Its time to watch your P’s and K’s

Farmers were warned of increasing input costs in late 2021.  Many farmers in the area and the county rely on soil testing to predict fertilizer inputs for the upcoming year.  Our county continually sends in over 2,000 soil tests to the lab at the University of Kentucky.  The history of soil testing on many farms in the county goes back at least 30 years.   I have charted the results comparing the same fields year after year, test results, and they are consistent.  From time to time I am asked to review soil test results from a commercial company.  The fertilizer company wants to run their own tests for farmers in some situations, I use our tools to give a recommendation for fertilizer based on the recommendations in AGR 1, a University of Kentucky College of Agricultural long time researched publication on fertilizer recommendations.  

This year was no different, on farm in particular was not making clear sense, after reviewing the information, obtaining past fertilizer use, and discussing past cropping history we were set to discuss the issues at hand.  Fertilizer prices rose 35% in 2022, and there were no deals in late fall of 2021 to put on fall fertilizer.  The fertilizer test results from the commercial company were not out of line when comparing the last 5 years.  

However, I remembered a KATS training that I attended when Dr. Chad Lee asked everyone in attendance to take a soil probe in the field and take the first soil sample plug as if they were taking a soil test.  Over ¾ of the scouts took the first plug at the depth of 10-12 inches deep.  Even though the past 5 years soil test results were lining up the same or within a decent threshold, they were not what I expected from the farm I was dealing with as they were consistently applying well over an average soil sample that comes into our office.  Basically, they were adding much more fertilizer on the fields every year, than they were taking off in crop yields, and leaving no reserve for the next crop year.  

I asked the farmer to take their own samples, at the normal 4-inch depth on at least 5 fields.  It was a simple experiment to see if they were at least within a normal range of the previous samples that we were taken by the scout.  We realize that you can’t go back to the same spot that the scouts had previously taken, but it should be similar if they stay within the boundaries of the field.   The results were significantly different in the eyes of a farmer.  The soil test results came back with higher amounts of fertility found, and a lower recommended amount of fertilizer.  The savings on those 5 soil samples ranged from $27/acre to $158/acre.  there was a big enough difference for concern if the 50 'scout taken' soil samples are valid.  Considering an $85/acre average savings, a new plan needed to be designed as we were already close enough to planting time that we had no time to re-test all the fields.   We worked to determine crop history, history of crop production and we used AGR 1 Table 1 to determine the fertilizer prescription for each farm.  The farm operator was comfortable in going with a base recommendation which saved them an average of $72/acre on 2100 acres, this farmer saved $151,200 on fertilizer alone.     Even though we can take a soil test result from a commercial lab and make a recommendation with the UK Publication AGR 1, it is also important to know the way the sample was taken and ask a few hard questions to make everyone stop and think to save money without decreasing production.