I wrote about three things one can learn from soil testing in this post. Here, in part 2, I discuss four more things related to this subject.
4. Grass can grow well and produce a high quality surface across a range of soil chemical conditions. Don't forget the importance of light, water, soil air, and mowing. By comparison, soil nutrients are simple, and there is more leeway for variation in soil chemical properties. These plots were very low in calcium and magnesium by any interpretation, had potassium above the MLSN guideline but lower than conventional guidelines, and the pH of the plots was from 4.9 to 5.5. Even with these conditions, the grass is good.
5. Sand is a horrid growing medium for plants. The CEC is really low, the micronutrients are low, the accumulation of organic matter that is so beneficial in a normal soil actually causes problems with a sand, the pH is usually not well-buffered -- there are a lot of things not to like about sand as a nutrient supplying medium for turf. The soil tests on these test plots show this.
6. Available nitrogen (nitrate + ammonium) was pretty much the same for each plot, no matter the N source supplied (or not). There was 8.7 ppm N in the control plot that received no N, 8.3 ppm in the urea plot, 7.2 ppm in the 19-0-19 plot, and 6.3 ppm in the 15-0-26 plot. It is interesting that the control plot actually had more N than the plots that received N fertilizer. One would need to run a lot more samples to determine if this was just by chance, or if there is some cause for this -- a difference of 2 ppm in real terms is tiny. What we saw at the field day was grass that looked pretty much the same, no matter the fertilizer. When the conditions are right for mineralization, and when there is enough organic matter in the soil, N fertilizer may not be required. The control plot here looks just as good as the plots that received N, and the soil N was pretty much the same in all the plots.
7. For many nutrient experiments, it is difficult to see treatment effects when they are not done under controlled conditions. There were visual differences between the plots a month before the field day, after the first application of fertilizer treatments. But management of the turf, especially the irrigation applied to make sure everything looked at its best for the field day, seems to have increased N mineralization in the control plot and thus all the grass was supplied with enough N and K no matter the treatment. Doing experiments under controlled conditions is an easier way to detect small differences in treatment effects, if those treatments have only a small effect.
These demonstration plots were set up to use as a discussion point for the experiment about N:K ratios conducted under controlled conditions, described in this poster, this handout, and in these slides.