Confined microplot size for nitrogen-15 uptake by corn plants in a corn intercrop system

Abstract

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 large 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 (Lollum 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 suggests 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.