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Study of soils as related to site index of Douglas fir at Haney, British Columbia. Keser, Nurettin

Abstract

These soil studies were carried out on eight permanent plots at the University Research Forest, Haney, B.C. These plots ranged in Douglas fir site quality values 80 to 180 feet at 100 years. The soil of each plot was examined by means of soil pits and soil samples were taken for laboratory analysis. For each plot, topography, vegetation, general moisture condition, degree of stoniness, nature of soil and for each profile depth of horizons, soil color, texture, structure, consistence the amount and position of organic matter, drainage, physiologic depth, depth to mottling and special features of the profile such as hardpan, orstein, shot material, root mats were determined. In the laboratory, per cent soil skeleton, texture specific gravity of soils, bulk density, total-pore space, macro-pore space, micro-pore space, hydraulic conductivity and available water between 0.1 and 15.0 atmosphere (corrected for soil skeleton and/or soil stoniness), soil acidity, total cation exchange capacity, exchangeable calcium and potassium, and organic matter content were determined. Statistical analyses were conducted to determine the significancy of the values obtained in laboratory analysis. Regression equations were determined for evaluating site index from morphological soil characteristics such as horizon thickness, depth to mottling. The soils of the area were mainly derived from glacial till. Till is a coarse texture (coarse sandy loam to loamy sand) containing gravels, stones, and boulders. It was generally hard and impervious to water movement. The profiles generally have shown Aₒₒ, Aₒ, A₂, B₁₁, B₁₂, B₃ and C horizons, ^he development of eluvial and illuvial horizons (especially clay accumulation) appeared somewhat weak. Profiles have shown coarse texture similar to that of glacial till. The depth of profiles varied between 5 and 33 inches, the average range being from 20 to 30 inches. Two main soil groups were observed among the eight plots. Plots 2, 3 and 4 were minimal podzol (Order: Podzols), plot 1 was concretionary brown (Order: Brunosolic), and plots 5, 6, 7 and 8 are classified as intergrade between concretionary brown and minimal podzol. Generally the coarse skeleton comprises more than 50 per cent of the soil. All the soils were very low in clay content. Hydraulic conductivity was high. Micro-pore space showed higher per cent layers than macro-pore space. The available water was low in general due to texture. The preponderance of stones in the soil had an adverse effect on the water-holding capacity of the soil. Consequently, stoniness had to be taken into consideration in determining the actual volume of available water. All the soils were acid in reaction. The organic matter was high in upper horizons and decreased with depth. Total cation-exchange capacity exchangeable, calcium and potassium and calcium base saturation were low. Correlation studies between soil properties and site quality indicated that the physical soil properties were more important than chemical characteristics as an indication of soil quality. Texture, bulk density, porosities (macro-, micro and total), hydraulic conductivity did not show any correlation with site quality but were significant at the 5 per cent level between the plots (except micro-pore space). Available water was positively correlated with site quality when it was corrected for stoniness and coarse skeleton. Chemical properties were not significant between the plots and did not show any correlation to site quality. Morphological features such as thickness of B₁₁ horizon and depth to mottling were highly correlated to site quality and gave the smallest standard error of the estimate (± 21.3 feet). The study indicates that the volume of available water in the soil was most important for the growth of Douglas fir and that the site index of an area could be determined from a study of those morphological features of the soil which affects its water-holding capacity, as well as other morphological features such as depth to mottling.

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