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Tracing Nitrogen Movement in Corn Production Systems in the North Carolina Piedmont: Analysis of Nitrogen Pool Size

Wetland Biogeochemistry Inst., Louisiana State Univ., Baton Rouge, LA 70803-7511, Formerly Dep. of Soil Science, North Carolina State Univ.
Dep. of Soil Science, North Carolina State Univ., Univ., Raleigh, NC 27695-7619
Dep. of Soil Science, North Carolina State Univ., Mountain Hortic. Crops Res. and Ext. Center, 2016 Fanning Bridge Rd., Fletcher, NC 28732-9216.

^* Corresponding author.

The fate of N in North Carolina Piedmont corn (Zea mays L.) was traced using N pool size analysis. In 1989 and 1990, selected N pools [corn; weeds; surface residues; and soil NH ^{arrange="stack">+}₄ NO^-₃, and potentially mineralizable N (N_o)] were sequentially sampled in four reduced chemical input systems: (i) crimson clover (Trifolium incarnatum L.) with conventional tillage (clover-till), (ii) no cover crop with conventional tillage and 70 kg N ha^–1 as NH₄NO₃ (fertilizer-till), (iii) crimson clover with strip-tillage (clover-strip), and (iv) no cover crop with no tillage and 70 kg N ha^–1 as NH₄NO₃ (fertilizer-no-till). The largest of the repeatedly measured N pools was soil N_o, which accounted for <10% of the total Kjeldahl soil N. Soil N_o was highest in the clover-till treatment, and had large seasonal fluctuations: 170 to 255 kg N ha^–1 in clover- till, and 117 to 210 kg N ha^–1 in other treatments. Fertilizer treatments had higher inorganic N levels than did clover treatments only immediately after fertilizer application. Although clover shoots contained 97 to 134 kg N ha^–1 yr^–1, more than the N applied to fertilizer treatments, no significant differences among treatments in plant (corn + weed) aboveground N accumulation (38 to 132 kg N ha^–1) were observed. Of these totals, weed N accounted for 5 to 30 kg N ha^–1. Surface residue N content was highest in reduced tillage treatments. In reduced chemical input systems such as these, N transfers among soil N_o, weed, and residue pools may be as large or larger than N transfers among soil inorganic and crop pools.

Received for publication July 6, 1993.

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