THE MONTHLY BULLETIN 



CALIFORNIA STATE COMMISSION OF HORTICULTURE. 

 Vol. IV. May and June, 1915. Nos. 5 and 6. 



THE FERTILIZER REQUIREMENTS OF CITRUS TREES.* 



By H. J. Webber, Director Citrus Experiment Station, University of California, 



Riverside, California. 



When the Citrus Experiment Station was established at Riverside, 

 California, one of the first experiments inangnrated was a test of the 

 effect of various fertilizers on oranges and lemons. These experiments, 

 planned largely by Prof. Ralph Smith, were laid out and planted in 

 April, 1907. Each trial plat, of which there are 20, contains 6 trees 

 of Washington navel oranges, 6 Valencia orange trees, 6 Eureka lemon 

 trees, and 6 Lisbon lemon trees. The field used for the experiment 

 was virgin land, never before having been plowed. The trees planted 

 for the experiment were of the same age and comparative size, and 

 were all budded on sweet stock. 



In arranging the experiment the plats were planted by a uniform 

 plan in such a w-ay that each plat is separated on all sides from any 

 other plat by a guard row to prevent the treatment on one plat from 

 influencing the adjoining trees on the other plats. The arrangement 

 is also such that the irrigation of each plat is separate, and no waste 

 water from one plat passes on to any other plat, but is carried off on 

 a guard row. Each year since the trees have reached fruiting age, the 

 product of each tree has been gathered separately, counted, weighed, 

 graded and sized. It is thus possible not only to compare the differ- 

 ences in yield, but also the differences, if any, in the grade and the 

 average size of the fruit. Last year the chemical analyses of the fruits 

 from each tree Avere started, which will ultimately show what effect the 

 fertilization has on the chemical composition of the fruit. While some 

 differences are already apparent, the results from a single crop are 

 not sufficiently complete to allow conclusions to be drawn. 



The twenty different plats have each been given the same fertilizer 

 each year, but increasing gradually in quantity as the trees grew in 

 size. The three main elements of nutrition, nitrogen, phosphorus and 

 potassium, usually wanting in soils and thus used in most fertilizers, 

 are iised on different plats as single elements and in various com- 

 binations. One weakness of the experiment is in the fact that only 

 one ciuantity of a certain element is used. For instance, all plats 

 receiving nitrogen receive the same quantity of actual nitrogen, whether 

 it is derived from nitrate of soda, blood, or manure, and the same is 

 true in the case of phosphorus and potassium. 



*Paper No. 6, Citru-s Experiment Station, College of Agriculture^ University of 

 California, Riverside, California. Address before State Fruit Growers' Convention, 

 Los Angeles, California, November 12, 1914. 



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