Three experiments were carried out over a 2-year period to study the effect of plant density and spatial arrangement and the time of lifting on yield and root size of carrots. Plant density treatments ranged from 108 to 1553 plants/m2 and plant arrangement was varied by growing the plants in 1-, 2-, 3-, 4-, 5-, 10-, 18- and 36-row systems within a 152 cm bed; there were either two or three harvests in each experiment.
Total plant fresh weight, total root yield and mean root weight were not significantly affected by plant arrangement over the range studied, but they all progressively increased with later harvests. The asymptotic relationships between these yield variables and plant density were adequately described by the equation of Shinozaki & Kira (1956), the relationships being significantly different for each harvest.
Yields of canning-size roots (20–30 mm diameter) were influenced by time of harvest, plant density and the interactions between these two variables. The yield of canning-size roots increased with plant density to a maximum and then declined, the maximum yield being achieved at a higher density with later harvests. In two out of the three experiments there was no effect of spatial arrangement on canning root yields but in the third experiment there was a significant row system × density × harvest interaction.
The numbers of roots harvested per metre of row did not differ significantly between the ‘outer’ and ‘other’ rows for any row system treatment. The mean root weight, however, was consistently greater from the outer rows of systems with three or more rows and this ‘edge’ effect became larger with later harvests.
The results are discussed in relation to other published data and to carrot production. It is concluded that any of the tested row systems are equally satisfactory for carrot production and the choice can be based on such considerations as the availability of suitable harvesting equipment.