148 Commercial Gardening 



to 24 tons to the acre would not be too much. And in light, sandy, or 

 gravelly soils, which are notoriously hot and hungry, from 30 to 50 tons 

 per acre would be hardly sufficient to obtain good results. It will thus 

 be seen that although a light sandy soil may be had at a very low rent, 

 this advantage will vanish completely when the expenses of manuring 

 and cultivating are compared with those of loamy and clayey soils. 



A Warning". Although farmyard manure possesses the great virtues 

 mentioned it must be used with care and intelligence. In some places, 

 where large and cheap supplies are available, the soil is saturated with 

 manure. The greater the quantity of manure incorporated with a soil 

 the greater the necessity for plenty of fresh air to bring about decom- 

 position, and ultimately humus. Now, if a soil has not been deeply dug 

 or trenched, and it happens to be of a heavy nature, it is possible that 

 the rains will not pass away readily. Then the manure begins to get 

 sour, fresh air with its oxygen is driven out, carbonic acid gas develops too 

 freely, and the beneficial bacteria are suffocated or annihilated by their 

 enemies which come into being owing to the lack of fresh air. To avoid 

 these troubles the soil should be well and deeply dug, and whenever extra 

 large quantities of manure are used the soil should afterwards be dressed 

 with lime or chalk, basic slag, or nitrolim, to keep it in a sweet 

 condition. 



Green Manuring". This consists in growing a crop of some quick- 

 growing plant, which when near maturity is to be ploughed in or dug 

 into the soil, with the object of enriching it in humus or organic material 

 and nitrogen. Sometimes the crop is fed to cattle, and the manure from 

 the sheds is afterwards returned to the land. As one of the chief objects 

 of green manuring is to supply nitrates to the soil, such leguminous 

 plants as the Red, White, and Crimson Clovers, Peas, Vetches, Beans, 

 Lupins, &c., are favoured for the purpose, because the bacterial nodules 

 on their roots possess the power of fixing the free nitrogen from the air 

 (see p. 127). Such non-leguminous crops as Mustard, Rape, Buckwheat, 

 Borage, &c., are also grown as green manures because of their bulkiness 

 and rapidity of growth, and the large amount of humus, &c., they return 

 to the soil. 



Whichever of these crops is grown the effect upon the soil is beneficial. 

 The roots penetrate the soil and divide it into finer particles. Mineral and 

 metallic foods are dissolved by the secretions from the roots, and being 

 rendered soluble in water can be absorbed into the system of the crop. 

 The soil becomes drier by the absorption and transpiration of moisture 

 if it is inclined to be too wet; and eventually when the crop is ploughed 

 in, or dug in completely, large quantities of humus become incorporated 

 with the soil. As the green stems and leaves and roots decay in the 

 dark a certain amount of heat is generated, carbonic acid gas is liber- 

 ated and proceeds to dissolve the inorganic materials in the soil, and 

 all the wonderful chemical changes due to the presence of humus take 

 place in proper order to make the soil richer than it was before. 



