Growing point dynamics and spring growth of white clover in a mixed sward and the effects of nitrogen application

The effects of N applied in spring on the growth and development of white clover (Trifolium repens L.) in a mixed sward were investigated at Uppsala, Sweden. In early spring, the plots received 0 or 90 kg N ha−1 in the form of nitrochalk. The formation and loss of stolon branches were followed on marked stolons. The proportion of white clover in the total above‐ground dry matter (DM) of the sward fell substantially in both treatments during the 8‐week growth period, but more so in N fertilized than in unfertilized plots; fertilizer N increased the accumulation of grass DM, whereas it reduced the accumulation of white clover DM. Over time, there was a loss of white clover growing points and this loss was greatest in plots where N was applied. Branching occurred predominantly during the first half of the growth period and was unaffected by N application, whereas the loss of branches was more confined to the latter period and was increased in plots receiving N. Irrespective of node position, the size of the branches that died was comparatively small, and more branches were lost from young than from old node positions. It is concluded that the decline in the number of growing points in the N fertilized sward was mainly due to an increased loss of recently formed branches. As a consequence of its stimulating effect on grass growth, the N fertilized treatment initially led to a reduction in the R:FR ratio of light and subsequently also in the availability of photosynthetically active radiation within the canopy. These changes in the light environment of the sward caused morphological adjustments to be made by the white clover and may have contributed to the observed loss of branches.