What is in this article?:
- Soil and the importance of gypsum
- Research and soil testing
- Gypsum role in Mid-South soils discussed.
- Soil testing and aluminum's role also explained.
Research and soil testing
On how Espinoza’s gypsum research began…
“At one site where we were conducting an irrigation study we placed soil moisture sensors at 6 and 15 inches deep. We would notice that the plants would go under water stress, even with the sensors placed 15 inches deep showing moisture at field capacity. Initially we thought there was something wrong with the sensors.
“So, we dug up the soil and, sure enough, there was plenty of water deep down. But the roots weren’t able to grow down there and use the water because of the high aluminum levels.
“We began talking to farmers and they would say things like ‘no wonder I have to water so often. Otherwise, my crop would burn up. But it’s confusing because when I dig into the soil, the profile looks great.’
“Take deep soil samples and you may find that aluminum is the reason.”
How gypsum figures in…
“Our initial objective was to assess the use of gypsum as an anti-crusting agent. We had established strip plots where rates equivalent to zero-, one- and two-tons-per-acre gypsum had been applied for two consecutive years. But once we found the issue with the aluminum levels, our attention turned into testing the effect of the gypsum applications on aluminum solubility.
“So, we collected deep soil samples and noticed that where gypsum was applied, we lowered the solubility of aluminum to around 30 parts per million compared to 250 parts per million in plots where no gypsum was applied.
“We also dug up plants to look at the roots. It was obvious that plants growing in the plots that had received gypsum had deeper root systems.
“Of course, when you have plots that are 24 rows wide and 500 feet long, you have to wonder ‘are these observations influenced by the area we dug up?’ But while there was some aluminum variability in our soil samples, on average, the gypsum reduced its solubility considerably.”
Do soil tests normally look for aluminum? Is it a good idea for farmers who may be having these issues to ask the soil lab to test for it?
“Aluminum isn’t part of routine soil tests. In fact, the most appropriate way to test for aluminum is to look at ‘exchangeable aluminum’ fraction.
“The analysis involves the use of KCL as an extractant. You don’t use the extractants normally used by soil test labs. It’s a special test.
“But I don’t think it’s a bad idea for farmers to take a sample – maybe a sample from 12 inches to 18 inches deep – just to check.”
Regions where this is more of a problem?
“Many of the silt loams in the Mississippi Delta, including the Memphis, Loring, and Henry soil series have a fragipan, and thus could potentially have high aluminum levels in the subsoil.”
So are you ready to recommend that farmers apply gypsum to their fields?
“Well,we found this issue with pH, in all honesty, by serendipity.
I really believe it’s important to figure out more about the potential implications.
“We aren’t sure how long the gypsum effects last, how often we need to apply it or even the minimum amount of gypsum needed.
“And even if we see increased root volume does it translate to water savings? That’s the next question we need to answer. Maybe the plots that receive gypsum don’t need to be watered as frequently. If that’s the case, there’s certainly a very good justification to apply gypsum.”