128 THE BOOK OF NATURE STUDY 



in no way an exceedingly heavy dressing. If the soil is heavy 

 and is to be trenched in the autumn, the manure may with 

 advantage be mixed with the bottom layer of each trench. It will 

 keep the soil open to a good depth below the surface. Light sandy 

 soils are very porous to heavy rains, and there is risk on such 

 soils of valuable soluble matter being washed into the subsoil in 

 the winter and ultimately removed in the drainage waters. On 

 light soils, therefore, the farmyard manure is best applied in 

 the spring, just before the principal crops are put in. There is 

 obviously no necessity to take special precautions to keep sandy 

 soils open, and the manure, after being spread on the surface, 

 should in these cases be simply dug under. It will then be 

 within reach of the roots of the young plants. Old garden ground 

 is generally very rich in humus, owing to the decay of many 

 generations of plant roots. If, as is generally the case, the humus 

 contains much humic acid, the soil is distinctly acid, and un- 

 favourable to root and bacterial activity. Humic acid is best 

 neutralised by a dressing of lime. The lime may be in the form 

 of very finely ground limestone, or better, quicklime may be 

 put in small heaps on the garden, and just sufficient water 

 added to slake it, when the lumps of quicklime (thus converted 

 into calcium hydrate) will break into a fine powder, which should 

 be immediately spread over the surface of the soil and raked, 

 or gently forked in. About one bushel of lime per rod may be 

 applied. There is not much danger of an over-accumulation of 

 humic acid in most soils with sandy or gravelly subsoils, for such 

 soils are sufficiently aerated to permit the roots and bacteria to 

 flourish. Light soils are, however, often benefited by a dressing 

 of marl or other calcareous clay, and this dressing may profitably 

 be applied every six or eight years. 



Farmyard manure may in many cases be usefully supple- 

 mented by artificial mineral manures, namely, nitrate of soda, 

 sulphate of ammonia, or nitrate of lime (nitrogenous), super- 

 phosphate of lime, or bone flour (phosphatic) , and sulphate of 

 potash or kainit 1 (potassic). The experimental data respecting 



1 Kainit is mined from deposits occurring at Stassfurt and elsewhere in Germany, 

 and is composed of sulphates of potassium and magnesium together with chlorides of 

 potassium, magnesium, and sodium. 



