Ten years of research by Dr. Raj Khosla and his precision agriculture grad students at Colorado State University has produced a soil color based management zone technique that accurately optimizes Nitrogen use efficiency within and across zones in given corn fields.
“Once farmers realize the value of varying N rates based on field productivity zones, most want to add more N to bring the low zone productivity up. We’re helping them to change this paradigm thinking because more fertilizer in a low zone usually isn’t cost effective,” Khosla says. “Once we start talking in terms of raising the net dollar return of the entire field to the same level, that usually gets their attention. And we accomplish that by applying low rates to low producing zones, medium rates on medium zones and high rates in high productivity zones.”
In his presentation at the recent InfoAg precision farming conference, Khosla addressed several key efficiencies:
- Their SCMZ (soil color management zone) technique has three data layers — bare soil imagery, field topography and farmer experience (where farmers indicate high and low producing areas)
- In 9 out of 10 site years, this SCMZ method can accurately differentiate grain yield going from low to medium to high zones. And when N optimization prescription strategy is applied (low rates to low producing zones, medium rates on medium zones and high rates in high productivity zones) there is a significant increase in N use efficiency, and reduced N leaching as well.
- Research in Colorado has shown that N rates can be cut by up to 40 percent in parts of fields without losing any yield.
- The early days of using grid soil sampling to build prescription maps has shifted to management zones due to the constraints of grids — grid size too large to capture the spacial variability within a grid; difficulty of interpolating fertility levels between known sample points; fertility recommendation software ignores the inherent soil variability.
Listen to Khosla’s presentation to learn more:[audio:http://www.precision.agwired.com/wp-content/uploads/sites/3/2009/07/RajKhosla009.mp3]