URBANA, Ill. - The fertilizer applicator moving across the University of Illinois agricultural engineering farms passed a crucial test in the past year--an eye test.

U of I’s fertilizer applicator possesses something that you don’t usually find on farm machinery. It has a high-tech eye, a single camera mounted roughly 12 feet in front of the boom. Researchers tested the vision sensor last year and found that it was extremely accurate in determining whether plants are under stress due to a lack of nitrogen.

According to agricultural engineer Qin Zhang, the sensor's ability to detect nitrogen stress in plants was comparable to leaf tests using a SPAD meter.

This year, Zhang said, the goal is to merge the sensor with variable-rate technology. The result will be a machine that uses its high-tech eyesight to scan the plants as it moves across the field. The resulting data is then sent to a computer that controls the variable-rate applicator. The applicator varies the rate of fertilizer according to the nitrogen needs of different plants. And it does the job on the fly in real time.

As Zhang and fellow agricultural engineer Alan Hansen put it, such machines are the next big step for variable-rate technology.

Currently, Hansen explained, farmers must map the field in a separate pass, either aerial or on-ground. Then the map is plugged into a computer and used to vary the rate of fertilizer. But there is a considerable delay between creating the map and actually applying the nitrogen.

With this new system, the images are taken and processed literally seconds before the fertilizer is applied.

To determine nitrogen stress in corn plants, the applicator-mounted sensor analyzes the reflectance of light coming from the plants, Hansen said. But this is no easy task. The sensor must be able to distinguish the light bouncing off of the plant from the light bouncing off of the background soil. What’s more, it must be able to do the job under all kinds of environmental conditions.

“If you have a cloudy day, your camera will see the crop differently,” he pointed out. Therefore, the sensor must be able to take into account the effect of a cloudy day on light reflecting from the plants.

According to Zhang, the variable-rate sprayer is able to change the rate of nitrogen being applied by individual nozzles, making it possible to vary the rate on different rows. The key is making sure that the right nozzle hits the right plants with the right amount of fertilizer as determined by the on-board sensor and computer.

U of I work on this project dates back to 1997, when it was started by professors John Reid and Shufeng Han with funding from the Case Corporation. Zhang is now leading the effort to create a prototype applicator by 2003—a machine that is fully capable of scanning the crop, determining nitrogen stress and varying the rate of fertilizer applied all in one single pass. This work is being funded by the Illinois Council on Food and Agricultural Research.

According to Hansen, the new developments in sprayer technology may have the potential of reviving interest in variable-rate technology. As he explained, the first wave of enthusiasm over variable-rate equipment in the 1990s has waned because of economic considerations.

The selling point has always been more accurate applications with variable rates. Increased accuracy would bring savings in chemicals, not to mention less risk to the environment.

“But there’s still some skepticism as to the economic benefits of this technology,” Hansen said.

Since the early days, however, the technology has become more reliable and computing power has soared, he added. Combine those advances with an ability to vary rates on-the-go in real time and the variable-rate system may eventually find itself riding a new wave of interest.

Source: Alan Hansen, (217) 333-2969, achansen@uiuc.edu; Qin Zhang, (217) 333-9419, qinzhang@uiuc.edu