Dryland Soil Nitrogen Conservation As Influenced By Tillage, Cropping Sequence, and Nitrogen Fertilization.

Management practices are needed to reduce dryland soil N losses through N leaching and N₂O emissions (a greenhouse gas) by increasing soil N storage and reducing N fertilization rate without influencing crop yields. The effects of tillage and cropping sequence combination and N fertilization rate were studied on N contents in dryland crop biomass, surface residue, and soil at the 0- to 120-cm depth, and estimated N balance from 2006 to 2011 in eastern Montana. Treatments were no-till continuous malt barley (NTCB), no-till malt barley-pea (NTB-P), no-till malt barley-fallow (NTB-F), and conventional till malt barley-fallow (CTB-F), each with 0, 40, 80, and 120 kg N ha^-1. Biomass and surface residue N were greater in NTB-P or NTCB than in CTB-F and NTB-F in all years, except in 2006 and 2011, and increased with increased N rate. Soil total N (STN) at 0 to 60 cm decreased at 254 kg N ha^-1 yr^-1 from 2006 to 2011, regardless of treatments. At most depths, soil NH₄-N content varied, but NO₃-N content was greater in CTB-F than in other cropping sequences in all years, except in 2006. Estimated N balance after accounting for all sources and sinks of N after six years was greater in NTB-P with 40 kg N ha^-1 than in other treatments. No-till continuous cropping increased biomass and surface residue N storage but conventional till crop-fallow increased soil available N. Because of increased soil N storage and reduced N requirement to malt barley, NTB-P with 40 kg N ha^-1 may reduce N loss due to leaching, volatilization, and denitrification compared to other treatments.