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Root zone soil moisture is an important component in water cycling through the soil-plant-atmosphere continuum. However, its measurement in the field remains a challenge, especially non-invasively and repeatedly. Here, we developed a new method that uses ground-penetrating radar (GPR) to quantify root zone soil moisture. Coarse roots were chosen as reflectors to collect GPR radargrams. An automatic hyperbola detection algorithm identified coarse root reflections in GPR radargrams and determined the velocity of GPR wave, which then was used to calculate the average soil water content of a soil profile (ASWC) and soil water content in a depth interval (ISWC). In total, GPR reflection data of 55 root samples from three computer simulation scenarios and two field experiments in sandy shrubland, one burying roots at known depths and the other under the undisturbed condition, were used to evaluate the proposed method. Both the simulated and the field collected data demonstrated the effectiveness of the proposed method for measuring root zone soil moisture with high accuracy. Even in the two field experiments, the root-mean-square errors of the estimated ASWC and ISWC relative to measurements from soil cores were as low as 0.003 and 0.012 m3·m−3, respectively. The proposed method offers a new way of quantifying root zone soil moisture non-invasively that allows repeated measurements. This study expands the application of GPR in root and soil study and enhances our ability to monitor plant-soil-water interactions.

Soil macropores consist of biopores and non-biopores, which are different in morphological features and ecological functions. We aimed to separate biopores and non-biopores and investigate the response of their three-dimensional (3D) characteristics to land use and fertilization. Intact soil cores sampled from the subsoil (20–30 cm) under a combination of two land uses, paddy and upland fields, and three fertilization treatments, no fertilizer (Control), chemical fertilizer (NPK), and chemical fertilizer plus organic manure (NPKM), were scanned with X-ray computed tomography (CT). A methodology was proposed to separate biopores and non-biopores and the 3D characteristics of the pores were quantified. Based on the proposed methodology, soil biopores were well isolated from non-biopores. The volume of the biopores contributed 30.1–58.0% and 66.3–74.1% of the volume of the total macropores in the upland and paddy subsoils, respectively. The biopores in the paddy subsoil had a lower mean pore volume (MPV) and mean branch number (MBN), but a larger branch angle than those of the biopores found in the upland subsoil. The porosity, MPV, surface area (SA) and connectivity of non-biopores were significantly higher in the upland subsoil than those in the paddy subsoil. The NPKM treatment significantly increased the volume of the large-sized biopores in the upland subsoil and the tortuosity of the biopores in the paddy subsoil, whereas the fertilization effect on non-biopores was minor. Our results demonstrate that subsoil biopores and non-biopores can be effectively distinguished according to the proposed methodology and that their 3D characteristics respond differently to land use and fertilization.

Belowground interactions can greatly modify fine root (≤2 mm in diameter) traits to increase soil resource acquisition for tree growth. We examined how mixed forests alter fine root traits compared to pure forests. A pseudo-experimental tree cluster design was used to select small-area plots of single and mixed species in a Pinus massoniana–Lithocarpus glaber (PM–LG) forest and a L. glaber–Cyclobalanopsis glauca (LG–CG) forest. In each plot, soil cores were sampled down to 30 cm at a 0.5 m interval between target and neighbouring trees. Fine roots in soil cores were then divided by species to determine biomass and morphological traits. The mixed PM–LG plots exhibited significantly higher fine root biomass while the mixed LG–CG plots had no significant differences in fine root biomass compared to their respective pure plots. In pure plots, P. massoniana had higher fine root biomass and lower specific root length (SRL) and specific root area (SRA) than L. glaber, whereas fine root traits were similar for L. glaber and C. glauca. Compared with pure plots for a given species, fine root biomass in the entire soil profile decreased for P. massoniana but increased for L. glaber in mixed PM–LG plots. In mixed LG–CG plots, fine root biomass decreased for each species at all soil depths. Whether positive interactions of fine roots occur is dependent on tree species composition. Fine root biomass was greater in mixed forests where tree species showed contrasting growth strategies and root traits, such as PM-LG forests, thus suggesting positive interactions.

To gain a better understanding of how rapidly microbial communities respond to different magnitudes of perturbation that mimic minor or catastrophic disturbances. Two montane sites in the western Cascade Mountains of Oregon with adjacent areas of forest and meadow vegetation were studied. A reciprocal transplant experiment evaluated both minor (soil cores remaining in the same vegetation type) or more severe disturbance (soil cores transferred to a different vegetation type). The biomass and composition of the bacterial and fungal communities were measured for 2 years following the establishment of the experiment. Minor disturbance (coring) had little impact on microbial biomass but transferring between vegetation type showed greater fungal biomass in soil incubated in the forest environment. The composition of bacterial communities was not influenced by coring but responded strongly to transfers between vegetation sites, changing to reflect their new environment after 2 years. Fungal community composition responded somewhat to coring, probably from disrupting mycorrhizal fungal hyphae, but more strongly to being transferred to a new environment. The response of the microbial community to major disturbance was rapid, showing shifts reflective of their new environment within 2 years, suggesting that microbial communities have the capacity to quickly adjust to catastrophic disturbances.

Background and Aims We developed a method for processing roots from soil cores and monoliths in the laboratory to reduce the time and cost devoted to separating roots from debris and improve the accuracy of root variable estimates. The method was tested on soil cores from a California oak savanna, with roots from trees, Quercus douglasii, and annual grasses.

Management practices, such as fire and mowing, can affect the distribution and quality of roots and soil C and N in grasslands. We examined long-term (13 years) effects of annual fire and mowing on fine (

Development of direct and indirect methods for measuring root turnover and the status of knowledge on fine root turnover in forest ecosystems are discussed. While soil and ingrowth cores give estimates of standing root biomass and relative growth, respectively, minirhizotrons provide estimates of median root longevity (turnover time) i.e., the time by which 50% of the roots are dead. Advanced minirhizotron and carbon tracer studies combined with demographic statistical methods and new models hold the promise of improving our fundamental understanding of the factors controlling root turnover. Using minirhizotron data, fine root turnover (y−1) can be estimated in two ways: as the ratio of annual root length production to average live root length observed and as the inverse of median root longevity. Fine root production and mortality can be estimated by combining data from minirhizotrons and soil cores, provided that these data are based on roots of the same diameter class (e.g., < 1 mm in diameter) and changes in the same time steps. Fluxes of carbon and nutrients via fine root mortality can then be estimated by multiplying the amount of carbon and nutrients in fine root biomass by fine root turnover. It is suggested that the minirhizotron method is suitable for estimating median fine root longevity. In comparison to the minirhizotron method, the radio carbon technique favor larger fine roots that are less dynamics. We need to reconcile and improve both methods to develop a more complete understanding of root turnover.

In order to quantify N2-emissions from a spruce and a beech site at the Hoglwald Forest, a new measuring system was developed, that allowed simultaneous, direct determination of N2- and N2O-emission with high accuracy (detection limit approx. 10 μg N m−2 h−1 for N2 and

The minirhiozotron (MR) root observation method was studied versus root length density (RLD) obtained from soil cores. Two plant species, acacia (Acacia saligna) and wheat (Triticum aestivum L.) were grown in a 1-m3 container on Silt Loam (Typic Torrifluvent) and on fine dune sand (Typic Torripsamment), respectively. Roots of both plants were measured periodically by the two methods. The MR observation tubes (MROT) were inserted, either vertically or at 45°. The correlation between the number of roots obtained by the MR and RLD was significant for the entire profile. However, an appreciable error in root estimation by the MR root observation method at the upper 10-cm soil might occur. No significant difference was obtained from MROT oriented vertically or at 45°. The differences between the correlation coefficients of the two methods were not significant, for both plants and soils, indicating that this correlation expresses the geometry of the two measurement systems, not affected by plant or soil types. We concluded that the MR method may be used as an in situ, non-destructive root measuring method with reasonable confidence.

Aims Tree roots are spatially highly heterogeneous and it thus requires large numbers of samples to detect statistically significant changes in root biomass. The objectives of this study were to understand and quantify the sources of error in the assessment of fine root biomass (

Applications and limitations of the minirhizotron technique (non-destructive) in relation to two frequently used destructive methods (soil coreing and ingrowth cores) is discussed. Sequential coreing provides data on standing crop but it is difficult to obtain data on root biomass production. Ingrowth cores can provide a quick estimate of relative fine-root growth when root growth is rapid. One limitation of the ingrowth core is that no information on the time of ingrowth and mortality is obtained.

Detailed knowledge of the distribution of roots in the soil is important in understanding the extraction of water and nutrients from soil. Various techniques have been developed to monitor root-length density under field conditions. Excavation techniques, including soil cores, have long been considered to give reliable estimates of root-length density, but these techniques are laborious in sample collection and tedious in determination of root lengths. An attractive alternative for monitoring root-length density has been the minirhizotron whereby a periscope is inserted into a clear tube permanently installed in the soil for repeated and rapid measures of root development. The objective of this study was to compare the ability of the minirhizotron technique to measure root-length density as compared to the root-core technique.

The root systems of apple trees from five orchards ranging in age from 1.5-y to 14-y were sampled to depths of between one and two metres using soil cores. Although trees came from orchards which differed in soil-type, tree spacings and management, consistent patterns were found in root systems. In orchards of 4-y and older, roots of adjacent trees met so that soil volumes within the planting grids (i.e, tree spacings of approximately 5 m inter-row×4 m intra-row distances) were completely explored, although not completely occupied by roots. Mean root-length densities declined with depth for these orchards. In the 1.5-y orchard, roots from adjacent trees did not meet and root-length densities declined with radial distance from the stem as well as with depth. Root-length densities in the top 1 m ranged from zero to about 1.0 cm.cm−3 in all orchards and were highly variable. The proportions of core samples having zero values for root-length density were used to subdivide the root zone into volumes in which all samples contained roots, and volumes in which some samples had no roots. Results suggest that roots in an ‘average’ tree penetrate to at least one metre depth in all but very young orchards so that soil in this volume is fully explored. Volumes filled by roots and volumes occupied at any particular root-length density appear to reach a maximum at about 4 years. Volumes of soil occupied at any particular root-length density were equal in all orchards older than 4 years. This suggests that root growth was balanced by root death. In contrast woody roots continue to accumulate with time.

Dynamic load is a technique which can be used to secure large pedons successfully in duplex profiles with massive clay B horizons. Data show that soil profiles obtained by this method have minimum change in soil physical properties including structure and compaction.

This study compares the efficiency of pot trials in the glasshouse or outdoors, and trials on undisturbed soil cores (100 cm deep; 15 cm wide), at simulating field trials. Yields of spring barley (Hordeum vulgare, cv Julia) were measured at sites on seven soil series on 11 farms, and also on undisturbed soil cores from the same sites, and in pot trials using disturbed soil from the same sites, to ascertain how far data from the core and pot trials (simulation procedures) could be used to generate the models, regressions or generalisations that were produced by more laborious and time-consuming field trials.

A study was made of the relationship between the number of roots (Nr) observed on unit area of the freshly exposed, horizontal faces of soil cores, and the amounts of roots (per unit volume) present in the same cores. Soil cores, 7 cm diameter, were extracted to depths of 1 m from cereal crops in 1976 at three field sites located on clay soils. Sampling was either at the start of stem elongation, or at anthesis. Estimates of root length per unit soil volume (L) were derived from Nr by assuming random orientation of roots in the soil.

Nitrogenase activity by the roots of some tropical grasses was detected by the acetylene reduction technique. In some cases particular plant species, evaluated at different times from different sites, displayed marked variations in nitrogenase activity. Acetylene reduction by root samples which had undergone preincubation under low O2 displayed an increase of approximately 5-fold when compared to plant-containing soil cores. These increases in nitrogenase activity correspond to an increase in the number of nitrogen-fixing bacteria associated with the roots.

A method is described for rapidly estimating the depth of penetration and density of roots of cereal crops under field conditions. Counts of living roots, traversing horizontal faces of soil cores, were made for winter wheat growing on direct-drilled and ploughed land.

The root systems of Scots pine in a plantation were studied by three methods; soil coring, soil monoliths, and a root trench with observation windows were used to estimate root length, root diameters and the initiatio of new root tips. The vertical and horizontal distribution of roots is described and root distribution has been related to distance from the tree and soil heterogeneity. It was found that the initiation of new root tips was not readily relatable to the soil environment and the usefulness of the root window technique for observing new root tips is questioned.

Root distribution of four Vitis cultivars at one location in Texas was asessed using trench profile and soil core sampling methods. Greater differences were obtained among cultivars utilizing the latter method when comparing root dry weights. Surface area of roots extracted from soil samples was estimated using a calcium nitrate slurry dip. This technique was found to be unreliable. Vitis champini cv. Dogridge maintained the greatest above-ground canopy and the most extensive root system. In measuring root numbers and dry weight, V. rotundifolia cv. Noble ranked at or near the bottom with V. vinifera cv. Barbera and V. labruscana cv. Concord being intermediate. Overall schematic root system patterns for each cultivar indicate that Noble is shallow rooted, having more than 35% of the total roots in the 0–15 cm depth. In contrast, ten percent of the total Dogridge roots were found at the 90–105 cm depth.

From soil cores extracted at 5 day intervals from 3 May to 6 August it was found that the biomass of fine roots in a Sitka spruce plantation, 14 years old, fluctuated with maxima in late May and mid July. The earlier peak coincides with increasing soil temperatures during a period of high incident precipitation and the latter developed when the soil profile was rewetted. Fine root biomass and soil moisture tension (SMT) were significantly and negatively correlated in three of four soil horizons. Root mortality occurred whenever incident precipitation failed to maintain soil moisture tension near zero. In the very open pored horizons the critical SMT for root death was unexpected small

As part of an investigation into the primary production of a forest the activity of fine roots was estimated by taking weekly soil cores from 24 May to 27 September in the 11 year of growth of a plantation of Picea sitchensis. Distinct maxima were found in 1) starch and soluble carbohydrate concentration in the root, mid-June, 2) root weight/soil volume, early July, and 3) root length/soil volume, late July with a second maximum in early September. However, root concentrations in the soil were the same at the end as at the start of the period and it is suggested that the fine root system of the forest had reached a dynamic equilibrium.

Cotton (Gossypium hirsutum L. cv. H14) seedlings were raised in soil of differing soil water content in specially designed pots in which the roots had access to freely available water and nutrients located 2.5 cm below the base of the soil core. The time for root emergence from the soil core and the rate of root growth were measured daily from sowing to harvest. The root and shoot dry weight and leaf water potential were measured at the final harvest 16 days after sowing. As soil water content decreased, the root emerged from the soil earlier and the initial rate of root elongation was faster. In spite of the availability of freely available water, the plants in the soil at low water contents had significantly lower leaf water potentials than those in soil at high water contents. The root: shoot ratio increased as the soil water content decreased. This arose from an absolute increase in root weight, with shoot weight not being significantly affected.

Four methods of measuring root distribution in a spring oat crop were compared: minirhizotrons installed vertically, minirhizotrons installed at an angle of 45°, core-break root counts and direct measurement of lengths of root washed from soil cores.

It was determined experimentally whether the amount of roots, viewed by endoscope in observation tubes (cm cm−2) is related to root density (cm cm−3) in adjacent bulk soil, determined by core sampling. For wheat plants the results can be summarized by the equation: root length (cm cm−2, endoscope)=0.29 times root density (cm cm−3, soil cores). Results for potato plants could not be interpreted as unequivocally as for wheat.

Unfertilized and NPK-fertilized plots in the long term fertility trial at Los Banos, Philippines were used to observe the effect of nitrogen fertilizer on heterotrophic N2-fixing activities in plow layer soil and in association with wetland rice. The activities were measured in the field byin situ acetylene reduction assays. Acetylene reduction activity of the plow layer soil in the paddy field was measured by soil cores. No appreciable difference was found-between fertilized and unfertilized plots.

The extent of nitrogen fixation in native grassland on clay soil was measured using the C2H2 reduction assay. Undisturbed soil cores incubated in microcanopies in the field indicated fixation rates of 2 kg N/ha per season. Less nitrogen fixation activity was found in associated cultivated soils. Other sites on different soil associations were found capable of fixing 1 kg·N/ha or less per growing season. The fixation by several legumes and nodulated nonlegumes ranged up to 1.8 μg/cm2. h.

A method for intensively sampling soil for nitrogen fixation potential using acetylene reduction assay is discussed. Acetylene was generated from calcium carbide. Soil cores were incubated in Mason jars with specially adapted lids. Air samples from the jars were stored and transported over dry KOH in 10 ml serum vials. The method overcomes many problems associated with other sampling procedures, and produces statistically reproducible data.

A simple method is described for the presentation in three dimensions of an undisturbed root system which is extracted from a soil core. A nylon mesh is threaded into the soil core in order to support the root system whilst the soil is removed by washing. The support for the root system provided by the nylon mesh is replaced by gelatin, the whole being transferred to a perspex box. In this way, an undisturbed root system may be studied, photographed, and preserved.

Apparatus is described which enables large numbers of soil cores to be collected from depths up to 70 cm in small plot areas with little disturbance of the soil within the corers.

Soil cores incubated under air atmosphere with C2H2 at partial pressure of 0.1 kPa, reduced NO3 − to N2O. Glucose and nitrate at higher concentration stimulated the N2O production. Further reduction of N2O to N2 seemed to be temporarely inhibited. However after 12 h N2O concentrations decreased, irrespective of soil treatment.

Study was designed to quantify the effects of freezing soil cores prior to washing on estimates of below-ground biomass. Cores were extracted from nearly pure stands of 3 native grasses growing in a southern USA mixed-grass prairie. Estimates of crown + rhizome biomass in the top 10-cm of the soil profile did not differ as a function of pre-washing treatment (frozenvs unfrozen). However, estimates of root biomass were 26% less from frozen (434 g m−2) than unfrozen samples (585 g m−2).