942 Report on Crop PrRopvucrion OF THE 
productive capacity in every part and untoward conditions such 
28 fungi and injurious insects were to affect one part no more 
than another, then we could measure with great accuracy the 
relative influence of different fertilizers or different quantities of 
the same fertilizer. Such desirable conditions as these are not. 
to be found. Only approximate accuracy is reached in field 
experiments, even under the most favorable circumstances; and 
for this reason the accompanying figures should not be taken as 
representing fixed or absolute relations. The experiments con- 
vey lessons, however, which appear to the writer to be plain. 
In the first place it is entirely clear that the limit of produc- 
tion as determined by season and other conditions outside of the 
supply of food was nearly reached in the Purdy field with the 
first 500 lbs. of fertilizer applied. This is equivalent to stating 
that the profits were mostly realized from the first 500 lbs. of 
fertilizer, the manure cost of the gain in yield being only 16.6 
cents per barrel. While with the increasing quantities of fer- 
tilizer used there was on the average a corresponding increase 
of crop, this greater production but very little more than paid 
for any application of fertilizer above 500 lbs. The data show 
that the additional yield of onions resulting from each 500 lbs. 
increase of fertilizer above the first 500 Ibs. had a fertilizer cost 
of $0.79 to $2.28 per barrel. The profits of such manuring are 
uncertain, depending upon market conditions. 
It is to be noticed, moreover, that the added growth due to the 
first 500 lbs. of fertilizer was not uniform in the different years. 
In 1800 conditions were favorable for an onion crop, a fairly 
large yield being secured, and the highest returns of any year 
were obtained from the commercial plant-food added to the soil. 
The year 1898 gave the smallest crop of any of the four. Com- 
paring the effect of the fertilizers in these two years, we see that 
500 lbs. of fertilizer caused an increase in 1900 of 64.6 bbls. of 
onions per acre and in 1898 only 11.7 bbls. It should be noted 
that in 1898 the yield, though small, was progressive with the 
increase of fertilizer, while in 1900 the yield with 500 Ibs. of fer- 
tilizer was as large as with the heavier manuring. All this 
