Soil water drying and recharge rates as affected by tillage under continuous barley and barley-canola cropping systems in northwestern Canada

In areas of the northwestern Canadian Prairies, barley and canola are grown in a short growing season with high rainfall variability. Excessively dry soil in conventional tillage (CT) in dry periods and excessively wet soil i n no-tillage (NT) in wet periods could cause a significant decrease in crop production by influencing the availability of soil water. The effects of C T, NT and NT with a 7.5-cm residue-free strip on the planting rows (NTR) on soil water drying (-dW/dt) and recharge (dW/dt) rates were studied in 1992 and 1993 during wet and dry periods to evaluate the impact of NTR, NT and CT systems on soil moisture condition. The soils, Donnelly silt loam and Do nnelly sandy loam (both Gray Luvisol) were selected and soil water content by depth was measured by time domain reflectometry. Water retained at 6 mat ric potentials from -5 to -160 kPa were observed. In the field study, -dW/d t was significantly greater in CT than in NT in the silt loam for the 0- to 30-cm layer during the first 34 d after planting in 1992. The 0- to 30-cm soil layer in CT and NTR dried faster than in NT during a period immediatel y following heavy rainfall in the silt loam in 1993. The drying coefficient (-K-d) was significantly greater in CT and NTR than in NT in the silt loam soil in 1993 and in the sandy loam soil in 1992 in the top 30-cm depth. Th e recharge coefficient (K-r) was significantly greater in NT and NTR than i n CT for the silt loam soil. The NTR system increased the -dW/dt by 1.2 x 1 0(-2) to 12.1 x 10(-2) cm d(-1) in 1992 and 1993 in the silt loam soil and by 10.2 x 10(-2) cm d(-1) in 1993 in the sandy loam soil as compared with N T. The dW/dt was 8.1 x 10(-2) cm d(-1) greater in NTR in 1992 and 1993 in t he silt loam soil and was 1.9 x 10(-2) greater in NTR in 1992 than in CT in the sandy loam soil. The laboratory study indicated that NT soils retained more water than the CT soils. The NTR practice maintained better soil mois ture conditions for crop growth than CT in dry periods than NT in wet perio ds. Compared with NT, the NTR avoided prolonged near-saturated soil conditi ons with increased soil drying rate under extremely wet soil.