How Does Nitrogen and Perenniality Influence Belowground Biomass and Nitrogen Use Efficiency in Small Grain Cereals?

Abstract

Perennial cropping systems typically exhibit extensive root systems that contribute to important ecosystem services. However, the root systems and the distribution of roots throughout the soil profile in novel perennial grains have yet to be reported. In addition, understanding the full impact of perennial grain cropping systems on belowground processes requires knowledge of how N regimes might influence biomass partitioning and N retention. Here, we quantified root biomass distribution, crop biomass allocation, and whole‐crop fertilizer N use efficiency (NUE, defined as the ratio of plant N to total N fertilizer applied) in annual winter wheat (Triticum aestivum L. ‘Caledonia’) and perennial intermediate wheatgrass [IWG, Thinopyrum intermedium (Host) Barkworth & D.R. Dewey] across three N treatments over a 3‐yr period. Nitrogen treatments included Low N (90 kg ha−1 of poultry manure), Mid N (90 kg ha−1 of urea), and High N (135 kg ha−1 of urea). As a perennial plant, IWG had significantly greater root biomass than annual wheat to the 40‐cm depth (p < 0.05), but no differences were found between the crops at deeper depths. Nitrogen treatments did not affect root biomass, except for IWG in its fourth year (p < 0.05). Regardless of N level, IWG always had greater whole‐crop NUE than annual wheat (p < 0.05). Results demonstrate that IWG roots represent a large pool of N that contributes to enhanced NUE and ultimately greater N retention than in annual wheat roots.