The Story of the Soil Part 11

"I think not," said Percy." Let me see.--Just what do you understand by nitrification?"

"Getting nitrogen from the air, is it not?"

"No, no. That explains it. Getting nitrogen from the air is called nitrogen fixation. This action is carried on by the nitrogen-fixing bacteria, such as the clover bacteria, the soy bean bacteria, the alfalfa bacteria, which, by the way, are evidently the same as the bacteria of sweet clover, or mellilotus. Then we also have the cowpea bacteria, and these seem to be the same as the bacteria of the wild partridge pea, a kind of sensitive plant with yellow flowers, and a tiny goblet standing upright at the base of each compound leaf,--the plant called Ca.s.sia Chamaecrista by the botanist."

"Nitrification is an altogether--"

"Well, I declare! Excuse me, Sir, but that's Charlie calling the cows. Scotts, I don't see where the time has gone! You'll excuse me, Sir, but I must look after separating the cream. You will greatly oblige me, Mr. Johnston, if you will have dinner with us and share our home to-night. In addition to the pleasure of your company, I confess that I am mightily interested in this subject; and I would like especially to get a clear understanding of that nitrification process, and we've not had time to discuss the potash and 'phosphoric acid,' which I know cost some of our farmers a good part of all they get for their crops, and still their lands are as poor as ever."

"I appreciate very much your kind invitation, Mr. Thornton. I came to you for correct information regarding the agricultural conditions here, and you were very kind and indulgent to answer my blunt questions, even concerning your own farm practice and experience. I feel, Sir, that I am already greatly indebted to you, but it will certainly be a great pleasure to me to remain with you to-night."

For more than two hours they had been standing, leaning, or sitting in a field beside a shock of cowpea hay, Percy toying with his soil auger, and Mr. Thornton making records now and then in his pocket note book.

CHAPTER XV

COEDUCATION

PERCY took a lesson in turning the cream separator and after dinner Mrs. Thornton a.s.sured him that she and her sister were greatly disappointed that they had not been permitted to hear the discussion concerning the use of science on the farm.

"We have never forsaken our belief that these old farms can again be made to yield bountiful crops," she said, "as ours did for so many years under the management of our ancestors. 'Hope springs eternal in the human breast.' I stop with that for I do not like the rest of the couplet. We can see that some marked progress has been made under my husband's management, although he feels that it is very slow work building up a run-down farm. But he has raised some fine crops on the fields under cultivation,--as much as ten barrels of corn to the acre, have you not, Dear?" she asked.

"Yes, fully that much, but even ten barrels per acre on one small field is nothing compared to the great fields of corn Mr. Johnston raises in the West. and it makes a mighty small show here on a nine-hundred-acre farm, most of which hasn't been cropped for more than twenty years; and even then it was given up because the negro tenants couldn't raise corn enough to live on.

"I've talked some with the fertilizer agents, but they don't know much about fertilizers, except what they read in the testimonials published in the advertising booklets. I have had some good help from the agricultural papers, but most that is written for the papers doesn't apply to our farm, and it's so indefinite and incomplete, that I've just spent this whole evening asking Mr.

Johnston questions; and I haven't given him a chance to answer them all yet."

"I am sure you have not asked more questions this afternoon than I did this forenoon," Percy remarked; "and all your answers were based on authentic history or actual experience, while my answers were only what I have learned from others."

"Well, if we were more ready to learn from others, it would be better for all of us," said Mr. Thornton. "Experience is a mighty dear teacher and, even if we finally learn the lesson, it may be too everlasting late for us to apply it. Now we all want to learn about that process called nitrification."

"It is an extremely interesting and important process," said Percy.

"It includes the stages or steps by which the insoluble organic nitrogen of the soil is converted into soluble nitrate nitrogen, in which form it become available as food for all of our agricultural plants."

"Excepting the legumes?" asked Mr. Thornton.

"Excepting none," Percy replied. "The legume plants, like clover, take nitrogen from the soil so far as they can secure it in available form, and in this respect clover is not different from corn. The respect in which it is different is the power of clover to secure additional supplies of nitrogen from the air when the soil's available supply becomes inadequate to meet the needs of the growing clover. If the conditions are suitable for nitrogen-fixation, then the growth of the legume plants need not be limited by lack of nitrogen; whereas, nitrogen is probably the element that first limits the growth and yield of all other crops on your common soils."

"Now, what do you think of that, Girls? With millions of dollars'

worth of nitrogen in the air over every acre, our crops are poor just because we don't use it. I wish you would tell me something about the suitable conditions for nitrogen-fixation, Mr. Johnston.

You understand, Girls, that nitrogen-fixation is simply getting nitrogen from the inexhaustible supply in the air by means of little microscopic organisms called bacteria, which live in little b.a.l.l.s called tubercles attached to the roots of certain plants called legumes, like cowpeas and clover. Corn and wheat and such crops can't get this nitrogen. Now, Mr. Johnston is telling about nitrification, a process which is entirely different from nitrogen-fixation. Excuse me, Mr. Johnston, but I wanted to make this plain to Mrs. Thornton and Miss Russell."

"I am glad you did so," Percy replied. "As I was saying, nitrification has no connection whatever with the free nitrogen of the air.

"All plants take their food in solution; that is, the plant food taken from the soil must be dissolved in the soil water or moisture.

Of the essential elements of plant food, seven are taken from the soil through the roots into the plant. These seven do not include those of which water itself is composed. Now, these seven plant food elements exist in the soil almost exclusively in an insoluble form.

In that condition they are not available to the plant for plant food; and it is the business of the farmer to make this plant food available as fast as is needed by his growing crops.

"The nitrogen of the soil exists in the organic matter; that is, in such materials as plant roots, weeds, and stubble, that may have been plowed under, or any kind of vegetable maker incorporated with the soil, including all sorts of crop residues, green manures, and the common farm fertilizers from the stables. When these organic materials are decomposed and disintegrated to such an extent that their structure is completely destroyed, the resulting ma.s.s of partially decayed black organic matter is called humus. The nitrogen of the soil is one of the const.i.tuents of this humus or other organic matter. It is not contained in the mineral particles of the soil. On the other hand the other six elements of plant food are contained largely in the mineral part of the soil, as the clay, silt, and sand. thus the iron, calcium, magnesium, and pota.s.sium, all of which are called abundant elements, are contained in the mineral matter, and usually in considerable amounts, while they are found in the organic matter in very small proportion. The phosphorus and sulfur are found in very limited quant.i.ties in most soils, but they are present in both organic and mineral form.

"Practically the entire stock or store of all of the elements in the soil is insoluble and consequently unavailable for the use of growing plants; and, as I said, some of the chief plans and efforts of the farmer should be directed to the business of making plant food available.

"The nitrogen contained in the insoluble organic matter of the soil is made soluble and available by the process called nitrification.

Three different kinds of bacteria are required to bring about the complete change."

"Are these bacteria different from the nitrogen fixing bacteria?"

asked Mr. Thornton.

"Entirely different," Percy replied, "and there are three distinct kinds, one for each of the three steps in the process.

"The first may be called ammonia bacteria. They have power to convert organic nitrogen into ammonia nitrogen; that is, into the compound of nitrogen and hydrogen; and this step in the process is called ammonification.

"The other two kinds are the true nitrifying bacteria. One of them converts the ammonia into nitrites, and the other changes the nitrites into nitrates. These two kinds are known as the nitrite bacteria and the nitrate bacteria.

"Technically the last two steps in the process are nitrification proper; but, speaking generally, the term nitrification is used to include the three steps, or both ammonification and nitrification proper.

"Now, the nitrifying bacteria require certain conditions, otherwise they will not perform their functions. Among these essential conditions are the presence of moisture and free oxygen, a supply of carbonates, certain food materials for the bacteria themselves, and a temperature within certain limits.

"You may remember, Mr. Thornton, that more soil nitrogen is made available for cowpeas during the summer weather than for clover during the cooler fall and spring?"

"Yes, I remember that distinction."

"I declare," said Miss Russell, "Tom talks as though he had been there and seen the things going on. I haven't seen you using any microscope."

"Well, I tell you, I've mighty near seen 'em," was the reply. "Mr.

Johnston makes everything so plain that I can mighty near see what he saw when he looked through the microscope."

"I greatly enjoyed my microscopic work," said Percy, "and still more the work in the chemical laboratory where we finally learned to a.n.a.lyze soils, to take them apart and see what they contain,--how much nitrogen how much phosphorus, how much limestone, or how much soil acidity, which means that limestone is needed. Then I also enjoyed the work in the pot-culture laboratory, where we learned not to a.n.a.lyze but to synthesize; that is, to put different materials together to make a soil. Thus, we would make one soil and put in all of the essential plant food elements except nitrogen, and another with only phosphorus lacking, and still another with both nitrogen and phosphorus present, and all of the other essential elements provided, except pota.s.sium, or magnesium, or iron. These prepared soils were put in gla.s.s jars having a hole in the bottom for drainage, and then the same kind of seeds were planted in each jar or pot. Some students planted corn, others oats or wheat or any kind of farm seeds. I grew rape plants in one series of pots, and I have a photograph with me which shows very well that all of the plant food elements are essential.

"You see one pot contained no plant food and one was prepared with all of the ten essential elements provided. Then the other pots contained all but one of the necessary soil elements, as indicated in the photograph."

"Why, I never saw anything like that," said Mrs. Thornton.

"But I have many a time," said her husband, "right here on this old farm; I don't know what's lacking, of course, but some years I've thought most everything was lacking. But, according to this pot-culture test, you can't raise any crops if just one of these ten elements is lacking, no matter how much you have of the other nine; and it seems to make no difference which one is lacking, you don't get any crop. Is that the fact, Mr. Johnston?"

One pot with no plant food, and one with all the essential elements provided, and still others with but one element lacking. All planted the same day and cared for alike.

"Yes, Sir," Percy replied. "Where all of the elements are provided, a fine crop is produced, but in each case where a single element is omitted that is the only difference, and in some cases the result is worse than where no plant food is supplied. It seems to hurt the plant worse to throw its food supply completely out of balance than to leave it with nothing except what it draws from the meager store in the seed planted. Of course all the pots were planted with the same kind of seed at the same time, and they were all watered uniformly every day."

"Those results are very striking, indeed," said Miss Russell," but I suppose one would never see such marked differences under farm conditions?"