THE HROADHALK WHEAT SOILS. 
107 
It is aUn. as ivgards citric-acid-soluble phosphoric acid, appreciably 
richer than the other plats in the second and third dept lis, though 
not to the same extent as plat 5. 
Ii would seem that the full supply of soluble salts has either exerted 
a solvent action on the natural store of otherwise unavailable phos- 
phoric acid in the soil, or, which is more probable, that the liianurial 
phosphates have entered into some sort of combination with the saline 
bases and have been retained in a less insoluble condition than where 
these have been absent or toss in quantity. This kind of solvent 
action is greatest where a full BUpply of saline matters has accom- 
panied that of phosphatic manure, but it is also shown to exist in 
the case of t he smaller separate applicat ions of potassium, magnesium, 
and sodium >alts. 
On plal LI, where phosphates and ammonium salts only have ben 
used, although there has been less demand on the phosphoric acid, 
bhe quantity of citric-acid-soluble phosphoric acid is least. This is 
show n in tin* following table ■ 
Table 58. 
Broadbalk wheat soils, samples collected in October, rsn.i 
13, L' h », ami 11. 
rials 
Tat 
Annual manuring. 
Phosphates, potassium, sodium.; and mapnesium salts 
Ammonium -.alts, phosphates, and potassium, -.odium, and mag- 
nesium salts 
Ammonium salts, phosphates, and potassium salts 
Ammonium salts, phosphates, and magnesium salts 
Ammonium salts, phosphates, and sodium salts 
Ammonium salts and phosphates only 
Ratio of excess of 
citric - acid - soluble 
phosphoric acid 
found per acre (as 
compared with un- 
man u red plat) to 
calculated excess of 
total phosphoric 
acid, the calculated 
excess in each case 
being takeu as 100. 
First !t 
inches. 
37 in?hes. 
r rent. 
Pe r een t. 
48 
50 
50 
50 
36 
34 
35 
31 
33 
33 
31 
39 
In the case of the dunged plats there is a far larger excess of phos- 
phoric acid unaccounted for. It may be remembered that plat 2b has 
yearly received since 1S43 a dressing of U tons per acre of farmyard 
manure. Plat 2a w as unmannred from 1849 to 1883, except that a por- 
tion of it received alkaline salts. Since 1883 it has received the same 
treatment as plat 2b, viz, 14 tons of dung per annum. The former 
plat has yielded on the average, for fifty years, over 34$ bushels of 
wheat and 32± hundredweight of straw per acre, a better yield than 
that of any of the other plats already considered, though inferior to 
thai of plal 8, already alluded to, which in addition to a full dressing 
of mineral manures has received 600 pounds of ammonium salts per 
annum. 
