Long-term spring wheat response to summerfallow frequency and organic amendment in southern Alberta

A long-term rotation experiment was established in 1951 to determine the influence of summerfallow frequency and organic amendment on the yield and quality of unfertilized spring wheat (Triticum aestivum L.) on a Dark Brown Chernozem (Typic Haploboroll) at Lethbridge, Alberta. Wheat was grown either continuously (W), in a 2-yr summerfallow-wheat rotation (FW), or in a 3-yr fallow-wheat-wheat rotation (FWW). No fertilizer N was applied and P, at 22 kg ha−1, was applied to all wheat crops starting in 1985. The 3-yr rotation was also amended with livestock manure (FmWW) and modified to include a hay mixture of alfalfa (Medicago sativa L.) and crested wheatgrass (Agropyron cristatum L.) (FWWHHH). Annual grain production was affected by summerfallow frequency and organic amendment, with the lowest grain production obtained in the FW rotation. Amendment with livestock manure resulted in the highest grain yields for wheat grown on summerfallow, while 3 yr of hay in the rotation produced the highest stubble wheat yields. These higher grain yields were accompanied by a 12–31% increase in grain N uptake. Decomposing hay roots increased plant-available N as reflected in the highest grain N concentration and grain N yield in the FWWHHH rotation. Evaluation of grain yields under a range of moisture deficit conditions revealed that a year of summerfallow was often insufficient to recharge soil water depleted by 3 yr of hay in the FWWHHH rotation. Both summerfallow and stubble wheat yields were positively influenced by May rainfall. Overwinter precipitation contributed significantly to the variability observed in stubble wheat and hay yields. In the absence of fertilizer N additions, organic amendments such as animal manures and hay residues are effective means of increasing crop productivity and grain quality in semiarid regions. Key words: Hay, manure, rotation, spring wheat, summerfallow, Triticum aestivum L.