Fertilizer and soil nitrogen use by corn and border crops in a strip intercropping system

Corn (Zea mays L.) has greater yield potential when strip-inter-cropped than when monocropped, but this potential may be compromised by a failure to understand how N requirements change with row position and the possible N competition of adjacent crops. A four block, completely randomized, split-plot experiment was conducted on a Haig loam soil (fine, smectitic, mesic Vertic Argiaquolls] in southern Iowa, to determine crop utilization of N fertilizer point-injected into corn rows. Nitrogen fertilizer uptake was evaluated in (i) corn rows injected with labeled N fertilizer; (ii) corn rows adjacent to the injected rows; and (iii) plants at the edge of the adjacent soybean (Glycine max (L.) Merr.] and oat (Avena sativa L.)-alfalfa (Medicago sativa L.) strips. Main treatments consisted of three tillage systems: conventional tillage (CT), reduced tillage (RT), and no-till (NT). Subplot treatments consisted of point injection of 15N-enriched NH4NO3 (67 kg N ha-1) in-row at three row positions within the corn strips. Grain and stover yield, Kjeldahl N, and isotope composition of plant materials were determined. Corn yield and labeled-N recovery differed with tillage to the extent that tillage affected early and total season moisture availability. Labeled-N recovery in labeled rows did not differ with row position. Labeled-N recovery in unlabeled rows or crop borders was typically less than 5% of that recovered by labeled rows. Nitrogen is primarily recovered by the row to which it is applied; therefore, row-by-row precision applications seem to be an appropriate management tool.