Soil Type and Moisture Regime Effects on Fertilizer Efficiency Calculation Methods in a Nitrogen-15 Tracer Study
1992
Torbert, H. Allen | Mulvaney, R. L. | Vanden Huevel, R. M. | Hoeft, R. G.
Research was conducted to determine the extent to which the method of calculation affects estimates of fertilizer N efficiency using ¹⁵N as a tracer. Corn (Zea mays L.) was grown at three locations in Illinois that varied widely in soil type. Three early-season moisture regimes (ambient, ambient + 100 mm of excess water, and ambient + 150 mm of excess water) were established to obtain different fertilizer N efficiencies on each soil. Application of ¹⁵N-enriched KNO₃ (168 kg N ha⁻¹) was made to a Drummer silty clay loam (fine-silty, mixed, mesic Typic Haplaquoll) at DeKalb, a Cisne silt loam (fine, montmorillonitic, mesic Mollic Albaqualf) at Brownstown, and a Plainfield sand (mixed, mesic Typic Udipsamment) at Havana, IL.. Fertilizer N efficiency was calculated from the difference between N uptake by fertilized versus unfertilized plants, from the amount of ¹⁵N recovered in the plant, and from the recovery of I5N in both the plant and soil. for the Drummer and Cisne soils, the three calculation procedures gave different percent fertilizer N efficiencies when averaged across moisture treatments, and different trends among moisture treatments. for the Plainfield soil, percent fertilizer N efficiency values were lower than those obtained for the Drummer or Cisne soil, and the method of calculation had very little effect. The results indicate that, for most soils, N fertilizer efficiency ratings vary with the method by which they are calculated. The present study demonstrates a need for standard terminology to help identify parameters used to define fertilizer efficiency.
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