Maximum Rooting Depth Research Articles

The use of lysimeter data for the test of two soil–water balance models: A case study

AbstractTwo soil–water balance models were tested by a comparison of simulated with measured daily rates of actual evapotranspiration, soil water storage, groundwater recharge, and capillary rise. These rates were obtained from twelve weighable lysimeters with three different soils and two different lower boundary conditions for the time period from January 1, 1996 to December 31, 1998. In that period, grass vegetation was grown on all lysimeters. These lysimeters are located in Berlin‐Dahlem, Germany. One model calculated the soil water balance using the Richards equation. The other one used a capacitance approach. Both models used the same modified Penman formula for the estimation of potential evapotranspiration and the same simple empirical vegetation model for the calculation of transpiration, interception, and evaporation. The comparisons of simulated with measured model outputs were analyzed using the modeling‐efficiency index IA and the root mean squared error RMSE. At some lysimeters, the uncalibrated application of both models led to an underestimation of cumulative and annual rates of groundwater recharge and capillary rise, despite a good simulation quality in terms of IA and RMSE. A calibration of soil‐hydraulic and vegetation parameters such as maximum rooting depth resulted in a better fit between simulated and observed cumulative and annual rates of groundwater recharge and capillary rise, but in some cases also decreased the simulation quality of both models in terms of IA and RMSE. The results of this calibration indicated that, in addition to a precise determination of the soil water‐retention functions, vegetation parameters such as rooting depth should also be observed. Without such information, the rooting depth is a calibration parameter. However, in some cases, the uncalibrated application of both models also led to an acceptable fit between measured and simulated model outputs.

Root biomass and distribution of five agroforestry tree species

Knowledge of the quantitative assessment and structural development of root systems is essential to improve and optimize productivity of agroforestry systems. Studies on root biomass recovery by sieves of different mesh sizes (2.0, 1.0, 0.5 and 0.25 mm) and root distribution for four-year-old individuals of five agroforestry tree species viz.; Acacia auriculiformis A. Cunn. ex Benth, Azadirachta indica A. Juss, Bauhinia variegata L., Bombax ceiba L. and Wendlandia exserta Roxb. were conducted at the research farm of Rajendra Agricultural University, Pusa, Bihar, India. The results indicated that the 0.5 mm sieve was adequate for recovery of the majority of roots. All the tree species exhibited a large variation in root depth and horizontal root spread four years after planting. The maximum root depth was recorded in W. exserta (2.10 m) and minimum in B. variegata (1.00 m). Horizontal root spread was 2.05 m in B. ceiba and 8.05 m in A. auriculiformis. Root spread exceeded crown cover for all species. The primary roots were more horizontal than the secondary roots. The length and diameter of the main root were highest in A. indica (108.3 cm) and B. ceiba (23.2 cm), respectively. Highest length and diameter of lateral roots were recorded in B.variegata (201.6 cm) and A. indica (1.8 cm), respectively. Total root biomass among different species accounted for 18.2–37.9% of the total tree biomass. Results of this study infer that although all the species have potential to conserve moisture and improve fertility status of the soil, A. auriculiformis is the most effective for promoting soil fertility. The deep rooted W. exserta and A. auriculiformis will be preferred for cultivation under agroforestry systems and could reduce competition for nutrients and moisture with crops by pumping from deeper layers of soil.

A comparison of cultivation techniques for successful tree establishment on compacted soil

Soil compaction is often responsible for the poor establishment of trees on restored brownfield sites. This paper examines the root development, survival and growth of Alnus cordata, Larix kaempferi, Pinus nigra and Betula pendula after cultivation with complete cultivation, a standard industrial ripper and a prototype ripper. The industrial ripper was used in one pass across the experimental plots and the prototype ripper in both two and four passes. While the maximum root depths, after five growing seasons, attained by trees were similar to the target soil loosening depths for the cultivation techniques, the total number of roots suggests that root development was not uniform across the soil profile. All treatments significantly increased both the maximum root depth and total number of roots compared with the untreated control; the complete cultivation had approximately double the number of roots compared with the other treatments. Larger average root diameters and a higher percentage of coarse roots also suggest that roots experienced physical restriction in the control, two-pass prototype and industrial ripper plots. Similarly, while all species had attained significantly greater height growth on the treated soils compared with the control, the height of A. cordata, L. kaempferi and B. pendula was greatest after complete cultivation. The results demonstrate that complete cultivation is the most effective method of alleviating soil compaction for tree establishment. © Institute of Chartered Foresters, 2008. All rights reserved.

Rooting depth and above-ground community composition in Kalahari sand woodlands in western Zimbabwe

Abstract:The pattern of coarse-root distribution was analysed in the woody plant community along a 200-m edaphic gradient on a Kalahari sand woodland catena in Zimbabwe. The root systems of 45 trees and shrubs were excavated, mapped, and digitized to analyse rooting depth and architecture. Patterns of change in the above-ground community were also identified along this transect. Rooting depth increased, and the centre of mass of the root profile shifted towards the maximum rooting depth as a function of distance up the catena. The data also suggest that interspecific variation in rooting depth may increase up the catena. The below-ground pattern was accompanied by above-ground changes: species richness and basal area also increased up the catena. It is hypothesized that increasing soil depth allows greater coexistence of alternative water-use strategies, resulting in the observed increase in species richness up the catena.

Improving Drought-Avoidance Root Traits in Chickpea (Cicer arietinum L.) -Current Status of Research at ICRISAT

Chickpea (Cicer arietinum L.), an important food legume grown in the semi-arid tropical and Mediterranean regions, suffers substantial yield loss due to drought at the end of the growing season (terminal drought), as the crop is largely grown rainfed in post-rainy season on progressively receding soil moisture conditions. Root traits have been identified to postpone dehydration (drought avoidance hereafter) under moisture stress. The root length density (RLD) in the relatively shallow soil layers and the maximum root depth (RDp) were found to positively influence the seed yield under terminal drought environments. Considerable progress has been made to improve the methodology for sampling and analysis of roots. Using a PVC cylinder technique, the mini-core collection (n=211) of chickpea germplasm was evaluated for a number of root traits, including root biomass, RLD and RDp. A few germplasm accessions were identified to have a more prolific root system than the previously identified germplasm line ICC 4958, the best-known source of high root biomass. The germplasm accession ICC 8261 was identified to have the best combination of both RLD and RDp. Molecular markers have been identified for one major quantitative trait locus (QTL) that accounts for about one-third of the variation in root biomass (as measured by total root dry matter) and RDp from study of recombinant inbred lines (RILs) derived from a cross between ICC 4958 and Annigeri. New RIL populations, developed from two other crosses (ICC 8261 × ICC 283 and ICC 4958 × ICC 1882) involving parents having larger variation for root traits than between Annigeri and ICC 4958, are being studied to identify additional QTLs for root traits. Marker-assisted breeding for improvement of root traits in chickpea is expected to promote the development of varieties with greater drought avoidance.

Oak regeneration in southeastern bottomland hardwood forest

Oaks ( Quercus spp.), such as cherrybark oak ( Quercus pagoda Raf.), are valuable timber species in bottomland hardwood (BLH) forests of the southeastern U.S. Oak regeneration is affected by plant flooding tolerance; wind disturbances or forest harvests; and interactions with seed predators and herbivores. We investigated oak regeneration (seedling establishment and early growth, composition of seedling and sapling banks) in experimental openings, from 7 to 40 m radius, created by group-selection harvest in a BLH forest. Seed dispersal, seed predation, and microsite conditions on the forest floor, rather than canopy openness, were the first filters on oak regeneration. In the first 3 years after gap creation, naturally established oak seedlings were most abundant in relatively ‘undisturbed’ microsites with litter cover and around gap edges. Swamp chestnut oak ( Quercus michauxii Nutt.) germination was inhibited in pits, and seedling establishment was greatest under edge or less open canopy. Cherrybark oak seedling establishment and growth were reduced by seed predation and shade. Six years after acorns were planted, swamp chestnut oak seedling height and maximum root depth were greatest in gap centers. Ten years after gap creation, oaks were more abundant beneath the surrounding forest canopy, but were tallest in gap centers. Thus, in contrast to its lack of influence on acorn germination and initial establishment, canopy openness appears to filter oak persistence and height growth in the seedling bank. Forest management that provides level or raised microsites beneath thin canopy and protection from seed predation can facilitate oak seedling establishment in southeastern BLH forests. Maintaining a thin to open canopy can promote oak persistence in the seedling bank; growth into the sapling bank may require reopening the canopy if gap centers have grown up over time. Although longer study time is needed to capture regeneration from seed germination through ascent from the sapling layer into the subcanopy and canopy strata, this large field experiment has revealed there is no optimal gap size for oak regeneration. Rather, biotic interactions, canopy openness, and particularly flood duration at the microsite scale create complex patterns of oak abundance and heights in the seedling and sapling layers following disturbance in bottomland hardwood forests.

Genotypic differences in root penetration ability of wheat through thin wax layers in contrasting water regimes and in the field

A significant proportion of arable land in south-western Australia is highly susceptible to subsoil compaction, which limits access of roots of wheat to water and nutrients at depth. Genotypic variation in the ability of roots to penetrate a hardpan has been reported for other cereals, using a pot technique, where a thin wax-layer of paraffin wax and petroleum jelly is placed in a soil column to simulate a hardpan. Previously we have modified and validated this technique for measuring root penetration ability of wheat seedlings under contrasting water regimes. Here we report on a series of five experiments (runs), two in well-watered and three in drought stress conditions, which evaluated seminal and nodal root penetration ability through thin wax layers among 24 Australian wheat cultivars and breeding lines (entries). These results were compared with observations on their rooting depths in two contrasting soil types in field trials, including a sandy duplex that contained a hardpan and a red clay that increased in soil strength with depth. Nodal roots ceased growth early under soil water deficit, and water uptake was instead dependant on seminal roots under conditions imposed in the pots. Plants were then reliant on the ability of seminal roots to penetrate the wax layer. Eight entries had superior root penetration ability in both well-watered and drought stressed conditions. Roots of three other entries, which failed to penetrate the wax layers, died under drought stress conditions. In field trials, there was a significant interaction between site and entry for maximum root depth. Our results from the pot studies and field trials indicate that there exists genotypic variation in root traits that are required to penetrate uniformly hard soil, dry soil or soil containing a hardpan. As four of the eight superior entries also showed superior root penetration ability at both sites in the field, there was an overall consistency, but there were exceptions at individual field sites. Factors likely to result in such exceptions were discussed, and topics for further research identified.

Riparian Ecosystem Management Model: Sensitivity to Soil, Vegetation, and Weather Input Parameters1

Abstract: The Riparian Ecosystem Management Model (REMM) was developed by the U.S. Department of Agriculture‐Agriculture Research Service (USDA‐ARS) and its cooperators to design and evaluate the efficiency of riparian buffer ecosystems for nonpoint source pollution reduction. REMM requires numerous inputs to simulate water movement, sediment transport, and nutrient cycling in the buffer system. In order to identify critical model inputs and their uncertainties, a univariate sensitivity analysis was conducted for nine REMM output variables. The magnitude of each input parameter was changed from −50% to +50% from the baseline data in 12 intervals or, in some cases, the complete range of an input was tested. Baseline model inputs for the sensitivity analysis were taken from Gibbs Farm, Georgia, where REMM was tested using a 5‐year field dataset. Results of the sensitivity analysis indicate that REMM responses were most sensitive to weather inputs, with minimum daily temperature having the greatest impact on the nitrogen‐related outputs. For example, the 100% change (−50% to +50%) in minimum daily temperature input values yielded a 164.4% change in total nitrogen (N), a 109.3% change in total nitrate (NO3), and a 127.1% change in denitrification. REMM was most sensitive to precipitation with regard to total flow leaving the riparian vegetative buffer zone (199.8%) and sediment yield (138.2%). Deep seepage (12.2%), volumetric water content (24.8%), and pore size index (6.5%) in the buffer soil profile were the most influential inputs for the output water movement. Sediment yield was most sensitive to Manning’s coefficient (46.6%), bare soil percent (40.7%), and soil permeability (6.1%). For vegetation, specific leaf area, growing degree day coefficients, and maximum root depth influenced the nitrogen related outputs. Overall results suggest that because of the high sensitivity to weather parameters, on‐site weather data is needed for model calibration and validation. The model’s relatively low sensitivity to vegetation parameters also appears to support the use of regional vegetation datasets that would simplify model implementation without compromising results.

Rooting depth and soil moisture control Mediterranean woody seedling survival during drought

Summary Seedling survival is one of the most critical stages in a plant's life history, and is often reduced by drought and soil desiccation. It has been hypothesized that root systems accessing moist soil layers are critical for establishment, but very little is known about seedling root growth and traits in the field. We related seedling mortality to the presence of deep roots in a field experiment in which we monitored soil moisture, root growth and seedling survival in five Mediterranean woody species from the beginning of the growing season until the end of the drought season. We found strong positive relationships between survival and maximum rooting depth, as well as between survival and soil moisture. Species with roots in moist soil layers withstood prolonged drought better, whereas species with shallow roots died more frequently. In contrast, biomass allocation to roots was not related to establishment success. Access to moist soil horizons accounted for species‐specific survival rates, whereas large root : shoot (R:S) ratios did not. The existence of soil moisture thresholds that control establishment provides insights into plant population dynamics in dry environments.

Root penetration rate - a benchmark to identify soil and plant limitations to rooting depth in wheat

Data on wheat rooting depth was compiled from 36 agronomic experiments conducted in southern NSW from 1990 to 2004. Rooting depth was measured by direct soil coring and observation of roots using core-break or root washing techniques. Maximum rooting depth varied from 80 to 180 cm and was influenced by the depth of soil wetting, soil type and the duration of the vegetative phase (sowing to anthesis) as determined by interactions of sowing date, variety and seasonal conditions. The root penetration rate (RPR cm/day), defined as (maximum root depth measured at or after anthesis) / (days from sowing to anthesis), emerged as a simple but unifying parameter which could be used to estimate the potential rooting depth of wheat on different soils. RPR, expressed on a thermal time basis, was highly correlated with that expressed on a simpler time basis (r = 0.92). Incomplete wetting of the soil profile reduced maximum rooting depth and RPR in 12 of the 36 crops studied, and root penetration in the subsoil was clearly restricted in soil layers with less than 45 to 50% plant available water. Soil type influenced the RPR. The average RPR for wheat was 1.13 ± 0.04 cm/day on Red Kandosols (n = 11), 1.01 ± 0.07 cm/day on a Red Sodosol (n = 3) and 0.79 ± 0.03 cm/day on Red Chromosols (n = 10). The RPR was relatively constant across cultivars and sowing dates within these soil types, although there was some evidence for a reduction in RPR with later sowing independent of time or thermal time. We suggest that the RPR (cm/day) established for wheat on various soil types provides a useful tool for wheat growers to estimate the rooting depth and available water and nutrients in-season. It also provides a benchmark to indicate potential subsoil limitations to crop growth, and for researchers investigating opportunities to increase the maximum rooting depth of wheat through management or breeding.

A flexible approach to managing variability in grain yield and nitrate leaching at within-field to farm scales

We up-scaled the APSIM simulation model of crop growth, water and nitrogen dynamics to interpret and respond to spatial and temporal variations in soil, season and crop performance and improve yield and decrease nitrate leaching. Grain yields, drainage below the maximum root depth and nitrate leaching are strongly governed by interaction of plant available soil water storage capacity (PAWC), seasonal rainfall and nitrogen supply in the water-limited Mediterranean-type environment of Western Australia (WA). APSIM simulates the interaction of these key system parameters and the robustness of its simulations has been rigorously tested with the results of several field experiments covering a range of soil types and seasonal conditions in WA. We used yield maps, soil and weather data for farms at two locations in WA to determine spatial and temporal patterns of grain yield, drainage below the maximum root depth and nitrate leaching under a range of weather, soil and nitrogen management scenarios. On one farm, we up-scaled APSIM simulations across the whole farm using local weather and fertiliser use data and the average PAWC values of soil type polygons. On a 70 ha field on another farm, we used a linear regression of apparent soil electrical conductivity (ECa) measured by EM38 against PAWC to transform an ECa map of the field into a high resolution (5 m grid) PAWC map. We then used regressions of simulated yields, drainage below the maximum root depth and nitrate leaching on PAWC to upscale the APSIM simulations for a range of weather and fertiliser management scenarios. This continuous mapping approach overcame the weakness of the soil polygons approach, which assumed uniformity in soil properties and processes within soil type polygons. It identified areas at greatest financial and environmental risks across the field, which required focused management and simulated their response to management interventions. Splitting nitrogen applications increased simulated wheat yields at all sites across the field and decreased nitrate leaching particularly where the water storage capacity of the soil was small. Low water storage capacity resulted in both low wheat yields and large leaching loss. Another management option to decrease leaching may be to grow perennial vegetation that uses more water and loses less by drainage.

Predicting on-farm soybean yields in the pampas using CROPGRO-soybean

Soybean is the main rainfed crop in a wide range of latitudes and sowing dates of the Argentine Pampas. It is sown alone or as a second crop after other winter and summer crops. Modelling approaches have proved to be helpful in the decision making process. The on-farm evaluation of CROPGRO is rather difficult since input data are scarce and frequently of worse quality than those from experimental works. Moreover, CROPGRO simulation of water dynamic processes and their relation with biomass production has not been comprehensively evaluated in soybean crops. The aims of this study were (i) to evaluate the CROPGRO-soybean performance, with emphasis on water demand and supply and biomass production under water limited conditions, (ii) to generate a revised CROPGRO model improving those aspects, and (iii) to compare simulations outputs using the original and the revised CROPGRO models, with on-farm crop data set. In the revised model, we multiplied potential evapotranspiration by 1–1.22 when LAI increased from 0 to ≥4.0. We set a root extension rate of 4.0 cm/thermal day and a maximum rooting depth of 2.5 m. Finally, we included a nonlinear equation to simulate the relationship between relative transpiration and relative gross photosynthesis. The ability of the revised CROPGRO-soybean to simulate water content depletion and biomass production was tested against several experiments with an imposed drought period. We also calibrated cultivar parameters using “ad hoc” tests in a range of environments (combinations of sowing dates and locations). The models were evaluated with data from 155 commercial farms. V (%) (root mean square error as percentage of the observed mean) for the total cycle length, vegetative period, and reproductive phase simulations were 7, 13 and 15%, respectively. The revised CROPGRO was more accurate in simulating crop yield, biomass, harvest index and yield numeric components. V (%) values ranged from 11 to 17% (revised version) and from 13 to 22% (original version). Besides, V (%) values for yield were 16% with the revised model versus 32% with the original one, considering only paddocks with higher water stress level. The robust prediction of phenology, biomass and yield components obtained with the revised model across different environmental conditions, support its use in the decision making process of the soybean crop at the farm scale.

The effect of nitrogen fertilization on root distribution of winter wheat

The effect of nitrogen fertilization on root length (RL) distribution of winter wheat (Triticum aestivum L.) was investigated. The study was conducted in Prague-Ruzyne on clay loam Chernozemic soil in the years 1996–2003. Two (N0, N1) and three (N0, N1, N2) treatments, unfertilized (N0), fertilized with 100 kg (N1) and 200 kg N/ha (N2) were studied in 1996–2000 and 2001–2003, respectively. Nitrogen rate 100 kg/ha had no effect on RL in soil layers (P > 0.1) in years 1996–2000 and 2002–2003 and there was not significant interaction between N treatment and soil layer except for year 1998 (P < 0.01). Nitrogen fertilization affected RL distribution significantly (P = 0.013) only in 2001 due to reduction of root growth in subsoil layers in treatment N2 (200 kg N/ha) in comparison with N0 and N1. The effect of N fertilization on total RL in rooted soil volume was insignificant. There was a significant effect of year on total RL (P < 0.01) but not of interaction of year and N treatment. Roots reached, with the exception of two years, the depth between 100 and 130 cm. Nitrogen fertilization (N1) had no effect (P = 0.59) on rooting depth (RD) in years 1996–2000 but there was a significant effect of interaction between year and N fertilization on RD (P < 0.01). In the second experimental series (2001–2003) N fertilization rate 200 kg N/ha significantly reduced maximum RD (P < 0.01) in comparison with N0 and N1. The year had highly significant effect on RD.

Evaluating warm-season grass production in temperate-region pastures: A simulation approach

The pasture submodel of the Integrated Farm System Model (IFSM) was modified to simulate the biomass production and nutritive dynamics of a warm-season (C 4) grass monoculture. Predictions of yield and nutritive value were calibrated and evaluated with 5 years of field data from grazed switchgrass ( Panicum virgatum) pastures in Pennsylvania, USA. Uncertainty analysis of biomass at the beginning of each growth cycle showed that each estimated yield was sensitive to the amount of biomass that started its growth cycle but not to those of previous growth cycles. Sensitivity analysis showed that predicted yield was most sensitive to physiological parameters such as proportion of photosynthate partitioned to shoots, specific leaf area, structural growth per unit carbohydrate, leaf photosynthetic efficiency, and the light extinction coefficient. Sensitivity of yield to maximum rooting depth increased during periods of drought. For 10 of 13 simulated sampling dates, confidence intervals of field-observed and predicted mean yield overlapped, and half of predicted mean annual yields were within ±32% of observed values. The model predicted seasonal crude protein (half of predictions within ±25%), neutral detergent fiber (all within ±12%), and in vitro true digestibility (all within ±16%) more accurately. Refining the model’s representation of warm-season grass phenology and calibrating it to simulate other field experiments may improve predictions of seasonal biomass production. The whole-farm model with a warm-season grass component will provide a useful research and teaching tool for evaluating the long-term economic and environmental sustainability of dairy and beef production systems in warm temperate regions.

Root water uptake and profile soil water as affected by vertical root distribution

Water uptake by plant roots is a main process controlling water balance in field profiles and vital for agro-ecosystem management. Based on the sap flow measurements for maize plants (Zea mays L.) in a field under natural wet- and dry-soil conditions, we studied the effect of vertical root distribution on root water uptake and the resulted changes of profile soil water. The observations indicate that depth of the most densely rooted soil layer was more important than the maximum rooting depth for increasing the ability of plants to cope with the shortage of water. Occurrence of the most densely rooted layer at or below 30-cm soil depth was very conducive to maintaining plant water supply under the dry-soil conditions. In the soil layers colonized most densely by roots, daytime effective soil water saturation (S (e)) always dropped dramatically due to the high-efficient local water depletion. Restriction of the rooting depth markedly increased the difference of S (e) between the individual soil layers particularly under the dry-soil conditions due likely to the physical non-equilibrium of water flow between the layers. This study highlights the importance of root distribution and pattern in regulating soil water use and thereby improving endurance of plants to seasonal droughts for sustainable agricultural productivity.

Decline in alkali meadow vegetation cover in California: the effects of groundwater extraction and drought

Summary Throughout arid regions of the world, groundwater is extracted for human population centres. In the Great Basin and Range region of the USA, we lack basic information regarding some plant communities detailing the extent to which vegetation is threatened by groundwater extraction. This is particularly true for alkali meadow vegetation, which is restricted to zones of shallow groundwater yet is not a riparian plant community with obligate wetland properties. To increase our understanding of the relative importance of groundwater and precipitation in maintaining alkali meadow vegetation cover, we used a 16‐year record of plant cover derived from satellite data of Owens Valley, California, USA, in conjunction with concurrent depth‐to‐water and precipitation measurements, to analyse vegetation response to anthropogenic and climatic changes in water availability. Groundwater decline varied from 0·5 to 5·0 m throughout the study area, with the largest changes occurring at sites closest to pumping wells. The entire region experienced a 6‐year drought (1987–92), during which annual precipitation remained below the 50‐year median. Meadow plant cover over the 16‐year study period was correlated with groundwater depth, but plant cover was generally unresponsive to annual precipitation variability. Sensitivity to groundwater decline was greatest for plots with a higher cover of herbaceous perennials. The results showed that this plant community is groundwater dependent, and that this characteristic buffers the system from the effects of drought. However, at sites with extensive groundwater decline, the remaining plant cover became weakly correlated with precipitation only after groundwater declined below a threshold depth located at 2·5 m, representing the average plant rooting depth. Synthesis and applications. Sustainable water development that seeks to pump groundwater without adversely affecting vegetation cover and plant assemblages must recognize the maximum rooting depth of groundwater‐dependent plant species. When groundwater is within the root zone, management decisions can be made to either increase or decrease vegetation cover through modification of groundwater depth. When groundwater is below the root zone, vegetation cover is low and susceptible to changes in precipitation. Quantitative satellite measurements of vegetation cover might aid the monitoring and sustainable management of water resources.

Effect of Root System Morphology on Root-sprouting and Shoot-rooting Abilities in 123 Plant Species from Eroded Lands in North-east Spain

The objective of this study was to test whether the mean values of several root morphological variables were related to the ability to develop root-borne shoots and/or shoot-borne roots in a wide range of vascular plants. A comparative study was carried out on the 123 most common plant species from eroded lands in north-east Spain. After careful excavations in the field, measurements were taken of the maximum root depth, absolute and relative basal root diameter, specific root length (SRL), and the root depth/root lateral spread ratio on at least three individuals per species. Shoot-rooting and root-sprouting were observed in a large number of individuals in many eroded and sedimentary environments. The effect of life history and phylogeny on shoot-rooting and root-sprouting abilities was also analysed. The species with coarse and deep tap-roots tended to be root-sprouting and those with fine, fasciculate and long main roots (which generally spread laterally), tended to be shoot-rooting. Phylogeny had an important influence on root system morphology and shoot-rooting and root-sprouting capacities. However, the above relations stood after applying analyses based on phylogenetically independent contrasts (PICs). The main morphological features of the root system of the study species are related to their ability to sprout from their roots and form roots from their shoots. According to the results, such abilities might only be functionally viable in restricted root system morphologies and ecological strategies.

Effect of Sowing Date and Cultivar on Root System Development in Pea (Pisum sativum L.)

In many species, root system development depends on cultivar and sowing date, with consequences for aerial growth, and seed yield. Most of the peas (Pisum sativum L.) grown in France are sown in spring or in mid-November. We analyzed the effect of two sowing periods (November and February) and three pea cultivars (a spring cultivar, a winter cultivar, a winter recombinant inbred line) on root development in field conditions. For all treatments, rooting depth at various dates seemed to be strongly correlated with cumulative radiation since sowing. Maximum root depth varied from 0.88 to 1.06 m, with the roots penetrating to greater depths for February sowing than for November sowing in very cold winters. The earlier the crop was sown, the sooner maximum root depth was reached. No difference in root dynamics between cultivars was observed. In contrast, the winter recombinant inbred line presented the highest root density in the ploughed layer. These findings are discussed in terms of their possible implications for yield stability and environmental impact.

Effects of Soil Structure on Pea (Pisum sativum L.) Root Development According to Sowing Date and Cultivar

Spring peas are known to be very sensitive to compaction, particularly when sowing takes place soon after winter. Winter peas, which are sown in autumn, should present an opportunity to sow the crop in better soil structural conditions than for spring peas, because of more favourable moisture conditions at that time. As environmental conditions have a big influence on root systems, it is important to determine the effects of soil structure on pea root systems for different cultivars and sowing dates. A spring pea cultivar and a winter pea cultivar were both sown at two dates (one in autumn and one in spring) on soils with different plough-layer structures (compacted and uncompacted) at two sites in 2002 and one site in 2003. Soil structure was characterised by bulk density and the percentage of highly compacted zones in the ploughed layer. Root distribution maps were produced every month, from February to maturity. Root development was described in terms of general root dynamics, root elongation rate (RER) in the subsoil, final maximum root depth (Dmax) and root distribution at maturity. Root depth dynamics depended on compaction and its interaction with climatic conditions. The effects of compaction on RER in the subsoil depended on the experimental conditions. Dmax was reduced by 0.10 m by compaction. Compaction also reduced root distribution between 10 and 40% in the ploughed layer only. Pea cultivars differed in sensitivity to soil compaction, with a direct effect on the final depth explored by roots. These results are discussed in terms of their relevance to water and nutrient uptake.

Root depth of native and sown perennial grass-based pastures, North-West Slopes, New South Wales. 1. Estimates from cores and effects of grazing treatments

Studies were undertaken on native and sown perennial grass-based pastures as part of the Sustainable Grazing Systems National Experiment to estimate root depth and describe root distribution in these pastures. Samples from soil cores (0–210 cm maximum sampling depth) taken in 1997 (before grazing treatments were imposed) and 4 years later in spring 2001 were used to examine the effects of different grazing regimes on root length density (cm/cm3), root mass density (mg/cm3), root volume density (cm3/cm3), and diameter (mm) at each of 3 sites. In spring 1997, mean maximum root depth was 107 cm for a native perennial grass pasture near Barraba and 74 cm for a pasture sown with phalaris (Phalaris aquatica) and subterranean clover (Trifolium subterraneum) near Nundle, with values being lower for a native pasture near Manilla (65 cm for a Brown Vertosol and 97 cm for a Red Chromosol). For all pasture types, >20% of root mass density, root length density or root volume density was in the 0–5 cm soil layer and >60% was at a depth of 0–30 cm. At all sites, mean total root mass was around 1000 kg DM/ha. After 4 years of grazing (spring 2001) there were relatively few significant effects of grazing treatment on root length density, root mass density, root volume density, or root diameter. Effects that were significant mostly occurred at 0–5 cm for the native pastures and 0–50 cm for the sown pasture. For the Barraba native pasture, root length, volume and mass densities (0–5 cm) were higher (P<0.05) in the continuously grazed, low stocking rate treatment compared with all other treatments. Similarly, for the Manilla native pasture, root length density was higher (P<0.05) in this treatment at soil depths of 0–5 and >5–10 cm compared with all other treatments. In contrast, for the Nundle sown pasture, root length density (0–5 cm) was lowest (P<0.05) in 2 continuously grazed treatments compared with those that were strategically grazed in autumn and spring.