Productivity of Gramineae Species From Nitrogen Produced By Autumn Olive and Cowpea Grown in Soils of Differing Quality.

Applying ecological principles to the current industrial agricultural practices has the potential to lessen human impact on the environment and enhance long-term food sustainability.  Interplanting crops with biologically nitrogen fixing (BNF) plants is an agroecological method that offers promise for enhancing nitrogen use efficiency in agricultural systems.  In this study, six treatment pairs were used to analyze the effect of the BNF plants autumn olive and cowpea on corn and switchgrass.  Leaf chlorophyll content, leaf number, rate of photosynthesis, transpiration rate, and biomass accumulation for treatment pairs grown in two soils of different type and quality were measured weekly. Acetylene reduction was used to confirm nitrogen fixation in the BNF plants and to estimate nitrogen availability in the soil for both plants.  Autumn olive and cowpea demonstrated high rates of nitrogen fixation at 3.8 ethylene-acetylene GC peak area ratio per gram fresh weight of nodules per minute of incubation.  Leaf number and biomass were higher in switchgrass growing with autumn olive as compared to switchgrass monoculture.  These data suggest a nitrogen benefit to switchgrass from interplanting with autumn olive.  Corn leaf number and leaf chlorophyll content were also significantly higher when grown with autumn olive, although this effect is potentially exaggerated because the autumn olive plants were smaller than cowpea or corn plants.  Corn, cowpea, and autumn olive exhibited greater productivity in Perrinton (higher quality) soils than in the coarser textured Oshtemo soil.  Although autumn olive is an aggressive invasive, our results indicate that growing it in interplanted production systems could provide real-time nitrogen supplementation to fossil-fuel derived nitrogen fertilizer, particularly in switchgrass stands produced for biomass