Can soil testing prevent nitrogen issues?
Written by
Michael Sullivan
Reviewed by
Prof. Martin Thorne, Ph.D.Soil testing prevents nitrogen issues from stunting your crops before yield potential is lost. I have visited fields with yield potential reduced by 30 percent because the nitrogen deficiency was not recognized until mid-season when the soil nitrate level was observed at 12 ppm (which is half of the ideal range). Regular soil testing allows you to obtain a nutrient deficiency map for the field and allows you to surgically apply the nutrient(s) versus applying blindly.
Critical Testing Times
- Test pre-planting: 3 weeks before seeding
- Mid-season: At 50% crop maturity (e.g., V6 in corn)
- Post-harvest: Guides offseason amendments
Ideal Parameters
- 25-50 ppm nitrate-N for most row crops
- pH 6.0-7.0: Maximizes nitrogen availability
- CEC >10 meq/100g for adequate retention
Cost vs. Benefit
- $15/test saves $200/acre in lost yield
- Labs provide NPK + micronutrient data
- DIY kits offer instant nitrate readings (85% accuracy)
A soybean farm in Nebraska for which I consulted increased its yield by 20% via testing twice a year. In the spring, the testing indicated their nitrate levels at 18 ppm, so they applied 40 lb N/acre. In the fall, the nitrate levels were elevated to 28 ppm with good fidelity, so the following year they reduced their input of fertilizer by 25% and continued to build on the yield.
To make sense of the tests you are doing, context is key! For example, last year, a client's pH of 5.8 was too low to unlock the existing nitrogen, even with levels of nitrogen at 35 ppm. We applied lime first and then fertilizer after that. Two months later, with no further applications of nitrogen, the available nitrate levels jumped to 42 ppm. This is display and proof that balance is better than just relying on a numerator!
Read the full article: Nitrogen Deficiency in Plants: Signs & Solutions
