Drought conditions this season have affected the amount of soil nitrate left in the soil profile. We can see this in regional summaries, with higher soil nitrate carry over this fall. When fields are split into productivity zones for soil sampling, the drought effects on soil N become even more apparent. In a dry year, soil water holding capacity (soil texture) and topography are two key factors in explaining yield differences in different areas of fields.
Here is an example of a zone sampled field from eastern North Dakota. In the zone map, you can see the differences of over 30 lb/a in the N levels between the three zone samples. You will also notice from the topography map, that the highest ground (red) is the zone with the highest N level in this field. In a drought year like 2012, the high ground probably ran out of water, limiting yield and leaving more nitrogen in the soil profile. We have received many comments from zone sampling customers about the wider range in soil N levels between zones this fall compared to years with normal rainfall. Zone sampling is one way to pick up the large swings in the soil N levels following normal years and drought years as well. (Thanks to Shawn Kasprick from Simplot Grower Solutions for the zone field example).