Discussion and Summary
Results of most agronomic researches are measured in terms of increased yields as bushels or tonnage of crops per acre. Biological assays now point out that these measures may not be accurate when agronomic products are to render their service in sustenance for animals. The values of improved varieties, of fertilizer treatments, of rotations, or soil management practices are based primarily on the number of bushels or pounds as increase over others that will be produced during a period of years by a new variety or practice. Other visible factors, such as quality, resistance to disease, and drought resistance, have been considered of secondary importance. Little or no attention has been given to chemical differences in the feeds or foods caused by different agronomic changes that could profoundly influence the animals and humans that consume these plant products.
The data of animal gains presented herewith demonstrate that forages and grains from the same soil given different treatments have varied widely in their capacities to produce animal gain. When the chemical composition of the feeds was changed by the different soil treatments, the animal response was not correlated closely enough to warrant the acceptance of the chemical analyses as an index of nutritive value. There is the strong suggestion that differences in feeds are brought about by soil treatments other than those commonly measured by standard methods of feed analyses. Only through assays with animals can these differences be determined.
On a soil low in lime and phosphorus, addition of phosphorus alone increased the efficiency of forage when fed to lambs. When limestone was added in addition to the phosphate, the nutritive value of the hays was further improved. Differences in the amount of improvement due to the different soil treatments varied from year to year. However, the relationship with reference to soil treatment held true in all trials. It appears that nutritional differences were greatest in seasons unfavorable for plant growth. The protein and mineral contents of these hays did not differ as widely as their efficiencies in producing animal gain. This would indicate that the soil treatments brought about other composition changes not commonly measured. The animals made more gain from each unit of grain consumed as a supplement to the phosphated hay than to the untreated hays, and those fed hay from the soil receiving lime and phosphate made more gain on the grain consumed than did those receiving hay from the land where only phosphate had been applied. All animals fed on the hay from the soil receiving both lime and phosphate had a higher oil and yolk content. There was a significant difference in the nitrogen, sulfur, and phosphorus contents of the wool. Further differences were obtained when the wool was scoured by means of alkali. In the alkali solution the wool from the lambs fed the phosphated hay decomposed while that from the soil receiving both lime and phosphate retained its luster and carded out to give customary fluffiness. It is significant that a simple treatment applied to the soil changed the composition of plants, altered the physiology of animals consuming the hay, and affected the appearance and properties of the wool. Since the wool qualities were changed by soil treatments, it is not unreasonable to assume that other body processes could have been altered so as to affect profoundly the metabolic and reproductive processes in the animals.
The addition of any plant nutrient to a soil without regard to the amount applied as related to the kind and supply of the nutrients in the soil may not always give feed of improved nutritive value. Evidence is presented where the addition of fertilizer or lime brought about an unbalanced nutrient condition in the soil which actually resulted in crops of lower efficiency than where no nutrient additions were made.
Timothy hay grown on soil having an excess of nitrogen, alfalfa with an excess of lime or phosphorus, and soybeans grown on a soil made deficient in potash through excessive applications of lime have all been lower in nutritive value than where no soil treatments were added. However, when these treatments were balanced by the addition of other plant nutrients, the quality of the feed was improved over that from the untreated soil. These results would indicate that tonnage yields are not a complete measure of the value of soil treatment and that maximum feeding value of forages can be obtained only when all soil nutrients are present in the proper ratios.
Since grains are only produced by crops after vegetative growth has been completed, the composition can not be altered as much by soil treatments as can that of forages (8). Nevertheless, the effect of soil treatments on the nutritive quality of grains was demonstrated. Trails with kafir and corn showed that the nutritive values of these grains produced on poor soils may be improved by addition of moderate amounts of the deficient elements. However, when some elements are added in excessive quantities, the nutritive value may be reduced below that of the untreated grains. Pressure tests have shown that the hardness of corn may be markedly influenced by soil treatment. It is not unreasonable to assume that grains varying in hardness will contain different organic compounds that may have a different effect on animal metabolism.
When animals were given a chance to show preference for grains from differently treated soil, wide variations in choice were found. In corn, hardness is one of the principal factors observed to influence choice. However, with such grains as oats and wheat the preference of animals for the grain from a particular soil treatment can only be attributed to chemical properties.
These results all point to differences in the value of plants as animal feed brought about by soil treatments, and that there are other differences in these plant products than are commonly determined by standard feed analyses. It has been well established that lignin accumulates within the plant when some growth factor, such as climate, or lack of fertility produces slow growth of plants. It is possible that this material could prevent the animal's digestive juices from attacking the cell contents and that the feed would pass through the animals undigested.
The functions of the different nutrients in plant metabolism are not well known. Where deficiencies exist, it is possible that some organic compounds, highly essential in animal growth, might not be synthesized within the plant and thus result in a feed of lower nutritive value. Since all results indicate that feeds produced under well-balanced fertility conditions are usually most effectively utilized by animals, it is not unreasonable to believe that an excess of some element might also prevent the synthesis of these compounds essential for animal growth, or that it might cause compounds to be formed that would be injurious.
All of these results point to the necessity of knowing the fertility properties of individual soils. If nutritious feeds are to be produced for animal and human consumption, then the soil on which they are grown must contain not only all the proper elements for plant growth, but these must be presented by the soil in proper ratios. It is only through proper and intelligent management that farm acres can be made to produce high yields of quality products. On soils of low productive capacity, the soil treatment can be expected to give benefits in addition to those of merely increasing the tonnage yields. The full value of these treatments, however, cannot be measured as yet without the use of animal assay.