Russian thistle skeletons provide residue in wheat-fallow cropping systems

Growers in low-precipitation (< 300 mm annual) dryland areas of the inland Pacific Northwest of the USA practice a wheat (Triticum aestivum L.) -fallo w rotation where only one crop is grown every two years. When when wheat yi elds are low, it is difficult to maintain adequate surface residue for eros ion control during the ensuing fallow cycle Russian thistle (Salsola iberic a) is a major broadleaf weed in low-crop-production years, and it often pro duces 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" d uring fallow was determined Treatments were: 1) traditional (tillage), 2) m inimum (herbicides and tillage), and 3) delayed minimum (herbicides and del ayed tillage). Russian thistle infestation occurred 2 of the 4 yr when wint er 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 wit h traditional tillage. Minimum tillage also increased surface wheat residue compared to traditional tillage an all sampling dates. Results show the va lue of conserving Russian thistle skeletons for erosion control in low crop residue situations when this weed is likely to be present in large amounts .