Optimizing relative seed frequency of intercropped pea and spring barley

Abstract In order to optimize relative seed frequency of intercropped pea ( Pisum sativum L.) and spring barley ( Hordeum vulgare L.), to achieve maximum relative yields and to gain a better understanding of interactions between yield formation and accumulation of nitrogen (N) and sulphur (S) under field conditions, field trials were conducted at several sites in Germany on long-term (>10 years) organically cultivated arable land in two years. These field trials investigated the effects of intercropping and the calculation of relative seed frequency in pea-barley mixtures to achieve maximum relative seed and shoot yields, as well as N and S accumulation. Under the given environmental conditions, a high degree of complementarity over a wide range of growing resources achieved relative total seed yields (RYT) of 1.35 and an increased N and S accumulation in the shoot of the mixture of 35% and 29% compared to the means of the pure stands of pea and spring barley. The increased complementarity of S resources (RYT S shoot = 1.29) was obviously a consequence of promoted vegetative growth caused by the increased complementarity of N resources of the cereal-legume mixture. To achieve the maximum seed yield and maximum N and S accumulation in substitutive mixtures of pea and spring barley, a relative seed frequency of 42%–88% pea seeds to 12%–58% spring barley seeds of their monocrop seeding rate has been calculated to be optimal. The availability of N in the soil of the respective environment, quantified by N accumulation in barley shoots, did not influence optimal relative seed frequency of the intercrop.