20 VEGETABLE GROWING IN NEW SOUTH WALES. 



the soil and the best means of applying it. Humus (which is partially 

 decayed vegetable matter) absorbs arid retains moisture in the soil, and 

 prevents surface evaporation. A surface soil fairly rich in humus, exercises 

 much the same influence on the underlying soil as does a mulch of dead 

 leaves or other vegetable matter. During dry spells, and under the influence 

 of the hot winds usually prevalent under such conditions, the loss of moisture 

 from the soil by surface evaporation is enormous, and in soils destitute of 

 humus this loss is so rapid as to result in the drying up of the soil and 

 the wilting of the crops. The final result of such conditions is the formation 

 of scalded spots, and the complete removal of the fine surface soil in the form 

 of dust. 



The humus in the soil is the ingredient which is most subject to alteration 

 and destruction. As soon as it has lost its moisture and become dry it is 

 rapidly burnt out by the combined action of sun and air, so that it is exactly 

 in those circumstances where its presence is most essential that it is most 

 liable to destruction, and where the necessity of renewing it is most urgent. 

 The presence of humus in the soil also tends to improve its texture by 

 lightening it and loosening it, and preventing compaction of the surface. It 

 is thus of special value in the amelioration of stiff soils. It is the principal 

 source of nitrogen in the soil, and by its decay under the influence of soil 

 organisms, ammonium salts arid nitrates are produced, which are the forms 

 in which this important element is assimilated by the plant. 



From the foregoing it will be seen that humus is one of the most important 

 of the soil's constituents, arid any great variation in the amount present 

 profoundly affects the value of the soil for cultural purposes. Indeed, the 

 vegetable grower may well regard the addition of material that will in time 

 increase the humus content of his soil as of much greater significance than 

 the application of commercial fertilisers that will provide even a large 

 amount of nitrogen, phosphoric acid, or potash. 



In addition to humus content, farmyard and stable manures and street 

 sweepings also contain appreciable quantities of these three important items 

 of plant-food, but those quantities occur in such forms that they are lost or 

 readily lose their value if the manure is exposed to the action of the 

 weather for any considerable time. Proper treatment of the manure heap is 

 therefore necessary prevent loss by leaching or by fermentation, and it is 

 always better to put such manures in a compost heap. The material is then 

 better prepared for incorporation in the soil, and weed seeds are destroyed 

 before they have opportunity to germinate on the land. 



The Compost Heap. 



The compost heap is a most valuable adjunct to the vegetable garden, and 

 it is a very great pity that it. is not to be found more frequently even'on the 

 ordinary farm. 



