Competition for and utilisation of sulfur in sole and intercrops of pea and barley

Deficiency of plant available sulfur (S) has been recognised as a limiting factor for crop production in many regions of the world. However, knowledge of the effect that low S availability has on the growth dynamics and nitrogen (N) use of cereal-legume intercrops is limited. Pea (Pisum sativum L.) and barley (Hordeum vulgare L.) were grown in a pot experiment as sole crops and intercrops with or without the addition of S in the form of gypsum. At three consecutive harvests total aboveground biomass and corresponding soil samples were taken for analysis. Harvested biomass was analysed for total S and N content and soil samples for their sulfate content. The cumulative Relative Efficiency Index (REIc) was used to study the interspecies growth, N and S dynamics in the intercrop and the Land Equivalent Ratio (LER) was used to evaluate intercrop performance. In the initial growth phase earlier germination gave barley a growth and nutrient use advantage compared to pea (REIc values < 1). However, shortly after this pioneer phase, the importance of initial size differences decreased relative to the effect of species identity in determining the competitive strength of the two species and by the end of the growth period pea was very dominant (REIc values > 1). The limited availability of soil N played a pivotal role in creating the nutrient and growth dynamics observed in the intercrop and increasing the availability of S did not change this markedly. Most likely as a result of its N₂ fixing ability the pea component came to dominate the intercrop both with respect to yield and nutrient accumulation, accounting for 77% of total dry matter production, 90% of N uptake and 85% of S uptake, averaged across S treatments. LER values calculated on the basis of total aboveground dry matter, and N and S accumulation all exceeded 1, indicating that available growth resources were used more efficiently by the intercrop than the average sole crop.