1922.] Experiments with Phosphates and Slags. 



525 



plots were grazed by cattle and sheep in order to secure a close 

 grazing bottom and so protect and keep the surface soil cool. In 

 1920 the meadow was reserved for hay, and throughout the season 

 the plots were visited at least every week, a close watch being 

 kept on the progress of the various plots. The high soluble slag 

 and the " superphosphate and lime " plots were the first to 

 make a start, followed by the plots that received the finer ground 

 rock phosphates. During the whole of May the superiority of 

 the plots receiving the finer ground rock phosphates over those 

 receiving the same phosphates, only more coarsely ground, could 

 be distinctly seen. As the season progressed the distinction 

 became less and less visible, until at the beginning of July it was 

 quite impossible to see any difference. 



The high soluble basic slag (Plots 5 and 17), and Plot 15 

 (superphosphate and lime), were distinctly ahead during the 

 whole season, but the rock phosphate plots gradually lessened 

 the difference as the season progressed, although they never 

 actually succeeded in catching up. 



When the wild white clover came into flower the effect was 

 remarkable. Figs. 4 and 5, showing Plot Iv (untreated) and 

 Plot H (Cleveland phosphate) give some idea of the contrast 

 which met the eye. So thick was the crop of wild white clover 

 that the farmer decided to cut the plots for seed.* 



Plots 1-19 are strictly comparable, having been sown at the 

 same time, and a useful comparison of the effectiveness of the 

 various phosphates may be made from the yields of hay. 



There can be little doubt that the highest soluble types of 

 open hearth basic slag and basic superphosphate are the 

 most effective phosphates at Horndon. Some of the rock 

 phosphates, however, were nearly as effective. The hard Ameri- 

 can Florida Pebble phosphate was inferior to the softer North 

 African phosphates, as not only was shown in the weights of 

 hay, but was plainly to be seen on walking over the plots. 



No gain from fine grinding is apparent in the weights of hay, 

 but an earlier start was undoubtedly made by the plots receiving 

 the finer ground phosphate, and where a meadow is reserved for 

 grazing it is possible that the extra cost of giinding would be 

 well repaid. 



The open hearth fluorspar slag, after giving promising results 

 during the first two years, proved a poor plot in 1920 when com- 

 pared with the h i gh so luble slag, Plot 17. All the rock phosphate 



* Only the plots were cut for liav, and no attem]it was made to harvest tlio 

 rest of the field, as the crop was not considered to be worth the labour 

 involved in doing so. 



