University of California
Nutrient Management for Vegetable, Fruit & Nut Crops
Walnut
Growing walnuts in Oregon. J. Olsen. (2006) Oregon State Univ. Extension Service, EM897.
Nitrogen fertilization recommendation for walnut. P.H. Brown, Q. Zhang, M. Stevenson, R.C. Rosecrane.
Walnut research reports :: tree nutrition (UC Fruit & Nut Research & Information Center website)