Tuesday, January 31, 2012

Soil Sampling

 One of my favorite fall activities is soil sampling.  Soil sampling is the process of collecting samples of soil from a field. The soil is then sent to a lab where the soil is tested for such things as nutrient levels, soil ph, cation exchange capacities.  The results are sent back to us and we determine if we need to add any soil amendments such as lime or possibly fertilizer. 
My soil probe. 

Pulling soil cores while Joe watches.

Pulling the soil cores is a simple process.  What I like about soil sampling is the fact that I get to do a post harvest survey of the fields.  I look at the corn stalks left after the combine has gone through.  I look to see is the stalks are small and spindly or thick, if the stalks are firm or if the stalks have been cannibalized by the plant during the growing.  It's an agronomy nerds heaven.  We also look to see if  there was a good late season plant stand.  Once corn gets above shoulder high in the summer it's tough to get across a field to do a thorough inspection.  But, in a Mule after harvest we can still check to see what was there and start making plans for next year. 

Self portrait

On our farm we do grid soil sampling.  We grid our farms on 2 acre grids - so that means we take a soil sample every two acres.  An acre is about the size of a football field.  We use GPS equipment to record where we take the samples so we can replicate the sampling process in 4 to 5 years.  My parents started grid soil sampling in 1993 so some of our farms have been grid sampled 4 times.  With the sampling history along with our combine yield monitor maps we can take care of different parts of fields independently of each other.

When I first started out as an agronomist many, many years ago, we did composit soil sampling.  We would take several soil probes from a field and mix it all together for a sample.  We usually divided a field into 20 acre increments but it was tough replicating this sampling process because of the variability of the soils in such a large area.  Today, with grid sampling we take one core from the center of the grid point and then 10 more cores about 10 paces out from the center.  This gives us a representative sample of that point. 

I'm not poohooing composit soil sampling - we still use it in certain situations on our farm.  However, GPS equipment is a great tool to use for gathering information on our land. 

Soil cores taken out of the probe.

Joe playing  plotting sampling points with our
Mesa - GPS equipment.

The soil phosphorus levels on a farm from 2007 and then 2011

On the maps above the yellow areas show where the phosphorus levels were low in 2007.  Our agronomy inputs suppliers have fertilizer spreaders that take the soil prescriptions written for a field and apply the specific fertilizer only where it is needed.   On the map from 2007 you can see that the phos levels have come up in the previous low areas and are stable in the rest of field.  This makes economic as well environmental sense.

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