Effect of Humus, Compost, and Vermicompost Extracts on the Net Energy Concentration, Net Energy of Lactation, and Energy Yield of Dactylis glomerata and Lolium perenne

Abstract

The purpose of the research was to examine whether selected organic materials could increase the net energy concentration, net energy of lactation, and energy yield of two grass species. The main factors in the experiment were soil conditioners with the content based on compost, vermicompost and humus extract, applied separately and supplemented with NPK fertilizers. The second factor is grass species, Dactylis glomerata and Lolium perenne. Mineral fertilizer and compost extract resulted in a reduction in net energy concentration by about 5%. The largest value of net energy of lactation (NEL) was obtained after the application of humus extract with NPK. The average value of the energy yield was the biggest on units where biological extracts were applied together with NPK. That increase was from 63% for NPK applied together with humus extract to 76.5% for the NPK applied with compost extract. Of the applied humic substances, those applied together with mineral fertilizer had the greatest impact on net energy value and NEL. The use of compost extract contributed to a substantial increase in the yield of feed energy. Other biological substances applied together with mineral fertilizer also had a positive impact. Weather conditions in various years of the research differentiated feed energy values. Due to the complexity of the environment (soil, climate, plant), it is impossible to provide a universal combination of fertilizers that increases the energy value of forage. Therefore, it is important to carry out practical field experiments that will indicate the optimal fertilizer combinations suitable for the selected region.

1. Introduction

Systems for feeding dairy cows (DLG) intended to balance energy and nutrients for high performance cows have been applied in Poland since 1999. The use of the standards to formulate basic rations for livestock brings benefits, increasing productivity and reducing production costs. Based on net energy of lactation (NEL) in the case of dairy cows, the DLG system, and a variety of others, determines the value of the energy of feed stuffs [1]. According to Jonker et al. [2], the content of energy and protein in the correctly balanced ration affects an optimal course of lactation and milk composition. Juszczak and Ziemiński [3] reported that animals at the height of the lactation period suffer from low energy and protein content in the feed when nutritional needs outweigh the possibility of nutrient intake to maintain nutritional balance. However, an excess of protein in the feed can also be harmful as it can cause an increase in the number of milk somatic cells. As the literature indicates [4,5], feed energy value varies depending on the plant species, growing season, fertilizer used, irrigation, and the stage at which the plants are harvested.

Cocksfoot grass is successfully cultivated in unfavourable hydrothermal conditions [6,7]. The literature reports that cocksfoot grows well in drought conditions [8] and under water stress [9]. Research conducted on acidic soils of Lithuania showed that the highest yield of cocksfoot was obtained with high nitrogen fertilization with simultaneous liming [10]. In turn, perennial ryegrass is sensitive to high soil moisture and drought stress [11]. The yield of ryegrass increases with the phosphorus content in the soil; therefore, this species is used for the remediation of soils with a high content of P [12]. Nevertheless, the soil factor was omitted from the experiment, which focused instead on the effects of fertilization and the weather conditions.

In the era of organic farming, which excludes the use of mineral fertilizer, biological growth-enhancing products are increasingly used. Another reason to use of biological preparations is the reduction in mineral fertilization by 20% in the EU by 2030 [13]. In Poland, biological products are enumerated in the list of fertilizers and soil conditioners drawn up by the Institute of Soil Science and Plant Cultivation (IUNG) in Puławy. Although there have been some research studies concerning the effect of soil amendments on the quantitative and qualitative properties of grass [14,15,16,17,18,19], there is no information available in the literature on the application of biological products to improve the energy value of grass.

Three biological preparations with different compositions were selected for the study: compost extract, vermicompost extract and humus extract. In order to verify the validity of the use of biopreparations, they were compared with NPK mineral fertilization. Additionally, biological preparations were combined with mineral fertilization to see if their effect would be better together or separately. The aim of the research was to determine how biological preparations used separately and in combination with NPK affect the net energy concentration, net energy lactation and the energy yield of two grass species.

2. Materials and Methods

2.1. Experiment Location

The experiment was set up in the autumn of 2018. The three-year research was conducted in the experimental field at the University of Natural Sciences and Humanities in Siedlce (52.169° N, 22.280° E), Poland. With a split-plot arrangement, the experimental units were plots of 3 m³ with three replications.

The study was conducted on the soil with the granulometric composition of light loamy sand, classified as technosol [20]. Chemical analysis showed that it was of slight acidic pH (pH = 6.6), with a concentration of C_org of 12.30 g kg⁻¹ DM and N_total of 1.250 g kg⁻¹ DM. The assimilable macronutrients concentration (mg kg⁻¹ DM) was P–790; K–1060; Mg–1260; Ca–1820.

2.2. Experimental Factors

The main factors in the experiment were biological fertilizers, with the trade names of UGmax (compost extract, CE), Eko-Użyźniacz (vermicompost extract, VE), and Humus Active Papka (humus extract, HE), applied separately and supplemented with NPK fertilizers, according to the Institute of Soil Science and Plant Cultivation in Puławy, and their composition is presented in Table 1. In the present experiment, they were tested on two fodder grass species, Dactylis glomerata var. Bora and Lolium perenne var. Info, sown in the autumn of 2018 with sowing rates of 18 and 23 kg ha⁻¹, respectively. They were used each year in the spring before the growing season with the following doses: compost extract-0.6 dm³ ha⁻¹, vermicompost extract-15 dm³ ha⁻¹ and humus extract-50 dm³ ha⁻¹.

Mineral nitrogen, phosphorus, and potassium (NPK) fertilizers were used at the following doses: N–150, P (P₂O₅)–80, K (K₂O)–120 kg ha⁻¹.

2.3. Weather Conditions

Meteorological data for the years of research were obtained from the Hydrological and Meteorological Station in Siedlce (Table 2).

In the first year (2019), optimal precipitation was only in May and August. In the remaining months of that growing season, rainfall was at least twice as low as the annual mean. The years 2020 and 2021 were rich in rainfall, but dry periods also occurred. The average temperature in 2019 was about 13% higher than the average temperature according to the annual mean. The temperatures recorded in 2020 and 2021 were close to the annual average.

2.4. Analysis

Net energy concentration in 1 kg of dry matter was determined using the following formula [21]:

NE = 1.50 − 0.02·CF(1)

where:

• NE—Net energy concentration in 1 kg DM,

• CF—Crude fibre content (% DM).

Net energy of lactation was determined with the following formula [22]:

NEL = 6.998 − 0.061·CF + 0.014·TP(2)

where:

• NEL—net energy of lactation (MJ kg⁻¹ DM),

• CF—crude fibre content (% DM),

• TP—total protein (% DM).

Energy yield of the fodder was determined using the following formula [5]:

PE= P·100 (0.968 − 0.0063·CF + 0.033·TP)(3)

where:

• PE—forage energy yield (JP ha⁻¹),

• P—dry matter yield (dt ha⁻¹),

• CF—crude fibre content (% DM),

• TP—total protein content (% DM).

During each of the three growth cycles, the plants were cut three times per year (May, July and September). During plant harvest, the green mass of each plot was cut and weighed. Then, samples of the plant material (1.0 kg on average) were taken for chemical analyses. The dry weight of plants was determined by the drying and weighing method. For chemical analyses, the dry plant raw material was ground (including leaves, stems and inflorescences).

The content of total protein and crude fibre in plant material was measured with near-infrared spectroscopy, using the NIRFlex N-500 spectrometer (BUCHI, Flawil, Switzerland) with the INGOT calibration package for dry feed.

The results of the research were processed statistically using three factor analysis of variance. The significance of the impact of experimental factors on the tested characteristics was verified with the Fisher–Snedecor test, while Tukey’s test was used to evaluate differences between means. The calculations were conducted with the Statistica 13 Program (TIBCO Software Inc., Palo Alto, CA, USA).

3. Results and Discussion

3.1. Net Energy Concentration in 1 kg DM

Both grass species differed in their average concentration of net energy (NE) in 1 kg of dry matter; it was significantly greater by 7.5% in Lolium perenne (1.098) than in Dactylis glomerata (1.022). The latter did not respond to different fertilizer treatments in a statistically significant way (Table 3). In turn, Lolium perenne had the largest NE concentration on the plots where vermicompost extract was applied (1.145) and where humus concentrate was used together with mineral fertilizer (1.121). Mineral fertilizer and compost extract, both applied separately, resulted in a reduction in this parameter by about 5% compared to the control; it was not, however, a statistically significant difference. Analysing the response to all treatments, it was found that the largest concentration of NE as an average for both species was after vermicompost application (1.082), and after treatment with a combination of humus extract and mineral fertilizer (1.084). According to Wiśniewska-Kadżajan [21], applying manure and mushroom substrate both alone and with mineral fertilization, it was found that the net energy concentration in forage ranged from 0.93 to 0.95, and different kinds of treatment did not differentiate the values significantly. In the present experiment, the highest increase in NE concentration (1.076) was observed in the second growing season in 2020 (Table 3). The abundance of rainfall and moderate temperatures in 2020 could have contributed to the accumulation of NE in the plants. This was supported by a decrease of 4% in NE in seasons (years) when dry periods and higher temperatures prevailed.

The concentration of energy in 1 kg DM of plants depends, to a large extent, on weather conditions. Grass species displayed different sensitivity to changing weather during the first growing season (Figure 1a) when Dactylis glomerata had the lowest concentration of NE (1.007), while Lolium perenne had the highest (1.123). NE concentration in both species decreased in the last year (2021), which could have been caused by alternately occurring dry and wet periods. NE was the smallest in the first harvest (1.020) and then increased with successive ones by about 3.5% to its maximum in plants of the third cut (1.097). For both grass species, net energy concentration also increased in subsequent harvests, and the difference between the first and the last was about 7%, being statistically significant (Figure 1b).

3.2. Net Energy of Lactation

The average net energy of lactation (NEL) was greater in Lolium perenne forage (5.98 MJ kg⁻¹ DM), and the 4% difference between both grass species was statistically significant (Table 4). The NEL results for the two species ranged from 5.64 to 6.12 MJ kg⁻¹, which classified them as good quality forage [1]. According to Abas et al. [4], NEL for grass hay was 3.78 MJ kg⁻¹ and for alfalfa hay 5.20 MJ kg⁻¹. Analysing the response of the species to different treatments, the value of the NEL of Dactylis glomerata showed no significant variation. In turn, Lolium perenne had the largest NEL on units where vermicompost extract was applied (6.12 MJ kg⁻¹ DM). The responses were similar in the case of humic extract (6.03 MJ kg⁻¹ DM), compost extract in combination with mineral fertilization (6.03 MJ kg⁻¹ DM), and humic extract applied with mineral fertilizer (6.06 MJ kg⁻¹ DM). According to Kujawiak and Zarudzki [1], forage with the NEL value from 6.0 to 6.5 MJ kg⁻¹ DM is of very good quality.

By comparing the values of NEL for different treatments, as an average for both species, the largest was obtained after the application of humus extract with mineral fertilizer (5.95 MJ kg⁻¹ DM). Mineral fertilizer applied on its own did not increase it (5.77 MJ kg⁻¹ DM), and neither did compost extract (5.72 MJ kg⁻¹ DM). Those values do not differ significantly in terms of statistical significance. However, the average NEL values for fertilization indicated that the feed was of good quality [1]. On average, the largest NEL was observed in the second year (5.92 MJ kg⁻¹ DM), with a significant reduction in the third year (5.80 MJ kg⁻¹ DM). The differences in the net energy of lactation content between different growing seasons were probably caused by weather conditions. The results of the research indicated that wet periods during a growing season promoted the accumulation of net energy of lactation in grass forage, while dynamic changes in meteorological conditions, as in 2021, decreased it.

NEL in different growing seasons varied depending on the grass species (Figure 2a). In Dactylis glomerata fodder, this parameter remained at a similar level (5.69–5.78 MJ ha⁻¹ DM), not showing significant differences in all three growing seasons. In turn, for the feed of Lolium perenne, the largest NEL value was recorded in the first (6.06 MJ ha⁻¹ DM) and second (6.05 MJ ha⁻¹ DM) years of the research, while in the third this parameter decreased considerably to 5.83 MJ ha⁻¹ DM, i.e., by about 3.6%. The greatest value of net energy of lactation was in the last harvest (5.84 and 6.15 MJ ha⁻¹ DM), and the smallest in the first (5.59 and 5.85 MJ ha⁻¹ DM). Both grass species had the same tendency of increasing the value of the NEL parameter from the first to third harvest by about 4.5% on average (Figure 2b).

3.3. The Yield of Feed Energy

Feed energy yields vary depending on the plant species, growing season, fertilizer treatment, irrigation and the stage at which the plants are harvested [4]. Analysing the average annual energy yield (Table 5) for both grass species, it was found that Dactylis glomerata with 14,704 JP ha⁻¹ had, by 14%, better results than Lolium perenne (12,855 JP ha⁻¹). In the case of Dactylis glomerata, a significant increase in the annual energy yield compared with the control was reported after the use of compost extract, together with mineral fertilizer, while Lolium perenne responded with a higher value to vermicompost applied together with mineral fertilizer.

The average value of the energy yield was the biggest on units where biological extracts were applied together with mineral fertilizer. That increase was from 63% for NPK applied together with humus extract (to 15,806 JP ha⁻¹) to 76.5% for the NPK applied with compost extract (to 17,121 JP ha⁻¹). There was a statistically significant increase by about 35% in the energy yield on plots with vermicompost (13,124 JP ha⁻¹) by about 35%. For the other two biological materials used on their own, an increase was not significant. Ciepiela et al. [5] found that the energy yield increased with the dose of nitrogen. The authors recorded a 4320 JP ha⁻¹ energy yield on the control unit, while on units with nitrogen at a dose of 60 kg ha⁻¹ it was 8363 JP ha⁻¹. As an average for grass species and treatments, the largest yield of feed energy was in the first (14,985 JP ha⁻¹) and second (15,008 JP ha⁻¹) years, and the smallest in the third (11,345 JP ha⁻¹). Significantly lower results in the third year might have been caused by plant aging, which decreased both the amount of protein relative to raw fibre and the yield of dry matter.

The largest statistically significant average energy yield was in the second harvest (4729 JP ha⁻¹), and the smallest in the third (4314 JP ha⁻¹). Differences in quantity between harvests were probably caused by varied weather conditions during the growing seasons of the three-year experiment. Each year, dry periods prevailed before the second harvest, which may have contributed to total protein accumulation without increasing crude fibre content. This had a positive impact on the energy yield. In turn, its low value in the third harvest was probably due to a lower yield of plants.

As it is presented in Figure 3a, the annual energy yield of Lolium perenne was at a similar level throughout the experiment (from 11,761 to 13,434 JP ha⁻¹), while for Dactylis glomerata it declined from 16,600 JP ha⁻¹ in the first year to a significantly lower value of 10,929 JP ha⁻¹ in the last year. Higher amounts of the annual energy yield of Dactylis glomerata in relation to Lolium perenne may be due to its characteristics. Generally, Dactylis glomerata in comparison with Lolium perenne contains more protein and produces higher dry matter yields, which could have affected its energy yield [23,24]. This fact was confirmed by previous studies conducted in Poland under similar physical and chemical conditions of the soil [18,19,25]. The energy yield of Lolium perenne throughout the growing season was at a similar level, from 4356 JP ha⁻¹ in the first harvest to 4177 JP ha⁻¹ in the third (Figure 3b). A more dynamic situation was in the case of Dactylis glomerata, for which the yield in the second harvest (5167 JP ha⁻¹) was statistically significantly greater than in the third (4451 JP ha⁻¹).

This species had a high dry matter yield in the first and second harvests, but it decreased in the third, leading to a lower energy yield [23]. In a study on the energy yield of Lolium perenne, the Research Centre for Cultivar Testing in Słupia Wielka, Poland, observed considerable changes in the values [26]. It ranged from 9062 JP ha⁻¹ (the first harvest) to 1858 JP ha⁻¹ (the third harvest) in 2015 and from 6133 JP ha⁻¹ (the first harvest) to 2355 JP ha⁻¹ (the third harvest) in 2016.

4. Conclusions

• Of the applied biological materials, humic substances applied together with mineral fertilizer had the greatest impact on net energy value and net energy of lactation (NEL).

• The use of compost extract contributed to a substantial increase in the yield of feed energy. Other biological substances applied together with mineral fertilizer also had a positive impact.

• Lolium perenne feed had a higher net energy of lactation and concentration of net energy than Dactylis glomerata; in turn, the latter one had a higher annual yield of feed energy than the former.

• Weather conditions in various years of research differentiated feed energy values. In 2020, the year with the largest amount of rainfall during most months of the growing period, the feed had the highest value of energy concentration, net energy, and net energy of lactation.

• Due to the complexity of the environment (soil, climate, plant), it is impossible to provide a universal combination of fertilizers that increases the energy value of forage. Therefore, it is important to carry out practical field experiments that will indicate the optimal fertilizer combinations suitable for the selected region.

Author Contributions

Conceptualization, J.S.; methodology, J.S.; software, M.T.; validation, J.S. and M.T.; formal analysis, M.T.; investigation, J.S.; resources, K.J.; data curation, M.T. and K.J.; writing—original draft preparation, J.S.; writing—review and editing, M.T.; visualization, K.J.; supervision, J.S.; project administration, J.S.; funding acquisition, J.S. All authors have read and agreed to the published version of the manuscript.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

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Figures and Tables

Figure 1. Net energy of Dactylis glomerata and Lolium perenne in consecutive (a) growing seasons and (b) harvests (in 1 kg DM). Means in columns marked with the same lower-case letters do not differ significantly.

Figure 2. Net energy of lactation of Dactylis glomerata and Lolium perenne in consecutive (a) growing seasons (b) harvests (MJ kg−1 DM). Means in columns marked with the same lower-case letters do not differ significantly.

Figure 3. The energy yield of Dactylis glomerata and Lolium perenne in consecutive (a) growing seasons and (b) harvests (JP ha−1).

Table 1

Soil conditioner composition based on manufacturers’ data.

Name	CE	VE	HE
Macronutrients (g kg−1)
N	1.2	0.6	0.2
P	0.2	0.3	1.3
K	2.9	0.7	4.6
Ca	-	-	3.0
Mg	0.1	-	0.5
Na	0.2	-	-
Micronutrients (mg kg−1)
Mn	0.3	-	15
Fe	-	-	500
Zn	-	-	3
Cu	-	-	1
Mo	-	-	-
Microorganisms
	lactic acid bacteria, photosynthetic bacteria, Azotobacter, Pseudomonas, yeast, Actinomycetes	Endo micorrhiza, fungi, bacteria, enzymes of earthworms	Useful microorganisms

Table 2

Average air temperature and sum of atmospheric precipitation in consecutive months of the growing seasons.

Year	Month
	Apr.	May	June	July	Aug.	Sept.	Oct.	Means
Temperature (°C)
2019	13.1	17.0	18.3	20.4	20.6	15.9	9.6	16.4
2020	8.6	11.7	19.3	19.0	20.2	15.5	12.0	15.2
2021	6.6	12.4	20.4	22.7	17.1	12.9	8.6	14.4
Means	9.4	13.7	19.3	20.7	19.3	14.8	10.1	15.3
Multiannual means	8.5	14.0	17.4	19.8	18.9	13.2	7.9	14.2
Precipitation (mm)
2019	5.9	59.8	35.9	29.7	49.3	17.4	9.5	29.6
2020	6.0	63.5	118.5	67.7	18.0	38.8	17.6	47.2
2021	42	30	34	50	95	42	6	42.7
Means	18.0	51.1	62.8	49.1	54.1	32.7	11.0	39.8
Multiannual means	33.0	52.0	52.0	65.0	56.0	48.0	28.0	47.7

Table 3

Net energy concentration in 1 kg DM.

	Fertiliser Effect								Means
	0	NPK	CE	VE	HE	CE + NPK	VE + NPK	HE + NPK
Means for species
Dactylis glomerata	1.010 Ba	1.020 Aa	0.993 Ba	1.018 Ba	1.037 Ba	1.026 Ba	1.022 Ba	1.047 Ba	1.022 B
Lolium perenne	1.104 Aab	1.048 Ab	1.053 Ab	1.145 Aa	1.113 Aab	1.109 Aab	1.089 Aab	1.121 Aa	1.098 A
Means for growing seasons
2019	1.030 Aa	1.032 Aa	1.045 Aa	1.097 Aa	1.080 Aa	1.094 Aa	1.053 Aa	1.088 Aa	1.065 AB
2020	1.105 Aa	1.072 Aa	1.037 Aa	1.083 Aa	1.063 Aa	1.050 Aa	1.083 Aa	1.116 Aa	1.076 A
2021	1.037 Aa	0.997 Aa	0.987 Aa	1.066 Aa	1.082 Aa	1.058 Aa	1.030 Aa	1.048 Aa	1.038 B
Means for harvests
I	1.035 Aa	0.971 Ba	1.005 Ba	1.054 Aa	0.997 Ba	1.033 Aa	1.014 Aa	1.055 Aa	1.020 B
II	1.035 Aa	1.038 ABa	1.091 ABa	1.050 Aa	1.041 ABa	1.077 Aa	1.076 Aa	1.082 Aa	1.061 AB
III	1.102 Aa	1.100 Aa	1.112 Aa	1.094 Aa	1.089 Aa	1.091 Aa	1.077 Aa	1.114 Aa	1.097 A
Mean	1.057 ab	1.034 ab	1.023 b	1.082 a	1.075 ab	1.067 ab	1.056 ab	1.084 a

0—Control; NPK—mineral fertiliser; CE—compost extract; VE—vermicompost extract; HE—humus extract; Means in lines marked with the same small letters do not differ significantly; Means in columns marked with the same capital letters do not differ significantly.

Table 4

Net energy of lactation of Dactylis glomerata and Lolium perenne in consecutive harvests and growing seasons (MJ·kg⁻¹ DM).

	Fertiliser Effect								Mean
	0	NPK	CE	VE	HE	CE + NPK	VE + NPK	HE + NPK
Means within species
Dactylis glomerata	5.70 Ba	5.73 Aa	5.64 Aa	5.73 Ba	5.79 Ba	5.77 Ba	5.76 Ba	5.83 Ba	5.74 B
Lolium perenne	5.99 Aab	5.82 Ab	5.80 Ab	6.12 Aa	6.03 Aa	6.03 Aa	5.97 Aab	6.06 Aa	5.98 A
Means within growing seasons
2019	5.74 Aa	5.77 Aa	5.77 Aa	5.96 Aa	5.91 Aa	5.98 Aa	5.86 Aa	5.96 Aa	5.87 AB
2020	5.99 Aa	5.90 Aa	5.78 Aa	5.93 Aa	5.88 Aa	5.83 Aa	5.96 Aa	6.05 Aa	5.92 A
2021	5.80 Aa	5.65 Aa	5.62 Aa	5.88 Aa	5.94 Aa	5.88 Aa	5.77 Aa	5.83 Aa	5.80 B
Mean within harvests
I	5.76 Aa	5.56 Ba	5.64 Ba	5.82 Aa	5.65 Ba	5.78 Aa	5.72 Aa	5.85 Aa	5.72 B
II	5.76 Aa	5.78 Aa	5.93 Aa	5.82 Aa	5.81 Aa	5.93 Aa	5.93 Aa	5.94 Aa	5.86 AB
III	6.01 Aa	6.01 Aa	6.01 Aa	5.98 Aa	5.97 Aa	5.98 Aa	5.94 Aa	6.06 Aa	6.00 A
Mean	5.84 ab	5.77 b	5.72 b	5.92 ab	5.91 ab	5.90 ab	5.86 ab	5.95 a

0—Control; NPK—mineral fertiliser; CE—compost extract; VE—vermicompost extract; HE—humus extract; Means in lines marked with the same small letters do not differ significantly; Means in columns marked with the same capital letters do not differ significantly.

Table 5

The effect of different treatments on the annual energy yield of Dactylis glomerata and Lolium perenne (JP ha⁻¹).

	Fertiliser Effect								Means
	0	NPK	CE	VE	HE	CE + NPK	VE + NPK	HE + NPK
Means within species
Dactylis glomerata	9970 Ab	13,871 Ab	13,572 Ab	14,606 Aab	12,519 Ab	18,658 Aa	17,614 Aab	16,820 Aab	14,704 A
Lolium perenne	9432 Ab	13,912 Aab	10,751 Ab	11,643 Ab	10,775 Ab	15,583 Aab	15,951 Aa	14,791 Aab	12,855 B
Means within growing seasons
2019	9771 Ab	15,171 Aab	13,711 Ab	14,782 Aab	12,989 Ab	18,553 Aa	18,312 Aa	16,591 Aab	14,985 A
2020	10,199 Ab	15,879 Aab	13,082 Ab	13,775 Ab	11,481 Ab	19,850 Aa	18,639 Aa	17,160 Aab	15,008 A
2021	9133 Ab	10,624 Bab	9693 Aab	10,816 Aab	10,472 Aab	12,960 Bab	13,396 Bab	13,667 Aa	11,345 B
Mean	9700 c	13,892 b	12,162 bc	13,124 b	11,647 bc	17,121 a	16,782 a	15,806 ab
Means within harvests
I	3427 Ac	4641 Ab	4102 Abc	4562 Abc	3982 Abc	5873 Aa	5711 Aab	5327 Aab	4703 AB
II	3281 Ac	4682 Ab	4301 Abc	4410 Abc	4028 Abc	5941 Aa	5829 Aab	5363 Aab	4729 A
III	2952 Ab	4535 Aab	3851 Ab	4087 Ab	3515 Ab	5269 Aa	5218 Aab	5087 Aab	4314 B
Mean	3220 c	4620 b	4085 bc	4353 bc	3841 c	5695 a	5586 a	5259 a

0—Control; NPK—mineral fertiliser; CE—compost extract; VE—vermicompost extract; HE—humus extract; Means in lines marked with the same small letters do not differ significantly; Means in columns marked with the same capital letters do not differ significantly.

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