Response of Lachenalia growing in soil to nitrogen fertilization during the nursery phase

Abstract

During the nursery phase, Lachenalia flower bulb producers plant bulblets propagated from leaf cuttings, for enlargement. They strive for a high yield of good quality bulbs that are of a marketable size within a year. In this regard nitrogen is of vital importance since it stimulates vegetative growth. Very little has been known about the nitrogen requirements of Lachenalia plants that are cultivated in soil. Hence the response of two Lachenalia cultivars (Rupert and Ronina) to combinations of nine nitrogen levels (0, 30, 70, 120, 250, 330, 420 and 520 kg ha⁻¹) and three application times (⅓ with planting and ⅔ ten weeks after planting; ⅓ with planting, ⅓ ten weeks after planting and ⅓ sixteen weeks after planting; and ¼ with planting, ¼ ten weeks after planting, ¼ sixteen weeks after planting and ¼ twenty one weeks after planting) was studied in a glasshouse using topsoil of a fine sandy loam Bainsvlei form. Nitrogen promoted the growth of Lachenalia plants irrespective of cultivar. The largest leaf area for Rupert was measured between 250 and 420 kg N ha⁻¹ and for Ronina between 180 and 520 kg N ha⁻¹. Both bulb circumference and firmness were influenced positive by higher nitrogen levels whereas nitrogen application time did not show such a clear trend. Bulb circumference was the largest where 330 kg N ha⁻¹ was applied and the firmest bulbs where 420 and 520 kg N ha⁻¹ was applied for Rupert and Ronina respectively. Nitrogen content of the bulbs increased with an increase in nitrogen levels. Bulbs that received their nitrogen in four equal applications had the highest nitrogen content. The glucose content decreased whereas the sucrose and starch content increased with higher nitrogen levels. Cultivar and nitrogen application times had variable effects on the carbohydrate content of the bulbs. The optimum nitrogen level varied between 250 and 330 kg N ha⁻¹ and the best response was obtained when this nitrogen was applied in four equal applications throughout the season.