Laboratory Methods for Estimating Plant Available Nitrogen in Soil1
- J. A. Ryan,
- J. L. Sims and
- D. E. Peaslee2
Biological and chemical methods for obtaining an index of soil N availability to a test crop under different levels of N fertilization were evaluated on 15 Kentucky soils having a range of organic matter contents of 0.72 to 2.79%. Organic matter, N mineralized during aerobic incubation at 30C or 40C for 7 or 14 days, and extractable NH4+-N after incubation under waterlogged conditions for 7 or 14 days at 30C and 14 days at 40C were all significantly related to N uptake and relative increase in N uptake by ‘X-1605’ grain sorghum (Sorghum vulgares) during 18 weeks of growth in the greenhouse.
When the soils were amended in the laboratory with P and K or P, K, and Ca and incubated under waterlogged conditions, the relationship between extractable NH4+-N and N uptake by sorghum improved greatly over unamended soils. Nitrogen mineralized during aerobic incubation and NH4+-N after incubation of amended soil under waterlogged conditions were among the better predictors of both N uptake and relative increase in N uptake.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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