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Population Density and Planting Date Effects on Kenaf Performance¹

Population density and planting date can have substantial effects on kenaf (Hibiscus cannabinus L.) performance in temperate climates. The effects of population densities of up to 395,000 plants/ha on kenaf have been evaluated in Maryland. Because positive yield responses have been derived from higher populations at other locations, the effects of five population densities [247,100 (PI), 370,700 (P2), 494,200 (P3), 617,800 (P4), and 741,300 (P5) plants/ha] on ‘Cuba-2032’ and ‘Tainung-1’ were studied in 1976 and 1977 on the Eastern Shore of Maryland. Soil was a Bertie silt loam (fine-loamy, mixed thermic Aquic Hapludult). Yields of Tainung-1 were maximized at approximately 370,000 plants/ha whereas yields of the less vigorous Cuba- 2032 were maximized at approximately 500,000 to 700,000 plants/ha. Plants grown at P1 and P2 generally achieved greater height and stem diameter than those grown at P3 to P5; stand reduction was generally higher at P3 to P5 than at P1 and P2. Neither height nor stem diameter was significantly correlated with percent stand reduction. The primary cause of stand loss was probably greater intraspecific competition at the higher populations.

Early (28 April) and late (19 May) planting of kenaf led to comparable dry matter yields in a 1970 study in Maryland. We concluded that a more detailed study of planting date was needed and experiments were conducted in 1976 and 1977 on the Eastern Shore of Maryland. Soil and cultivars were the same as for the density studies. Planting dates were 5 May in 1976 and 11 May in 1977 (D1), 19 May (D2), 2 June (D3), 16 June (M), and 30 June (D5). Planting on D1 and D2 generally led to significantly (0.01 level) greater yields than did planting on D3 to D5. Date of planting had no substantial effect on height; stem diameter and stand reduction responses were erratic.

Key Words: Hibicus cannabinus L. • Dry matter yield • Height • Stem diameter • Stand reduction • Cultivar

² Research agronomist and agriculturalist, respectively.

Received for publication November 28, 1980.