Maize and potato growth responses to heterogeneous nitrogen and shoot competition

Due to uneven fertilization, organic matter decomposition and complex community structure, soil nitrogen distribution was highly heterogeneous in intercropped farmlands. Consequently, intercropped crop growth was simultaneously influenced by inter-specific competition and heterogeneous nitrogen. However, there has existed limited knowledge on the relationship between inter-specific competition and heterogeneous nitrogen for crop growth. In the study, the intercropping of maize and potato, an overyielding system in the world, was choose as study objective; the crops were planted in large pots with control-released nitrogen fertilizer, applied either homogeneously or heterogeneously, with or without shoot competition. Plant biomass was measured and then relative interaction index (RII), root foraging precision (RFP) and land equivalent ratio (LER) calculated. The calculations explored the characteristics of the responsiveness of the two crops to heterogeneous nitrogen and shoot competition. The study showed that LER was greater under heterogeneous than under homogeneous nitrogen condition. This was probably due to higher RFP of the two crops under shoot competition. Under shoot competition, however, potato biomass was lower in heterogeneous nitrogen treatment. This was the contrast for maize, whereas without competition, growth of both crops was enhanced by heterogeneous nitrogen treatment. These variations in growth were consistent with those in functional traits including root shoot ratio (RSR), root leaf ratio (RLR), leaf mass fraction (LMF) and root mass fraction (RMF). Consistent with the variations in growth under homogeneous nitrogen treatment, heterogeneous nitrogen treatment increased maize RII and decreased that of potato. Thus while potato had competitive advantage under homogeneous nitrogen treatment, maize had competitive advantage under heterogeneous nitrogen treatment. These results suggested that heterogeneous nitrogen treatment enhanced crop growth and changed relative competitive ability of intercropped crops. Also shoot competition affected characteristics of root foraging of crops. Our study therefore demonstrated that interactions, which affected crop performance, occurred between shoot competition and homogeneous nitrogen treatment. This finding enriched existing knowledge on nitrogen use characteristic which enhanced understanding of complex crop growth performance in intercropped systems.