Effects of ammonium and nitrate nutrition on yield and quality in endive.

We have investigated the effect of 8 mM NH4-N and 8 mM NO3-N nutrient solutions on two cultivars ('Pancalieri Castello' and 'Nepal') of endive (Chicorium endivia L. var. crispum Hegi) grown using the nutrient film technique. Growth (leaf number and area), yield (head fresh mass), quality (dry matter, colour, and nitrate content of leaves), and some chemical and physiological characteristics were evaluated (e.g., total Kjeldahl nitrogen, inorganic ion and chlorophyll contents, SPAD index, osmotic potential, and membrane permeability). Endive yield (230 g plant-1, on average) was not suppressed by ammonium nutrition. No symptoms of ammonium toxicity were detected. Cation antagonism did not occur. The contents of chlorophyll a and total chlorophyll in ammonium-fed plants increased, as did the SPAD index (39.2 in ammonium-fed plants vs. 30.6 in nitrate-fed plants). Membrane permeability and total osmotic potential were not altered. Independently from the form of N applied, differences in morphogenetic features between the cultivars emerged. 'Pancalieri Castello' produced heads characterised by higher weight, more expanded leaves, and with lower sugar content compared to 'Nepal'. From a commercial viewpoint, ammonium-fed plants had a marketable yield of a nitrate-free product, without damage from ammonium, or defects in morphological features.