Annual ribwort plantain and alfalfa mixtures enhance forage accumulation and reduce nitrate

Nitrate (NO₃) leaching from alfalfa (Medicago sativa L.) cultivation in autumn and sustaining high forage accumulation under dry conditions is a serious problem in farming. In this study, mixtures of alfalfa and ribwort plantain (Plantago lanceolata L.) had agronomic advantages for forage accumulation compared to corresponding mixtures of alfalfa and a grass species (meadow fescue [Festuca pratensis Hudson]). The ribwort plantain and alfalfa mixtures accumulated twice as much forage as the reference mixtures with meadow fescue. Most of the forage accumulation was accounted for ribwort plantain due to poor initial alfalfa development. Ribwort plantain suppressed alfalfa and all weed species from as early as July and continued increasing forage accumulation until early autumn. At the same time, ribwort plantain contributed more than meadow fescue to a reduction in NO₃-N. Significantly lower NO₃-N shares in the soil were observed, on average, in mixtures with ribwort plantain and alfalfa in the 0.6- to 1.2-m soil depths in autumn. Due to the inhibition of nitrification by ribwort plantain, NH₄-N was present in the soil solution of the sandy soil at the trial site to a greater extent in autumn compared to alfalfa and the mixtures with meadow fescue. Due to the highly competitive power of ribwort plantain, it should only be sown in mixtures with alfalfa at seed rates of 100 germinating seeds m⁻².