CHAPTER XXV. 

 SOILS IN RELATION TO PLANT FOOD AND PLANT GROWTH. 



(The following is based on a pamphlet : 

 " Agriculture in New Zealand," published 

 by the Educational I^epartment of the 

 New Zealand Expeditionary Force). 



The fertilitj^ of a soil depends upon its 

 ability to supply plants with certain con- 

 ditions and substances essential to growth ; 

 these include: (1) Water; (2) Air; (3) 

 Temperature ; (4) Food : (5) Adequate root 

 room ; (6) Absence of injurious substances 

 and of harmful soil inhabitants (such as de- 

 nitrifying bacteria, fungi, harmful protozoa 

 and larvjB of insects). 



The Food of Pl.ants. — Plants require 

 certain elements, each of the first ten in 



the following list are required in varying 

 proportions, any deficiency below require- 

 ments reduces growth. All the mineral 

 substances are absorbed from the soil 

 through the roots in dilute solution: — 



Plant- food is often the limiting factor 

 in soils, and the elements usually not 

 naturally sufficiently available to produce 

 large crops are phosphorus, nitrogen, pot- 

 ash and lime. Food supply can be in- 

 creased by adding fertilisers, ploughing 

 in crops — preferably legumes — and feeding 

 crops and foods to animals on the land. 



Soils are formed by the weathering of 

 rocks and bj^ the addition of vegetable 



ELEMENTS OF PLANT FOOD. 



Element. 

 (A)— Carbon. 



(B) — Hydrogen. 

 (C)— Oxygen. 



(D)— Nitrogen. 



(E)— Phosphorus. 

 'F) — Potassium. 



'G)— SULPHTXR. 



(H)— Magnesium. 

 (I)— Calcium. 



fJ) — Iron. 

 (K)— Sodium and 



Absorbed as 



f Carbon dioxide from air. 

 (^Carbonates from soiL 



. Water from soiL 



f Nitrates from soiL In legnni 

 \ through root nodules. ... 



Phosphates from soil. 



Potash salts from soil. 

 Sidphates from soil. 

 Magnesium salts from soil. 



I Calcium or lime compouii 

 \ from soil. 



Iron salts from soil. ... '... 



Chlorine are beneficial to plants hav 

 mangels, beets, and asp 



Function or Effect on Pl.\nt. 



/ Starch, sugars, oils, and protein pro- 



L duction. 



f Carrier of Plant Food. 



I Maintains turgidity. 



j Formation of Starch. 



I Sugars, Oils, and Proteins. 



/' Promotes growth of herbage and leaf 



I growth in trees. 



I Delays maturity. 



V Essential for Proteins. 



I Promotes root growth. 



I Hastens maturity. 



"j Seed and Fruit production. 



I Occurs in Proteins. 



( Starch and Sugar production. 

 Disease resistance. 



[ Fruit production. 

 Occurs in Protein. 



r Too large a quantity, requires to be 



I neutralized by lime until proportion 



' is two of lime to one of magnesium 



j Required essentially by legumes; also 



j for the seeds of fruits, and for cauli- 



I flowers and cabbages. 



/ Necessary for the formation of green 



t colouring matter of leaves, 

 ing their origin near the seashore, e.g., 

 aragiis. 



