80 BULLETIN 479, U. S. DEPARTMENT OF AGRICULTURE. 
Two classes of fertilizers may be distinguished : " Complete " fer- 
tilizers, which contain all the important elements necessary for plant 
growth, and "incomplete" fertilizers, which furnish only one or 
more of these elements. 
COMPLETE FERTILIZERS. 
Stall manure, consisting of the animal excrement and the litter on 
which it is found, is a very effective fertilizer, not only because it 
contains the most essential plant foods — nitrogen, potassium, and 
phosphoric acid — but because it improves the physical qualities of 
the soil and by numerous microorganisms increases its activity and 
fermentation. Sheep and horse manure are richest and decompose 
rapidly. Cattle manure decomposes less rapidly. The former is best 
for application to compact, the latter to loose soil. As manure is not 
usually to be had in sufficient quantities at a nursery and is often 
difficult and expensive to obtain, it is frequently used in compost. 
Where humus can be obtained it has been found to be excellent, 
both as a fertilizer and for its effect in improving the physical 
quality of the soil. 
The value of compost as a fertilizer is decided by the material 
entering into it and the treatment given compost heaps. Organic 
substances of every kind may be used for this — weeds, raw humus, 
turf, and even street sweepings. To this material is added quick- 
lime for more rapid decomposition and horse manure in layers. 
Ashes may also be used to strengthen it. Weeds hoed from the 
nursery may be used alone for compost. In such cases it is neces- 
sary to mix them in thin layers with quicklime, allow the heaps to 
remain untouched for some time, and then stir repeatedly. T\ "hen 
thoroughly decomposed it is ready for use. 
One of the German head foresters gives the following formula 
for making good compost: The first layer, about J inch thick of 
organic substances, grass, heather, weeds, sawdust, etc., is sprinkled 
with a thin layer of unslaked lime, then another layer of grass and 
Aveeds is added, then a layer of lime, etc. In this manner it is heaped 
up like charcoal but shaped broader and lower so as to catch the 
rain, and then covered on all sides with carefully crushed earth. 
The slaking of the lime begins after a few days and in from 2 to 4 
days later is completed. During this time the heaps should be 
examined twice a day and all crevices in the earth covering closed in 
order to keep the heat, steam, and ammonia from escaping. After 
from 4 to 6 weeks the material is ready for use. 
