Impact of fly ash amendment and incorporation method on hydraulic properties of a sandy soil

Coal fly ash has physical and chemical characteristics that make it useful as a soil amendment, one of the more important being the potential to permanently improve the soil water relations of sandy, drought-prone soils. We axemined changes in the infiltration rate and water holding capacity of a sandy soil after application of high rates (up to 950 Mg ha(-1)) of a Class F fly ash. Fly ash was applied to large field plots by either conventional tillage (CT; moldboard plow-disk) or intensive tillage (IT; chisel plow-rotovate-disk), and to microplots using a rototiller. Infiltration rate (i) was measured in both studies with a disk permeameter on three occasions over a 12-month period. Ash effects on gravimetric water content (theta(g)) at the 0-40 cm soil depth were measured during a 168 hr period following a 2.5 cm rainfall event and water release curves (33 to 500 kPa) were constructed in the laboratory using soils from the large plots. In both studies i was decreased by similar to 80% one year after addition of fly ash and theta(g) in ash-amended soil was higher than unamended soil throughout the 168 hr monitoring period. Soil water distribution varied with tillage; the IT treatment had the highest theta(g) increases in the 0-20 cm depth while the CT treatment had theta(g) increases throughout the 0-40 cm depth. Soil water content and distribution in ash-amended microplots were similar to IT treatments. Fly ash amendment not only increased water holding capacity but also increased plant available water by 7-13% in the 100-300 kPa range. These results suggest fly ash amendment may have the potential to improve crop production in excessively drained soils by decreasing i and increasing the amount of plant available water in the root zone.