Potential yield in carrots (Daucus carota L.): Theory, test, and an application

Abstract

There is little published information on the physiological behaviour of carrots at the crop level. Here we derive and test a simple model for the potential yield of carrot crops. The model calculates green leaf area index (L) using a daily time step. Dry matter production is related linearly to light interception, calculated from L and canopy light extinction coefficient (k). Two stages of growth are distinguished. In stage 1, leaf expansion on each plant is unaffected by neighbouring plants. Stage 2 commences when L reaches a critical value and the plants start to interact. Compared to stage 1, stage 2 has slower leaf expansion and a k which varies with plant density. Dry matter partitioning between shoots and the storage root depends on L. We calibrated the model for two processing cultivars, 'Chantenay Red Core' and 'Red Hot', using data from a 1997-98 plant density experiment in Hawke's Bay, New Zealand. The model accounted for 72% of the observed variation in root size and 79% of the variation in yield. We tested the model against results from two experiments in 1995-96 and 1996-97. In both experiments the same two cultivars were sown at three different sowing times. Overall, the model accounted for 72% of the observed variation in root size and 66% of the variation in yield, showing that it is portable to other environments. Finally, we applied the model to interpret the effects of sowing date in these two experiments. Previous attempts were confounded by variation in plants m-2 with sowing date. The model allowed us to separate the effects of these factors, and indicated that early sowing substantially benefited yield. (C) 2000 Annals of Botany Company.