Soil type and moisture regime effects on fertilizer efficiency calculation methods in a nitrogen-15 tracer study.
Torbert H.A. | Mulvaney R.L. | Vanden Heuvel 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 15N in both the plant and soil. For the Drummer and Cisne soils, the three calculation procedures pvt 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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