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Lois-Weedon system clearly shows what tillage and spacing 

 can do without a particle of manure for a good many years. 



123. Climatic influence, It should be mentioned here 

 that deep cultivation is not so essential in warm climates as in 

 cold climates. Disintegration of deep-seated soils is favoured 

 by warmth, which generates COs gas from organic matter 

 and from disintegrating carbonates. Boussingault traced dis- 

 integration to a depth of 300 ft. in a warm mine. The 

 corrosive action of air and water goes on much faster in 

 warmer than in colder climates. The air in the pores of the 

 cultivated soils is highly charged with COg ; CC>2 is also 

 found in natural waters usually to the extent of nearly i %, 

 and more in water that has passed through soils containing 

 limestones and vegetable matter. The CO 2 enables water 

 to. dissolve and convey to the plants many fertilizing sub- 

 stances which are hardly soluble in pure water. Phosphate 

 of lime and phosphate of iron are not altogether insoluble in 

 water charged with COg. 



124. Formation of nitrates. Every well-tilled field may 

 again be regarded in the light of a saltpetre-bed. The value of 

 nitrates for crops cannot be overestimated, and the formation 

 of Potassium and Calcium nitrates is facilitated by open tilth 

 in the presence of organic matter and a little moisture, by 

 the action of nitrifying bacterra. The value of keeping land 

 in tilth during the dry months (i.e., from December to 

 May) cannot therefore be over-stated. During the wet months 

 ploughed up soils should be in crop, or else the excess of 

 plant-food made available by tillage operations would be 

 washed away by rain. 



125. Drainage and Irrigation. The object of draining 

 the soil is to admit air, which water-logging would prevent. 

 Where a field is so situated that draining is not feasible, 

 the land should be ridged before sowing for the kharif 

 season. Some crops are injured more than others by water- 

 logging! but no crop except some varieties of winter and 



