S02 



THE AGRICULTURAL NEWS. 



September 12, 1914. 



FUNGUS NOTES, 



THE EFFECT OF GRASS ON FRUIT TREES. 



liifoiuuUiL.n a.> to tl.f liaiinf ul ettV-ct on tree- of t!if gn iwth 

 rif plants near or under them .should be of great interest to all 

 growers of permanent crop.s, and the question of such an 

 effect often arises in a practical form in the earlier .stages of 

 the formation of coco-nut, cacao and citrus plantations. The 

 in\estigatio!is outlined lielow, which have been carried on 

 8ince 189-5 l)}' the Duke of Bedford and >Spencer U. Pickering, 

 liave had reference princiijally to the effect of gras.s on 

 temperate fruit trees, but as will be seen, the authors have 

 recently extended the scope of their experiments so as to 

 raise the whole question of tlie influence of one growing crop 

 iq)on another. The information concerning the researches 

 lias lieen obtained from the Thirteenth Annual Report of the 

 "Woliurn Experimental Fruit Farm, and from a paper in 

 the Journal of A'tiindtwal Science for Miiv lOl-t (Vol. VI, 

 pp. 1.36-1.51). 



THE NATURE OK THE EFFECT. 



It is found at AVuliurn that trees whose roots are 

 situated in soil which is allowed to remain, or to become, 

 grassed over are in some way very adversely affected, with 

 the result that their growth is checked or even entirely 

 f»rrested. 



The realitj- and intensity of the effect have been estali- 

 li.shed by a long continued series of experiments, in which 

 the growth of the trees in grassed and ungrassed plots has 

 been measured in respect of the size of the lea\-es, the weight 

 of the trees as a whole, of the prunings, and of the crops. 



The following table summarizes observations made for 

 six years in the case of cherries, pears and plums, and seven 

 to ten years in the case of apples. The figures are relative to 

 <i value of 100 in the case of trees in tilled soil. 



Cherries 

 Pears 

 Plum.- 

 Apples 



In appearance the affected trees, apart from their defi- 

 cient growth, .show at an earlj- stage leaves which are light and 

 unhealthy in colour, and in the case of apple trees fruits which 

 are yellow or red when they should lie green; fruits from 

 trees which are feeling the full effect are small and ill- 

 developed. 



Trees sulyected to the influence in their earlier growth 

 may be permanently stunted e\en though the grass may be 

 pvibsequently removed. 



It is important to note that the effect varies greatly in 

 different soils, and apparently the conditions at Woburn are 

 particularly favourable for its manifestation, but the authors 

 question whether it is totally absent in any case. It is most 

 pronounced in soils which are shallow, ditticult ti:> aerate and 

 not very rich, least so in soils whose characters are the 

 reverse of these. 



It is not necessary for the development of the effect that 

 the whole of the roots .should lie under grass: it becomes 

 evident when a proprirtion of the roots penetrate beyond 

 a tilled area to a grassy one, and recovery begins as soon as 

 some of the grass is removed or some of the roots grow 

 Isuyond it; 



It was thought possible that the effect of the grassing 

 •of well established trees would be slight as compared witii 

 ■thai which results when they are in grass from the time of 



planting, but trials showed that the deleterious action liecame 

 noticeable in the first season, and very strongly marked in the 

 subsecjuent ones. 



ISVESTIG.\TION OF POSSIBLE CAUSES. 



The explanation eventually adopted has not been directly 

 reached, Imt ap])ears to lie the only one remaining when other 

 suggested explanations have lieen tested and have failed. 

 These included questions of the influence of the grassy 

 covering on the aeration of the soil, the amount of carbonic 

 acid in it, the soil moisture, the food supply, the alkalinity of 

 the soil, and its physical condition. 



With regard to considerations rif water sujiply, it is 

 pointed out that the effect is produced in dry years and in 

 wet ones, and that the trees show none of the usual signs of 

 suffering from drought. Further, determinations of soil 

 moisture have shown that no unfa\'oiiralilc difference in thi.* 

 respect exists, while the artificial supply of water to trees 

 growing in pots did not cause any diminution in the effect of 

 grass planted around them. 



The question as to food supply has been tested by 

 manuring in various ways and it has been sho«ni that the 

 effect cannot be due to any impoverishing of the soil. 



THE TOXIN HYPOTHESI.S. 



These and the other possible factors having been elimin- 

 ated by exhaustive and apparently conclusive experiments, 

 the authors claim that the facts are best explained by assum- 

 ing that the grass has a directly poisonous effect on the roots 

 of the trees, not necessarily by means of an excretion, but 

 possibly by means of some substance produced or set free 

 by the decay of the debris of the growing grass roots. 



In apparent c<intradiction of the toxin theory it was found 

 that the watering of plants in pots with the leachings from 

 grass growing in sand, .so far from being deleterious actually 

 had a beneficial effect upon them. When however the gras.«. 

 was grown in trays with gauze bottoms, which were in con- 

 tact with the .soil beneath but prevented the grass roots from 

 penetrating into it, the ill effects were nearly if not quite as 

 marked as when the grass was grown in the ordinary way. 

 This suggested a comparison with the effect of partial sterili- 

 zation of .soil by heat, which results in an immediate 

 condition very unfavourable to plant growth, fullowed by 

 a condition very distinctly more favourable than the original 

 one. This could be accounted for l>y assuming the formation 

 of a sulistance which is poisonous in itself, but which is 

 converted by oxidisation into another which is highly 

 beneficial. Such a hypothesis would equally well explain the 

 action of the leachings from the grass. Owing to the assumed 

 fugitive nature of the toxin it would be very ilitticult of 

 identification, and it has in fact not lieen isolated. 



As correlative evidence it maij- be mentioned that the 

 effect of grass growing at such a distance that it is not 

 actually over the roots is a beneficial one. 



EXPERIMENTS WITH HERBACEOUS PLANT.S. 



In their later paper the authors discuss the results of 

 several series of experiments for the inxestigation of the effect 

 of grass and of clover, grown in trays, on tobacco, tomatoes, 

 barley and nmstard grown in the pots beneath. Further, the 

 influence of grass, clover, and mustard, grown in the trays, on 

 the same crops grown in the pots beneath has been examined. 

 In five out of six series the effect was unfavourable, often 

 highly unfavourable. 



So far the results are parallel with those obtained with 

 the grassed fruit trees, but a further development ensued 

 which from a practical point of view- puts a .somewhat ditt'er- 

 ent complexion on the matter. Hitherto the crops grown in 



