The Influence of an Innovative Bioproduct on Soil and Substrate Characteristics during Strawberry Cultivation

Abstract

Farming systems should be sustainable in order to protect the soil from diseases and pests while preserving the environment and generating economic and social benefits. The use of biological products can help reduce the negative characteristics that damage the soil and increase the likelihood of healthy plant growth. Therefore, the aim of this study was to investigate the influence of biotreatment on the physical properties of different soils and substrates as well as strawberry (Fragaria × ananassa) yield. In the laboratory trials, “Asia” strawberries were grown one by one in special containers on different soils and substrates: loam (L), clay (C), sandy loam (SL), compost soil (CS), and coconut fiber (CF). The soils and substrates were treated once a week with a biological product based on molasses and magnesium sulfate and fertilized with a complex fertilizer: NPK11-11-21 + K₂O + Mg, S, B, Cu, Fe, Mn, Mo, and Zn, enriched with potassium. Soil and substrate temperature, moisture, density, total porosity, aeration porosity, electrical conductivity as well as strawberry yield were measured in the test containers containing the plants. Studies have shown that the use of bioproducts does not significantly improve the physical properties of soils and substrates. However, the trend of the results shows that using the bioproduct for a longer period of time would have a greater effect on the physical properties of the soils and substrates, especially for peat-based substrates prepared for greenhouse use. Berry yields increased significantly (46.6% and 100%) with biotreatment in the CS and CF variants.

1. Introduction

Soil is the ecological life support system. Preserving and maintaining a thin layer of humus is the first and foremost priority in the ecosystem chain. The intensive use of mineral fertilizers and the inappropriate application of fertilization techniques in agriculture have negative effects on both the environment and human health [1,2]. There is a risk that the soil will be depleted and the physical and chemical properties of the soil will deteriorate, ultimately resulting in heavy yield losses [3]. The use of insecticides contributes to soil degradation. Beneficial bacteria present in the soil, which are needed to maintain a stable microflora in the soil, are killed [4]. In agriculture, in order to achieve economic and social benefits and preserve the environment, farming systems should be sustainable [2,5]. Consumers increasingly value agricultural products with high nutritional and functional value and ecologically sustainable production and are therefore turning to biological products (natural-origin biological preparations) [6,7,8]. The focus is on the positive effects of biological products on soil and plants, although they have a variety of other effects [9]. The species of plant mainly determines the appropriate composition of the biopreparations to be used [10].

Using biological products can help reduce the negative characteristics that damage the soil, increase the likelihood of healthy growth throughout the growing season, and ensure a high-quality harvest without damaging the environment [4,11]. Biotreatment is able to ensure the productivity of the soil, not only during the growing season but also when the soil is resting and not in use. The natural microorganisms present in the bio-preparations can help improve soil fertility and maintain the soil in good condition. Microorganisms can mobilize elements that are important for plant nutrition and increase the availability of nutrients in the soil to plants through nitrogen fixation, humification, mineralization, phosphorus release, and other processes. To do this, it is important to create a suitable environment for microorganisms and to support them in their life cycle [12,13,14,15].

Recently, the choice of biological products has become more wide-ranging. The main purpose of a biological product is to stimulate natural biological processes. The activity of good bacteria determines the physical and chemical properties of the soil, leading to a reduction in soil density, an increase in the overall porosity of the soil [16], an improvement in the formation of root hairs, and a greater susceptibility of plants to better nutrient uptake [17]. Other plant growth processes are also activated by active rootless development. Spraying plants with solutions of biological preparations leads to more intensive plant growth and development, much faster photosynthetic processes, and faster transfer of assimilates from the leaves to the roots, resulting in increased plant productivity and higher plant yields [18,19,20]. Other researchers claim that bioproducts increase the amount of organic carbon in the soil, which has a positive effect on soil productivity. It is likely that the increase in soil organic carbon has a role in reducing soil density and increasing overall porosity [21,22]. According to [23], soil density is also influenced by soil water content. The application of bioproducts has been shown to reduce soil hardness by up to 28% and increase total porosity by up to 25% in the second year of the study [24]. An increase in total soil porosity of up to 74% was observed as a result of the interaction between the long-term application of biological products and meteorological conditions [25].

Studies have shown that the use of molasses and its mixtures with organic and mineral fertilizers improves soil fertility and increases the yield of spinach, sugar beet, corn, lettuce, and other plants [26,27,28,29,30]. Molasses mixtures increase the amount of carbon, nitrogen, and potassium in the soil and its availability to plants, thus improving the conditions of plant germination and growth and the quality indicators of the harvested crop [27,30,31]. The use of molasses and its mixtures for sandy soil is especially useful as it improves soil productivity and increases the activity of enzymes in the soil, the aggregation of soil particles, and the availability of nutrients. However, the long-term use of these mixtures in clayey soils can compact the soil [32,33].

The use of molasses and its mixtures with other fertilizers has many positive properties for soil and plants, but experimental studies and evidence are still lacking, and the mechanisms underlying the positive effects on soil fertility and health remain unclear [34]. Therefore, it is very important to continue research on growing plants in open ground, greenhouses, and pots and educate plant growers [32]. The use of molasses as a production waste for plant fertilization is important for optimizing agriculture and reducing agricultural environmental pollution [31,35].

The positive effects of bioproducts on the soil environment, yield, and quality, as well as their potential for use in agriculture as a substitute for conventional pesticides or fertilizers, have encouraged researchers to further their knowledge in this field. Therefore, the aim of this study was to investigate the influence of biotreatment on the physical properties of different soils and substrates as well as strawberry yield.

2. Materials and Methods

2.1. Experiment Design

The laboratory research was carried out in April–September 2019 in the specialized greenhouse of the VMU Academy of Agriculture, which is equipped to maintain natural climatic conditions (greenhouse air temperature: 22 °C, relative air humidity: 70%). In this study, laboratory experiments in a greenhouse with “Asia” strawberries (Fragaria × ananassa) were carried out by growing them in special containers with different soils and substrates (Figure 1): loam (L), clay (C), sandy loam (SL), compost soil (CS), and coconut fiber (CF). The compost soil was a mixture composed of peat and cattle manure (ratio 4:1). After crushing and sieving, 1 kg m⁻³ of the mineral fertilizer NPK12-10-16 was added to the compost soil. The soil was supplemented with 20–50 mg L⁻¹ magnesium (MgO). The pH of the compost soil was 5.5–7.0. Coconut fiber is a natural primer made of coconut fiber. The salts in the coconut shell were removed, and the pH of the coconut fiber was 6. According to the recommendations of strawberry growers [36], the most suitable soil for the strawberry variety “Asia” is loam. Therefore, loam (L) was chosen as a control variant among different soils. When choosing different soil substrates for growing strawberries, it was taken into account that slightly acidic (pH 5.5–6.8) soils are best for strawberries, which we used in this study. One strawberry seedling was grown in each of the different containers (40 pieces). Strawberry seedlings were planted in the SE1 (super elite) category (seedlings grown in a greenhouse from a mother seedling (candidate) in the first year). The containers had a capacity of 10 L. Research was carried out in 40 containers: 5 different samples (soils and substrates) in 4 replicates without biotreatment and 20 samples with biotreatment.

The soils and substrates were treated with a biological product: an organic fertilizer based on molasses and magnesium sulfate (BIO1). The composition also included calcium carbonate, sodium hydrogen carbonate, and dolomite. It is believed that the use of BIO1 can reduce the need for mineral fertilizers and improve the physical properties of soils and substrates. Soils not affected by the biological product BIO1 were identified as controls. Also, this BIO1 activates and aerates the soil, promotes the surface composting process, and restores the soil structure. Impaction was carried out once a week during the strawberry growing season from May to July at a ratio of 1.0 g of bioproduct per 1.0 L of water. The bioproduct rate was selected based on producers’ recommendations. Complex fertilizers supplemented with micronutrients were used to encourage the flowering of the berry bush and the setting of berries. The plants were fertilized once a week during the growing season from May to July with a complex fertilizer: NPK11-11-21 + K₂O (21.2) + Mg (2.6 mg L⁻¹), S (25), B (0.05), Cu (0.03), Fe (0.08), Mn (0.25), Mo (0.002), and Zn (0.04), enriched with potassium. Fertilizer rates were selected based on the recommendations of producers and growers. When the plants were fully established, laboratory measurements were started. The temperature, moisture content, density, total porosity, aeration porosity, and electrical conductivity of the soils and substrates were measured in the test containers containing the plants. Soil density, total porosity, and aeration porosity were measured after the end of the growing season.

2.2. Measurement of Soil and Substrate Temperature, Moisture, and Electrical Conductivity

Substrate temperature, moisture content, and electrical conductivity were measured at depths of up to 10 cm using a portable “HH2 Moisture Meter”. Soil moisture, temperature, and electrical conductivity were measured once a week in June, when the plants were most intensively producing aboveground mass, and in July, after the strawberry flowering when the berries started to grow intensively. In the absence of any morphological changes in the plant, the measurements were reduced to every 10 to 15 days until the end of the vegetation.

2.3. Measurement of Soil and Substrate Density, Total Porosity, and Aeration Porosity

The air permeability of the soil is an important physical property that determines the growth and development of plant roots. Total and aeration porosities determine soil water and air regulation. Samples were taken at a depth of 10 cm with a Nekrasov drill to determine the density and porosity of the soils and substrates. The density and porosity of the soils and substrates were calculated after the samples had been dried to an air-dry mass. The density of the soils and substrates was determined using the weight method by calculating the mass and volume ratio. The total and aeration porosities were determined using a vacuum air pycnometer. The total porosity $P_T$ was calculated according to the following formula [37]:

$$P_T=\left(1-\frac{{\rho }_s}{{\rho }_{s.p.}}\right)·100\%$$

(1)

where ${\rho }_s$ is the density of the soils and substrates in g cm⁻³, and ${\rho }_{s.p.}$ is the solid phase density of the soils and substrates in g cm⁻³.

The aeration porosity $P_A$ was calculated according to the following formula [37]:

$$P_A=P_T-(\omega ·{\rho }_s)$$

(2)

where $\omega$ is the soil and substrate moisture in %.

2.4. Determining the Yield of Strawberry

Ripe strawberry berries were collected from each bush and weighed (g). After that, the strawberry yield per square meter was calculated, and the data were converted into tons per hectare.

2.5. Statistical Analysis

To evaluate the reliability of the results, the data were assessed using the dispersion and correlation analysis methods [38]. The arithmetic means, their standard deviations, and confidence intervals were established with a probability level of p < 0.05 and p < 0.01. Significant differences between the investigated data options were established by calculating the least significant difference between LSD_0.05 and LSD_0.01.

3. Results and Discussion

3.1. Effect of Biotreatment on Soil and Substrate Temperature, Moisture, and Electrical Conductivity

At the start of the laboratory tests, the temperature of the soils and substrates without biotreatment varied from 23.45 to 24.03 °C; over the whole period of the study, the temperature varied from 21.7 to 27.8 °C (Figure 2a). Meanwhile, at the start of the laboratory tests, the temperature of the soils and substrates with biotreatment varied from 23.3 to 23.73 °C; over the whole period of the study, the temperature varied from 22.2 to 28.1 °C (Figure 2b). Evaluating the different soils and substrates over the whole study period, the highest temperature increase (on average, about 1.06 °C) was observed in variant L with biotreatment compared to without biotreatment. In variants C, SL, CS, and CF, the temperature increase with biotreatment was lower (0.74, 0.82, 0.46, and 0.61 °C, respectively) compared to without biotreatment. In June, the ambient temperature increased, which resulted in an increase in the soil and substrate samples. The main source of soil temperature is solar radiation [39]. The lowest temperature in June was found in the CS and CF variants, both with biotreatment and without biotreatment. In July, the temperature of the soils and substrates for both treatment variants decreased compared to June and varied between 21.7 and 24.38 °C without biotreatment and between 21.88 and 24.78 °C with biotreatment. The highest difference (1.1 °C) in temperature was in the loamy soil. In August, the temperature of the soils and substrates varied between 22.68 and 25.03 °C without biotreatment and between 23.45 and 25.4 °C with biotreatment. Studies by other researchers have shown that bioproducts do not affect soil temperature at the beginning of experiments, but soil temperature starts to increase after a longer period [40]. This was also observed in our experiment. In conclusion, although a slightly higher sample temperature was observed in the variants with biotreatment than in the variants without biotreatment, this effect of biotreatment on the sample temperature was not significant. Furthermore, no significant differences were observed between the different samples in both treatment cases. It is likely that due to the short-term use of bioproducts, a slight increase in temperature was observed, but no significant differences between the variants were observed. Previous studies have shown significant increases in soil temperature due to the long-term use of bioproducts [25].

Soil moisture was measured during the growing season (Figure 3) and was related to soil susceptibility. Irrigation was applied as needed with a uniform volume of water (1 L per variant (plant)). Evaluating the entire research period and all soil media, variant C showed the highest (on average, about 16%) increase in moisture with biotreatment compared to without biotreatment. In the CF variant, the moisture was higher with biotreatment until 27 June. In other cases (L, SL, and CS) the moisture was higher without biotreatment than with biotreatment. Soil additives can have a positive effect on water infiltration and retention [41], but in our research, this was not the case in all soils and substrates. Using a biofertilizer consisting of bacteria and fungi in a greenhouse experiment, a team of researchers obtained significantly higher water yields but without significant differences [42]. Without biotreatment, a significant increase in moisture content (from 34 to 78%) was found in CS compared to the control L. With biotreatment, a similar trend was found, with the moisture content in CS increasing from 34 to 50% (p > 0.05). According to [43], the soil temperature influences soil moisture. Comparing the control (L) with other variants (C, SL, and CF) without biotreatment and with biotreatment, the moisture content was not significantly higher or significantly lower throughout the research period.

Another soil property is electrical conductivity, which allows variations in the physical properties of soil to be detected and their influence on crop yields to be revealed [44,45]. The results of the electrical conductivity studies on soils and substrates are shown in Figure 4.

The results showed that in the CF variant, for almost the entire research period, except for 9 July, the electrical conductivity was found to be, on average, about 20.53 mS m⁻¹ lower with biotreatment compared to without biotreatment. Also, in variant C, the electrical conductivity was lower (on average, about 9.7 mS m⁻¹), except for 6 June, 21 June, and 9 August. This finding is supported by studies carried out by a team of researchers who found lower electrical conductivity in soils with higher sand content [46]. During the entire period of the experimental study, an increase in electrical conductivity of about 62.33 mS m⁻¹ was determined in the L variant when the bioproduct was used compared to the variant where the bioproduct was not used. These results are likely due to the higher soil density and soil temperature in the L variant when the bioproduct was used. This is in line with the results of scientists who have shown that the addition of bioproducts with molasses can increase electrical conductivity [47]. Comparing the electrical conductivity results of the SL variant with biotreatment and without biotreatment, the electrical conductivity decreased after using the bioproduct on 29 May, 21 June, and 24 July and increased in the other periods. In the CS variant, electrical conductivity decreased on 6 June, 13 June, 24 July, 6 July, and 9 August and increased in the other periods.

3.2. Effect of Biotreatment on Soil and Substrate Density, Total Porosity, and Aeration Porosity

After harvest, density tests on strawberry substrates showed that biotreatment did not have a significant effect on soil density (Figure 5). However, in variant C, the biological preparation had the greatest influence on the change in soil density compared to L, SL, CS, and CF. In variant C with biotreatment, the density was 0.08 g cm⁻³ lower compared to without biotreatment (SL—0.02 g cm⁻³, CS and CF—0.01 g cm⁻³). The density in the clay loam with biotreatment was found to be non-significantly higher (1.35 g cm⁻³) compared to the variant without biotreatment (1.33 g cm⁻³). However, in both cases, the density was within the recommended limits (1.2–1.4 g cm⁻³). Comparing different soil media with the control, the density of L was significantly lower in all the studied variants with biotreatment but only in the CF and CS variants without biotreatment. According to [16], when the same biological preparation was applied for two years, the density of the loam soil decreased significantly in the second year of the study. This is influenced by the activation of microbiologic processes. Other authors have suggested that the use of biochar can increase the density of the compost, making it easier to transport [48].

Studies of the total porosity of the soils and substrates showed that in all variants, the total porosity increased with biotreatment, except for the L variant, compared to without biotreatment (Figure 6). In the L variant, biotreatment reduced the total porosity by about 1% in the C and SL variants, and a slight increase (0.75% and 0.77%, respectively) in the total porosity was determined. A slightly higher increase in total porosity was found in the CS and CF variants (2.25% and 3.0%, respectively). The authors of [16,24] found that using the same biological preparations for two years, the total porosity of loamy soil increased significantly in the second year. In addition, in our experiment, total porosity in samples without biotreatment was significantly higher at the 99% probability level in the CS and CF substrates compared to the control L. With biotreatment, total porosity was significantly higher in variant C at the 95% probability level compared to the control L, while it was significantly higher at the 99% probability level in the CF and CS substrates.

The aeration porosity of the substrates where strawberries were grown varied from 31.54% to 86.01% without biotreatment and from 31.76% to 89.64% with biotreatment (Figure 7). Aeration porosity at p > 0.01 was found to be higher in CS and CF substrates compared to the control variant (L) both after using BIO1 and without it. The increase in aeration porosity was more influenced by the biological preparation in the CF variant than in the C, SL, and CS variants. In the CF variant with biotreatment, the aeration porosity was found to be 3.63% higher compared to without biotreatment (C—0.02%, SL—2.39%, CS—3.03%) and 1.38% lower in the L variant. Increased aeration porosity is likely influenced by the activation of microbiological processes and increased soil temperature. However, microbiological processes have not been investigated. Other researchers [45] have also noted increased soil porosity after the application of biological preparations. Ref. [49] found that biochar increased total soil porosity by 10–15%.

The same trends as with the total porosity were observed when analyzing data on the aeration porosity of the soils and substrates. However, here, the CS variant stood out, with the use of bioproducts significantly increasing the aeration porosity. It is likely that using a biological product for a longer period of time would have a stronger effect on the physical properties of the samples, especially those made on a peat base and prepared for use in greenhouses. This is even more true because, over time, the microbial biomass and activity in the soil decrease [50]. Other scientists claim that due to the use of biological products and other biostimulators, the amount of organic carbon in the soil increases [20,22]. This affects the decrease in soil density and the increase in porosity [51]. In addition, previous studies have shown an increase in total soil porosity of up to 74% due to the long-term use of bioproducts [25].

3.3. Effect of Biotreatment on Strawberry Yield

The highest yield of berries from one plant (2.88 t ha⁻¹) was obtained in sandy soil without biotreatment (Figure 8). The second highest berry yield was determined in loamy soil (2.17 t ha⁻¹) without biotreatment and in the CS variant with biotreatment (2.14 t ha⁻¹). Biotreatment increased the berry yield only in the CF and CS variants, which are commonly used in greenhouses, by 100% and 46.6%, respectively. It is likely that higher moisture and higher aeration porosity had a positive effect on CF and CS yields. In clay soil, biotreatment did not have a positive effect as the berry yield was 100% higher without biotreatment. In loamy soil, the berry yield was about 1.24 times higher without biotreatment compared to the variants in which the biological preparation was used. In clay soil, bioproducts influenced the plant’s extremal growth, resulting in no berry yield. The reduced porosity in variant CF without treatment could have had a negative influence on the yield.

The CF and CS variants showed a better ability to retain moisture than L, C, and SL. It could have influenced the yield increase in CF and CS variants with biotreatment compared to variants without biotreatment. Also, the higher temperature found in our research in containers with biotreatments could have led to enzyme activity, which resulted in a higher berry yield [52]. Ref. [43] states that soil temperature affects the availability of plant nutrients that are essential for plant growth. Nutrient availability to the host plant is an important factor in disease control [53]. Other researchers claim that the attraction of rhizobacteria helps plants absorb nutrients [54]. Optimization of the plant nutrition system increases crop yield [11,55,56,57].

4. Conclusions

Experimental studies on the process of growing strawberries in a greenhouse revealed a positive effect of the biological product on the physical properties of soils and substrates in variants C, SL, CS, and CF, which was not observed in variant L. In variants C, SL, CS, and CF, there was a decrease in electrical conductivity, a decrease in density (0.08, 0.02, 0.01, and 0.01 g cm⁻³, respectively), and an increase in aeration porosity (0.02%, 2.39%, 3.03%, and 3.63%, respectively). The change in physical properties of the soils and substrates was not significant; however, the trend of the results of the research shows that using the biological product for a longer period of time would have a greater effect on the physical properties of the soils and substrates.

Research has shown that biotreatment has a positive effect on strawberry yield in the CF and CS variants. In the CF variant with biotreatment, the strawberry yield from one seedling was 100% higher compared to without biotreatment (CS—46.6%). However, in the other tested samples, biotreatment did not have a positive effect. The yield obtained was significantly lower compared to the variants without biotreatment. This could have been influenced by a higher temperature increase after using the bioproduct and an inappropriate amount of moisture in the samples.

In the future, bio-based products will be widely used as they can contribute to improving soil health, reducing chemicals, and protecting the environment. Therefore, the importance of bioproducts will increase in various aspects of the agricultural sector, such as crop production, animal production, and horticulture, including greenhouses. However, at the same time, many unanswered questions regarding the composition of bioproducts, the amount of use, and the most appropriate time will need to be investigated and scientifically substantiated by researchers.