CHAPTER IV. 



CROPS. 



The dry matter, nitrogen, and ash constituents in average crops. 

 Cereal Craps. — Characteristic composition — Mode of feeding — 

 Most suitable manuring. Meadow Hay. — Characteristic compo- 

 sition — Demand for ash constituents — Influence of manures on 

 quantity and quality — Grass land especially adapted for obtaining 

 nitrogen from the atmosphere. Leguminous Crops. —Character- 

 istic composition — Special source of nitrogen — Clover sickness. 

 Boot Crops. — Characteristic composition — Differences in the 

 nutrition of turnips, mangels, and potatoes. Forest Growth. — 

 Large production of dry matter for small consumption of ash 

 constituents and nitrogen. Adaptation of Manures to Crops. — 

 The feeding power of each crop must be taken into account — 

 Economic distribution of manure in a rotation— The practical 

 value of manures only known by experiments on each farm. 

 Influence of Climate and Season. — Effect of excess or deficiency 

 of water and heat — Influence of preceding winter. Crop Besidties, 

 — Their action — Differences between different crops; Weeds.-— 

 Their beneficial and injurious actions. 



To understand the chemistry of crops we must first 

 inquire as to their composition. The following table 

 shows the average composition of ordinary farm crops, 

 and of the annual produce of three descriptions of forest. 

 By " pure ash " is understood the ash minus sand, 

 charcoal, and carbonic acid. 



The composition of grain is tolerably constant ; but 

 the composition of straw, leaves, roots, and tubers will 

 vary very considerably, according to the character of 

 the soil, the manuring, and the season. The com- 

 position of fodder and root crops is thus especially 

 liable to variation. Some information on this subject 

 will be found on page 137. 



