Soybean Harvest

Residue Management for Moisture Conservation

With the exception of the northwest region, moisture limitations have been the norm in 2018 across Manitoba. Most regions received <200 mm over the growing season (map of accumulated precipitation). Ground water levels are also trending lower than normal in some areas (aquifer levels here).

We may be entering a new dry cycle, meaning we need to revisit strategies to conserve soil moisture. Drier conditions also give us the opportunity to reduce or eliminate tillage in part of the crop rotation in conventional-till systems.

Any type of tillage results in higher evaporative water loss compared to untilled soil (Figure 1). Each cultivator pass in the spring can remove approximately 10-12 mm of water from the soil.

Research conducted in Manitoba in the early 1980s showed that zero-till conserved moisture early in the growing season and increased crop water use efficiency by decreasing evaporation and surface runoff and by increasing infiltration and the amount of trapped snow.

Management Ahead of Soybeans and Pulses

On heavy clay at Indian Head, SK, zero-till increased field pea yield by 10%, flax by 23%, and spring wheat by 21% compared to conventional-till from 1987 to 1990, when growing season precipitation was 164-233 mm. During that period, researchers in Manitoba found that the performance of wheat, canola and peas grown on cereal stubble did not differ between conventional till (residue cover 20-42%) and zero-till (residue cover 62-88%) at Portage la Prairie (clay loam) and Carman (very fine sand), where growing season precipitation ranged from 91-242 mm. With crop productivity proving equal or better under zero-till than conventional-till systems, zero-till has been widely adopted across the Prairies where moisture deficits are typical.

Unfortunately, incorporating soybeans into crop rotations has resulted in re-introduction of tillage for long-time zero-tillers. Incorporating residue increases soil temperature, which in turn can increase emergence rates. Recently completed research in Manitoba, however, demonstrated no difference in soybean yield between tilled wheat stubble and zero-till wheat, oat and canola stubble when soybeans were planted within May 17-26 and soil temperature (>10°C) (see full report here).

Management after soybeans and pulses

Introducing zero-tillage may seem like a radical practice in the eastern half of the province. Though it may have been unpractical with cereal-oilseed rotations, the introduction of low-residue crops like soybeans, peas and dry beans into rotations makes experimenting with conservation tillage less risky. Recent on-farm research conducted in Manitoba found that seeding corn and wheat into zero-till soybean stubble had no effect on yield (Table 2). At a 2-inch depth, no difference in soil moisture or temperature was observed across any tillage treatment at any site during the emergence period the following spring. Even when soybean residue is left on the soil surface without incorporation, soybean residue broke down and ground cover was reduced by 31 – 57% from fall to spring (see full report here).