The productivity of grassland may change greatly with ageing. Frequently, a productive ley period, occurring in the first time after (re)seeding, is followed by a period in which productivity decreases. Under conditions favourable to grassland this may be temporary. A production level finally can be attained almost equalling that of young reseeded grassland, but mostly not that of liberally fertilized grassland sown in arable crop soil. Especially changes in organic matter content in the soil, activity of the earthworm population, the occurrence of "soil sickness" and an insufficient longevity of the sown species can be involved.Grassland with a high clover percentage in the sward may react differently to these changes than grassland with a low clover content. In the present research usually no clovers were sown. A decrease in the organic matter content of the soil had a negative effect on productivity; this negative influence was evident almost from sowing onwards, decreased gradually and asymptotically with ageing and could be compensated for the most part by N fertilizing. Sowing grass in an arable crop soil, with a liberal N dressing resulted in more productive grassland than reseeding. This difference in productivity ,was only temporary. A low earthworm population caused mat formation, an unfavourable physical condition and a lower gross yield. Disappearance of the sown grass species and varieties may result in a decreasing productivity.