The yellow leaves generally indicate a lack of nitrogen for nutrients. It can also indicate a lack of moisture in the soil, and having a very acidic soil can cause nutrient tie-up in soil. If you are soaking the soil about one foot deep with a weekly watering then look to the other items. You may want to check the pH of your soil. If it is below 6.0 you should add about 40 lbs of lime per 1,000 square feet of area. So calculate the square feet of your plot and adjust the lime up or down from the 40lbs. If the pH is good and your watering ok, then look to add some urea around your berry plants. Apply the granular like you would be salting food. Just a light sprinkle around the stems.