March, 1910.] 



257 



Miscellaneous. 



resulted and, in many cases, where no 

 account has been taken of local condi- 

 tions, actual serious harm has accrued 

 from it. Like all other agricultural 

 operations, that of the application of 

 green dressings is one which is governed 

 by complex, rather than simple, con- 

 siderations. 



It is evident that the results of such 

 a method of manuring, as far as subse- 

 quent crops are concerned, depend on 

 two factors : (1) the effect on the buried 

 plants, (2) the effect on the soil. As a 

 matter of convenience, the subject will 

 be dealt with iu relation to these two 

 facHbrs. It is not within the scope of 

 an article like the present one to give 

 illustrative examples, so that reference 

 is made to the chapter on Green Manur- 

 ing in Professor J. G. Lipman's* Bacteria 

 in Relation to Country Life, pp. 237-63, 

 where a very complete account of the 

 practice may be found. 



That the plants used in green dress- 

 ings must undergo great changes before 

 they can be of any use to the crops 

 which they are intended to benefit is 

 a matter of common knowledge. These 

 changes take place through the action 

 of bacteria, and, owing to adverse con- 

 ditions, they may be delayed, or even 

 affected in such a way as to render the 

 action of the manure positively harmful. 

 This is the case in light, as well as in 

 heavy, soils. Iu the first instance, the 

 fact that such soils are liable to quick 

 drying may, iu the eveut of this taking 

 place, so iuterfere with the normal bac- 

 terial action as to cause the buried 

 material, when the soil becomes wet 

 again, to lose its most valuable consti- 

 tuent — nitrogen— instead of undergoing 

 those changes which would render that 

 element more available. In the second 

 case, an excessive rainfall, or insufficient 

 drainage, will induce a formation of 

 acid substances which will act as a 

 preservative against that decay upon 

 which the material absolutely depends 

 for its effectiveness. 



For reasons which aie closely con- 

 nected with what has just been stated, 

 green dressings should never be buried 

 deeply. The depth of cover may be 

 greater in light soils than in those which 

 are heavy. The same considerations 

 govern the procedure when it is a 

 question of applying the dressing when 

 fresh, or after it has been dried. A soil 

 with a large water-holding capacity is 

 more likely to induce beneficial changes 

 in the dried, than in the green material, 

 while, on the other hand, a light, well- 

 drained, sandy soil will show the oppo- 



* The Macmillan Company, New York, 1908. 



site tendency. Nevertheless, with some 

 crops and uuder the best conditions, 

 fresh green dressings and dry green 

 dressings show an equal efficiency as 

 providers of nitrogen. 



Setting aside other considerations, as 

 far as the crop which is intended to 

 provide the green dressing is concerned, 

 the best time to apply the latter is when 

 it just reaches maturity ; that is to say, 

 at f rating time, when about half of the 

 leaves have turned yellow, for at this 

 period the plant has reached the limit 

 of production for that season. An addi- 

 tional reason for not allowing the 

 manuring crop to stand too long is that 

 the water-content of the soil may be 

 reduced to such an extent as to decrease 

 the number of beneficial bacteria to a 

 degree which will inhibit its proper 

 action when it is eventually ploughed in. 



Such a consideration, however, namely 

 that of the age which the manurial 

 dressing should reach before it is applied 

 to the land, is governed by another im- 

 portant factor. Iu soils in the tropics, 

 where bacterial actiou takes place very 

 quickly, there is a danger that the food 

 which has been rendered available to 

 plants and which, consequently, has be- 

 come all the more soluble, may be 

 largely washed out of the soil before the 

 crop which is intended to benefit by it 

 has reached the stage when it is capable 

 of taking it in. Thus it is unmistakably 

 indicated that, under the climatic condi- 

 tions of the West Indies, land which 

 has been treated with green dressings 

 must be put to use soon after their appli- 

 cation, in order that loss due to waste- 

 age may be avoided as far as possible. 



Dependence is often placed merely 

 upon one or two kinds of plants for the 

 provision of green dressings. This 

 should not be so, especially where there 

 are facilities for raising, and experiment- 

 ing with, a number of different sorts. 

 The diseases and pests to which various 

 plants are liable have very distinct 

 limitations in respect to each kind of 

 plant, and it is reasonable to conclude 

 that several different kinds of plants, 

 raised on a given area, are likely to 

 give a much better yield than one or 

 two varieties. In the matter of legu- 

 minous plants, the consideration is 

 further advanced. A reference to the 

 article on ' Soil Inoculation ' in the Agri- 

 cultural News, Vol. VIII, No. 184," of 

 May 15, 1909, will make it plain that 

 different leguminous plants require 

 different varieties of bacteria for the 

 purpose of nitrogen-fixation, and that, 

 therefore, the raising of as many kinds 

 of those plants as is possible in a given 



