Alfalfa prep

  The following is a conversation I have had the last several days with vhaby, which I started after seeing him offer his help on establishing alfalfa.  When I first saw him offer this, I wasn't ready at that point to head down that path, but now I am going that way.  Anyway, he offered up that it would be okay to post the conversation.  I do have more that I will be asking him, but will do it in the context of this thread.  Y'all are welcome to join in.                   

 

Reed

 

reede, on 03 Jun 2016 - 9:18 PM, said:

Dr. Haby,

Reed Edwards here in Laurens, SC. I have seen you offer advice on alfalfa planting, and I would love to get your input if you wouldn't mind. I have soil samples, along with a listing of the ammendments that I have added over the last couple of years. The field is planted in Tifton 85 Bermuda, and UGA is promoting the interseeding of alfalfa into bermudagrass, which is the way that I am leaning at this point. For starters, the field is located at 34°27'33.9"N 82°01'13.9"W, just outside of Laurens, SC.
Thank you for your time.

Reed Edwards

Mr. Edwards,

 

I have looked at your soils. Most of the area represented by the L&L you provided appears to be a Cecil sandy loam. Cecil may have about 8 inches of sandy loam underlain by a red clay. The descriptive terms used in describing your Cecil soil do not indicate any wetness that would be a problem with alfalfa. The soil is indicated as well drained which is good for alfalfa. The soil slope is also suitable for seeding alfalfa, especially since you would be interseeding alfalfa into a standing crop of Tifton 85 bermudagrass after it goes dormant this fall.

 

Where there might be a problem is the subsoil acidity. The surface of a Cecil at the original site where it was first described is listed as slightly acid, but the next depth of red clay is said to be strongly acid and the next horizon below that is described as very strongly acid. Acid soils contain soluble aluminum that is toxic to alfalfa roots. Aluminum toxicity prevents alfalfa roots from growing deep into the soil to take up water. In my area where we normally receive an average of 45 inches of rainfall per year with a very dry July and August, this is a problem. In your area where you receive a better distribution of rainfall throughout the summer months, acid subsoils might not be as great of a problem if the limed soil surface stays moist. I would suggest that you collect soil samples by one foot depths to about 48 inches deep from at least 5 random locations across the field intended for alfalfa. You will need four plastic buckets in order to keep each foot depth from the five locations in individual buckets. Mix the five subsamples in each individual bucket and take out a representative sample to send to your soil testing lab and ask them to analyze the samples for pH.

 

If the pH is 5.5 or higher, aluminum will not be a limiting factor. If the pH is below 5.5, this won't kill the alfalfa, but its growth will be limited by not being able to take up the water it needs for optimum growth. Again, if the limed surface soil remains wet by frequent summer rains, subsoil acidity will not be as much of a problem as it can be here.

 

I'm assuming that you will be making hay out of this bermudagrass/alfalfa system. If you intend to graze it, realize that cattle will prefer the grass until they are forced to taste the alfalfa, after which they will prefer the alfalfa and leave the grass.

 

If I can assist you further in this venture, please don't hesitate to contact me.

 

Thank you very much for taking the time to do this.  I did take subsoil samples when I took my soil samples over the entire farm back in March.  Went down to 24 inches, in 6 inch segments.  At that point, the soil surface had a pH of 6.3, while the 3 subsoil layers (6-12), (12-18), and (18-24) each had a pH of 6.2.  I have applied 2 tons of dolomitic limestone since then to bring the soil pH up to where it needs to be.  Also, last summer I applied 2 tons of gypsum per acre. 

I actually started doing a little study last fall, after not finding the answers I was looking for in pH fluctuation.  My pH on this field, from spring to fall, dropped a half a pH unit.  I decided at that point to soil sample this field once a month for a year, to try to get an idea of what cycles there are.  You explained some of this in a post here after I had started doing my samples, and I decided that I would continue through the year.  That will take me through October, at which point my alfalfa should be in the ground. 

pH has been the stubborn thing to get moved.  When I have added pH adjusting ammendments(lime and wood ash over the last year and a half) I have gotten increases in CEC and organic matter levels, with little movement in pH.  Of course, those other things are good changes, just not what I was expecting with what I was adding.  Knowing that it has been slow to rise, was my reason for going with the 2 tons of lime this spring.

Anyway, thank you very much for your time, and if there are other things I should be considering, I would welcome the advice. 

 

Reed Edwards

 

Alfalfa prep