The deficit of quality roughage is among the most important problems of agriculture in many countries. Forage crops grown in field agriculture are one of the most important sources of quality roughage. In cases where the area allocated to forage crops and production are insufficient, it is essential to obtain the highest yield and quality of fodder from the unit area. In this sense, cultural practices are an important factor in increasing the yield and quality per unit area. Within the scope of these applications, providing plants with appropriate amounts of the plant nutrients that are deficient is of great importance. For the development of plant resistance mechanisms and healthy plant development, macronutrients as well as microelements must be present in the soil in sufficient quantities and, more importantly, in an absorbable form. Therefore, as in many other crops, balanced plant nutrition practices should be given importance in order to increase the yield and quality of forage crops.
       
Today, the focus in animal husbandry is generally on high forage yield. Feed quality is of secondary importance. However, this situation not only causes significant problems in the nutrition of animals but also results in the production of poor quality animal products. For this reason, importance should be given to studies on plant nutrients to increase feed quality as well as feed efficiency. While research focuses more on macronutrients, microelements that play a role in many physiological processes in both plants and animals are neglected. This study is an original study in this sense.
       
Boron (B) is feeding the soil and the crops grown with B has gained great importance in cultivation systems where chemical fertilizers and high-yielding varieties are used intensively. Boron application is the second most important micronutrient in crop production after zinc and plays a critical role in plant growth and development (Safdar et al., 2023). Boron plays a role in cell wall formation, sugar transport, nucleic acid and carbohydrate metabolism and nitrogen (N) fixation in plants (Rahman et al., 2020; Ati et al., 2024). In addition, B has an effect on germination, flower formation, pollen formation, fruit set (Mathew et al., 2013; Panda et al., 2024), seed yield (Ullah et al., 2024) and dry matter (Nagar and Kumar, 2022) increase. Considering these functional functions of the B element in plants, forage crops, mostly used in their vegetative parts, can be affected positively or negatively depending on the dose applied from B used as fertilizer. Additionally, legumes are a plant group that is more sensitive to B deficiency. In some studies, it has been reported that B applications positively affect growth, yield and quality in soybean (Nagar and Kumar, 2022), groundnut (Kumar et al., 2022) and lentil (Nema et al., 2022). There are very limited number of studies on B application in forage legumes. From this perspective, this study examining the B responses of legume forage crops is the most comprehensive study.
       
While the uptake of B by plants depends on the physical (such as clay mineralogy, temperature and moisture) and chemical (such as soil B content, organic matter and pH) contents of the soil (Nagar and Kumar, 2022), responses to B fertilization may naturally vary among plant species, with some plants being more sensitive to B deficiency and toxicity than others. Moreover, the inadequate availability of B minerals in the soil may limit plant growth and also affect forage crops (Naik et al., 2025). Therefore, the responses of different legume forage plant species to B doses in the same ecology constitute another important unique value of this study. The aim of this study was to determine the effects of B fertilization applied at different doses on forage yield, quality and mineral content of different legume forage crop species in B deficient soil.

The experiment was carried out in the 2023-2024 vegetation period in the Research and Experiment Land of the Faculty of Agriculture of Siirt University (37^o58'13.20''N-41^o50'43.80''E, 887 m), located in the Southeastern Anatolia Region of Türkiye, which has semi-arid climate conditions. During the period in which the research was conducted (December 2023-June 2024), the average temperature was recorded as 14.0^oC and the total rainfall was 553.0 mm. The soil of experimental site was clay loam in texture, salt-free (electrical conductivity= 0.05 dS m^-1) and slightly alkaline (pH= 7.80) in reaction. The trial soils are in the calcareous class in terms of lime content (1.98%) and the organic matter content (0.60%) is very low. Soil was poor in available phosphorus (P) (55 kg P₂O₅ ha^-1), calcium (Ca) (1110 ppm) and B (0.82 ppm) while high in potassium (K) (440 kg K₂O ha^-1) and magnesium (Mg) (259 ppm). In the study, narbon vetch (Vicia narbonensis L. cv. Görkem) (NV), forage pea [Pisum sativum ssp. arvense (L.) Poir. cv. Özkaynak] (FP), berseem clover (Trifolium alexandrinum L. cv. Derya) (BC) and Persian clover (Trifolium resupinatum L. cv. Demet-82) (PC) species were examined. Etidot-67 (Disodium Octaborate Tetrahydrate, Na₂B₈O₁₃.4H₂O) with 20% pure B content was used as boron fertilizer.
       
The experiment was laid out in randomized block design consisting of 5 B doses treatment (B₀= 0, B₁= 1, B₂= 2, B₃= 3 and B₄= 4 kg ha^-1) with four replications. The field trial was planned and carried out separately for 4 plant species. Boron fertilizer was applied to the soil before sowing. In addition, nitrogenous (urea, 46% N) and phosphorous (triple super phosphate, 43-44% P₂O₅) fertilizers were applied to each plot in homogeneous amounts according to the soil analysis results before planting. During sowing, the sowing norm was applied as 100 live seeds per m² for NV and FP, 25 kg ha^-1 for BC and 15 kg ha^-1 for PC. Sowing of all species was done on December 20, 2023. Plants were harvested at full flowering stage (between April 30-June 2, 2024).
       
The number of days to flowering was calculated in days from the sowing date until the date when flowering was observed in 50% of the plants in the plot. Morphological measurements were made on 10 plants randomly selected from the 4 rows in the middle of each plot before harvesting. Natural plant height was determined by measuring the height between the soil surface and the top point of the plant, without disturbing the natural state of the plant or removing the plant. Natural plant height was measured on lodging-prone NV and FP plants. For plant height, the distance from the soil surface to the top of the plant was measured. Plant height measurements were made on BC and PC, which have no lodging problems. The main stem length was determined by lifting and straightening the plant and measuring the distance between the soil level of the main stem and the tip of the main stem with the help of a meter. The main stem length was also determined in plants whose natural plant height was measured. Main stem thickness was measured with a digital caliper 10 cm above the soil surface. Green forage yield was determined by mowing and weighing the remaining part of each plot after removing the edge effects and green forage yields per hectare were determined by taking into account the harvest area. At the end of the cutting, a random sample of 500 g green fodder was taken from each plot in a paper bag and dried in sun and then in an oven for final drying at a temperature of 65^oC to a constant dry weight. Hay yields per hectare were determined by determining the dry herbage ratio of the dried herbage samples and multiplying it by the green forage yields of the parcels. Forage quality analyses such as crude protein (CP), acid detergent fiber (ADF), neutral detergent fiber (NDF), P, K, Ca and Mg were determined using the #IC-0904FE calibration set (WinISI, 2024) with the Near Infrared Reflectance Spectroscopy device (Brogna et al., 2009). The CP yield (kg ha^-1) was calculated by multiplying the CP content (%) with hay yield. Relative feed value (RFV) was determined according to the method reported by Van Dyke and Anderson (2000). The classification reported by Rohweder et al., (1978) was used to evaluate the quality grade of the forage according to the CP, ADF, NDF and RFV data determined in the dry matter of legume species.
       
Variance analysis was performed on the obtained data according to the randomized complete block design, separately for each forage legume species (Yurtsever, 1984).

Yield attributes and forage yield
 
The number of flowering days did not vary according to B doses in legume forage plant species. The flowering date of 50% of the plants in the plot was recorded as May 15, 2024 in NV, April 28, 2024 in FP, April 26, 2024 in BC and May 26, 2024 in PC.
       
The growth and yield of forage legume species were generally significantly affected by B doses. Data regarding to the yield attributes and yields of NV, FP and BC species were significantly increased with increasing levels of B up to 2 kg ha^-1. However, the effect of B doses on PC was seen starting from 1 kg ha^-1 dose. The highest values in terms of natural plant height in NV and FP species (47.0 and 86.1 cm, respectively) and plant height in BC (82.6 cm) were determined at the B₂ dose. Unlike these three species, the highest plant height in PC was determined at B₁ and B₂ doses; however, the difference between these doses and the control and B₃ doses was insignificant. The highest main stem length in the NV was determined at the B₂ dose with 71.7 cm, while in the FP, it was determined at the B₂ (110.4 cm) and B₃ (109.1 cm) doses. The effect of B doses on main stem thickness was significant (p<0.05) in FP and BC, while NV and PC were not affected by B doses. The highest stem thickness was determined at B₂ dose (4.25 mm) in FP and B₃ dose (4.47 mm) in BC (Table 1).


       
The highest green forage yield was determined in the NV, FP and BC at the B₂ dose (16903, 46373 and 23583 kg ha^-1, respectively), while in PC, it was obtained at the B₁ (11945 kg ha^-1) and B₂ (11795 kg ha^-1) doses. The lowest green forage yields were found in NV and PC at B₄ doses and in other species at B₀, B₁, B₃ and B₄ doses. Hay yield showed the same pattern as that of green forage yield. The highest hay yield was obtained in NV at B₁ (3093 kg ha^-1), B₂ (3243 kg ha^-1) and B₃ (3167 kg ha^-1) doses, while it was determined as B₂ treatment (7911 and 5932 kg ha^-1, respectively) for FP and BC and B₁ (2660 kg ha^-1) and B₂ (2578 kg ha^-1) doses for PC. The lowest hay yield was determined as B₀ and B₄ for NV, B₀, B₁, B₃ and B₄ for FP and BC and B₄ for PC (Table 1).
       
Boron determines plant growth and yield by influencing various physiological processes, including pigment contents. Boron fertilization significantly increased the forage yield and yield-effective plant growth parameters in all species considered in the present study compared to the control. These effects of the B element varied according to some species. It was also reported by Rodrigues et al., (2024) that B requirements differ among species. When the forage yield and growth factors were evaluated together, 2 kg ha^-1 B application gave the highest values in NV, FP and BC species, while PC responded positively to B application up to 1 kg ha^-1 dose. The positive effect of B on growth characteristics and forage yield may be due to its role in cell elongation, nitrogen fixation capacity, formation of meristematic tissues, transport of sugars, photosynthesis and carbohydrate metabolism and nucleic acid synthesis (Rahman et al., 2020; Abdelwanis et al., 2022). The beneficial effect of B on yield was consistent with the results of others in BC (Sidhu and Kumar, 2018), alfalfa (Taherian et al., 2019), sainfoin (Chen et al., 2024) and grass pea (Sayed et al., 2024).
       
Providing B in appropriate doses has a positive and significant effect on plant growth, development and yield as it positively promotes physiological events in the plant. Excessive application of B may cause deterioration in meristematic tissues and deformations in plant development. In fact, it was observed that the forage yields decreased significantly in the B4 dose in the NV and in the B3 dose in the FP, BC and PC. Similar finding was reported Sheoran (2020) and Petrová and Soudek (2022). The different responses to B in the species considered in the present study indicate that there is a very narrow range between B deficiency and toxicity, as stated by Al-Amery and Khrbeet (2025). Therefore, application B requires careful consideration. Because available B in the soil that is deficient in one crop may have toxic effects on another crop (Geng et al., 2023).
 
Forage nutritive value and mineral content
 
CP, ADF and NDF concentrations are the main quality indicators of roughage. In the present study, the CP content of NV species was significantly (p<0.05) affected by B applications, while the effect of B was insignificant in other species. The highest CP content in the NV species was determined at the 1 kg ha^-1 B dose (22.91%). Crude protein of this plant decreased significantly, especially after the B₂ dose (Table 2). The results obtained by Dhassi et al., (2021) in alfalfa support the current research findings. Additionally, Nema et al., (2022) reported that increases in protein content were achieved with boron application. This positive effect according to control in NV plant of B can be explained by the fact that boron, an essential component of RNA, plays a role in ribosome production and therefore protein synthesis. The role of B in protein synthesis was also reported by Akshit et al., (2020). CP levels of other species varied between 17.93% and 25.65% (Table 2). Values of forage protein concentrations vary considerably depending on species, soil fertility and plant maturity (Newman et al., 2006). When these CP values determined according to B doses are compared with the values requested for alfalfa (18-25%) (Newman et al., 2006), it can be said that they are in the sufficient protein range.


       
From the results of this study, it was evident that B application greatly affected the CP yield of legume species. The highest CP yield were determined at B₁ (707.9 kg ha^-1), B₂ (700.9 kg ha^-1) and B₃ (668.9 kg ha^-1) doses in NV, B₂ (2030.0 and 1113.0 kg ha^-1, respectively) in FP and BC and B₁ (593.5 kg ha^-1) and B₂ (570.4 kg ha^-1) doses in PC (Table 2). Maximizing yield due to B application in the plant, boron which helps protein synthesis also maximizes protein yield. In terms of CP yield similar findings were observed in fodder sorghum by Verma et al., (2021) and in lentil by Nema et al., (2022).
       
Quality parameters such as ADF and NDF ratio were not affected by B applications in all species considered (Table 2). The RFV is an index representing forage quality (Newman et al., 2006). In the present study, the variation in RFV according to boron doses was also found to be insignificant (Table 2). Similar findings were also reported by Konuşkan et al. (2020). 
       
It is a well-known fact that animal feed must contain sufficient protein to maintain the health of animals. ADF, composed of lignin and cellulose and NDF, composed of hemicellulose, cellulose and lignin, are important indicators of feed fiber (Rohweder et al., 1978). The higher the percentage of ADF and NDF, the lower the value of CP that leads towards lower fodder quality (Atique-ur-Rehman et al., 2022). According to the classification reported by Rohweder et al., (1978), the species of NV, FP and PC produced forage of the “best quality” class, while BC produced forage of the “very good” class in terms of CP, ADF, NDF and RFV. Therefore, B deficiency or excess did not reduce the forage quality of the species considered.
       
The relationship between B and other elements is a very interesting subject in terms of plant nutrition. In the present study, B application had no significant effect on the mineral content of legume species except Ca (p<0.05) content of NV and K (p<0.01) content of BC. In the NV, Ca concentration increased significantly at B₁ and B₂ doses compared to the control and then tended to decrease. While a significant increase was detected in terms of K in the B₁ dose in BC compared to the control, other doses were in the same statistical group as the control subject. Although insignificant, changes in K and Ca in other species also showed a similar trend (Table 3). The decrease in K and Ca in plants after a certain dose can be explained by the toxic effect of B at high doses. Similar findings were reported by Kaya and Ashraf (2015) and El-Shazoly et al. (2019). The fact that B concentration does not have a significant effect on P and Mg accumulation can be explained by the fact that the plants were grown under optimum P conditions and that Mg in the soil was at sufficient levels. Dhassi et al., (2021) reported that B application had no significant effect on P, K, Ca and Mg absorption in alfalfa. While some research reports express an antagonistic relationship between B and P (Long and Peng, 2023), another report mentions a synergistic relationship (Masood et al., 2019). However, the B x P interaction is not yet clear (Vera-Maldonado et al., 2024). Similar inconsistent reports have also been reported regarding the interaction of B and Mg (Long and Peng, 2023). The interactions of B with P, K, Ca and Mg in forage plants have not been researched much. Current information does not allow the formulation of concrete hypotheses on B-macro element interactions. Further studies are needed on this subject.


       
Macro minerals are essential for growth and reproduction of the livestock (Talukdar et al., 2016). Therefore, the adequacy of roughage in terms of mineral elements is also an issue that needs to be examined. It is reported that the amounts of Ca, P and K in feeds used in rations for ruminants should be at least 0.90, 0.40 and 1.00%, respectively (Muller, 2009) and Mg should be 0.25% (NRDC, 2001). According to these limit values in the literature, while Ca, K and Mg values   were at a level sufficient to meet the needs in all species, P levels were found to be insufficient in the species of NV, BC and PC.

When plant growth characteristics, forage yield and quality parameters were evaluated together, it was concluded that 1 kg ha^-1 B application for NV and PC, 2 kg ha^-1 B application for FP and BC were the most effective doses. Even when all other conditions such as irrigation and fertilization are at optimum levels, micro-level B applications have proven to be productive and beneficial. Therefore, it is essential to provide plants with sufficient amounts of B for optimum production under different conditions. Nowadays, in order to increase the feed efficiency per unit area, soil analyses must be carried out and fertilization programs must be arranged and when micro elements such as B are deficient, B applications must be evaluated by taking into account the differences between plant species. Similar studies are needed for different forage crop species and different soils in the future.

The present study was supported by the Scientific and Technological Research Council of Türkiye (TÜBİTAK) Directorate of Science Fellowships and Grant Programmes (BİDEB) under the project number 1919B012309672 within the scope of the 2209-A - Research Project Support Programme for Undergraduate Students, first term of 2023. We thank TÜBİTAK-BİDEB for their support.
 
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The authors declare that there are no conflicts of interest regarding the publication of this article. No funding or sponsorship influenced the design of the study, data collection, analysis, decision to publish, or preparation of the manuscript.