Scientific Agriculture. 



342 



[April, 1912, 



land farming. Here certain manures 

 cause the very fine particles of a soil to 

 become cemented together to form com- 

 pound particles, thus producing a coarser 

 texture and a lighter soil, whereas 

 another set of manures have the opposite 

 effect, and by destroying the compound 

 particles already existing in a soil a finer 

 texture is produced. To the former class 

 belong those manures which contain 

 large quantities of organic matter,and on 

 which on undergoing change in the soil 

 yield humus, a substance which has a 

 decidedly beneficial effect on the texture 

 of soil. In the latter class may be placed 

 many artificial manures of the type of 

 ammonium sulphate, etc. 



By applying representatives of these 

 two classes to a paddy soil and contrast- 

 ing the relative effects on the crops, it is 

 possible to arrive at a general conclusion. 

 Such an experiment has been in oper- 

 ation on the Central Farm, Coimbatore, 

 for several years in which the effect of 

 a green manure was tested against 

 similar land to which a mixture of 

 bone-meal and potassium sulphate 

 was applied as a manure. As in both 

 cases, nitrogen, phosphoric acid and 

 potash were added to the soil with the 

 manures applied, such an experiment 

 gives directly the effect of the bulky 

 organic manure. With daincha as the 

 green manure crop, a yield of 4,200 lbs. 

 of paddy was obtained, with wild indigo 

 about 3,100 lbs.,, and with Calotropis leaves 

 3,877 lbs., whereas the comparison plot 

 only yielded 2,052. Another plot to 

 which another type of bulky organic 

 manure was added, namely, castor-cake, 

 yielded 3,550 lbs. of paddy. Thus the 

 addition of a bulky organic manure to 

 a paddy soil gives better crops than a 

 manure containing little organic matter, 

 but which has approximately the same 

 manurial value. Consequently it may 

 be stated that the first essential of a 

 paddy manure is that it should contaiD 

 a large proportion of organic matter 

 capable of producing humus, thus 

 counteracting the tendency of such soil 

 to become finer in texture and heavier 

 in character. 



Taking the next factor, the fact that 

 the land is kept fully saturated with 

 water throughout the greater part of 

 the growing season means that there is 

 practically no free oxygen present in 

 the soil, and this draws at once a sharp 

 distinction between paddy cultivation 

 and that of ordinary field crops. The 

 presence or absence of air in a soil deter- 

 mines to a very great extent the course 

 of the changes undergone by the nitro- 

 gen of a manure before it is incorporated 

 with the plant tissues and in ordinary 

 soils the nitrogen of the manure after 

 undergoing many intermediate changes 

 unites with the oxygen of the air to 

 form nitric acid, a substance which is 

 easily absorbed by the crop and the 

 nitrogen it contains easily utilized for 

 the purposes of the plant. On the other 

 hand in paddy soils, no oxygen being 

 present, instead of nitric acid, ammonia 

 is produced, but it has been shown in 

 Japan that the paddy plant readily 

 assimilates this substance, and conse- 

 quently the products of the decompo- 

 sition of many manures in such soils are 

 suitable for the needs of the plant, and 

 there is no need to endeavour to alter 

 the ordinary course of affairs in this 

 respect. 



Fermentations which take place in the 

 absence of free oxygen are known as 

 anaerobic fermentations, and that this is 

 the type of fermentation which takes 

 place in paddy soils is shown by the 

 composition of the bubbles of gas which 

 are evolved, The gases found are the 

 same as those obtained from marshes 

 and bogs where the fermentation is 

 known to be anaerobic. Under these 

 anaerobic conditions, nitrates are decom- 

 posed, and the nitrogen they contain 

 liberated in the free state, a form in 

 which nitrogen is of no value as a plant 

 food to paddy as well as to all cereal 

 crops, and consequently manures con- 

 taining nitrates should not be used for 

 the manuring of paddy. 



Further, as those soils are kept satur- 

 ated with water, any substances which 

 are soluble in water, and which are 

 not retained by the soil are liable to 

 be washed away and lost, and nitrogen 



