Printed Nitrate Sensors for In-Soil Measurements

Managing nitrate is a central concert for precision agriculture, from delineating management zones, to optimizing nitrogen use efficiency through in-season applications, to minimizing leaching and greenhouse gas emissions. However, measurement methods for in-soil nitrate are limiting. State-of-the-art soil nitrate analysis requires taking soil or liquid samples to laboratories for chemical or spectrographic analysis. These methods are accurate, but costly, labor intensive, and cover limited geographic scope. Some colorimetric tests are available which give qualitative nitrogen information. Other researchers rely on measurements of applied nitrate, leaching, and uptake to calculate mass balance equations for larger areas, but errors in estimates of inputs or outflows lead to errors in nitrate concentration. Alternatively, NDVI or other vegetative indices can be used to estimate spatial variation of nitrate in plant material, but by the time nutrient deficiencies are evident in these indices, it may be too late to correct.