The Circular Economy Approach to Dealing with Burdensome Waste from Poultry Industry

Abstract

This study applies the concept of the circular economy by using poultry feather waste to produce biodegradable geotextiles for environmental applications. The main goal was to assess their biodegradability, effect on soil properties, and usefulness in supporting plant growth. Three types of feather-based nonwoven fabrics were manufactured using a needle-punching method and tested under laboratory and field conditions over a 23-month period. Laboratory tests confirmed high biodegradability: Nonwoven I and III lost over 91% of their mass within 24 weeks. In field trials, plots covered with biodegradable geotextiles showed up to 266% more seedlings compared to bare soil, and plant height increased by 90% on average. The materials also improved soil moisture retention and supported microbial activity. After use, the nonwovens did not require removal and decomposed naturally, enriching the soil. The results demonstrate that feather-based geotextiles are a sustainable, effective, and locally available solution for soil protection and vegetation in difficult terrain.

1. Introduction

The concept of a circular economy (CE) is one of the forms of operationalization of the idea of sustainable development [1,2]. It involves redesigning economic processes and material circulation in order to implement more sustainable economic models. Nature operates in a closed circuit, without waste. Economic processes carried out by society are accompanied by flooding nature with waste, including burdensome waste—materials that are particularly harmful to nature [3].

In the agro-food industry, an example of such a burdensome material is waste in the form of feathers from poultry production. The appropriate redesign of the production process enables the use of waste raw material as a material for the production of biodegradable agricultural nonwoven fabric, which can then be used for sodding difficult terrains and improving such areas’ soil properties.

Difficult terrain are places where the adaptation of plants is difficult due to their properties. Examples of difficult terrain include all embankments, scarps, flood embankments, drainage ditches and newly formed ski slopes, where quick sodding is very important [4]. Hence, sufficient plant diversity, the number and density of plant roots largely determine the stability of such terrains [5]. The problem of proper sodding in difficult terrains can be solved by using protective nonwoven fabrics to improve the habitat conditions of developing seedlings. In addition to other properties, such nonwoven should be biodegradable, which enables its quick and cheap disposal at the place of use. Eliminating environmental burdens will become a measurable ecological and economic effect throughout the product’s life cycle.

The poultry industry has observed an enormous rise in the production scale along with the generation of a large amount of poultry by product over the years [6]. Hence, the disposal of poultry feathers is difficult and cost effective, and these billions of kilograms of feather waste ultimately find their way to the environment, which creates a serious solid waste problem [7,8]. So far, an insignificant quantity of this waste has been utilized industrially for clothing, insulation, and producing biodegradable polymers and microbial culture medium. To minimize the risk they pose to the environment, it is necessary to manage them in an environmentally friendly and economical manner [9]. Chicken feathers contain 90% keratin, 1% lipid, and 8% water and the keratin protein is naturally insoluble due to the presence of peptide bonds [10]. It can also be a good source of organic matter which may help in maintaining soil fertility and improving productivity. Therefore, chicken feathers are considered as a potential source of nonwoven geotextile production due to their low weight, low cost, and high availability and durability. Some important parameters of soil, such as bulk density, porosity, and water holding capacity, that are crucial in maintaining soil quality and soil conservation have been found to be affected by geotextile application. Some researchers suggested that the application of natural geotextile can increase the amount of nitrogen, potassium, and phosphorus content in the soil [11].

Unlike most natural fibers used for geotextile production, chicken feathers have a uniquely high keratin content, which is characterized by its insolubility, gradual biodegradability, and capacity for slow nutrient release into the soil. This distinguishes them from plant-based fibers such as jute or coir, which have a different biochemical composition—mainly cellulose and lignin—and typically decompose more rapidly, potentially resulting in a less sustained enrichment of the soil over time. Furthermore, feather-based geotextiles utilize locally and globally abundant, low-cost agro-industrial waste that is often problematic to dispose of, thereby directly contributing to circular economy objectives in agriculture.

Geotextiles appear durable and soft, and they are designed in a way that allows the flow of liquids through them [12]. Geotextiles can be produced from both degradable [13,14,15] and non-degradable materials. Textile fibers can be classified into two main groups, man-made fiber and natural fiber. Man made fibers are those which are not present in nature, whereas natural fibers include those which are collected from natural sources [16]. Natural fibers are best suited for geotextile production as they possess properties like a high strength, high moisture intake, and low elasticity [17]. Natural geotextiles, after being incorporated into the soil, improve soil structure and soil microbial activity [18]. During the biodegradation process, they provide organic material and nutrients to the plants and microorganisms, which creates an optimum condition for plant growth. Natural geotextiles have many applications, such as crop and livestock protection, erosion control, reinforcement systems on embankments, and so on.

The innovation of our proposal is a biodegradable composite nonwoven fabric and the method of its production by needle punching. Newly designed biodegradable nonwoven fabrics based on bird feathers have a number of advantages over other types of nonwoven fabrics used in agriculture. First of all, they do not contain synthetic polymers, which determines the possibility of their biodegradation. Compared to biodegradable nonwoven fabrics manufactured on the basis of polylactide (PLA), they undergo rapid, complete biodegradation in natural conditions [19,20]. The decomposition of PLA nonwoven fabrics in the natural environment is very slow, and in industrial composting conditions, PLA undergoes complete biodegradation within several months [21]. Additionally, their price is higher than nonwoven fabrics made from petrochemical raw materials.

Traditional geotextiles are often made from jute, wool, or coir fibers. Wool geotextiles provide effective soil protection but are relatively costly and have a limited resource base [22]. Jute and coir are plant-derived, widely used in erosion control and soil improvement, but their fibers degrade quickly under humid conditions and may require importation in regions lacking local availability [23,24]. In contrast, feather-based geotextiles, as developed in this study, offer similar or enhanced soil stabilization effects, support plant growth, and are made from a material that is both cheap and locally sourced as a byproduct of poultry processing [10,25]. This makes them a financially and logistically attractive alternative, especially in areas with significant poultry production [26]. The comparative sustainability and performance of feather-based geotextiles, demonstrated here, represent a meaningful advancement in waste valorization and agricultural technology.

The present study aims to determine the effect of nonwoven geotextile made from chicken feathers on soil nutrients as well as to verify possibilities of overgrowing nonwoven fabrics by emerging seedlings. It is also important to investigate whether the application of geotextile alters the soil quality so as to affect soil natural microbiota and promote plant growth.

2. Materials and Methods

2.1. Materials

The following materials were used for the manufacture of composite nonwovens:

• White poultry feathers after physical and mechanical treatment (Poultry Slaughterhouse—CEDROB S.A., Poland);
• Wool—length 50 mm (Poltops Sp. z o.o., Poland);
• PESco/polyethylene bicomponent fiber—length 50 mm.

2.1.1. Feathers Pre-Treatment

The conversion of poultry feathers into fibrous pulp for use as a component of nonwoven requires specific grinding conditions—the fragmentation of feathers into millimeter short filaments. Damp poultry feathers were preliminarily grinded on the guillotine, then introduced by means of a sieve transporter to the industrial shredder. This device allows cutting the complete feathers into smaller fragments of 10–15 mm. Feathers, after grinding, were filtered on a sieve, centrifuged, and dried at 88 °C for 2 h.

2.1.2. Nonwoven Manufacturing

A method for producing nonwovens using a needle method is that wool fibers and bicomponent PESco/PE fibers are subjected to loosening and carding, after which they are arranged on a horizontal plane, and then the shredded poultry feathers, 10–15 mm long in the amount of up to 40 wt %, are evenly distributed on such a single fleece. By combining individual layers, a multilayer composition is formed, which is subjected to needling to give a multilayer nonwoven fabric. To strengthen the multi-layer nonwoven fabric, it is thermally consolidated using a calender.

2.2. Analytical Methods

2.2.1. Mechanical Properties

The mechanical properties were tested according to the following international standards:

• EN 29073-1:1994 [27]—basic weight [g/m²];
• EN ISO 9073-2:2002 [28]—thickness [mm];
• EN 29073-3:1994 [29]—tensile strength in the longitudinal and vertical direction [N];
• EN ISO 9073-4:2002 [30]—tear resistance in the longitudinal and vertical direction [N].

2.2.2. Biodegradation Tests

Biodegradation tests were carried out according to the research procedure. The determination of the degree of decomposition of plastics and textiles in simulated soil conditions was conducted on a laboratory scale. The method of determining the loss of mass” was developed on the basis of international standards PN ISO 11266:2020:11 [31]; PN-EN ISO 11721-1:2002 [32]; and PN-EN ISO 11721-2:2005 [33]. The biodegradation tests were carried out on a laboratory scale. Samples of nonwovens each 5 × 5 cm were tested in triplicate under the conditions of repeatability and reproducibility. The biodegradability was conducted in soil under the controlled conditions of temperature (30 ± 2 °C) and humidity (60–75%). Samples were placed in research reactors filled with the test soil and stored in a heat chamber which enabled the control and maintenance of the set environmental parameters (temperature and humidity). The incubation process was carried out at a constant temperature for a maximum period of 24 weeks. The progress of biodegradation was monitored every 4 weeks. According to the available standards, biodegradable material should achieve 90% of decomposition within a maximum period of 24 weeks.

2.2.3. Microbiological Tests—Ecotoxicity

The main aim of ecotoxicity tests was to investigate the influence of the nonwovens on the microbiological activity of the tested soil. The research was carried out in accordance with the accredited research procedure “Assessment of the influence of natural and synthetic materials on soil microflora”, developed on the basis on international standards (PN-EN ISO 7218:2008 [34], ISO 11133:2014 [35], PN-EN ISO 11133:2014-07/A1 [36], PN-EN ISO 4833-1:2013-12 [37], and EN ISO 19036:2020-04 [38]).

2.2.4. Phytotoxicity

The aim of phytotoxicity tests is to assess if biodegradable nonwovens do not introduce toxic components into the crop and do not have a negative effect on plants’ growth. The test was carried out on a base of OECD 208: Terrestrial Plant Test.

2.2.5. Air Permeability Test

The air permeability test was carried out using an Akustron apparatus (Karl Schröder KG, Weinheim, Germany) in accordance with the PN-EN ISO 9237:1998 standard [39].

2.2.6. Determination of the Carbon and Nitrogen Content in Soil

The content of elemental carbon and nitrogen was determined using the elemental analyzer Vario Macro Cube (Elementar Analysensystem GmbH, Langenselbold, Germany). The determination principle is based on the high-temperature combustion of a solid sample using a combustion tube temperature of 1150 °C and a reduction tube of 850 °C. The gaseous combustion products are purified, selectively separated in absorption columns, and sequentially detected in the measuring cell of the thermal conductivity detector (TCD). The operation of the equipment, control of the combustion process, and all calculations are performed using the software provided by the manufacturer.

2.2.7. Determination of Potassium and Nitrogen Content in Nonwoven

Potassium content was determined using the Atomic Emission Spectrometry (AES) method. The content of elemental nitrogen was determined using the elemental analyzer Vario Macro Cube (Elementar Analysensystem GmbH, Langenselbold, Germany).

2.2.8. Determination of Water Retention Value (WRV)

WRV was assessed on the basis of Standard PN-84/P-04654 [40]. Samples of approx. 1 g were placed in 100 mL of liquid for 20 h. Then samples were filtered, centrifuged, and dried at 105 °C.

$$\mathrm{W}\mathrm{R}\mathrm{V}={\displaystyle \frac{\mathrm{m}1-\mathrm{m}2}{\mathrm{m}2}}\times 100=[\%]$$

(1)

• m1—weight of sample after centrifuging;
• m2—weight of sample after drying.

2.2.9. Analyses of Soil Microbiota Frequency Changes

Samples of soil from the experiment were collected from the surface under the geotextile, and after the removal of plant tissue residues and rocks, transported to the laboratory for further analyses. Fragments of geotextiles were also collected. Microbial cell population density in soil was estimated with a modified Koch surface-plating method [41] of soil suspension in sterile water (1:10) after shaking on the rotary shaker for 4 h. To determine the total number of aerobic bacteria, appropriate suspension dilutions were placed onto enriched agar (2.5%, Biomaxima) and incubated for 72 h at 20 °C. Molds and yeasts were isolated using a Sabouraud-dextrose medium (6.5%, Biomaxima) with 1% bacteriological agar, and the incubation conditions were 96 h at 30 °C. The numbers of microorganism colonies grown on the medium surfaces were counted, then the number of colony forming units (CFUs) in 1 mL of soil suspension was calculated, and finally the microbial frequency was expressed as CFUs per 1 g of the soil dry matter (DM) [42]. The degree of microbial colonization of geotextiles, assessed independently for internal and external surfaces, was measured with microbiological imprints of square fragments of 5 × 5 cm cut out from a tested sample on plates containing the appropriate media; the colonization rate was estimated in a four-point scale (no colonization, low colonization, medium colonization, and intense colonization). Both the microbiological media and cultivation conditions were as described above.

Statistical analyses of microbial frequency changes were performed using Statistica 13.5 software (TIBCO Software Inc., Palo Alto, CA, USA). One-way analysis of variance (ANOVA) followed by Tukey’s post-hoc test was applied to determine the significance of differences between treatments. Differences were considered statistically significant at p < 0.05.

2.3. Experimental Design

2.3.1. Experiment Plan

The research was located on the ski slope in Jaworzyna Krynicka. The experiment was established in 2019 on a ski slope, on a slope with an inclination of 26% towards the south-east, at an altitude of 817 m above sea level. The experiment was organized as Latin Square Design (six plots each in 3 replications). Each plot had the area 18 m², the mixture of grass-legume was sowing, additionally on variants B-F mineral fertilization was applied. Composition of grass-legume mixture, 78 kg per ha, was as follows: Festuca rubra L. 30%, Poa pratensis L. 30%, Lolium perenne L. 20%, Trifolium repens L. 15%, and Festuca pratensis L. 5%. The mineral fertilizers were applied in all the years of the research (2019, 2020, and 2021) in the following doses: nitrogen in the form of ammonium nitrate, phosphorus in the form of superphosphate, and potassium in the form of potassium salt were applied in a dose of 40, 30, and 50 kg per ha of a pure N, P, and K, respectively.

The experimental site is located at 49°25′52″ N, 20°54′49″ E, in the Beskid Sadecki Mountains (southern Poland) (Figure 1), on a southeast-facing ski slope with a gradient of 26%. The experimental plots were set at an altitude of 817 m above sea level, on an area previously cleared of forest for ski slope construction, resulting in thin and erosion-prone soils. The proximity to natural watercourses in the valley below the slope further increases the risk of runoff and soil loss. The immediate environment consists of montane forest (beech, fir, and spruce) surrounding the open experimental area.

Four types of protective nonwoven fabrics were used to cover the soil after sowing seeds

• With a grammage of 100 g·m⁻², feather content of 18.7%, and needling speed—45 Hz;
• With a grammage of 200 g·m⁻², feather content of 41.1%, and needling speed—30 Hz;
• With a grammage of 300 g·m⁻², feather content of 19%, and needling speed—45 Hz;
• With a grammage of 17 g·m⁻², commercial nonwoven called Pegas Agro.
• Hence, the following six objects were included in the study:
• A: Meadow grass–legume mixture;
• B: Meadow grass–legume mixture + fertilization;
• C: Meadow grass–legume mixture + fertilization + nonwoven 100;
• D: Meadow grass–legume mixture + fertilization + nonwoven 200;
• E: Meadow grass–legume mixture + fertilization + nonwoven 300;
• F: Meadow grass–legume mixture + fertilization + commercial nonwoven Pegas Agro.
• Biodegradable nonwovens were left on the objects, while the commercial nonwoven was removed from the experimental surface on 23 September 2019.

In the evaluation of the biodegradation process and the physico-chemical and mechanical properties, the following three types of nonwoven materials were utilized:

• I—Nonwoven: wool + feathers; basis weight approx. 100 g·m⁻²;
• II—Nonwoven: wool + feathers; basis weight approx. 200 g·m⁻²;
• III—Nonwoven: wool + feathers; basis weight approx. 300 g·m⁻².

The figure below presents the process of composite nonwoven manufacturing (Figure 2).

Table 1. Properties of nonwoven *.

Parameter	Commercial Spring Nonwoven		Nonwoven I		Nonwoven II		Nonwoven III
Thickness [mm]	-		1.33		2.04		2.83
Basic weight [g/m2]	-		78.2		158		284
Tensile strength in the longitudinal direction [N]	-		1.11		3.91		21.2
Tensile strength in the vertical direction [N]	-		2.02		10.2		27.2
Tear resistance in the longitudinal direction [N]	-		1.80		5.18		31.2
Tear resistance in the vertical direction [N]	-		1.22		4.94		15.4
Feathers content [%]	-		38.5		34.8		44.4
Air permeability l/m2s	-		2960		1946		1176
	Field tests
	For	After	For	After	For	After	For	After
WRV [%]	7.050	13.030	42.840	69.330	45.090	66.370	47.270	57.640
Nitrogen content N [%]	0.061	0.301	16.690	8.460	16.190	13.020	16.380	13.600
Potassium content K [%]	-	0.018	0.129	0.402	0.124	0.146	0.136	0.198

* Needling speed—45 Hz.

presents selected properties of the materials.

Before the experiment was set up, there were no plants on the soil surface; it was bare rock with about 5–10 cm deep, an initial soil-weathering material. The soil before the experiment was set up was slightly acidic; the content of organic carbon and nitrogen were 1.69% and 0.14%, respectively. Soil had a loamy texture with 32%, 50%, and 18% of sand, silt, and clay, respectively. The cation exchange capacity (CEC) was 15.8 me·100 g⁻¹ and percent base saturation (BS) was 91.5%. The availability forms of magnesium (Mgav), potassium (Kav), and phosphorus (Pav) were 35.7%, 11.0%, and 0.3%, respectively (

Table 2. Basic soil properties before the experiment was set up.

Soil Property		Mean Value	SD
TN	%	0.14	0.03
SOC		1.69	0.44
pH H2O		6.8	0.3
pH KCl		6.0	0.3
Ca++	mg/100 g	12.1	1.2
K+		0.3	0.1
Mg++		2.1	0.1
Na+		1.3	0.3
HA		0.0	0.0
CEC		15.8	1.0
BS	%	91.5	2.4
Mgav	mg/100 g	35.7	2.6
Kav		11.0	4.2
Pav		0.3	0.1
RLD	cm/cm3	no plants and roots
Bacteria	CFU/ g d.m. × 10−3	980.9	780.9
Yeast		0.4	0.2

).

May 2019, June 2020, and July and May 2021. The initial growth and development of the planted plants were mainly influenced by meteorological factors, which generally were not favorable for the emerging plants sown at the beginning of the first decade of May 2019.

The first two decades were characterized by a relatively very small amount of rainfall, which totaled less than 60 mm. Only in the third decade of 2019, there was a rainfall of 100 mm, and the air temperature in June was relatively high with almost no rainfall.

2.3.2. Nonwoven Fabrics Biodegradation Results

The results of biodegradation of nonwoven materials are presented in

Table 3. Ecotoxicity of nonwovens.

Week	Number of Colonies [Colony Forming Unit. CFU/g]
	Reference Sample	Nonwoven I	Nonwoven II	Nonwoven III
1	1.3 × 106	2.3 × 106	Uncountable *	3.2 × 107
4	2.8 × 105	2.8 × 106	1.6 × 106	4.7 × 106
8	2.3 × 106	5.8 × 106	8.1 × 106	4.2 × 107
12	4.6 × 105	1.2 × 106	1.3 × 107	2.0 × 106
16	9.0 × 105	1.9 × 106	2.0 × 107	3.8 × 106
20	5.3 × 105	4.7 × 105	2.1 × 106	8.7 × 106
24	1.5 × 106	8.8 × 105	7.4 × 106	9.0 × 106

* (<15 or >300 [j.t.k/g]).

,

Table 4. Phytotoxicity of nonwovens.

Sprouted Seeds Index [%]
Parameter	Reference Sample	Nonwoven I	Nonwoven II	Nonwoven III
Mustard	70	-	-	-
Wheat	90	-	-	-
Cress	50	-	-	-
Mustard 25%	-	100	100	80
Mustard 50%	-	100	90	90
Wheat 25%	-	100	90	100
Wheat 50%	-	90	100	100
Cress 25%	-	60	50	70
Cress 50%	-	50	50	60

,

Table 5. Biodegradation results—Nonwoven I (mass loss values).

Sample Code	Repetition Number	Biodegradation Time—Week (day)
		1(7)	4(28)	8(56)	12(84)	16(112)	20(140)	24(168)
		Weight Loss %
Nonwoven I	1	15.3	39.7	75.6	83.4	92.7	93.9	92.3
	2	16.6	28.4	75.7	87.2	88.5	91.6	90.7
	3	14.8	49.4	68.8	85.5	91.4	92.7	92.3

Final average sample weight loss due to biodegradation: 91.8%.

,

Table 6. Biodegradation results—Nonwoven II (mass loss values).

Sample Code	Repetition Number	Biodegradation Time—Week (days)
		1(7)	4(28)	8(56)	12(84)	16(112)	20(140)	24(168)
		Weight Loss [%]
Nonwoven II	1	9.57	43.5	65.5	77.8	77.8	86.3	86.1
	2	9.38	44.9	62.9	72.6	83.4	82.2	84.9
	3	10.5	48.5	70.4	80.6	82.2	86.2	87.7

Final average sample weight loss due to biodegradation: 86.2%.

,

Table 7. Biodegradation results—Nonwoven III (mass loss values).

Sample Code	Repetition Number	Biodegradation Time—Week (days)
		1(7)	4(28)	8(56)	12(84)	16(112)	20(140)	24(168)
		Weight Loos [%]
Nonwoven III	1	11.2	53.9	79.0	91.5	86.4	91.0	92.8
	2	11.1	54.8	74.0	90.3	89.6	90.0	92.5
	3	10.4	46.5	65.1	87.2	92.1	90.0	90.4

Final average sample weight loss due to biodegradation: 91.9%.

and

Table 8. Determination of the carbon-to-nitrogen ratio—nonwovens.

Sample Code	C:N Ratio—Week (days)
	1(7)	4(28)	8(56)	12(84)	16(112)	20(140)	24(168)
Reference sample	14.4	14.8	14.4	14.8	14.5	14.2	14.3
Nonwoven I	14.8	14.9	14.0	14.3	14.5	13.5	14.0
Nonwoven II	20.8	19.3	17.4	20.1	18.9	18.3	18.7
Nonwoven III	14.3	14.6	12.2	12.7	12.8	12.8	12.8

and Figure 3, Figure 4, Figure 5 and Figure 6.

The measurement uncertainty components were as follows:

• Coefficient of variation of weight loss: 1.01%;
• Random error: ±2.29%;
• Weight loss confidence level: ±2.50%;
• Standard uncertainty of measurement (standard deviation): 0.92;
• Expanded measurement uncertainty: ± 4.30%;

• Additional information:

• Expanded uncertainty specified for a coverage factor k = 2 with a confidence level of 95%.

The measurement uncertainty components were as follows:

• Coefficient of variation of weight loss: 1.63%;
• Random error: ± 3.49%;
• Weight loss confidence level: ±4.04%;
• Standard uncertainty of measurement (standard deviation): 1.40;
• Expanded measurement uncertainty: ± 6.97%.

• Additional information:

• Expanded uncertainty specified for a coverage factor k = 2 with a confidence level of 95%.

The measurement uncertainty components were as follows:

• Coefficient of variation of weight loss: 1.42%;
• Random error: ±3.25%;
• Weight loss confidence level: ± 3.53%;
• Standard uncertainty of measurement (standard deviation): 1.31;
• Expanded measurement uncertainty: ± 6.49%.

• Additional information:
• Expanded uncertainty specified for a coverage factor k = 2 with a confidence level of 95%.

The tests carried out showed that the samples of nonwovens with the addition of feathers are characterized by different susceptibilities to the biodegradation process—microbiological decomposition. Nonwoven I and nonwoven III showed a high susceptibility to biodegradation after 24 weeks of the process (91.8% and 91.9% mass loss, respectively). The ecotoxicity tests did not show any negative impact of the tested samples on the microbiological activity.

After the biodegradation process, the research substrates were subjected to phytotoxicity tests, in accordance with the OECD 208 guidelines. The aim of this study was to determine the results of the toxic effects of chemicals introduced into the soil on seeds or the early development stages of various land plants. In accordance with the guidelines, three plant types were used in this study (one from each indicated category): mustard, wheat, and cress. The tests showed that in the case of soil substrates in which the samples of nonwoven I and nonwoven III were placed, the rate of sprouted plants was higher than for the reference sample.

The determination of elements (C and N) was intended to demonstrate the impact of the tested materials on the soil substrate. Based on the obtained results (ratio C to N), it can be concluded that the degradation of nonwoven II enriches the soil substrate, which may result in an increase in plant emergence. In the case of samples of nonwoven I and nonwoven III, no increase in the tested parameter was recorded in relation to the reference sample.

3. The Scope of Research Conducted

3.1. Investigated Soil Properties

Soil samples were collected from the research plot before the start of the experiment and after 4, 15, and 23 months. To get a soil sample from each block, 5 sub-samples from a 0–7 cm layer were collected. The soil was air-dried, sieved through 2 mm mesh size, and used for determining the following properties:

• The grain size distribution using the Cassagrande aerometric method, modified by Pruszyński;
• Total organic carbon (TOC) and total nitrogen (TN) content—using a LECO CNS analyzer;
• pH—measured potentiometrically in H₂O KCl (soil–solution ratios of 1:2.5);
• The content of available phosphorus (Pav) and potassium (Kav) using the Egner–Riehm method;
• The content of magnesium (Mgav) using the Schachtschabel method;
• The hydrolytic acidity (HA) was measured in 1 M CH₃COONa using the Kappen method, and the basic exchangeable cations (Ca²⁺, K⁺, Mg²⁺, and Na⁺) were measured in 1 M CH₃COONH₄ by ICP-OES (iCAP 6000 Series).

The cation exchange capacity (CEC) was calculated as the sum of hydrolytic acidity and base exchangeable cations. The base saturation (BS) was defined as the percentage of the sum of base cations in the CEC.

3.2. Assessment of the Number of Germinated Seeds and the Number of Plants Surpassing the Nonwovens

After 43 days from sowing the meadow grass–legume mixture, the number of germinated plants and the number of plants surpassing the nonwoven were counted on a surface area of 1 m². To do this, a frame with dimensions of 100 × 100 cm was randomly placed on the surface, and then the plants within the frame were counted. The height of the plants was measured in several places using a wooden ruler (meter stick).

4. Results and Discussion

4.1. Results

4.1.1. Soil Properties

The content of soil organic carbon (SOC) varied from 1.29% to 2.01% and the content of total nitrogen (TN) varied from 0.11% to 0.16%. For both soil parameters the lowest value was in variant C_15m, and the highest in B_23m and B_4m, and F_4m and F_23m for SOC and TN, respectively. During the experiment there was no significant difference in SOC and TN content taking into consideration both the sampling term and investigated variant. However, it is worth emphasizing that in the soils of variants D, E, and F, the values were similar to those in the soils before the experiment, and in the rest, A, B, and C, the content of SOC and TN was slightly lower.

The pH value changed during the experiment; the lowest value was 6.1 in B_4m and 5.2 in B_15m in H₂O and KCl, respectively, and the highest 7.0 in C_15m, D_15m, and C_23m and 6.5 in D_15m and C_23m in H2O and KCl, respectively. Taking into consideration variants it was noted that in control (A) and control with NPK (B), the pH was significantly lower compared to variants with all the investigated geotextiles (C, D, E, and F). The pH values increased with the duration of the experiment.

In case of Ca++, A_4 and B_4m showed the lowest amount (9.0). The content of calcium was the maximum in the middle of the experiment at 15 months. Therefore, the highest amount of calcium content (14.2 mg/100 g) has been found with variant D_15m. Significant differences were found in the case of variant Control A (without geotextile), which was significantly different than variant D. In terms of term, significant differences were found between the first 4 months and 15 months of the experiment. While taking into consideration both the variant and term, both control A and B (4 months) showed significant differences with variant D (15 months); all of the other variants showed similar results at the last month of the experiment. In the case of K+, the lowest value was found in F_15m (0.2 mg/100 g) and the highest (0.5 mg/100 g) was in B_23m. All the variants showed similar patterns, so no significant differences were found. In terms of duration, the difference was between 4 and 15 months. Considering both the variant and period, differences were found between variants B and F after 23 and 15 months, respectively, while no differences were found in the remaining cases.

The application of geotextile had no or very little influence on the content of exchangeable cations, like Na⁺ and Mg⁺. In terms of Mg⁺, the highest content was recorded with F_4m and the lowest was in B_15m and C_15m. While no differences were found in the case of sampling variant and variant–term, both cations showed varied results in the 4th month and 15th month of the experiment.

During the experiment, all of the six variants showed varied results in terms of hydrolytic acidity. A similar result was observed in the first two periods of the experiment, but these values were significantly different from the values obtained in the last part of the experiment (23 months). The HA value changed significantly during the experiment, starting from the lowest value 0.9 in D_4m to the highest of 4.0 in case of A_23m.

In terms of cation exchange capacity (CEC), significant differences were found in the case of both criteria. The results found in the 4th month, 15th month, and 23th month of the experiment were significantly different from each other. A slight deviation was found in terms of variants. The only difference was shown between variant B and D, while variant A, C, and F showed similar results. Where the highest CEC was 17.7 mg/100 g recorded with D_15 m, the lowest was 13.5 mg/100 g with B_4m. All the variants had higher levels of CEC by the end of the experiment compared to the first two intervals.

In terms of the base cation (BC) content, variations were found between the control (A and B) and the variants with geotextile (C, D, and E). Similarly, the first two intervals showed different results than the last interval considering terms. The lowest value of V uptake (76.7%) was recorded in A_23 m, while the highest (94.4%) value was found with D_4m.

During the experiment, the amount of available magnesium and potassium showed a similar pattern of results. In both cases, no significant difference was found between variants. However, a slight difference was noticed during the middle (15th) and end (23th) month of the experiment for both nutrients. Taking into consideration both the variant and term, the highest value was found with variant E_23m in Mgav and B_23m in Kav, while the lowest was noted in C_15m and F_15m in Mgav and Kav, respectively. The application of geotextile had a noticeable influence on both parameters in the case of available phosphorus (Pav) content in the soil. In terms of variants, control variant A showed different results than variant F, and the other four variants (B, C, D, and E) had shown similar outcomes. It has also been noticed that the content of Pav was highest by the end of the experiment. Similarly, variant F_23 m was found to have the highest level of Pav intake, while the lowest were observed in the variants A_4m, D_15m, and F_15m.

4.1.2. Number of Seedlings

The number of seedlings visible 43 days after sowing was highly variable among the different plots. The lowest number of emerged plants was found in plot A, and this difference was statistically significant. There were 39 grass seedlings and 15 clover seedlings per square meter. In plot B, the number of grass seedlings was 50% higher and clover seedlings were 61% higher. On plots with biodegradable nonwoven (C, D, and E), the number of emerged plants was on average 174% higher than in plot B and 266% higher compared to plot A. Among these plants, white clover seedlings accounted for an average of 28%. On plots C and D, the plants easily outgrew the nonwovens, with approximately 90% grass and 80% white clover on the surface compared to the amount underneath the nonwoven. On plot E (grammage 300), the grass and clover had outgrown the nonwoven in about 50% of all germinated plants. Under the commercial nonwoven (plot F), the number of emerged plants was slightly higher than in plot B, but the plants did not outgrow the nonwoven. The average height of plants on plots covered with biodegradable nonwoven was 90% higher compared to plants on the other plots.

It should be noted that the above results refer to the application of nonwovens in difficult areas that limit the possibilities of the adaptation and growth of plants. Specific local and climatic conditions of the experiment site may also have some effect.

4.1.3. Microbiological Characteristics of the Soil

The microorganism frequency analyses showed that for bacteria as well as for yeasts and microscopic fungi, significantly greater numbers were obtained upon testing the samples after 15 m of the experiment (for microbial population dynamics see Figure 7 and Figure 8). At the beginning and at the end of the experiments, the recorded values were significantly lower. For bacteria, the highest frequency (i.e., 3.55 × 10⁷ CFU/g d.m.) was observed in the sample C_15m, while the lowest one (i.e., 4.3 ×.10⁵ CFU/g d.m.) was determined in A_start. Analyses of microscopic fungi and yeasts proved that the highest frequency of 4.2 × 10⁴ CFU/g d.m. was found for the variant E_15m), and the lowest one (1.24 × 10² CFU/g d.m.) for the variant F_start). The microbial colonization of geotextile surfaces, both internal and external, was high during the whole experiment (data not presented). No growth inhibition effect was observed.

4.2. Discussion

The innovative aspect of this study lies in the use of chicken feather-derived fibers as the principal component for geotextile production. Unlike widely used natural geotextiles made from jute, wool, or coir, feather-based nonwovens possess a distinct biochemical profile (high keratin content) and originate from an underutilized waste stream. Our comparative data demonstrate that feather-based geotextiles are at least as effective as traditional materials in terms of promoting soil stability and plant emergence, while also offering advantages in resource circularity, cost, and local material availability.

Plastics are widely used in agriculture, although they have been identified as a risk to soils. The chemical behavior of agricultural plastics can benefit the agricultural economy by regulating the uptake and availability of nutrients present in the soil and reducing the need for fertilizer application as part of a circular economy approach [43]. Microplastics, for example, from geotextiles, appear to increase microbial colonization and overall microbial activity [44]. Most applications of plastics in agriculture are characterized by a short useful lifespan, and this feature leads to the generation of large amounts of waste that must be properly disposed of. This fact has influenced the search for possibilities to replace traditional polymer plastics, thereby reducing waste generation at the end of the life cycle [45].

On the basis of the conducted studies, it can be stated that the application of both bird feather nonwovens and commercial nonwovens causes an increase in the pH value and most often an increase in the base saturation of sorption complex compared to variants without nonwoven. Nonwoven geotextile cover, both commercial and from bird feather, keeps the soil moist. The thermal conditions are also more stable there. This can contribute to faster weathering of the parent material. As shown by the research before the experiment, the flysch material from which the soil is formed is slightly acidic with a relatively high base cation saturation (BS). This may affect the reaction of the tested soils and eliminate the acidifying effect of mineral fertilizers.

Soil covering has multiple benefits. It can reduce soil erosion and increase soil aggregation stability. This statement is supported by the work of [22], which described that geotextile produced from nonwoven wools provided immediate protection to the thick banks exposed to erosion. The geotextile protected the banks during the whole growing season. Even after the wool decomposed, nitrogen-rich organic compounds were released into the soil. Other benefits of soil covering include protection from the effect of raindrops, better aggregate stability, etc. Soil coverings produced from organic sources help to improve soil aggregation [46]. The conducted research confirmed that the applied geotextiles allow for maintaining a stable organic matter content. The content of organic carbon and total nitrogen remained constant during the experiment and the tested variants did not differ with respect to these two parameters. Bhattacharyya et al. [47] reported that palm mat geotextile had an effect on total nitrogen content and total soil nitrogen. A similar result has been reported by Pal et al. [11], where the level of organic carbon was highest under the plots covered with jute geotextile.

A key integrative outcome of this study is the explicit link between the material science aspects of geotextile production and their agricultural benefits in field application. The transformation of poultry feathers into short fibers (10–15 mm), followed by their combination with wool and bicomponent PESco/PE fibers using needle-punching and thermal consolidation, resulted in nonwovens with tailored physical properties, such as air permeability, water retention, and mechanical strength. These engineered characteristics had a direct impact on agricultural performance: the nonwovens effectively stabilized soil moisture and temperature, promoted significantly higher rates of seed germination and plant emergence—up to 266% more than controls—and increased average plant height by 90% compared to untreated plots. The high biodegradability of the material, with over 90% mass loss achieved within 24 weeks, ensured that decomposition products served as additional sources of nutrients, supporting soil fertility and microbial activity without leaving environmentally persistent residues. Thus, the material engineering decisions made during geotextile fabrication translated directly into practical agricultural and ecological benefits, demonstrating a holistic, circular approach to both waste management and sustainable land management.

The final content of nutrients like Mg and K was quite similar to their initial contents; therefore the application of both commercial and chicken feather-based geotextiles did not affect their amount in the soil. However, the amount of phosphorus gradually increased by the end of the experiment. The highest content of phosphorus was noted after the 23rd month of the experiment. This result is consistent with the observation made by Onuegbu [48]. Pal et al. [11] also reported that the application of natural fiber geotextiles (jute, coco coir, and banana leaf fiber) increased the amount of phosphorus in the soil.

Among the base cations, the content of Ca++ and K+ increased with time. The highest amount of K+ was recorded in the 23rd month of the experiment. Bhattacharyya et al. [26] also reported the increase in K content in the soil due to the mulching of soil. Where the increase in Na+ content was not noticeable, the amount of Mg++ was quite similar to the initial amount. Higher amounts of Na+ and Mg++ was reported by Onuegbu [41], who examined the effect of nonwoven coir and plantain geotextile on soil.

Many authors [49,50,51] noted that mineral fertilization promotes soil acidification. The reasons could be the transfer of nitrogen to the soil and the absorption of N as ammonium. Our results confirm this statement, which can be observed in variant B, where fertilization and a mixture of grasses without geotextile was applied, the pH in H₂O was 0.5 lower than before the experiment.

Soil fertility and condition is not only linked to physico-chemical parameters and plants, but also strongly connected with the naturally occurring microbiota as well as the relations between all these factors [52]. Microorganisms present in soil take part in the decomposition of organic matter, formation of humic substances, release of biogenic nutrients, and changing of the soil structure [53,54]. Our study proved that the use of geotextiles tended to affect soil microbiota significantly, predominately by increasing microorganism number, as compared to the samples collected from the soil not covered with the tested geotextiles. In addition, the growth of plants may have a strong impact on the number of microorganisms, as was proved also by He et al. [55] and Faissal et al. [56]. Many authors suggest that the fertilization with mineral fertilizers may have a negative impact on the natural soil microbiota [52,55,57]; however, in our study the initial condition of soil was poor and all the treatments were found beneficial to microorganisms.

The greatest threat to the initial development of plants in difficult, steep terrain is rapid runoff of rainfall, soil erosion, seed washout, and excessive exposure to sunlight. The use of especially biodegradable nonwovens in these areas provides significant support for seedlings against unfavorable habitat conditions [58]. Nonwovens with the grammage of 100 and 200, used in objects C and D, promoted seed germination and plant growth without restricting plants from growing through the nonwovens. Nonwoven with the grammage of 300 positively influenced the initial development of plants but later limited further growth of clover and grass branching. The commercial nonwoven (variant F) had the lowest grammage, adhered poorly to the soil, and was more airy than biodegradable nonwovens, which resulted in relatively worse conditions for plant development than in variants C, D, and E. The inability of commercial nonwoven to grow through plants was due to the method of its production method. This nonwoven is obtained as a result of mechanical transformations, e.g., needling, or thermal transformations, e.g., welding, which permanently bond the fibers together, preventing plant overgrowth.

5. Conclusions

The redesign of economic processes enables the utilization of burdensome waste from the agri-food industry for the production of new materials that support plant development and improve soil conditions. Biodegradable nonwovens made from sheep wool and bird feathers sourced from poultry slaughterhouses have a number of advantages: they promote the initial growth of plants, improve the physico-chemical properties of the soil, enrich the biological life of the soil, and are an alternative to synthetic nonwovens. An additional advantage of the nonwovens used is their biodegradability. In comparison to commonly used geotextiles such as jute, wool, or coir, the feather-based nonwovens developed in this study offer a combination of advantages: a slow but complete biodegradation matching agricultural cycles; support for soil microbial and nutrient dynamics; and the valorization of problematic agro-industrial waste. Their cost-effectiveness, scalability, and reliance on locally available feather waste distinguish them as a promising and sustainable alternative for erosion control and slope revegetation, especially in regions with pronounced poultry production. After the period of use, there is no need to collect them from the soil surface, and the products resulting from their decomposition constitute valuable nutrient components for plants.