Welcome to Book of the Week – a weekly feature offering you a glimpse between the pages of an Acres U.S.A. title. Get the Book of the Week email newsletter delivered directly to your in box! This week’s Book of the Week feature is Albrecht on Soil Balancing by Dr. William A. Albrecht.
The behavior of potassium in the clay colloid, as revealed by chemical analyses and treatments, must be reconciled with its behavior in the plant. Potassium is lower than calcium in exchangeable form on the soil colloid, yet the former makes up 1.68 percent in plants in contrast to 0.62 percent for calcium as averages.
In view of the shifting ratios of these two exchangeable nutrients on the colloid with increasing degree of soil development, the question arises whether vegetation reflects corresponding differences in composition. As a test, chemical analyses of different crops were assembled. The different crops were allocated according to dominance on (a) slightly developed, (b) moderately developed, and (c) highly developed soils. Though the numbers of cases are not extensive enough to warrant unqualified conclusions, they are suggestive, as presented in Table 2.
The data show that the increasing degree of soil development, which gives decreasing calcium in relation to potassium on the colloid clay, gives correspondingly increasing potassium over calcium in the plant composition. Plants are lower in percentages of both potassium and calcium as the soil is more highly developed, but the potassium content drops to about one half while the calcium drops to about one seventh in going from slightly developed to highly developed soils. At the same time, the combined percentages of potassium, calcium, and phosphorus drop to two fifths. The ratio of phosphorus to potassium in the vegetation was constant.
If these are the facts in general for the assay of the soil by means of vegetation, it would seem that, among the plant nutrients on the colloid, potassium moves most actively into vegetation as the soil is more highly developed.
In previous experiments soybeans were grown on colloidal clay supplied with exchangeable calcium and potassium in different ratios, but with constant supplies of calcium, nitrogen, and phosphorus, to determine whether the varying ratios influence plant composition. The results demonstrated that the increase of potassium relative to calcium increased the vegetative yield; reduced both the percentages and the totals of nitrogen, of phosphorus, and of calcium in the vegetation; and increased both the percentage and the total of potassium according to the variable supply offered. All these characteristics suggest a crop of more proteinaceous nature containing higher concentrations of calcium and phosphorus when calcium dominates on the colloid, and of a more carbonaceous nature when potassium is high relative to calcium.
As a further test of the hypothesis, soybeans were grown similarly but for three successive crops in order to exhaust the soil fertility. The carbonaceous phases of the plants were separated into sugars, starch, and hemicellulose. In the first crop, nodule bacteria were withheld and the soybeans were grown as a nonlegume. The second and third crops were nodulated and behaved as legumes.
The results showed that in the first, or nonlegume, crop the total sugars were low and decreased in concentration while the vegetative yield was increasing with the increasing ratio of potassium to calcium. More noticeable, however, was the behavior of the starch, the concentration of which almost doubled and the total almost trebled with increasing potassium. When the same kind of plants behaved as legumes, their sugar concentrations were much higher and again suggested decrease with extra potassium. The starch concentrations were lower than those for the nonlegume, but increased for increments of potassium initially put on the colloid. The greater exhaustion of nutrients from the colloid by the third crop indicated that lowered soil fertility, like excessive potassium in relation to calcium, gave dominance to the carbonaceous character of the crop, as shown by the higher sugar and starch contents in the latter of the two leguminous crops.
The hypothesis that relative calcium reduction in the soil tends to reduce the proteinaceous nature of the vegetation is further supported by the decreasing protein content of wheat in going from west to east in Kansas, as reported for 1940. Between western Kansas, with an annual rainfall of 17 inches, and eastern Kansas, with 37 inches, the protein in the wheat dropped from 18 to 11 percent. This traverse represents a distinct change in the original grass vegetation and a reduction in the amount of calcium in the soil, the calcium carbonate being at greater depths in the profile.
Still further support of the hypothesis is given by the recent studies of Allen with percolating nutrient solutions for soybeans, and of Converse et al., with colloidal nutrient media for corn. Both show the association of the calcium-potassium ratio with protein content, whether the crop was legume or nonlegume.
Although calcium and potassium are seemingly reciprocals in plant composition, calcium supporting the proteinaceous and potassium the carbonaceous properties, there is a question whether the high level of phosphorus associated with the former and its low level with the latter are not involved. Apparently the phosphorus level deserves attention in connection with this ratio.
About the Author:
Dr. William A. Albrecht was chairman of the Department of Soils at the University of Missouri College of Agriculture, for over four decades. He held four degrees from the University of Illinois. He traveled widely and studied soils in the United States, Great Britain, on the European continent, and in Australia. He was respected and recognized by scientists and agricultural leaders from around the world.
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