Managing Chlorosis in Waterlogged, Dryland Winter Wheat.

The Palouse region of southeast Washington and northwest Idaho is among the most productive dryland wheat regions of the United States. This semi-arid region is characterized by a Mediterranean climate, hence stored soil water is essential for summer crop growth. Many soils in the region, however, contain hydraulically restrictive soil horizons (e.g. argillic layers) which lead to the development of seasonal perched water tables, especially at converging topographic positions. Winter wheat often exhibits chlorosis in these waterlogged areas during early growth stages. The objectives of the experiment were to (1) utilize remote and proximal sensing to detect, map and monitor, and diagnose wheat chlorosis and (2) identify primary and secondary controls for chlorosis, potentially including plant and soil N deficiencies, soil redox status, soil temperature, and crop root growth dynamics. A variety of crop, soil and root sensing instruments were installed to make continuous and episodic measurements in saturated areas within five wheat fields in the Palouse region of eastern WA and northern ID (USA). Results indicate that a spring top-dress application of ammonium or nitrate increased the Normalized Difference Vegetation Index, chlorophyll concentration, leaf area index towards levels of adjacent non-chlorotic plants. In unfertilized plots, rooting depth was correlated with biomass, chlorophyll concentration, and water table depth. Therefore, the chlorosis of winter wheat was diagnosed as a soil N deficiency symptom caused by restrictions in rooting depth under waterlogged conditions. The addition of fertilizer in spring alleviated deficiency symptoms, but even untreated plants recovered once conditions permitted roots to obtain N at lower depths. Waterlogging reduced crop yield by 20% and decreased the number of live tillers and plant height, but spring top-dressing reduced yield losses by 25%.