Russian thistle skeletons provide residue in wheat-fallow cropping systems

ABSTRACT:

Growers in low-precipitation (< 300 mm annual) dryland areas of the inland Pacific Northwest of the USA practice a wheat (Triticum aestivum L.) -fallow rotation where only one crop is grown every two years. When wheat yields are low, it is difficult to maintain adequate surface residue for erosion control during the ensuing fallow cycle. Russian thistle (Salsola iberica) is a major broadleaf weed in low-crop-production years, and it often produces more dry matter by grain harvest than the wheat crop it infests. In a 4-yr study, the effect of 3 tillage management treatments on retention of above-ground wheat residue and dead Russian thistle plants or “skeletons” during fallow was determined. Treatments were: 1) traditional (tillage), 2) minimum (herbicides and tillage), and 3) delayed minimum (herbicides and delayed tillage). Russian thistle infestation occurred 2 of the 4 yr when winter wheat failed and was replaced by spring wheat. Russian thistle skeletons were preserved as an important source of surface cover during fallow using minimum tillage, whereas they were wind-blown from the field or buried with traditional tillage. Minimum tillage also increased surface wheat residue compared to traditional tillage on all sampling dates. Results show the value of conserving Russian thistle skeletons for erosion control in low crop residue situations when this weed is likely to be present in large amounts.