitation	78.9	61.7	45.3	32.3	36.6	218.2	-

. Relatively high temperatures were recorded during the two years of the experiment. Temperatures during the experiment were much higher compared to multi-year average temperatures in all months. During the summer months (VII-VIII), the mean temperature exceeded 20 °C (Table 1). In September, the average temperature was 16.2–17.2 °C and in October 12.8–14.2 °C (however, in 2019, the temperatures were 6% and 10% lower in the two months, respectively).

In terms of the amount of precipitation, it should be noted that 92% of rainfall was observed in the months of August and September 2018 (52 and 61 mm m⁻², respectively). This period was preceded by drought (in July precipitation did not exceed 1 mm m⁻²). In total, 123 mm of water per m² fell throughout the observation period. On the other hand, in September 2019, precipitation was half the level (30 mm) of the previous year. A different trend was observed in October 2019, when there was 2.5 times more precipitation (23 mm) compared to the previous year. A lower value for precipitation and noticeably higher values for temperature were recorded in 2018 and 2019 in comparison with the multi-year average, indicating climatic changes related to increasing temperature and deepening periods of drought.

2.3. Plant Growth Measurement

Plant material was sampled three times during the vegetation period. Each time, the material was collected from 10 randomly selected sites in a field of 1 m² area, at a height of about 4 cm above the ground. Aboveground parts of plants were harvested on rainless days, after the morning dew had subsided. Terminal (from outer rows) plants from the external rows were not included in the chemical analysis; thus avoiding the so-called edge effect. Harvested plants were weighed and the percentage of dry matter was determined. Dry biomass weight was determined by drying samples (specific weight, 500 g) to 60 °C for up to 48 h, then drying them at 105 °C for 4 h (dry weight by the gravimetric method).

2.4. Chemical Analysis

From each randomly selected site in a field (n = 10), the representative subsamples for chemical analysis were taken (n = 10) [29]. The concentration of nutrients was determined in a laboratory at the Department of Animal Nutrition and Feed Science, Wroclaw University of Environmental and Life Sciences, Wrocław, Poland.

The dry matter (DM) for laboratory samples was examined by the gravimetric method at 105 °C for four hours according to the Polish standard [30]. Chemical composition of the green fodder was assessed according to the methods given by the AOAC International Official Methods of Analysis [31] including:

(a)

Crude protein (CP) content by multiplying the nitrogen percentage (N %) determined in the sample using a Kjeltec 2300 Foss Tecator apparatus (AOAC: 984.13) with factor (6.25).

(b)

Crude ash (CA) by combustion of the sample in a muffle furnace (Czylok Company, Jastrzębie-Zdrój, Poland) at 550 °C for 24 h (AOAC: 942.05).

(c)

Ether extract (EE) by the Soxhlet method comprising the extraction with ethyl ether (AOAC: 920.39A).

(d)

Crude fiber (CF) by the Hennenberg–Stohman method (AOAC: 978.10) using a Fibertec Tecator Foss apparatus for laboratory analysis.

Mineralization of the samples was determined with a Mars 5 version 194A06 (CEM Corporation, Matthews, NC, USA) microwave mineralization system using HNO₃. Neutral detergent fiber (NDF) and acid detergent fiber (ADF) levels were determined according to the Van Soest methods (1991) [32] using an Ankom 200 Fiber Analyzer (Ankom Technology Corporation, NY, USA).

The gross energy (GE) of the seed was determined in a calorimetric bomb—calorimeter KL-11 “Mikado” (Precyzja-Bit Sp. z o.o., Bydgoszcz, Poland).

2.5. Statistical Analysis

The data obtained from sampling at three harvest dates were initially prepared in Microsoft Office 365 Excel and then all numerical data were evaluated using one- or two- way ANOVA carried out with Statistica version 13.3 computer software [33]. Differences in mean values between treatments were analyzed for significance (p < 0.05 or p < 0.01) using the Duncan test. The relationship between dry matter and crude protein was determined by Pearson’s correlation coefficients.

3. Results

3.1. Effect of Harvesting Date on Green Fodder Yield

Guizotia abyssinica yield was significantly dependent on the date of harvest (

Table 2. Effect of harvesting date on green fodder yield (mean ± SD for harvest date) (n = 10).

	Yield (t ha−1)				p-Value
Number of Days after Sowing	In 2018		In 2019
	Green Matter	Dry Matter	Green Matter	Dry Matter
58	20.8 A	2.0 A	23.2 A	2.4 A	**
	±0.93	±0.09	±3.38	±0.34
68	25.9 B	3.5 B	28.9 B	4.1 B	**
	±4.63	±0.62	±3.25	±0.08
90	32.5 C	6.9 C	36.9 C	8.0 C	**
	±3.78	±0.26	±3.25	±0.91

** Significant differences marked within a column with different capital letters indicate p ≤ 0.01.

). Delaying the harvest date contributed to increased yields of both fresh and dry matter.

The green matter yield of Guizotia abyssinica amounted to 20.8 t ha⁻¹ in 2018 (fresh mass) at the first date of harvesting (Table 2). The increase in fresh matter yield per ha between the first and second sampling dates was ca. 25%. On the other hand, the yield in the second decade of October, i.e., 90 days after sowing, amounted to 32.5 t ha⁻¹ and was a further ca. 25% higher compared to that noted in the first observation period. The highest yield of green fodder was obtained at the third harvest date (90 days from sowing), gaining 6.85 t ha⁻¹. The yield was higher in the second year of the study (2019) compared to the green forage yield obtained in 2018. The average temperature in 2018 was actually higher; however, the distribution of precipitation was uneven compared to 2019 and this plant requires moderate rainfall. Water deficiency significantly affects chemical composition of oilseed crops as well as the yield.

Similar relationships between increasing green and dry matter yield were observed in 2019. The significantly highest green matter yield was observed 90 days after sowing. The increase in green matter yield in 2019 between first and second harvests was around 24%, between the second and third harvest around 28%, and between the first and third harvest around 59%. Although not evaluated statistically, the yield in 2019 was numerically greater than in 2018.

3.2. Effect of Harvesting Date on Fodder Chemical Value of Guizotia abyssinica

The average values of the basic nutrients based on the chemical analyses are presented in

Table 3. Effect of harvesting date on chemical composition of green fodder (n = 10).

Factors	Chemical Composition
	DM	CP	CF	EE	CA	NFE	NDF	ADF	GE
	%	g kg−1 DM							MJ kg−1
Treatments
2018
58	9.7 A	154.5 A	157.6 A	21.6 A	165.8 A	500.5 A	326.5 A	285.3 A	19.6 A
	±0.55	±0.04	±0.01	±0.01	±0.05	±0,48	±0.03	±0.05	±0.90
68	13.3 B	154.1 A	169.2 B	24.8 B	139.1 B	512.8 B	355.6 B	281.9 B	20.6 B
	±1.68	±0.25	±0.11	±0.01	±0,02	±1.46	±0.25	±0.19	±0.55
90	21.1 C	100.7 B	219.4 C	16.6 C	98.7 C	562.0 C	363.5 C	279.1 C	21.2 B
	±1.45	±0.18	±0.17	±0.03	±0.11	±0.21	±0.21	±0.25	±0.71
2019
58	10.5 A	148.3 A	154.2 A	18.9 A	155.2 A	582.2 A	328.4 A	267.7 A	18.6 A
	±0.64	±0.17	±0.02	±0.01	±0.02	±0.41	±0.14	±0.29	±0.63
68	14.2 B	126.4 B	166.8 B	16.6 B	134.8 B	587.4 B	335.4 B	281.6 B	18.9 A
	±0.38	±0.16	±0.04	±0.07	±0.02	±0.59	±0.04	±0.28	±0.34
90	21.7 C	78.2 C	194.6 C	11.6 C	89.9 C	605.2 C	359.0 C	312.1 C	19.7 B
	±0.75	±0.12	±0.01	±0.05	±0.01	±0.23	±0.09	±0.10	±0.24
Two-factor analysis of variance
Year
2018	14.6	136.5	182.1	21.0	134.5	525.1	348.5	282.1	20.5
2019	15.5	117.7	171.9	15.7	126.6	591.4	340.9	287.0	19.3
Days
58	10.2	151.4	155.9	20.3	160.5	541.4	327.5	276.5	19.4
68	14.0	140.314	168.0	20.7	137.0	550.1	345.5	281.6	19.8
90	21.08	89.5	207.0	14.1	94.3	583.6	361.2	295.6	20.5
Source of varation, p-value
Year	0.000	0.000	0.000	0.000	0.000	0.000	0.000	0.000	0.000
Days	0.000	0.000	0.000	0.000	0.000	0.000	0.000	0.000	0.000
Year × Days	0.000	0.000	0.000	0.000	0.000	0.000	0.000	0.000	0.027

58, 68, 90—number of days after sowing. DM—dry matter; CP—crude protein; CF—crude fat; EE—ether extract; CA—crude ash; NFE—nitrogen-free extracts; NDF—neutral detergent fiber; ADF—acid detergent fiber; GE—gross energy. Significant differences marked within a column with different capital letters indicate p ≤ 0.01.

. Chemical composition was differentiated according to the term of the harvest. In 2018 and 2019, the character of the dry matter of green fodder was statistically significant according to date of harvest. At the first harvest date, i.e., 58 days after sowing, the green fodder was characterized by about 10% DM content. After 90 days, the increase in DM content was more than two times higher and amounted to more than 21% (Table 3). On the base of correlation, as DM increased, so did CF, NFE, and GE content. In contrast, DM content was negatively correlated with CP, EE, and CA (

Table 4. Matrix of correlation coefficients between dry matter (DM) and crude protein (CP) vs. chemical composition.

Specification	2018				2019
	DM		CP		DM		CP
	r	p-Value	r	p-Value	r	p-Value	r	p-Value
DM
CP	−0.912	**			−0.991	**
CF	+0.952	**	−0.985	**	+0.991	**	−0.999	**
EE	−0.713	**	+0.919	**	−0.990	**	+0.999	**
CA	−0.964	**	+0.921	**	−0.991	**	+0.999	**
NFE	+0.953	**	−0.982	**	+0.985	**	−0.995	**
GE	+0.546	*	−0.497	*	+0.554	*	−0.543	*

DM—dry matter; CP—crude protein; CF—crude fat; EE—ether extract; CA—crude ash; NFE—nitrogen-free extracts; GE—gross energy ** Significant differences marked within a column indicate p ≤ 0.01; * Significant differences marked within a column indicate p ≤ 0.05.

).

Protein content was significantly dependent on harvest date in each year of the experiment. As the vegetation of plants progressed, the protein content in green fodder decreased significantly, achieving the lowest value 90 days after sowing (Table 3). Protein content, determined in the first and second terms of 2018, was undifferentiated and amounted to ca. 154 g kg⁻¹ DM. On the third date of harvesting, the value of CP decreased by 35% and amounted to 101 g kg⁻¹ DM. There were significant negative correlations between CP vs. other chemical composition (CF, NFE, GE) (Table 4).

In both years, the results indicated a significant increase in the content of CF, NFE, and NDF during the whole vegetation period. For the last term of sowing in 2018, increases in the proportion of CF (39%), NFE (12%), and NDF (11%) in dry matter were noted. In 2019, we found increasing values of CF, NFE, and NDF as well. The highest values were observed in the last term of sowing compared to the previous one. The increase in the content of the analyzed values was lower in 2019 and amounted to 26%, 4.5%, and 9%, respectively.

Similarly, GE content systematically increased in the samples taken in individual periods (by 8% in 2018 and by 6% in 2019) and this was mainly related to an increase in NFE content in the samples. On the other hand, there was a decrease of ca. 60% in EE and CA content. However, values determined in 2018 were higher than in the following season. In the case of ADF, different results were obtained. In the first year of the research, the level of ADF decreased, while in the second year it increased.

By two-factor ANOVA, years and days had significant effects. The statistically significant interaction between the two factors was also detected (Table 3).

The observed differences in CP and EE yields were due to the yield of the plant and its nutrient content (Figure 2). Guizotia abyssinica harvested at the third date was characterized by high yield and high protein and fat content per unit area in 2018 and 2019.

4. Discussion

In the area of the field experiment, the average temperature was 18.3 °C in 2018 (VII–X) and 12.2 °C in 2019 (IX–X). Analyzing the value of temperature in the vegetation period (IX–X) amounted 15.7 °C in 2018 and 14.5 °C in 2019 (Table 1). The recorded values for individual months were lower than the maximum daily averages. The total precipitation during the field experiment was 123 mm m² in 2018 and 78 mm m² in 2019 (Table 1). Therefore, Guizotia abyssinica did not show its full growth potential (during the summer months) due to moisture deficiency. On the other hand, in the first growth cycle of this plant, in October in 2018, due to its strongly developed root system reaching up to 30 cm depth, the scant rainfall did not significantly (p > 0.05) affect the further growth of this plant. In the second growth cycle, in the same month, the amount of rainfall was 23 mm m². The plants were able to enter the flowering phase 90 days after sowing. On the basis of available literature, this plant reaches maturity between 110 and 120 days after sowing, and its height ranges from 0.5 to 1.5 m [16,34]. However, Bulcha (2007) [35] report that this plant can reach up to 2 m in height. Quinn and Myers (2002) [12] highlighted that Guizotia abyssinica prefers a temperature between 19 and 30 °C. It should be noted that this plant is highly adaptable and can be successfully used under subtropical [7] or temperate climate conditions [17]. This plant requires moderate rainfall and grows in areas with temperate and tropical climates.

The yield of Guizotia abbisynica can be improved by manipulating agronomic practices to ensure optimal environmental conditions. Varieties vary in yield potential depending on a number of physiological processes which are controlled by both genetics and environments. The productivity of this crop can be increased with an appropriate sowing date as was examined in this experiment.

Seeding rates in Guizotia abbisynica cultivation vary from 5 to 10 kg ha⁻¹ in Ethiopia and 5–8 kg ha⁻¹ in India [36]. Regarding the cultivation practice of different varieties, the recommended sowing rates are 6–10 kg ha⁻¹ and 12–15 kg ha⁻¹ for early and late sowing, respectively. In our field experiment, 9 kg of Guizotia abyssinica was sown per hectare in both years. Bulcha (2007) [35] reported that in Ethiopia, 5–15 kg of seeds per hectare are sown at a depth of 1–3 cm, while in India, 5–8 kg ha⁻¹ is recommended. The best results for this crop are obtained when sowing is performed either immediately after rainfall or onto moist/humid soil.

Field studies conducted in the Navsari region of India during 2011–2012 by Surve et al., (2018) [37] indicated that the average yield of Guizotia abyssinica was about 22 t ha⁻¹. In our field experiment, a similar yield was achieved 58 days after sowing. In Mili et al., (2012) [38] the value of yield of Guizotia abyssinica decreased significantly, taking into account delay in sowing date. The same results in yield due to delay in sowing were reported by Nayak and Paikray (1991) [39]. This does not apply to our own research. After 32 days, the yield of green fodder in our own experiment increased by ca. 12 t ha⁻¹ in 2018 and by ca. 14 t ha⁻¹ in 2019 and this was caused by weather conditions (high temperatures and scant precipitation). The higher yield could also have resulted from the fertilization that was applied in our experiment (46 kg ha⁻¹ of nitrogen supplied to the soil during seed sowing).

The available literature indicates that Guizotia abyssinica does not require fertilization. However, Surve et al., (2018) [37] found that the application of phosphorus fertilizers increases yields by up to 50%. Additionally, Stepiševic et al., (2014) [17] showed that the yield value of this plant is affected by nitrogen fertilization. According to these authors, the application of fertilizers in the cultivation of Guizotia abyssinica contributes to an increase in the yield of seeds (by more than 2 tonnes per hectare) and vegetative parts of the plant. Fertilizer doses for that crop according to Bulcha (2007) [35] are 23/23 (N/P₂O₅) kg ha⁻¹. Vegetative growth generally increased when more than 30 kg ha⁻¹ nitrogen fertilizer is applied. Higher levels of nitrogen can cause lodging and drenching which reduces yield [40]. Yield levels are 200–300 kg ha⁻¹, although with good management it can reach even 500–600 kg ha⁻¹ [16].

Harvest days depending on the variety are 130–200 days (Este), 136–175 days (Fogera), 130–200 days (Kuyu), and 144 days (Shambu) [41]. In a study by Peiretti et al., (2015) [15], a lower dry matter content than that found in our study was obtained under the conditions of the western part of Italy in the Po river valley. The western Italian region was characterized by higher precipitation compared to the values recorded for Opolskie province. In the Italian study, 68 days after sowing, the dry matter content was 114 g kg⁻¹. Thus, the dry matter level was affected by the amount of precipitation occurring especially in the initial phase of plant growth. In our experiment, DM content also increased with plant growth in both years. The obtained DM level could have been affected by the scant precipitation between the analyzed harvesting dates. On the other hand, under Italian conditions the dry matter content determined at 80 and 87 days after sowing decreased and was 101 g kg⁻¹ [15].

Under favorable conditions, plants start producing seeds after about 3–4 months’ growth and DM content is about 16%. In the case of scant rainfall, the DM content of the plants increases, which determines its use as raw material for biodiesel or biogas production [16].

On the other hand, Karimdjanovich (2017) [13] reported that the content of CP ranged from 7.8 to 12.0% in DM of green mass. The nitrogen content of the plant depends on, among other factors, the growth phase of the plant, the chemical form of the fertilizer applied, and the soil conditions. Limited precipitation and lower temperature (noted in September 2019 vs. 2018) may have affected the CP level in harvested forage and reduced photosynthesis in the plants during their growth. According to Peiretti et al., (2015) [15], CP content decreased from 163 to 86.0 g kg⁻¹ DM from early vegetation to grain filling stage, respectively. In our research the same tendency was observed.

Analyzing the EE content of Guizotia abyssinica grown under Polish weather and soil conditions, higher levels were found than in studies conducted by other authors. Peiretti et al., (2015) [15] obtained a crude fat content of 148 g kg⁻¹ DM at 73 days after sowing, followed by a level of 120–130 g kg⁻¹ DM between 87 and 121 days after sowing (i.e., at bud formation and flowering stage). Karimdjanovich (2017) [13] reported that the crude fat content of this crop’s green matter ranged from 24 to 32 g kg⁻¹. It is probable that the low level of crude fat in our own studied material was caused by insufficient precipitation during the growing season [42].

In our study, we found a decrease in CA content with the progress of plant growth in each year. In contrast, in an Italian study [15], CA content was constant at 150–160 g kg⁻¹ DM between 68 and 87 days after sowing.

Karimdjanovich (2017) [13] claimed that the content of NFE compounds can range from 392 to 507 g kg⁻¹ in Guizotia abyssinica. In addition, 10.3–12.2% are sugars, which may have a beneficial effect on the quality of the silage obtained from these plants. In our study, NFE values were much lower. On the last term of sowing, this value was 562 g kg⁻¹ DM. These values could also be explained by the lower intensity of the photosynthesis process due to the lack of available water in the soil. According to Peiretti et al., (2015) [15], all fiber component contents increased with maturity as well as NDF in our study. In their study, NDF and ADF concentrations increased from 381.7 to 550.7 g kg⁻¹ DM and from 233.7 to 352.6 g kg⁻¹ DM, respectively, from the early vegetative stage to the grain-filling stage. In our study, ADF in 2018 increased from 326.5 to 363.4 359 g kg⁻¹ and, in 2019, 328.4 to 359 g kg⁻¹ DM. In turn of ADF the same trend was only observed in 2019 while in 2018 the values decreased from the first to third sowing date.

GE content increased systematically in the studied samples collected during the different periods. The determined gross energy value was 3–5 MJ higher than that in Peiretti et al., (2015) [15]. In the cited work, the average value for GE (calculated for the period between 68 and 87 days after sowing) was 16.13 MJ kg⁻¹DM, while in our study this value was from 19.6 to 21.2 MJ kg⁻¹.

In a study carried out in the north-western part of the Apennine peninsula [15], a linear increase in NDF content was found, ranging from 382 to 551 g kg⁻¹ DM (from 68 to 143 days after seed sowing, respectively). A similar increasing trend was observed under Polish conditions. However, NDF values were lower compared to the Italian study. The results obtained under Polish conditions may have been due to the less favorable atmospheric factors, especially the low moisture levels at the beginning of plant growth.

5. Conclusions

Differences in harvesting date had a significant impact on the yield and chemical composition of Guizotia abissynica, which is consistent with the hypothesis proposed at the beginning of the experiment. Significant differences are found in changes in nutrient quality associated with increasing plant maturity. The green fodder harvested at the final stage of growth was characterized by high levels of dry matter (over 21%) and carbohydrates (from 56.2 to 60.5%). In contrast, CP and EE values were low: 10% (in 2018) and 7.8% (in 2019); and almost 1.7% (in 2018) and 1.2% (in 2019). The trends in fiber content versus maturity stage are the opposite of those for protein. As the percentage of fiber increases, its digestibility decreases because lignification makes it unavailable. The mean GE value for the green fodder with a concentration of about 20–21 MJ kg⁻¹ can qualify it as feed for ruminants or for silage production for this group of animals.

Future research with Guizotia abissynica should focus on the adaptation of cultivars to Polish climatic conditions and the adaptation of cultivars to the changing climatic conditions of Poland. In addition to the environmental conditions, i.e., climate and soil, the yield of this crop is also influenced by agrotechnical procedures, including harvest time. The most favorable date for harvesting green forage is 90 days after sowing, due to the significantly highest yield of fresh and dry matter of green forage as well as chemical composition. The highest yield of fresh and dry matter of green fodder was observed at the last harvest date, i.e., after 90 days, with the following results: in 2018, 32.5 t ha⁻¹ of fresh mass (ca. 7 t ha⁻¹ DM) and in 2019, 36.9 t ha⁻¹ (ca. 8 7 t ha⁻¹ DM).