Influence of Artemisia dubia Wall and Pig Manual Digestate on Winter Wheat Productivity and Grain Quality

Abstract

Sustainable agriculture aims to use biological resources to improve crop quality and productivity. This approach promotes alternatives, such as replacing synthetic pesticides with biological ones and substituting mineral fertilizers with organic fertilizers. Field trials were conducted using two different factors: fertilizer treatments (ammonium nitrate and pig manure digestate) and plant protection treatments (pesticides, Artemisia dubia Wall biomass mulch, and strips). After harvesting the winter wheat, the productivity and quality (weight of 1000 grains, protein, gluten, starch, sedimentation of grains) were evaluated. The two-year studies showed that pig manure digestate positively affected winter wheat grain quality. Mugwort biomass outperformed other plant protection options in three key grain quality indicators (protein, gluten, and sedimentation). Furthermore, in 2023, the highest grain yield of 5798 ± 125 kg ha⁻¹ was observed in the pesticides and pig manure digestate treatment. The quick impact and mode of action of vegetation pesticides were more easily felt over the two years of study, leading to the highest yield of wheat grains compared to other plant management measures. This study shows that mugwort biomass can positively influence wheat grain quality, a significant milestone in utilizing nonfood crops as alternatives for agricultural productivity.

1. Introduction

Wheat is one of the most important crops in the world due to its nutritional value, demand, adaptability, and economic significance [1,2]. Wheat grains are used for food, fodder, and technical products [3]. Nowadays, wheat is a potential source of starch or even protein extraction. Therefore, grains have an international market value and play an important role in exports for many countries in the world [4].

In Lithuania, the share of crop production in the total agricultural production is 68%, of which cereals account for 34.9%. The main crop grown is winter wheat as it is more productive, and quality is less dependent on weather conditions. According to data from the Official Statistics Portal, the winter wheat harvest in Lithuania in 2023 reached 4.2 million tons [5].

Wheat yield and grain quality are crucial for maximizing crop utilization and ensuring economic benefits for farmers. The growing societal demands, alternative uses of grains, and the critical need for climate change mitigation are driving the development of new, innovative technologies in agriculture [6]. Nevertheless, due to the need to reduce the harmful impact of agriculture on the environment, the use of less intensive production methods is currently one of the priorities of the European Union’s agricultural policy (European Green Deal), which recommends the economical use of mineral fertilizers and plant protection products in agricultural production [7]. All the mentioned issues are the key drivers for the creation of new technologies.

The influence of different fertilizers (synthetic and organic) and synthetic plant protection measures on the quality of the crop is increasingly being studied. However, the availability of new innovative technologies for farmers remains limited.

Wheat-growing technologies have been analyzed for many years, focusing on optimizing fertilization and incorporating new crop varieties in agriculture. However, the most important are environmental factors that strongly influence crop productivity and quality. Greater attention must be paid to natural resources and their efficient use in the face of changing climate conditions. Similarly, all new technologies and the use of natural products must ensure the optimal nutrition level for wheat and other crops with no environmental hazards.

Nitrogen is one of the vital nutrient elements necessary for proper plant growth, as using nitrogen fertilizers increases grain yields and improves the soil quality for final consumption. As a result, the use of nitrogen fertilizers has increased dramatically. However, it is estimated that only 30–40% of nitrogen in fertilizers is taken up by plants and stored in grain, so excessive use of fertilizers leads to high nitrogen losses and environmental pollution [8]. For this reason, agronomists must optimize nitrogen fertilization to improve crop nitrogen uptake. On the other hand, reducing nitrogen fertilization would lead to lower crop productivity. Therefore, there is an urgent need for new ways of farming to achieve optimal results and ensure environmental and economic benefits.

An option and solution for lowering synthetic nitrogen sources might be using different organic fertilizers such as manure, compost, digestate, etc. Most of them are well studied, but the decline in livestock in countries has led to a lower quantity of manure. At the same time, the rest of the organic sources need to solve the problem of biodiversity loss in the fields effectively. Hence, introducing new, innovative alternatives in the wheat management system is a good alternative for synthetic fertilizers in agriculture.

Since 2007, Lithuanian Research Centre for Agriculture and Forestry (LAMMC) researchers and others worldwide have been analyzing the potential and quality of new crops introduced to their countries that could be grown in moderate-climate regions [9,10,11]. It must be noted that the changing climate allows the growth of new crops, which are becoming potentially new biomass sources for different purposes. One possible biomass source is Artemisia dubia. In earlier studies, Artemisia dubia showed great potential as a high-yielding crop [12]. Further studies are being conducted to evaluate the quality and content of different active compounds, and the results are promising [11,13]. Artemisia dubia (mugwort) biomass as an organic resource offers a novel approach to improving soil health and promoting sustainable agriculture. Its application as an organic amendment and biopesticide can lessen the dependence on synthetic fertilizers and chemical pesticides. As initial results presented a very positive effect on crop germination and reduction in weeds, this research hypothesized that the use of biomass of Artemisia dubia as mulch or growing in strips might help meet wheat’s nitrogen requirements or, at the very least, reduce the need for synthetic fertilizers and crop protection products. Hence, this study aims to evaluate the effect of mineral and synthetic fertilizers and Artemisia dubia Wall on winter wheat yield and grain quality.

2. Materials and Methods

2.1. Field Experiment

The experimental study was conducted for two years (2022 and 2023) in central Lithuania in an (55°40′ N, 23°87′ E) agricultural field at the Institute of Agriculture, LAMMC. However, research began in 2021 with the field experiment established in a randomized complete block design of nine treatments in four replicates. The soil of the experimental fields was Endocalcari-Epihypogleyic Cambisol. Before the study, soil samples were taken from a depth of 0–20 cm and subsequently analyzed with key chemical parameters having a neutral pH_KCl of 6.52, P₂O₅—102 mg/kg, K₂O—118 mg/kg, organic carbon—1.08%, total carbon—1.39%, and total nitrogen—0.14%. The first sowing year was 15 September 2021, for winter wheat “KWS Emilis”, with a sowing rate of 210 kg ha⁻¹. For the subsequent year, winter wheat of the same variety was also sown in autumn (19 September 2022).

Each experimental plot measured a length of 10 m and a width of 3 m. Two factors were analyzed: Factor A—fertilizers (mineral fertilizers and organic fertilizers) and Factor B—plant protection (pesticides, mugwort (Artemisia dubia) biomass, mugwort strips). Single-component mineral fertilizers, ammonium nitrate, potassium sulfate, and superphosphate were used in the field experiment. Single-element phosphorus and potassium fertilizers were used to maintain a balance of nutrients. A nitrogen application dose of 170 kg ha⁻¹ of active substance was supplied through synthetic fertilizers and pig manure digestate. The organic fertilizer used was pig manure digestate, which was obtained from agricultural–industrial sources in Lithuania, with the pig manure treatments used as their primary feedstock. The chemical analysis of the pig manure digested showed the nutrient composition of nitrogen (0.244%), phosphorus (0.047%), and potassium (0.113%). Organic and synthetic fertilizers were applied two times: 90 kg ha⁻¹ at the first stage at the beginning of plant vegetation after winter, and 80 kg ha⁻¹ at the second stage when the second node of winter wheat was visible.

Mugwort biomass was incorporated before winter wheat sowing at 8000 kg ha⁻¹. The biomass spread on each plot was carried out with a harrow. Mugwort strips were planted and seeded between wheat fields measuring 1.5 m × 20 m. The wheat was sown 3 m wide.

2.2. Meteorological Conditions

During the sowing of winter wheat in September 2021 and 2022, respectively, the average monthly temperature was similar, at about 10.9 °C. In the following autumn months, the air temperature was higher in both years than the annual air temperature average (Figure 1).

The highest temperature differences were in the winter months of 2022–2023. December–February stood out the most because the air temperature was hot in these months compared to the annual average. When analyzing the spring air temperature of both years, it was observed that in March, it was 1.7–2.4 °C higher than the annual temperature.

At the beginning of winter wheat germination, September and October 2021 differed not only in lower air temperature but also in the amount of precipitation (Figure 2). During these months, which are very important for the germination stage, the rainfall was about 30 mm below the annual average. A similar precipitation trend remained in the fall of 2022.

March is also characterized by low rainfall. However, in 2022, from April to July, there was a lot of precipitation—about 370 mm fell during this period.

2.3. Measurement of Traits

2.3.1. Wheat Grains Yield

Winter wheat was grown in field plots measuring 30 m², and harvesting was carried out with a 2.05 m wide Wintersteiger Delta (Wintersteiger Operations GmbH, Innkreis, Austria) combine. After harvesting, the grain obtained was first weighed and the data were recorded. The results were then converted into yield, showing how many kilograms of grain were obtained from one hectare. The yield was calculated by dividing the total yield (in kilograms) by the field area (in hectares).

2.3.2. Weight of 1000 Grains of Wheat

A sample of 1000 grains was taken from the harvested grain mass to investigate other quality parameters. The 1000 grains per mass Pfeuffer Contador seed counter (Pfeuffer GmbH, Kitzingen, Germany) was used for determination. The grains were weighed after careful separation. The calculation was performed in triplicate for all 9 treatments.

2.3.3. Protein, Gluten, Starch, Sedimentation of Grains

The quality of winter wheat grains was determined using the Infratec™ 1241 (Foss, Hillerod, Denmark) device to assess grain quality indicators such as protein starch, gluten, and sedimentation levels. Large samples were analyzed with the Infratec instrument to detect impurities, separating fine particles and ensuring that grain samples contained no more than 1% foreign matter.

2.4. Statistical Analysis

All statistical data were analyzed using R studio 4.3.2 software [14]. Tukey’s HSD test (α < 0.05) was used to test the difference between means at the 5% probability level. Means and statistical deviations were also calculated using the R studio 4.3.2 program.

3. Results and Discussion

3.1. Grain Yield

The yield of wheat depends on several biological processes that take place from sowing to maturity [15]. These processes are facilitated by using inputs such as fertilizers and plant protection measures, upon which the grain yield depends. The different fertilizers applied during the growing season and the applied plant protection impacted winter wheat yield. In 2022, the highest yield of 7083 ± 85 kg ha⁻¹ was achieved using pesticides and pig manure digestate. Similar yields were observed in variants where pesticides were used in combination with pig manure digestate or synthetic fertilizers. Studies have shown that winter wheat yields reach their highest levels when pesticides are used and plants are fertilized with mineral, organic fertilizers, or their combination. Using organic fertilizers, especially pig manure digestate, is a widely accepted strategy to increase crop yields and soil organic carbon stocks [16]. This is due to the availability of easily absorbed macro- and micronutrients present in digestate obtained from biogas plants [17]. Additionally, in 2022, a significantly lower grain yield (p < 0.05) was found in the mugwort strip across all the treatments. The warm and dry spring significantly impacted the winter wheat harvest in 2022 (Figure 3). The increased temperature accelerates wheat development, thus shortening the critical period and reducing the capture of solar radiation, negatively affecting the grain yield [18]. Portuguese scientists Dias and Lidon showed that high temperatures during the grain-filling stage promote leaf senescence and reduce grain weight [19].

Nitrogen from organic fertilizers often has little effect on crop growth in the first year of fertilization because organically bound nitrogen is released slowly into the soil over a medium to long period [20]. Therefore, the yield of wheat in the first and second year of vegetation, using only pig manure digestate and combining mineral fertilizers with organic ones, differed significantly. Furthermore, in 2023, after using pesticides and NPK, the grain yield reached the highest level (5798 ± 125 kg ha⁻¹), a yield decline compared to 2022. In 2018, M. Doyeni and his colleagues [21] conducted a study in which, using pig manure digestate, the wheat yield was about 30 percent smaller. In the article, the authors compared wheat yields using various animal-waste-based digestates and highlighted that pig manure digestate produces the highest yield under optimal climate conditions.

It must be reiterated that the wheat yield decrease observed in all the variants in the second year of the experiment (2023) compared with 2022 was due to low rainfall and unusually high temperatures during the growing season. Additionally, the plant stress from the drought in 2023 adversely impacted wheat growth and development, leading to reduced yields. Nevertheless, winter wheat productivity trends remained similar in both crop years. Furthermore, mugwort strip had lower yields in 2023 across the treatments: NPK (3036 ± 247 kg ha⁻¹), PMD (2980 ± 84.5 kg ha⁻¹), PMD + NPK (2644 ± 337 kg ha⁻¹). Yields were similar when comparing individual organic or synthetic fertilizers with co-digested fertilization. The reason may be that organic manure releases nutrients slowly, and when used together, nutrients may not be supplied quickly [22].

In summary, it can be stated that the yield of wheat grains is the highest when using vegetation pesticides compared to other plant protection measures. Throughout both years of the study, the trend in yield differences remained consistent. It was observed that fertilizing winter wheat with either pig manure digestate or mineral fertilizers can produce similar yields.

3.2. 1000-Seed Weight

The size of the wheat seed affects not only its emergence and establishment but also its yield. Larger wheat seeds yield higher yields than smaller seeds [23]. Drought can significantly reduce the weight of 1000 grains and the overall grain yield [22]. The two-year study showed that the 2023 drought did not impact the treatments where pesticides and mugwort biomass were used (Figure 4). However, in 2023, the weight of 1000 grains differed significantly in the variants used in mugwort strips.

According to Zareian [23] and other scientists, the weight of 1000 grains can affect the yield. However, based on the obtained data from this study, the mass of 1000 grains did not significantly impact yield. In 2022, the analysis of wheat grain yield and 1000-seed weight showed that, in all the treatments, the 1000-seed weight was higher than in 2023. This increase can be attributed to a better nitrogen supply and other essential nutrients [24]. The optimal supply of nutrients, especially nitrogen, promotes healthier plant growth, improves grain formation, and optimizes yields. As a result, the weight of 1000 grains can increase, which is an important indicator of the quality and quantity of the wheat harvest.

3.3. Protein, Gluten, Starch, Sedimentation of Grains

Grain characteristics such as protein content, wet gluten content, sedimentation volume, and starch properties are essential in defining the final consumption quality of wheat products [25]. In Lithuania, as in other European countries, such as Germany and Great Britain, wheat grains are evaluated according to protein concentration (over 12.8%), with nitrogen being the most critical plant nutrient in terms of crop formation [26]. When assessing wheat grain quality, attention is often paid to grain protein content, an important characteristic of wheat grading in Northern European countries [26]. In the first year of harvest (2022), the protein content of grains differed statistically significantly (p < 0.001) depending on the type of fertilizer, and plant protection measures also had a significant effect (p < 0.05). The highest protein content (11.4%) was found in the mugwort strip variants fertilized with mineral fertilizers in 2022—11.4%. There was no statistically significant difference between the variants sprayed with pesticides, with the protein content being 0.2% smaller. The variants of combined fertilization stood out the most, with lower protein content, ranging from 7.83 to 8.63%.

The grain protein content trend remained similar in the following year’s harvest (2023). The results of the 2023 research showed that the grain protein content was about 11% greater compared with 2022. The variations in the wheat protein content in the years must have been affected by unfavorable environmental conditions such as drought and heat stress. This aligns with the earlier report by Jingya et al. (2023) [27], where unfavorable environmental conditions significantly affected wheat protein content. The results of the 2023 study showed that the grain protein content was about 11% higher. Additionally, while some studies have reported the negative influence of drought on wheat protein content, the drought stress observed in 2023 played a unique role in the increased protein content. This confirms that the influence of drought during the reproductive growth stages usually increases grain protein concentration. Similarly, the increase in protein content was related to the effects of drought stress at the grain-filling stage and increased protein fractions [22]. Aside from the abiotic stress, the contributory effect of fertilizing with pig manure digestate on the grain protein content cannot be ignored. Doyeni et al. (2021) [21] reported that the protein content of wheat grains exceeded 11% in pig manure digestate fertilization. This is because nitrogen uptake increases with fertilizer N, which significantly boosts grain protein.

Figure 5 shows a significant difference in grain sedimentation indicators (p < 0.001) for both years in the treatments of organic fertilizer, mineral fertilizers, and their combination. Similarly, there was a significant difference (p < 0.05) in the interaction between both factors for both years (Figure 5). These differences were observed in both harvest years. Nevertheless, in neither the first nor the second year of harvest, the amount of sedimentation did not reach the average sedimentation volume, which is about 60 mL. This volume is significant because it positively correlates with protein content, as reported in the literature [3]. This means that although the type of fertilizer affects grain sedimentation rates, the final sedimentation rate was still lower than that generally associated with higher protein content. Such results can affect grain quality, especially when considering protein content and its impact on the final product.

Similar to protein content, grain sedimentation volume was higher in the second year of harvest, indicating high protein quality and quantity [28]. In 2022 and 2023, some variants involved fertilizing grains separately with mineral (NPK) and organic fertilizers alongside mugwort biomass. In these cases, the grain sedimentation volume was lowest in 2022 and highest in the second harvesting year. In 2022 and 2023, there were variants where, using mugwort biomass, the grains were fertilized separately with both mineral (NPK) and organic fertilizers. In these variants, the grain sedimentation volume was the lowest in 2022, and the highest in the second year of harvesting. It can be assumed that mugwort biomass had a positive influence on positively influenced sedimentation volume in the second year of winter wheat-fallow. This may be related to improved soil condition and better uptake of nutrients, which occurs over a more extended period, mainly when organic fertilizers are combined with mineral fertilizers.

Gluten is one of the quality characteristics of wheat, which can be divided into four categories [29]. The categories are classified as follows: “bad” for values below 50, “medium” for values between 51 and 70, “strong” for values between 71 and 85, and “very strong” for values above 86 [30]. Based on the information provided, the gluten content obtained in the field experiment ranged from 17.1 ± 0.05% to 26.2 ± 0.57%. According to the classification of gluten quality, these results would be classified as the first category (bad) because their values were less than 50%. These data are shown in Figure 6, corresponding to the lowest gluten quality category.

A study conducted in 2022 found that the highest amount of gluten in grain was achieved with the use of mineral fertilizers. Also, different crop protection treatments, including pesticides and mugwort strips, had the highest levels of gluten. However, the gluten content of these variants differed by only 0.2% compared to all variants in the study. Different results were obtained in the 2023 crop quality study, with gluten content being the most significantly (p < 0.001) affected using pig manure digestate. It is important to mention that gluten content in grains, as well as protein content, can increase due to drought or heat stress [22]. This is confirmed by the gluten results obtained and compared in 2022 and 2023.

Starch, which makes up 65–70% of the dry weight of cereal grains, is composed of glucose polymers [22]. The results of the conducted studies showed that the starch content in the grains varied from 68.2 ± 0.36% to 73.8 ± 0.20% (Figure 6). The starch content differed the most in winter wheat crops fertilized with combined mineral and organic fertilizers in the first and second years of harvesting. However, no significant difference was observed between the factors (fertilization and plant protection).

It is important to note that drought stress affects starch content in grains differently to protein or gluten. Drought stress reduces starch content in mature grains by affecting enzyme activity, which interferes with the transport of carbohydrates from the source (leaves) to the grain, thereby reducing starch accumulation in the growing grain. This effect may vary depending on growth stages and intensity of drought stress [22].

4. Conclusions

The intrinsic benefits of using bioresources, such as organic fertilizers and nonfood crop biomass, offer sustainable alternatives to the heavy reliance on inorganic or chemical inputs in agricultural systems. When winter wheat was fertilized with pig manure digestate, or NPK, during the two years of the study, the differences remained in trend, just as environmental significantly impacted winter wheat productivity and quality. An adequate supply of nutrients, especially nitrogen, promotes healthier plant growth, improves grain formation, and increases grain nutrient content, which can increase the 1000-grain weight—required for wheat yield quality and quantity. This further explains the similarity in wheat yields found in pig manure digestate or mineral fertilizer treatments.

Additionally, the two-year studies showed that pig manure digestate positively impacted winter wheat grain quality over the years. Mugwort biomass outperformed other plant protection options in three key quality indicators (protein, gluten, and sedimentation). This suggests that mugwort biomass can positively influence wheat grain quality.