Impact of Tillage Intensity on the Development of Faba Bean Cultivation

: At the time of tillage, the properties of the soil change, thereby changing the conditions of crop development and, ultimately, their productivity and quality. The effect of non-inversion tillage or no-till on faba bean development is still not widely understood. For this reason, on the basis of a long-term experiment (since 1988), investigations of tillage systems using deep and shallow ploughing, chiselling, disking and no-till were undertaken at Vytautas Magnus University, Agriculture Academy, Lithuania, in 2016–2019. The aim of this study was to highlight the interaction between tillage methods and crop vegetative conditions, and its effect on faba bean development parameters. Soil chiselling generally led to better faba bean canopy development rates than other treatments. Faba bean roots developed somewhat better in non-tilled plots. Different tillage methods had less impact on faba bean development than vegetative conditions during the growing seasons. This shows that, due to rapid climate change, the conditions of each vegetative season are unique, which may lead to signiﬁcant changes in crop development parameters. In addition, in this case, agrotechnologies must be precisely used, such as the use of varieties resistant to abiotic stresses, as well as technical and technological approaches. The complex effects of these agrotechnological elements should be investigated in more detail.


Introduction
One of the main challenges of the 20th and 21st centuries has been to produce enough food for humanity, preserve the environmental quality, and maintain the economic wellbeing of rural communities [1,2]. Intensive use of agro-technologies has led to climate change, degradations in soil and water quality and the environment for humans and animals, and threats to human health [3,4]. The list of negative consequences related to the use of intensive farming technologies is growing [5]. Soil tillage intensity influences the soil's chemical, physical and mechanical properties, gas flows, and the development of faba bean cultivation, production and quality [6][7][8][9]. Conservation tillage helps produce an appropriate soil environment for growing crops, mainly through reducing the intensity of tillage and the retention of plant residues [10].
In the European Union (EU) and other countries, different cropping systems have been planned, and new greening programmes have been developed to reduce the negative environmental impacts [2]. In Lithuania, since 2015, farms have had to comply with the requirements of the greening programme [5]. One of the requirements of the greening program is crop diversification [11]. Therefore, it is mandatory to grow two to three different crops on farms. The second important requirement is the identification of ecologically important areas. Perhaps the most acceptable way to implement this requirement is to ensure that at least 7% of the area carries nitrogen-fixing plants. Besides this, Lithuania is a favourable environ for growing faba beans [11]. Today, faba beans are the second most widely grown grain legume in the EU. The faba bean is grown in climates ranging from temperate to semi-arid, using different cultivars and different crop-management techniques [12]. The faba bean (Vicia faba L.) contains valuable human nutrients [13], provides proteins in human diets and animal feed, and also has medicinal value [14,15]. The faba bean is also very important in crop rotations [11,[16][17][18]. The introduction of legumes into the crop rotation is an important way to maintain an acceptable soil fertility level [19] and reduce the incidence of weeds, diseases and pests [20]. Faba beans bio-accumulates atmospheric nitrogen and are therefore classified as one of the most efficient sources of nitrogen [14,21,22]. In Southern Europe, faba beans have shown the highest N yields [23,24]. This ecological service is usually employed in the intercropping of corn, potato and rapeseed cultivations [25]. In addition, faba beans generally improve the productivity of the following crops [26]. According to Unkovic et al. [27], the N 2 fixation of legumes can be influenced by the previous cropping sequence, periods of fallow, cropping intensity, and reduced tillage.
Plant roots perform many functions, and they influence the development processes of the ecosystem [28,29]. Root function is very important to plant health and yield. Quantifications of root growth and root distributions are necessary to understanding plant-soil interactions. The depth and distribution of roots are important parameters governing water and nutrient uptake by faba bean plants [30]. Faba bean (Vicia faba L.) is a crop with a shallow root system with little osmoregulation, and it is very sensitive to high temperatures and water stress [31,32]. Husain et al. [33] reported that faba beans have a potentially advantageous adaptation to water deficit that allows them to change their root and aboveground biomass according to the soil moisture conditions. Depending on the nodule bacteria, the leguminous plant in question, and the soil and climatic conditions, effective symbiosis can enable it to accumulate up to 400 kg ha −1 nitrogen during the growing season [34].
According to the index of chlorophyll content, it is possible to determine the condition of plants and the conditions of nitrogen nutrition and partially predict plant productivity. When there is a lack of nutrients, the amount of chlorophyll in young plants begins to decrease, and under favourable conditions, it increases [35].
Lithuanian and foreign researchers do not yet have a precise and comprehensive answer to the question of how faba bean cultivation under different tillage and vegetative conditions and intensities may be affected, and what are the interactions between these factors. Complex detailed research is required to answer these questions. The research tasks are as follows: (1) to determine the impact of tillage intensity and vegetative conditions on faba bean canopy height, biomass and photosynthetic parameters; (2) to establish the effect on faba bean root biomass and nodulation; (3) to find the interactions between faba bean development parameters and vegetative conditions. We hypothesize that faba bean development can remain consistent when tillage systems are kept steady for long periods, and depends more on the vegetative conditions.

Site Description
The investigations were performed in 2016-2019 at the Experimental Station (54 • 52 N, 23 • 49 E) of Vytautas Magnus University, Agriculture Academy, Lithuania on the basis of longterm stationary field experiment. This experiment has been started in 1988. The Lithuanian climate is surplus humid, and the average annual precipitation rate is 600-650 mm. The vegetative season lasts up to 150-180 days. The soil at the experimental site is a silty loam (45.6% sand, 41.7% silt, 12.7% clay) Planosol (Eutric Endogleyic Drainic) [36]. The soil in the experiment is approx. neutral, rich in available phosphorus (up to 384.0 mg kg −1 ), contains average amounts of available potassium (up to 201.0 mg kg −1 ), is rich in available magnesium (up to 634.0 mg kg −1 ), and has average amounts of total nitrogen (1.20-1.73 g kg −1 ).

Meteorological Conditions
In the last two decades, the Lithuanian climate has become more unstable in the relation to temperatures and precipitation rates. As one can see in Figure 1, all seasons in this period were different. When the beginning of the vegetative period was arid, the middle and end of the period could have been highly humid. The same has been observed for air temperatures. The warmest vegetative season was 2018, and the coldest was 2017. The highest precipitation rates were in 2016, while cop levels fell drastically due to a lack of moisture in 2019. available magnesium (up to 634.0 mg kg −1 ), and has average amounts of total nitrogen (1.20-1.73 g kg −1 ).

Meteorological Conditions
In the last two decades, the Lithuanian climate has become more unstable in the relation to temperatures and precipitation rates. As one can see in Figure 1, all seasons in this period were different. When the beginning of the vegetative period was arid, the middle and end of the period could have been highly humid. The same has been observed for air temperatures. The warmest vegetative season was 2018, and the coldest was 2017. The highest precipitation rates were in 2016, while cop levels fell drastically due to a lack of moisture in 2019.

Experimental Treatments and Agronomic Practices
We used the following crop rotation model in our experiment: winter oilseed rape, winter wheat, faba bean, spring barley. The experiment was performed with four replications in a randomized complete block design (RCBD). There was a total of 20 plots, with the sizes of each being 14 × 9 m.
In autumn, the soils were tilled differently: deeply and shallowly ploughed with a mouldboard plough; chiselled; disked, and not tilled (Table 1). Faba beans were cultivated using the conventional technology, which has been described in detail by Kimbirauskienė et al. [9]. Faba bean seeds were sown at the end of April or beginning of May (Table 2). Local fertilization (NPK 7:16:32, 300 kg ha −1 ) was performed during the sowing operation. The distance between rows was 25 cm, and the sowing depth was approx. 5-6 cm in the tilled plots. In the nom-tilled plot, the distance was 2-3 cm. The "Fuego" (Vicia faba var. minor) variety was developed in Germany at Norddeutsche Pflanzenzucht Hans-Georg Lembke KG. The sowing rate was 200-220 kg of grain per ha (40-45 seeds per m 2 ). Before sowing, the seeds were inoculated with a Rhizobium leguminosarum bacterial preparation (approximately 200 mL of preparation per 100 kg of seeds). A single application of herbicide (a.i. aclonifen 600 g L −1 ) was given just after the sowing of the faba bean. Insecticide (a.i. lambda-cyhalothrin, 0.15 L ha −1 ) was applied from the middle of May up to the beginning of June. The fungicide (26.7% a.i. boscalid and 6.7% a.i. pyraclostrobin, 1 L ha −1 ) was applied in June [37].

Methods and Analysis
The parameters of faba bean development parameters were determined at the beginning of the faba bean flowering stage (BBCH 60-63). Ten faba bean plants were picked from each experimental plot for the ensuing study. In total, 20 samples were taken for a total of 200 plants. In the laboratory, the heights of each plant were measured. After this, the plants were divided into canopy and roots, and weighed to determine the green biomass. The symbiotic nodules on the roots were also quantified. The biomass samples were dried in a thermostat at 105 • C to a constant weight. The dry biomass of the canopy and roots was thus determined. The leaf chlorophyll index was measured with a chlorophyll index meter CCM-200 plus (Opti-Sciences). Ten measurements per sample were performed. The assimilation area of the faba bean leaves (cm 2 ) was measured with a leaf area measuring device-Win Dias (Delta-T Devices Ltd., Cambridge, UK). For this analysis, we used all the leaves of the 200 plants that were taken. All results were recalculated to derive average indices of a single faba bean plant.
Two-way analysis of variance (ANOVA) was used to assess the statistical significance of the results. Dispersion analysis was performed on the LSD test for mathematical statistics. We used the statistical software package SYSTAT, version 10 [38]. Different upper case letters indicated significant differences between tillage treatments, and different lower case letters indicate significant differences between conditions in experimental years. The same letters indicate no significant differences at p ≤ 0.05 > 0.01.
Correlation analysis was applied to evaluate the causes of the studied traits. We used the program STAT ENG in the package ANOVA [39][40][41]. The analysis matrix included data on precipitation rates and air temperatures during the 4 year's vegetative seasons, s of plants, leaves' chlorophyll index and assimilation area, biomass of faba bean canopy and roots, and root nodulation. We calculated the correlations among all possible combinations.

Height of Faba Bean Canopy
After performing a statistical analysis on the results of two factors, we saw that the heights of faba beans differed significantly in differently cultivated soils (factor A) differed significantly (Table 3). On average, the tallest plants grew in the DC and SC plots. Vegetation conditions (factor B) influenced the average faba bean plant height significantly. The highest faba beans grew in 2017, when the average daily air temperature was lower than the long-term average, and the precipitation was more evenly distributed than in the other years of the experiment. This is because faba bean is a temperate-climate crop. However, at present, many faba bean varieties can successfully grow in a wide range of climates [42][43][44]. In our experiment, the precipitation rate and average air temperature weakly correlated with the average height of the faba bean plant. According to Chaves et al. [45], the most common environmental factors limiting plant productivity are drought and extreme temperatures. Research conducted by Šliogerytė [46] has also proven that the water deficit had a negative impact on the physiological indicators of plants. Faba beans have coping mechanisms that allow them to mitigate the potential negative effects of water stress. According to Husain et al. [33], these mechanisms consist of slowing down vertical growth, slightly decreasing the rate of leaf-area expansion slightly, greatly increasing root growth, producing leaves of smaller specific area and shedding leaves. We found a significant interaction between both experimental factors. The highest average faba bean plant height (101 cm) was measured in 2017 in the SC plots, and the lowest was in 2016, in the SC plots (51.2 cm) ( Table 3).

Faba Bean Leaves Chlorophyll Index
The tillage intensity (factor A) had no significant effect on the faba bean leaves' chlorophyll index. However, the vegetation conditions of the experimental years had a significant influence (factor B) ( Table 4).  [47,48]. Drought and surplus moisture rates were shown to have the greatest negative effects at the time of flowering [21]. In our experiment, the meteorological conditions had a significant impact, but the interaction between factors A and B was non-significant. The chlorophyll index was mainly correlated with the average air temperature (r = 0.437, p > 0.05). In addition, the chlorophyll index was also greatly correlated with the amount of magnesium in the soil, and the abundance of annual and perennial weeds at the beginning of the growing season (r = 0.570; −0.859; −0.776, p > 0.05).

Faba Bean Leaf Assimilation Area
The leaf assimilation area is important to photosynthetic productivity [49,50]. In our experiment, tillage treatments (factor A) had a less strong influence on the assimilation area of faba bean leaves than the vegetation conditions of the research year (factor B) ( Table 5), and the greatest assimilation areas were observed in the DC plots. The year 2017 was the most favourable for the development of faba beans, and the areas of the faba bean leaves were the largest (1153.6 cm) in this year. No significant interaction was found between the two experimental factors. A correlation analysis of the experimental data shows a high correlation between the leaves' assimilation area and the plant's average height (r = 0.937, p ≤ 0.010 > 0.001). Precipitation rate and average air temperature were weakly correlated with leaves' assimilation areas.

Faba Bean Canopy Dried Biomass
The assimilation area of the leaves has a strong effect on photosynthesis productivity. The highest biomass of dried canopy in the faba bean plants was found in the DC plots ( Table 6). The biomass was lowest in the NT plots. Conversely, in an arid and warm Mediterranean environment, Badagliacca et al. [51] and Volpi et al. [52] found that faba bean grain productivity in non-tilled or minimally tilled plots was higher than in conventionally tilled plots. In our experiment, the meteorological conditions during the vegetative periods had a significant effect on the dried biomass of the faba bean canopy.
The highest dry faba bean canopy biomass was observed in 2019; this year's vegetation period was sufficiently dry but was warmer than that of other research years. Conversely, under Mediterranean conditions, Madejón et al. [53] found a lack of precipitation had a negative impact on faba bean canopy biomass, but did not affect grain production. Under arid conditions, reductions in faba bean productivity were also established by Belgian scientists [54]. We found a slight correlation between the average air temperature and the canopy dried biomass under boreal climate conditions (r = 0.337, p > 0.05). No interaction between the two experimental factors was found. Robertson and Swinton [1] found that the productivity of the crops depends on the chlorophyll concentration in the leaves. In our experiment, we also found an average correlation between faba bean plant canopy dried biomass and the leaves' chlorophyll index (r = 0.433, p > 0.05) and assimilation area (r = 0.404, p > 0.05).

Faba Bean Roots Dried Biomass
According to the average data on factor A, the greatest (8.0 g) average dry biomass of faba bean plant roots was observed in NT and DC plots (Table 7). Similarly, Muñoz-Romero et al. [55] found that no-tillage was more favourable for the development of faba bean roots because of improvements in the soil's hydrological conditions. Similarly, the benefits of no-tillage have been highlighted by López-Bellido et al. [56].
According to the average data on factor B, just like the canopy of the plant, the roots also developed most effectivelly in 2017. No significant interaction between the factors was found.
It is known that tillage systems effect soil properties such as bulk density, aggregation and pore continuity, temperature, aeration and moisture levels, which can affect root growth [57,58]. In our experiment, we found a negative correlation between air temperature and roots dried biomass (r = −0.505, p > 0.05). Precipitation rate had a positive effect (r = 0.381, p > 0.05). Research conducted by Šliogerytė et al. [46] showed that a moisture deficit disturbs the distribution of dry mass in the plant, causing more to accumulate in the roots than in the above-ground part. Similarly, we found a negative correlation between faba bean canopies' dried biomass and roots' dried biomass (r = −0.520, p ≤ 0.05 > 0.01). We also found correlations between roots dried biomass and plant canopy height (r = 0.545, p ≤ 0.05 > 0.01), chlorophyll index (r = −0.726, p ≤ 0.010 > 0.001) and leaves' assimilation area (r = 0.565, p ≤ 0.05 > 0.01). In addition, the dry biomass of the roots of the faba bean at the time of flowering correlated with the volume of pre-crop residues on the topsoil after faba bean sowing (r = 0.703, p > 0.05), the density of the crop at the beginning of the growing season (r = −0.926, p ≤ 0.05 > 0.01), the total weediness of the crop at the beginning of the growing season (r = −0.928, p ≤ 0.05 > 0.01), and the amount of magnesium in the soil in the 15-25 cm layer at the beginning of vegetative period (r = 0.980, p ≤ 0.010 > 0.001).

Number of Nodules on Faba Bean Roots
In our experiment, in differently cultivated soil (factor A), the number of nodules on the roots of the faba bean plant differed insignificantly (Table 8). Despite this, the greatest number of nodules were found in the SP and NT plots. López-Bellido et al. [59] similarly concluded that the number of nodules is also influenced by the chosen method of tillage and which plants are grown. Trinick et al. [60] found that an adequate supply of and balance between photosynthetic products must be ensured so as to maintain the required number of nodules on the roots [61]. In our experiment, leaf chlorophyll index slightly correlated with the number of nodules (r = −0.327, p > 0.05) and canopy dried biomass (r = −0.610, p ≤ 0.05 > 0.01). We also found correlations between the number of nodules and roots dried biomass (r = 0.397, p > 0.05).
When examining the influence of factor B, it was found that the most favourable year for the development of bean symbiotic nodules was 2017, during which the average number of nodules on the roots of the bean plant was the highest (111.6 units), and was 1.4 to 1.8 times higher than in subsequent years of the experiment. According to the Amanuel et al. [62] and Puschel et al. [63], the roots of faba beans and other legumes with root nodules are very sensitive to nitrogen, phosphorus, potassium and water levels. In our experiment, a moderately strong positive relationship was established between the numbers of symbiotic nodules and soil phosphorus content, potassium content, and nitrogen content in the 15-25 cm soil layer at the beginning of the growing season (r = 0.681; 0.585; 0.523; p > 0.05). A positive relationship was also found between soil structural stability, number of earthworms and number of nodules (r = 0.815 and 0.611, p > 0.05). In addition, precipitation rates and air temperatures weakly correlated with the numbers of nodules. We did not find significant interactions between the experimental factors.

Conclusions
The use of different tillage methods (factor A) had a weaker influence on faba bean development than did vegetative conditions during the growing seasons (factor B). Despite this, DC generally showed better faba bean canopy development rates than other treatments. Faba bean roots developed slightly better was in NT plots.
As we expected, the vegetative conditions during growing seasons (factor B) had a more significant influence on faba bean development indicators than did tillage methods (factor A). In addition, due to rapid climate change, the conditions of each vegetative season are becoming more unique, which could significantly affect crop development parameters. In this case, agrotechnologies must be used more precisely, including using faba bean varieties resistant to abiotic stress, and employing effective tillage and operate sowing, inter-cropping, balanced fertilization and plant protection approaches, along with other technical and technological considerations. This complex effects of agrotechnological elements on faba bean agrocenosis should be investigated in greater detail in the near future.