Dr. Terry Bates and Jennifer discuss the multiple decade multiple factorial study that helped form our knowledge on vineyard nutrition and basis of our recommendations.  The original West Tier publication back in 1969:
Shaulis N, Steele RD. 1969. The interaction of resistant rootstock to the nitrogen, weed control, pruning, and thinning on the productivity of Concord grapevines. J Am Soc Hortic Sci 91:122–129. 

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