654 Journal of Agriculture . Victoria. [10 Nov., 1917. 



For the purpose of comparison the f allowing table gives the percent- 

 age of plant food soluble in water in the case of other crops. 



These analyses were conducted on the absolutely overhead dry matter 

 of the matured crop. 



Table XIV. 

 Soluble Plant Food in the Above Gkoitnd Poetion of Various 



Mature Plants. 



Excepting lucerne, it is found that jiractically all the potash and 

 phosphoric acid, as in the case of the potato haulm, is soluble in water. 

 The nitrogen content, although more soluble in the rye, vetches, and 

 mustard, than in lucerne or the potato haulm, is mainly contained in a 

 form insoluble in water. 



Wliilst the meagre scope of the work done on this question precludes 

 any definite statement the results show a difference in solubility deserv- 

 ing of further work. 



The Amount of Plant Food Removed Per Acre by the Potato Plant. 



Harvesting, as far as the potato crop is concerned, means the digging, 

 collection, and removal of the potato tubers. 



Approximately one-fifth of the total tuber weight per acre equals 

 absolutely dry matter, and approximately one-half of this weight is 

 equivalent to the weight per acre of dried haulms. Organic matter, as 

 is well known, is of paramoimt importance to the soil, and the partly 

 dried potato haulm is readily broken down in the soil to form humus. 

 Taking a 10-ton potato crop, the amount of absolutely dry matter con- 

 tained in the tubers is approximately 2 tons. The amount of absolutely 

 dry haulms from this crop would be 1 ton, making a total of 3 tons of 

 dry matter. 



Computing from the analysis of the potato haulm (Table VI.), we 

 find that a 10-ton crop of potatoes will return to the soil from the haulms 

 approximately 45 lbs. of nitrogen, 7 lbs. of phosphoric acid, 84 lbs. of 

 potash, 51 lbs. of lime, and 25 lbs. of magnesia to the soil per acre, accom- 

 panied or associated with approximately 1 ton of organic matter which, 

 in itself, is of great importance as a soil improver. 



Stated in terms of artificial fertilizers, the nitrogen returned per 

 acre by the dried haulm is equal to 2 cwt. of ammonium .sulphate. The 

 potash to 1^ cwt. of potash sulphate, and the phosphoric acid (7 lbs.) 

 would be equal to approximately 40 lbs. of superphosphate — all 

 amounting to an appreciable dressing of a complete fertilizer with the 

 additional advantage of supplying the raw material for the fonnation 

 of humus. 



These figures would be supplemented to a small extent when the 

 roots are taken into consideration. On the other hand, a 10-ton potato 



