I find that the site for A&L Canada, a commercial company that specialises in this sort of thing to be an invaluable resource. If you have specific questions, they are more than willing to correspond with you

I disagree with Dr. Sawicka.  I am a precision agronomist in South Dakota, we have seen an increase in yield and profit with corn (Zea maize, L.).  However, when you use the term prescriptive planting, are you referring to precise seed singulation, variable rate seeding, precision hybrid placement?  These are two separate issues.  Equipment is now available to change hybrids/varieties on the fly.  It is widely accepted that poor seed singulation results in yield loss; Doerge et al. found that for every inch of standard deviation of plant spacing over 2 inches, there is a yield loss of 4 bushel per acre. Variable rate seeding has been shown to increase profit by $30/acre at $3.50 corn.  Profits are increasing beyond this due to seed savings and proper seeding rates in different growing environments.  Matching hybrids/varieties to micro-environments in-field is likely to add an additional $20 - $30/acre.  Initial capital investments for equipment can be depreciated over 5-10 years, agronomy service providers are improving their business plan to reduce up-front cost for field prescriptions, some are simply building it into the cost of seed/fertilizer and spreading their costs over all products sold regardless if a customer requests the service or not.  There are a lot of softwares 'out there' that are push-button type products that make claims to provide the optimal seeding rate and/or hybrid for your field.  Most require at least 5 yrs of yield monitor data.  Beware!  There is a lot of products that are not based on science and do not allow you to change algorithms or use your own technique for writing the prescription.  I have not seen any other research for variable rate seeding of soybeans, wheat or any other crop but I do know that some softwares are allowing users to create a prescription for those crops.  What science they use is unknown to me.

If you want a detailed list of the most common technologies applied to Precision Farming practices, take a look at the following explanatory items:

• High precision positioning systems (like GPS) are the key technology to achieve accuracy when driving in the field, providing navigation and positioning capability anywhere on earth, anytime under any all conditions. The systems record the position of the field using geographic coordinates (latitude and longitude) and locate and navigate agricultural vehicles within a field with 2cm accuracy.

•Automated steering systems: enable to take over specific driving tasks like auto-steering, overhead turning, following field edges and overlapping of rows. These technologies reduce human error and are the key to effective site management:

• Assisted steering systems show drivers the way to follow in the field with the help of satellite navigation systems such as GPS. This allows more accurate driving but the farmer still needs to steer the wheel.
• Automated steering systems, take full control of the steering wheel allowing the driver to take the hands off the wheel during trips down the row and the ability to keep an eye on the planter, sprayer or other equipment.
• Intelligent guidance systems provide different steering patterns (guidance patterns) depending on the shape of the field and can be used in combination with above systems. 

• Geomapping: used to produce maps including soil type, nutrients levels etc in layers and assign that information to the particular field location. (see picture on the left)

• Sensors and remote sensing: collect data from a distance to evaluating soil and crop health (moisture, nutrients, compaction, crop diseases). Data sensors can be mounted on moving machines.

• Integrated electronic communications between components in a system for example, between tractor and farm office, tractor and dealer or spray can and sprayer.

Caption: Seeder using a geomapping system

• Variable rate technology (VRT): ability to adapt parameters on a machine to apply, for instance, seed or fertiliser according to the exact variations in plant growth, or soil nutrients and type.