Across the 55 field tests an average reduction in 14 lbs of nitrogen per acre was used when the sensors were regulating the application rate. During the wet spring of 2008 the modified applicators increased the yield by an average of 8 bushels per acre. Scharf said the sensors chose higher rates than did farmers, which compensated for nitrogen lost through the excess rain. Those results, plus the increased yield from other tests raised profit by a $17 per acre average across all farms.
So what is the downside? Scharf says the sensor system costs $10,000 to $16,000 and there is a learning curve in being able to use it. He says that is the only hurdle to wider adoption, but he also says it will take a culture change in farmers switching from fall application to a spring side-dress application of nitrogen. However, with heavy rains that either prevent the fall application or leach out nitrogen before it can be used by the corn, there is more of an incentive to apply it closer to the time it is used by the corn plant.
A perfect world would have the corn plant use all of the nitrogen that is applied to satisfy its needs; however that is difficult to achieve. In too many cases excess nitrogen has been applied and in other cases nitrogen has been leached from the root zone before it could be used by the corn. One means of more accurate application is with the use of sensors which detect nitrogen deficiency in the corn and regulate the flow to apply the appropriate amount. The result has been a reduction in the amount of nitrogen applied, compared to typical rates, along with no negative impact on yield.
Source: FarmGate blog