Soil Fertility and Nutrient Management

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Soil Fertility and Nutrient Management Prepared
for Follow the Grain
by Clain Jones, Extension Soil Fertility
Specialistclainj_at_montana.edu 406 994-6076
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Questions

• How many of you grew up on a farm?

• How many of you have taken Soil Resources (LRES
  201)?

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Goals Today

• Introduce basics of soil fertility
• Focus on nitrogen and phosphorus cycling and
  differences in their plant-availability
• Explain yield response curves
• Discuss nutrient management strategies to
  increase efficiency of fertilizer use
• Answer your questions

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There are 14 mineral nutrients that have been
found to be essential for growth of most plants
The macronutrients are simply needed in larger
amounts by the plant than the micronutrients.
Nutrient deficiencies of the bolded nutrients
have been observed in Montana
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Mobility in soil of selected nutrients
Why important?
Can affect optimum fertilizer placement
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Banding Phosphorus
Banding P is much more effective than banding N,
because P is much more immobile in the soil.
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For more information on soil fertility and plant
nutrition, refer to Nutrient Management Module 2,
and for more information on Fertilizer Placement,
look at Module 11 http//landresources.montana.e
du/nm
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Nutrient Reactions and Cycling

• Will focus on N and P because these have best
  chance of limiting yield.

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The N Cycle
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Mineralization Release of minerals as organic
matter (O.M.) is oxidized, releasing available
N Organic-N ? Plant-Available N
If have higher than normal O.M. (gt3), can back
off on N fertilizer by 20 lb/ac.
Immobilization Incorporation of available N
into microbial cells or plant tissue Plant-Availab
le N ? Organic-N
If leave more than ½ ton stubble, increase N
fertilizer by 10 lb/ac.
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Movement of P is largely through erosion/runoff,
NOT leaching. Why?
P Cycle
P binds strongly to soil
Why simpler than N cycle?
No gas phase
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• Soluble P concentrations in soil are generally
  very low (0.01 1 mg/L), especially in
  calcareous soils, whereas soluble N levels are
  often high (1 - 50 mg/L).

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Questions so far?
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N Deficiency Symptoms
Alfalfa

• Pale green to yellow lower (older) leaves Why
  lower leaves?
• Stunted, slow growth
• Yellow edges on alfalfa

N is MOBILE in plant
Corn
Spring Wheat
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P Deficiency Symptoms
Adequate P

• Dark green, often purple
• Lower leaves sometimes yellow
• Upward tilting of leaves may occur in alfalfa
• Often seen on ridges of fields

Low P
Alfalfa
Wheat
Lettuce
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QUESTIONS SO FAR?
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How do you determine if need to add fertilizer
(other than symptoms)?
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Generalized Crop Yield Response Curve
What will the Economic Optimum Yield depend on?
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EB 161
http//www.montana.edu/wwwpb/pubs/eb161.pdf
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N Rate Guidelines (Jacobsen et al., 2005)
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Phosphorus
Example Winter wheat Olsen P 10 ppm P2O5 needed
42.5 lb/ac
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Big Issues in Soil Fertility Right Now?

• Record high fertilizer prices.
• Environmental water quality, sequestering
  carbon requires nitrogen, and energy to make N
  fertilizer is higher than energy from on-farm
  fuel use.

Some Solutions?

• Increase efficiency of fertilizer use through
• Optimizing fertilizer rate, fertilizer placement
  (subsurface application) and timing
• Variable rate application (precision agriculture)
• c. Diversifying cropping system, especially by
  adding N-fixing legumes.

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Timing
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What makes yield?
Heads/area x Kernels/heads
x Weight/kernel
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When are yield components set?
Weight/kernel set
Head/acre set
Kernels/head set
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Impacts of nitrogen
Nitrogen late Weight/kernel Higher grain protein
Nitrogen early Number of tillers and
kernels/head Grain protein from remobilized N
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Variability in soil N, grain protein, and grain
yield across a field
Source Dan Long Location Liberty County
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As diversity of cropping system increases

• Efficiency of fertilizer use increases. Why?
• Different rooting depths scavenge nitrogen and
  phosphorus at different depths
• Deep rooted crops can bring nutrients from
  subsurface to surface for use by shallow rooted
  crops (winter wheat ? pea)

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Some basics on effects of cropping systems on
soil nitrogen (N)

• Previous crop affects
• - Amount of N Small grain and oilseed stubble
  ties up N Legumes release N
• - Vertical distribution of N Depends on rooting
  depth
• - Timing of N release Spring vs winter
  crop Legumes decompose quickly Small grain and
  oilseed stubble slowly

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Conclusions

• Nitrogen is much more soluble and mobile than
  phosphorus.
• Nitrogen levels are largely dependent on
  breakdown of organic matter (and fertilizer).
• Phosphorus levels are low in Montana.
• Fertilizer needs can be determined if know soil
  test levels and yield potential.
• Increasing fertilizer use efficiency will
  continue to be a critical goal for small grain
  farmers. Fortunately, there are several
  strategies to meet this goal, including
  diversification of cropping system.

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Want more information on soil fertility?

• http//landresources.montana.edu/soilfertility