312 cox. 



Some of the above samples represent small areas, others exceptionally 

 large ones and still others unusual or peculiar conditions. Certain ones 

 represent soils of known low fertility and the analyses were undertaken 

 in order to determine the cause : barring these, the data show that Philip- 

 pine soils are highly fertile. 



From the chemical standpoint alone I believe that in the Philippines 

 it is the abnormal \"irgin soil that is not inherently suited to the majority 

 of crops. 



Many attempts have been made to classify and to explain the relative 

 productivity of soils according to the results of chemical analyses, but the 

 problem is too intricate; often the percentage of the various constituents 

 bears no necessary relation to the crop producing power, for the chemical 

 composition is only one of many factors involved in the soil problem. 



PHTSICAI. AXALTSES. 



A consideration of the physical composition of a soil is very important. 

 There are instances where tT\-o soils having the same chemical composition 

 ' and physical texture showed themselves to be very different, owing to 

 local peculiarities, but other things being equal the physical nature (the 

 amount of organic matter and the size of the inorganic grains) bears 

 a close relation to crops and will often explain conditions encoimtered. 



The organic and mineral constituents of a soil may indicate high 

 fertility but the physical condition may be such as to render it the op- 

 posite. A soil which contains a large amount of sand or himius is usually 

 porous, on the other hand one in wliich. the content of these constituents 

 is small is usually stiff and impervious to water. To be prodtictive a soil 

 must have gravel, sand, clay and silt in the proper projDortions not to 

 be impervious to water and air. Variation in the amount of humus is 

 frequently the essential difference between a soU and its subsoil, the latter 

 having the less organic matter, although there also may be a marked 

 difference in the porosities of the two. 



The porosity^ the aeration and toxicity, the water holding and absorb- 

 ing power, the movement and distribution of the moisture and soluble 

 constituents of the soil, and the depth of the water table depend largely 

 on the textui'e and, therefore, the di'ainage of a soil and its resistance to 

 drought are intimately connected with its physical nature. These same 

 factors in turn control the character and quantity of beneficial bacteria 

 in the soil. 



Some crops require an abundance of water during a certain period 

 while others require a uniformly moist soil. Lowland rice, an example 

 of the former, in most regions is usually grown on a heavy soil with an 

 impervious subsoil in order that it may have sufficient water during the 

 growing period. Such a sod, unless it is very rolling, would probably 



