SOILS AND MANURES 367 



Government Experiment Farm, Potchefstroom, Transvaal, in- chap. 

 dicate {Holm, 1) that these manures greatly increase the yield, VI11 ' 

 and that profits are obtained on the expenditure ; from 

 3^ muids per acre without manure the yield was raised to 

 8 muids, an increase of about 133 per cent. 



331. Superphosphate Alone. — At Stanger, Natal, in 1903-4, 

 the use of concentrated superphosphate, at the rate of 120 lbs. 

 5 oz. per acre, resulted in an increased yield of 4 muids 82 

 lbs. per acre (Anon., 1). At Koedoespoort, Pretoria, in 1907-8, 

 the increase was only 240 lbs. of grain per acre and in 1908-9, 

 360 lbs., and the net cash gain (at 10s. per muid) from the use 

 of this manure only 5s. 4d. per acre (Watt, R. D., 2). In the 

 experiments at Potchefstroom, superphosphate proved the most 

 profitable manure to use, the average yield for the three years 

 being 14 muids 97 lbs. per acre, a gain of 300 per cent, and a 

 net gain of £2 os. iod. per acre, estimating the value of the 

 crop at 8s. per muid. The cost of the manure was 18s. 8d. 

 per acre (Holm, 1). 



332. Bone-meal Alone. — In the experiments at Potchef- 

 stroom no increase was obtained the first year from the use of 

 bone-meal alone. But in the second and third years the 

 yield was good. The average for the three years was 6 muids 

 164 lbs. per annum (Holm, 1), which is very low, showing that 

 this manure when used alone, on this particular type of soil, 

 did not supply the requirements of a good maize crop. 



333. Superphosphate and Bone-meal Mixed. — 'Holm (1) con- 

 cludes that a mixture of superphosphates and bone-meal is 

 likely to give the best results of any artificial manure, especially 

 in the first and perhaps also in the second year ; after that only 

 bone-meal need be applied. The mixing of bone-meal with 

 superphosphate facilitates the sowing of the latter. An English 

 Agricultural Chemist states that: "By mixing and allowing 

 them to stand some little time before using, the action of the 

 superphosphates on the bone-meal tends to increase the solu- 

 bility of the phosphates in the bone-meal, which in a dry climate 

 is an advantage ". To get the best results, the bone-meal must 

 be very finely ground ; according to competent agricultural 

 chemists, " the bulk of that offered on the South African market 

 is too coarse". Such coarse particles may remain many years 

 in the soil before they are rendered available for plant-food, 



