Wood ash, the residue remaining from the combustion of bark, sawdust and yard waste for energy generation for forestry product operations, is an effective liming material on acid agricultural soils. In northwestern Canada where the use of agricultural lime is constrained by high transportation costs, wood ash should be an appropriate substitute for lime. Here we compare the effects of wood ash and lime on crop production and soil properties of an acid soil in northwestern Alberta. Effects of Wood Ash vs. Agricultural Lime on Crop Production and Soil Chemical and Physical Properties Y. K Soon, M. A. Arshad, R. Azooz and N. Lupwayi, Beaverlodge, Alberta T0H 0C0, Canada Introduction Materials and methods Crop yield There were few lime treatment x crop type interaction, so only yields averaged across crops are presented. Canola tended to exhibit the smallest (or no) response to lime amendment. In Fig. 1, the crop yields expressed as a percentage of the check yield for each year showed that: (i) applying a low rate of lime as a band in the seed row had no effect on crop yield; (ii) except for agricultural lime in the first year (2002), amending the acid soil with 6.7 Mg ha -1 of wood ash or agricultural lime significantly increase crop yield; and (iii) yield was consistently slightly higher with wood ash than with lime but the difference was not significant. Yield response due to lime or wood ash was typically 20% greater or more compared to the check, and was low in 2006 probably because of moisture stress due to drought that year. Results and discussion Wood ash is a suitable substitute for agricultural lime for amending acid soil for crop production. It is comparable to lime in increasing soil pH and soil aggregation. In addition, wood ash has an advantage over agricultural lime in containing a modest amount of phosphorus. Most acid soils in northwestern Canada are also deficient in P, and amending these soils with wood ash should reduce P fertilizer requirement. This aspect of wood ash use require more field studies to quantify the extent to which P fertilizers can be reduced. Conclusions Agriculture and Agri-Food Canada Agriculture et Agroalimentaire Canada © 2003 The experiment was conducted on an Albright silt loam (Dark Gray Luvisol) near Beaverlodge, Alberta. The soil (0-10 cm) had 220 g sand kg -1, 340 g clay kg -1, 38 g organic C kg -1, and a pH (1:2, soil:0.01 M CaCl 2 ) of 4.9. Long-term mean annual temperature is 2 o C, and annual precipitation is 452 mm. The experimental design was a randomized, complete block design with three replicates. In spring 2002, agricultural lime and wood ash (none and 6.72 Mg ha -1 ) were broadcast applied and incorporated to at least 5 cm depth, and the plots were seeded to perennial forage (timothy grass and creeping red fescue) and annual crops (barley, canola and field pea grown in rotation). An additional set of plots received a band application of 300 kg granulated agricultural lime at seeding each year (until 2005). The plots were 5 x 10 m each and received no further tillage after lime incorporation. Soil samples were taken in 2003, 2004, 2005 and 2007, and pH, ammonium fluoride extractable P, and dry aggregate distribution measured. These and crop yield data were analyzed by Proc Mixed Procedure (SAS Institute 1997) Soil pH Differences in soil pH between years were minor, therefore only the averages of years are shown (Fig. 2a). Banding lime at 300 kg ha -1 had no measurable effect on pH, however, wood ash or lime at 6.7 Mg ha -1 increased soil pH by at least 1.7 pH units in the surface 5 cm, and by 0.3 pH unit in the next 5 cm layer. Little pH change was exhibited in the cm layer. The data indicated that wood ash had a similar liming effect as agricultural lime, at least through six growing seasons. Available soil P In addition to neutralizing soil acidity, wood ash also increased available soil P (Fig. 2b). Extracted P in the surface 5 cm of soil from the wood ash plots was double that of the check plots, and significantly higher (P=0.01) in the 5-10 cm layer. More available P with wood ash may at least partly explain the slightly higher yields observed with the wood ash treatment. Wood ash typically contains 1-14 mg P kg -1 ( Soil aggregation Agricultural lime or wood ash applied at 6.7 Mg ha -1 resulted in increased soil aggregation as measured by mean weight diameter (MWD) (Table 1). This can be attributed mostly to calcium added in the amendments. The crop grown before sampling also affected MWD with canola resulting in low MWD and the grasses in high MWD. Fig. 2: Effect of soil amendment on soil pH and extractable P Table 1: Lime treatment effects on soil aggregation as measured by mean weight diameter (mm). Data from 2003, 2004, 2005 and SEM=0.12 Check300 kg lime 6.7 Mg lime 6.7 Mg WA 4 yr mean Minimum Maximum , Measured in the 0-10 cm depth, and averaged across crops.