Fall Field Goals
Natalie Rector, Michigan State University Extension, Fall 2004
There’s more to fall than football and harvest. If you are planning to buy one dime of
fertilizer or spread one tank of manure, be sure soil and manure tests are taken to direct your
nutrient management plans.
Soil sampling
Who better to take soil samples than the person who drove the harvest equipment. They
watched the grain go through the machine, they know where the good and bad spots are. They
know where the tree and stone pile are buried and where the back of the field drops off to that
good black dirt. Take this knowledge and soil test accordingly.
Soil samples should represent no more than 20 acres to reduce variability. Divide fields
by the soil types, which are often reflected in yield and crop performance. If the back half of the
field is darker soil and drops off to the woods, then sample this area separate from the front half.
If there is an eroded knoll that does not perform well, but only represents a small area, do not take
any probes in this area, as it will throw off the sample by not being typical of the area. If the
eroded knoll amounts to a large area, then sample it separate.
Use your field knowledge to direct where to sample and when to divide samples. If
several small fields are one large field today, then sampling based on how the old fields used to
be may show differences. Soil maps can be helpful in determining soil changes, especially on
rental fields with less personal history.
Each soil sample should be made up of 15-20 individual probes. Sample the area in a
zigzag pattern, randomly reaching all the areas but avoiding the headlands. Dry them on
newspapers on the floor and then mix the dry soil for a representative sample.
If someone familiar with the farm jumped on an ATV, they could probably do over 300
acres in a morning, maybe half the farm in a day. This ends up costing about 25 cents per acre!
Now think about how much money is spent per acre on fertilizer. Is it worth investing 25 cents
per acre when you’re planning to spend $40 per acre on fertilizer?
For livestock producers, hauling manure should be considered the same as planning
where fertilizer would be best utilized. When manure nutrients are directed to a field that doesn’t
need them, and another field will require purchased fertilizer, there is a missed opportunity to
save on cash flow and recover some of the cost of hauling manure down the road.
Manure sampling
No sooner than the crops are off the field, the manure tanks begin rolling. Some
livestock producers only have to complete this task once or twice a year. In these instances, the
opportunity to pull a representative manure sample only comes along twice a year as well.
Taking a manure sample at the time of mixing and hauling will be the most representative
of the nutrients that are going to the field. Combining a current manure sample with an accurate
calibration of the rate per acre will provide data that is not only invaluable for your crop and
fertilizer plan, but will also keep you in compliance with the Right to Farm guidelines and
prepare you for any additional requirements such as comprehensive nutrient management plans
(CNMP) for CAFO farms or NRCS environmental quality incentive program (EQIP) funds.
There is both a science and an art to taking a good manure sample. If a baseline of
manure values has not been achieved, sample each time the storage is emptied. Then sample
every couple years to keep a check on the nutrients. Remember, it is manure, and varies with
seasons, feed rations and water systems, but a trend should emerge.
For systems that are only emptied once a year, take a sample each year. Systems that are
uncovered will be more variable than under-barn concrete pits, so sample outside storages more
frequently.
Sampling liquid manure
Sample manure that is in the manure tank and ready to go to the field. Either dip into the
opening on the top of the spreader or from the bottom unloading port. Semi-solid manure scraped
from the barn will be moderately mixed when loaded into the box spreader. Again, sample back
out of the spreader.
Take several samples from several loads, mixing them together for a representative
sample.
After collecting 5-10 sub-samples, mix them and fill a plastic sample jar ¾ full, leaving
room for expansion during freezing.
If there is a noticeable change in consistency of the manure from the beginning loads to
later loads, take samples accordingly. Liquid manure in the beginning loads will be different
from thicker manure toward the bottom of the storage.
Mail samples, frozen, to the manure testing lab, and mail early in the week to avoid
samples sitting somewhere over a weekend.
Bedded pack manure can be sampled by using a pitchfork or shovel, taking 10-20 subsamples from different depths. Mix these to obtain a composite sample. Two composite samples
may be a good idea, taking the average of the results.
Rate per acre leads to nutrients per acre
A good manure test is only valuable if the rate of manure application per acre is accurate.
Weigh a load of manure and then measure the square feet that one load covers in a field. Divide
this by 43,560 sq. ft. in an acre to see how much of an acre one load covered. When weigh scales
is not available, use a 5 gallon bucket, packed to similar density of a manure spreader and weigh
the bucket of manure. A five-gallon bucket is approximately 2/3 of a cubic foot. So if you
calculate the cubic feet of the manure spreader the weight could be estimated.
Accurate calibration and manure tests will provide excellent data on the rate per acre of
nutrients.
Records
Soil tests, manure sampling and calibration have been completed. The only thing left is
record keeping. For Right to Farm nusiassance protection, livestock producers need to be
keeping records of manure applications. Information maintained should include the manure
analysis, soil test reports, rates of manure applications for individual fields previous crops grown
and yield data. Weather data the day of applications is also good to keep. Other useful items,
especially for improving calibration and knowing the nutrients per acre, include which manure
storage the manure came from, how many loads were hauled and how many acres were covered.
Fall is a great season in Michigan. Take time to enjoy a football game or two but also be
sure to update soil samples, manure tests and calibrate and record manure applications.