Monolith Method of Root-Sampling in Studies on Succession and Degeneration

• Published in: Botanical gazette (Chicago, Ill.) Ill.), 1950-03, Vol.111 (3), p.286-299
• Main Authors: Weaver, J. E., Voigt, John W.
• Format: Article
• Language: English
• Subjects: Clay loam soils; Claypan soils; Grasses; Pastures; Prairie soils; Prairies; Rooting depth; Silt loam soils; Silty soils; Soil horizons
• ISSN: 0006-8071
• DOI: 10.1086/335595

1. A modification of the new, monolith method of securing complete samples of an entire root system is illustrated. Blocks of soil 2.5 feet wide, 3 inches thick, and 3-6 feet in depth are taken from a vertical wall of a trench. The method permits a study of the intimate relations of roots and soil and of measuring root production quantitatively at various soil levels. 2. The roots of Andropogon furcatus were very heavy in climax prairie on Wabash silt loam (91.1 gm. per sample). They were uniformly distributed, decreased gradually in weight with depth, and extended downward 6 feet. 3. When Poa pratensis replaced Andropogon furcatus after several years of overgrazing, its root system was relatively light (55.6 gm.), entirely confined to the surface 3 feet, and had 89.9% of its weight in the surface foot of soil. In a similar pasture of P. pratensis and Bouteloua gracilis in (upland) Carrington silty clay loam, root weight was still less (28.2 gm.), and roots of P. pratensis were only 2 feet deep. Thus, susceptibility of blue-grass pastures to drought and to invasion by deeply rooted weeds is more readily comprehended. 4. Root distribution in bunch-grass prairie was remarkably uniform below a depth of 3 inches and not unlike that under sod-forming species. Root weight was only slightly concentrated beneath the bunches. 5. The broad monolith method often revealed the presence of widely spreading roots of Panicum virgatum and Andropogon furcatus at depths of 3-24 inches below adjacent stands of Poa pratensis. This indicated invasion of territory 12-24 inches horizontally beyond that shown by the top and rhizomes in the surface soil. Such wide spreading of roots had not been recorded before in studies of native grasses in climax prairie. 6. Adaptation of the roots of Agropyron smithii to soils with claypans illustrates three distinct environments under-ground and remarkable soil-root relationships. A granular A horizon of mellow, moist soil resulted in a well-branched, heavy, normal development of roots. In the blocky, prismatic, very compact claypan beneath, roots were fewer, branching was poor, and roots penetrated the soil with difficulty. In the mellow, moist soil below the claypan, root branching greatly increased, occurred in all planes, and total weight of roots was a third greater in this more favorable environment. Such soils affect normal succession, since many climax species cannot thrive where they occur.