The effect of nitrogen fertilisation on the growth, yield and quality of swiss chard (Beta vulgaris var. cicla)

English: The sustainability of subsistence farming associated with the health of rural communities’ necessitated research on Swiss chard as it forms an integral part of food consumed by the poor in developing countries. Two separate pot experiments were carried out during the 2005/06 and 2006/07 seasons in the glasshouse of the Department of Soil, Crop and Climate Sciences at the University of the Free State. The objective of this study was to determine the effect of nitrogen fertiliser on growth, yield and quality of Swiss chard. The first pot trial was conducted to evaluate the effect of five nitrogen levels (0, 50, 100, 200, 400 kg N ha-1) and four application times on the growth, yield and quality of two Swiss chard cultivars (‘Fordhook Giant’ and ‘Rhubarb’). Two Swiss chard seedlings were planted per pot, filled with topsoil of the fine sandy loam Bainsvlei form. Two weeks after planting plants were thinned to one seedling per pot. Different nitrogen levels were applied to the relevant pots as follows: once every second, fourth, sixth or eighth week. It was only the total dry mass per plant and total nitrogen content per leaf of ‘Rhubarb’ plants that was significant higher than that of ‘Fordhook Giant’. The other parameters measured for the two cultivars did not differ significantly from each other. Nitrogen levels positively influenced the early growth, yield and quality parameters measured. It was the highest nitrogen level (400 kg N ha-1) that resulted in the highest number of leaves harvested, leaf fresh and dry mass, leaf area and leaf nitrogen content. Nitrogen application times significantly influenced only the early growth of Swiss chard plants and the nitrogen content of leaves. Early plant growth reacted better where nitrogen was split into three equal applications (T4). The total nitrogen content of Swiss chard leaves was significantly higher where nitrogen was split into five equal (T2) or three equal (T4) applications. In the second pot trial the effect of different nitrogen sources applied at different levels on the growth, yield and quality of Swiss chard cultivars was determined. The response of Swiss chard plants to nine nitrogen levels (0, 100, 200, 300, 400, 500, 600, 700, 800 kg N ha-1) from six different nitrogen sources (ammonium nitrate, potassium nitrate, calcium nitrate, ammonium sulphate, urea ammonium nitrate and urea) were studied. Based on the findings of this study, nitrogen significantly influenced growth, number of leaves harvested, leaf fresh and dry mass, leaf area and leaf nitrate content of ‘Fordhook Giant’ plants with best results obtained at 800 kg N ha-1. Nitrogen sources did not influence either the total number of leaves harvested nor the fresh mass of harvested Swiss chard leaves. In both cases, ammonium nitrate gave the best results and calcium nitrate the poorest. Urea influenced the leaf area positively followed by urea ammonium nitrate, with calcium nitrate resulting in the smallest leaf area per plant. Dry mass of Swiss chard leaves was also significantly higher where urea was used as nitrogen source compared to where calcium nitrate was used. No significant differences amongst the other nitrogen sources. Ammonium nitrate and potassium nitrate significantly stimulated the accumulation of nitrate in Swiss chard leaves, whereas the other nitrogen sources did not play any role in nitrate accumulation in the leaves of Swiss chard.