1. Introduction
Plant-derived protein for both ruminant and nonruminant livestock rations, especially protein from non-genetically modified crops, is in short supply in Europe. Relatively little attention has been given to the possibility of meeting this need with perennial forage legumes, which are currently primarily used as a source of protein and fiber for ruminants. However, various species from this group, in addition to producing biomass with high protein concentration and digestible fiber, provide environmental services that contribute to goals of improving sustainability of European agriculture [
1]. Important traits, from the point of view of contemporary challenges, include durability and a generally well-developed root system, which allows for year-round protection of soil against erosion, nutrient run-off, and nutrient leaching. Moreover, perennial legumes, and especially separated stems, have been proposed as potential biofuels. Alfalfa (
Medicago sativa L.) is a high yielding forage legume that meets these criteria. Literature sources indicate that fodder galega (
Galega orientalis Lam.) may be a competitive species, especially in more challenging edaphic and climatic conditions of northern Europe and where insect or disease pressure limit alfalfa usefulness.
Fodder galega originated in the Caucasus region. Its cultivation began in Finland and Estonia about 50 years ago [
2,
3], and the agricultural usefulness of the species was confirmed in central Europe, Russia, Canada, and Japan [
4,
5,
6,
7,
8,
9]. In the establishment year, galega produces relatively low yields, but in the following years the yields of dry matter range from 5 to 15 Mg ha
−1 [
10,
11]. It is exceptionally durable, especially when harvested 2 to 3 times per year in northern environments [
7,
12], having persisted 20 years in northern Poland [
13]. It tolerates drought and cool temperatures during the growing season, typical of northern Europe and, in such conditions, yields similarly to alfalfa [
10,
12,
14]. It is suitable for soil protection [
15] and can also be used for energy purposes [
10,
11,
16]. The level of anti-nutritional substances (alkaloids) in green forage is very low, which distinguishes this species from
G. officinalis [
17,
18]. There are also no reports of galega being significantly impacted by diseases or insects.
From the perspective of feed value, leafiness is an important characteristic of fodder galega. The leaves of this species are relatively large, from 14–25 cm long. They have an odd-pinnately compound structure and consist of 9–15 oval elongated leaflets, each 3–6 cm long. At the base of the leaf are ovate stipules 1–1.5 cm long. Ignaczak [
6] and Teleuţă et al. [
8] report that in the spring cut, before flowering, and in the autumn cut, the proportion of leaves in the biomass dry matter ranges from 50% to 70%. When plants have developed pods, the percentage of leaves in the spring cut is still more than 20%, and in the late-summer cut, more than 40% [
19]. The concentration of crude protein in fodder galega leaves ranges from 27% to 31% [
6]. Moreover, the leaves are much richer in macro- and micronutrients than the stems [
19].
Galega has an erect growth habit, with large-diameter, hollow stems 0.8–1.5 m tall. Stemminess is generally considered a serious drawback, contributing to a reduction in forage nutritive value. Stem proportion in the total biomass is much greater in the spring cut than in the late-summer cut. According to Pahkala and Pihala [
19], stem proportions are 73% and 46%, and according to Ignaczak [
6], 58% and 30% in spring and late-summer, respectively. Therefore, Meripõld et al. [
20] recommend that the first cut should be used for bioenergy production and the second cut for forage.
Earlier research focused mainly on evaluation of yield and forage nutritive value of whole-plant galega [
21,
22,
23]. Ignaczak et al. [
13] and Andrzejewska et al. [
24] reported a much greater nutritive value of separated leaves and stem tips and inflorescences compared to whole plants. The chemical composition of leaves and stems of perennial legumes is significantly different and this has led to exploring possibilities of their separation, either at harvest or post-harvest [
13,
25,
26,
27]. With stratified harvest, leaves could be used as a protein source for monogastric livestock, and stems for certain groups of ruminants or for energy purposes. Therefore, it is justified to investigate the chemical composition of galega leaves and stems at different stages of development and different times in the growing season. Previous information on the forage nutritive value of galega leaves and stems is sparse and, as a rule, not compared to other similar species. Alfalfa is the appropriate species to compare with fodder galega, not only because these crops are used for similar purposes, but also because alfalfa is the best known and described species among the perennial legume forage crops [
28,
29,
30].
The aim of the study was to compare the yield structure of fodder galega and alfalfa, as well as the forage nutritive value of leaves, stems, and whole plants expressed as crude protein, fiber fractions, neutral detergent fiber digestibility, and in vitro true digestibility at different harvest times.
3. Results
3.1. Leaves
The proportion of leaves at each harvest time was greater in galega forage than in alfalfa, on average by 35% (
Table 3). For galega, this value ranged from 497 to 622 g kg
−1 DM, and for alfalfa from 354 to 495 g kg
−1 DM. In spring growth, the proportion of leaves in young galega (1.1) was at the same level as in the summer growth (2.1 and 2.2), while in alfalfa, the proportion of leaves in spring growth was always lower than in the summer growth.
Dry matter concentration of galega leaves was generally similar to that of alfalfa leaves. The exception was the earliest spring harvest time (1.1), when galega leaves contained significantly less dry matter than alfalfa leaves. Dry matter yield of galega leaves was on average 98 g m−2 (31%) greater than that of alfalfa, which resulted from significant differences between species in the spring growth. In the spring growth, as galega plants developed, the yield of leaves increased, which could result from increased leaf number and the size of the leaf blades. Such a tendency was not observed in alfalfa.
Alfalfa leaves contained, on average, 21 g kg−1 more protein than galega leaves, which resulted from a significantly greater concentration of this component in alfalfa leaves in the summer growth (2.1, 2.2). Moreover, it was observed that in the spring growth, the rate of decrease in protein concentration in galega leaves was faster than in alfalfa leaves. Mean protein yield of galega leaves was 11 g m−2 (17.8%) greater than that of alfalfa, which was a consequence of large interspecies differences in leaf yield of spring growth. For galega, leaf protein yields in spring harvests were always significantly greater than from summer harvests. Such a relationship was not observed in alfalfa, where leaf protein yields were similar in spring and summer.
Regardless of the harvest time, galega leaves were characterized by greater ADF, NDF and NDFD, but lower IVTD and ash, compared to alfalfa leaves. Ash concentrations in alfalfa leaves in spring growth declined as the plants aged, while in galega this level did not change. In summer growth, crop maturity had no effect on ash concentration in leaves of either species.
3.2. Stems
Stem proportion in galega was significantly lower than in alfalfa (
Table 4). Dry matter concentration in the stems increased progressively with development of plants in both species in the spring growth, while in the summer growth, it increased only for galega. However, the average stem dry matter yield of both species was comparable. This trend was also observed for crude protein concentration and yield, and ADF concentration. On average, galega stems contained more NDF and this NDF was less digestible, and contained less IVTD and ash. There were also interspecific differences at some harvest times. The stems of galega in spring growth, collected at the first two harvest times, contained significantly more ADF and NDF than alfalfa, and NDFD was usually lower (1.2, 1.3 and 2.1). On average for both species, spring growth was characterized by a higher stem proportion and greater dry matter and protein yields.
3.3. Whole Plants
The data on characteristics of whole plants (
Table 5) show that galega was taller than alfalfa, by an average of 8 cm. Greater interspecific differences occurred during spring than during summer, when the trend was opposite, indicating that alfalfa regrew faster after harvest than galega. Both crops were characterized by a similar mean dry matter concentration when averaged over the growth period and harvest time, but at harvest time 1.1 and 1.3 alfalfa contained significantly more dry matter than galega. During summer growth, differences between species were not significant.
The average dry matter yield of whole-plant galega was significantly greater than that of alfalfa, which was mainly due to significant interspecies differences in the second (1.2) and third (1.3) harvest of spring growth. Galega protein concentrations were greater than alfalfa at each harvest of spring growth but this trend was reversed in the summer growth. Similar relationships were found in protein yields. Averaged over all harvest times, galega protein concentration was 11 g kg−1 greater than alfalfa, and the protein yield of galega was 13 g m−2 greater than that of alfalfa.
Galega and alfalfa had similar levels of ADF, NDF, NDFD, and IVTD, but significant differences were noted at some harvest times. At the last harvest time (2.2), galega had a lower ADF concentration than alfalfa, but NDF concentration was greater in galega at two other harvest times (1.2 and 2.1). The spring growth of galega harvested at full flower (1.2) had lower NDFD than the alfalfa, but galega had greater NDFD in both harvests of summer growth. Significantly greater IVTD of alfalfa was found only once in the growing season—in full-flower spring growth (1.2). The concentration of ash was always greater in alfalfa than in galega.
As plants matured in both growth periods, the trends and levels of the assessed characteristics were similar for both species, and typical of most perennial forage legumes. In the spring growth, as plants matured, both height and dry matter yield increased. The concentration of crude protein decreased significantly, but protein yield remained at the same level. Concentrations of fiber (ADF and NDF) increased, fiber digestibility (NDFD), and dry matter digestibility (IVTD) decreased, and ash concentrations decreased with the progressive development of both species. It is worth noting, however, that in spring growth of galega, no significant differences were found between the second and third harvest times (1.2 and 1.3) for ADF, NDF, NDFD, and IVTD, while in alfalfa the differences between each subsequent developmental stage were significant. This indicates that nutritive value changes of galega occur earlier than that of alfalfa as the crops mature. To some extent, this was also true for forage harvested from the summer growth. The height, dry matter yield, protein concentration and yield, as well as ADF, NDF, and ash concentrations did not change significantly between the initial and final flowering stages of the galega plants. On the other hand, NDFD and IVTD decreased.
The leaf to stem ratio of galega was 66% to 100% greater than in alfalfa across growth periods and harvest times (
Table 6). There was no obvious association of ratio values with growth period or maturity.
4. Discussion
The results of this research support earlier reports of the high proportion of leaves in galega, especially in spring growth before flowering, and in the summer growth [
6,
8]. In galega, the proportion of leaves was, on average, 35% greater, and yield of leaves 45% greater than alfalfa. This contributed to galega yielding 22% more leaf protein than alfalfa, despite a lower concentration of crude protein in galega leaves.
An important foliage index is the leaf/stem ratio [
28,
29]. This index for galega was almost twice as high as for alfalfa (
Table 6). The proportions of leaves and stems in alfalfa vary depending on environmental conditions, plant variety, height, density, as well as development stage [
23,
30,
33,
34,
35]. According to a review by Lamaire and Belanger [
36], decreasing alfalfa leaf/stem ratio is clearly correlated with a decrease in feed digestibility. In our study, as plants grew and matured in spring growth, the leaf/stem ratio changed to a greater extent in galega than in alfalfa, and yet the decrease in NDFD and IVTD of galega was comparable to or even lower than in alfalfa.
In terms of nutritive value parameters, galega leaves were generally inferior to alfalfa. The protein concentration was, on average, 8% lower, but particularly large interspecific differences of 23% to 25% occurred in the summer growth period. The concentrations of ADF and NDF were 24% and 28% greater, respectively, in galega leaves. The differences in leaf NDFD and IVTD, although statistically significant, were small. Alfalfa, on the other hand, contained more ash in both leaves and stems. Lower nutritive value of galega leaves may result from their morphological structure, where the proportion of petioles and petiolules is significant, and their chemical composition likely differs from that of the leaf blades. It has been reported that, similar to alfalfa [
37], Ca and K are dominant among the galega minerals [
6,
16,
21]. Although nutritive value of separated galega leaves is slightly inferior to alfalfa leaves in terms fiber concentrations and digestibility, this does not preclude them as a feed suitable for monogastric livestock, especially as a protein source.
The available literature is sparse on the amino acid composition of galega leaf protein. However, Skórko-Sojko et al. [
38] report that the protein from whole-plant galega contains less lysine, threonine, tryptophan, leucine, isoleucine, valine, tyrosine, and phenylalanine compared to the protein of alfalfa. Compared to clover protein, galega protein is richer in sulfur amino acids (methionine, cysteine), phenylalanine, tyrosine, isoleucine, leucine, and valine.
In this study, for the first time, a detailed analysis of the chemical composition of galega stems was performed. Previously, it had been indirectly assumed that length and diameter of galega stems equate to low nutritive value, and their use for non-fodder purposes had been suggested [
39]. The current results fully confirm this assumption and justify the utility of fractionating the structural components of galega green forage during harvest [
13].
When relating the current results to agricultural practice, it should be taken into account that alfalfa is harvested for feed according to a different pattern, usually three or four times during the growing season, which does not allow reaching the full flower stage. With an optimal harvest schedule, alfalfa yield and nutritive value will likely be greater than in the current experiment. The aim of the study, however, was to evaluate galega, which is usually harvested twice per growing season to optimize yield, nutritive value, and persistence.
With a two-harvest system, typical for galega in northern Europe, with first harvest at bud stage and the second harvest at the full flower stage, 1370 kg ha
−1 of crude protein can be harvested in separated leaves (
Table 3). This protein yield compares favorably to protein yield of soybean produced in colder, northern environments. Mean soybean yield for Canada from 2015 to 2019 was 3100 kg ha
−1, for Ukraine 2500, and Russia 1500 [
40]. Assuming 40% crude protein in soybean seeds, crude protein yield for soybean is approximately 1240 kg ha
−1 in Canada, 1000 kg ha
−1 in Ukraine, and 600 kg ha
−1 in Russia. Additionally, considering the extreme longevity of galega (7,12,13), production costs, including tillage, establishment, and herbicides, are lower for galega than soybean or other annual protein crops. The added benefits of growing a long-lived perennial crop are reduction in soil erosion and enhanced carbon sequestration associated with permanent groundcover. Prototype equipment has been developed to accomplish segregated leaf and stem harvest of galega (13).
5. Conclusions
Due to the large proportion of leaves in whole-plant galega, forage nutritive value in bud or early flower stages is comparable to, and crude protein concentration is superior to, that of alfalfa. Nutritive value of separated galega leaves is remarkably greater than whole plants. The nutritive value of galega stems is lower than alfalfa stems, as indicated by higher NDF concentrations, and lower NDFD and IVTD values. Therefore, with the separate harvest of leaves and stems, it is justified to use them for non-fodder purposes, such as energy, mulch, or plow-down residue. The relatively high leaf protein yield with a two-harvest system, combined with previously documented persistence for greater than 20 years and no serious pests, make galega an attractive crop for fractional harvest of leaves for monogastric livestock feed, especially as a protein supplement, in northern regions.