Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/24/2008
Publication Date: 1/8/2009
Publication URL: http://hdl.handle.net/10113/26825
Citation: Hodgen, P.J., Ferguson, R.B., Shanahan, J.F., Schepers, J.S. 2009. Uptake of point source depleted 15N fertilizer by neighboring corn plants. Agronomy Journal. 101: 99-105. Available: http://agron.scijournals.org/cgi/reprint/101/1/99 Interpretive Summary: Conventional N management strategies for corn production systems in the U.S. are characterized by low N use efficiency (NUE), environmental contamination and concerns regarding use of N fertilizers in crop production. Hence, development of alternative N management strategies that maintain crop productivity, improve NUE and minimize environmental impact will be essential to sustaining corn production systems. To improve NUE some have proposed using active sensor reflectance (self-illuminating) measurements of corn canopy N status to guide spatially variable in-season N applications, beginning at early vegetative growth and proceeding through silking. Ground-based active sensors make it possible to collect canopy data that are useful for making on-the-go N fertilizer application decisions. These technologies raise questions about plant-to-plant competition for targeted fertilizer N applications. The answers to these questions are confounded by the amount of leaf area and aerial domain of the individual plants. To help understand the issue of fertilizing individual plants to address differences in plant chlorophyll content and biomass to optimize yield, isotopic N fertilizer was injected beneath the center plant in a series of plants in a row. Other plants in the row received the same amount of N fertilizer injected in the same position. One series of plants received the injected fertilizer at the nine leaf stage and another set at the tasseling (VT) stage. Seven to 10 days after injection of the N fertilizer the plants were destructively harvested and divided into three major components. The amount and location of the isotopic fertilizer within the plants was determined relative to the targeted plant that directly received the isotopic fertilizer. In total, 45% of the isotopic N taken up within a week or so went into the plant immediately above the source when applied at the nine-leaf stage. In contrast, 63% of the N isotope taken up went into the targeted plant when the fertilizer was applied at the VT stage. Adjacent plant uptake accounted for 37 to 55% of the isotopic N uptake. The data presented in this study indicate variable rate application schemes should realistically “sense” a three- to five-plant sequence when plants are ~6 inches apart, because roots at the V12 and R1 growth stages were intermingled as far as 14 inches away from a point fertilizer N source.
Technical Abstract: Ground-based active (self-illuminating) sensors make it possible to collect canopy data that are useful for making on-the-go nitrogen (N) fertilizer application decisions. These technologies raise questions about plant-to-plant competition for targeted fertilizer N applications. This study evaluated the extent to which fertilizer N applied to an individual corn plant might be intercepted by adjacent plants in the row. Depleted 15N ammonium-nitrate was injected under the center maize plant while the four neighboring plants on each side in the row received the same rate as natural abundance ammonium-nitrate fertilizer. Above ground biomass was collected 10 (at V12) and 7 (at R1) days after each fertilizer application. Plants were separated into three components at each sampling date. The uptake pattern of depleted 15N indicated an individual maize plant acquires most of its in-season N from an area within ~40-cm radius. Adjacent plants ~18-cm away from the tagged-N source contained 32 to 40% of the total depleted 15N that was taken up by all nine plants in the sequence. Maize plants ~36 cm from the point source only acquired 5 to 13% of the depleted 15N source that was taken up by all nine plants.