Partitioning of Applied Nitrogen in Corn and Switchgrass in Soils of Variable Depths in Central Missouri, USA.

Deployment of biomass feedstock production systems in marginal lands with minimal external inputs is being recommended for sustainable feedstock supply. While nitrogen is critical for plant growth, injudicious application of fertilizer nitrogen in such marginal lands could magnify the existing non-point source pollution problems. Many marginal soils are shallow with an underlying impervious claypan boundary that restricts movement of water and roots. The objective of this study was to investigate the uptake and dissipation of applied nitrogen in corn and switchgrass based cropping systems in soils with a wide range of depth to claypan (DTC). Ammonium (¹⁵N) sulphate (5% atom enrichment) was applied in the switchgrass and corn microplots (46 x 46 cm²). Plant materials was harvested after the growing season along with soil cores up to a depth of 60 cm. Plant and soil samples were dried and ground into fine particles and sent to the Stable Isotope Laboratory at the University of California, Davis for analysis. Several nutrient uptake parameters were calculated based on the amount of isotope labelled nitrogen in plants and soil. Results showed that while there was no trend (13 to 18%) in the recovery of fertilizer nitrogen (RFN%) among the shallow and deeper soils, plant uptake and utilization of the applied fertilizer was more efficient in the deeper soils as evident from the nitrogen derived from fertilizer (NDF%) and utilization of fertilizer nitrogen (UFN%). These results suggest that the applied fertilizer was better utilized in soils that are deeper in comparison with shallower soils.