Influence of alfalfa escapes on estimating spring barley yield

In Wyoming, spring barley (Hordeum vulgare L.) can follow alfalfa (Medicago sativa L.) in irrigated rotations. To avoid serious wind erosion, this conversion should be done using conservation tillage. However, this can be complicated by alfalfa escapes. The relationship between the level of established alfalfa interference and barley is unknown. Establishment of the season-long impact of alfalfa escapes on barley yield would be important for crop-loss assessment. Forecasting the impact on production would be valuable as a decision making tool. The objective of this study was to estimate yield losses from season-long interference of alfalfa escapes and to forecast impact of alfalfa escapes on spring barley yield. Replicated field studies were conducted under sprinkler irrigation at a site near Torrington, WY. Herbicide treatments were used to provide for barley production across a range of levels of alfalfa interference. Barley yield response was regressed on various measures of alfalfa infestation. Consistency of regression over years for barley yield on end-of-season alfalfa stand or alfalfa yield allowed for simple interpretation of the expected barley yield reduction, as well as calculation of the expected barley yield given a specific level of alfalfa infestation. Use of a growing season visual assessment of alfalfa control did not result in consistency of regression slopes over years. Calculation of an expected barley yield based on models developed using alfalfa stand and alfalfa yield was accomplished. The predictors are -84.747 and -0.5577 for alfalfa plants 0.5 m(-2) and kg ha(-1) alfalfa yield, respectively.