STARCH CROPS ^7^7 



genous manure, either i 14 cwt. ammonium sulphate, i i<, cwt. cyana- 

 mide, ^/^ cwt. ammonium nitrate or 281.6 gallons purin. The question 

 of the effect of the nitrogen in purin and the commercial manures was 

 approached after the nitrogen, potash and phosphate requirements of the 

 soils had been determined. All the manures, except ammonium nitrate, 

 were spread about a fortnight before seeding. The purin, which contained 

 3 to 4 parts per thousand of nitrogen, was distributed on two occasions, 

 a fortnight and a week before planting. Half of the ammonium nitrate 

 was applied as a top dressing, when the young plants appeared, and the 

 other half about a fortnight later. 



The soils used for the experiments were : 



i) a very light sandy loam derived from the disintegration of banded 

 sandstone, deficient in chalk and potash. 



2) a stonj^ diluvial soil, rather impervious, deficient in chalk and 

 potash. 



3) two siliceous loams of tertiary age containing plenty of chalk 

 and a sufficiency of potash. 



4) two clay soils derived from disintegrated basalt, containing a 

 fair amount of chalk and plenty of potash. 



The farms on which the experiments were carried out are worked 

 under the system of intensive cultivation. 



The land was prepared about the middle of April, the manures were 

 applied at the end of the month and Industr^^ potatoes were planted in 

 rows between May 7 and 11. The development of the crops was normal, 

 but those on the sandy land suffered from drought in the summer of 1915. 



The results of the experiments were set out in tables from which the 

 following conclusions have been drawn, showing the great importance of 

 the use of manure : 



i) Nitrogen is usually the factor which determines the yield of 

 potatoes, particularly on good clay soils, but on sand}^ soils mineral manures 

 (potash, phosphate) seem to be more important in this respect. 



2) A maximum yield cannot be obtained on strong land without 

 potash and phosphate manuring, even with heavy applications of nitrogen. 



3) Of the nitrogenous manures tested anmionium sulphate always 

 gave the best results on all types of soil, though cyanamide and ammonium 

 nitrate were not far behind. 



4) Purin gave such satisfactory results that it can be strongly re- 

 commended as a manure for potatoes. 



5) The highest starch jdelds were obtained with potash and ]jhos- 

 phates without the addition of nitrogen. Purin only caused a small re- 

 duction in the proportion of starch, while the other nitrogenous manures 

 brought about a nmch greater decrease. The potato seemed to be very 

 sensitive to the use of cyanamide and ammonium nitrate, as these manures 

 encouraged rotting. Potash manuring always caused an increase in the 

 proportion of starch. 



5) The quantity of nitrogen applied in the manure is not always 

 reflected by the crop yield. For example, ammoniiun sul])hate, of which 



