Submitted to: Asian Conference on Precision Agriculture
Publication Type: Proceedings
Publication Acceptance Date: 8/30/2009
Publication Date: 10/14/2009
Citation: Dao, T.H., Miao, Y. 2009. Sensing Site-Specific Variability in Soil and Plant Phosphorus and Other Mineral Nutrients by X-Ray Fluorescence Spectrometry. Asian Conference on Precision Agriculture. Interpretive Summary: To attain optimal crop yields, phosphorus (P), nitrogen (N), and potassium (K), have become essential production inputs. Although significant progress has been made in real time management of N inputs, P sources have not received the same degree of scrutiny. Early emergence and uniform crop stand establishment is one of the most important yield contributing factors. Phosphorus is a critical nutrient for early seedling growth and a uniform application of starter P fertilizer is traditionally placed below the seeds at planting. However, soil P often is highly variable within a field and contributes to extremes in P availability that can be detrimental to plant growth and the environment. The problem is more acute in fields amended with animal manure, which is highly heterogeneous in composition. While numerous analytical techniques can provide the needed information, they differ widely in analytical sensitivity, labor, time, and the cost of chemicals used per analysis, and transportability, thereby on-site or on-farm analysis. With recent technological advances in material science, measurements of light elements with faint fluorescence, although difficult, are becoming more feasible. These light elements include many plant nutrients such as P, magnesium, calcium, and K. Because of the rapid and non-destructive nature of the analysis, X-ray fluorescence spectrometry (XRFS) is adapted to both on-site and post-harvest laboratory analysis of soil and plant tissue samples. We found a number of significant advantages over prevalent wet chemistry techniques, including minimal sample preparation, rapid analysis times thus high throughput, multi-element detection, and on-site field use with portable analyzers for environmental studies as well as site-specific nutrient management applications, and the development of practices to minimize the footprint of agricultural production and laboratory chemical analysis on the environment.
Technical Abstract: Detection and rapid response to in-season changes of soil nutrient availability and plant needs with weather conditions and site-specific characteristics are essential to the optimal performance of an agronomic crop production system. With recent advances in material science, detector design and sensitivity, and improved sample-target-detector geometry, quantitative determinations of light elements with low energy fluorescence are becoming more feasible. The non-destructive multi-element capability of X-ray fluorescence spectrometry (XRFS) has been applied to obtain compositional data on soil and plant samples in two large-scale field studies of nutrient management and mitigation of nutrient losses to the environment. The objectives are to demonstrate the benefits of XRFS in achieving accurate and timely compositional information. Significant relationships between XRFS-phosphorus concentrations and indices of plant availability supported the role of such methodology as a real-time soil phosphorus and other mineral nutrient sensor for site-specific precision management of nutrient inputs. Thus, the technology has an essential role in increasing nutrient-use efficiency and crop productivity while reducing nutrients losses from the farm.