May 1907.] 



295 



Plant Sanitation 



Burial op Prunings. 



The burial of primings is a practice peculiar to tea cultivation. Its advan- 

 tages are theoretically two-fold. Breaking up the upper layers of the soil preserves 

 the moisture in the subsoil, so that cultivated lands lose less in times of drought than 

 those uncultivated ; and to some extent the burial of primings thus ensures a culti- 

 vation, at least a partial one, which would not otherwise be obtained in tea growing. 

 In the second place, the nitrogen in the primings is ultimately converted into food 

 for the plant. As most of the objections to treating primings in any other way are 

 based on the loss of nitrogen, it is worth while to enquire further into this point. 



The nitrogen is of no use to the plant until it is converted into nitrate. The 

 primings are decomposed by bacteria, or fungi, or both, and the nitrogen in the 

 residue is converted by other more specialised bacteria into nitrate. Now, although, 

 in Ceylon, leaves and twigs decay fairly rapidly on the surface of the soil, it seems to 

 be a well-authenticated fact that primings buried in holes persist for a much longer 

 time than they would intemperate climates. I have had primings, dug up at the 

 end of six mouths, which showed hardly any decay ; they had been buried in the 

 approved fashion with basic slag. It seems probable that at least one factor militates 

 against the successful working of soil bacteria ; they do not flourish in an acid 

 medium. When the medium, i.e., soil or primings, becomes in the slightest degree 

 acid, decomposition can only be effected by fungi. The growth of fungi on the prim- 

 ings indicates that the medium is acid. The amount of lime in the basic slag is 

 apparently insufficient to neutralise the acids formed by the organic matter. It may 

 be suggested that the slow decay is connected with a decomposition by fungi only, 



When the primings are decomposed, the nitrogen has still to be converted 

 into nitrate by special nitrifying bacteria. These again do not nourish in an acid 

 medium (they are absent from peaty soils) ; they are practically confined to the first 

 nine inches of the soil, and they require for successful working a free aeration of the 

 soil and a base to neutralise the acids produced. With deep burying as usually 

 practised, it cannot be said that any of these conditions are realised and the process 

 of conversion will, to say the least, certainly not be rapid. Until the bacteriology of 

 the process has been examined, it must remain a moot point, how much of the im- 

 provement noted after burying primings is due to the nitration of the nitrogen in 

 them, and how much is due merely to the disturbance of the soil. 



But where root disease is known to exist, the burial of primings should 

 certainly be discontinued. We are relying on fungi for their preliminary decompo- 

 sition, and as all the tea root fungi can live comfortably as saprophytes, the process 

 is a cordial invitation to them to extend their operations. Except in the case of 

 Rosellinia, exact proof of their acceptance can only be obtained by growing to 

 maturity the mycelium found in the holes, and as the material even from one hole is 

 no small quantity, pot cultivations must evidently be pretty extensive if any posi- 

 tive result is to be obtained. This is now beiug attempted in the case of the low- 

 country tea root disease. The species which causes the disease has not yet been 

 obtained from them, but more than half of those which have grown from the prim- 

 ings belong to the same group of fungi. I agree that no hard aud fast rule can 

 be laid down in this matter, but I must point out that in several recent in- 

 stances objections of this type have always been made after the hard and fast 

 rule has been laid down by the advocates of one practice. 



I shall be glad to receive, from the lowcountry for the present, samples of 

 primings taken from the holes six months after burial. Those which show some 

 mycelium should be included, but the sample should not consist wholly of these. 

 They should be packed in tins to avoid death or retardation from drying ; two 1 lb. 

 biscuit tins would afford sufficient material for one pot. Details of any root disease 

 should accompany the spociuaeua, 



