FURROW EROSION AND AGGREGATE STABILITY VARIATION IN A PORTNEUF SILT LOAM

Numerous soil factors, including aggregate stability, affect erosion rates from irrigated furrows. Since aggregate stability varies within growing seasons, furrow erosion may vary as well. The study objectives were to (1) measure furrow erosion and aggregate stability periodically over two growing seasons, (2) statistically characterize the temporal variation in furrow erosion and aggregate stability, and (3) relate variation in erosion rates to changes in aggregate stability and other soil properties. Erosion rates from replicated, previously unirrigated furrows in fallow plots on a Portneuf silt loam (coarse-silty, mixed, mesic Durixerollic Calciorthid) at Kimberly, Idaho, USA, were measured every 2-3 weeks from mid-May through mid-August 1988, and from late-April to late-August 1989. During each 6.5-h irrigation, three furrows in 1988 and four furrows in 1989 were irrigated at an inflow rate of 11.3 I min(-1). At each irrigation, soil samples were taken to a depth of 5 cm from the bottom of furrows adjacent to or near those irrigated. From these samples, soil gravimetric water content was measured and aggregate stability was determined by wet sieving. Erosion from furrows not previously irrigated varied greatly when measured throughout two growing seasons. For both years, erosion rates were significantly lower later in the growing season than earlier. For a 4.0% slope area in 1988, furrow erosion rates varied over the entire season by a factor of six or more while aggregate stability varied (increased) by only 17%. Thus, aggregate stability was not significantly correlated with furrow erosion rates.