A variety X nitrogen fertilization experiment with sugar beet seed by Bion Tolman is selected as an example showing the characteristics of a perfectly normal environment for crop increase, wherein the quantitative response of the crops to nitrogen fertilization and the relative seed-yielding abilities of three varieties of sugar beets may be accurately evaluated. The characteristics of normality are that experimental yield curves must show full homology with the curves of the standard yield diagram, which is based on the Mitscherlich-Baule yield equation y=A (1-10(-0.301x). The experimental curves obtained in Tolman's experiment coincide fully with normal curves of the diagram, and fulfill the condition that the spread between two values of y for any two values of A must increase as x increases, while the ratios between the yields of the varieties corresponding to given amounts of a plant nutrient shall be a constant. Conformity with this law is held to be a distinguishing mark of a normal soil for crop increase as regards varieties simultaneously grown thereon. Agronomists and plant physiologists are thus provided with means for distinguishing and evaluating normal and abnormal conditions for crop increase in field and pot tests. Conditions for making a most conclusive fertilizer test or variety comparison are, in the one case, to use graded amounts of one plant nutrient against two or more levels of a second nutrient in which the soil is also deficient, using a standard variety as the test crop, and in the second case to plant two or more varieties with graded amounts of one nutrient in which the soil is deficient. The resulting yield curves are then examined for the described characteristics of normality. In this agrobiologic method the diagram automatically reduces all variables, normal and abnormal, to a common denominator, which is not accomplished in any agrobiologic sense by the ordinary Fisherian analysis of variance.

The foregoing paper is the ninth of a series of contributions by the writer to this JOURNAL (beginning in 1943) concerning uses of the standard yield diagram. On the basis of extended experience with this diagram the following conclusions have been reached: 1. The Mitscherlich-Baule yield equation y=A (1-10(-0.301x) accurately represents the course of crop increase under the action of increasing concentrations of a growth factor only when the soil is agrobiologically uniform and free from elements unfavorable to plant growth. 2. The very fact that the Mitscherlich-Baule equation holds with exactness only in normal environments makes it an invaluable tool for the use of agronomists, soil scientists, and plant physiologists who are called on to assess the quantitative relations between plants and their nutrients under the heterogenous conditions of practical plant culture. The standard yield diagram is a very convenient means of applying the Mitscherlich-Baule equation to such conditions. 3. When so applied, the diagram functions as a standard of reference by which it may be ascertained whether the course of crop increase in a field test or a pot test with plant nutrients has been normal or has been interfered with by nonnormal influences; at the same time a measure of the effect of the interfering influence may be obtained. 4. In well-replicated tests there are two principal causes that distort the normal course of crop increase under the action of increased concentrations of a plant nutrient, viz., fertilizer unbalance due to an excess of the more concentrated nutrient (far-end depression), and initial inhibition of the normal effect of one nutrient (near-end depression). 5. Application of the diagram to the data of a field experiment with a plant nutrient establishes the A value or maximum yield that may possibly be obtained by extended use of that nutrient on that field in its apparent present condition. Comparison of the attained level of production with the calculated perultimate level or AQ value of the crop plant will indicate the range within which it may be possible to raise further the level of production by removal of adverse conditions or by increasing the concentrations of other nutrients. Chief among the adverse nutritional conditions are the sources of the two types of yield-depression. 6. In the preceding paper (3) it was shown how the law of homologous yield curves establishes criteria for distinguishing between normality and abnormality in a combined variety-fertilizer test and provides a basis for a more accurate rating of the yielding abilities of varieties of crop plants. In this final paper of the series, it is shown that the rule of halved increases establishes an additional criterion for the normality of a two-nutrient test, and how application of this rule assists in evaluating the influence of far-end depression.

A study was made from 1938 to 1940 at Aroostook Farm, Presque Isle, Maine, to determine the rate of and total absorption of nitrophosphoric acid, potash, calcium oxide, magnesia, and sulfur by different varieties of potatoes when these nutrients were supplied at varying rates under Aroostook County conditions. Data obtained in 1939 with the Green Mountain variety fertilized with an average of 2,500 pounds of 4-8-8 per acre are presented. The Green Mountain variety of potato elaborated 50% of its total dry weight during the 31-day period 51 to 81 days after planting. During the first 50 days after planting the Green Mountain variety absorbed 8.1% of the total major nutrients while producing only 3.2% of the total growth. Of the total amount of the six major nutrients absorbed during the season, 71% was absorbed during the 31-day period 51 to 81 days after planting. The absorption of nutrient elements occurs relatively more rapidly than the elaboration of dry matter during the early stages of growth. The reverse situation takes place during the latter part of the growing season. The peak rate of absorption of nutrients was found to occur approximately 10 days prior to the peak rate of dry matter elaboration. The peak rate of absorption of nutrients occurred during the interval 61 to 70 days after planting, or 30 to 40 days after emergence. During this period 27.1% of the total nutrients taken up during the season were absorbed. In 1939, during this 10-day period of maximum absorption, an acre of potatoes absorbed the following approximate amounts of nutrients in pounds per acre per day: Nitrogen, 3.8; phosphoric acid, 0.6; potash, 6.4; calcium oxide, 1.6, magnesium oxide, 0.9; and sulfur, 0.3. The highest contents of nutrients found in potato plants with tubers included of the Green Mountain variety fertilized with an average of 2,500 pounds of 4-8-8 under 1939 conditions were about 143 pounds of nitrogen (N), 26 pounds of phosphoric acid (P2O5), 232 pounds of potash (K2O), 56 pounds of calcium oxide (CaO), 30 pounds of magnesia (MgO), and 11 pounds of sulfur (S) per acre. A larger crop such as produced under 1943 conditions absorbed larger quantities of these nutrients, particularly N and K2O. The proportion of the nutrients absorbed that were translocated into the tubers was approximately as follows: four-fifths of the P2O5, two-thirds of the nitrogen, six-tenths of the sulfur, one-half of the K2O, four-tenths of the MgO, and about one-twentieth of the CaO. The tubers in the 387-bushel crop under 1939 conditions contained 95 pounds of nitrogen, 20 pounds of P2O5, 117 pounds of K2O, 3.2 pounds of CaO, 12 pounds of MgO, and 6 pounds of S. The relation of the rate and amount of absorption and translocation of mineral nutrients by potatoes in Aroostook County, Maine, to fertilizer practices is discussed.