The effect of earthworms (Lumbricidae) and "grass sickness" on the productivity of grassland

Alle in het rapport beschreven proeven tonen aan dat grasland ingepast in een vruchtwisselingssysteem betere resultaten geeft dan heringezaaid grasland. Het positieve effekt is echter van korte duur; na een jaar is er weinig verschil meer. In de proeven werd ook de invloed van regenwormen bestudeer

Attenuation of disturbances introduced by dynamic links in precision motion systems using model-based observers

This paper presents an extension to the Unknown Input Disturbance Observer (UIDO) and the Disturbance Estimation Filter (DEF). This extension enables the inclusion of the mechanics of dynamic links to the observer model, in order to attenuate the specific disturbances introduced by those dynamic links. A design method of the state space feedback gain based on the dynamics, and an observer gain based on basic Kalman filter theory is given. It is shown how the observer is designed for a practical example; the cable schlepp within the wafer stage of a lithography machine. Using a simple model of the cable schlepp the disturbance observer design has been validated with an experiment on an actual machin

Changes in productivity of grassland with ageing

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