1. Introduction
In recent years, the use of products increasing plant resistance, soil fertility, and, consequently, the yield has become a new area of interest. Some of those products make it possible to limit the use of traditional mineral fertilizers or eliminate them [
1,
2,
3]. They are applied to the soil as soil conditioners or to leaves. An example of one such product is Tytanit, containing titanium [
4,
5,
6,
7]. Tytanit contains 8.5 g dm-3 of the chelated form of titanium. Titanium belongs to the elements with the lowest phytoaccumulation index, with the exception of plants taking up a lot of silicon, i.e., nettle and some trees that accumulate up to 100 mg of Ti kg
−1. The action of titanium on plants is based on stimulating the activity of certain enzymes, e.g., catalase, peroxidase, lipoxidase, or nitrate reductase. In addition, this element increases chlorophyll content in the leaves, which has a positive effect on the yield of crops [
8]. Pais [
9] reports that despite the observed beneficial effect of water-soluble titanium compounds on vital functions, this element is not included in the components needed for the proper development of animal organisms. Titanium (Ti) has a beneficial effect on physiological and biochemical processes in plants, contributing to an increase in the yield [
10]. According to Kolenčík et al. [
11], it primarily affects quantitative and nutritional parameters, such as the oil content of sunflower seeds. According to Buettner and Valentine [
12] and Radkowski and Radkowska [
13], it increases the chlorophyll content of leaves, accelerates their growth and development, and reduces the sensitivity of plants to adverse environmental conditions. Studies on the reaction of plants to titanium have focused mainly on vegetables and some other crops [
6,
14,
15]. The recommended concentration of Tytanit for use in agricultural practice is 0.02–0.04%. To cereals, it is applied during tillering, stem shooting, and flag leaf stages. The literature confirms its beneficial effect on the yield and its quality. However, there have been very few reports on the use of titanium as a stimulant in the cultivation of forage grass species, such as
Festulolium braunii [
16,
17]. According to Borowiecki [
18], this grass has a high yield potential and good nutritional value [
19,
20]. According to Sosnowski and Jankowski [
21],
Festulolium maintains good growth and development potential in successive years of use, and its characteristic feature is the high proportion of leaves in relation to generative shoots [
22].
In the assessment of grass species, it is important to determine their chemical composition, including the content of cell wall components affecting forage intake and their digestibility and energy value [
23,
24]. The key components of cell walls are cellulose and hemicellulose, structural carbohydrates [
25,
26,
27]. They make forage structure and fill the rumen as ballast matter. The levels of individual carbohydrates in plants vary considerably. The effect and direction of content changes are important from a nutritional point of view. As plants grow, the level of crude fibre increases, including the share of lignin, which reduces forage digestibility. Since some amounts of lignin, which is alkali-soluble, pass to nitrogen-free extracts, the digestibility of this fraction is much lower than other fibre fractions, which contain relatively well-digested hemicellulose. According to van Soest [
28], hemicelluloses are better digested than cellulose. Their digestibility was estimated by the author at 79%, ranging from 72.3 to 85.7%. Cellulose is digested by ruminants at about 50%, ranging from 36.5 to 63.5%. Therefore, the aim of the experiment was to determine the effects of the foliar application of Tytanit, at the same time comparing it with the effects of mineral nitrogen, on the cellulose and hemicellulose content and its effect on
Festulolium braunii digestibility.
4. Discussion
As the most significant component of plant cell walls [
34], cellulose consists of interconnected glucose molecules [
35]. According to Bach Knudsen [
25], its structure prevents it from being penetrated by water molecules, which has a decisive influence on the fact that it is insoluble in water. Cellulose is found in large quantities in young plants, while in older ones its micelles are impregnated with lignin due to the hardening of plant tissue associated with aging. According to Jankowska-Huflejt and Wróbel [
36], of all feedstuffs, pasture forage (249.8–271.0 g kg
−1 DM) contains the least cellulose; in meadow plants it is larger, ranging from 287.7 to 299.7 g kg
−1 DM, with the largest amounts in hay (294.4–302.0 g kg
−1 DM). It should be emphasized that dairy cows digest only a third of cellulose [
37]. The results showed that in the plant material, cellulose content, averaged across treatment combinations and growing seasons, was 318.0 g kg
−1, with Salama and Navar [
38], Ciepiela [
26], and Todorov et al. [
37] recording similar amounts.
In this study, significant variation of cellulose content was also recorded across harvests, with the highest in the first (329.40 g kg
−1) and the lowest in the third (298.33g kg
−1). In the first year, a very uneven distribution of precipitation was recorded (
Table 1), which could have affected the yield and nutritional value of the plant. This trend was confirmed by Ciepiela [
26], who found the most cellulose in
Festulolium grass of the first growth cycle (286.1 g kg
−1) and the least of the third (265.4 g kg
−1). The higher content of structural carbohydrates in the first harvest can be explained by a smaller number of leaves produced by the plants. Frankow-Lindberg and Olsson [
22] found that the share of leaf blades in the first harvest of
Festulolium was 42%, with 75% in the third. In the research of Wiśniewska-Kadżajan and Jankowski [
39] on
Festulolium braunii, cellulose content was slightly different.
Cellulose content in plants treated with the lower nitrogen dose increased from 305.71 to 333.01 g kg
−1 when the higher amount was applied. Different results were recorded by Ciepiela [
26], who found that an increase in nitrogen dose from 50 kg ha
−1 to 150 kg ha
−1 resulted in a statistically significant reduction in
Festulolium cellulose amounts, from 288.1 to 268.4 g kg
−1DM. In the present experiment, however, the combined higher dose of nitrogen and Tytanit resulted in a statistically significant decrease, from 329.99 to 301.68 g kg
−1. Similarly, according to Ciepiela [
26], plants treated with Tytanit and a higher dose of nitrogen contained less cellulose. This phenomenon may have been caused by the varying ratio of leaf blades to stems, which determines the nutritional value of forage plants. On the plots with Tytanit applied in combination with higher amounts of nitrogen, a much higher yield of
Festulolium biomass was obtained than on those with Tytanit only or on those with traditional nitrogen fertilization [
16]. An important component of plant cell walls is hemicellulose [
39]. Consisting mainly of pentoses and hexoses, according to Bach Knudsen [
25], it serves as a reserve material deposited in the structure of the cell wall together with cellulose fibres. Numerous studies [
40] have shown that hemicellulose is digested completely a few hours after its intake by dairy cows. In successive years, the higher dose of nitrogen did not affect this content in a consistent way. In turn, the higher dose of Tytanit, in all years, contributed to lower hemicellulose content. Wadas and Kalinowski [
41] noted an increase in Na content in potato tubers. Tytanit is used on many crops and many authors confirm its positive effect on the quantity and quality of plant yield [
11,
14,
42]. Additionally, according to Ciepiela [
26], the same biostimulant significantly reduced the amount of hemicellulose in
Festulolium, but the effect of higher doses of nitrogen was not always statistically proven. The results showed that the higher dose of Tytanit used on its own contributed to a statistically significant decrease in hemicellulose content of
Festulolium from 184.7 to 175.0 g kg
−1. Similar amounts were recorded by Wiśniewska-Kadżajan and Jankowski [
39] in
Festulolium braunii (167.8–206.9 g kg
−1), lower than those obtained by Ciepiela [
26].
Lignification (i.e., tissue hardening) reduces forage digestibility, its energy value, and dry matter intake [
25,
37]. The research indicated that the average degree of
Festulolium lignification was 7.4%, varying over growing seasons and treatments.
According to Stachowicz [
43], grassland forage intended for ruminants should be at least 65% digestible. According to Podkówka and Podkówka [
44], cellulose and excessive amounts of hemicellulose with lignin limit plant digestibility and energy value. The results showed that the average value of dry matter digestibility in
Festulolium was 62.61% and did not fully meet the above standard set by Stachowicz [
43]. Slightly lower digestibility of Tytanit-treated plants were recorded by Sosnowski et al. [
6], with 57.7% for
Trifolium pratense and 55.5% for hybrid alfalfa.
The difference between the effects of Tytanit used on its own and of the combined dose was statistically significant. Sosnowski [
1] found that the digestibility of
Festulolium braunii dry matter was 60%, with no change after soil conditioner application, while mineral fertilizers significantly reduced the parameter to 48.5%.
In his other research, Sosnowski [
2] recorded higher digestibility (approximately 60.0%) of an alfalfa and
Festulolium braunii mixture. The number of harvests has a significant impact on forage digestibility, but it is also related to the development phase and the rate of plant aging [
45,
46].
In the present study, the digestibility of
Festulolium steadily improved in a statistically significant way in successive harvests, from 61.05% in the first to 64.51% in the third. These results were confirmed by Truba et al. [
7]. Jankowski and Malinowska [
3] recorded the highest digestibility in the forage of the second harvest (54.25%) and the lowest of the first (51.51%). The number of harvests during the growing season has a major impact on forage digestibility, which is also closely related to the developmental phase and the rate of plant aging of [
45,
46]. In the research of Gaweł and Żurek [
45], they recorded the digestibility of dry matter of grass–legume mixtures harvested five times at the level of up to 80%.