Rich Koenig, Associate ScientistExtension Soil Fertility Specialist

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Soil fertility considerations in direct seeding

• Rich Koenig, Associate Scientist/Extension Soil
  Fertility Specialist

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Discussion Topics

• Soil changes as a result of direct seeding
  (compared to conventional tillage)
• Implications of these changes on nutrient
  management
• Nitrogen mineralization
• Cold, wet soils and nutrient placement
• Enhanced immobilization and volatilization
  potential
• Other
• Other topics and recent research results, as time
  permits
• Chloride
• Phosphorus
• Split nitrogen applications
• Nitrogen management for wheat

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Physical changes

• Improved aggregation (formation of clods)
• Increased density (compaction) in soils prone to
  this problem (fine textures)
• Reports of short term increase in compaction
  problem
• Aggregates eventually become more stable and
  compaction problem eases
• Improved water infiltration and percolation
• Reduced runoff, erosion, etc.

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Physical changes

• Stratification of residue
• Layering on the surface vs. incorporation
• Higher soil moisture, particularly at the surface
  
• Lower soil temperature due to the insulating
  effect of residue and higher moisture
• Lower oxygen concentration at the surface
• Collectively, cool, wet soils limit biological
  and root activity, and nutrient uptake by plants

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Biological changes

• Overall higher microbial biomass (more/larger
  organisms out there)
• Different groups of microbes
• Increase in fungi biomass compared to bacteria
• Mycorrhizae fungi and associated benefits on
  nutrient uptake
• Perhaps a lower level of microbial activity
• Slower and different metabolism
• Physical effects residue not in contact with
  soil
• Different location of microbes and activity (in
  residue layer rather than in the mineral soil)

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Biological changes

• Lower nitrogen mineralization rates per unit of
  organic matter (remember biological process)
• Lower surface temperature
• High moisture and lower oxygen levels
• Crop residues not in contact with the soil and
  not physically broken down by tillage
• Potential for immobilization and volatilization
  with broadcast nitrogen
• Root growth and nutrient availability issues with
  lower temperatures

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Chemical changes

• Short term - lower mineralization contributions
  to the total N supply
• Eventually, an overall higher level of organic
  matter leading to greater mineralization
  contributions to the total N supply
• Nutrient and pH stratificationor layering
• Phosphorus, potassium, other immobile nutrients
• Many unknowns here

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Stratification of acidity under direct seeding
6 inches
No treatment
6 inches
Broadcast lime
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(No Transcript)
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Aside how fast are changes reversed in a return
to tillage?

• Immediately for soil temperature and moisture
  conditions
• As little as 2 months to completely reverse soil
  aggregation and other physical improvements
• Immediate increases in nitrogen mineralization,
  carbon dioxide evolution and perhaps nitrous
  oxide emissions

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• Implications

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Nitrogen mineralization

• Issue 1
• Initial conversion to direct seeding results in
  the accumulation of organic matter with a
  required accumulation of organic nitrogen
• Consider this
• 1 organic matter in 1 foot of soil
• 40,000 lb organic matter/acre
• 15,000 lb organic carbon/acre
• 1,500 lb organic nitrogen/acre
• Transition period varies with environment and
  cropping system (5-10 years commonly quoted)

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Example of different scenarios
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Nitrogen mineralization

• Issue 2
• Rates of organic matter mineralization are lower
  due to cooler and wetter (lower oxygen) soil
  conditions
• Research
• No-till mineralization rates were 44 of
  conventional till rates in a Missouri corn
  rotation
• No-till mineralization rates were 52 of
  conventional till rates in canola residue from
  Canada
• 3.4x higher rates of mineralization with
  conventional compared to no till in Georgia with
  sourghum
• Larger differences in residue of cereals than
  legumes

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Nitrogen mineralization

• How to deal with this?
• Options during the transition to direct seeding
• Dont take the mineralization credit
• Dont include surface organic residues in soil
  samples
• Use a lower N mineralization estimate
• 10 to 15 lb N for each organic matter up to 3
  (compare to 20 lb N for each in conventional
  till)
• Factor in immobilization

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Mineralization in Palouse conventional till
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Nitrogen mineralization

• After the transition to direct seeding
• Monitor soil organic matter levels (now need to
  include surface residues)
• Look for stable numbers over time completed the
  transition
• Continue to use lower factor for N mineralization
  per organic matter

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Colder and wetter soils

• Reduced root growth and efficiency of nutrient
  uptake, especially in spring
• Mycorrhizae may partially offset this effect
• Emphasize the importance of subsurface banding of
  phosphorus and nitrogen
• Emphasize the importance of starter fertilizers
  placed with or near the seed, especially for
  spring crops

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Immobilization and volatilization potential

• Limited to surface broadcast applications of
  nitrogen for immobilization and urea-based forms
  for volatilization
• Subsurface banding to place nitrogen below
  residue limit immobilization
• Broadcasting nitrgoen when temperatures are low
  and precipitation is imminent to limit
  volatilization

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Direct seed fertility recommendations emphasize

• Importance of soil testing
• Difficulty in estimating nitrogen mineralization
  during the transition and later
• Importance of subsurface placement of nitrogen
  and immobile nutrients
• Importance of starter fertilizers
• Some unknowns

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• Chloride studies

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2004-05 and 2005-06 Winter Wheat Chloride Studies

• Comprehensive study
• 2 locations Pullman and Farmington (soil test
  chloride 18-19 lb/ac in top 2 feet)
• 2 sources ammonium chloride and potassium
  chloride
• 2 application times fall (deep band) and spring
  at herbicide treatment
• 2 rates 0 and 30 lb chloride/acre
• 5 varieties Falcon, Finch, Madsen, ORCF 101,
  Tubbs

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Leaf spot on Clearfirst in PNW
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Average chloride timing effects (plt.01)
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Average chloride source-rate effects
No statistical difference

Significantly different from Cl treatments
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Average yield response - all site-years
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11 Average response (bu/ac)
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0
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Madsen no chloride
With chloride
Finch no chloride
With chloride
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Flag leaf spots - 2005 Pullman study
stripe rust