LONG-TERM SOIL MOISTURE STATUS IN SOUTHERN ALBERTA

Abstract

Nineteen years of soil moisture content data at Lethbridge and two locations near Turin (Turin 1 and Turin 2) in southern Alberta were examined to evaluate the efficiency of follow for conserving moisture, and to calculate the long-term mean amount of water recharge during growing and nongrowing seasons under a fallow-cereal, 2-yr rotation and a continuous cropping system. Soil samples were taken annually from 1969 to 1987 to a depth of 120 cm in 30-cm intervals in the spring (early May) and fall (late September). A method for testing differences of means between nonstandard data using localized uncertainty associated with sliding polynomial smoothing was used to test for differences in the soil moisture contents due to cultural practices. The available soil moisture content of the soil to 120-cm depth was at least 50% of available water-holding capacity (AWHC) of the profile for the fallow treatment at Lethbridge and Turin 2, and, except in some years, at Turin 1. At seeding time, there was an average of 69 mm more available water (AW) in the fallow field than in the continuous cropping field at Lethbridge and 30, 35 and 27 mm more AW in the fallow field than in the fresh stubble field of a fallow-cereal, 2-yr rotation for Lethbridge, Turin 1 and Turin 2, respectively. The overall mean precipitation conserved as soil moisture for the fallow-cereal rotation practice was 23, 29 and 23% for Lethbridge, Turin 1 and Turin 2, respectively. The significantly higher soil water content at the 90- to 120-cm depth for the fallow field than for other fields during various periods of time indicates that the soil water recharge from precipitation might be deeper in the fallow field than in continuous cropping and fresh stubble of fallow-cereal rotation fields. The deeper soil water recharge could increase the available soil moisture for crop production and it could also contribute to ground water recharge. Key words: Soil water, available water content, continuous cropping, summerfallow