A. Smit

Root characteristics of selected field crops: data from the Wageningen Rhizolab (1990-2002)

Since being built in 1990, the rhizotron facility in Wageningen, the Wageningen Rhizolab, has been used for experiments on crops (e.g. Alfalfa, Brussels sprouts, common velvet grass, field bean, fodder radish, leeks, lupins, maize, potato, beetroot, ryegrass, spinach, spring wheat, winter rye and winter wheat). In the experiments, horizontal glass minirhizotron tubes combined with auger sampling were used to assess rooting characteristics. For this paper we took the root data from these experiments and looked for a general relationship between thermal time/time after planting and rooting depth, the velocity of the root front and root proliferation. For certain depths (fixed by the depth at which the horizontal minirhizotrons were installed) a simple linear regression was established between the average root number per cm2 minirhizotron surface area and thermal time after planting. The compartments selected for each crop were those in which there had been a control treatment and/or in which conditions for rooting were considered to be optimal. We performed regression analyses per compartment and per depth, but only for the period after planting in which a linear increase of root numbers vs. thermal time was observed. After averaging the results, the regression procedure yielded two parameters of rooting for each crop: (a) the actual or thermal time at which the first root appeared at a certain depth and (b) the root proliferation rate after the first root had appeared. In this way, inherent crop differences in rooting behaviour (rooting depth and root proliferation) became apparent. For each crop, the ‘velocity of the root front’ after planting could be established (calculated in cm (°C day)−1). This parameter differed greatly between crops. Some crops (such as leeks and common velvet grass) explored the soil profile slowly: the root front moved at a velocity of only 0.07 cm (°C day)−1. Among the crops whose roots grew down much faster (0.18–0.26 cm (°C day)−1) were cereals and fodder radish. For a day with an average temperature of 15 °C these rates would have corresponded with the root front travelling approximately 1–4 cm per day. In the crops studied the root front velocity did not correlate with the root proliferation rate.

Twenty-Five Years of Life Lessons

For 25 years, Physical Geography students of the University of Amsterdam have experienced a 6-week field training in the cuesta landscape in Luxembourg around Diekirch. They studied the geology of the Gutland and surrounding areas, such as Ardennes and Eiffel. They mapped geomorphological patterns, studied soil development and looked at relationships between forest vegetation and the landscape in their particular area of approximately five square km, with many steep slopes. They also learned to overcome the physical and social challenges of such a fieldwork. A number of former students of different generations will give their opinion on what they learned and how this period in life helped them shape their current and future careers.