EFFECT OF FERTILIZER ON SOIL pH AFTER 17 YEARS OF CONTINUOUS CROPPING IN SOUTHWESTERN SASKATCHEWAN

Abstract

Measurements of soil pH were made in the 0- to 2.5-cm, 2.5- to 7.5-cm, and 7.5-to 15-cm depths of a loam soil in two long-term (17 yr) continuous wheat rotations. One rotation received only ammonium phosphate fertilizer, while the other rotation received ammonium phosphate fertilizer plus ammonium nitrate fertilizer at an average rate of N of 35 kg∙ha−1∙yr−1. Soil pH was not measured at the start of the experiment. Measurements made at eight times between April and October 1983 showed that average pH in the surface 15 cm was lower in the rotation receiving N and P, compared to the one receiving only P, by about 0.5 pH units (pH 5.9 vs. 5.4 in dilute CaCl2). The soil pH varied considerably during the growing season and seemed to be inversely related to soil NO3-N. These pH changes occurred in a well buffered soil with CEC of 23.5 meq∙100 g−1. Scientists recommending that producers on the Prairies move to a more extended crop rotation so as to reduce land degradation, should bear in mind that eventually there may be a need to lime the soils to maintain production since such a system will necessitate the increased use of N fertilizers. Key words: pH changes during growing season, pH versus depth, soil acidity