1. Response of cotton canopy reflectance to petiole nutrients;Bajwa S.;Wayne E. Sabbe Arkansas Soil Fertility Studies AAES Research Series,2004
2. Remote Sensing of Plant Nitrogen Status in Corn
3. Biggs G. L. T. M. Blackmer T. H. Demetriades-Shah K. H. Holland J. S. Schepers and J. H. Wurm. 2002. Method and apparatus for real-time determination and application of nitrogen fertilizer using rapid non-destructive crop canopy measurements. U.S. Patent no. 6393 927.
4. Optical crop sensor for variable-rate nitrogen fertilization in corn: i - plant nutrition and dry matter production
5. Bremner, J. M., and C. S. Mulvaney. 1982. Total nitrogen. In Methods of soil analysis: Part 2. Chemical and microbiological properties, ed. A. L. Page, R. H. Miller, and D. R. Keeney, 595–624. Madison, Wisconsin: American Society of Agronomy, Soil Science Society of America.