FERTILIZER
As the amount of soil is limited and the number of plants that it has to support is great, the soil should be made quite rich and should be further fertilized from time to time with a little liquid manure. This can be best obtained by taking a strong barrel or large keg and filling it about half full of water. Then fill an ordinary coarse potato sack with cow-stable manure and set the sack in the barrel for a few days. A tap in the bottom of the barrel is most convenient for drawing off the liquid manure. A little of this will also be found valuable for watering dahlias, roses, and other garden plants during the summer.
SOIL STUDIES
The classes of soil should be reviewed. Pupils should gather examples from many places. The samples may be kept in bottles of uniform size and should include not only the four types but varieties of each, also various kinds of loam.
EXERCISES AND EXPERIMENTS
SOIL CONSTITUENTS
1. With a sharp spade, cut a piece about twelve inches deep from (1) the forest floor, (2) an old pasture field. Note character and order of the layers of soil in (1) leaves, humus, loam, sand, or clay; in (2) grass, dead grass, humus, loam, sand, or clay. Observe soils shown in railway cuttings, freshly dug wells, post holes.
2. Note the effect produced on the soil of a field by (1) leaving it a few years in pasture, (2) ploughing in heavy crops, (3) applying barn-yard manure. In all these cases vegetable matter is mixed with the soil.
3. Dry some good leaf-mould. Throw a handful on the surface of some water. The mineral matter sinks, while the vegetable portion remains suspended for some time. Try this experiment with gravel, sand, and clay. Note that the gravel sinks rapidly, the sand less rapidly, and that the clay takes a long time to settle. If the water be kept in rapid motion, the finer soils will all remain suspended till motion becomes slower. Apply this in geography. The bed of a stream will consist of stones if it be swift, of sand if less swift, and of clay if very slow. How are alluvial plains formed?
4. Place half an ounce of dry humus on an iron plate or fire-shovel and heat strongly in a stove. Note that it begins to smoke and a large part smoulders away to ashes; the mineral portion remains. Weigh the part left and find what fraction of the humus consisted of vegetable material.