2 26 Journal of Agriculture. [8 April, 1907 



tlian I per cent, of ash. Some idea of the relative proportions of the 

 \aluable ash constituents can be obtained from the following comparati\e 

 values per loo parts of ash: — 



^iP^e^* Leaves. ^J'^.^n' Potatoes. 



Straw. Grain. 



Potash ... ... 10 ... 20 ... 30 



Lime ... ... ... 6 ... 12 ... 3 



Magnesia ... ... i ... 6 ... 11 



Sulphuric acid ... ... 2 ... 4 ... --,■■■ 5 



Phosphoric acid ... ... 5 ... 9 ... 48 ... 10 



The nitrogen practically does not appear in the ash, but in ordinary 

 decomposition in the soil it is slowly set free as nitric acid, which combines 

 with the bases in the soil to form soluble nitrates. 



T/ie value of Trees as humus-producers can hardly be over-exaggerated, 

 for the benefits conferred upon soil by the presence of humus in it are many 

 and various. It increases the water-holding capacity of the soil. Thus 

 a soil containing a fair quantity of humus will hold from two to three 

 times as much water available for tihe plant's use as a pure sand. The 

 presence of humus, and in this respect the humus formed from the decaying 

 leaves of trees is especiallv valuable, increases the chemical actions in the 

 sail, and causes more of the insoluble constituents of the soil to be rendered 

 soluble and available for mineral plant food. In addition to this, the 

 humus itself has a special power of retaining these soluble constituents in 

 such a manner that the loss by washing from the soil by rain is reduced 

 to .a minimum, while at the sam«e time they can still be absorbed by the roots 

 of the plant, and ha.nded over as they are required. Finally, humus 

 lightens heavy soils, and favours their aeration. 



A simple experiment to show the beneficial action of humus upon the 

 roots of plants is to place on a heavy soil or clav surface a layer of leaf 

 mould or wel!-rotted manure an inch or tw"o thick, and cover this with 



3 or 4 inches of clay or clayey soil. Soaked seeds planted on the surface 

 soon strike doiwnwards, and if the plants are dug up and examined by the 

 time the stems are half-a-foot to a foot high, it will be found that the 

 greater part of the root-system has been de\eloped in the layer of humus. 

 This is especially well shown by the garden " Nasturtium," but also by 

 cereals and other agricultural plants, although, w'hen the plants are older 

 the roots are forced to strike deeper in search of water. 



In warm climates the decomposition of humus in the soil is rapid, 

 and hence there is little danger in this State of any excessive accumulation 

 of humus leading to souring of the soil. The latter can, in fact, always be 

 overcome b\ drainage and liming, and such soils, when properly handled, 

 often pro\e to be of great fertility. Forest fires, b\ I)urning the humus off 

 the soil, do incalculable damage, which, under primitive ancestral con- 

 ditions, appears to have been made good in the following way : — After 

 a severe bush fire had burnt off the humus and left the naked inorganic 

 soil more or less fully exposed, seeds of Acacia and other plants lying 

 dormant in the soil, and thus brought near to the surface, germinated. 

 Acacias and other leguminous plants, bv the aid of their root-tubercles, 

 are able to obtain nitrogen from the air, and so develop readily in 

 inorganic soils in which humus is deficient or absent. It is only in humus 

 or organic soils that supplies of nitrates are continually being formed, 

 any slight production of nitrates in, or addition of nitrates to, an inorganic 



