Effects of interspecific interactions and nitrogen fertilization rates on above-and below-growth in faba bean/mazie intercropping system

Plant root systems play an important role in uptake of water and nutrients from soil.The spatial distribution,morphology of plant roots and above-ground growth can be influenced by interspecific interactions and N fertilization.Legume/cereal intercropping is broadly recognized as a sustainable production pattern because it can offer improved productivity,more effective utilization of resources,and reduce industrial N input by exploiting biological N2 fixation as a more economic and environmentally-friendly way. Little is known about the effects of below-ground interactions on the root morphology of intercropped crops under field.In order to verify the effects of legume/cereal intercropping and N fertilization on the root spatial distribution of cron root systems and their root morphological characters,as well as above-ground growth,a plot experiment featured by root separation by means of barrier and different N fertilization experiment were conducted at Wuwei Experimental Station(latitude 38°37′N,longitude 102°40′E) of Gansu Academy of Agricultural Sciences in 2007.Both experments were designed as 2 × 2 two factors block design with three replicates.The roots of both crops at 0-120 cm soil layer were sampled at the harvest stage of faba bean by auger,i.e.at the tasselling stage of maize.The spatial distribution and morphological characterics of roots,above-ground biomass and N uptake of both crops,and nodule biomass of faba bean were analysized.Furthermore,the correlationships between above-and below-ground growth parameters were also analysized. The results showed that interspecific interactions and nitrogen application increased the root bulk density,root length density,root surface area and root volume of faba bean and maize in the vertical and horizontal dimensions.Root average diameter was reduced by interspecific interactions,and increased by nitrogen application.Root length density and root surface area of both crops were positively correlated with grain yield and N uptake,while the relationships between root length density and surface area,and nodule biomass of faba bean were negative.And the soil moisture at the tasselling stage and grain yield N uptake of maize showed the significant negative correlations.The roots of intercropped maize could extend into the space of intercropped faba bean,whereas the less roots of intercropped faba bean expanded into the space of maize roots,suggesting the intercropping extended the root ecological niche of maize in the horizontal dimension.The roots of faba bean and maize mainly distributed in 0-40 cm and 0-60 cm soil layer,respectively.It was found that the roots of intercropped maize at 60-120 cm soil layer were more than that of mono-cropped maize and maize with root barrier,and the deeper distribution of roots of intercropped maize should be in favor of competition-recovery growth at the later growth stage. In conclusion,both intercropping and N fertilizer expanded the root spatial niche of intercropped crops in the vertical and horizontal directions,and changed the root morphology of both crops.They increased the water and nutrient uptake,and the productivity of intercropping system was thus raised.