EXTENSION COURSE IN SOILS. 45 
it is often well to make an application at a time when the crop is in 
especial need of help or stimulation in its growth. 
Need of decaying vegetable matter in the soil. — Doubtless one of the 
greatest needs of the soils of the United States is more nitrogen 
through the growth of leguminous crops. This is especially true in 
the South, where long summers and much sandy soil cause the vege- 
table matter quickly to become depleted. Growing legumes for green 
manure, or, preferably, feeding the legumes and returning the manure 
to the soil, are the cheapest and most effective ways of supplying 
nitrogen for staple crops. Other advantages which green manure or 
barnyard manure have over commercial nitrogenous substances in 
the soil are: (1) They do much to maintain the moisture content; (2) 
they improve the texture; (3) they increase the temperature; and (4) 
they promote bacterial action. These advantages should never be 
overlooked in farm practice. Some of these benefits to the soil from 
decaying vegetable matter have been mentioned in previous lessons, 
but they will bear repetition. 
EXERCISES, LESSON VI. 
Materials required. — Four boxes; some poor, sandy soil; a few peas, oats, or grains 
of corn; sodium nitrate, ammonium sulphate, and pulverized limestone. 
Leguminous plants. — If conditions permit, carefully dig up different species of 
leguminous plants and examine the roots for nodules. If plants are carelessly removed 
from the ground the nodules will be pulled off and remain in the soil. If plants are 
taken up with a spade or shovel so that considerable earth remains on the roots, and 
then if the soil be very caref ally washed away, an examination of the fine roots will 
show the nodules. These will vary on different legumes from the size of a pinhead 
to that of a small pea, or even larger. If plants can not be dug out of doors, peas or 
beans planted in a box and kept growing well will show the nodules after a few weeks. 
Inoculation.—- -It will be found interesting as a field test to sow two strips side by 
side of some leguminous plant not commonly grown in the community, inoculating 
the seed used for sowing one strip and sowing the other strip from uninoculated seed. 
Cultures for inoculation may be secured by applying to your State experiment station 
or to the United States Department of Agriculture, Washington, D. C. After growing 
some six weeks the roots of plants from the two plats should be carefully examined 
for nodules. After two or three months of growth note whether there is a difference 
in the growth of plants on the two plats. 
Salts containing nitrogen. — Fill four boxes with poor sand. Plant either peas, oats, 
or corn in all four boxes. Keep warm and moist until the seeds are up. Mix into the 
soil of one box a good sprinkling of sodium nitrate ; mix a like quantity of ammonium 
sulphate into the soil of the second box, and ammomium sulphate and powdered 
limestone into the soil of the third; leave the fourth box undisturbed. Keep all the 
plants in good condition for growth and watch for a few weeks. Note results. 
PROBLEMS. 
1. A 30-bushel wheat crop removes from 1 acre about 48 pounds of nitrogen; a 50- 
bushel oat crop removes about 50 pounds; and a 65-bushel corn crop removes about 
85 pounds of nitrogen per acre. How many pounds of nitrogen are removed from 
the soil on a grain farm where 30 acres of wheat are raised averaging 20 bushels per 
