In-Field Soil Phosphorus Measurement System

Crop growers in the United States, and in developed countries worldwide, apply large amounts of phosphate fertilizers to their fields. In the US for example, growers annually apply over 4,000,000 tons of phosphate fertilizer. Fertilizer rates are typically applied in excess of the crop need, since the cost of fertilizer is low relative to the loss in crop yield if a given nutrient is yield-limiting. Over-application of fertilizers can be harmful in some situations. Phosphorus increases may cause algae blooms in fresh-water ecosystems. An excess of P in the soil also can increase the risk of P runoff and leaching. Soils that are P-deficient, due to poor management or inaccurate sampling and application methods, can experience yield reductions. The economic and environmental concerns of both extremes demonstrate the importance of keeping phosphorus levels within a proper range. Phosphorus levels within a field often range from soils that are P-deficient to those are significantly above a sufficiency threshold. In order to deal with spatial variability, a large number of soil measurements must be taken on each field. Using conventional lab analyses, sampling at the scale needed for accurate mapping of phosphorus levels is not feasible. In-field measurements represent an appealing alternative. This project will develop the test equipment required to evaluate sensor technologies in a side-by-side comparison. The sensors to be used in this project have shown initial feasibility to meet the criteria. However, they have not been widely tested using unprocessed soil cores, nor has a thorough side-by-side comparison been conducted. In order to perform this feasibility comparison test, equipment will be devised to collect and process the soil cores, and bring them into contact with the sensors. Results from in-field sensors will be compared with laboratory-analyzed soil tests. The results of this Phase I project will establish a clear direction for the development of an in-field sensing system during a Phase II.