Effects of plant population and season on kenaf (Hibiscus cannabinus L.) grown under irrigation in tropical Australia I. Influence on the components of yield

Abstract

Abstract The relationships between plant population and the yield components of kenaf ( Hibiscus cannabinus ) cv. Guatemala-4 grown under irrigation in tropical Australia were examined. Plant arrangement and plant density were varied independently. The responses in both a wet season crop (sown in October), sampled at three ages until flowering, and a dry season crop (sown in May), sampled at flowering, are reported. Flowering occurred at 203 days in the wet season crop and at 105 days in the dry season crop. At all samplings, all measured components of yield (bark yield, core yield, and tops and foliage yield) were unaffected by plant arrangement for inter-row spacings between 0.28 m and 0.75 m. The response to plant density within the range of 132,000 to 923, 000 plants per hectare was modified by both season and age. At flowering in the dry season crop, all the components of yield increased as density increased, with complete plant survival at all densities. In contrast, at flowering in the wet season crop, variation in the components of yield was independent of density and there was a marked reduction in plant survival of up to 50% at high densities. The yield of total dry matter at the highest density at flowering was 7.7 t ha −1 in the dry season crop compared with 19.2 t ha −1 in the wet season crop. The Shinozaki-Kira relationship in which the reciprocal of plant weight is linearly related to density was fitted to the data for each sampling. This relationship, using plant density at establishment, was obtained only where there was minimum reduction in plant survival. Due to the ability of kenaf to compensate, an excellent fit was obtained in response to plant density at sampling irrespective of season or crop age.