34 MANUAL OF TROPICAL AND SUBTROPICAL FRUITS 



important in connection with avocado culture in Florida. The 

 following extracts from a paper by Krome, published in the 

 1916 Report of the California Avocado Association, present 

 the results of several years of experimentation : 



"The nature of the plant food required by the avocado has not 

 been very satisfactorily determined, but it has become evident that 

 a scheme of fertilization must be worked out differing considerably 

 from that which has been generally adopted for citrus. Broadly 

 speaking the application of commercial fertilizers deriving their ele- 

 ments of plant food from wholly chemical sources has not proved 

 successful. In many instances, through lack of more definite infor- 

 mation, growers have given their avocados the same fertilizers which 

 they have used on their citrus trees. Where the formulae have been 

 those most frequently applied to citrus, with nitrogen derived from 

 sulphate of ammonia or nitrate of soda, potash from sulphate of 

 potash, and phosphoric acid from acid phosphate, the results with 

 the avocado have been generally unsatisfactory. However, when 

 the formula used has been of the type known as 'young tree ' fertilizer, 

 carrying a proportionately higher percentage of ammonia largely 

 derived from organic sources, better effects have been obtained. 



" It has become fairly well established as a fact that of two avocado 

 trees of the same variety, one which is well nourished and kept in 

 growing condition during the entire summer and fall will produce 

 larger and finer appearing fruit than one which is permitted to become 

 more or less dormant through lack of fertilizer, but it is quite certain 

 that the semi-dormant tree will carry its fruit without dropping for a 

 considerably longer time. There is therefore a rather delicate adjust- 

 ment to be made in order to bring the tree into condition such that 

 it will hold its crop until late in the season and at the same time will 

 not 'go back' to an extent that will be seriously detrimental to its 

 further development or jeopardize the crop for the following season. 



"Following such applications of fertilizer as are made to restore 

 the tree to good condition after it has passed through the period of 

 bloom and fruit setting there should certainly be at least one further 

 fertilizing during the summer or early fall to provide the nourishment 

 necessary for the production of the crop. And it may be added here 

 that the drain on an avocado tree in bringing its fruit to maturity 

 seems to be vastly greater in proportion than the same effort on the 

 part of a citrus tree. The writer cannot vouch for the soundness of 

 the theory, but it has been thought that this is probably due to the 

 different character of the fruit. In the case of any citrus, water con- 

 stitutes a large percentage of the fruit either by weight or volume, 

 while with the avocado the proportion of oils is much higher and it 



