4 BULLETIN 47 ? U. S. DEPARTMENT OF AGRICULTURE. 
cial fertilizers, 1 from which there are important residual effects on 
other crops in the rotation. The clean culture practiced aiso brings 
all weeds into thorough subjection. The yields per acre of all farm 
crops have been greatly increased since the extension of potato 
growing. 
BY-PRODUCTS FOR FEEDING AND MANURE. 
That 40 per cent of the entire crop is fed to live stock has already 
been pointed out. This is important for a diversified and profitable 
sj^stem of farming, since it not only gives a large return in meat from 
the 19,000,000 swine thus supported, but contributes an indispensable 
supply of stable manure to the upbuilding of the soil. The nearly 
100,000,000 bushels that are made into alcohol are mostly worked up 
in farm distilleries, and the resulting by-product, or mash, possesses 
considerable value for feeding cattle, and thus returns the greater 
part of the fertilizing elements in the crop to the land. The more 
than 50,000,000 bushels that are converted into starch, dextrin, and 
related products enter quite largely into Germany's export trade. It 
should also be mentioned that potato tops are now dried and used for 
stock food on many estates. 
A MAXIMUM ACREAGE THE POLICY. 
For all these reasons the German farmers seek to plant a maximum 
acreage of potatoes, and when, through the abundance of their har- 
vests, their various markets are oversupplied there is not so much 
talk of reducing production as of finding some neAv outlet for the 
surplus. This is illustrated by the development of the potato-drying 
industry. Previous to 1894 there had been an overproduction of 
potatoes and low prices, to relieve which the Government united with 
the organizations of the distillers and starch makers and with sev- 
eral agricultural societies to offer prizes, aggregating 30,000 marks, 
for the most practical and economical method of drying potatoes. 
After thorough tests of the apparatus designed by the competitors 
these prizes were awarded to several firms. That the method was 
successful has been demonstrated by the rapid increase in the num- 
ber of factories for drying potatoes, which now number 371. In 1910 
more than 12,200,000 bushels of potatoes were dried in these factories. 
COMPARISON WITH AMERICAN CONDITIONS. 
SOD. FERTILITY. 
The disparity in the average yields of Germany and the United 
States is not due so much to the superior quality of the German soils 
1 The average expenditure for potato manures on 140 German estates was $10.68 per 
acre, less than is frequently used in Maiue or in the trucking districts of other States. 
See Howard, W. H., Produktionskosten der wichtigsten Feldfriichte, Aufl. 3, Berlin, 1908. 
