64 TRUCK-FARMING AT THE SOUTH. 



has assumed a dark clear color, when the liquor may be 

 used, or Peruvian guano, at the rate of a quarter pound, 

 or any of the ammonia salts, at the rate of two ounces 

 dissolved in a gallon of water, may be substituted. 

 Liquid manure should be applied just before a rain; at 

 any rate, the soil should be moist, as there is then no 

 danger of the liquid passing through the soil and be- 

 yond the reach of the roots. One gallon of water is 

 capable of absorbing one thousand one hundred and fifty 

 gallons of gaseous ammonia. Owing to its inconvenience, 

 truck-farmers rarely use liquid manure. 



CHAPTER IV. 

 THE ROTATION OF CROPS. 



It is as advantageous for the market-gardener as for 

 the general agriculturist to grow his different crops in 

 succession. Various theories have been proposed to ex- 

 plain the phenomena attending the growth of certain 

 crops on the same soil for a number of successive years. 



Chemical analysis shows that, while all plants are com- 

 posed of nearly the same elements, they exist in each 

 kind in varying proportions. It is supposed that a plant 

 requiring for its full development more of one inorganic 

 element than another, exhausted the soil of the former to a 

 greater or less degree, and rendered that gradually unfit for 

 its own continued growth, while a different plant, somewhat 

 differently constituted, would still find in the soil all the 

 elements it required for its maturity in sufficient quantity, 

 and in an available condition. 



When it was ascertained that, if all the elements known 

 to be taken f f om the soil by a certain crop, were returned 

 to it in fertilizers, and even more of these than it had 

 lost, the crop still continued to depreciate, the theory of 

 exhaustion of the soil then failed to be a satisfactory solu- 



