Nitrogen Cycling from Fall Applications of Biosolids to Winter Small Grains.

Fall-applied biosolids for small grain production in Virginia poses a NO₃^- leaching risk if more biosolids-borne organic and ammonia N are mineralized and nitrified than small grains can assimilate during the fall and winter. Moisture retention and infiltration properties of soils can exacerbate this risk. The influence of eight biosolids and urea N treatments on five parameters related to winter small grain production and environmental N dynamics was studied: 1) Mid-season biomass production, 2) Mid-season soil inorganic N, 3) Mid-season mineralizable N, 4) Grain yield, 5) Post-harvest soil residual inorganic N. Four field studies were established in fall 2012, and six were established in fall 2013. Anaerobically digested (AD) and lime stabilized (LS) biosolids were applied at estimated plant available nitrogen (PAN) rates of 50 kg N/ha and 101 kg N/ha in the fall. The 50 kg N/ha biosolids treatments were supplemented with 50 kg N/ha as urea in spring. Urea N was split applied at 0, 50, 101 and 151 kg N/ha, with 1/3 applied in fall and 2/3 in spring. Treatment did not affect mid-season soil inorganic N or mineralizable N in 2012-2013. Biosolids treatments produced more mid-season biomass on some coastal plain soils during both years. Increasing N rate and splitting N application increased grain yield and reduced residual NO₃-N in the coarser-textured coastal plain soil in 2012-2013. This effect was especially pronounced in biosolids-amended plots. Increasing N rate increased grain yield but did not affect on residual NO₃-N in the finer-textured coastal plain soil in 2012-2013.