Diversifying Crop Rotation Boosts Systems Productivity By 35%.

In many rainfed dry areas, summerfallowing practices are used to conserve rainwater for the crop in the following year. Summerfallowing with tillage promotes the release of N through the mineralization of soil organic matter. However, summerfallowing leaves land without any crops planted for one entire growing season. A summerfallow is a lost production opportunity with negative impacts on the environment. In the recent decades, producers in the northern Great Plains of North America have been using alternative systems to retain the beneficial features of summerfallowing with little or no environmental impact. However, quantitative data are lacking in terms of how a pulse-based diverse cropping system may enhance soil water conservation, improve soil N availability, and increase systems’ productivity compared to traditional cereal monoculture. A 3-yr cropping sequence study was conducted in southwestern Saskatchewan in which various rotational sequences were evaluated for five cycles between 2005 and 2011. The results showed that the total amount of water in the depth of 1.2 m at planting varied largely from year to year and is a reflection of the quantity of water remaining at the harvest of the previous crops and the postharvest water recharge to the soil profile. Both pulse- and summerfallow-based systems enhanced soil N availability, but the pulse system did so through biological fixation of atmospheric N₂, whereas the summerfallow-system enhanced soil N through ‘mining’ soil with depleting organic matter. Averaged across the five cycles of the 3-yr crop sequences, the pulse system increased total grain production by 35.5%, improved protein yield by 50.9%, and enhanced fertilizer-N use efficiency by 33.0% compared with summerfallowing system. Diversifying cropping systems with annual pulses can serve as an effective alternative to summerfallowing for enhancing N use efficiency and increasing systems’ productivity in rainfed dry areas.