Nutritionally Important Chemical Constituents and Yield of Carrot ( Daucus carota L.) Roots Grown Organically Using Ten Levels of Green Manure

Abstract

In a field experiment carried out over two years (1995, 1996) carrots were grown organically on a sandy loam soil. A broad range of mineral nitrogen (N-min) levels at carrot emergence was obtained by depleting or amending the soil by removing or supplying different amounts of green manure. With N-min values ranging from 22 to 162 kg N ha -1 at carrot emergence, the N uptake of the carrot crop increased linearly from 70 to 200 kg N ha -1 . The yield increased with N-min at lower levels of N, but levelled off above 90-100 kg N ha -1 . In fresh carrot roots the concentrations of total N, ten individual amino acids, total sum of amino acids, two amides, asparagine and glutamine, and g -carotene increased linearly with the soil concentration of N-min at carrot emergence. Nitrate N increased exponentially with N-min, reaching levels of 340 mg NO 3 kg -1 fresh weight under some conditions. The concentrations of potassium, calcium, glucose, fructose, sucrose and six individual free amino acids were unaffected by the N-min level. Magnesium was decreased at the lowest deliberately depleted N-min levels, whereas the concentration of dry matter and vitamin C decreased linearly with increasing N-min levels. Significantly lower concentrations of dry matter, total N, nitrate N, vitamin C and total sum of free amino acids were found in the warm and sunny year 1995 with the highest yield of carrot roots, whereas the contrary was found for g -carotene.