notes on Northeast Nebraska Agriculture Conference 2025

December 16, 2025, Norfolk NE

Keynote: advances in nutrient management, Glen Rabenberg, SoilWorks LLC

• Nitrate (NO3-, high pH) is a growth stimulant for plants, vegetative growth
• Ammonium (NH4+, low pH) stimulates reproductive growth
• pH is incredibly important: above pH 7 no H+ is available to the plant. Below 6, plenty of H+ but other problems.
• Soil tests need to show both kinds of N or you're only getting half the story.
• Calcium is the mother of all minerals: if not >68%, mom's not in the house.
• Magnesium is one of 3 electrolyte minerals: hangs onto & stabilizes N.
  • over 15% you will see plenty of N in soil, need Ca to make it available.
  • Ca+Mg make dolomite, and N is released.
• above pH 8, microbes can't make ammonia, so plants can't fruit.
• N2 is 78% of our every breath, but it takes soil microbes to fix it.
• Given N to a plant that wants C is like promising steak and giving hot dogs.
• C:N ratio is too low on most farms. Needs to be like 16:1.
  • once you manage C, managing N becomes much easier.
• Refractometer measures sugar content: above 14 brix, insects stop eating plants.
  • Mg reflected in darker green leaves: more chlorophyll
  • There can't be Mg in soil without aeration.
• Phosphorus is dad if Ca is mom: without sufficient P, stuff goes wrong.
• handheld EC meter (electrical conductivity): if EC is too high, >1.0, microbes shut down.
  • want to see a consistent reading 0.3-0.5 across soil depth.
  • need a higher EC at reproductive time, 0.6-0.9.
• Soil has a positive charge during the day, negative at night.
  • sky and soil are always opposite charge
  • cellular growth happens more at night, respiration

Adding C to increase nutrient use efficiency: Todd Zehr, Soil Biotics

• Good soil is 47% carbon! Corn residue is ~44% C.
• dead microbes are up to half the total C in soil.
• ABC: Aminos, Biology, and Carbon
• Humates or humic + fulvic substances may be 70 million years old! Promote breakdown of OM by supporting microbes.
• Manure is great, but don't use too much! makes microbes lazy. Most effective at 10:1 or 20:1 C:N.
• Inorganic C takes a long time to break down: limestone, shells
• no one product is a silver bullet: need to fix your soil biology.
• prefer sap test to tissue test: more consistent results.
• everything's about balance
• humates chelate nutrients, preventing leaching.
• brace roots on corn are a bug, not a feature: indicate it's not finding the nutrients it needs.
• plants get 95% of nutrients from soil solution.
• Calcium stabilizes OM, increases C retention
• humic acid is too large to enter plant, but fulvic acid can, transports nutrients.
• microbial foods: kelp & fish

Soil and Plant Health, the Untold Story: Glen Rabensberg

• compost is a simulation of healthy soil
• "5% OM is utopia" no, not really, it's the C:N ratio
• Healthy plants are 47% C by dry matter, 43% O, 4% H, 3% N, and 3% minerals including minimum 2% Ca and 0.3% P. So all other minerals account for at most 0.7%.
• Soil penetrometer (compaction meter) should indicate 100-150 PSI for healthy soil respiration. Above 200 PSI microbes can't breathe, and above 300 PSI roots can't survive.
• Why C:N ratios matter:
  • most ag soils are 8:1
  • beneficial soil microbes require at least 16:1
  • beneficial mycorrhizal fungi require at least 18:1
  • balanced aerobic compost is 30:1 - 33:1
• Top 5 things for soil & plant health:
  1. available Calcium at all depths
  2. available Phosphorus
  3. organic C:N ratio
  4. Oxygen
  5. microbes
• Many agronomists don't check that pH is appropriate... needs to be 6.4-6.5 for agriculture
• hydrogen makes up more of a plant than nitrogen, but not available at high pH.
• How to reduce soil pH? S just makes sulfuric acid. But CO2 will also bring pH down, so add C.
• Even a thin soil crust will prevent O2-CO2 circulation.
• To get C:N ratio up, add Ca to release N to plants.
• tilling can't hurt soil fungi if C:N below 18:1 because fungi can't live that way anyhow.
• Most growers now have 1/3 to 1/2 brix they should - sequester more carbon!
• sunlight will never oxidize potassium.

Changing nutrition management systems with rhizophagy: Jeffrey Kleypas, Advancing Eco Agriculture

• plants manage the largest dairy in the world! (milking microbes)
• oxidative stress is the milking process.
• soluble fertilizer fails to deliver under climatic stress.
  1. first loss: plant communication
  2. reduced exudates: microbes go to sleep
  3. microbial starvation, species shift
  4. breakdown of relationship between plant & microbes
  5. nutrient imbalance in plants
  6. soil degradation
  7. plants become chemically dependent
• dry conditions: reduced diffusion, salt stress, nutrient lock-up
• wet conditions: leaching, denitrification, reduced O2, compromised rhizophagy
• regenerative advantage: rhizophagy provides better resilience in extreme conditions, builds nutrient density in plant.
• regenerative system:
  • soil test, including unavailable nutrients
  • bulk nutrient corrections: gypsum, K, N, manure
  • bio system application in-furrow
  • foliar application, managed with sap testing
  • carbon cycle: cover crops, biochar, manure