4 Subtropical Vegetable-Gardening 



ments that are derived from the soil are of only minor im- 

 portance. Although their combined weight is only 

 from 1 to 5 per cent of the plant, the absence of any of 

 these may materially interfere with its growth. Most 

 vegetables get all their carbon from the air, and they can 

 only get it in the light. They take in most of the other 

 elements along with water by their roots, and they can 

 only continue to do this when water is evaporating out 

 from their leaves. Hence it is seen why they must have 

 enough sunlight. 



WHY LAND BECOMES POOR 



It will be clear from what has been said that if crops are 

 repeatedly removed from the land, some element or ele- 

 ments will be depleted or exhausted, or, as is ordinarily 

 said, the land becomes poor. 



Different crops do not remove an equal amount of the 

 different elements, and even different individual plants 

 of the same crop vary considerably in the amount of any 

 one element that they take from the soil. Some crops 

 take much nitrogen from the soil and return only a part 

 of it when their roots and fallen leaves decay ; others take 

 only a small amount of nitrogen from the soil and give 

 much back; the former make the land poorer, while the 

 latter make it richer in nitrogen. When a piece of land 

 is " tired " of one crop, it is often able to produce some other 

 crop in fair quantity. To keep soil in such condition that 

 it will produce a crop in paying quantities, we must main- 

 tain the necessary elements in sufficient quantity; we 

 must fertilize. 



