758 DISCUSSION ON WHEAT: 
The diagram No. 2 shows the results obtained during a selected period 
of thirteen years, when there were four plots receiving regular increments of 
nitrogen. ‘The vertical distance between the dotted line (cost of production) 
and the curve of returns shows the profit or loss accruing from the varying 
quantities of manure. Up to a certain point, the better the farming the 
higher the profit; beyond this the profit falls off. The curve illustrates the 
law of diminishing returns and also Lawes’ dictum that ‘high farming is 
no remedy for low prices.’ 
The general principles which have just been illustrated that the earlier 
increments of nitrogen may produce increased yields more than proportionate 
to themselves, while later amounts are followed by a constantly diminishing 
increase—i.e., that the curve of production is first concave and then convex 
—is true not only of nitrogen but of manure generally and of any of its 
simple constituents, should the experiments begin with a deficiency and end 
with an excess. The principle is also applicable to water supply and to 
many other factors, each of which may limit the crop production. For 
example, in arid climates the yield is generally unaffected by the supply 
of nitrogen because it is determined wholly by the water supply, enough 
nitrogen being always present to satisfy the needs of a larger crop than the 
limited water supply will permit of. 
Phosphoric Acid.—Unlike barley and turnips, wheat does not respond to 
large quantities of phosphoric acid, but is well able to satisfy its require- 
ments from the soil. Phosphoric acid, of course, is necessary, but its most 
marked effects are secondary. It hastens maturity, and is therefore effective 
in a backward season or in late districts, since it enables a crop to be 
harvested in time which otherwise might be damaged or lost. Extraordinary 
returns are obtained for small quantities of superphosphate in Australia. 
Potash.—Wheat is usually able to satisfy its potash requirements from 
the soil, but at Rothamsted, on the plots which have become depleted of 
potash, the deficiency is shown by a reduced yield, especially in dry seasons, 
and by increased tendency to disease, rust, &c. 
Organic Matter.—Autumn-sown wheat is less dependent than most farm 
crops on good texture of the soil, and grows freely even when the amount of 
humus in the soil is a low one. On the Rothamsted plots, where wheat has 
been grown for so long with manures containing no organic matter, no 
difficulty is experienced in obtaining a plant; the seed germinates and grows 
away freely. Similarly Prout at Sawbridgeworth has grown wheat and 
other cereals on the same land since 1864, using no farmyard manure, and 
growing clover (the roots and stubble of which would supply some humus) 
only about once every seven years. In England it is not customary to use 
much manure for wheat; in the Eastern Counties farmyard manure is very 
generally put on the temporary hay or clover before it is ploughed for wheat, 
but this is to some extent a matter of convenience in handling the manure. 
Beyond this, specific manures are rarely employed, except perhaps soot or 
a top dressing of nitrate of soda in the spring if the plant is backward. 
Wheat is usually grown after clover or a well-manured mangold crop, and 
therefore on land recently enriched with nitrogen; an excess of phosphoric 
acid is also generally applied to the turnip crop in the rotation, and its 
influence persists until the wheat crop comes round. 
(2) Ratnratt.—Wheat being a deep-rooting plant and sown in Eng- 
land in autumn, is less dependent on spring and summer rainfall than most 
other crops. Thus the very dry years—1854, 1864, 1898—were all good wheat 
years; indeed, an old English proverb runs: ‘ Drought never bred dearth 
in England.’ The lowest rainfall was in 1864 (18.5 inches) and the crop 
was above the average, especially on the plot receiving dung. Further, the 
great wheat-growing districts of England are also those of lowest rainfall. 
Wheat is, therefore, one of the crops best adapted to dry regions, probably 
