Optimizing relative seed frequency of intercropped pea and spring barley

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.