Temporal and spatial root development of cauliflower (Brassica oleracea L. var. botrytis L.)

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Row crops are often inefficient in utilizing soil resources. One reason for this appears to be inefficient rooting of the available soil volume. Five experiments were performed to study the temporal and spatial root development of cauliflower (cv. ‘Plana’). The crop was grown with 60 cm between rows, and root development was followed in minirhizotrons placed under the crop rows, 15 cm, and 30 cm from the crop rows. Soil was sampled and analyzed for nitrate content at the final harvest and once during growth. In two of the experiments N fertilizer rate was varied and in two of the other experiments two cultivars were compared (cv. ‘Plana’ and ‘Siria’).

The rooting depth of cauliflower was found to be linearly related to temperature sum, with a growth rate of 1.02 mm day−1 °C−1. Depending on duration of growth this leads to rooting depths at harvest of 85–115 cm. Soil analysis showed that the cauliflower was able to utilize soil nitrogen down to at least 100 cm.

With Plana differences in root growth between row and interrow soil were only observed during early growth, but with Siria this difference was maintained until harvest. However, at harvest both cultivars had depleted row and interrow soil nitrate equally efficient. Nitrogen fertilizer did not affect overall root development significantly.

The branching frequency of actively branching roots was increased in all soil layers from about 6 to 10 branches cm−1 by increasing N fertilizer additions from 130 to 290 kg N ha−1. Increasing N supply increased the number of actively branching roots in the topsoil and reduced it in the subsoil.

The average growth rate of the roots was always highest in the newly rooted soil layers, but fell during time. At 74 days after planting very few roots were growing in the upper 60 cm of the soil whereas 70% of the root tips observed in the 80–100 cm soil layer were actively growing. Within each soil layer there was a large variation in growth rate of individual root tips.

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