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Abstract
To optimise the production of Swiss chard, high levels of nitrogen fertiliser are often applied. This may have adverse effects on both the economy of fertilisation and the nutritional value of the human diet. Very little is known about both the optimum levels and influence of different sources of nitrogen on this crop under South African conditions. Glasshouse experiments were therefore conducted to determine the integrated effects of nitrogen level and source on the yield and quality of Swiss chard. Three Swiss chard seedlings were planted in each 4 L pot and later thinned to one plant per pot. Nine nitrogen levels (0, 100, 200, 300, 400, 500, 600, 700 and 800 kg ha-~ N) and six nitrogen sources (ammonium nitrate, calcium nitrate, potassium nitrate, ammonium sulphate, urea ammonium nitrate and urea) were combined in a factorial arrangement with four replications. The number of leaves harvested, leaf area, fresh and dry leaf mass, and leaf nitrogen content increased with increasing nitrogen levels up to 800 kg ha-~ N. Dry leaf mass was significantly higher where urea was applied compared to calcium nitrate. Although the different nitrogen sources did not differ significantly at the corresponding application levels, the nitrate accumulation within Swiss chard leaves was significantly increased with the use of ammonium nitrate.
