Fertility and Nutrients
Getting more from less
Improving efficiency with low-tech solutions.
November 28, 2007 By Top Crop Manager
Spending wisely on inputs is one of the most important ways to manage risk
and increase crop production efficiency. And often, wisdom plays a more important
role in profitability than all the high-tech tools put together. Call it low-tech
if you want, but using knowledge that is, in many cases, free for the asking
is a key way to improve crop production efficiency.
|One pass seeding improves fertilizer use efficiency. Photos
Courtesy Of Bruce Barker.
"Climate, the biggest factor affecting crop production, isn't controllable.
However, farmers are seasoned guessers and they have many tools available to
make the most of the information that is available," explains David Larsen,
a soil and nutrient management specialist with Saskatchewan Agriculture and
Food at Moose Jaw. "Opportunities to maximize returns exist from greater
utilization of inputs and lowering the cost of inputs required."
Managing nutrients to manage costs
Nutrient management is one of the most important and costly parts of crop production
and, next to climate, it has the greatest impact on crop production. Larsen
says that a basic message worth repeating is that the soil test is the single
best method to prevent under or over-expenditure on fertilizer. A soil test
will provide a guideline for which nutrients should be applied and how much
should be applied. He says that nutrients in the soil are nutrients that do
not have to be applied as fertilizer, and that is an important way to keep costs
Another key component to consider is soil moisture. Stored soil moisture affects
yield targets, and by extension, how much fertilizer can be applied. "Stored
spring soil moisture is like fuel in the tank. It won't be enough to get you
to the end of the season, but if you know how much you have, you'll have an
idea how far you can go," explains Larsen.
Stored soil moisture, plus expected in-season rainfall can be used to create
yield targets for fertilizer planning: use a soil moisture probe to estimate
the plant-available water per foot of soil.
|Table 1. Available water stored per foot of moist soil
for various soil textures.
|Soil water (in/ft of moist soil)
|Source: AAFC Swift Current.
The next step in using soil moisture knowledge is to apply it to yield equations
developed by the University of Saskatchewan during the 1980s. While the yield
equations may not be completely applicable today, since they are based on older
varieties of grain, at least they can provide a rough guide to expected yield
targets for fertilizer budgeting.
Larsen provides the following example of determining target yield based on
soil moisture and average growing season precipitation. If a loam soil in the
Dark Brown soil zone had three feet of stored soil moisture, the soil would
have approximately 1.5 inches of plant available water per foot, or 4.5 inches
in total. With an expected growing season rainfall of 7.0 inches, total plant
available water for the growing season (WU) would be 11.5 inches. Using the
yield equation for wheat as an example, the estimated yield would be 38 bushels
per acre: (11.5 – 2) x 4 = 38.
"Farmers can use these equations as a quick reference point to get started
in setting yield equations," says Larsen.
Reducing reliance on fossil fuels
Martin Entz, a professor with the Department of Plant Science at the University
of Manitoba, says that today's grain cropping systems require approximately
6000 MJ/ha of fossil fuel energy each year. Forty to 50 percent is required
for nitrogen fertilizer production, 20 percent is fuel used to power farm machinery,
while the inputs of machinery production, pesticide manufacturing and seed production
consume approximately 10 percent each.
"The best strategies for energy savings involve using less nitrogen fertilizer
and less fuel," says Entz.
With good residue management and seed establishment, one low disturbance pass
can produce similar or better yields than multiple passes with higher disturbance
systems. One pass seeding cuts fuel and labour costs dramatically, and those
reduced costs are one of the major benefits of no-till seeding. Entz says that
Manitoba research shows that shifting from intensive tillage to a no-tillage
system was found to reduce energy use by 15 percent, without reducing crop output.
Improving nitrogen use efficiency is another method of improving the bottom
line. Larsen recommends banding, preferably soil banding, as a key nitrogen
fertility strategy. Conversely, broadcasted nitrogen is very susceptible to
gaseous loss (volatilization) when soils are warm and moist, and there is wind
at the soil surface.
Applying nitrogen fertilizer as close to seeding as possible, or at seeding,
as is the case with one pass seeding systems, also improves nitrogen use efficiency.
If fall banding nitrogen must be done, applying when the soil temperature falls
below 10 degrees C will help prevent losses.
Pulse crops in rotation can also make a significant contribution to fertilizer
use efficiency. Pulses vary in their ability to fix nitrogen and also in their
nitrogen contribution to subsequent crops. Larsen says that non-nitrogen benefits
such as increasing soil organic matter and physical structure, and stimulating
biological activity in the soil can be just as important as the nitrogen credits
left by the pulse crop.
Entz explains that growing grain legumes once every four years, instead of
only non-N fixing crops, reduces fertilizer use by 25 percent, which is approximately
a 12 percent reduction in overall energy use during a four year rotation.
|Table 2. Yield equations for wheat, barley and canola by
|Y = (WU – 2.5) x 3.5
|Y = (WU – 2.5) x 5.3
|Y = (WU – 2.5) x 2.0
|Y = (WU – 2.25) x 3.75
|Y = (WU – 2.25) x 5.7
|Y = (WU – 2.25) x 2.5
|Y = (WU – 2.0) x 4.0
|Y = (WU – 2.0) x 6.0
|Y = (WU – 2.0) x 3.0
|Y = (WU – 1.75) x 4.25
|Y = (WU – 1.75) x 6.4
|Y = (WU – 1.75) x 3.3
|Y = (WU – 1.5) x 4.5
|Y = (WU – 1.5) x 6.7
|Y = (WU – 1.5) x 3.6
|Y = (WU – 1.25) x 4.75
|Y = (WU – 1.25) x 7.2
|Y = (WU – 1.25) x 4.0
|Y = yield in bushels per acre. WU = water use; inches of
plant available stored soil water plus expected growing season precipitation.
|Source: Adapted from 'Criteria for Targeting Yields in
Saskatchewan', Soils and Crops Workshop, 1991. Karamanos and Henry.
The amount of nitrogen retained for subsequent crops varies by soil, climate
and pulse crop grown, but the underlying message is that a legume crop grown
in rotation will generate a nitrogen credit. All of it may not be available
in the first year after production, but it will become available over subsequent
years. "The rule of thumb is that the pulse crop's contribution of nitrogen
in the year after production is 11 pounds per acre of nitrogen in dry soil zones
and 25 pounds per acre of nitrogen in wetter soil zones," says Larsen.
Green manuring pulse crops is another effective strategy for building soil
fertility to reduce reliance on fossil fuels. Green manuring, the plowing down
of the crop prior to full bloom, produces large quantities of organic matter
and nitrogen for the subsequent crop. Research has shown that at early bud,
sweet clover contains 68lb/ac of nitrogen in the top growth and roots, alfalfa
73lb/ac of N, and red clover 55lb/ac of N.
"Chemical desiccation is just as effective as plowdown, so green manuring
fits well with reduced tillage systems as well," says Larsen.
Entz says Manitoba research found that legume cover crops (green manuring)
can add 30 to 50 pounds of N per acre to the soil, reducing N fertilizer needs
by as much as 50 percent in the following crop. Adding a legume cover crop every
other year will result in an approximately eight to 10 percent reduction in
rotational energy use.
If perennial forages are already included in the rotation, Entz explains that
cycling the perennial stands through the crop rotation more frequently, a three
year alfalfa stand instead of a six year stand for example, greatly reduces
nitrogen fertilizer requirements in the following grain crop since soil nitrogen
contribution from perennial forages is typically maximized after three years.
Compared with straight grain rotation, including perennial forage legumes in
the crop (50 percent forage in rotation) reduces rotational energy use by approximately
Livestock production can also be an important component in improving nutrient
systems. Beyond spreading manure on the land, Entz says that livestock grazing
instead of haying increases soil nutrient build-up during the forage phase,
further reducing the nitrogen, phosphate and potassium fertilization required
in subsequent grain crops. Part of the reason cattle grazing provides better
soil fertility is that a greater amount of the nutrients found in manure and
urine is captured by the soil, rather than lost to the atmosphere in the winter
Entz also believes that a larger fundamental shift must take place on a regional
basis to further improve farming efficiencies and to help reduce the reliance
on fossil fuels. Today's specialized agriculture does not allow for easy integration
of cropping and livestock systems, and new technology is not helping cut costs
or improve profitability.
"Much of the new technology offered to grain producers is okay, but it's
a bit like rearranging deck chairs on the Titanic," says Entz. "We
need to reorganize agriculture on a regional basis to develop more mixed farms
or include more regional integration of the livestock and grains sector. While
on-farm integration is better, regional integration is better than no integration."
Ultimately, improving agriculture's efficiency through the use of low-tech
tools depends on knowledge and the wise application of a systems approach to
production. With nitrogen fertility and fuel as the major component of crop
inputs, management decisions that build soil fertility and reduce fuel consumption
will help to minimize costs and risks.