The Use of Biodegradable Film in the Cultivation of Soybean with a Short Growing Season as an Example of Agro-Innovation in a Sustainable Agriculture System

Abstract

The aim of the study was to assess the yield of three soybean varieties of different earliness classes (Merlin, Coraline, and Viola) grown using two sowing dates (early vs. optimal) and different technologies (soil protected with biodegradable film vs. without soil protection–conventional cultivation). A three-year (2019–2021) field experiment was conducted at the Bayer Technical Advisory Center in Chechło, Poland (50°23′ N 18°44′ E). The three-factor experiment was set up in a randomized split-plot design in three replicates. The experimental factors were (i) sowing date, (ii) cultivar, and (ii) cultivation technology. The effect of agrotechnical factors and their interaction with the weather on selected biometric traits and seed yield was assessed. The results indicated that the weather conditions and its interaction with agrotechnical factors significantly influenced the biometric traits and seed yield of soybean. Optimal hydrothermal conditions significantly increased analyzed parameters and seed yield. However, too much rainfall in August had negative effects on biometric traits. It was proved that, early sowing adversely affected soybean yield. Sowing at the optimal date, i.e., the end of April, resulted in a yield of 3.8 t ha⁻¹. The use of biodegradable film in the year with more rainfall increased soybean yield by 1 t ha⁻¹ compared to the year with less rainfall. The early ‘Merlin’ cultivar grown in the system with biodegradable film produced significantly more pods and seeds per plant and a higher pod weight per plant. The cultivars with a longer growing season (‘Viola’ and ‘Coraline’) responded negatively to cultivation in the modern technology. The use of biodegradable film is recommended for cultivars with a short growing season, sown at the optimal time and in regions with moderate to high rainfall totals during the growing season.

1. Introduction

The increase in the economic importance of soybean in Europe is due to its multifaceted uses in the food, feed, and pharmaceutical industries [1]. From year to year, farmers are showing increased interest in the cultivation of soybean, which is a promising species for the European continent in the light of climate change [2,3]. Farmers see great opportunities in cultivating soybean as an alternative to other legume crops, due to its yield potential and lower water requirements compared to pea or field bean [4]. The main factors limiting soybean yield are the temperature and rainfall conditions at the time of sowing and initial growth. Suboptimal conditions during germination and/or emergence (i.e., insufficient or excessive water, low soil temperature, or weed infestation) adversely affect the health of plants, thereby reducing soybean yield [5]. In central Europe, warm winters and springs have recently been observed, which has prompted scientists to verify the accepted ‘optimal’ sowing date for soybean, i.e., from the last 10 days of April to the first 10 days of May [6]. Previous research [7,8] indicated that sowing late (after the first 10 days of May) or substantially early (mid-April) adversely affects soybean yield. Sowing soybean in April entails the risk of cold stress, which prolongs the emergence of plants, exposing them to infection by fungal diseases. The main reason farmers choose to sow soybean early is to obtain higher seed yields. To meet the expectations of farmers, innovative technological solutions are proposed to prolong the growing period. The use of biodegradable films is a proven solution in the cultivation of ground vegetables, improving temperature and moisture conditions for crop plants [9,10]. No scientific studies have been conducted showing that film can be useful in soybean cultivation. If the new technology of growing soybean under biodegradable film is to be implemented, it seems useful to test possible sowing dates (late vs. early) in order to optimize soybean cultivation in the new technology.

According to Kasirajan and Ngouajio [11], the use of biodegradable films has many advantages. The most important of these include weed control, reduction in soil evaporation, and protection against frost during germination. The main factor inhibiting the development of this technology in wide-row crops is the high cost associated with purchasing the film and having it installed on the field, as well as environmental aspects associated with microplastic residues in the soil.

Soybean is a thermophilic species which requires specific temperature and rainfall conditions for successful germination [3]. Due to the soil and climate conditions of central Europe, soybean is sown in the final 10 days of April/first 10 days of May, which results in lower yield than in the south of Europe. For this reason, cultivars with a longer growing period and higher productivity than early cultivars are recommended. Soybean is also very sensitive to weed infestation in the first period of growth (germination, emergence, and formation of the first trifoliate), which often determines the condition of the plant throughout the growing season [3,4]. To improve agricultural procedures for soybean, in the present study an innovative technology was proposed to improve conditions for the growth and development of soybean plants in field cultivation. No studies have been conducted to verify the suitability of biodegradable film technology in soybean cultivation to support seed germination and protection against weed infestation. In the perspective of climate change and the new EU strategy of reducing the use of plant protection products in agriculture, there is a need for the improvement of agricultural procedures for soybean, taking into account complementary agrotechnical factors, including sowing date, the use of biodegradable film, and the choice of cultivar.

The aim of the study was to assess the yield of three soybean cultivars of different earliness classes (early, late, and very late) using two sowing dates (early vs. optimal) and different technologies (soil protected by biodegradable film vs. no soil protection). An additional aim of the study was to verify the hypothesis that the use of biodegradable film in early sowing increases soybean yield.

2. Materials and Methods

2.1. Study Site and Experimental Design

A three-year (2019–2021) field experiment was conducted at the Bayer Technical Advisory Center in Chechło, Poland (50°23’ N 18°44’ E). The three-factor experiment was set up in a randomized split-plot design in three replicates. Factor I—sowing date (early sowing—1; optimal sowing—2), factor II—soil cover (biodegradable film—BF+; no biodegradable film—BF−), factor III—cultivar earliness class (early cultivar—‘Merlin’, late cultivar—‘Viola’, and very late cultivar—‘Coraline’). The experiment was set up on brown soil with medium humus content of 1.3%. The particle size distribution of the soil was as follows: soil particles of 2.0–0.05 mm—24.6%; 0.02–0.05 mm—44.3%; 0.02–0.002 mm—26.7%; up to 0.002 mm—4.3%. The content of available nutrients in the soil was as follows (mg/100 g of soil): P₂O₅—18.1, K₂O—16.8, N—69.6, and MgO—10.4. Taking into account the content of elements in the soil and the requirements of soybean, Polifoska 6 NPK(S) 6–20–30–(7) was applied in the amount of 250 kg ha⁻¹, and ammonium nitrate 32%N was applied as a starter fertilizer in the amount of 20 kg ha⁻¹.

Soybean was sown in the first third of April (10 April)—early sowing—and the last third of April (30 April)—the optimal sowing date for the region. The sowing date was the same for all years. Soybean was sown when the soil temperature reached +8 °C, using a Zurn D82 plot seeder. The area of the plots was 12 m². The density was 70 plants m⁻². For a germination rate of 95% and 1000-seed weight of 145 g, the sowing rate was 107 kg ha⁻¹. The sowing depth was established at 3 cm. The row space was 25 cm. The seeds were treated with Fix Fertig seed dressing, containing Bradyrhizobium japonicum rhizobia, which do not occur naturally in Polish soils.

Immediately after sowing, the soil was sprayed with the herbicide Sencor Liquid 600 SC (metribuzin 600 g/L) in the amount of 0.55 L ha⁻¹. Herbicidal protection was limited to one application of herbicide directly after sowing. SamcoTM biodegradable film was used to limit weed infestation. The biodegradable film completely covered the plots. The plots on which the biodegradable film was used were covered following spraying with the herbicide.

Plants were harvested on two dates: the second 10-day period in September (Merlin cultivar) and the last 10-day period in September (Coraline and Viola cultivars).

2.2. Biometric Analysis

For biometric measurements, 20 plants from each treatment were collected and examined in detail, including determination of shoot length, height of the first pod setting, dry weight of plants, average pod number per plant, average seed number per plant, average pod weight per plant, and average seed weight per plant. Following harvest with a combine, the moisture content of the grain yield and the 1000-seed weight (TSW) were determined.

2.3. Statistical Analysis

Statistical analysis of the results was performed using TIBCO® Statistica 13.3 software. The analysis of variance (ANOVA) at a probability of p < 0.01 was used and included an interaction of the factors with the years. Significant differences among means were defined using Tukey’s test. The letters above the error bars indicate the significance at p < 0.01 confidence level. Error bars represent the standard deviation (SD) values.

3. Results

3.1. Weather Conditions

Analysis of the weather conditions reveals that 2021 was the most divergent from the long-term average rainfall totals (

Table 1. Temperature and precipitation in 2019–2021.

Year	APR	MAY	JUN	JUL	AUG	SEP	Mean/Total
Mean temperature
2019	10.6	12.1	22.4	19.6	20.9	14.5	16.7
2020	9.44	11.4	17.7	18.9	20.3	14.9	15.4
2021	6.00	11.9	18.9	20.4	17.1	14.4	14.8
1991–2021 long-term average	9.6	14.4	17.8	19.7	19.5	14.9	15.9
Precipitation total (mm)
2019	38.2	94.0	10.6	23.0	5.00	1.80	172.6
2020	4.20	56.0	1.40	4.00	15.0	12.8	93.40
2021	27.6	92.0	79.0	83.2	185	29.4	496.8
1991–2021 long-term average	57	82	87	107	77	77	487

), which was confirmed by the Selyaninov index characterizing temperature and moisture (

Table 2. Characteristics of weather conditions during study periods based on Selyaninov K index.

Year	APR	MAY	JUN	JUL	AUG	SEP
2019	1.20 (md)	2.58 (vw)	0.16 (ed)	0.39 (vd)	0.08 (d)	0.04 (ed)
2020	0.15 (ed)	1.64 (mw)	0.03 (ed)	0.07 (vd)	0.25 (ed)	0.29 (ed)
2021	1.53 (o)	2.59 (vw)	1.39 (o)	1.36 (o)	3.61 (ew)	0.68 (vd)

). The 2021 growing season was distinguished by a very favorable rainfall distribution in June and July, which often determines the number of flowers and pods formed and the final yield. The year 2020, due to rainfall deficits in April and from June to September, was a dry year (93.4 mm rainfall during the growing season), and 2019 was an average year (172.6 mm).

Temperature and rainfall conditions during the study period were characterized in terms of rainfall deficits and the Selyaninov index (K) (Table 2). The Selyaninov index [12] was calculated according to the following equation: K = P/0.1 Σt, where P is the total monthly precipitation in mm, and Σt is the sum of monthly average air temperatures >0 °C.

Values for the K index were divided into 10 classes, making it possible to identify both extremely dry and extremely wet conditions. The classes were as follows: extremely dry (ed) K ≤ 0.4; very dry (vd) 0.4 < K ≤ 0.7; dry (d) 0.7 < K ≤ 1.0; moderately dry (md) 1.0 < K ≤ 1.3; optimal (o) 1.3 < K ≤ 1.6; moderately wet (mw) 1.6 < K ≤ 2.0; wet (w) 2.0 < K ≤ 2.5; very wet (vw) 2.5 < K ≤ 3.0; extremely wet (ew) K > 3.0.

The values of the K index showed that hydrothermal conditions were optimal in 2021. The year 2020, due to the rainfall deficits in April and from June to September, was characterized as dry. The year 2019, with very wet periods as well as very dry ones, was characterized as average (Table 2).

The weather was shown to have a strong effect on the morphological traits of the soybean plants. Drought (2020) significantly shortened the height of the first pod setting compared to the years with more rainfall. The pod number and mass per plant and the seed number and mass per plant were significantly higher in the dry year and significantly lower in 2019.

3.2. Biometric Traits

The sowing dates significantly influenced the biometric traits (

Table 3. Biometric traits of soybean according to sowing date, use of soil protection, cultivar, and year.

Treatment		Plant Length (cm)	Height of 1st Pod Setting	Number of Pods per Plant	Number of Seeds per Plant	Mass of Seeds (g)	Mass of Pods (g)	1000-Seed Weight	Seed Yield (t ha−1)
Year (Y)	2019	68.1c	13.9a	22.7b	49.5c	8.52b	9.39b	169.0a	3.08b
	2020	94.1b	6.77c	41.1a	82.7a	11.8a	18.9a	152.0b	3.14b
	2021	114.1a	11.3b	39.8a	75.8b	12.1a	17.5a	162.6a	3.63a
p < 0.05		<0.0001	<0.0001	<0.0001	<0.0001	<0.0001	<0.0001	<0.0001	<0.0001
Sowing date (S)	1 (early)	87.3b	11.7a	30.9b	59.9b	9.63b	14.4b	159.7	2.81b
	2 (optimal)	96.9a	9.66b	38.2a	78.7a	12.5a	16.2a	162.7	3.75a
p< 0.05		<0.0001	<0.0001	<0.0001	<0.0001	<0.0001	<0.0001	ns	<0.0001
Soil protection (P)	Film	91.9	11.6a	35.3	69.6	10.8	14.7	162.3	3.32
	No film	92.3	9.82b	33.7	68.9	11.3	15.9	160.2	3.24
p < 0.05		ns	<0.0001	ns	ns	ns	ns	ns	ns
Cultivar (C)	Merlin	88.3c	10.9ab	39.3a	78.6a	12.1a	17.6a	154.3b	3.14b
	Coraline	96.4a	11.5a	31.1b	62.4b	10.5b	13.8b	172.3a	3.46a
	Viola	91.6b	10.1b	33.1b	66.9b	10.5b	14.5b	157.2b	3.24ab
p < 0.05		<0.0001	<0.0001	<0.0001	<0.0001	<0.0001	<0.0001	<0.0001	<0.01
S × P		<0.0001	ns	ns	ns	ns	<0.02	ns	ns
S × C		ns	<0.0001	<0.0001	<0.0001	<0.0001	<0.0001	ns	ns
P × C		<0.0001	<0.0001	<0.0001	<0.0001	<0.0001	<0.0001	<0.01	ns
S × Y		<0.0001	<0.0001	<0.0001	<0.0001	<0.0001	<0.0001	<0.0001	<0.0001
P × Y		<0.0001	<0.0001	<0.0001	<0.0001	<0.0001	<0.001	<0.0001	<0.0001
C × Y		<0.0001	<0.0001	<0.0001	<0.0001	<0.0001	<0.008	<0.0001	<0.0001
S × P × C		<0.0001	<0.0001	<0.0001	<0.0001	ns	ns	ns	ns
S × P × Y		ns	<0.0001	<0.0001	<0.0001	<0.0001	ns	ns	<0.0001
S × C × Y		ns	<0.0001	ns	ns	ns	ns	<0.0001	ns
P × C × Y		<0.0001	ns	<0.0001	<0.0001	<0.0001	<0.0001	<0.0001	ns
S × P × Y		<0.0001	<0.0001	<0.0001	<0.0001	<0.0001	<0.0001	<0.0001	ns

Letter indicators at averages determine the so-called homogeneous groups (statistically homogeneous). The occurrence of the same letter pointer at averages (at least one) means that there is no (no) statistically significant difference between them.

). The optimal sowing date (last 10 days of April) was more favorable for the development of the plants. Early sowing (3 weeks early) negatively influenced the biology of the yield. These plants had significantly fewer pods and seeds and a lower seed mass, as well as a higher first pod setting than plants sown at the optimal time.

The use of biodegradable film had a significant positive influence only on the height of the first pod setting. Soybean plants in the treatments with biodegradable film formed their first pod significantly higher than in the control. In addition, the use of this protection caused a non-significant increase in the number of pods and seeds per pod and in the 1000-seed weight (Table 3).

The choice of cultivar revealed significant differences in morphological traits. The early Merlin cultivar had a significantly higher seed number and seed mass per plant than the cultivars with a longer growing period.

The number of pods, number of seeds, and pod mass were influenced by the interaction of the cultivar and sowing date and by the interaction of the cultivar and soil protection (Figure 1). Significantly more pods and seeds and a higher pod weight were observed for the Coraline cultivar sown at sowing date one (Figure 1a–c). The Merlin cultivar had significantly more pods and seeds and a higher pod weight in the system with biodegradable film (Figure 1d–f).

A statistically significant interaction of the factors with the years of the study was confirmed (Table 1, Figure 2 and Figure 3). The year 2019 was the least favorable for the development of the morphological traits of the soybean plants, whose values were significantly lower than in the other years. The years 2020 and 2021 were more favorable for the development of pods and seeds in the Merlin cultivar grown in the technology with biodegradable film compared to the control (Figure 2a–d,e–h and Figure 3a). Sowing soybean at sowing date two (optimal) was more favorable (higher rainfall during the cycle of cultivars) for soybean in terms of the number and weight of pods and seeds in 2021 than in 2019 and 2020 (Figure 2i,j).

The interaction of the year, cultivar, and technology (biodegradable film) significantly affected the pod number per plant (Figure 3a). The early Merlin cultivar, with the shortest growing period, responded best to cultivation in the new technology, resulting in a significant increase in the number of pods in 2020 and 2021. In the same years, the Coraline cultivar produced significantly more pods in the traditional technology. The late Viola cultivar was the least susceptible to the change in cultivation conditions; irrespective of the means of soil protection, the Viola cultivar produced a similar number of pods. The number of pods was slightly determined by the weather conditions during the vegetation period, which was most favorable in 2020 (Figure 3a). The Viola proved to have low stability in pod setting, which can be related with individual response to environment patterns.

The use of biodegradable film at different sowing dates and for cultivars of different earliness classes significantly affected the number of pods (Figure 3). The Merlin and Viola cultivars sown at sowing date two and following the use of biodegradable film produced significantly more pods than in the traditional technology, i.e., without film. The very late Coraline cultivar, on the other hand, produced more pods at sowing date two, but in the traditional technology, in which the soil was not covered with biodegradable film (Figure 3b).

3.3. Seed Yield and 1000-Seed Weight

Soybean yield was significantly influenced by the experimental factors, the weather, and their interaction. In the relatively dry years (2019 and 2020), the seed yield was significantly lower than in the year with more rainfall during the growing season. The difference in the average soybean yield was 0.5 t ha⁻¹.

The sowing date had a very strong influence on the soybean yield, as the difference was 0.94 t in favor of the optimal sowing date, i.e., at the end of April.

The use of biodegradable film was not shown to statistically significantly increase the yield of the soybean cultivars. However, there was a trend indicating a non-significant increase in yield, on average by 0.10 t ha⁻¹. The very late Coraline cultivar produced higher yield (3.46 t ha⁻¹) than the Merlin cultivar (3.14 t ha⁻¹).

The interaction of the factors with the weather significantly influenced the soybean yield (Figure 4). The very late Coraline cultivar produced significantly higher yield in the year with higher rainfall totals than in the dry years. In 2020, the dry year, the early Merlin cultivar produced slightly higher yield (3.2 t ha⁻¹) than the Coraline cultivar (3.1 t ha⁻¹), with significantly lower yield in the same year (Figure 4a). Soil protection had a significant effect on soybean yield.

The sowing date significantly influenced soybean yield in the years of the study (Figure 4). Significantly higher yields (years 2019 and 2021) were obtained for sowing date two. The higher precipitation totals in 2019 and 2021 resulted in a significant increase in soybean yield compared to 2019 (Figure 4c). The use of biodegradable film at sowing date two was most favorable to soybean yield, but only in the years with higher rainfall totals (Figure 4d).

The sowing date and soil protection influenced the 1000-seed weight (TSW) of soybean in the interaction with years (Figure 5). A significantly higher 1000-seed weight was noted for all of the cultivars (Merlin, Viola, and Coraline) in the relatively wet year (2019), compared to the dry year (2020), in the traditional technology. In 2021, with higher precipitation, a significantly higher 1000-seed weight was noted for the Merlin and Viola cultivars in the technology with biodegradable film (Figure 5a).

The 1000-seed weight was significantly influenced by the sowing date interacting with the year and choice of cultivar (Figure 5b). The Merlin and Coraline cultivars produced a significantly higher seed weight at sowing date two in 2019. The Viola cultivar at sowing date one produced a significantly higher 1000-seed weight in 2021 than the other cultivars. The 1000-seed weight was significantly influenced by soil protection and cultivar (Figure 5c). The Coraline cultivars produced a significantly higher seed weight in the technology with biodegradable film compared to other cultivars.

4. Discussion

The choice of earliness class of cultivars, sowing date, and soil protection methods remain important agrotechnical factors for the yield potential of soybean. The results of the study clearly indicate that the biology of soybean yield is determined not only by the weather in different years and the level of agricultural techniques—high-input vs. low-input [13]—but also by the technology applied [6,14].

Our study showed that soybean produced yields of 3.08–3.75 t ha⁻¹ and that the yield depended on the sowing date, the earliness class of the cultivars, technology, and weather. The sowing date significantly influenced soybean yield. Sowing at the optimal time resulted in significantly higher yield, on average by 0.94 t ha⁻¹, compared to sowing 3 weeks earlier. The use of modern technology—covering the soil with biodegradable film—in combination with the early sowing date had no positive effect in the form of increased soybean yield.

The use of biodegradable film had a positive effect on the biometric traits and yield of the early Merlin cultivar. The Merlin cultivar sown at the optimal date and with biodegradable film produced significantly more pods than in the traditional technology, i.e., without film. We suppose that soybean cultivars with a shorter growing season are more susceptible to abiotic stresses. Tested technology may have reduced the exposure of the plants to the stresses associated with the growing season under certain hydrothermal conditions. Due to the innovative nature of the study, the results cannot be compared with the literature data. Previous research has been conducted to determine the effect of the use of biodegradable film on soil biology, germination, and initial soybean development.

Li et al. [15] showed that the accumulation of plastic waste (with or without biodegradable plastic) in the soil can positively or negatively influence the growth rate of plants, especially at the early stage of development. The authors indicate factors (e.g., the soil type, plant species, climatic conditions, and agricultural management practices) which determine the direction of changes in the rate of growth and development in field cultivation of plants with the addition of film. Li et al. [15] mainly showed a negative effect of biodegradable film, with the addition of non-degradable film (1%), on the vitality of soybean seedlings and the biomass obtained during flowering. The authors confirmed that the accumulation of plastic debris in soil could affect plant growth. However, further large-scale field studies are needed because the environment is too complex and so many different factors (e.g., soil type, plant species, climate conditions, and agricultural management practices) affect plant growth under field conditions. Lwanga et al. [16] indicate various reasons for the negative effect of biodegradable film on plant biology which are due to the functioning of the biology of soil contaminated with residues of microplastic indirectly affecting the fauna, flora, and physical properties of the soil and the circulation of elements. Qi et al. [17] showed that the biomass of shoots and roots was inhibited in wheat crops treated with biodegradable macroplastic in the first two months of growth but observed no difference when the plants were harvested after four months. In the treatments with macroplastic mulch containing polyethylene (PE), no significant difference was noted in the biomass of shoots, whereas the root biomass decreased significantly after both two and four months. Li et al. [15] reported that the biomass of soybean shoots decreased slightly at the flowering stage (about two months after sowing) but differed significantly at harvest, mainly in the treatments with a high content of macroplastics. In the present study, the biodegradable film without plastic had varied effects on the condition of the plants. The main factor determining plant development was the weather conditions during the growing season, while the presence of biodegradable film had a smaller effect.

5. Conclusions

The interaction of sowing date and biodegradable film was not shown to significantly affect soybean yield. Weather and the interaction of weather with the experimental factors were shown to have a strong effect on the biometric traits and seed yield. Early sowing in the growing season with excessive rainfall negatively affected soybean yield. In the case of the optimal sowing date—the end of April—and rainfall totals of 172–496 mm, soybean produced yield of 3.8 t ha⁻¹. The use of biodegradable film in the year with more rainfall increased soybean yield by 1 t ha⁻¹ compared to the drier year. In the year with more rainfall, the average air temperature in the months of April and May was on average three degrees Celsius lower than in other years during this period. Therefore, the use of biodegradable film protected plants from the cold during the germination and seedling stage, resulting in a positive response in plant growth. Future large-scale field studies are needed.

The early Merlin cultivar grown in the system with biodegradable film produced a significantly higher number of pods and seeds per plant and higher pod mass per plant. The cultivars with a longer growing season, ‘Viola’ and ‘Coraline’, responded negatively to cultivation in the modern technology. The use of biodegradable film can be recommended in areas with moderate to high rainfall for cultivars with a short growing period sown in the last 10 days of April, because these conditions determine the biodegradability of the film.