FERTILIZERS AND PLANT PRODUCTS 173 



there are many species all struggling with one another, hardy 

 varieties are essential, hence the wild forms of the clover 

 plant are particularly suited for development in a pasture. 

 Seed which has been sown on well-tilled land for many 

 generations has no necessity to struggle with other species, 

 is weakened in the process, and is no longer able to fight for 

 itself. There is a great difference between land which is 

 laid up for hay and land which is down to permanent 

 pasture. The species which will establish themselves in 

 the two kinds of soil are not the same, and, therefore, it is 

 not desirable that land should be sometimes cut for hay and 

 sometimes grazed, since no permanent equilibrium would 

 result. In the Tree Field experiment at Cockle Park the 

 use of basic slag has completely altered the physical properties 

 of the soil, the deep roots of the clover having altered the 

 physical texture of the soil down to about twelve inches in 

 depth. Somewhat similar to the action of wild white 

 clover in the British Isles is the action of the celebrated 

 dub grass of India, a grass which possesses a creeping stem, 

 which opens up the soil in a more efficient way than many 

 other forms of grass. Where land is cut for hay for any period 

 of time, one-sided manures become impractical. Well- 

 balanced manuring is far more important for this purpose 

 than for crops which are grown in a rotation. Generally 

 speaking, it is the heavy land which should be down to grass, 

 and such lands will not usually require much potash. The 

 lighter lands should properly be ploughed, and not be 

 permanently down to grass at all. Grass should only be 

 part of the ordinary rotation on such lands, where it should 

 be " seeds hay " for one or more years. Where land is down 

 permanently to hay, very generous manuring is necessar3\ 

 At Cockle Park, on Palace I^eas Field, which has been cut 

 for hay for over twenty years, slag has been found very 

 profitable, but is not yielding such big crops as more mixed 

 systems of manuring. For obtaining large crops of hay. 

 farmyard manure is almost essential, although very fair crops 

 have been obtained by phosphatic manures, supplemented 

 by potassic manures. The relative feeding values of the 



