The study was conducted to evaluate the influence of silicon application on the botanical composition of grass–legume mixtures as well as the nutritional value of individual species and mixtures. The two-factor field experiment was established in a split-block arrangement. The two grass–legume mixtures, consisting of Dactylis glomerata, Festulolium braunii and Trifolium pratense or Medicago x varia and grass mixture—Dactylis glomerata, Festulolium braunii and Lolium perenne, were sown on arable land. Silicon foliar and mineral NPK fertilization was applied in three variants: NPK (non-Si-fertilized), NPK+Si (Herbagreen), NPK+Si (Optysil). Changes in the botanical composition in the sward of mixtures during the study period were influenced by the competitiveness of individual plants and weather conditions, whereas the effect of foliar fertilization with silicon was only slightly marked. The nutritional value of individual species of grasses and legumes varied over the years and also depended on the application of silicon. The greatest content of crude protein (CP), irrespective of the species and variant of silicon fertilization, was noticed in years with no drought. Our research confirmed the beneficial effect of silicon fertilization, independent of weather conditions, on the CP content and on the reduction of crude fibre (CF), neutral detergent fibre (NDF) and acid detergent fibre (ADF) in plants, especially when Herbagreen was applied. The nutritional value of the mixtures under applied silicon fertilization depended on botanical composition. In the conditions of low rainfall, a large share of F. braunii and an approximately 20% contribution of T. pratense resulted in a higher content of CP. These results may be used in the fertilization practices of temporary grassland for enhancing nutritional value, especially crude protein content, and on the reduction of fibre in the sward.

Research on mitigating the effects of water scarcity by applying silicon to perennial grasses is still insufficient. This study was conducted to investigate the effect of spring and summer droughts and silicon applications on gas exchange parameters; the morphometric characteristics of root systems; and the biomass distribution of Festulolium braunii, Festuca arundinacea, and Lolium perenne cultivars. Plants were treated with a drought during the tillering phase once a year (during spring or summer regrowth) for 21 days. Foliar nutrition with silicon was applied twice under the drought conditions. Grasses in a pot experiment were cut three times during vegetation. The plants that were exposed to the drought had lower values of the gas exchange parameters than those that were well watered. The beneficial effect of silicon was related to the reduction of excessive water loss through transpiration during the spring drought. Under the drought and silicon applications, the water use efficiency, root dry mass, and length increased compared to the control. Moreover, silicon increased the proportion of both the finer and thicker roots in F. braunii and L. perenne, while the distribution of the root diameter changed least in the more resistant F. arundinacea. Silicon also reduced the carbon content in the roots and increased root carbon accumulation. Our results indicated that Si may help perennial forage grasses cope better with drought stress. This was due to the allocation of carbon to the roots to develop the fine root network, increasing the length and root biomass and improving the water use efficiency.

To improve sward efficiency and maintain high feed quality in organic farming—as well as compensate for yield losses under anticipated drought periods—alternative fertilization practices should be considered. In this context, this study aimed to assess the response to summer drought of grass–clover sward in organic cultivation under various conditions of foliar fertilization with silicon (Si) (without Si, Si applied with multicomponent fertilizer Herbagreen, Si applied with growth stimulator Optysil). The research was conducted at the certified organic field in the 3rd, 4th and 5th year of mowing utilization (from 2015 to 2017). The studies demonstrated a beneficial effect of Si application on the yield of the grass–clover sward, especially under multicomponent fertilizer. Both fertilizers increased roots mass, but growth stimulator (containing mainly Si) had a stronger impact, especially with rainfall scarcity. In such conditions the application of Si decreased flavones concentration in plants and increased values of chlorophyll index. This study also indicated the potential for applying Si fertilizers to improve content of nutrients (crude protein, organic matter digestibility, potassium and phosphorus) in the sward. The results of presented studies may be used in fertilization practice of organic crop for enhancing sward productivity and to compensate for yield losses under condition of rainfall deficiency.

Periodic and repeated water scarcity has become an increasing concern on grasslands, causing not only to a reduction in productivity but also negative alterations in the carbon balance. The objective of this work was to comprehensively investigate some physiological performance traits of forage grasses, their roots morphometric features and distribution of biomass under simulated water deficit applied in different terms over a period of study. Plants were exposed to water shortage for 21 days, and then grown in optimal substrate moisture conditions. The gas exchange parameters and the main traits of root system architecture of three grass forage species and their cultivars were analyzed: Festulolium braunii (Richt.) A. Camus, cvs. Felopa and Sulino, Lolium perenne L., cvs. Bajka and Gagat and Festuca arundinacea Schreb. cvs. Odys and Rahela. Rapid decrease in the values of parameters related to the gas exchange process in grasses in the following days of water shortage was noticed. Water use efficiency (WUE) value was low in drought conditions due to increased transpiration of plants and was associated with a low C:N ratio in shoots. No obvious, positive effect of previously experienced drought stress on survival of tested grass species after another stress was observed. Cutting of plants after drought period most probably underlied the lack of memory and also additional factor weakened plant regrowth. When the drought was applied for the second time in spring during intensive plant growth, higher biomass allocation to the roots was observed. It was associated with the reduction of plant dry biomass, a decrease of carbon accumulation and the C:N ratio in the shoots. Due to the drought applied for the second time in summer, some biometric features of the roots were strongly and positively correlated with WUE, which is an important feature from the point of view of yield optimization and moisture use by plants.

Limited water resources and natural drought may result in reduced water availability for the population’s needs and the maintenance of the proper vegetation condition. Understanding the impact of drought on turfgrass species is essential to developing strategies that enhance the adaptability of plants to drought stress. It is vital for maintaining green areas in cities under changing climatic conditions. Therefore, studies on the ability of turfgrasses to recover after periods of drought without irrigation are becoming increasingly essential. We conducted research to determine the possibility of reducing the negative impact of drought stress on the photosynthetic efficiency, the morphometric features of plant shoots and roots, and the distribution of biomass of Lolium perenne lawn cultivars in the initial period of growth by applying biostimulant with silicon. We also investigated how drought and silicon (Si) application affect the leaf and root anatomical structure of L. perenne plants. Studies on the influence of drought on the physiological, biometric parameters and anatomical characteristics of two L. perenne cultivars were carried out under two levels of soil moisture (well-watered plants—control and drought caused by the cessation of watering) and also two variants of Si application (with and without Si application). Plants were exposed to drought in the tillering phase for 21 days. After this time, all plants were provided with optimal soil moisture conditions for the next 14 days (recovery period). Measurements of physiological parameters and biometric features of plants were evaluated in four terms: after 7, 14 and 21 days of drought and after recovery. Drought stress in L. perenne cvs. resulted in decreasing values of physiological parameters, especially maximal fluorescence, the quantum efficiency of photosystem II and photosynthetic electron transport rate compared with the values of features in well-watered plants. These adverse impacts were reflected in decreased biomass-related traits: shoot number, shoots and roots biomass, as well as area and length of roots. The application of Si reduced the detrimental effects of drought by accelerating plant growth after stress and increasing the values of most of the investigated physiological parameters. Under drought stress conditions, Si application led to the development of two-cell-layer exodermis, which reduced the water losses in L. perenne roots and shoots and, as a result, improved the drought tolerance of plants.

Drought and allelopathic conditions impact the germination of seeds of grass and legume species used in mixtures on grassland. This study evaluated the effects of drought and Medicago sativa root extracts at different pH levels on the germination and characteristics of seedlings of Lolium perenne and selected Medicago species. Two experiments were carried out: the first explored the effects of drought induced by PEG solutions (0.0, −0.3, and −0.6 MPa) under silicon (Si) application; the second studied the influence of Medicago sativa root extracts (12 and 24 g/100 mL H₂O) and variable pH solutions (control, 5.0, and 6.5) on seed germination. Germination was carried out on Petri dishes for individual species and in two-species mixtures. The drought conditions did not affect the germination capacity of seeds, but it increased the dry weight of the seedlings of the tested species. The application of silicon decreased the root length of the seedlings of all species, independent of the germination conditions. The higher concentration of M. sativa root extract combined with the studied pH solutions had an inhibitive impact on the germination capacity of L. perenne. Our findings revealed that the lower concentration of M. sativa root extract had a beneficial effect on the morphological features (length of roots and leaves, fresh and dry weight) of the seedlings when germination was carried out separately for both species. In the mixture, the effect was especially marked for L. perenne (only in terms of the root length and fresh weight of seedlings). The applied root extracts in combination with the acidic pH conditions limited the germination capacity and growth of the seedlings of L. perenne the most when germination was performed separately. It was concluded from this study that silicon application did not improve the germination capacity of seeds under drought conditions, whereas the germination of L. perenne seeds in a mixture with M. sativa mitigated the negative allelopathic effects of M. sativa root extracts on the seed germination capacity and morphological features of seedlings of L. perenne.