Productivity and forage quality of smooth brome and alfalfa in monocultures and crop mixture in semiarid climate

Perennial grasses are vital for livestock feed and play a critical role in maintaining and enhancing soil fertility. This study evaluated the productivity of perennial grasses, specifically alfalfa (Medicago sativa L.) and smooth brome (Bromus inermis Leyss.), grown as monocultures and in a binary mixture, under rainfed conditions in a semiarid climate on dark-chestnut soil. The research aimed to elucidate the dynamics of formation of forage yield across multiple years of cultivation. The study was performed in the field trials with randomized design in four repetitions; the outcomes were analyzed through common analysis of variance with estimation of the Fisher’s least significant difference. The results revealed that the monocultures of smooth brome and alfalfa exhibited significantly lower yields (in terms of dry matter and feed units) compared with the alfalfa-brome mixture. Over the study period, the alfalfa’s initial dominance in the mixture gradually declined, with smooth brome becoming the dominant species by the end of the cultivation cycle. The forage quality, assessed according to crude protein and fat content, was highest in the alfalfa monoculture and the alfalfa-brome mixture, whereas the smooth brome monoculture was inferior. Although the smooth brome monoculture provided the lowest yields of feed units and digestible protein, they contributed essential crude fiber in the mixture, which supports healthy digestion in cattle. The alfalfa-brome mixture extracted the highest amount of nitrogen from the soil but, due to alfalfa’s nitrogen-fixing capacity, maintained sufficient nitrogen return to sustain soil fertility. By contrast, the smooth brome monoculture extracted the least nitrogen and did not contribute to soil nitrogen accumulation. The alfalfa monoculture exhibited the highest coefficient of nitrogen fixation, though the difference compared with the mixture was statistically non-significant. Consequently, the mixture of alfalfa and smooth brome, with varying dominance over the years of cultivation, enhances dark-chestnut soil fertility and provides balanced green fodder for cattle without requiring mineral nitrogen fertilizers or irrigation.