Abstract
’Shogoin’ turnip plants (Brassica rapa L.) were grown in sand culture under five nitrate:ammonium (NO3:NH4) ratios (N:N of 1:0, 3:1, 1:1, 1:3, 0:1). The leaves expressed symptoms of NH4 toxicity (reduced growth and curly leaves with dark‐green areas surrounding yellow spots) when NH4 was the dominant nitrogen (N) form. Increasing NO3 in the nutrient solution significantly (p<0.01) increased leaf and root fresh weight and dry weight. Leaf nutrient concentration and composition of all elements analyzed, except N and calcium (Ca), responded quadratically (p<0.01) to NO3:NH4 ratios, and the highest values were observed with the 1:0 [for molybdenum (Mo)], 3:1 ([or magnesium (Mg)], 1:1 [for boron (B), coper (Cu), iron (Fe), manganese (Mn ), and zinc (Zn)] or 1:3 [for phosphorus (P) and potassium (K)] treatments. Nitrogen and Ca leaf concentration responses were linear and highest at 0:1 and at 1:0, respectively. Cultural practices and fertilizer applications should maintain NO3 as the dominant N form in the root zone, and the continuous use of NH4‐ based or NH4‐releasing fertilizers is not recommended for the production of high yields of turnip greens.
Notes
Former Graduate Assistant. Present address: Micro‐Macro International, Inc., 183 Paradise Blvd., Suite 108, Athens, GA 30607.
Professor of Horticulture.