Effect of nitrogen on growth, quality and nutrient uptake of cabbages grown in sand culture

Abstract

The effect of nitrogen (N) application level on head yield and quality, growth and nutrient uptake of cabbages (cv. Rampo) was investigated in a sand culture experiment. Plants were harvested at a minimum of 2-week intervals over a 13-week period and N levels (2, 7, 14, 29 and 43 mmol/L as nitrate) were applied each day in a complete nutrient solution which was formulated to provide a stable and balanced nutrient supply. A gamma cubic response surface model fitted actual growth and nutrient uptake data quite precisely (R2 > 0.99) over the range 2-43 mmolb N. This model was used to derive the predicted plant growth and nutrient uptake rates. Head maturity occurred 12 weeks after transplanting when increases in the level of applied N, up to 14 mmol/L, increased the dry weight of roots, stem, leaf and head, and the fresh weight of head. Higher N levels reduced the weight of plant parts. Heads with the lowest percentage of dry matter were produced over the 7-14 mmol/L N application range. Growth rate of tops was low during the 4-week period after transplanting. It then increased rapidly to the maximum predicted value of 43 g/plant.week which was calculated to occur 9 weeks after transplanting at an N application level of 21 mmo/L. Similar growth rates were recorded over the 14-29 mmol/L N application range. Growth rates declined slightly at higher N levels and declined at later growth stages. Predicted nutrient uptake rates followed a similar response pattern to growth rates. The maximum uptake rates (g/plant.week), calculated to occur 8 weeks after transplanting at an N application level of 21 mmol/L, were: N, 1.30; potassium, 2.50; phosphorus, 0.23; calcium, 0.71; magnesium, 0.14; and sulfur, 0.60. We conclude that on low fertility soils, in order to achieve optimum nutrition and hence maximum growth rates and quality of cabbages under field conditions, the application rates of N and K fertilisers need to be flexible to meet the high nutrient demand which occurs after head formation and before final harvest.