Brown Chernozemic Soil Research Articles

MICROMORPHOLOGICAL EVIDENCE OF ILLUVIAL CLAY IN HORIZONS DESIGNATED Bt IN THE FIELD

Semi-quantitative counts of areas of oriented, apparently illuvial clay in thin sections of B horizons showed that less than half of the 44 horizons designated Bt in the field had at least 1% apparently illuvial clay, and the counts for more than 1/3 was 0.2% or less. Many of the horizons that did not meet the micromorphological criteria of a Bt (at least 1% illuvial clay) contained much more clay than the associated Ae horizon and a higher proportion of fine clay than the associated C. Most of the soils having Bt horizons with more than 1% apparently illuvial clay were soils of humid to sub-humid regions, Luvisolic soils and Black or Dark Gray subgroups of Chernozemic or Solonetzic soils; none were Brown or Dark Brown Chernozemic or Solonetzic soils. Comparisons of counts of apparently illuvial clay in thin sections by four operators showed that compatibility of results varied among samples and that prior consultation resulted in an increased degree of agreement. Problems of distinguishing illuvial clay in thin sections are discussed and illustrated.

Amino Acid Composition of Cicer Milkvetch Forage1

AbstractCicer milkvetch (Astragalus cicer L.) is a hardy and persistent forage legume that has potential in some regions of western Canada. This study was undertaken to determine the amino acid composition and protein quality of cicer milkvetch in comparison with that of alfalfa (Medicago sativa L.). Samples of both legumes were harvested at the mid‐ to late‐bud stage of growth from a replicated field test on an Orthic Dark Brown Chernozem soil developed on alluvial parent material (Lethbridge loam). Samples were dried at 70 C for 20 hours and then analyzed for 18 amino acids. The limiting amino acid in both legumes is methionine. The protein score, an estimation of protein quality for monogastric animals, was calculated for both forage legumes. It was 67 for cicer milkvetch and 70 for alfalfa relative to 100 for “ideal protein”, as defined by FAO‐WHO Expert Group (1965). Therefore, the nutritional quality of cicer milkvetch protein is similar to that of alfalfa as a supplement to cereal proteins for monogastric animals.

Factors influencing the stability of labelled microbial materials in soils

The effect of freshly added substrate on carbon turnover of a microbial population and the priming action on stabilized soil organic constituents were investigated in the laboratory. 13C-labelled glucose. NH 4NO 3, or both were added to samples of a Brown Chernozemic soil which had been initially amended with 14C-glucose and incubated 2 months under field conditions. At the end of 14 days laboratory incubation. 39 per cent and 33 per cent of the 13C had been respired as CO 2 from the glucose and glucose plus NH 4NO 3 treatments, respectively. These two treatments resulted in a marked priming of native 12C during the second and third days of incubation and a second priming peak during the fifth day. In contrast, there was only a small priming action of the 14C-labelled materials. Addition of NH 4NO 3 by itself had no effect on the amount of 12C or 12C respired. Appreciable amounts of 14C were mineralized following treatments known to partially sterilize soil. Freezing and thawing was more effective than wetting and drying, but less effective than CHCl 3 vapour in releasing stabilized 14C materials. The amount of labelled- 14C mineralized during incubation after treatment with chloroform vapour was greater than could he accounted for by the decrease in soil biomass.

Turnover of microbial tissue in soil under field conditions

The microbial population of a Brown Chernozemic soil was labelled in situ by adding 14C-glucose and 15NH 4 15NO 3 to the plow layer. The loss of 14C, nitrogen immobilization-mineralization reactions, bacterial numbers (plate count, direct count) and fungal hyphal lengths were determined periodically throughout the growing period in amended and unamended microplots and in the surrounding field soil. After 5 days, 90 per cent of the labelled N occurred in the organic form with little subsequent mineralization. Of the labelled C added, 63, 56 and 39 per cent, remained in the soil after 3, 14 and 104 days, respectively. The ratio of fungal C to bacterial C increased as soil moisture decreased. Viable (plate count) and total numbers of bacteria in samples from unamended plots and field soil were significantly correlated with each other and with soil moisture. Fungal hyphal lengths from amended soil were also significantly related to moisture but the rate of loss of 14C and mineralization of 15N were not. The synthesized microbial material (tissue and metabolites) exhibited a high degree of stability throughout the study. The half-life of labelled C remaining in the soil after 30 days was calculated to be 6 months compared to only 4 days for the added glucose C. The amount of energy used for maintenance by the soil population under field conditions was calculated from measurements of biomass C, respired labelled C and respired soil C.

DECOMPOSITION OF 14C-LABELLED PLANT MATERIAL UNDER FIELD CONDITIONS

Mature, uniformly labelled (14C, 15N), chopped, wheat straw incorporated in the plow layer of a Brown Chernozemic soil and a Gray Wooded soil was allowed to decompose in the field. Labelled grass material (14C) was added to the surface of an adjacent virgin Brown Chernozemic soil. After 4 yr of normal cropping practices, one-fifth of the C of added straw remained in the Brown soil and one-sixth in the Gray Wooded. The initial decomposition rate of straw was retarded in plots under wheat as compared with those under fallow. Decomposition of labelled grass was initially dependent on sufficient rainfall to compress it to the soil surface. When winter periods are excluded from the time scale, the half-life of resistant straw components or soil organic matter derived from the straw was equivalent to 24 mo in Gray Wooded soil and 48 mo in Brown soil. Resistant grass material decomposed more slowly with a half-life of 96 growing mo. Distribution of labelled C among the various fractions of soil organic matter after different periods of time was investigated. The rapid decline of labelled straw from the fraction that floated in water, the high specific activity of fulvic acid, coupled with fluctuations in humic acid and the fraction <0.04 μ suggested a higher degree of biological activity in the Gray Wooded soil. In the Brown soil, the major transfer of labelled C was from the floated fraction to the humin (>0.2 μ) suggesting that the rate of decomposition was controlled to a greater extent by abiotic factors.

The Nature of K‐feldspars of a Chernozemic Soil in the Canadian Prairies

AbstractThe nature of the K‐feldspars of an Orthic Brown Chernozemic (Aridic Haploboroll) soil profile developed from glacial till deposits in Saskatchewan, Canada, was studied. The K‐feldspars from selected size fractions between 20 and 2,000µ were concentrated by heavy liquid separation at a specific gravity of 2.59. X‐ray powder diffraction analysis was used to identify orthoclase and microcline, to estimate their relative proportion, and to determine the obliquity, which is the degree of departure from the monoclinic symmetry of K‐feldspars.The concentration of K‐feldspars by heavy liquid separation greatly facilitated the subsequent X‐ray diffraction analysis. All the samples studied contained both orthoclase and microcline, and at least some of the K‐feldspar crystals appear to be perthitic in nature and have a high degree of exsolution. The diffractograms of the comparable size fractions from the major genetic horizons were similar and the proportions of orthoclase to microcline were comparable in the same size fractions. The proportions of orthoclase to microcline usually increased as the particle size decreased in all of the horizons, indicating that this differentiation occurred at the time of deposition of the soil parent material. The obliquity values of microcline of the various size fractions, ranging from 0.82 to 0.87, appeared to be uniform throughout the profile.The obliquity of K‐feldspars and proportions of orthoclase to microcline may have a potential use as a guide in establishing the geological origin of soil parent material and in confirming its uniformity.