OTHER MANURIAL FACTORS 95 



that once the need for phosphates has been satisfied at Lambourne 

 End the hay crop could be increased by the addition of some 

 other essential plant food. It seems very probable, however, that 

 at Horndon-on-the-Hill, after the need for phosphates has been 

 satisfied, rainfall is the limiting factor as far as the hay crop is 

 concerned. 



THE SECOND LIMITING MANURIAL FACTOR 



It has been previously stated that the experiments were started 

 with the object of ascertaining the relative manurial value of various 

 types of insoluble phosphates. No attempt was therefore made to 

 include dressings of potassic and nitrogenous manures. Out of the 

 eight experimental centres dealt with here there are two Hassobury 

 and Farnham at which the response to phosphates, measured by 

 the hay crop, is negligible. A very marked improvement in the 

 quality of the meadow has resulted at Farnham, as has already been 

 pointed out (Table XIII), but even in a favourable season the 

 increased weight of hay resulting from the application of the various 

 phosphates has been very small indeed. Moreover, the productive 

 level of this type of soil is exceedingly low, and the same remark 

 applies to Hassobury, where also the crop seldom passes the 10 cwts. 

 per acre level. 



An examination of the analytical data presented in Table VII 

 shows that the Hassobury soil is reasonably well supplied with phos- 

 phoric acid, and has, in fact, practically twice as much available 

 phosphoric acid as any of the other experimental soils. The percentage 

 of available phosphoric acid is well above Dyer's limit of 0-01 %(7). 

 This is not the case at Farnham, where the soil is markedly deficient 

 in available phosphoric acid, and it seems reasonable to conclude 

 that a deficiency of another essential plant food is the cause of the 

 low productivity at Hassobury, and is preventing a response to the 

 dressings of phosphates applied at Farnham. 



Both soils are well supplied with nitrogen, and as readily available 

 nitrogen has been slowly accumulating at Farnham without having 

 any appreciable effect on the hay yield, it does not seem that a lack 

 of nitrogen is responsible for the poor crop returns. The Hassobury 

 soil, though devoid of calcium carbonate and possessing a Hutchinson 

 and MacLennan lime requirement of -13 %, gives no response to the 

 heavy dressing of lime applied to Plot 15. Moreover, the soil at 

 Farnham has an adequate supply of calcium carbonate. The low 



