THE CIIEMISTUY OF THE SOU,. tf 7 



application of potash manures is oiten beneficial. The addition of potash 

 salts alone is, however, not usually of much benefit, and they are generally 

 applied together with superphosphate. (See page 114.) 



Turnips.— A crop of 17 tons roots per acre contains 49,000 lb. of root and 

 leaf, and removes from the soil 112 l'». nitrogen, 149 lb. potash, and 33 lb. 

 phosphoric acid, in round numbers. They thrive best on light loams, loose 

 and open. The land for the turnip crop requires more thorough tillage and 

 pre\ ious preparation than for most other crops; but this question is outside the 

 scope of the present discussion. They are a crop that requires heavy manuring, 

 and a liberal dressing of farmyard manure is favourable to their successful 

 cultivation. Though the quantity of potash is larger than in the potato crop, 

 potash manures have not the same marked benefit. Their weak point appears 

 to be their inability to make use of the phosphoric acid in the state in which 

 it exists in the soil ; hence the manures from which they derive especial 

 benefit are those containing phosphoric acid, such as superphosphate or bone- 

 dust ; | cwt. to 1 cwt. superphosphate per acre is the average proportion. 



Mangolds. — A mangold crop of 22 tons weighs 67,000 lb. roots and leaves, 

 and removes 147 lb. nitrogen, 300 lb. potash, and 53 lb. phosphoric acid. 

 Mangolds are deep feeders, and require a deep and well-tilled soil. They 

 form an exception to most root crops in that they are capable of utilising the 

 phosphoric acid and potash present in the soil, and the manures that specially 

 benefit them are those containing nitrogen. On a rich land, or one already 

 well-manured with farmyard manure, the application of a soluble nitrogenous 

 manure alone is of marked benefit, though, as a rule, it is added together 

 with superphosphate. 



Beetroot is also a crop that requires nitrogenous manures in conjunction 

 with bone-dust or superphosphate. 



Leguminous Crops. 



Crops such as the pea, bean, lupin, lucerne, clover, vetch, &c, stand mid- 

 way between the cereals and root-crops in regard to the amount of fertilising 

 materials they contain. The following figures show the composition of beans 

 and of red clover. 



Beans. — A crop of 30 bushels grain consists of 2,000 lb. grain and 2,200 lb. 

 straw, and contains 99 lb. nitrogen, 67 lb. potash, and 29 lb. phosphoric 

 acid. 



A Bed Clover crop of 2 tons contains 102 lb. nitrogen, 83, \ lb. potash, and 

 25 lb. phosphoric acid. 



In addition to the above, leguminous crops contain a large proportion of 

 lime, amounting in the clover crop to 90 lb. None of the cereals contain 

 more than 10 lb. lime in the entire crop. Potatoes contain about 27 ; 

 mangolds, 43 ; and turnips 70 ; so that it will be seen that the proportion of 

 lime in the leguminous crop is considerable. 



They thrive best on calcareous soils, and derive special benefit from the 

 addition of lime as a manure. 



But the most striking peculiarity about this class of plants lies in the fact 

 that they are practically independent of the soil for their supply of nitrogen. 

 It has long been a vexed question, and is still undecided, whether plants are 

 able to utilise the nitrogen of the air by means of their leaves. There is no 

 satisfactory evidence hitherto of this fixation of nitrogen by the leaves of 

 growing plants, and it is quite certain that the amount thus obtained is 

 inconsiderable, and not sufficient to enable them to thrive independently ot 

 the soil-nitrogen. 



