1922.] Ground Mineral Phosphates as Manures. 709 



Trials in Essex, 1915. — Dr. Kobertson commenced trials in 

 Essex in 1915 with mineral phosphates and basic slag. The 

 results of these trials are given in the September issue of 

 this Journal, page 519. He concludes that as a source of phos- 

 phate for the manuring of grass land, the value of mineral 

 phosphates is very close to that of high-grade basic slag, and 

 that, of the various types of rock phosphate, Gafsa (a North 

 African phosphate) seems to be the most suitable for direct 

 application. 



Trials at Cockle Park, 1917.— In October, 1917, 11.1 cwt. 

 per acre of high-grade basic slag and 8.3 cwt. per acre of 

 Tunisian phosphate were applied to small plots of old pasture 

 of a poor character at Cockle Park. Each dressing contained 

 200 lb. phosphoric acid. The dressings were repeated in 

 October, 1920. A recent inspection of these plots shows a 

 marked improvement over the untreated plots, and it is dim- 

 cult by observation to say which have been most effective. 



It is again urged that the greatest importance should be 

 attached to fineness of grinding. The eye is not a safe test in 

 judging of this fineness, so that samples should be obtained 

 before purchase for examination and guarantees as to fineness 

 of grinding. It is usual to guarantee that 80 per cent, of basic 

 slag and other finely ground mineral phosphates will pass 

 through a No. 100 sieve, containing 10,000 holes per square 

 inch. It is now possible to obtain these mineral phosphates, 

 with a guarantee that 80 per cent, will pass through a No. 120 

 sieve, containing 14,400 holes per square inch. 



Trials at Cockle Park, 1922. — An important trial of phosphatic 

 manures on poor grass land was commenced at Cockle Park in 

 the North Field, Paradise, in February, 1922. Alongside the 

 other dressings North African phosphates were applied to two 

 plots at the rate of 6 cwt. per acre. This contained 63 per 

 cent, of phosphates. In one case the fineness of grinding was 

 79 per cent, through a No. 100 sieve, and in the other 83 per 

 cent, through a No. 120 sieve. The results already indicate 

 that the more finely ground phosphate has developed 

 clover and pasture plants more effectively than the other, and 

 also that, so far, the results of this finely ground phosphate 

 are quite comparable with that of high-grade basic slag. 



The following table shows the approximate costs of high- 

 grade basic slag and of finely ground North African phosphate, 

 as offered to farmers in the north of .England in September 

 last : — 



