Fertilize for Higher Feed Value
THE COW WAS one of the early fertilizer producers and distributors. Animal manures were put out by her as probably the first fertilizer. The nitrogen in her product was strongly emphasized for the nitrate salts collected from manures during the French Revolution for making gunpowder. The cow uses nitrogen fertilizers as the most demonstrative way of bringing to our attention the fertility shortage in the soil. She demonstrates the soil’s need for fertility and gives suggestions on fertilizing it for more vegetative production every time she drops her voidings on a grassy area.
After the earlier observations of the cow in these activities, we began to talk about “manures and fertilizers.” But today with fossil fuels and technologies as replacement of the horse for power, and with economic pressure on the soil for higher yields and higher monetary returns per acre, we do not use that binomial term. We omit the word “manure.” We use, instead, only the term “fertilizer.” Lately, we have not been observing the cow closely to study her performance of fertilizing in which she returns fertility to no small extent of what she takes away in the vegetation which she harvests. We have credited her with the capabilities in applying fertilizer to the fields for increased vegetative bulk per acre. We have, however, not noticed that she refuses to consume as feed that high yield of vegetation resulting from her application of her own fertilizer, namely her urine and her feces. That refusal exhibits itself, in most any pasture, by the spots of tall green grass growing taller and greener, while she eats the short grass around them still shorter. The cow has been most modest about her abilities as a soil manager via fertilizer treatments. By her refusal she has long been admitting that she produces and distributes a manuring combination which increases the vegetative yields of crops, but doesn’t grow into them the nutritional quality making good feed. The producers and distributors of fertilizers of commerce suffer under a similar situation but the confessional exhibition of it is not given such prominence.
For legal purposes (not necessarily for biological services to growing plants and their services to growing animals), the term “fertilizer” has been defined as “Any substance containing nitrogen, phosphorus and potassium,* or any other element or compound recognized as essential or used for promoting plant growth, or altering plant composition, which is sold or used primarily for its plant nutrient content …”** On examining this definition, it is clear that the emphasis rests on (a) “promoting plant growth” and (b) “sold or used …” Little emphasis commonly goes to that part of the definition which says “altering plant composition.” Our criterion of fertilizer values in soil treatments has been, almost singly, the increased plant growth or the greater mass of resulting vegetation. Emphasis on that criterion has simultaneously promoted fertilizer sales with the common reminder that the extra vegetative mass pays for the fertilizer costs and with a margin. In little or none of the sales promotion of fertilizers do we emphasize fertilizer use for its services in “altering plant composition” to give it higher value as animal feed. The placing of emphasis by careful choice and use of certain phraseologies, and the astute omission of others, seems to be exercised most adroitly by those selling fertilizers. Perhaps this merely emphasizes the shortage in research information of just what a fertilizer does under what conditions.
As another bit of phraseology for advantage or emphasis in the definition of fertilizers, there is the specification of the fertilizer contents, namely “Nitrogen, phosphorus and potassium and any other element or compound recognized as essential or used for promoting plant growth.” The history of the technological developments giving major or minor amounts of available fertilizer materials reminds us that the phosphates were the first extensive commercial fertilizer. With the later availability of Chilean nitrate, the element nitrogen became prominent. Still later, the triumvirate of nitrogen, phosphorus, and potassium held main sway in the fertilizer market. At this date, nitrogen is in decided prominence again as the result of the chemical fixation of nitrogen with reportedly about 55 industrial plants fixing this fertilizer element in many chemical forms.
It is the making of a closer connection between the term “nitrogen” as a part of the definition of fertilizers, and the additional phrase there, namely “altering the plant composition” with which the following discussion is concerned. It aims to relate the former as cause to the latter as effect. Then it aims also to include the cow’s consideration of soil treatments, that is, the use of nitrogen to alter the plant composition as that quality of the herbage meets with the cow’s approval of it as feed of high quality for growing young animals rather than for merely fattening castrated males.
Nitrogen is the Keystone in the Arch of Fertility Supporting Crop Production
It is significant to remind ourselves that before the advent of chemically fixed nitrogen as fertilizers, the soil’s supply of nitrogen depended on that which was fixed biologically through the symbiosis between bacteria and the legume plant species, or through free-living bacteria in those soils naturally rich in calcium and other inorganic fertility, while also relatively high in organic matter. In that natural fertility situation, extra nitrogen came into the growth cycle via biological fixation to give more of it in the crops, more of it in turnover as decay in the soil, and more of it there in mobile nitrogen as ammonia, nitrite and nitrate forms. It was on those soils also where the ecological pattern included, not only more proteinaceous vegetation, but also more animal protein per acre in the many ruminant grazers ranging widely and subsisting as strictly herbivora.
We need to remind ourselves that it was, first, the presence of all the commonly considered, favorable physical and chemical conditions in the soil, and then, second, the biological fixation of the nitrogen which built up the proteins in the crops. The plant species with the complex physiologies represented by nitrogen fixation and high protein concentrations of such high values as feed for growing animals, demanded first that the inorganic fertility supplies be at high levels and in balanced ratios accordingly. Plants were then able to take nitrogen from the atmosphere.
Consideration of these unusual soil requisites for the natural production of high feed values, in terms of choice food proteins, raises the question whether our use of chemically-fixed nitrogen will not be disappointing in the quantity and quality of protein it encourages unless this product of the late fertilizer technology is used on soils of (a) high organic matter, and (b) high fertility in all the inorganic essentials except the nitrogen. Will fertilizer nitrogen serve best for growing higher feed values in forages save as (a) we choose crops of higher protein potential and (b) all other requisites of fertility in the soil have been supplied to the best of our knowledge.
“Crude Protein” Remains too Crude
In support of the above doubts, research studies offer accumulating chemical data and biochemical facts from bioassays using various animals, mainly rabbits, and even insects. The term “crude protein,” as concentration, is no longer sufficiently critical as a criterion for classifying feeds, especially the feed values of what is included in the common term “proteins.” Consequently the feed values have been more carefully and critically measured in terms of the array and the quantities of the different amino acids which the proteins contain according to the microbiological assay of their hydrolyzation products. This measurement of the different amino acids rather than the determination of the amounts of crude proteins is helpful, since now eight amino acids have been listed as essential for the human, ten for the laboratory rat, and specific numbers and amounts may soon be expected in reports for each kind of domestic or other animal.
Analyses of forages for their inorganic contents and for their amino acids, in relation to the fertilizer treatment and history of the management of the soil growing them, have given opportunity to examine both a non-legume and a legume forage grown under known soil treatments. Timothy hay in the former category was so examined for soil treatments with emphasis on applied nitrogen and trace elements. Red clover hay, in the latter category, from Sanborn Field was studied in relation to a wide variety of soil treatments and a long history of the soil management. These hays were analyzed for their inorganic compositions and their amino acid concentrations, and were then used in nutrition experiments with rabbits and crickets. The red clover was more critically studied than was the timothy hay.
Nitrogen Fertilizers on Timothy Do Not Make High Quality Proteins in its Hay
That timothy is one species of plant which apparently cannot be a feed of highest quality, even under nitrogen fertilization supplemented by much else (including the trace elements), was demonstrated by the poor gains in weights of weanling test rabbits fed on it. This fact was established under several tests, including the attempts to separate the effects of the individual trace elements as fertilizers. It was demonstrated most pronouncedly by the many deaths of rabbits from the heat in 1954, when they were fed on the timothy hay; but by no deaths when this feed was supplemented with other proteins fed the stock rabbits.
Weanling rabbits were fed wheat grain and timothy hay, only to have the high summer temperature kill many of them as the experiment progressed. The losses by death in the experiment were replaced at fortnightly intervals from the stock rabbits which were in the same environment but had not died while on a ration of the same wheat but this combined with green grass. At the close of the designed test period, and after losses amounting to over 70 per cent of the animals, the diet was modified by adding 10 grams of dried skim milk powder daily per rabbit. With the heat wave continuing and at temperatures higher than those of preceding periods, the extension of the test gave no fatalities from the heat after the introduction of the dried skim milk supplement into the ration.
Chemical analyses of the timothy hay, given in Table 1, suggest that the concentrations of many of the inorganic elements were lowered as the result of increased growth under the stimulation by the nitrogen fertilizer applied. This seems to be the case for most of the elements, save magnesium. The nitrogen fertilizer, as an addition to the basic fertilization with limestone, phosphates, and potash, failed to help this crop (rather it hindered it) in delivering higher concentrations of most of the inorganic essentials.
According to the biochemical data for the array of the amino acids in Table 2, the nitrogen fertilization increased the percentage of total nitrogen in the hay for the second and third increments of applied nitrogen but not, in general, for the first of it applied. The concentrations of the separate ten essential amino acids were also increased by the third increment of nitrogen, though not generally by the second. The first fertilizer increment served, in general, to reduce their concentrations. These facts suggest that under a heavy basic fertilization of all else, the first increment of nitrogen fertilizer increases the production of carbohydrate, or vegetative mass, and reduces the concentrations of the proteins in it though the total protein per acre is increased. It raises the carbohydrate-protein ratio. This occurs when the nitrogen is the major and seriously limiting deficiency in the fertility and the resulting forage gives a still wider nutritive ratio. However, even with its higher concentrations of the amino acids, the timothy hay was not a good feed for protection against the heat wave, unless supplemented by dried skim milk. We had not made the timothy hay a feed of high nutritional value.
Red Clover Protein was a Much Superior Feed Value than Timothy Protein
That the red clover, as a legume hay, is far superior in feed quality than the timothy hay was shown clearly by a continuation of the rabbit feeding tests with timothy hay under the continuing high temperatures. This repeat of the previous trial used more of the stock rabbits which were given the same wheat and timothy hay again in the same ratios, save for some corn and other grains added to the wheat. The fatalities from the heat wave repeated themselves. After these had amounted to more than 30 percent, the red clover hay was substituted for the timothy hay. From the date of that change forward, no more heat fatalities occured under continued high temperatures. Here then was clear evidence of some factor or factors in the red clover of protective values equivalent to those in the dried skim-milk powder in terms of giving rabbit survival under the physiological stress of the continued high temperatures which had previously attained a maximum of 113° F.
Qualities of Protein in Red Clover Differ According to Fertility Differences in the Soil Growing it
These results were the occasion for the inorganic chemical analyses and the microbial assays of the amino acids of the red clover hay from three plots in the three-year rotation of corn, wheat, and clover, and from the eight plots of the four-year rotation of corn, oats, wheat and clover—all in the clover crop on Sanborn Field in 1954—in order to use these hays as the source of crude protein of a single legume plant species. These hays were used in constant total amounts of crude protein in making a ration for the rabbits. This was balanced as well as possible in all other nutritional factors in order to learn the differing qualities of the crude protein as determined by the fertility treatments of the soil growing this legume hay. The soil treatments of the 11 plots growing the clovers in 1954 are listed in Table 3. The inorganic chemical compositions of the hays by plots are listed in Table 4 for seven elements. The clover hays’ contents of four nonessential amino acids are given in Table 5, while the concentrations of nine of the essential amino acids are listed in Table 6. The compositions of the feeds as modified to test the biological values of the proteins in the red clover hays are given in Table 7.
That the soil treatments made very significant differences in the feed value of the proteins in the red clover is shown by the wide variation in gains in the weights of the rabbits when the amounts of crude protein taken by them was a constant, save for the hay from one plot, No. 26, in the three-year rotation, as shown by the data in Table 8. In spite of the fact that the rabbits were consuming constant amounts of crude protein, that is, constant amounts of nitrogen, in the hay when all else was also held constant, yet the gains in weight per animal and the gains in weight per unit of the essential amino acids varied widely. The weight gains per rabbit for the hays from different clover per plots and their different soil treatment varied from a low of 34 grams in four weeks for the clover on the plot, No. 25, given manure and supplemental nitrogen in the three-year rotation, to a high of 241 grams (more than 700 percent) for the clover grown on the plot, No. 36, formerly given lime and 4-12-4 fertilizer but later given magnesium limestone, crop residues, and fertilizers according to soil test suggestions, including the trace elements. The gains as grams per milligram of the nine essential amino acids in the feed varied from a low of 10.6 for the clover from plot No. 25, cited above, to a high of 77.9 (again more than 700 percent) for plot 39, in the four year rotation formerly given the same treatment as plot 36 and later duplicating that also save for a continuation of the treatment by calcium limestone rather than by the magnesium stone.
A Big Market Remains for Fertilizers for Growing Higher Quality Proteins
The improvement in the protein quality of the feed which soil treatments can bring about depends, in no small measure in the first place, on the crop on which the nitrogen fertilizer is used. The effectiveness of nitrogen in this respect depends, in the second place, on the fertilization beforehand by the other nutrient essentials. Red clover grown in a rotation on well-fertilized soil converted its nitrogen into crude protein for much higher feed values of it than did the well-fertilized timothy, including increments of nitrogen as soil treatments. In the latter crop other treatments did not contribute as much to the protein quality as they did in the former. Even with our help and hope to improve the quality of the crude proteins they still remained too crude to the test animals.
It is highly significant to note that the bioassays of the red clover from Sanborn Field suggest that (a) the return of crop residues, (b) the use of calcium and magnesium limestones, and (c) the attempts to balance the soil fertility according to the soil tests with the addition of trace elements, were all essential contributors to the higher feeding values in the red clover for growing weanling rabbits. These factors in fertility under the crop of constant delivery of even crude protein as commonly measured were the variables to the extent of 700 percent in the nutritional quality of the forage grown by them.
In terms of these bioassays there is the suggestion that while fertilizing for higher feed values still be an extension of the market for fertilizers far beyond those areas which supply fertilizers for increased yields of bulk only, it will be, apparently, also a tremendous challenge to learn how we can fertilize the soil to grow the increase in protein quality accordingly.
* Some fertilizer laws say phosphoric acid and potash.
** From the Missouri Fertilizer Law, 1953.
