LETTUCE 213 
phate or perhaps untreated phosphatic rock with stable 
manure at the barn or as it is thrown from the railroad 
cars, 
Various forms of commercial fertilizers are sometimes 
used in the forcing of lettuce. Greenhouse plants are 
easily injured by excessive applications of chemicals, 
such as nitrate of soda, acid phosphate and muriate of 
potash, and large amounts should not be used at any 
time. Sayre draws the following conclusions from fer- 
tilizer experiments made at the Indiana Experiment 
Station: 
“In regard to the experiments last year which were reported at 
the meeting of the Society of Horticultural Science, the items of 
principal interest were as follows: None of the fertilizer treatments 
except manure were beneficial, but the manure plots were greatly 
superior and indicated that manure was by far the best and most 
economical fertilizer. Our report was chiefly concerned with the 
effect of various fertilizers on the nitrogen content of the plant. 
An analysis of the plants shows that the chemical composition, at 
least in regard to nitrogen, was appreciably affected by the fertility 
of the soil, and could be modified by the addition of chemical fer- 
tilizers. The addition of phosphorus to the soil tended to decrease 
the percentage of nitrogen in the plant, and the application of nitro- 
gen in addition to phosphorus tended to offset the phosphorous effect 
and raised the nitrogen content of the plant, but there is a definite 
limit to which the nitrogen content can be raised. Nitrogen alone 
slightly decreased the nitrogen content of the plant as might be ex- 
pected from any element added in excess. Nitrogen unquestionably 
tended to promote leaf growth, while phosphorus tended to hasten 
maturity.” 
Most growers of lettuce apply lime to the beds about 
oncea year. See Fig. 72. 
Preparation of soil—The preparation of greenhouse 
soils has been fully discussed in Chapters V and VI. 
Stable manure is generally applied for the first crop in 
the fall, and, if desired, additional amounts for subse- 
quent crops. It may be well decayed, though some 
growers prefer fine manure that is comparatively fresh. 
