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using Reflectance Techniques
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(1: Agricultural Engr. Dept., Texas A&M University, USA The success of U.S. agriculture is attributable to the effective use of agricultural chemicals. In 1996, 98% of over 70 million acres were received nitrogen treatment for corn plants. This heavy reliance on chemicals raises many environmental and economic concerns. In this research, for an effective use of agricultural chemicals, a plant nutrient sensor is being developed. The overall objective of this research is to develop a real-time multispectral sensor that can detect nitrogen deficiency in crop plant using spectral response from plant canopies. In this project corn is chosen as a testing crop for the nutrient sensor. One of the problems in developing a nutrient sensor would be variability of spectral response resulted from different canopy colors. Even when two different corn plants have same amount of nitrogen in their canopies, their spectral response would be different if their canopy colors are different. In this project, as a preliminary step for developing a nitrogen sensor, a characteristic color for each variety needs to be distinguished. Two different corn varieties are chosen for a preliminary testing: light color leaf and dark color leaf. Corn plants are grown in a greenhouse during a winter period for a preliminary testing of the sensor system. Three different levels of nitrogen treatment (adequate, moderate and low) are applied to corn plants while other nutrients are supplied equivalently for all treatment levels.
A photodiode array is used to detect multispectral reflectance in the range of 400-1100 nm from corn canopies for a real-time field use. A multifunction I/O board is utilized with a Pentium processor for the remaining computing tasks. With a development of this sensor system, fertilizers could be applied specific locations where they are needed rather than applying whole field. This could be one of stepping stones for eventual farm automation. Wonsuk Lee and Stephen W. Searcy. 1999. Assessing nitrogen stress in corn varieties of varying color. Paper No: 99-3034. Presented at the 1999 Annual International ASAE Meeting, July 18-21, Toronto, Ontario, Canada. Examples of nitrogen treatment effects on corn growth. Left half: Asgrow RX938, 180 lb/ac N, Right half: Asgrow RX938, 0 lb/ac N
Color difference between varieties with no N treatment RX897 (left), RX901W (middle), and RX938 (right) Example spectral reflectance of corn leaves measured by a spectrophotometer RX897 Ear leaf with 5 different N treatments.
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