Submitted to: Journal of Soil and Water Conservation
Publication Type: Abstract Only
Publication Acceptance Date: July 8, 1999
Publication Date: N/A
Technical Abstract: Increases in soil organic C (SOC) from dairy manure help restore productivity of southern Idaho soils eroded by irrigation to expose calcareous subsoil. SOC increases likely improve these soils' structure, but such improvements have not been quantified. We studied SOC effects on aggregate stability before and after irrigation that simulated droplet impact under outer spans of the region's center pivots. We measured stability by wet sieving field-moist, 1- to 4-mm aggregates from the uppermost 5 mm of recently roller-harrowed Portneuf silt loam (Durinodic Xeric Haplocalcid) sampled just before and ca. 10 days after irrigation. We positioned two half-circle spray heads 6 m apart and facing each other to irrigate field plots. Each head had a rotating, 6-groove spray plate, was operated at 140 kPa nozzle pressure, and was 3 m above the soil surface. In October 1998, we applied about 130 mm of water at a constant 70 mm h/1 intensity in a single irrigation to replicated, 1 x 2 m plots differing in SOC due to past years' management. Prior to irrigation, aggregate stability increased nearly linearly from 78 to 93% as SOC increased from 3.6 to 10.7 g kg/1. Irrigation decreased surface aggregate stability by one third at each of three SOC concentrations. On average, for every 10 g kg/1 (i.e., 1%) increase in SOC, aggregate stability increased by 21 percentage points before irrigation and by 16 after irrigation. SOC increases from manure applied to soils with exposed subsoil were well correlated with increases in surface soil aggregate stability both before and after irrigation.