Division S-8 - Notes: Evaluation of a nitrogen-15 microplot design in furrow-irrigated cotton

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, Maricopa in 1991 (Casa Grande sandy loam) and Marana in 1995 (Pima clay loam). The purposes of the experiments were to evaluate the dimensions of an 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 L.). 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.