165 



Arguing from these data, it follows that — 



(i.) if it be on account of its direct action that the manure is being 

 used, and if an immediate return be required, rotten dung, containing 

 a larger proportion of available matter, should be used ; 



(ii.) if the main object be the improvement of the mechanical con- 

 dition of the soil, then fresh, unrotted manure should ba applied in 

 order that the full benefit may be obtained; 



(iii.) in wet weather manure should be applied fresh to minimise the 

 risk of loss by drainage, and should at such a time be dug in rather 

 than be placed on the surface ; 



(iv.) in the case of the planting of young trees, the planter should 

 either use well rotted manure or apply the fresh manure three or four 

 months before planting; 



(v.) when it is to be applied to fruit trees, the cultivator will find it 

 advisable to place it in the form of a mulch, that, in addition to feed- 

 ing the roots, it may help to conserve soil moisture. 



Green manuring. — The growing, for manurial purposes, of a legu- 

 minous crop constitutes another method of increasing the supply of 

 humus in the soil and of all the constituents of plant food. For this 

 purpose a crop is grown and dug (or ploughed,) in as it stands One 

 of the leguminous crops, e.g , cow pea or velvet bean, is chosen be- 

 cause of the power possessed by these plants of fixing the atmospheric 

 nitrogen and storing it up in the form of compounds in the small 

 swellings on the roots. Digging such a crop into the soil will there- 

 fore, besides increasing the amount of humus, return all the plant- 

 food removed from the soil, adding at the same time a quantity of 

 nitrogen obtained from the air, but in a form suited to the require- 

 ments of plant life Many small cultivators, who are in the habit 

 of growing red peas for the market, are unfortunately so ignorant of 

 the special property of these crops, that they pull up the whole of the 

 plant to obtain the pods ! This trash is often burnt. After the removal 

 of the pods, the rest of the plant ought to be dug into the land, that the 

 fertility instead of being decreased, may be actually increased. 



Since plants, with the exception of these pod-bearers are able to take 

 in nitrogen only in the form of nitrates, or salts formed from nitric 

 acid, these manures have to undergo various changes before the ni- 

 trogen is available to plants, A most important change is that known 

 as nitrification, which consists in the conversion of the ammonia, pro- 

 duced by the decay of the manure, into nitric acid, and the combina- 

 tion of this with lime or potash to form soluble nits ates This process 

 is constantly going on in fertile soils, and is due to the action of bac- 

 teria. The planter can help on this action by seein* that his land is 

 properly ventilated —an essential condition of nitrification — and well 

 supplied with lime. Nitrates will be formed also in a heap of decay- 

 ing animal and vegetable matter, if the heap be mixed wish lime and 

 watered with liquid manure, care being taken to loosen it at frequent 

 intervals to allow the air to enter. By this means most of the estate 

 refuse can be utilised as manure. 



Seaiceed may also be regarded as a general manure, in that it sup- 

 plies all the constituents of plant food ; but since of the three chief 



