Manure Effects on Soil N in Eroded and Non-eroded, Sprinkler-irrigated Soil.

Manure effects on nitrate-N transport through irrigated, low-organic matter calcareous soil are not well known.  This field study quantified the effects of a one-time fall application of stockpiled dairy manure and urea on in-season and over-winter nitrate-N transport through non-eroded and eroded (desurfaced) soil, termed topsoil and subsoil, respectively.  The study was conducted for 29 months in Portneuf silt loam (Durinodic Xeric Haplocalcid) cropped to sugarbeet (Beta vulgaris L.), then winter wheat (Triticum aestivum L.) near Kimberly, ID.  We applied four treatments to subsoil: a control and manure applied at dry rates of 23, 46, and 69 Mg ha^-1, and three treatments to topsoil: a control, urea applied at 84 kg N ha^-1 (per soil test), and manure at 46 Mg ha^-1.  The commonly applied 23 Mg ha^-1 manure rate supplies about 139 kg N ha^-1 via mineralization the first year.  Irrigations were scheduled using predicted evapotranspiration, were usually 12 h long, and applied water at 4 mm h^-1 with a solid-set sprinkler system.  One 32-mm-diameter, 1.83-m-deep soil core was collected from each plot, fall and spring, from November 2002 to April 2005.   During the first winter in the topsoil’s 46 Mg ha^-1 treatment, the N content of the first 0.3 m decreased 65% (to 40 mg kg^-1) while in the second 0.3 m it increased 80% (to 90 mg kg^-1).  The entire site’s profile N mass per unit area in the first winter increased 33%, along with a doubling of each manure-amended profile’s N proportion at the 0.6 to 1.2 m depth.  By the third fall, the N in all treatments was 10 mg kg^-1 or less to a depth of 1 m or more.  Profile N was greater below than above 0.9 m in nearly every treatment from Fall 2003 through Fall 2004.