25 



the nitrates formed in the soil lying fallow. Weeds are smothered 

 out by a thick crop like this, and humus is added to the soil when the 

 crop is dug in and has rotted. Vetches, being a leguminous crop, 

 add to the nitrogen in the soil, but unfortunately they have a drying 

 effect on the soil, as they are not dug in till the following spring. On 

 the other hand, mustard can be dug in in about eight weeks after 

 sowing, and so takes much less water out of the soil, which is also open 

 to winter rains. On the whole, for a Ught sandy soil mustard is the 

 better crop, vetches being more suitable for a heavy soil. 



Leaf-mould. — ^This, when thoroughly decayed, forms a valuable 

 ingredient in potting soil. Good newly-fallen leaves from hardwood 

 trees contain in one ton about 10-15 lb. nitrogen, 3 lb. phosphoric 

 acid, and 6 lb. potash. Thus its chief value lies in contributing 

 humus to the soil, and generally improving it mechanically, rather 

 than in supplying much plant-food. Oak leaves make the best leaf- 

 mould, beech leaves coming next. A stiff clay soil may be much 

 improved by the addition of leaf-mould. 



Peat. — There are two kinds of this material which are called peat. 

 One, consisting of the decayed rhizomes and roots of bracken, is much 

 used in the cultivation of orchids and ferns, and the more fibrous it 

 is the better. The other kind, the real peat, consisting of decomposed 

 plants, which are submerged for part of the year, and sand, is an acid 

 soil, but is used as an ingredient in potting Azaleas, Heaths, 

 Rhododendrons, &c. 



Lime. — ^No proper manuring can be practised with good results 

 unless a sufficient quantity of carbonate of hme is present in the soil. 

 If less than '5-1 per cent, is found, an apphcation is needed. A rough 

 test for hme in the soil is to take a sample of soil and pour on it some 

 hydrochloric acid. If the soil effervesces freely it may be con- 

 sidered to contain about i per cent. ; if not, then lime is required. 

 Both physical and chemical improvement in the soil is brought about 

 by the addition of lime. On clay soils the former effect is most 

 marked. The clay particles, which are very small, and stick together 

 very fast when moistened, are cemented together into larger particles 

 by the action of lime ; thus the water is allowed to drain away, the soil 

 becomes airier and drier, and consequently warms earlier in the 

 spring, and less sticky, and so easier to work. Also it will not crack 

 in dry weather, as the soil-water will be able to rise to the surface 

 better. 



Sandy soils are also benefited physically, the smaller particles 

 being cemented together in a similar manner. 



As regards the chemical action, lime prevents the soil from becoming 

 acid. Acidity in the soil is brought about by the decay of vegetable 

 matter, and when the soil is acid fungi flourish, and bacteria are 

 hindered from carrying out the process of nitrification. Nitrogenous 

 manures are not the only ones rendered more easily available by lime, 

 both phosphatic and potassic manures requiring it. The action of 

 lime on phosphatic manures is to increase their solubiUty, by forming 



