The development of lucerne root morphology traits under high initial stand density within a seven year period

The root system of plants is generally regarded as a factor, which is in relation to important agronomic and ecological characteristics. The aim of this study was to investigate the effect of high initial stand density on the reduction in development of lucerne root morphology traits and how long-term this effect would be. In spring 2003, a field experiment with six lucerne entries in randomized blocks was established. Broadcast sowing was used and the seeding rate was 5000 germinated seeds per m2. In 2003-2009, the plants were sampled in each plot in autumn; the average depth of sampling was 0.2 m. The stand density reached an average value of 860 plants per m2 in the autumn of the seeding year and this strongly reduced the root weight, tap-root diameter, position and number of lateral roots. The subsequent decrease of stand density to 57 plants/m2 in 2009 was not linear but it was extremely quick from the 1st to 2nd year and, by contrast, it was extremely slow in the last three years. It indicates that older plants with larger tap-root diameter probably have a higher persistency. All evaluated root traits were developed slowly, nevertheless, they reached common values during a seven year period. The intensity of the relation of stand density to root weight or tap-root diameter increased over time whilst it decreased to the ratio of root-branched plants. Results suggest that an assessment of density in samples should be recommended for the varieties evaluation in case of irregularly-spaced plants because the differences in root morphology among varieties could be caused by the differences in density among the varieties. It is possible to conclude that lucerne stands under higher initial density provided a strongly reduced speed of root development with an impact on important agronomic traits connected with root morphology.