b. G-eneral soil characteristics 



(1) Most of the agricultural soilB are loams and silt loams 

 physically suited for tillage. 



(2) Natural fertility is low. Even soils of high humus con- 

 tent require heavy fertilization annually for high 

 yields. Soils from volcanic ash are particularly low in 

 phosphate. Essentially all of the agricultural soils 

 respond well to proper fertilization; nitrogen and 

 phosphorous are the elements that give the largest yield 

 increases for most crops. 



(3) In general, the upland soils are moderately to strongly 

 acid. The alluvial soils are only slightly acid, par- 

 ticularly if used as rice paddies. 



c. Fertility gtatuB 



(1) The soil fertility trend i-s upward on the ag-. •■ultural 

 lands. 



(a) A large proportion of the crops harvested is re- 

 turned to the land as night soil, animal manures, 

 mulches, and composts. 



(b) Importation of food and the use of fish, seaweed, 

 and similar marine products in the diet are in- 

 direct sources- of additional soil nutrients. 



(c) Large importations of fertilizer materials, es- 

 pecially phosphate (about 1,000,000 metric tons 

 annually during 1936-40) , and fixation of atmos- 

 pheric niftrogen as nitrogenous fertilizers' (400,000 

 metric tons of nitrogen annually during 1936-40) 

 add greatly to the soil nutrients supply. 



(d) Vegetation is removed from non-arable land and 

 applied to agricultural land as compost and ashes. 



(e) Leaching of plant nutrients is partially compen- 

 sated by nutrients in irrigation waters. 



(2) The soil fertility trend is downward on the non-arable 

 land. 



(a) Forest products are removed for lumber and fuel. 



(b) Grasses and shrubs are removed for feed and com- 

 posts . 



(c) Plant nutrients are lost by leaching. 



(d) Ho replacement of any consequence is made. 



(e) Sheet erosion is favored for periods on many forest 

 lands by clear-cutting practices. 



17 



