INNOVATIVE¹⁵N MICROPLOT RESEARCH TECHNIQUES TO STUDY NITROGEN USE EFFICIENCY UNDER DIFFERENT ECOSYSTEMS

Abstract

Use of labeled 15 N techniques can help improve and refine knowledge required to understand the dynamics of the N cycle under agricultural systems. The examples reported in this paper illustrate that, with creativity and careful planning, use of 15 N-enriched or depleted fertilizers can be used in many types of N experiments with various crops, cropping systems, and in many types of agroecosystems. The objective is to report examples of a wide range of field studies that researchers can hopefully draw upon to design and utilize N isotope techniques that accomplish the objectives for their own research. Examples of microplot studies with and without physical barriers are discussed along with some of the strengths and limitations of each approach. Even though 15 N technology offers considerable opportunity to understand N cycling, it too has limitations to its use. Types of fertilizer 15 N materials and methods for applying 15 N materials are discussed including some discussion about the use of ammonium versus nitrate forms; literature sources are provided for additional reading about the use of 15 N techniques. 951

Decomposition of Nitrogen‐15 Labeled Hoop Pine Harvest Residues in Subtropical Australia

“…2b) than with bare earth. The use of mixed residues was also in agreement with Follett (2001) who stressed the need to conduct 15 N research under realistic management conditions. In addition, mixing of the foliage, branch, and stem materials in the combined-residue microplots would alter the substrate quality (such as C/N ratio) for microbial decomposition, which might also result in different decomposition kinetics of the mixed residue components than those of single component microplots (Xu et al, 1993b).…”

“…due-derived N has been limited by the availability of A major management change within hoop pine planadequately 15 N-labeled and representative material. Agtations in Southeast Queensland, Australia, has been ricultural research has made use of 15 N-labeled clover the retention of harvest residues on site, pushed into (Wivstad, 1999), maize, and wheat (Thomsen et al, 2001). continuous mounds, or windrows, along the contour Nitrogen-15 enriched foliar material has been produced by spraying the leaves of trees with a 15 N-enriched nutri-T.J. Blumfield, Z.H.…”

Nitrogen Fertilizer Use Efficiency of Furrow‐Irrigated Onion and Corn

“…Plant samples were collected from inside and outside of the 15 N microplot area to detect potential lateral movement of 15 N fertilizer and to compute relative fraction of plant 15 N inside and outside of the microplots. Results of these measurements (Follett, 2001) show essentially no lateral movement of 15 N across the irrigation furrow between onion beds. Average maximum detectable distance that the 15 N had moved along the rows, beyond the microplot ends, as a result of cultural practices and irrigation was 0.4 and 0.3 m for the 18 May and 25 June applications of 15 N fertilizer, respectively.…”

15N Fertilizer recovery in different tillage–straw systems on a Vertisol in north‐west Mexico

“…High summer temperatures and the shorter cropping cycle lead to lower maize yields in summer compared to winter in the Yaqui Valley. Maize yield in the micro‐plots was lower than the whole plot because micro‐plots are less representative of one‐row crops compared with two‐row crops like wheat, and the plant population is lower and more variable (Follett, ). For yield evaluation, the whole plot average is more representative, showing that CTB produced significantly lower maize yields than the other treatments.…”