Effect of cropping frequency, wheat classes, and flexible rotations on yield, production, and nitrogen economy in a Brown Chernozem

Non-Peer ReviewedProducers in the semiarid Canadian prairies frequently summerfallow (F) to conserve water, control weeds, and to maximize soil N reserves; however, this practice often results in soil degradation. A crop rotation experiment was initiated in 1987 on a medium textured, Orthic Brown Chernozem at Swift Current, to determine the most ideal cropping frequency for this region and whether a fixed rotation such as fallow-wheat-wheat (F-W-W) would be more effective than flexible rotations in which fallowing is decided each spring based on criteria such as available soil water (if water), or the need to control perennial weed infestations (if weeds). The study also compares the production of traditional Canada Western Red Spring (CWRS) wheat class with the newer higher yielding (Hy), Canada Prairie Spring (CPS) wheat class. The rotations included F-W-W, F-W-W-W, F-Hy-Hy, Continuous wheat (Cont W), Cont W (if weeds), and Cont W (if water). Over the study period (1987-1998), weather conditions were generally favourable and yields were above average for this region. Canada Prairie Spring wheat out-yielded CWRS by 35% when grown on fallow and by 15% when grown on stubble; however, straw yields of the two wheat classes were similar on fallow and CPS was 7% less than CWRS on stubble. Harvest index (HI) averaged 45% for CPS and 40% for CWRS wheat. Grain N concentration averaged 25.5 g kg-1 for CWRS and 22.5 g kg-1 for CPS; straw N concentration averaged 4.0 g kg-1 for CWRS and 4.6 g kg-1 for CPS. Nitrogen yield for grain from CPS was 13% greater than from CWRS when grown on fallow, but class had no effect when wheat was grown on stubble. Nitrogen yield of straw was generally not affected by wheat class. Nitrogen yield of the above-ground plant parts generally mimicked grain N yield responses. Nitrogen harvest index (NHI) averaged 80% for both wheat classes, whether grown on fallow or stubble. On a rotation basis, F-W-W-W and Cont W (if weeds) produced 9% more grain than F-W-W, while Cont W (if water) produced 24% more grain, and Cont W and F-Hy-Hy produced 29% more grain than FW-W. Nitrogen production in the grain, straw and above-ground plant material was lowest in F-W-W, highest in Cont W, and intermediate for other rotations