32 MANUAL FOR SUGAR GROWERS. 



subject worthy of attention and study on the part of 

 all practical sugar growers. 



Even if plant-food is present in sufficient quantity 

 for the requirements of a crop, there are various cir- 

 cumstances, as we have seen, greatly influencing 

 fertility ; it is well known, for instance, that varia- 

 ations of the weather will cause greater differences 

 in crops than can be obtained by manuring. 



A soil must be capable of retaining plant-food and 

 moisture, and thus, as shown above, must contain a 

 due proportion of clay and humus. A clay soil, on 

 the other hand, may become so close as to be un- 

 fertile, owing to the absence of sufficient air, so 

 essential for root-growth and for nitrification, and 

 also be so dense as to offer great resistance to the 

 entrance of the fine, delicate root-tips and root-hairs. 

 This question has been already discussed when 

 treating of condition or heart (page 18). 



It is important to remember that the points by 

 which good condition is determined are such as do 

 not admit of expression by figures in a statement of 

 a chemical analysis ; so that two soils may show a 

 very similar chemical composition, yet differ materi- 

 ally in fertility, owing to difference in condition. 

 In this the practical field observations of the planter 

 are of great value, and chemical analysis can only 

 supplement, and not supplant, this. The application 

 of piirely chemical manures to land in bad heart is 

 a mistake frequently made, and tends to discredit 

 the value of chemical aid in manuring. The planter 

 should carefully avoid this error, the remedy for 

 which lies in the correct exercise of his own judg- 



