June 1908.] 



553 



Scientific Agriculture. 



adding humus, and thus improving the 

 soil's texture and its power of absorbing 

 and retaining moisture. When such a 

 crop is buried, the surface soil becomes 

 enriched by the nourishing materials 

 which the crop during the period of 

 its growth has drawn from the air aud 

 from the lower portion of the subsoil, 

 and this material is now placed within 

 the reach of the succeeding crop. 



During the growth of the plant the 

 soil has, in addition, been stirred up and 

 disintegrated by the development of 

 the roots. When ploughed under, pro- 

 vided that sufficient mositure and 

 warmth are present, the buried mass de- 

 composes with more or less rapidity, and 

 the succeeding crop gets the benefit of 

 the fertilising ingredients contained in 

 the decaying mass of vegetation in a 

 readily-available form. The resulting 

 humus is of the greatest value, not only 

 as a source of plant-food, but in improv- 

 ing the soil's texture, in preventing too 

 rapid evaporation, and in enabling the 

 soil to absorb and retain water, thus 

 rendering it less liable to suffer during 

 dry spells. 



A further important result is the form- 

 ation of carbonic acid by the decom- 

 position of the buried crop. Carbonic 

 acid is given off abundantly in the fex- 

 menatation of mass, and assists in the 

 disintegration of the soil and in rendering 

 available the plant-food contained in it. 



Green-manuring is effective both in 

 sandy and on heavy clay soils, aud, indeed 

 on all soils deficient in humus. On sandy 

 soils the effect of green-manuring is to 

 consolidate the soil, the humus formed 

 binding the particles together. On clay 

 soils, the effect of the addition of humus 

 and the addition of carbonic acid is to 

 loosen and aerate them. When condi- 

 tions as to warmth and moisture are fa- 

 vourable, and the crop decomposes fairly 

 rapidly, the production of soluble plant- 

 food proceeds with considerable rapidity. 

 This is especially the case in respect of 

 nitrogen, which is the principal manurial 

 ingredient. Nitrification (that is, the 

 conversion of the nitrogenous material 

 of the plant into soluble nitrates) takes 

 place quite rapidly. In sandy soils, green 

 manure nitrifies more rapidly than 

 manures like dried blood, bone-dust, &c, 

 and only less slowly than ammonium 

 sulphate ; while in stiff clay soils the 

 green crop nitrifies very much more ra- 

 rapidly than either sulphate of ammonia 

 or animal manures. 



With regard to the kind of crop to be 

 used for the purpose of green-manuring, 

 a good deal of latitude is permissible. 

 Any crop that is rapid and luxuriant in 



growth, and that can be readily turned 

 under, is suitable for the purpose, and 

 the selection will be guided by consider- 

 ations such as the time of year at which 

 it is to be grown, its suitability to soil 

 and district, &c, Amongst the most 

 effective class of crop for the purpose are 

 leguminous plants, such as clover, cowpea, 

 lupines, &c, since these are specially 

 valuable on account of their power of 

 obtaining their nitrogen from the air. 

 They are, therefore, especially suitable 

 for soils poor in nitrogen, and are of 

 high value in enriching the soil with this 

 ingredient. There are, however, many 

 other crops which are suitable for the 

 purposes, and frequently used, such as 

 mustard, buckwheat, &c. These are all 

 rapid growers, and can be grown as 

 catch-crops — that is to say, after the 

 main crop has been harvested and before 

 the succeeding one is sown. The practice 

 of growing a crop of tares or vetches after 

 the wheat crop has been harvested is 

 very common in Europe, and can be 

 followed successfully here in districts 

 where the autumn rainfall is sufficient. 

 Such a catch crop occupies the ground 

 at a time when it would be otherwise 

 unoccupied, and, during its growth is 

 collecting plant-food from air and soil, 

 which is utilized for manuring the 

 succeeding crop. 



The practice of green-manuring is of 

 special value in orchard work, where the 

 green crop can be grown and ploughed 

 under between the rows. 



It must be borne in mind, in all cases, 

 that green-manuring depends for its 

 success upon conditions favourable to 

 the decomposition of the buried green 

 crop, namely, sufficient warmth and 

 moisture. A crop ploughed under in the 

 late autumn or winter will nitrify only 

 slightly, and the same applies to plough- 

 ing under a crop in a dry season. If the 

 land is quite dry the crop will remain 

 buried without decomposition for a con- 

 siderable period, and its benefit is lost. 



Proportion of Nitrogen supplied to 

 Soil by Green Manuring. 



With regard to the actual amount of 

 material supplied to the land by plough- 

 ing under a green crop, some experi- 

 ments were carried out at the suggestion 

 of Mr. Allen, the Fruit Expert of the 

 Department. 



The produce of one spuare yard of 

 crops of vetches, at Wagga, Bathurst, 

 and Hawkesbury College, was harvested 

 carefully, tops and roots, and forwarded 

 for analysis. In the case of the Wagga 

 sample, the roots were obtained by 

 washing away the soil, and Mr. 



