Your plots are lacking certain micronutrients. Besides the big-three nutrients—nitrogen, phosphorus, and potassium (N-P-K)—provided in common fertilizers, plants also need an array of micronutrients to thrive, including copper, zinc, cobalt, manganese, and boron. These interact with the soil and major fertilizers in complex ways to promote photosynthesis, root formation, cell-wall division, and other vital plant functions. They also help control harmful types of fungus, and they assist beneficial microbes in the soil. A lack of them can cause any or all of the symptoms above. Just like N-P-K, they need to be replenished periodically.