46 THE farmers' handbook. 



arid regions, and Hilgard attributes it to the larger content of lime which 

 these soils contain. It is well known that the addition of lime to clay 

 renders the clay pulverulent and incoherent on drying. There are, however, 

 reasons which make it difficult to accept this as a complete explanation of the 

 cause of the incoherent nature of our soils. In the first place the quantity of 

 lime, though larger than in the case of the soils from the more humid parts 

 of the State, is not by any means excessive, and it is only exceptionally that 

 they contain as much as is found in the average of the soils examined by 

 Hilgard. In connection with this matter, some experiments were made in 

 our laboratory in regard to the behaviour on drying of clay soils mixed 

 with different quantities of lime. It was found that a clay soil containing 

 •53 per cent, lime (an amount above the average in our soils) when moistened 

 and subsequently dried, became quite hard — as hard as clay which contained 

 no lime — and that the addition of 15 per cent., making 2 per cent., in all 

 (an amount which is above the average of the soils quoted by Hilgard), had 

 very little effect indeed upon the texture of the soil when dried. It required 

 the addition of at least 3 per cent, (about 15 tons per acre 1 foot deep) to 

 reduce the soil when dry to the crumbly condition characteristic of the soils 

 of this region. It would seem, therefore, that some other causes, probably 

 the absence of humus, operates in addition to bring about this state of things. 

 This is a subject that will repay further investigation. 



Nitrification in soils from arid regions. 



The nitrifying power of the soil is one of the most, if not the most, 

 important index of its fertility, since not only does a vigorous nitrifying 

 power ensure to the plant sufficient nitrates, which are essential to its proper 

 development, but the conditions which promote nitrification, namely, aera- 

 tion, moisture, and warmth, are exactly those which make for fertility. 



Nitrifying organisms appear to be present in the soils examined from all 

 parts of the State, with the exception of swamp-soils on which water has 

 lain for some period, and of extremely sandy soils. Sourness of the soil is 

 detrimental to their growth, and, what is of special interest to our purpose, 

 dryness of the soil affects the vitality of these organisms very strongly. In 

 dry soils, such as are met with in the region we are discussing, their vitality 

 is considerably affected, and their development, when placed under favour- 

 able conditions, is very slow. When they have once started to develop, however, 

 their further growth proceeds fairly rapidly. It would appear that dry 

 conditions, though they do not actually destroy the nitrifying organisms 

 reduce them to a dormant condition. 



The beneficial effects of irrigation were strongly marked in some samples 

 from rice-fields near Bangkok. These were received in small, hermetically- 

 sealed tins, and were quite moist on arrival. The nitrifying organism was 

 present in large quantity, and its development was extraordinarily rapid. 



Excessive heat has, of course, also a detrimental effect upon these organisms, 

 and both excessive heat and want of moisture are conditions which prevail in 

 the class of soil under discussion. Hence these soils are characterised by the 

 slowness with which the nitrifying process takes place; but although the 

 vitality of these organisms is impaired; or their condition modified, to the 

 extent that their development is exceedingly slow, in no case are they absent, 

 and when once they commence to develop, the development continues at a 

 normally rapid rate. The conditions which favour their development within 

 the soil, namely, aeration, moisture, and equable temperature, are conditions 

 which will result from properly conducted irrigation. Similarly, the nitrogen- 



