XO The Philippine Journal of Science 1914 



soil with certain beneficial bacteria after proper conditions have 

 been found suitable or established. 



In this paper, we do not give complete data with regard to 

 the soils of Luzon, but we desire to place on record as many 

 facts as possible concerning the fertility of some of the agri- 

 cultural sections of Luzon, based on chemical and physical 

 analyses and to a certain extent on such field observations as 

 we have been able to segregate. In some sections of the island 

 we have been able to carry on our work much more thoroughly 

 than in others. From certain sections we have little data, 

 except an occasional analysis, which shows the general nature 

 of the soil. Where the chemical and physical data are fairly 

 complete, they may be taken together with the meteorological 

 and agricultural data of the district and used not only to develop 

 the district itself, but to interpret the probabilities of success 

 of certain crops in new districts. 



No analysis is more accurate than the sample which it rep- 

 resents; therefore, the errors of sampling should be reduced 

 to a minimum. All samples were collected according to the 

 directions for taking soil samples, ^^ already published. 



THE CHEMICAL ANALYSIS 



The chemical analysis aims to give a general idea of the , 

 potential fertility of the soil, and in a way measures the crop- 

 producing power of a given land, provided that the climatic 

 conditions, physical texture, and bacterial activities are satis- 

 factory. Hilgard,^* from practical experience and extensive 

 investigations, found that this is invariably true with virgin 

 soils, while with soils that have been cultivated for centuries 

 under different cultural methods and in different crops other 

 factors not readily differentiated by chemical analysis alone are 

 presented. 



There are ten elements essential to the proper growth of plants 

 as follows :-= Carbon, oxygen, and hydrogen, the sources of 

 which are air and water; phosphorus, potassium, and nitrogen, 

 which are sometimes deficient in soils and have commercial 

 value as plant food; sulphur, calcium, iron, and magnesium, 

 which are required by plants in small amounts and are rarely 

 deficient in soils. Silicon, aluminium, sodium, chlorine, and 

 manganese are also commonly found in plants. 



''Cox, This Journal, Sec. A (1911), 6, 326. 



-' Loc. cit., Soils, 325, 843. 



■" Loc. cit., Hopkins, Soil, etc., 13. 



