March, 1912.] 



220 



Scientific Agriculture. 



able for root-development. The baleful 

 effect of grass is by no means confined 

 to apples : pears, plums and cherries 

 were found to be affected by it in the 

 same way, and to, probably, nearly the 

 same extent ; though in the case of these 

 trees the standards suffered less than 

 the dwarfs. 



It is possible that in some soils where 

 the effect produced is not great, grass 

 might be advantageous from a commer- 

 cial point of view, for the check given 

 to the growth of the tree tends to 

 increase its cropping, and grass effects 

 the colouring matter of all parts of the 

 tree; generally resulting in a high colour- 

 ing of the fruit. Such results were 

 obtained at Ridgmont when the ground 

 was grassed up to 5 or 6 feet from the 

 stem of the tree. 



To what distance grass should be re- 

 moved from a tree so as to have no 

 effect on it must naturally depend on 

 the nature and size of the tree, as well 

 as on the nature of the soil ; with 

 freshly planted standard apple trees, in 

 soil which was not specially favourable 

 to the action of grass, a very consider- 

 able effect was produced when the grass 

 was 4 feet away from the stems ; on the 

 other hand, keeping a space free of grass 

 extending only 6 inches from the stem of 

 freshly planted dwarf trees was found 

 to have some beneficial effect, even in 

 the Ridgmont soil. The proportion of 

 roots extending into the grassed ground 

 which are sufficient to make the grass- 

 effect apparent, is remarkably small, 

 amounting in some cases examined to 

 onlyycVffth of the weight of the whole 

 tree. 



Forest trees appeared to be affected 

 by grass in the same way as fruit trees 

 when the grass is sown immediately 

 after planting ; six different kinds were 

 examined both at Ridgmont and in 

 some light sandy soil. The only 

 difference in the behaviour of them and 

 of the fruit trees was, that, in the case 

 of conifers planted in light soil, the effect 

 was much less than with other trees, 

 and some recovery occurred with them 

 as time went on instead of the effect 

 becoming intensified. 



The action of eighteen different grasses 

 on apple trees was examined, with the 

 general result that the action in all cases 

 was considerable, but was greater with 

 the strong-growing grasses than with 

 the weaker ones. Clovers had a similar 

 stunting effect, but the lightness in the 

 colour of the leaves, conspicuous with 

 trees under grass was absent when 

 clover was grown. 



The question of the action of grass 

 being explicable by its affecting the 

 aeration of the soil, by its altering the 

 amount of carbonic acid present, or by 

 its effect on the soil-temperature was 

 investigated some years ago, and any 

 explanation on such ground was found 

 to be inadequate. The question of soil- 

 moisture and of food-supply was also 

 investigated, with a similar result, and 

 further evidence has much strengthened 

 these conclusions.^ 



As regards soil-moisture, there are 

 general grounds for regarding a defi- 

 ciency of such moisture as affording no 

 explanation of the effect of grass on 

 trees, for this effect is produced in wet 

 seasons as well as in dry ones, and trees 

 which are affected show none of the 

 usual signs of suffering from drought ; 

 indeed, when vegetation suffers from 

 drought, it is the grass which shows the 

 effect much sooner than the deeper 

 rooted trees. Determinations were made 

 of the water contents of grassed and 

 tilled-soil at Harpenden at intervals 

 through the year, and it was found that 

 the grassed soil was slightly the wetter 

 of the two from the beginning of January 

 till the end of March, after which it 

 become the dryei , but the water contents 

 never fell below the limit which has been 

 found to be favourable for plant growth, 

 although in this very soil when grassed 

 the trees were showing all the symptoms 

 of grass-injury. In the plots at Ridg- 

 mont, where dwarf apple trees have 

 suffered so much from grass, various 

 determinations have all shown that the 

 grassed soil during the summer is actu- 

 ally wetter than the neighbouring tilled 

 ground. What the explanation of this 

 anomalous state of things may be is not 

 known, but it effectually disposes of the 

 view that the grass- effect there is due to 

 lack of moisture. In some experiments 

 the moisture in the soil has been increased 

 to various extents by supplying the trees 

 every week with water through pipes 

 under their roots, and though such trees 

 were slightly benefited by this treat cnent, 

 they still continued to show the effect of 

 the grass very strongly, and were far 

 less vigorous than similar trees in tilled 

 soil, though this was much dryer. Still 

 more conclusive experiments were made 

 by growing trees in pots and keeping 

 the water contents up to the same point, 

 by watering them two or three times a 

 week ; but even when the grass-roots 

 were prevented from coming into con= 

 tact with the tree roots by a layer of 

 wire gauze, and when the water was 

 supplied from below, so that the tree 

 got all that it wanted first, the effect of 

 the grass on it was nearly as great aa 

 ever. 



