242 



THE AGRICLTLTURAL NEWS. 



August 7, 1909. 



likely to be lost in drainage water and that the preven- 

 tion of such loss is a matter of supreme importance to 

 agriculturists. Green manures are especially efficacious 

 in this direction, for they take up those bodies and 

 form stable combinations with them, which are 

 subsequently rendered available by bacteria in the 

 ordinary way. A similar action takes place in regard 

 to other food-constituents, such as phosphoric acid, 

 potash and lime : not, however, because, like nitrates, 

 they are liable to be lost in the wash-water, but 

 tecause the green dressing unites with them in such 

 •a way as to render them more directly available. 

 These maintenance effects follow the use of any kind 

 of green dressing, but they are augmented, in the case 

 ■of leguminous ])lants, by the fact that the presence of 

 the latter helps to lessen the number of those 

 •organisms which cause soils to lose nitrogen. 



The second use ot the practice which is under 

 ■consideration, that of the provision of plant food in 

 addition to what is already e,xistent in the soil, is one 

 which, so far as has been satisfactorily demonstrated 

 •up to the present, is solely connected to the ability of 

 leguminous crops to add nitrogen to the soil. It is 

 •not the purpose of this article to deal with this aspect 

 of the subject ; if further information is required, atten- 

 tion is directed to the recent one on Soil Inoculation, 

 Ji.gr icultural Neuv, Vol. VIII., No. 18-i, of May 15, 

 1909, to which reference has already liecn made. It 

 will not be out of place, however, to draw attention, at 

 this stage, to the influence of former leguminous crops 

 ■on the later ones. The fact that a soil has already had 

 the benefit of nodule nitrification iiastens succeeding 

 ■efforts in this direction, for the reason that such a soil 

 already contains an amount of nitrogen sufficient to 

 stimulate plant-growth, and becaiise the fact that 

 'nodule bacteria have already been raised in it hastens 

 the infection of the later legumes with those usofal 

 •organisms. 



The kind of soil to which green dressings are 

 ■applied must, naturally, be an important factor in 

 Tegard to the results of such application. The action 

 in light, open soils must be verj^ different from the one 

 which will take place in those which are heavy. Their 

 •effectiveness is generally far greater in the former case 

 than in the latter. The lack of plant food in sandy 

 soils, their openness, their small capacity for holding 

 water and their lack of humus all contribute to the 

 great change for the good which often follows the 

 ■application of plant^matcrial. There is certainly the 

 fear that, in well-watered soils of this kind, acidity may 

 'result from the practice ; but this tendency may be 



controlled by judicious action in the matter and by the 

 use of lime as a corrective. It is quite another matter 

 in the case of heavy soils. These do not require applica- 

 tions of green dressings as often as they are demanded 

 by the lighter ones. They hold water well, the activity 

 of the bacteria which cause decay is smaller, they 

 retain nitrates to a much greater degree, and, under 

 good conditions of drainage, are much less likely to 

 suffer a loss of nitrogen from the action of bacteria. 

 None the less, such applications are eminently desirable 

 from time to time, because they have the effect of 

 quickly freeing otherwise slowly accessible stores of 

 potash and phosphoric acid, and because of their 

 improvement of the condition of the soil. 



Sufficient has already been said to indicate that 

 care must be exercised in the use of green dressino-s. 

 Damage to the soil will obviousl}' cause harm to the 

 plants which such dressings were intended ultimately 

 to benefit. By what criteria shall we chiefly judge in 

 particular instances, whetl.er benefit or harm will 

 accrue ' The answer is, as has been stated dififerentiy 

 already : By those in which the first consideration is 

 given to the conditions regulating the bacterial life, 

 both in the buried plants and in the soil. 



DIPLODIA DISEASE OF MAIZE. 



This is the title of an article, in the current 

 number of Sclenrr', written by Dr. E. F. Smith and 

 Florence Hedges. 



These investigators made observations on tlu.s disease of 

 corn, which is now becoming -serious in .some parts of 

 America, in order to determine its method of infection. 

 A careful e.xaunnation of .some cobs seemed to indicate that 

 the mycelium spread to the seed from inside the stem, and 

 that it was not a ca.se of local attack as was previously 

 believed. 



'I'd [irove tliis conclusively, plants were grown in jjuLs 

 with the soil previously inoculated with pure cultures of 

 Diplodia. In nearly every case the fructifications of Diplotllft. 

 ai)peared on the roots or at the collar of the plant, while the 

 niyceHum was traceable well np the stem and in the roots. 

 In one case, the fructifications appeared in the stem on the 

 fir.st four internodes and were especially abundant at the 

 nodes. It was fully determined that the mycelium in the 

 roots and stem was that of Diphnlia, as the pure cultures of 

 th'-' fungus were obtained from material inoculated with it. 



This makes it almost certain that tlie fungus attacks the' 

 roots first from the soil and finally spreads to the cob, so that 

 the same ground, when once infected, should never be used 

 for planting two crops of corn con.secu lively. It is also 

 suggested that the fungus may be the cause of the cornstalk 

 disease of cattle in the west of America, as well as of the 

 pellagra disease of human beings which results from tlic 

 consumptiou of mouldy corn. 



