PLANT FOOD
A soil, as I have said before to the boys, may contain all the food necessary for plant growth and still not support any good growth at all. That means then we ought to be able in some way or other so to understand the soil that it will be possible to unlock these good things for the plants to live on.
"I see a question in Josephine's and Miriam's faces. I guess that this question is concerning what the plant food is in soils. That is right, is it not?
"Well, I'll take that up first, then;—different ways of improving and increasing the goodness of the soil.
"The foods that are necessary and essential to plants and most likely to be lacking in the soil are nitrogen, potash and phosphorus. Now by no means must you think that these are the only chemicals which are foods, for there are something like thirteen, all of which do a share in the food supply. Oxygen and carbon are very necessary indeed. Oxygen is both in the air and in water. Carbon plants take entirely from the air. I might go on and tell you of iron, of sulphur, of silicon and all the others. But you would only get confused, so I am going to make you acquainted with these three entirely necessary ones. They are capricious; often missing, and when not missing hard to make into available food for plants.
"The soil contains many bacteria, small living organisms. These may be divided into two classes, the good ones and the bad ones. The good ones acting on nitrogenous matter put it in shape for the plant to absorb or feed upon. You see nitrogen may be in soil in quantities sufficient for nourishment. But unless it is in a compound available for use, it is of no value to the plant. Then there are the bad bacteria which act upon nitrogen in such a way as to form compounds which escape from the soil as a gas. That is pretty bad, is it not?
"How can the good bacteria be encouraged to grow, and the bad ones prevented from forming? The necessary conditions for the growth of good bacteria are air, water, darkness, humus matter and freedom from acid condition of the soil. If the soil is acid then these other 'chaps' set up their work; so we must see to it that our soils are well cultivated, well aired, have plenty of manure, and, if acid, have a liming, so that these bacteria missionaries can start their good work.
"The manure I spoke of above is the great source of nitrogen upon which most plants depend. There is nitrogen sufficient right in the air, but that again is not available. Certain plants like beans, peas and clovers belonging to the family of legumes are a great deal more fortunate than the rest of the plant families, for, under favourable conditions, they develop bacteria which make it possible to take into themselves free nitrogen. Just look here! See this narrow box; I can drop down one side of it. Here is a sheet of glass put on so you may look at the roots of the beans which are planted close to this glass side. Just observe the great extent of root system. Now see on the roots these white lumps, or nodules as they are called. These contain nitrogen-gathering bacteria. Some farmers in order to get more available nitrogen in the soil plant a crop of some legume. Then these root masses with their treasures on them are spaded into the soil.
"But most plants depend for nitrogen on manure. Whenever you see sickly looking foliage know that nitrogen is lacking, and supply manure in order to obtain it.
"The next element is potash. Its most common source of supply is wood ashes, not coal ashes. One may buy potash in the form of the muriate or sulphate. I told the boys before that potash was good for seed and fruit. Pretty necessary to have in the soil, is it not? Stunted fruit and poor seed mean lack of potash. Phosphorus helps in this work too, and also assists in the forming of fine flowers. Bone ash and phosphates are the sources of this food element.
"So if we just consider the classes of soils with which we have to deal, remember the foods that must be had, and the effects on plants where one (or all) of these is lacking, we have in our hands a help to soil troubles.
"Take sandy soil—what is its greatest need? I should say humus. It certainly should have more nitrogen. So add humus in the form of manure. Spread it on your piece of garden plot anywhere from two to six inches deep. This spaded in will, I think, do the work. You see sand allows water to trickle away too fast. Water must be held properly in the soil.
"The clay soil really needs air. The good bacteria will not work without this. So spade the soil up in the fall, and leave it weathering in huge lumps. Sand or ashes added in the spring helps the air question too. A sprinkling of lime over the surface tends to sweeten the entire soil; for clay soil, so often too wet, is liable to get sour. Lime also adds another plant food called calcium. It would not be bad to add some humus in order to have an even greater supply of nitrogen.
"The lime soil, light and sweet, needs humus too. It should have this to add body and ability to hold water.
"Sometimes it is well to add in the spring a sprinkling of phosphates; that is a chemical fertilizer. Chemical fertilizers are like tonics to the soil.
"All this very briefly puts us in touch with plant foods. I think you all know from your school work that plants take their foods in liquid form. These solutions of foods are very, very weak. That is another reason why we should see that, if possible, there is plenty of nourishment available in the soil, and plenty of water too.
"These bean roots and rootlets show the feeding area or places of plants. Notice the small roots which apparently have a fringe on them. These fringes we call the root hairs. These absorb, soak up the dilute food which is in the soil.
"It is very wonderful what power they have of penetrating the soil. See the bit of blotter I have put down the path of one bean's root course. It would seem to shut the rootlets entirely off from the soil.
"Jay will gently press the bit of blotter away from the soil. See here and there how these root hairs have wound their way through the blotter to the soil, their feeding place. It is well that plants have this power of seeking and finding food. Because it greatly increases their food chances.
"So much very briefly for plant food. I have not told you very much to be sure, but it is quite enough, I think, for a 'starter,' I wish to tell you a bit about the plant itself soon. A few experiments may liven up the subject. So I shall ask Josephine, Miriam, and Ethel to attend to those for us. We can take turns at demonstrating as Jay and Albert have to-day. So you girls must remember to drop in to see me—say, Wednesday of next week."