756 DISCUSSION ON WHEAT: 
North-West with the yield of Manitoba in the previous decade would bring 
a crop of more than 800,000,000 bushels. If there be such a surplus of 
good soil as three-fourths, ample room would be left for diversified crops 
and such rotations and following as might be needful in future years to 
meet the declining production of the prairie soils. 
After a reference to Sir William Crookes’ forecasts in 1898, and the 
extent to which later data had outstripped his modest expectations, 
Professor Brigham declared it ‘hazardous’ to set limits to wheat in view 
of possible unknown factors of production. 
Sufficient account had not been taken of the limitation of population 
among the nations of the higher standards, who are bread-eating peoples. 
Any presure on the wheat supply would foreshadow itself before the pinch 
came, and would tend to still further restriction of population. He agreed 
with an earlier conclusion of an American economist (Mr. D. A. Wells) that 
the world ‘for the first time in its history has now good and sufficient 
reasons for feeling free from all apprehensions of a scarcity or dearness 
of bread.’ Any increased demand in Western Europe, or more truly by 
North-Western Europe, would be fully met by developments in Canada, 
Russia, Argentina, Egypt, India, South Africa, and Australia, so that 
they might even leave out the United States, or even omit India should her 
wheat be needed at home to avoid periods of famine. Argentina was as 
yet undeveloped, and Russia backward in bringing her vast resources to 
full effect on the world’s market. North America had the land, progressive 
appliances, skilled energy, and facilities of transport to supply the bread 
market of coming decades. No citizen of the United States of America need 
harbour a jealous thought if in that market a major place should come to 
her northern neighbour. 
2. The Factors determining the Yield of Wheat. By A. D. Hat, 
M.A., F.R.S., and FE. J. Russewu, D.Sc. 
The Rothamsted experiments on wheat began in 1843 on the Broadbalk 
field on which wheat has been grown every year since. In the first few years 
a general idea was obtained of the requirements of the plant as regards 
manure; a scheme for the treatment of the plots was drawn up in 1851, 
and has been substantially adhered to ever since. 
(1) Foop.—The chief elements of nutrition derived from the soil or 
manure are nitrogen, phosphoric acid, and potash; lime, magnesia, soda, 
sulphuric acid, and silica also play their part, but are supplied in sufficient 
quantity by all ordinary soils. 
Nitrogen.—At the time the experiments were commenced the necessity 
for nitrogenous manures was denied by Liebig; several of the plots were 
therefore arranged to show the effects of different amounts and various 
forms of nitrogenous manure. It was soon demonstrated that nitrogenous 
manures were necessary and that the yield was proportional to the nitrogen 
supplied. The action of two sets of factors may be traced in the results. 
(a) If we have a series of plots, each receiving more phosphoric acid and 
potash than the plant can possibly require, the yield on each plot should be 
strictly proportional to the supply of nitrogen if the wheat plant be able to 
deal with all the nitrogen it receives. The amount of food a plant takes up, 
however, depends on the extent of the absorbing root surface. At first an 
increase in the amount of nitrogen in the soil increases the root system, and 
therefore the absorbing surface, as well as the amount of material that each 
unit of this surface can take up. Hence the yield is more than proportional 
to the supply, z.e., the second increment of nitrogen on Plot 7 produces a 
larger increase than the first increment on Plot 6. When yield is plotted 
