52 



Common Scab of Potatoes. 



[Apr., 



produced in the crop. This experiment with shght variations in 

 the amount of grass apphed, and in the manner in which it was 

 introduced into the soil, was repeated on the same plots in 1915, 

 1917 and 1919 and on some other plots in addition in 1915 and 

 1919. In every case similar results were obtained. 



The dry year of 1919 was the worst season for Common Scab 

 known in Yorkshire for some time past and the photograph of 

 that year's results is thus selected for reproduction here (Fig. 2). 

 In the Report mentioned, however, photographs of the four 

 years' results are given. 



Conclusion. — There appears to be no doubt that the intro- 

 duction of green organic matter into the soil may be regarded 

 as a means of securing a clean crop. The amount necessary to 

 secure the best result will naturally depend on the scab producing 

 propensity of the soil. Very good results have been obtained 

 v>dth 10 tons to the acre of fresh material on soil where the 

 control plot gave a badly scabbed crop. 



In estimating the quantity to apply, it should be remembered 

 that green plants contain approximately 75 per cent, water and 

 thus the amount of half dry or withered grass required will be 

 considerably less than that of fresh material. No trials have 

 been made with hay but there seems no reason to suppose that 

 thib would not act in the same beneficial manner. The secret 

 of success appears to lie in securing such an intimate admixture 

 of the vegetable matter with the soil that the young potatoes form 

 in a compost consisting largely of the decaying organic matter. 

 On a small scale, where the land is cultivated by hand, this is not 

 a difficult condition to secure. The grass may be applied in 

 different ways. It may be spread on the surface and forked in 

 before planting or, a part may be strewn in the trenches at 

 planting time, a further portion added with the soil in filling in 

 the trenches and the remainder strewn lightly over the surface 

 and worked into the soil on earthing up. 



On a larger scale, where green manuring can only be carried 

 out by ploughing in a green crop growing on the soil, it is diffi- 

 cult as yet to suggest by what method it would be possible to 

 secure an intimate incorporation of the green crop with the top 

 spit of soil, and at the same time to allow of subsequent cultiva- 

 tion-. It is not too much to hope, however, that the ingeiiuity 

 of the pi-actical agriculturist will find some w^ay in which this 

 difficulty may be overcome and the treatment applied. 



In the experiments recorded in the "Report, grass was the 

 only vegetable substance tested. In another experiment, good 



