Evaluation of a NITROGEN-15 microplot design in furrow-irrigated cotton

Abstract

Information is needed regarding an appropriate microplot design for use in furrow-irrigated row crop systems. Field experiments were conducted at two locations in Arizona, USA: Maricopa in 1991 (Casa Grande sandy loam [Typic Natrargid]) and Marana in 1995 (Pima clay loam [Typic Torrifluvent]). The purposes of the experiments were to evaluate the dimensions of a 15N microplot design used in a furrow irrigated row crop system. The experiments each utilized ammonium sulfate fertilizer with 5 atom% 15N enrichment applied at a rate of 56 kg N/ha in a simulated side-dress band application during the early bloom stage of development of upland cotton (Gossypium hirsutum). At each location, microplots were four 1.02-m rows wide and 1.00 m in length. Whole plant samples were collected at specific locations within and near the microplots. Collection of plant materials at a minimum distance of 25 cm from the microplot borders provided uniform 15N enrichment levels for determining fertilizer N uptake and recovery. Microplots with the dimensions of those used in this study are sufficient for collecting plant materials from a 1-m2 area, consisting of two 50-cm segments from the interior two rows of the four row microplot.