Effect of Legume Crops Grown Two Years Prior to Barley On Malting Barley Yield and Quality.

The high costs of inorganic nitrogen have resulted in increased interest in alternatives. Legume crops, with their ability to fix nitrogen, have the potential to reduce the requirement for inorganic nitrogen in subsequent crops. A field study was conducted at seven locations in western Canada to determine the effects of various crop residues on yield and quality of canola and malting barley grown in 2010 and 2011, respectively. Crop residues established in 2009 were wheat, canola, field pea, lentil, and faba bean grown for seed, and faba bean grown as a green manure. Inorganic nitrogen was applied to canola and barley at rates of 0, 30, 60, 90 and 120 kg/ha.  In 2010, the legume residues (especially faba bean green manure) mainly resulted in higher canola yields compared to wheat residue. Quality requirements for malting barley are strict, including a requirement for low protein.  As a result, producers can be reluctant to grow malting barley on legume crop residues due to the perceived negative effect on grain protein. Previous studies have found that growing malting barley the year following field peas did not have a major impact on protein levels. This study investigated the effect of the legume residues on malting barley two years after their establishment. Beneficial effects of the legume residues in enhancing barley yield compared to wheat residue were evident at most locations in 2011. As with canola in 2010, the faba bean green manure residue tended to be most consistent in enhancing barley yield which increased at five of the seven locations.  Yield increases with lentil and field pea residues occurred at four and three of the seven locations, respectively. Increases in kernel protein occurred at three of the seven locations with faba bean green manure and lentil residues, but only at one location with pea residue. Overall, the legume residues established in 2009 rarely resulted in unacceptable protein levels (> 12.5%) for malting. The greatest increases in protein content occurred with increases in inorganic nitrogen. Growing legume crops such as field pea in rotation with malting barley will likely result in positive yield benefits without compromising malting quality.