Dynamics of root length and distribution and shoot biomass of maize as affected by intercropping with different companion crops and phosphorus application rates

Maize-based intercropping, especially with legumes, can result in overyielding of the whole cropping system and lead to efficient utilization of soil phosphorus (P). Field experiments were conducted in 2010 and 2011 to investigate the mechanisms behind overyielding of maize via root length and distribution in intercropping systems and how P application and companion crops may influence the process. The main plots received P applications of 0, 40, and 80 kg ha−1 and the sub-plots comprised maize (Zea mays L.) intercropped with turnip (Brassica campestris L.), faba bean (Vicia faba L.), chickpea (Cicer arietinum L.), or soybean (Glycine max L.), and monocropped maize. At turnip harvest and maize at stem elongation, total root length, growth space and corresponding shoot biomass (on a per plant basis) of maize intercropped with turnip, faba bean and chickpea were suppressed, especially in maize/turnip intercropping. Roots of maize and associated crops can intermingle with each other and the stronger the associated roots, the more depressed will be the corresponding maize root development and shoot biomass. At faba bean and chickpea harvest and maize at tasseling, total root length, growth space and corresponding shoot biomass of intercropped maize recovered to the same values as monocropped maize on a per plant basis. At soybean harvest and maize at grain-filling stage, total root length, growth space and shoot biomass of maize intercropped with turnip, faba bean, chickpea and soybean surpassed those of monocropped maize and showed overyielding and later maturity phenomena until harvest on a per plant basis. Total root length of maize on a per plant basis in the top 100 cm of the soil profile at stem elongation and in the top 30 cm at grain-filling stage and the shoot biomass of maize from stem elongation to grain-filling stage and at harvest were sensitive to P application. There were no interactions between P application rate and cropping system. A 'competition-recovery-overyielding' process was found in the dynamics of root length, distribution and corresponding shoot biomass of maize intercropped with turnip, faba bean and chickpea and the dynamics of root length and distribution correlated well with the corresponding shoot biomass of maize.