Many people have said that grass is the major crop of British agriculture and this assertion has been heard with increasing frequency in recent years as the truth behind it has been more widely realised. In point of sheer acreage, more land in the United Kingdom is growing grass than any other crop but very little of that land is growing the maximum quantity of grass or even grass of top quality. Under these conditions, in a country such as ours where soil and climate are so favourable to grassland production,there is obviously great scope for improved management and utilisation. There have been great advances in this realm of agriculture in recent times. Grass strains have been improved by breeding, the employment of rotational grazing, new fertiliser techniques and conservation by ensilage are only a few of the means which science has developed to the benefit of grassland practice. The ready acceptance of new techniques has largely sprung from the exigencies of our current high cost economy. The emphasis on improved grassland husbandry has increased enormously as stock -farmers have endeavoured to make more use of their grass crop. This is a highly nutritious and relatively cheap food for grazing stock. Hence it is worth exploiting as a crop and is not mrerely to be taken for granted as if it were outwith the rules of good husbandry. Until very recently this exploitation has concerned the grazing season from May to October. The improvements in farm practice regarding summer grass have been considerable since the war. Now the exploitation is extending to the other "out -of- season " period and ways and means are being sought to grow and utilise fresh grass at this period. Before the final test of whether it is worth growing grass earlier and later in the season can be decided the practicability of so doing must be investigated. That task is the object of this work. It is well to realise that "in- season" and "out -of- season" are not so abrupt that the "in- season" period cannot be extended a little at a time at the expense of the "out -of- season" period. It is also worth considering that the cost of production of grass in the normal growing season is so low that even if it costs more to produce in the adverse period of the year its value is even greater at that time. In the late autumn other cheap forage crops like kale are available as substitutes for grass but in the early spring no such fresh substitute exists. It therefore seems worth while to study the factors affecting grassland growth in early spring with a view to shortening the effective winter period and so reduce the farmer's dependency on conserved foods and concentrates. To gain a benefit of even one week in earliness would be valuable when the cost of concentrates for a herd of dairy cows or a flock of ewes and lambs at this period is considered. By thinking along these lines it became obvious that much more knowledge was required of this topic from work done here in south east Scotland. In this way the work began. Since the conception of this study took place and more particularly since the actual trials were laid down in P stay 1956 there have been many difficulties. Mishaps, adverse weather, physical limitations on size and scope of the research projects but in some ways the most difficult of all has been the popular interest in work on this topic. The catch -phrase "early- bite" has become commonplace and almost every seedsman's catalogue and every vendor of fertilisers purports to have the answers to the problems of producing early spring grass. That some measure of advantage can be derived from these two means, the correct seeds and fertilisers, is true but it is obvious that far more basic knowledge must be gained than is possessed by the glib salesmen. The facts they use are often scanty, unsound scientifically and gained at second or third hand. That they do not have all the answers to all the problems is confessed by themselves privately and also by the avid interest of practical farmers for more information from those engaged in the systematic study of this topic. It is certain that much attention is being given by large commercial and government research institutions to this sort of work. It is hoped that the contribution given in this volume will aid these endeavours and provide some small benefit to British agriculture.