One of our customers in South Dakota soil sampled a field in 2011 before applying PRO CAL 40 gypsum and lime. They then resampled the field in 2015 to measure the differences they observed in soil test levels. This field was grid sampled on two-acre grids each sampling period. Below is a table showing the changes observed. These values are averages of the grid samples each time.
|pH||P1, ppm||K, ppm||Mg, ppm||S, ppm||Zn, ppm|
|2011 Soil Samples||6.3||21||389||1019||15||1.5|
|2015 Soil Samples||7||31||395||898||29||1.3|
Noteworthy is that nutrient availability will usually increase as you improve air/water management and get better biological activity. This happens with applications of gypsum. The pH increase is mainly due to the lime that was applied. The magnesium will often be lower since the calcium will displace the magnesium and allow it to be more mobile and move through the soil. As the magnesium levels decrease and calcium levels increase (PRO CAL 40 contains about 400 pounds of available calcium per ton) the soil becomes less sticky, more friable and softer. Sulfur increases because with each ton of PRO CAL 40 you apply, you are adding about 300 pounds of sulfur. Some of this will react with the magnesium and move through the soil profile.
How do these factors relate to crop response? It is difficult to correlate soil test levels to yield with great consistency, however we have observed that if you improve soil conditions and air/water management you will increase crop growth and decrease crop stress which both could translate to higher yields. Customers who have applied gypsum to fields with similar soil tests have noticed that the fields till much easier, are field-ready to plant sooner, and are softer soils eliminating the need to do deep tillage as was done previously. Also, legume crops have more nodules and larger nodules since there is a better environment for nodule growth or microbial activity. By improving the soil environment you decrease the risk of diseases which are favored by more saturated soil conditions and a more stressed crop.