288 SCIENCE AND FRUIT GROWING 



of those in tilled ground without the dung. The good done by 

 the dung in this case was probably the result of the alteration 

 in the physical surroundings of the roots, and not of the addi- 

 tional nutrient supplied, for experiments in pots under more 

 stringent conditions showed that extra nourishment, even when 

 supplied to the tree from below, did practically nothing to 

 counteract the baleful effect of the grass, the relative vigour of 

 the trees with and without such nourishment being 28 and 24 per 

 cent., respectively, of that of trees with no grass and with no 

 extra food. A determination of the total nitrogen contained 

 in the leaves of these trees showed that, whilst the grass had 

 reduced the nitrogen from 100 to 44, the extra nourishment had 

 mitigated the action of the grass only so far as to diminish the 

 reduction to 53 (XIII, 77). 



Similarly, the feeding off of the grass by sheep or poultry 

 was found to have no effect in diminishing the harm done by 

 grass. The following values were obtained with standard 

 apple trees planted in 1909 



Vigour of trees. 

 1910. 1911. 1912. 1913. 



No grass . . 100 100 100 100 

 Grass 76 30 6 5 



Grass fed off . 69 30 9 28 



During the first two seasons the feeding off was done by sheep, 

 and during the next two by poultry, and the rise in values during 

 the last season was evidently the result of much of the grass 

 round the trees having become destroyed by the birds (XIV, 47). 



So far from the action of grass on trees being explicable on 

 the ground that it impoverishes the soil, it, as a matter of fact, 

 actually enriches it. This has been fully established now for 

 many years, 1 and experiments at Woburn have demonstrated 

 that soil in which grass has been growing for ten or twelve 

 years is actually much more suited to the growth of trees than 

 soil in its vicinity which has been kept tilled : the vigour of the 

 trees grown in it when the turf was removed was more than 

 double that of the trees in the tilled ground, whereas in this same 

 rich soil, when the turf was replaced over the roots of the tree, 

 the vigour of the latter was only half that of trees in the poorer 

 ungrassed soil (XIII, 79). In other pot experiments, where the 



1 Lawes, J. B., and Gilbert, H., " Determinations of Nitrogen in the Soil 

 of some of the Experimental Fields at Rothamsted," Rothamsted Memoirs, 

 V, (6). Also Am. Assn. for the Advan. of Sci., Montreal, 1882 ; and Lyon 

 and Bizzell, Cornell Univ. Agric. Expt. Station, Memoir, I. 



