Long-term effects of cropping system on red clover proportion and crude protein concentration in mixed leys

Abstract: Red clover is an important crop in Sweden, being the most cultivated forage legume in the country. It has a high crude protein concentration and fast establishment, which makes it a welcome addition to a ley mixture. However, red clover is not persistent and generally little remains in the third harvest year. This is caused by a combination of several different factors such as management practices and diseases. To determine how these factors affect red clover persistence, literature on the subject was analysed and correlated with the results of an analysis of data from the long-term field experiment R8-71. R8-71 includes six-year crop rotations with different proportions of timothy-red clover ley in each rotation. Diseases and pests are the most common causes of red clover decline, and without their presence, red clover cultivars can persist for more than eight years. The analysis of R8-71 revealed typical signs of both clover rot and root rot. There was a sharp decrease in red clover proportion in the third harvest year, which is typical when plants are affected by root rot. Over time there was a decrease of clover proportion in the first harvest year in the crop rotation with the most frequent use of timothy-red clover ley, a typical sign of clover rot. It is known that the clover proportion of a ley and crude protein of the forage increases between the first and second harvest, and this was confirmed in this thesis. Having a three-year or five-year ley did not influence the persistence of clover within a crop rotation cycle. The clover proportion in the first and second harvest of the first production year declined with each crop rotation cycle. The crop rotation with a five-harvest year ley was the only rotation where the decline of clover proportion in the first production year was significant, but it was only significantly different from the change in clover proportion of the two-harvest year cropping system. In conclusion, red clover and crude protein concentration in the produced forage increased between the first and second harvest. Red clover persistence was not significantly affected by the proportion of ley within a rotation, but the proportion of red clover decreased over crop rotation cycles when the gap between leys with clover was less than two years.