SPRING SOIL WATER, PRECIPITATION, AND NITROGEN FERTILIZER: EFFECT ON BARLEY YIELD

Abstract

Results of a 5-yr field experiment were used to develop a regression model (R = 0.94) describing barley yield as a function of available soil water in the spring (W_s), growing season precipitation (GSP), and N fertilizer. Yields on independent fertility plots having W_s and GSP levels within the scope of the data used in deriving the equation were in close agreement with those predicted by the model. Equations were developed for W_s defined as soil water on either 15 May or 1 June and GSP from then until 31 July. Including rainfall received after 31 July in GSP decreased the accuracy of the model. At the levels of GSP occurring in the study, GSP and W_s affected yield to a similar degree, but with the long-term average GSP and W_s levels at Lethbridge, W_s was only about half as effective as GSP on stubble and one-third as effective on summer fallow. Growing season precipitation had a three times greater effect on barley response to N fertilizer than W_s. The model would allow a producer to base his fertilizer N rate on a gravimetrically determined W_s level at seeding and use the GSP probability as his risk level. Using the current cost:price ratio of N fertilizer and barley, he can optimize his N fertilizer level based on the measured W_s.