LIMITS OF ENDURANCE OF DIFFERENT FARM CROPS. 195 



Experiments with sodium carbonate. 

 Sodium carbonate is present in the water of many of the 

 artesian bores in New South Wales. As these waters con- 

 stitute in many cases the only available supply for irrigat - 

 ing, the question of the limit of tolerance of different crops 

 for this alkali is one of considerable importance. When 

 water charged with alkali is used for irrigating, the soil 

 frequently becomes covered with a white crust consisting 

 of sodium carbonate. This is due to capillary action which 

 brings the alkali to the surface where it is left as a deposit 

 on evaporation of the water. When the amount of alkali 

 present is considerable, the soil becomes quite hard, and 

 tillage operations are rendered very difficult and in some 

 cases impossible. These conditions were not reproduced 

 in the experiments, the surface of the pots being covered 

 by a mulch, so that surface evaporation was reduced to a 

 minimum, the soil was always moist, and the drainage 

 effectively prevented the accumulation of water or of water 

 charged with alkali. The experiments th eref ore represent 

 the action of the akali upon the plant itself, without refer- 

 ence to its possible deleterious effects upon the soil. 



Pots were filled with soil No. 1, and fertilised and sown 

 on June 3rd in the manner already described. The follow- 

 ing pots were prepared : — 



Pot 21, '01 per cent Na 2 Co 3 

 „ 22, '05 

 „ 23, -10 

 - „ 24, '50 

 „ 25, l'OO 

 „ 26, 3-00 



On July 1st, the appearance of these pots was as follows: 

 Nos. 21 and 22 had germinated well, growing well, (grain 



in the ear, Oct. 8th.) 

 No. 23 had germinated well, not quite so vigorous, back- 

 ward, (grain not forming Oct. 8tji.) 



