Sowing time, cultivar, plant population and application of N fertilizer on Kenaf in Spainʹs central plateau

Kenaf (Hibiscus cannabinus L.) is an annual plant presently being studied as a potential source of fibre for the production of paper pulp. Field studies on a Calcic Haploxeralf soil were performed between 1991 and 1993. The objective was to investigate the effect of sowing time (May, June and July), cultivars (El Salvador, Everglades 71 and PI-343129), plant population (3–50 plants m−2) and the addition of nitrogen fertilizer (0, 50, 100 and 150 kg N ha−1) on yield. In 1991 and 1992, May and June sowings produced similar harvests while a delay until July caused a 40% decrease in production. When grown at different plant populations, all three varieties of kenaf showed increased yield as plant population increased. This was accompanied by a reduction in stem-base diameter. Everglades 71 was found to have a growth cycle which was best adapted to the prevalent climatic conditions. The maximum dry stem yield of 20.9 t ha−1 was obtained by El Salvador in 1991. Nevertheless, this cultivar has an excessively long cycle for our climatic conditions. No marked effect on yield was observed when different quantities of N fertilizer were applied, nor did the time of application lead to appreciable differences. A decrease of 3°C in the mean temperature during 1992 compared with 1991, was possibly the main reason for a 33% yield decrease.