Wheat and Pea Response to Lime Source and Rate in Acidified Soils of Northern Idaho.

Soil pH has been declining in northern Idaho and eastern Washington for decades, due primarily to the long term use of synthetic nitrogen fertilizer and a strong cereal-based cropping system.  In some cases, plants grown in low pH are exhibiting aluminum toxicity, particularly in regions that were historically forested.  Although tolerant and adapted wheat varieties have been identified for this region, these varieties will not perform well as soil becomes progressively more acidified, and similar tolerance is not available for susceptible rotation crops such as barley, cool season legumes and canola.  To maintain or improve productivity, these fields will eventually require applications of lime to increase soil pH.  There are few local sources of high quality calcium carbonate, making lime application costly.  In addition, not all soils in northern Idaho are in need of lime application, necessitating additional information on regional soil pH and other soil factors that are influenced by soil acidity.  Research trials were established at three locations in northern Idaho and eastern Washington to examine three sources of lime application at three rates in both winter wheat and spring pea.  Modest rates of 500, 1000 and 2000 lb/acre of material were applied in replicated trials.  At one location, eight months after application of 2000 lb of calcium carbonate per acre, soil pH was found to increase by 0.3 units from 4.8 to 5.2 in the upper 0 to 7.5 cm of soil.  Furthermore, there was a 7.4 % increase in the base saturation (% of CEC) of calcium to 56.4 % and decrease in the aluminum concentration from 14.3 ppm to 2.6 ppm as determined by KCl extraction.  No yield response was observed in a tolerant winter wheat variety (Madsen).  However, in spring pea there was an incremental increase in yield observed with increasing application rates of lime.  Changes in soil pH and aluminum concentrations will continue to be monitored at these sites to evaluate the longer term impact of application.  Ultimately, rate and frequency of lime applications will need to be tailored to optimize crop yield responses under specific soil conditions.