Early Spring Yellowing In Small Grains

The small grains in the RRV are generally green right now. However, in a trip yesterday in south central ND to put out a research plot, there were a considerable number of fields with yellowing in small grains.

 

 

 

 

 

The obvious reason is lack of N. While this is often true, there are other possible causes, and it is not always N rate. Some of the yellowing is in streaks. No fertilizer applicator streaks in 30 foot strips across the field with an 80 foot boom, so the reason is not spreading error. Consider the combine width. Last years’ crop yields were good and there was a lot of residue. If the combine lacked good residue spreading tools, the residue was thicker behind the combine. This set the stage for two things this spring: First, N tie up, even with soybean residue is higher (many growers think the soybean N credit comes from residue breakdown and N release, but this is not true- a subject for a future pest report I think). Secondly, the thicker residue insulated the soil and caused the frost damage on foliage a couple weeks ago to be greater. So walk out into the fields and see if part or all of the yellowing is residual frost damage or not. A winter wheat field I was in yesterday had major frost damage on a couple leaves and contributed greatly to its yellow appearance from the road.

 

If the problem is N deficiency, from a lack of adequate preplant N, unanticipated residue N tie-up, or loss from leaching or denitrification, the symptoms up close are oldest leaves (lowest on plant) most yellow and newer leaves green. If as the image shows the lower leaves are greenest and the newer leaves yellow, the problem is S and needs to be dealt with by soluble S application, most commonly using either dry ammonium sulfate over the top, or stream-bar ammonium thiosulfate, which is never broadcast applied.

 

It might not be the best year to consider a new combine, but it is always a good time to consider a better chaff/residue spreader. Something that would size the residue coming out the back to better enable no-till/strip-till planting would be excellent and a combine that would more evenly spread the residue would make yellow streaks in spring fields far less likely.