8 



Farmyard Manure. 



[APRIL, 



has taken place in the manure itself. The composition of the 

 excreta being the largest of these factors, it will be necessary 

 first of all to trace the fate of the various manurial substances 

 in the food — compounds of nitrogen, phosphoric acid and 

 potash— during the process of digestion. Animals that are 

 not increasing in weight, such as working horses or full-grown 

 cattle which are being maintained in store condition, excrete the 

 whole of the nitrogen, phosphoric acid and potash they receive 

 in a liquid or solid form, the carbohydrates and fat of the food 

 being mostly got rid of as gases. But the fate of the manurial 

 constituents varies according as they are present in the food 

 as digestible or indigestible compounds ; for example, part 

 of the proteins of the food withstand the action of the digestive 

 ferments and are excreted unchanged in the faeces, but to a 

 much greater extent they are broken down into soluble com- 

 pounds which pass into the blood and eventually are excreted 

 as urea, uric acid, &c. ; in the urine. Similarly for the phosphoric 

 acid and the potash in the food — whatever is digestible is 

 excreted in the urine in some simpler combination, whatever 

 resists digestion passes out unchanged in the solid excreta. 

 Hence a great difference in the manurial value of the two 

 portions of the excreta ; the compounds in the urine — urea, 

 uric acid, soluble phosphates and potash salts — are either 

 ready for the nutrition of plants or require but slight further 

 changes to become so ; whereas in the solid dung the materials 

 have several stages of decomposition to go through before 

 they can reach the plant, and, having already shown them- 

 selves able to resist the attack of the animal's digestive ferments, 

 they are correspondingly unaffected by the ordinary decay 

 processes in the soil. The proportion the digestible bear to 

 the indigestible constituents of a food varies with the nature 

 and even with the mechanical condition of the material, also 

 with the kind and age of the animal ; roughly speaking, the 

 richer the food the greater the proportion that is digestible, 

 e.g., decorticated cotton cake contains 7 per cent, of nitrogen, 

 of which 87 per cent, is digestible and finds its way into the 

 urine, while hay only contains 1-5 per cent, of nitrogen, of 

 which only 50 to 60 per cent, is digestible. 



When the animal consuming the food is growing or fattening 

 or yielding milk, a certain proportion of the manurial con- 



