Another experiment, taking more time, is to place some clean sand in a flower pot, wet it, and sprinkle fine grass-seeds over it. Place in a warm room and the seeds will soon sprout and send small roots down into the sand.
These experiments show some of the characteristics of all soils composed largely of sand. We observed that sand when heated retains its heat for some time. Any soil having a large proportion of sand, when warmed by the sun will keep the heat after the sun has set or is hid by the clouds. We proved that water would flow quickly through it. A sandy soil is therefore a dry soil, and for this reason favorable to nearly all our useful plants. We saw that water would rise through sand by capillary attraction, which makes sand useful in soil in dry weather to bring water up from a damp subsoil to feed the roots of plants growing in the soil.
However, there are objections to sand. As we saw, it is loose and easily moved about by water. A sandy soil is therefore easily washed away by rains, and, if too sandy, may suffer great injury by washing in heavy storms. Water flows through sand quickly, and if there is no damp subsoil immediately beneath, the soil may get so dry that plants will burn up. The water may also wash down all the light organic matter out of reach of the plants.
We observed that sand is easily moved about. This is important in that all soils where plants are growing must be frequently stirred, to let air come into the soil, and to kill the weeds. A sandy soil is easy to hoe or plow, because the sand is loose. This saves time and money, or work in caring for plants, and is a business advantage.
If you carry out the experiment with seeds planted on sand you will observe that the roots of the young plants easily find their way through the sand in search of food and water. This shows that a soil containing sand is favorable to the growth of plants, because in it their roots spread in every direction.
Procure a small quantity of clay from some clay bank. Place in a warm place to dry, and in a day or two you can crush it into a soft, impalpable powder. Pinch a little between the fingers and it appears to stick together slightly. Place some in a bottle of water, cork it tight and shake the bottle. The powder floats in the water in clouds, till the water appears completely filled with it. Let the bottle stand and it will be many hours before the clay settles and the water becomes clear. Wet some of the dry clay, and it forms a sticky, pasty mass, that has a soft, greasy feeling between the fingers. Spread some of the soft, pasty mass over a sieve, and pour water on it and the water will hardly pass through the sieve at all. Spread some wet clay over a rough board, and pour water over it, and the clay will cling to the board a long time before it is swept away. Place a lump of wet clay in the sun and it will be many hours before it is entirely dry. Spread some of the wet clay over a dish and place it in the sun, and when it slowly dries it will be found full of cracks. Place a lump of wet clay in an oven and it will dry hard like stone.
Place some of the wet clay in a pot and scatter fine seeds over it. The seeds may sprout and try to grow, but they will probably perish as tender roots are unable to push their way through the sticky clay.
After all these experiments have been performed with the clay and sand, another experiment can be made by drying both the clay and sand and then mixing them together in equal parts. When well mixed place in a pot and scatter fine seeds upon the mixture. Water well, and place in a sunny window; and the plants will sprout and grow longer and better than in either the pure sand or pure clay.
These experiments with the lump of clay show that if soil consists wholly of clay, it must be a poor place for plants. In every hard rain the water, instead of sinking into the soil to supply the plants, would run away over the surface and be wasted. After slow soaking rains the soil would remain wet and cold for a long time. When the sun dries the soil it splits and cracks and tears the roots of plants growing in it. This sticky, pasty soil sticks to spade and plows and we find it hard, slow work to cultivate it. A pure clay from these would appear to be a poor soil for plants. We must not, however, be led astray by our experiments, as it is not easy to find a soil composed wholly of clay. It is usually mixed with other things and then forms a valuable part of the best soils. Sand alone would be a poor soil. Clay alone would be a poorer soil. Mixed together and mixed with other things, they make a part of all good soils.
Organic and Inorganic Matter.—Organic matter is something that has life, or has had life at some time. The organic matter in the soil has been supplied by animals and plants, in one way or another. All else is inorganic. Both organic and inorganic matters are necessary to the existence of plants. Peaty soils wholly organic will not grow plants, neither will sandy soils wholly sand. Inorganic matter forms the foundation of soils and generally forms from eighty to ninety per cent of the whole soil.