Soil tests are often rated low, medium or high. Low generally means that a
soil has a high probability of responding<greater yield> to that nutrient if
it is added. High soil tests generally mean that the probability of a yield
increase is very low or non existent. Medium often does not respond either
but it may in some instances.
Does the U of Md have data which shows that you need more fertilizer at high
soil test levels for vegetables. A small amount might be needed at planting
if the soils are cold and wet but 50 to 100 lbs/acre seems pretty high to
me. Agronomic crops would not respond in those conditions in MD. Yet many
continue to suggest it be added for insurance or other factors such we ought
to put back what we take out<soil buildup and maintenance philosophy>. When
this is used we can always justify more fertilizer. In my opinion this is
like irrigating a swamp because there was evapotranspiration that reduced
water levels a half an inch. I don't think many would support that but we
continue to do it with fertilizer.
I think that fertilizer recommendations ought to be based on sound field
calibration data but those who work in this area know that is often not the
case. We often have little data to back up the recommendations and so we
resort to all kinds of gimmicks and guesstimates to justify what we do. We
ought to print the back up data that supports our recommendations so the
consumer knows what they are buying or getting. Kind of like truth in
advertising. What a change that would bring about. We might see that the
emperor has very few clothes or none if that were done.
We may have all sorts of marvelous technology in the lab but if the
recommendations do not have a solid back up of good field data with similar
crops and soils it is the old garbage in garbage out story.
Years ago<1981> I did a substantial study of the soil testing area and found
all sorts of abuses. I suspect it still continues today. It depends on
whether we are trying to help farmers use inputs they need or whether we are
trying to sell something. There are credible soil testing services out there
but there are some that are not. For the farmers it is very difficult
because this is only one area among many that they need to manage and they
cannot be an expert on everything. I really think it would help if farmers
had the back up data available to them so they could make more informed
judgements. I don't know when this will happen or what it would take for
the soil testing establishment to move in this direction. It may come when
we get campaign finance reform.