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 Department of the 

 New Zealand Expeditionary Force). 



The fertility of a soil depends upon its 

 ability to supply plants with c:rtain 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 larvae of insects). 



The Food of Plants. — 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 by the addition of vegetable 



ELEMENTS oF PLANT FOOD. 



Element. 



(A) — C.4RB0N. 



(B) — Hydrogen. 

 (C)— Oxygen-. 



(D) — iSTlTKOGEN. 



(E) — Phosphords 

 <F) — Potassium. 



'G) — SULPHTJR. 



(H) — ^MAGNESitrir. 

 (I) — Calcium. 



(J) — Iron. 



(K) — Sodium and 



Absorbed as 



I Carbon dioxide from air.. 

 I, Carbonates from soil. 



Function or Effect on Plant. 



oils, and protein pro- 



Water from soil. 



j / Starch, sugars, 

 I. duction. 



[■ Carrier of Plant Food. 

 I iLaintains turgidity. 

 I Formation of Starch. 

 I Sugars, Oils, and Proteins. 

 /' Promotes growth of herbage and leaf 

 I growth in trees. 

 1 Delays maturity. 

 I, Essential for Proteins. 

 i' Promotes root growth. 

 I Hastens maturity. 

 "I Seed and Fruit production, 

 t Occurs in Proteins. 

 ( Starch and Sugar production. 

 J. Disease resistance. 

 [ Frmt 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 



I Calcium or lime compounds | I ^^n"^ff<^ ^''^''f/ 1^/ l^g""?^^; «'?.'> 



ffo,„ 5oji '^ II for the seeds of fruits, and for cauli- 



*. "■ ' M flowers and cabbages. 



! Iron salts from soil | ^'ecessary for the formation of green 



I I colouring matter of leaves. 

 Chlorine are beneficial to plants having their origin near the seashore, e.g., 

 mangels, beets, and asparagus. 



) Nitrates from soil. In legumes 

 1^ through root nodules 



Pliosphates from soil. 



Potash salts from soil. ... 

 SLiIphates from soil. 

 Magnesium salts from soil. 



lime 



