Average Root Depth Research Articles

The rooting patterns of woody and herbaceous plants in a savanna; are they complementary or in competition?

SummaryRoot patterns of three woody plants are described in relation to water profiles and average root depth of annual species on three contrasted soil types along a toposequence in a watershed of northern Cameroon. This watershed is in a Sudano‐Sahelian savanna where mean annual precipitation is 800 mm, entirely restricted to the period May‐June to September‐October. Results show great variations of root structure of woody plants according to the distribution of water in the soil during one year. Consequently, under the same climatic conditions, soil depths exploited by woody plants and herbaceous plants can either be the same or not. In the most degraded soils, water does not infiltrate deeply and roots of the two components of savanna are limited to the upper horizons. On the other types of soil, root distribution depends on the soil profile.RésuméLa structure racinaire de trois arbres ou arbustes est décrite, en liaison avec quelques profils hydriques et la profondeur racinaire moyenne des plantes annuelles, sur trois types de sol aux caractéristiques hydriques trés contrastées et situés le long d'une toposéquence d'un bassin versant du Nord‐Cameroun. Le bassin versant est localisé dans une savane soudano‐sahiliénne où la pluviosité annuelle moyenne est de 800 mm répartis entre mai‐juin et septembre‐octobre. Les résultats montrent une forte variation de la structure racinaire des plantes ligneuses en liaison avec la répartition de l'eau dans le sol au cours de l'année. Sous les mêmes conditions climatiques, la profondeur de sol exploitée par les espèces ligneuses et les espèces herbacées peut être ou non la même. Sur les sols les plus dégradés, elle est la même, dans les horizons de surface, à cause de la très faible infiltration de l'eau dans ces sols. Sur les autres types de sol, la répartition des racines dépend du profil pédologique.

Rooting Characteristics and Associated Drought Resistance of Zoysiagrasses

AbstractDeclining availability of water for landscape irrigation has increased the need for drought‐resistant turfgrasses. Though drought‐resistance mechanisms are known to include deep rooting in some plants, little is known concerning zoysiagrass rooting characteristics. This study was conducted to determine if differences in rooting parameters exist among zoysiagrasses, and if they are associated with drought resistance. Twentyfive zoysiagrasses cultivars and species [Zoysia japonica Steud., Z. matrella (L.) Merr., and Z. japonica Steud. ✕ Z. tenuifolia Willd. ex Trin.] were studied in polyethylene tubes in a glasshouse. Differences were observed for average maximum root depth (AMRD), total root weight, and root numbers and weights at increasing 100‐mm depth increments. Average maximum root depth was positively correlated with total root weight and root number and weight at increasing 100–ram depth increments. Grasses with superior AMRD, total root weight, and root numbers at deeper profile depths (300–500 mm) included QT2047, El Toro, DALZ8512, TC5018, Meyer, DALZ8514, and DALZ8516. In a previously reported field experiment, 11 of the 25 zoysiagrasses were rated for percent of plot area covered by green turfgrass (an indicator of drought resistance) under three levels of irrigation (0, 35, and 100% of turfgrass evapotranspiration [ET]). Average maximum root depth, total root weight, and root numbers at 200‐, 300‐, and 400‐mm depths in polyethylene root tubes were positively correlated with percent green plot cover in the field under deficit irrigation (0 and 35% ET), indicating that rooting depth, weight, and branching at lower depths are important droughtresistance mechanisms in zoysiagrasses.

Root system modification of faba beans ( Vicia faba L.), and its effects on crop performance. 1. Responses of root and shoot growth to subsoiling, irrigation and sowing date

Two experiments were conducted to investigate how increased root growth into the subsoil affects the performance of spring-sown faba beans grown in Canterbury, New Zealand. Experiment 1 (1983/84) compared subsoiling with conventional cultivation, with and without irrigation. Experiment 2 (1984/85) compared subsoiling with conventional cultivation for early and late spring sowings. The silt loam soil had an incipient fragipan at 40–60 cm depth. Rooting density in subsoil layers, and average rooting depth, were increased by subsoiling but total root length was increased only in the late sowing of experiment 2. Irrespective of irrigation or sowing date, subsoiling increased shoot dry matter (by an average of 10% at maturity) but it did not effect changes in seed yield. In experiment 1, irrigation decreased root growth and increased shoot dry matter, but it also decreased seed yields, probably because of lodging. We observed no interactions between subsoiling and irrigation, which suggests subsoiling can improve a crop's ability to avoid drought later in the season, even if there is early irrigation or rainfall. Early spring sowing substantially increased root production, shoot dry matter and seed yields. In other shallow-rooting species grown in similar soils and climates, seed yields will probably benefit from increased root growth into the subsoil, provided harvest index remains stable.

The Marquesas‐Line Swell

Mapping of depth anomalies in the central Pacific reveals a broad, shallow region herein termed the Marquesas‐Line Swell. It has the morphology and geoid signature typical of a midplate hotspot swell and probably marks the Tertiary trace of the Marquesas hotspot. The swell is elongate in the NW‐SE direction, about 800 m high, and about 1500 km wide. It appears to extend continuously between the Marquesas Islands and the Line Cross Trend. A positive geoid height anomaly over the swell can be separated from the large regional trend. The transfer function between depth anomaly and geoid height is not well defined but is consistent with local isostatic compensation with an average root depth about 30 km (±40 km, 95% confidence interval) below the swell's surface. Direct spatial comparisons between geoid height and depth anomaly suggest that this root depth is constant along the length of the swell and has a value of about 40 km (±10 km, 95% confidence interval). The crest of the swell appears to subside as normal seafloor which is only 25 m.y.old, the prediction of the lithospheric thinning hypothesis. A permanent density decrease within the lithosphere can also explain the subsidence and geoid height anomaly; roll‐cell dynamic uplift can explain the subsidence but is difficult to reconcile with the geoid data.

Plant Communities and Associated Soil and Water Factors of Shale‐Derived Soil in Northeastern Montana

Sites on different strata of Bearpaw shale and on alluvium derived from the shale in a small basin in northeastern Montana supported strikingly different plant communities, including three Nuttall saltbush, three big sagebrush, two greasewood, one western wheatgrass, one blue grama, one silver sagebrush, one foxtail, one buckwheat, and a community of mixed shrubs. Several soil factos were measured, but only total soil—moisture stress and soil—moisture volume gave rational ordinations of the communities studied. Total soil—moisture stress at the average root depth ranged from a high of 96 bars for a Nuttall saltbush community to only 19 bars for a mixed shrub community. The Nuttall saltbush community was found on soils having a high soluble salt content, high soluble sodium percentages, high total soil—moisture stress, and low infiltration rates. Soils at the big sagebrush site had low soluble salt content, relatively high soluble sodium, and intermediate total soil—moisture stress values. The wettest site, subject to spring flooding, was occupied by western wheatgrass. Quantities of water evapotranspired from each habitat (calculated as maximum soil moisture minus minimum plus increments added to soils by summer storms) when related to precipitation provided approximations of runoff from, or run—in moisture for, each habitat.

ROOT SPREAD CAN BE ESTIMATED FROM CROWN WIDTH OF DOUGLAS FIR, LODGEPOLE PINE, AND OTHER BRITISH COLUMBIA TREE SPECIES

Knowledge of the relationships between lateral root spread and crown width is needed to guide plans for providing optimum space per tree during silvicultural operations. Crown width is a valuable indicator of root spread of open-grown Douglas fir, lodgepole and ponderosa pines, and white, Engelmann and Sitka spruces. The association between root spread and crown width is less reliable in forest-grown trees but still useful.Detailed studies of root systems were made by excavation of roots of trees blown down in the U.B.C. Campus Forest by a typhoon in October, 1962. Roots of 89 Douglas fir, 81 western hemlock, 61 western red cedar, and 33 red alder trees were mapped and analyzed in relation to 18 tree and stand variables. In addition, average and maximum root depth, number of main roots, the ratio of maximum to average root spread, and portion of rooting zone occupied by roots were studied.Average and maximum radius of roots of Douglas fir and lodgepole pine were analyzed in relation to crown width, d.b.h., height, age and other tree and stand characteristics. Appropriate regression and correlation analyses were completed for all species and the possible advantages of ratio estimates were noted.Ratios of root spread to crown width were influenced by species, stand density, and kind of soil. Ratios averaged 1.1 for open- and 0.9 for forest-grown Douglas fir but were 2.4 for both open- and forest-grown lodgepole pine on peat or poorly drained soils.