What is the optimal pH for growing crops?

http://cceonondaga.org/resources/soil-ph-for-field-crops
Here’s a good read for you!

"The desirable pH range for optimum plant growth varies among crops. While some crops grow best in the 6.0 to 7.0 range, others grow well under slightly acidic conditions. Soil properties that influence the need for and response to lime vary by region. A knowledge of the soil and the crop is important in managing soil pH for the best crop performance."

The optimal pH can vary slightly based on the particular crop you're trying to grow, but generally a pH between 6-7 is going to be best. Why "best" at these levels? The availability of certain essential nutrients is affected by the pH. Soils that are too acidic or too basic will limit the availability of these essential nutrients and cause the crops to suffer because of this deficiency. 

Here's a chart that shows nutrient availability based on pH. 

1) How available most nutrients are when the soil is slightly acidic.

and

2) How some micronutrients aren't quite as available as we'd hope when soils are in the "optimal" range. 

So, while we need to shoot for a balanced pH, we still need to monitor the micronutrient levels through things like tissue testing and could potentially need to apply these nutrients as a foliar application. 

For additional reading on getting your soil into that optimal range, take a look at this article on the importance of lime to crop health. Also, make sure to utilize the best liming source for your farm depending on whether you need calcitic or dolimitic lime. 

The optimal pH for fields will depend on many factors including crop type, soil conditions, and region. But, in general, a recommended soil pH ranges from 6 to 7.