674 



freely along their passages. By the combined action of the freely 

 admitted air and water large quantities of mineral and organic 

 matter are converted into plant food. 



The soil is made up of organic and inorganic matter. The 

 inorganic matter is the result of the decomposition of rocks, and 

 the organic matter, or humus, from the decomposition of vegetable 

 or animal matter. 



There is a certain amount of vegetable nutter in the soil 

 derived from leaves, branches, and roots of previous crops, which 

 decay by oxidation, or slow combustion from the action of oxygen 

 on the vegetable matter, or from the combined action of oxygen 

 and the micro-organisms in the soil. The organic matter, or humus, 

 is converged into nitrates and carbonic acid, which acts on the 

 mineral matter in the soil by converting some of the inert food in 

 :1 into active food for the plants. The percentage of organic 

 matter, or humus, in a soil is, to a great extent, a measure of that 

 soil's fertility. The amount found in a good soil is from 5 to 10 per 

 cent. Humus is not directly a plant food, but the product of its 

 decomposition is a very rich source of plant food. Humus is very 

 insoluble in water, but has a very high power of absorbing and 

 retaining moisture. Humus has also the power of absorbing or 

 fixing ammonia. The humates. have the power of iixing bases, 

 such as potash, soda, lime, magnesia, carbonates, or, in other words, 

 they combine with these bases to form insoluble humic sails. When 

 a soil contains too much humus, as in a wet peaty soil, il is very 

 liable to contain free humic acid, which is poisonous to plants. 

 The best cure is drainage and a liberal dressing of lime, which 

 neutralizes the free acid. Light sandy soils nre very light in humus. 

 M<>st ot the soils of this colony are low in humus, therefore they 

 are great lv benefited by the application of farmyard manure, which 

 adds a large amount of humus, or organic matter. 



Green manuring is valuable for the same reason, and improves 

 Us physically as well as chemically. If such crops as mustard, 

 lupins, vetches, or peas are grown and ploughed in when they come 

 to Mower, they not only enrich the soil with organic matter, but 

 they bring up mineral matter lit for plant food from a lower depth 

 by virtue of the length of their roots, which go down into the soil 

 in search of food. They return not only all they took from the soil, 

 but also what they obtained from the nitrogen of the atmosphere. 



hnrning some of the surface clay on a heavy clay soil is a 

 means of rendering that class of soil more porous. Clay is a 

 hydrated silicate ot alumina. When wet it forms a stilt plastic 

 mass impervious to water and difficult to work. When clay is 

 burned it loses its power of hydration and is no longer plastic when 

 mixed with water. Tin- clay is made into a heap on some timber, 

 which is then tired. It is burned until it assumes a red color. It 

 is then scattered on the land, which by this means is made more 

 porous. 





