High crop yields often come under scrutiny because of the need for fertilizers and the perception of their potential environmental impacts. Newspaper articles, letters, and advertisements from well-intended, but poorly informed, citizens seem to perpetuate old myths and clichés about modern fertilization practices.
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Fertilizer nutrients support human nutrition
The
fact is, maintaining food production for the growing world population requires
the use of new technology and the intensification of management to grow more
food on the existing crop land...and fertilizer is essential for accomplishing
this.
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Sometimes
I get tired of hearing about the negative fertilizer issues that are associated
with our abundant, affordable, and nutritious food supply...a truly amazing
supply of healthy food that is clearly unprecedented in the history of the
world! Misapplication and misuse of agricultural fertilizers have undoubtedly
occurred and their impact on the environment needs to be minimized. But to
fairly judge the use of fertilizers, the risks of their use should be compared
with their benefits for food production.
I
have had people tell me that raising yields with commercial fertilizer is
somehow immoral and dangerous for our soils... that strictly organic or
specialty products will meet the demand of global food production. You probably
know about the “stink test”... that is, when something smells fishy there is
usually a reason why! Many of these ideas and claims just don’t pass stink the
test.
The
time has come for all of us dispel myths about fertilizers and nutrients, and
to convey a correct message to a world which is becoming increasingly urbanized
and removed from what agricultural production is all about... providing healthy
food.
How
Does Fertilizer Contribute to the Food Supply?
A
survey of U.S. crop production estimated that average corn yields would decline
by 40% without N fertilizer. Even greater declines would occur if regular
additions of P and K were also halted. Numerous long-term studies have also
demonstrated the contributions of fertilizer to sustaining crop yields. For example,
long-term studies in Oklahoma show a 40% wheat yield decline would occur
without regular N and P additions. A long-term study in Missouri found that 57%
of the grain yield was attributable to fertilizer and lime additions. Similarly,
long-term trials from Kansas show that 60% of the corn yield was attributable
to fertilizer N and P.
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| Poor plant nutrition... maize |
Few
people appreciate that corn yields have continued to increase in the Corn Belt
of the U.S. without a similar increase in N fertilization. In fact, N use efficiency
has increased at least 35% in the past 25 years (where less N fertilizer is now
required to produce a bushel of grain). Remarkably, more corn is being
harvested without increasing N fertilizer application rates. Some of this
improvement has also come from modern genetics and improved agronomic
management.
Is
Manure the Answer?
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| Use all nutrients wisely |
Animal
manure can provide a useful nutrient supply for growing crops...and it should
certainly be used in the most beneficial manner possible. However, many people
have the mistaken idea that manure has some special property for building
soils. Manures contain no more nutrients than were present in the animal feed.
Similarly, manures do not produce any organic matter that was not initially in
the animal feed. No nutrients or organic matter are produced during the digestion
process!
This
means that whatever organic matter or nutrients that are present in manure are
simply the result of harvesting crops from somewhere else. The hay, grain, or
silage that is harvested to feed animals is simply taken from one field and
then applied to another fi eld after passing through an animal... with the
inevitable loss of nutrients and C to allow the animal to grow.
Animal manures rarely contain the essential plant nutrients in the
proper ratio required for growing crops. Manure application frequently results
in imbalances and accumulation of nutrients in the soil that can pose an
environmental risk. Composts and manures can be good nutrient sources, but their
mineralization depends on complex interactions of both soil and environmental
factors that are difficult to predict, which commonly results in a lower efficiency
than fertilizer.
In an on-going study in England (begun in 1840), applications of
farmyard manure increased soil C and N to a greater extent than did fertilizer
N. However, soil physical properties such as aggregate stability and water infiltration
improved the most in the treatments receiving fertilizer N. Nitrogen leaching
following the recommended manure application (75 tons/A/yr) was almost twice
that from the fertilizer N treatment (250 lb
N/A/yr).
There will likely be more livestock and animal manure in the
future, and these animals will consume more grass and crops that must be
fertilized. But the animals will not provide new nutrients. Expanding urbanization
means more organic waste and biosolids to manage. But resistance to application
of these materials back on the land seems to be growing and their land
application is banned in many countries.
Can Low Analysis Fertilizers Help?
I recently received a testimonial for a special fertilizer where a
few pounds of a product with N-P2O5-K2O analysis of 8-2-2 was claimed to
meet all the nutritional needs for 10 acres of crops! It bothers me that some
educated people continue to believe these claims and provide a market for these
products.
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| Advertisement for Cricket Manure |
Consider for a moment that 2 lb of such a low-analysis fertilizer will
provide about 3 oz. of N, and 1 oz. of P2O5 and K2O spread over
the entire 10 acres. Then compare this with the removal of over 1,000 lb N, 500
lb P2O5, and 400 lb K2O in corn grain...or a high-yield potato crop on
this 10 acres will remove 2,000 lb N, 300 lb P2O5, and over
2,000 lb K2O. Think about the cost of some of these products and the amount
of nutrients in a small container and it just does not add up!
It might be great if manure composted in cow horns, homebrewed compost
tea, or bat guano could meet the nutritional needs of large-scale food
production, but this can never be the case. Perhaps we are always on the lookout for short cuts or simpler
routes to achieve consistently high yields.
Unfortunately, there are no ways to violate the laws of nature and
science. You can’t grow a successful crop without providing the basic building
blocks for the plant. This includes maintaining soil conditions, adequate
water, and proper nutrition. When you hear that someone has a totally new
concept for providing for the health of your crop, approach it with some
initial skepticism and ask for documentation.
I marvel that people will eagerly buy the latest miracle product,
but fail to sample the soil and to monitor their fields for fertility levels,
pH, or nematodes. But remember the stink test; when something smells bad, there
is usually a mess nearby. Proper crop nutrition plays a vital role in
maintaining the world’s food supply. Use fertilizer appropriately to get the
best results and don’t be afraid to speak out for farming practices that are
such a benefit to humanity.
A pdf version of this post is available here
