Soil water dynamics over 12 growing seasons on irrigated fully-phased dry bean–potato–wheat–sugar beet rotations under conventional and conservation management
Larney, F.J., Pearson, D.C., Dill, G.H, Schwinghamer, T.D., Zvomuya, F., Blackshaw, R.E. and Lupwayi, N.Z. 20xx. Soil water dynamics over 12 growing seasons on irrigated fully-phased dry bean–potato–wheat–sugar beet rotations under conventional and conservation management. Can. J. Soil Sci. (In press).
Plain language summary
This 12-yr (2000–11) study provided comparative analysis of plant-available water and its response to conservation soil management (four bundled pillars of reduced tillage, narrow-row dry bean, compost addition, cover cropping) for four major crops (dry bean, potato, soft wheat, and sugar beet) in the irrigated region of southern Alberta. The traditional visual monitoring or ‘crop condition’ irrigation scheduling approach used in our study was adequate for dry bean and sugar beet, as management allowable depletion (using a 60% plant-available water threshold) was exceeded on only 11–15% of neutron probe count days during 12 yr. The approach was less successful for wheat (management allowable depletion exceeded on 30% of count days) and potato (management allowable depletion exceeded on 43% of count days). Over the 12-yr, 51% of neutron probe count days showed significant crop species effects on plant-available water in the 0–50 cm layer. Dry bean had significantly higher plant-available water than potato on 28%, and wheat on 19% of count days, that agreed with lower water use requirements of dry bean vs. potato or wheat. However, dry bean and sugar beet had similar levels of plant-available water at 0–50 cm on 92% of count days, despite these crops having different effective root zones (0–60 cm, dry bean; 0–100 cm, sugar beet). While adoption of conservation practices led to instances of higher plant-available water, the magnitude of the effect depended on crop in the order: potato > dry bean > wheat > sugar beet.
Dry bean (Phaseolus vulgaris L.), potato (Solanum tuberosum L.), wheat (Triticum aestivum L.), and sugar beet (Beta vulgaris L.) are mainstays of irrigated crop production in southern Alberta. Concerns about soil quality and sustainability instigated a 12-yr (2000-11) rotation study to compare conventional (CONV) with conservation (CONS) management practices (reduced tillage, narrow-row dry bean, compost addition, cover cropping). Plant-available water (PAW) was measured using a neutron probe (10–16 count days season-1, n = 148) for all phases of 4-yr (dry bean–potato–wheat–sugar beet) rotations under CONS and CONV management. A visual monitoring approach was used for irrigation scheduling. For dry bean and sugar beet, management allowable depletion (MAD) was exceeded on only 11–15% of neutron probe count days over 12 yr. However, MAD was exceeded on 30% of count days for wheat, and 43% for potato. Significant crop × management interactions showed that PAW was higher with CONS management most frequently on potato, followed by dry bean, wheat, and sugar beet. This order reflected the prevalence of CONS practices directly impacting each crop. Regression analyses showed that potato, wheat, and sugar beet yield increased significantly as mean growing season water table depth (WTD) increased. This was explained by yield suppression due to excessive soil wetness in seasons with high rainfall and shallow WTD. The study provided comparative soil water dynamics for four major irrigated crops in southern Alberta, over a 12-yr period, which included record high and low growing season precipitation (220% to 40% of normal).