EFFECTS OF PLANT-POPULATION DENSITY AND RECTANGULARITY ON THE GROWTH AND YIELD OF POPPIES (PAPAVER-SOMNIFERUM)

Growth, yield and incidence of lodging of poppies were studied in Tasmania at 10–200 plants/m2 and at nominal rectangularities (within-row:between-row spacing) ranging from 1:1 to 10:1. In 1983/84 and 1988/89, there were asymptotic relationships between plant population density and both total dry-matter production and total head (capsule plus seed) yield at maturity. In 1983/84, a season with above-average wind, the incidence of lodging increased as density increased to > 50 plants/m2; morphine concentration decreased as density increased to > 100 plants/m2. This resulted in parabolic relationships between yield of erect (machine-harvestable) heads and yield of morphine from erect heads with plant density, the maximum morphine yield from erect heads being achieved at 70 plants/m2. In 1988/89, a season with below-average wind, the effects oflodging were less severe at high densities and the components of ‘erect’ yield were adequately fitted by an asymptotic function. Rectangularity of 1:1 gave higher total dry matter production, total head yield, yield of erect heads and morphine yield from erect heads than 4:1 and 10:1. Since calm conditions similar to those of 1988/89 occur only once in every 4 years, growers should be encouraged to establish c. 70 plants/m2. As most commercial crops in Tasmania are 150-175 mm rows, growing at 70 plants/m2 to maximize the effect of plant density would also approximate to the ideal rectangularity (2:1 in this case). © 1990, Cambridge University Press. All rights reserved.