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Confined Microplot Size for Nitrogen-15 Uptake by Corn Plants in a Corn Intercrop System

Dep. of Plant Science

Angus F. MacKenzie and Chandra A. Madramootoo

Dep. of Natural Resource Sciences, Macdonald Campus, McGill Univ., 21,111 Lakeshore Rd., Ste Anne de Bellevue, QC, H9X Canada
Dep. of Agricultural and Biosystems Engineering Dep. of Natural Resource Sciences, Macdonald Campus, McGill Univ., 21,111 Lakeshore Rd., Ste Anne de Bellevue, QC, H9X Canada

Pierre Dutilleul and Donald L. Smith^*

Dep. of Plant Science

^* Corresponding author (ac10{at}musica.mcgill.ca).

The high cost of labeled N fertilizer places practical limitations on measuring the fate of applied N. Applying of the labeled ¹⁵N to a microplot within a larger plot can reduce the cost. The objective of this study was to assess microplot dimensions required to produce reliable ¹⁵N data and cropping system effects on corn ¹⁵N uptake under a regime of monocropped corn (Zea mays L.) and corn intercropped with annual Italian ryegrass (Lolium multiflorum Lam.). Nitrogen was applied to large plots (15 by 75 m) at 270 kg N ha^–1 on a fine, silty, mixed, nonacid, frigid Typic Humaquept soil during the 1993 and 1994 growing seasons. Enriched N fertilizer was applied to 1.15 by 1-m² confined microplots located in opposite halves of the large plot in each year of the study. Corn plants inside the confined microplots were sampled at 0.1, 0.3, and 0.5 m from the end borders of each microplot. In 1993, monocropping resulted in increases in leaf, stalk, and total dry matter production of 22, 41, and 30%, respectively, within microplots and relative to intercropped corn. There were no cropping system effects for these parameters in 1994. Monocropping increased atom % ¹⁵N enrichment in corn grain and stalks and increased fertilizer N recovery in all plant tissue compared with intercropping in both years. There were no differences in atom % ¹⁵N enrichment and fertilizer N recovery for plants harvested at the three sampling positions. These results suggest that a confined microplot with an area as small as 0.4 by 1.15 m can provide a reliable measure of fertilizer N recovery for corn plants in monocrop or intercrop systems. Any or all of the five plants within the microplot could be used to supply a reliable estimation of ¹⁵N recovery by corn plants.

Received for publication April 16, 1997.

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