Quality of Red Clover Forage in Different Organic Production Systems

Abstract

The aim of this study was to determine the quality of organically grown red clover herbage and silage after being influenced by supplementary mineral fertilization. The experimental treatments were as follows: control treatment without fertilization (group C), treatment where kalimagnesia (Patentkali) was applied (group P), and treatment where potassium sulfate (SOP) was applied (group S). In each year of the experiment, first-cut herbage was harvested at the beginning of flowering and ensiled. The year of the study had a significant (p ≤ 0.05) influence on the analyzed parameters of herbage and silage, excluding the content of calcium (Ca), acetic acid (AA), and ammonia nitrogen (N-NH₃). The organic production system exerted a significant (p ≤ 0.05) effect on the concentrations of crude protein (CP), acid detergent lignin (ADL), water-soluble carbohydrates (WSC), minerals (P, K, Ca, Na), lactic acid (LA), ethanol, and N-NH₃. The pattern of fermentation was affected by both experimental factors. True protein (TP) content was determined at 70–84% CP in herbage and 53–65% CP in silages. The energy value and the protein value of herbage varied significantly across years of the study and in response to the combined effects of both experimental factors (p ≤ 0.05). Red clover grown in organic production systems supplied high-quality forage.

1. Introduction

In many temperate regions, red clover (Trifolium pratense L.) is a source of high-value feed for ruminants, similar to alfalfa (Medicago sativa L.) and forage grasses. Red clover can be fed as silage, haylage, and hay. It is known for its high rate of biological nitrogen (N) fixation, and it is able to fix up to 200 kg N∙ha⁻¹ per year [1]. Under optimal moisture conditions, the dry matter (DM) yield of red clover is comparable to or higher than that of alfalfa [2]. Red clover is characterized by high and stable yields, and it can be harvested four times during the growing season. This legume species is usually grown for two to four years. Its persistence can only be limited by the low K and Mg content in the soil and intensive management, particularly high grazing pressure and pathogens [3].

In general, legumes, including red clover, have high crude protein (CP) content, a low content of water-soluble carbohydrates (WSC), and a high buffer capacity (BC) [4]. Red clover tissues contain high levels of the enzyme polyphenol oxidase (PPO) that catalyzes the oxidation of phenols to quinones, which react with proteins. During the ensiling process, this mechanism contributes to preventing true protein (TP) degradation to simpler compounds such as non-protein nitrogen (NPN) [5]. This improves CP quality in red clover silage, which has a higher content of rumen undegradable protein (RUP) than alfalfa silage [1].

Depending on weather conditions, agronomic factors, and growth stage at harvest, red clover silage may contain 181–248 g of CP, 369–426 g of neutral detergent fiber (NDF), and 230–311 g of acid detergent fiber (ADF) per kg of DM on average [6]. Recent research has shown that the inclusion of red clover in ruminant diets improves performance production. This type of feed is willingly consumed by animals due to its high palatability, which results in a more efficient supply of essential nutrients [7,8]. As a component of ruminant diets, red clover contributes to reducing methane emissions and improving the fatty acid composition of milk in high-yielding dairy cows, mostly due to the higher digestibility of structural carbohydrates [1].

Red clover cultivation contributes to the sustainable intensification of agricultural production and reduces the environmental impact of agriculture by improving soil fertility [1]. Red clover is generally considered to be one of the best-preceding crops [9]. This legume species plays an important role in crop rotation as a forecrop because it reduces the prevalence of cereal diseases and acts as a natural protective barrier against monocotyledonous weeds. Red clover can also be used for phytoremediation [10]. The benefits of red clover, such as reduced use of N fertilizers and enhanced biodiversity, are important considerations in livestock production. In addition, forage legumes such as red clover constitute a key link in low-input and organic milk and beef production chains in Northern Europe [11]. Due to its relatively low fertilizer requirements, red clover is widely used in organic production systems [12].

In view of the potential advantages of making red clover silage in beef and dairy farms in the context of sustainable agriculture, the quality of red clover herbage and silage should be evaluated in the organic production system. Therefore, the aim of this study was to determine the quality of organically grown red clover herbage and silage in different supplementary fertilization treatments.

2. Materials and Methods

2.1. Treatments and Experimental Design

A three-year (2020–2022) field experiment was conducted under production conditions in an agricultural farm located in Zgniłobłoty in the Kuyavian–Pomeranian Voivodeship, Poland (53°17′ N, 19°14′ E). The experiments were carried out on clay loam soil containing 38% sand, 33% silt, and 29% clay in the upper soil horizon of 0–30 cm. The chemical properties of soil were determined in representative samples collected with Egner’s cane at a depth of 0–30 cm. Organic carbon content was 9.86 g∙kg⁻¹ of soil. Based on the recommendations of the Institute of Soil Science and Plant Cultivation, soil pH was classified as slightly acidic (pH 5.62 in 1 mol KCl dm⁻³), the content of P was 63.8 mg and 42.0 mg Mg and 56.1 mg K∙kg⁻¹ of soil.

Red clover was grown in the organic production system. The plantation was divided into three plots of 0.5 ha each. The first plot (group C) constituted the control treatment without fertilization; kalimagnesia (Patentkali; 30% K₂O, 10% MgO, 42.5% SO₃) was applied in the second plot (group P), and potassium sulfate (SOP; 50% K₂O, 42.5% SO₃) was applied in the third plot (group S). Regardless of the form of potassium fertilizer, the rate of potassium expressed as pure ingredient was identical in groups P and S, i.e., 80 kg of K₂O∙ha⁻¹. Kalimagnesia (Patentkali) was applied at 267 kg∙ha⁻¹, and potassium sulfate (SOP) was applied at 160 kg∙ha⁻¹. The fertilizers supplied the following rates of nutrients per ha: kalimagnesia (Patentkali)—80 kg K₂O, 26.7 kg MgO, and 45.4 kg S; potassium sulfate (SOP)—80 kg K₂O and 28.8 kg S. The fertilizers applied as a source of potassium were supplemented with S and Mg (kalimagnesia—Patentkali) and S (potassium sulfate—SOP). Both fertilizers can be used in organic farming, and their efficacy is not affected by soil pH. The fertilizers were applied in spring, at the beginning of the growing season, in the seed-sowing year (second year of red clover vegetation).

In each year of the experiment, first-cut herbage was harvested at the beginning of flowering. The herbage was collected with a disc mower at a height of 5 cm between 10:00 and 12:00. Then, the plant material was manually cut into chaff with a theoretical length of 30 mm and compacted in 3 dm³ micro-silos. The cylindrical-shaped micro-silos were made of acid-resistant stainless steel with two side box fasteners. The lids of the micro-silos were press-on and equipped with an internal silicone gasket. On the top of the micro-silos, there was a gas outlet in the form of a fermentation tube. Before ensiling, herbage samples were collected from each experimental plot for chemical analyses. The micro-silos were opened after 90 days, and the contents were stirred. Part of samples of each silage (0.5 kg) were frozen at a temperature of −25 °C, and the remaining samples were dried in Binder FED 115 dryers (Binder, GmbH, Tuttlingen, Germany) at a temperature of 60 °C for 48 h. The samples were ground to a 1 mm particle size in a mill for fibrous materials (ZM 200, Retsch, Haan, Germany). Herbage and silage samples were collected and prepared in six replicates (n = 6) for each treatment.

2.2. Analytical Methods

Red clover herbage and silage samples were analyzed to determine their proximate chemical composition, including DM, crude ash (Ash), crude protein (CP), ether extract (EE), and crude fiber (CF) by standard AOAC methods [13]. Carbohydrate composition was analyzed, including the content of neutral-detergent fiber (NDF), which was assayed with the use of heat-stable amylase and expressed exclusive of residual ash (aNDFom). The content of acid detergent fiber (ADF) was expressed exclusive of residual ash (ADFom), the content of acid detergent lignin (ADL) was determined as described by Van Soest et al. [14] using the ANKOM 220 fiber analyzer (ANKOM Technology Corp., Macedon, NY, USA), and the content of water-soluble carbohydrates (WSC) was determined by the anthrone method [15] with the use of the EPoll 20 BIO spectrophotometer (Poll Limited, Warsaw, Poland). Red clover herbage and silage samples were also analyzed to determine true protein (TP) content with the use of 10% trichloroacetic acid (TCA), as described by Licitra et al. [16].

Silage samples were analyzed to determine the content of the following minerals: P, K, Mg, Ca, and Na. The samples were wet mineralized with a mixture of hydrochloric acid and nitric acid in a 3:1 ratio. Mineralization in a MarsXpress microwave oven (CEM Corporation, Matthews, NC, USA) lasted one hour. The temperature was steadily increased to 170 °C. The minerals were transferred to 50 cm³ volumetric flasks, and deionized water was added. Blank (reagent) samples were prepared simultaneously. The content of minerals was determined by flame atomic absorption spectrometry (acetylene-air flame) on the Varian AA240FS atomic absorption spectrometer (Varian Inc., Palo Alto, CA, USA), fitted with an acetylene-air burner and cathode lamps. The minerals were determined at the following wavelengths: Ca—422.6 nm; Mg—285.2 nm; Na—586 nm; and K—766.5 nm. The P content of the minerals was determined by colorimetry using the Epoll-20 spectrophotometer (Poll Limited Sp. z o.o., Warsaw, Poland) at a wavelength of 405 nm. The solution was subjected to a color reaction with the molybdovanadate reagent.

The values of pH in red clover silages were measured with the HI 8314 pH meter (Hanna Instruments, Woonsocket, RI, USA). The concentrations of lactic acid (LA), acetic acid (AA), butyric acid (BA), and ethanol were determined as described by Kostulak-Zielińska and Potkański [17] and Gąsior [18]. Silage samples were homogenized (1:5 ratio of sample weight per water volume, w/v) and were filtered through polyamide gauze. The filtrate was passed through a soft filter, deproteinized with a 24% solution of metaphosphoric acid, and centrifuged (13,000 rpm, 7 min). Volatile fatty acids (VFAs) were separated by gas chromatography on the Varian 450-GC with the Varian CP-8410 autosampler (Varian Inc., Palo Alto, CA, USA), a flame-ionization detector (FID), CP-FFAP capillary column (length—25 m; inner diameter—0.53 mm; film thickness—1.0 μm), sample size of 1 μL, detector temperature of 260 °C, injector temperature of 200 °C, column temperature of 90 °C → 200 °C, and helium carrier gas (flow rate 5.0 mL·min⁻¹). Lactic acid content was determined by high-performance liquid chromatography (HPLC, SHIMADZU, Kyoto, Japan) with isocratic flow. Separation was carried out using the Varian METACARB 67H column (ORGANIC ACIDS COLUMN) (Varian Inc., Palo Alto, CA, USA), mobile phase of 0.002 M solution of sulfuric acid in deionized water, flow rate of 1 cm³∙min⁻¹, UV detector, and 210 nm. External fatty acid and ethanol standards were supplied by Supelco (Sigma-Aldrich, Saint Louis, MO, USA), and the LA standard was supplied by FLUKA (Chemie GmbH, Buchs, Switzerland). Ammonia nitrogen (N-NH₃) content was determined by direct distillation using the 2100 Kjeltec Distillation unit (Foss Analytical A/S, Hilleröd, Denmark).

2.3. Calculations and Statistical Analyses

The values of L/NDF and LA/AA ratios were calculated based on the analyzed groups of nutrients and selected fermentation products. The nutritional value of red clover herbage and silage was calculated based on their chemical composition using PrevAlim 3.23 software (INRAtion 3.0). Energy value was expressed as the feed unit for milk production (UFL) and the feed unit for meat production (UFV) per kg DM forage, which was calculated according to the following equations:

$$\mathrm{U}\mathrm{F}\mathrm{L}=\frac{\mathrm{M}\mathrm{E}·{\mathrm{k}}_{\mathrm{l}}}{1700}$$

$$\mathrm{U}\mathrm{F}\mathrm{V}=\frac{\mathrm{M}\mathrm{E}·{\mathrm{k}}_{\mathrm{b}\mathrm{p}}}{1820}$$

where

• ME—metabolic energy.
• k_l—coefficient of ME utilization in lactation processes.
• k_bp—coefficient of ME utilization in livestock processes and for growth.

Protein value was expressed as the content of protein digested in the small intestine when nitrogen is limiting (PDIN) and protein digested in the small intestine when energy is limiting (PDIE) per kg DM forage, which was calculated according to the following equations:

$$\mathrm{P}\mathrm{D}\mathrm{I}\mathrm{F}=1.11·\mathrm{C}\mathrm{P}·\left(1-\mathrm{r}\right)·\mathrm{s}\mathrm{j}\mathrm{p}$$

$$\mathrm{P}\mathrm{D}\mathrm{I}\mathrm{M}\mathrm{N}=0.64·\mathrm{C}\mathrm{P}·\left(\mathrm{r}-0.1\right)$$

$$\mathrm{P}\mathrm{D}\mathrm{I}\mathrm{M}\mathrm{E}=0.093·\mathrm{D}\mathrm{O}\mathrm{M}\mathrm{F}$$

$$\mathrm{P}\mathrm{D}\mathrm{I}\mathrm{N}=\mathrm{P}\mathrm{D}\mathrm{I}\mathrm{F}+\mathrm{P}\mathrm{D}\mathrm{I}\mathrm{M}\mathrm{N}$$

$$\mathrm{P}\mathrm{D}\mathrm{I}\mathrm{E}=\mathrm{P}\mathrm{D}\mathrm{I}\mathrm{F}+\mathrm{P}\mathrm{D}\mathrm{I}\mathrm{M}\mathrm{E}$$

where

• PDIF—proteins digested in the small intestine from feed.
• PDIMN—microbial protein synthesized in the rumen using available nitrogen.
• PDIME—microbial protein synthesized in the rumen using available energy.
• DOMF—digestible organic matter fermentable in the rumen.
• CP—crude protein.
• r—theoretical coefficient of CP distribution in the rumen (in sacco).
• sjp—actual intestinal digestibility of feed protein that is not broken down in the rumen.

In this study, the effect of organic production system where red clover was supplied with different mineral fertilizers on the proximate chemical composition of herbage and silage, carbohydrate fractions, content of TP and minerals, and selected fermentation parameters was evaluated in a three-year field experiment. The results were processed statistically by analysis of variance (ANOVA). The significance of differences between treatment means for the analyzed parameters was determined by Tukey’s test, and the significance of the combined effects exerted by both experimental factors was estimated by Levene’s test; the results were regarded as significant at p = 0.05. Principal component analysis (PCA) was performed based on the correlation matrix (Pearson’s correlation coefficient). Statistical calculations were performed, and data were visualized in the Statistica program (Statsoft version 13.1, TIBCO Software Inc., Palo Alto, CA, USA).

3. Results

3.1. Chemical Composition and Mineral Content of Red Clover Herbage

The year of the study had a significant (p ≤ 0.05) effect on the proximate chemical composition and carbohydrate fractions in red clover herbage, excluding the L/NDF ratio (p = 0.057) (

Table 1. Proximate chemical composition and carbohydrate fractions of red clover herbage.

Item	Year			Fertilization			SEM	p-Value
	1	2	3	C	P	S		Year (Y)	Fertilization (F)	Interaction (Y × F)
DM 1, g∙kg−1 FM	147 bd	164 bc	217 a	184 a	177 ab	167 b	4.823	≤0.001	0.031	0.036
Chemical composition, g∙kg−1 DM
Ash	87.6 a	73.3 b	89.8 a	87.9	82.2	80.6	1.929	≤0.001	0.280	0.002
CP	192 a	150 bd	172 bc	166 b	175 a	174 a	2.705	≤0.001	0.038	0.064
EE	25.4 b	26.4 b	28.8 a	25.6	27.3	27.7	0.443	0.004	0.102	0.012
CF	246 b	241 b	282 a	258	257	255	3.200	≤0.001	0.944	0.417
NDF	526 a	400 b	534 a	492	487	481	8.943	≤0.001	0.894	0.249
ADF	364 bc	298 bd	388 a	351	351	349	5.551	≤0.001	0.977	0.035
ADL	67.5 a	49.4 b	73.3 a	67.7 a	64.4 ab	58.1 b	1.901	≤0.001	0.006	0.005
WSC	160 bc	228 a	105 bd	154 b	167 ab	172 a	7.374	≤0.001	0.020	0.003
L/NDF	0.13	0.12	0.14	0.14 a	0.14 a	0.12 b	0.002	0.057	0.014	0.097

¹ DM—dry matter; FM—fresh matter; CP—crude protein; EE—extract ether; NDF—neutral detergent fiber; ADF—acid detergent fiber; ADL—acid detergent lignin; WSC—water-soluble carbohydrates; L/NDF—ratio of lignin to NDF; C—control group; P—treatment fertilized with kalimagnesia (Patentkali); S—treatment fertilized with potassium sulfate (SOP); SEM—standard error of the mean. Values followed by the same superscript letters (a–d) are not significantly different at p ≤ 0.05.

). The CP content of herbage was highest in the first year of the study, followed by the third year (p ≤ 0.001), and the differences noted between all years were significant. The concentration of CF in herbage was significantly (p ≤ 0.001) higher in year 3 than in years 1 and 2. The proportions of carbohydrate fractions varied considerably across the years of the study. Red clover herbage harvested in years 1 and 3 was characterized by the highest ADL content (p ≤ 0.001) and the highest proportions of hemicellulose and cellulose. Herbage harvested in year 2 had the lowest concentrations of NDF, ADF, and ADL (p ≤ 0.001) and the highest concentration of WSC (p ≤ 0.001).

The tested supplementary mineral fertilization induced significant differences in the content of DM (p = 0.036), CP, ADL, and WSC and in the L/NDF ratio (Table 1). The CP content of herbage was significantly (p = 0.038) higher in groups P and S than in group C. Group S herbage had a significantly lower concentration of ADL only relative to group C (p = 0.006), which led to significant differences in the values of the L/NDF ratio (p = 0.014). In turn, WSC content was significantly (p = 0.020) higher in group S than in group C. Intermediate values were noted in group P, with no significant differences relative to the other groups.

The statistical analysis revealed the interaction effect of both experimental factors for the content of DM (p = 0.036), Ash (p = 0.002), EE (p = 0.012), ADF (p = 0.035), ADL (p = 0.005), and WSC (p = 0.003) (Table 1). Although each of the factors affected CP concentration in herbage, their combined effects were not observed.

The mineral content of red clover herbage is presented in

Table 2. Mineral content of red clover herbage (g∙kg⁻¹ DM ¹).

Item	Year			Fertilization			SEM	p-Value
	1	2	3	C	P	S		Year (Y)	Fertilization (F)	Interaction (Y × F)
P	0.176 bd	0.227 bc	0.277 a	0.146 b	0.260 a	0.273 a	0.005	≤0.001	0.038	0.021
K	1.140 bd	1.560 bc	1.980 a	1.147 bd	1.391 bc	1.683 a	0.568	0.001	≤0.001	≤0.001
Mg	0.035 bd	0.243 bc	0.273 a	0.164	0.257	0.270	0.004	≤0.001	0.313	0.038
Ca	0.905	1.050	1.073	0.967 b	1.060 ab	1.170 a	0.028	0.927	0.009	≤0.001
Na	0.010 b	0.009 b	0.022 a	0.011 b	0.021 a	0.020 ab	0.002	≤0.001	0.045	0.040

¹ DM—dry matter; C—control group; P—treatment fertilized with kalimagnesia (Patentkali); S—treatment fertilized with potassium sulfate (SOP); SEM—standard error of the mean. Values followed by the same superscript letters (a–d) are not significantly different at p ≤ 0.05.

. The concentrations of the analyzed minerals were highest in the third year of the experiment, and significant differences were noted for the content of P, Mg, Na (p ≤ 0.001), and K (p = 0.001), with the exception of Ca (p = 0.927). The content of P, K, and Mg in herbage was significantly higher in year 2 than in year 1. Only the Na content of herbage was highly similar in the first and second years of the study.

Significant differences in the content of P (p = 0.038), K (p ≤ 0.001), Ca (p = 0.009), and Na (p = 0.045) in herbage were found between the examined supplementary mineral fertilization treatments (Table 2). The concentrations of the analyzed minerals were highest in group S, and the content of P, Ca, and Na was similar in groups S and P. Herbage harvested in the control treatment (without fertilization) was characterized by the lowest levels of minerals; only the differences in the Mg content of herbage between groups were not significant (p = 0.313). The interaction effect of both experimental factors was noted for the content of all analyzed minerals (p ≤ 0.05).

The principal component analysis (PCA) revealed clear relationships between the experimental factors and the analyzed parameters of red clover herbage (Figure 1). Both coordinate axes explained 78.22% of the variance, which implies that some of the results were significant. The following parameters were characterized by low strength of variance: Ash, EE, NDF, and ADF. An analysis of the similarity between experimental treatments revealed that they were grouped mainly based on the year of the study, whereas a lower number of parameters were grouped based on an organic production system. This indicates that the first experimental factor (year of the study) exerted the greatest effect on variation in the obtained results, whereas a combination of both factors exerted only a partial effect. Certain intragroup relationships pointing to stronger associations between the examined parameters and experimental treatments were observed. In the first group, the content of Ca, Na, P, Mg, and CP in herbage harvested in the first year of the study was strongly correlated with experimental treatments. In the second group, the content of K, CF, ADL, and DM and the L/NDF ratio in herbage harvested in the third year of the study were strongly correlated with experimental treatments. None of the parameters analyzed for herbage harvested in the second year of the study were strongly correlated with experimental treatments. Within supplementary mineral fertilization treatments, a correlation was found only between group C vs. DM content and the L/NDF ratio. The WSC parameter was positioned on the opposite side of the plot, pointing to a negative correlation relative to the remaining variables.

3.2. Chemical Composition and Fermentation Pattern of Red Clover Silage

Red clover silages produced in each year of the study were characterized by significant differences in nutrient content (p ≤ 0.05) (

Table 3. Proximate chemical composition and carbohydrate fractions of red clover silage.

Item	Year			Fertilization			SEM	p-Value
	1	2	3	C	P	S		Year (Y)	Fertilization (F)	Interaction (Y × F)
DM 1, g∙kg−1 FM	321 a	313 a	297 b	311	310	313	2.235	≤0.001	0.123	0.019
Chemical composition, g∙kg−1 DM
Ash	102 ab	109 a	92.0 b	102	108	99.9	2.100	0.002	0.716	0.001
CP	192 a	171 b	181 ab	170 b	181 a	182 a	3.116	0.019	0.014	0.042
EE	50.7 a	38.8 bd	44.2 bc	42.0	43.2	44.1	0.835	≤0.001	0.352	0.160
CF	344 a	314 b	303 b	316	319	321	3.362	≤0.001	0.381	0.078
NDF	457 b	547 a	551 a	522	528	527	5.173	≤0.001	0.727	0.033
ADF	363 a	320 bd	339 bc	340	334	332	3.133	≤0.001	0.150	≤0.001
ADL	80.9 a	68.6 bd	77.3 bc	73.1	74.7	73.7	0.907	≤0.001	0.143	0.085
WSC	33.8 a	22.5 bc	9.73 bd	26.1 a	22.1 ab	18.2 b	1.408	≤0.001	0.031	≤0.001
L/NDF	0.18 a	0.13 b	0.14 b	0.14	0.14	0.14	0.003	≤0.001	1.000	0.237

¹ DM—dry matter; FM—fresh matter; CP—crude protein; EE—extract ether; NDF—neutral detergent fiber; ADF—acid detergent fiber; ADL—acid detergent lignin; WSC—water-soluble carbohydrates; L/NDF—ratio of lignin to NDF; C—control group; P—treatment fertilized with kalimagnesia (Patentkali); S—treatment fertilized with potassium sulfate (SOP); SEM—standard error of the mean. Values followed by the same superscript letters (a–d) are not significantly different at p ≤ 0.05.

). The highest concentration of CP was noted in years 1 and 3 (p = 0.019). The proportions of structural carbohydrate fractions in silages were different than in herbage. Silage made from herbage harvested in the first year of the experiment had the lowest NDF content (p ≤ 0.001) and the highest concentrations of ADF and ADL (p ≤ 0.001), which was reflected in the lowest hemicellulose content (94 g∙kg⁻¹ DM), relative to silages made from herbage harvested in the second and third year, which had the highest NDF content. The concentrations of ADF and ADL were significantly (p ≤ 0.001) higher in silage produced in year 3 than in silage produced in year 2. As a result, hemicellulose content was considerably higher in silages made in years 2 and 3 (227 and 212 g∙kg⁻¹ DM, respectively).

Silages made in different supplementary mineral fertilization treatments differed only in the content of CP and WSC (Table 3). The concentration of CP was significantly (p = 0.014) higher in groups P and S than in group C. In turn, the content of residual WSC after the fermentation process was highest in group C, significantly higher than that in group S (p = 0.031) and comparable with that in group P (p > 0.05). The proportions of structural carbohydrate fractions were similar in silages made in all production systems (p > 0.05), which was reflected in the L/NDF ratio (p = 1.000), whose value was identical in all groups. The interaction effect of both experimental factors was noted for the content of DM (p = 0.019), Ash (p = 0.001), CP (p = 0.042), NDF (p = 0.033), ADF, and WSC (p ≤ 0.001).

Silages produced in three successive years were characterized by different patterns of fermentation (

Table 4. Fermentation pattern of red clover silage.

Item	Year			Fertilization			SEM	p-Value
	1	2	3	C	P	S		Year (Y)	Fertilization (F)	Interaction (Y × F)
pH	4.52 b	5.06 a	4.44 b	4.88	4.68	4.75	0.059	0.045	0.055	0.022
Fermentation pattern, g∙kg−1 DM 1
LA	47.2 a	27.3 b	26.6 b	33.2 ab	35.9 a	27.13 b	1.528	≤0.001	0.023	0.031
AA	17.8	15.8	12.8	15.9	15.8	14.8	0.789	0.075	0.330	0.079
BA	3.29 ab	3.84 a	1.93 b	3.81	2.69	3.19	0.253	0.007	0.612	0.013
Ethanol	5.47 a	1.53 bd	3.77 bc	2.21 b	3.27 a	3.75 b	0.297	≤0.001	0.006	≤0.001
LA:AA	3.02 a	2.05 b	2.26 ab	2.36 ab	2.71 a	1.97 b	0.145	0.019	0.016	0.028
N-NH3, g∙kg−1 TN	90.0	99.3	77.1	80.9 b	112 a	80.9 b	0.297	0.752	0.036	0.031

¹ DM—dry matter; LA—lactic acid; AA—acetic acid; BA—butyric acid; LA:AA—ratio of LA to AA; N-NH₃—ammonia nitrogen; TN—total nitrogen; C—control group; P—treatment fertilized with kalimagnesia (Patentkali); S—treatment fertilized with potassium sulfate (SOP); SEM—standard error of the mean. Values followed by the same superscript letters (a–d) are not significantly different at p ≤ 0.05.

). Silage made in year 1 had the highest concentration of LA (p ≤ 0.001), which accounted for 69% of total acids; the concentration of BA was lower than in year 2 and higher than in year 3, but the noted differences were not significant. Silages made in years 2 and 3 were characterized by lower concentrations of LA that accounted for 58% and 64% of total acids, respectively. However, these silages differed significantly (p = 0.045) in terms of pH. Silage produced in year 2 had the highest pH value (5.06) and the highest concentration of BA (p = 0.007), which was nearly twice (1.99-fold) higher than in silage produced in year 3. In the first year of this study, despite the highest rate of lactic acid fermentation, silage had a high content of ethanol (p ≤ 0.001), which was 1.5-fold and 3.6-fold higher on average relative to silages made in years 3 and 2, respectively. The year of the study also had a significant (p = 0.019) effect on the LA:AA ratio in silage.

Silages made from organic red clover herbage grown in different supplementary mineral fertilization treatments did not differ significantly (p = 0.055) only in terms of pH values and were characterized by different fermentation patterns (p = 0.023) (Table 4). The concentration of LA in group C was lower than in group P and higher than in group S, but the noted differences were not significant (p > 0.05). The LA content of silage was significantly higher in group P than in group S. Lactic acid accounted for 66%, 62%, and 60% of total acids in groups P, C, and S, respectively. The concentration of AA, the second fermentation product, was similar in all production systems (p = 0.330) and years of the study (p = 0.075). In contrast to the year of the study, the production system had no influence on the BA content of silage (p = 0.612), which ranged from 2.69 g kg⁻¹ DM (group P) to 3.81 g∙kg⁻¹ DM (group C). Group P silage had the highest ethanol content, with significant (p = 0.006) differences relative to the other groups, but it did not exceed 3.3 g∙kg⁻¹ DM. The LA:AA ratio varied significantly (p = 0.016) across groups; its value was highest in group P and lowest in group S, with no significant differences between group C and groups P and S, similar to LA concentration in silages. In group P, the N-NH₃ content of silage reached 112 g∙kg⁻¹ TN, and it was significantly (p = 0.036) higher than in groups C and S (80.9 g∙kg⁻¹ TN each).

The statistical analysis of treatment means revealed the interaction effect of both experimental factors for pH (p = 0.022), concentrations of LA (p = 0.031), BA (p = 0.013), N-NH₃ (p = 0.031), and ethanol (p ≤ 0.001) and the LA:AA ratio (p = 0.028) in silages (Table 4).

The PCA demonstrated certain relationships between the analyzed silage parameters and experimental treatments (Figure 2). Both coordinate axes explained 61.65% of the variance (compared with 78.22% in herbage), indicating that some of the results were significant. The following parameters were characterized by low strength of variance: ADF, L/NDF ratio, EE, ADL, ethanol, N-NH3, and BA. They provided little information due to their low values and very low variation. These data were least spread out.

The grouping of experimental treatments and the analyzed parameters of silage were not strongly determined by any of the experimental factors (Figure 2). In the plot, all groups conditioned by fertilization treatments were located close to the origin of the coordinate system. In comparison with herbage, silages were characterized by fewer intragroup relationships that point to stronger associations of the examined parameters and experimental treatments. In the first group, the content of LA and CF in silage made from herbage harvested in year 1 was strongly correlated with the experiment treatment. In the second group, the value of pH in silage made from herbage harvested in year 2 could be bound by a strong correlation with the experimental treatment. None of the factor loadings of variables were found within the experimental treatment in year 3. The greatest contribution of original variables to constructing the principal components was noted for WSC and pH. The NDF parameter was positioned on the opposite side of the plot, pointing to a negative correlation relative to the remaining variables.

3.3. Changes in True Protein Content during the Ensiling of Red Clover

The TP content of red clover herbage and silage varied significantly (p ≤ 0.001) across years of the study, but it was not influenced by fertilization (p = 0.231) or the combined effects of both experimental factors (p = 0.352) (Figure 3).

The TP content of red clover herbage was lowest in year 1 and highest in years 2 and 3 (Figure 3). In year 1, TP accounted for 70%, 71%, and 74% of CP in groups C, P, and S, respectively. In years 2 and 3, these values were significantly higher at 83%, 82%, and 84% CP (in groups C, P, and S, respectively) and 83%, 83%, and 82% CP (in groups C, P, and S, respectively).

The TP content of red clover decreased significantly during ensilage (Figure 3). Both years of the study and fertilization treatments induced significant (p = 0.003 and p = 0.035, respectively) changes in TP concentration during fermentation. In year 1, the TP content of silage was determined at 60%, 58%, and 50% CP (in groups C, P, and S, respectively). In year 2, TP content reached 53%, 65%, and 58% CP (in groups C, P, and S, respectively). The values noted in year 3 were 59%, 59%, and 55% CP (in groups C, P, and S, respectively).

An analysis of both experimental factors, i.e., year of the study and fertilization system, revealed that the TP content of herbage was lowest in year 1 in group C and highest in year 2 in group S (Figure 3). The TP content of silage was lowest in year 2 in group C and highest in year 2 in group P. However, the amount of TP degraded during ensilage was lowest in group C in year 1, where 14.3% of herbage TP was broken down into simpler compounds, i.e., non-protein nitrogen (NPN). The greatest extent of proteolytic changes in TP was observed in year 2 in group C (36.1% of herbage TP was degraded during ensilage).

3.4. Feed Value of Red Clover Herbage and Silage

The energy value (UFL, UFV) and the protein value (PDIN, PDIE) of red clover herbage, evaluated according to the INRA system, varied across the years of the study (

Table 5. Content of net energy and protein digested in the small intestine in red clover herbage and silage.

Item	Year			Fertilization			SEM	p-Value
	1	2	3	C	P	S		Year (Y)	Fertilization (F)	Interaction (Y × F)
Herbage, g∙kg−1 DM 1
UFL	0.83 a	0.81 a	0.75 b	0.79	0.80	0.80	0.009	0.024	0.998	0.014
UFV	0.77 a	0.75 a	0.68 b	0.73	0.73	0.74	0.011	0.038	0.998	0.012
PDIN	121 a	94.0 bd	108 bc	104	110	109	3.272	0.018	0.980	0.043
PDIE	93 a	84 b	85 b	86	88	88	1.194	0.048	0.998	0.055
Silage, g∙kg−1 DM
UFL	0.70	0.70	0.71	0.70	0.70	0.70	0.002	0.989	1.000	0.999
UFV	0.60	0.60	0.61	0.60	0.61	0.61	0.002	0.998	0.998	0.999
PDIN	110	103	105	104	106	106	0.902	0.998	0.998	0.998
PDIE	56	55	55	54	55	55	0.236	0.998	0.988	0.999

¹ DM—dry matter; UFL—feed unit for milk production; UFV—feed unit for meat production; PDIN—protein digested in the small intestine when nitrogen is limiting; PDIE—protein digested in the small intestine when energy is limiting; C—control group; P—treatment fertilized with kalimagnesia (Patentkali); S—treatment fertilized with potassium sulfate (SOP); SEM—standard error of the mean. Values followed by the same superscript letters (a–d) are not significantly different at p ≤ 0.05.

). The values of UFL (p = 0.024) and UFV (p = 0.038) were significantly higher in herbage harvested in years 1 and 2, compared with year 3. The values of PDIN (p = 0.018) and PDIE (p = 0.048) were higher in herbage harvested in year 1 than in years 2 and 3. The only significant difference between years 2 and 3 was noted in PDIN content, which was higher in year 3. Neither the energy value nor the protein value of herbage were affected (p > 0.05) by supplementary mineral fertilization treatments. The interaction effect of both experimental factors was noted for UFL (p = 0.014), UFV (p = 0.012), and PDIN (p = 0.043). The values of PDIE were not influenced by the interaction effect of the year of the study and fertilization (p = 0.055).

All silages were characterized by similar average net energy levels across years of the study and fertilization (0.70–0.71 UFL, 0.60–0.61 UFV) (Table 5). Differences in the protein value of silages between years of the study and fertilization were not significant and did not exceed 7 g∙kg⁻¹ DM for PDIN and 2 g∙kg⁻¹ DM for PDIE. The energy value and the protein value of silages were not influenced by the combined effects of the year of the study and fertilization.

4. Discussion

4.1. Chemical Composition and Mineral Content of Red Clover Herbage

In a two-year study by Żuk-Gołaszewska et al. [10], red clover herbage harvested under identical climatic conditions and in the same growth stage contained from 185 to 195 g CP∙kg⁻¹ DM on average, which is comparable with the value noted in the first year of the present experiment. In the remaining years and groups with different fertilization of the experiments, the CP content of red clover herbage was lower, comparable with that reported by Purwin et al. [19] (165.6 g∙kg⁻¹ DM) and with first-cut red clover herbage harvested in the same growth stage by Drobna and Jancovic [20] (175.42 g∙kg⁻¹ DM).

The quality of red clover forage is influenced by many independent factors, including maturity, crop species, and soil fertility. In general, red clover cultivars vary in quality depending on ploidy level and earliness [20]. Several authors [21,22] have described the influence of growing season and environmental conditions on the quality of red clover forage. Drobna and Jancovic [20] demonstrated that each of the tested red clover cultivars was characterized by higher CP concentration in the second year of the vegetation, which was not observed in the present study. The analysis of variance revealed that red clover herbage harvested in the second year of the experiment had lower CP content, which corroborates the findings of Żuk-Gołaszewska et al. [10].

Fertilization is also an important factor influencing the CP content in red clover. The statistically confirmed difference in the CP content between group C and groups P and S can be explained by the potassium fertilization used in the P and S groups. Potassium is one of the most important nutrients necessary for plant development. It plays a vital role in many physiological processes, including photosynthesis, which in turn affects the content of other nutrients. Potassium also enhances nitrogen uptake and protein synthesis, resulting in better leaf growth [23]. Magnesium, used in fertilization in the P group, and sulfur, used in the P and S groups, are also important for protein synthesis. Both minerals influence proper plant metabolism and protein synthesis [24].

The concentration of WSC in red clover herbage is one of the key indicators of its ensiling suitability, and it also affects energy value [25]. In the current study, WSC concentration varied significantly across years of the study and fertilization treatments, but it was high or very high. The average value recommended for red clover is 100 g WSC∙kg⁻¹ DM [26]. The WSC content of red clover herbage determined in this experiment is comparable with the values reported for grasses characterized by high ensiling suitability (140–220 g∙kg⁻¹ DM) [26]. In this experiment, the WSC content of red clover herbage tended to be higher in year 2, which is consistent with the findings of Żuk-Gołaszewska et al. [10] and is considered conducive to plant growth.

The content of NDF, ADF, and ADL (cell wall components) in red clover herbage was high in comparison with the values reported by Żuk-Gołaszewska et al. [10] for red clover herbage harvested under identical climatic conditions and in the same growth stage (423–494 g NDF, 316–334 g ADF, and 35.0–47.8 g ADL per kg DM). In the cited study [10], the average content of structural carbohydrate fractions was determined at 107–160 g hemicellulose and 281–286.3 g cellulose per kg DM, which is comparable with the values noted in this experiment. In the present study, the degree of lignification was considerably higher than that observed by Żuk-Gołaszewska et al. [10] in a two-year experiment where the L/NDF ratio ranged from 0.08 to 0.10.

In this experiment, the carbohydrate composition of red clover herbage varied significantly across the years of this study, which could result from differences in the growth rate of plants in successive growing seasons. Plant species differ in the rates of maturation and lignification, which are also affected by weather conditions during the growing season. The growth rate and vegetative development of plants are associated with changes in the leaf/stem ratio. According to the literature, the process of aging does not induce extreme changes in the quality of red clover, which are observed in many other perennial forage crops such as alfalfa [27,28].

Legumes, including red clover, need macronutrients derived from soil, in particular P and K, for normal growth and development. Potassium is the most abundant macronutrient in plant cells. It is required in large amounts for essential life processes in plants, including the activation of numerous enzymes [29], uptake of macronutrients and micronutrients [30], protein metabolism [31], and maintenance of cell membrane permeability and turgor pressure [32]. In the present experiment, an adequate supply of nutrients contained in fertilizers applied in groups P and S contributed to the high nutritional value of red clover herbage [33]. In group C, the concentration of CP was lowest, and the proportions of ADL and WSC were highest, most likely due to insufficient quantities of macronutrients, which accelerated senescence and lignification [32,33]. Potassium deficiency, which could occur in group C, limited the transport of photosynthetic assimilates from the source tissues to other plant parts through the phloem, leading to sugar accumulation in leaf tissue and decreasing the quality of harvested herbage [34,35]. In turn, an adequate supply of K in groups P and S enhanced the quality of red clover forage [33].

However, Bahaeldeen et al. [36] found that K fertilizer had no influence on alfalfa quality, and similar observations were made by Abusuwar et al. [37]. Moreover, research has shown that fertilizers can be absorbed by the soil complex without exerting any effect on plants [35,38], which could explain the absence of differences in the chemical composition of herbage with regard to other parameters whose values were similar irrespective of the content and plant-available K in soil or the application of supplemental MgO and S in experimental treatments (group P and S). According to Tomić et al. [33], the positive effect of K fertilization can be attributed to the key role played by this macronutrient in various processes in plant cells, but it had no significant effect on the formation of root nodules required for the assimilation of atmospheric N [33].

In the present study, the concentrations of minerals in red clover herbage were very low compared with the literature data. In the first year of the experiment conducted by Żuk-Gołaszewska et al. [10], the P content of red clover herbage was 10-fold higher (3.41–3.64 g∙kg⁻¹ DM) and K concentration was 20-fold higher (37.64–43.04 g∙kg⁻¹ DM) on average than the values determined in this study. The levels of other macronutrients analyzed by Żuk-Gołaszewska et al. [10] were also considerably higher than those noted in the current study. The cited authors reported the following average values: 3.07–3.85 g Mg∙kg⁻¹ DM, 13.29–16.12 g Ca∙kg⁻¹ DM, and 0.41–0.82 g Na∙kg⁻¹ DM [10].

The ability of a plant to obtain the appropriate concentration of essential minerals often depends on their availability in the soil environment, as well as the presence of appropriate transport proteins and the associated ion acquisition mechanisms in root cell membranes [39]. The availability of minerals depends not only on fertilization and the abundance of the soil matrix but, to a greater extent, on the molar fraction of the soil solution and the form of ions of a given element [40]. Abiotic factors such as pH, redox state, and temperature can influence mineral speciation and solubility, as well as biotic factors, which may explain the differences in content observed in subsequent years of the experiment and among groups with different fertilization in our own research [41]. According to Grusak [41], plant roots can modify the rhizosphere and influence nutrient availability by releasing protons, chelators, and/or chemical reducers.

4.2. Chemical Composition and Fermentation Pattern of Red Clover Silage

Silages produced in this study were characterized by a similar chemical composition to silages made from red clover grown in the conventional production system under identical climatic conditions and harvested in the same growth stage [4,42,43]. The decrease in ash content in silages observed in the subsequent years of the experiment, as previously noted in earlier silages, could be attributed to several factors [44]. In this experiment, differences in ash content at the same height as the red clover harvest could result from varying degrees of plant contamination during harvesting, particularly soil contamination [44].

According to the literature [45], the optimal pH of legume silages is 4.3–4.5. In the present study, red clover silages had higher pH values, excluding years 1 and 3. A high pH value (4.77) in red clover silage was also reported by Fijałkowska et al. [42]. The pH values that exceed the recommended range may be due to the large buffer capacity of silages, which is characteristic of legumes, including red clover. This is a result of the significant CP and ash contents recorded in the tested plants. Additionally, the occurrence of limited lactic fermentation may also contribute to a high pH value [46].

Silage acidity is determined mostly by LA, the major product of lactic acid bacteria. According to the literature, the optimal concentration of LA in legume silages is 60–80 g∙kg⁻¹ DM [45]; the average value noted in the present study was more than twice lower. The proportion of LA in red clover silages was close to that recommended for legume silage with DM content of 450–550 g∙kg⁻¹ FM [45]. In red clover silage, LA concentration may be lower as DM content decreases below 350–400 g∙kg⁻¹ FM because bacteria of the genus Clostridium can thrive under moist conditions and convert LA to AA [45]. However, silages produced in this experiment had lower DM content.

Acetic acid is another major organic acid found in silages in the second highest concentration after LA, and its recommended levels for legume silages are 20–30 g∙kg⁻¹ DM; the values noted in the present study were lower. Moderate concentrations of AA can be beneficial because this acid suppresses yeast growth in silage, thus improving its aerobic stability [45]. In high-quality silage, the LA:AA ratio should be 2.5 to 3.0 [45], and such a ratio was achieved in this experiment except in group S. An LA:AA ratio below 1.0 usually points to abnormal fermentation [45], which was not observed in the present study.

In well-fermented silages, BA should not be present at all. The presence of BA is a potential indicator of metabolic activity of Clostridium bacteria, which leads to DM losses and poor energy recovery [46]. Saccharolytic Clostridium spp. are able to metabolize sugars to BA, whereas proteolytic Clostridium spp. can covert LA to BA. Detection of BA and a lower-than-recommended proportion of LA in silage often point to the presence of Clostridium spp., and the pH levels of silages produced in this study were higher than the optimal range [44,45].

Based on the values of the analyzed parameters, the fermentation process was described as limited, with low LA concentration [47]. The quality of the produced silages was satisfactory in terms of N-NH₃ content that did not exceed 120 g∙kg⁻¹ TN [45]. However, low LA concentration, high pH levels, and the presence of BA were indicative of poor fermentation [44]. The high pH values and low LA concentration observed in this study are typical of alfalfa silage [44].

4.3. Changes in True Protein Content during the Ensiling of Red Clover

In the current study, red clover herbage had a high content of TP expressed as a percentage of CP. On average, TP accounts for 76% to 76.5% of CP [48], but higher proportions have also been noted [49]. In red clover silage, TP accounts for 60–93% CP on average [48]. The concentration of TP in the herbage of crop plants is determined primarily by nitrogen fertilization, which increases the share of NPN in the CP pool [42]. However, in this experiment, not even the starting dose of nitrogen fertilizer was applied at the beginning of the growing season, so the level obtained depended only on the amount and form of nitrogen already available in the soil solution, as well as the amount of nitrogen assimilated by red clover [41]. Krawutschke et al. [50], in a three-year study of alfalfa and red clover, found that in all years studied, the share of TP was lower in the spring vegetation period. However, in the summer and autumn periods, the TP content increased with the growth and development of plants. Changes in the amount of TP during vegetation may be a consequence of the process of remobilization of nitrogen absorbed into the generative parts of plants, which becomes activated, and as a consequence of this process, there is an increase in the share of TP. However, in the case of red clover, differences in TP concentration depending on ploidy have also been demonstrated [51].

In the case of silage, the TP content is determined by the extent of proteolytic transformations, which depend on the activity of enzymes in plant cells, their duration of action, intensity, DM level, the rate of pH reduction in the ensiled mass, and the plant species itself [42]. Many studies have shown that red clover naturally undergoes limited proteolysis during ensiling, which is due to the presence of the PPO enzyme [52]. Polyphenol oxidases are enzymes that catalyze the hydroxylation of monophenol to ortho-diphenol and the oxidation of ortho-diphenol to orthoquinone. Quinones are strong oxidants and very strong electrophiles that undergo numerous biochemical reactions to produce numerous secondary products. Orthoquinones can react with each other or with proteins and amino acids. These orthoquinone reactions with proteins are believed to lead to a reduction in proteolytic processes in red clover silage [53].

4.4. Feed Value of Red Clover Herbage and Silage

The energy value of red clover herbage determined in this study was comparable with the INRA standards [54] for red clover harvested in the first flower bud’s visible stage (UFL = 0.81; UFV = 0.74). Lower values, which were noted in the third year of the experiment, were close to the INRA standards [54] for red clover harvested at the end of flowering (UFL = 0.75; UFV = 0.67). The energy value of green forage, including red clover herbage, is usually highest in the early growth stages and decreases during the growing season with plant maturation and aging. In a two-year experiment conducted by Żuk-Gołaszewska et al. [10], red clover harvested at the beginning of flowering had UFL of 0.86–0.87, depending on the cultivar. According to the cited authors [10], differences in the energy value of green forage may result from different WSC concentrations and different proportions of structural carbohydrate fractions. In the current experiment, red clover herbage had higher concentrations of WSC and ADL compared with the values reported by Żuk-Gołaszewska et al. [10].

The values of PDIN and PDIE determined in red clover herbage in this study were comparable with those recommended by INRA [54] for red clover and alfalfa harvested at the beginning of flowering (104 g PDIN and 87 g PDIE∙kg⁻¹ DM and 112 g PDIN and 85 g PDIE∙kg⁻¹ DM, respectively). Drobna and Jancovic [20] analyzed the effects of variety, cut, and growing year on the quality of red clover harvested at the beginning of flowering and reported PDIN of 99.31–126.47 g∙kg⁻¹ DM and PDIE of 77.57–83.13 g∙kg⁻¹ DM.

According to Buxton [21], the differences in the energy value and protein value of red clover herbage between years of the study are influenced by the environment where plants are grown, which is associated with year-to-year, seasonal, and geographical variation in forage quality even when herbage is harvested in the same stage of maturity each year. The documented seasonal variation in forage quality suggests that analyses of stability focus on testing stability between cuttings in the same year rather than between successive production years [55]. Drobna and Jancovic [20] found that the feed value of red clover cultivars was affected by the growing year. The analysis of variance performed by the cited authors [20] revealed that all analyzed quality characteristics were significantly influenced by the year of harvest and that the content of energy, PDIN, and PDIE was higher in the first year of red clover production, which was also confirmed by statistical analysis in all fertilization treatments in the present study.

Regardless of the year of the study or fertilization, the energy value of red clover silages was 0.2 UFL lower on average, relative to the values recommended by INRA [54] for silages made from red clover harvested in the first flower bud’s visible stage (0.89–0.90 UFL). The above differences could result from sugar losses during fermentation, which are associated with reduced digestibility of organic matter. Secondary fermentation decreased the energy value of silages because LA was converted by microorganisms to BA with a lower energy value [44,45].

The results obtained in the present experiment indicate that the applied potassium fertilization in the P and S groups, as well as the magnesium and sulfur introduced with the fertilizers, made it possible to achieve concentrations of basic nutrients comparable to the values obtained in the conventional production system. The harvested herbage, as well as the silage made from it, was characterized by a very good CP composition, as evidenced by the high proportion of TP. The experiment proves that red clover can be grown for forage in an organic production system, and the resulting forage will be characterized by very good or good chemical parameters.

The quality of silage produced in this experiment was satisfactory to moderate due to limited lactic fermentation, low LA content, and optimal concentrations of AA, BA, N-NH₃, and ethanol. A comparison of the energy and protein values of the red clover silages produced in this study with those recommended for red clover, alfalfa, and grass silages suggests that they can be a good source of protein for ruminants, but diets should be supplemented with energy.

5. Conclusions

Based on the experiment, it was shown that the fertilization used in the ecological production system allowed for obtaining a higher content of CP, WSC, P, K, Ca, and Na in the collected red clover greens compared to the control group without fertilization. The prepared silage also had a higher CP concentration in the fertilized groups. The obtained fermentation parameters indicate good quality of all silages; however, red clover silage from group P was of significantly higher quality. Proteolytic transformations concerned all silages, and their highest level was in the second year of the experiment in the control group, which indicated the lowest quality of CP. The energy and protein value of herbage and red clover silage was not dependent on fertilization. The recorded values indicate that red clover silage grown in an organic system may be a good source of protein and energy in the feed ration.