Water uptake profile response of corn to soil moisture depletion

The effects of soil moisture distribution on water uptake of drip‐irrigated corn were investigated by simultaneously monitoring the diurnal evolution of sap flow rate in stems, of leaf water potential, and of soil moisture, during intervals between successive irrigations. The results invalidate the steady‐state resistive flow model for the continuum. High hydraulic capacitance of wet soil and low hydraulic conductivity of dry soil surrounding the roots damped significantly diurnal fluctuations of water flow from bulk soil to root surface. By contrast, sap flow responded directly to the large diurnal variation of leaf water potential. In wet soil, the relation between the diurnal courses of uptake rates and leaf water potential was linear. Water potential at the root surface remained nearly constant and uniformly distributed. The slope of the lines allowed calculating the resistance of the hydraulic path in the plant. Resistances increased in inverse relation with root length density. Soil desiccation induced a diurnal variation of water potential at the root surface, the minimum occurring in the late afternoon. The increase of root surface water potential with depth was directly linked to the soil desiccation profile. The development of a water potential gradient at the root surface implies the presence of a significant axial resistance in the root hydraulic path that explains why the desiccation of the soil upper layer induces an absolute increase of water uptake rates from the deeper wet layers.     

Root growth and water uptake during water deficit and recovering in wheat

Root growth and soil water content were measured in a field experiment with wheat subjected to two periods of water deficit. The first period was induced early in the season between the early vegetative stage (22 DAS) and late terminal spikelet (50 DAS), the second period at mid-season between terminal spikelet (42 DAS) and anthesis (74 DAS). Total root growth was reduced under water deficit by a reduction in the top 30 cm, while the root system continued to grow in the deeper soil profile between 30 and 60 cm. Shortly after rewatering, the growth pattern reverted to fastest root growth rates in the shallow soil layers. In relative terms, the total root system increased in relation to the above ground dry matter under water shortage. The early-, the mid-season water deficit treatments, and the control treatment had total root length of 27.4, 19.4 and 30.6 km m^-2, respectively, about 2 wk before maturity. Evapotranspiration declined under water deficit, but water uptake in deeper layers increased. Water uptake per unit root length was reduced with water deficit and was still low shortly after rewatering. Remarkable was the increase in water uptake at 2–3 weeks after rewatering, both deficit treatments exceeded the control by almost 100%. This increase in water uptake followed the burst of new root growth in the upper regions of the soil. However, water uptake rates subsequently declined towards maturity, being between 0.15 L km^-1 d^-1 and 0.17 L km^-1 d^-1 for the early and mid-season water deficit treatments, slightly higher than the control, 0.12 L km^-1 d^-1. The results showed that the crop subjected to early water deficit could compensate for some of the reductions in root growth during subsequent rewatering, but the impact of the mid-season water deficit treatment was more severe and permanent.     

Plant nutrition and growth: Basic principles

Soil compaction may restrict shoot growth of sugar beet plants. Roots, however, are the plant organs directly exposed to soil compaction and should therefore be primarily affected. The aim of this study was to determine the influence of mechanical resistance and aeration of compacted soil on root and shoot growth and on phosphorus supply of sugar beet. For this purpose, a silt loam soil was adjusted to bulk densities of 1.30, 1.50 and 1.65 g cm^–3 and water tensions of 300 and 60 hPa. Sugar beet was grown in a growth chamber under constant climatic conditions for 4 weeks. Both, decrease of water tension and increase of bulk density impeded root and shoot growth. In contrast, the P supply of the plants was differently affected. At the same air-filled pore volume, the P concentration of the shoots was reduced by a decrease of soil water tension, but not by an increase of bulk density. Both factors also reduced root length and root hair formation, however, in compacted soil the plants partly substituted for the reduction of root size by increasing the P uptake efficiency per unit of root. Shoot growth decreased when root growth was restricted. Both characteristics were closely related irrespective of the cause of root growth limitation by either compaction or water saturation. It is therefore concluded that shoot growth in both the compacted and the wet soil was regulated by root growth. The main factor impeding root growth in compacted soil was penetration resistance, not soil aeration.FAX no corresponding author: +49551 5056299     

Simulation of the effect of root distribution on hydraulic redistribution in a desert riparian forest

Hydraulic redistribution (HR) of roots plays an important role in the water relations of desert riparian plants. In order to estimate the effect of vertical root distribution on the HR process of Populus euphratica Oliv. during the entire growth season, we performed simulation and scenario analyses based on the observed soil water potential and root distribution data. The results showed that our simulation model achieved a good accuracy. The initial value of soil water content could significantly affect the simulated soil water content at soil depths of >90 cm, but had only limited effect on soil water content in the 0- to 90-cm soil layers. Scenario analysis revealed that with increase in root distribution depth, the HR process extended from the upper and middle soil layers downward toward the middle and deeper soil layers: the deeper the root distribution, the more likely it was to trigger the HR process in deep soil layers. However, a deeper rooting system led to a decrease in the total amount of hydraulically redistributed water over the entire soil column. Redistributed water also significantly increased the soil water depletion and the soil water storage. However, the effects of redistributed water (HR vs. without HR) on water depletion and soil water storage were reduced with the deepening of root distribution. These results indicate that HR can obviously affect the moisture of the upper soil layers, while vertical root distribution significantly changes the spatial and quantitative characteristics of HR within soil columns.     

Mechanisms for the increase in phosphorus uptake of waterlogged plants: soil phosphorus availability, root morphology and uptake kinetics

Waterlogging frequently reduces plant biomass allocation to roots. This response may result in a variety of alterations in mineral nutrition, which range from a proportional lowering of whole-plant nutrient concentration as a result of unchanged uptake per unit of root biomass, to a maintenance of nutrient concentration by means of an increase in uptake per unit of root biomass. The first objective of this paper was to test these two alternative hypothetical responses. In a pot experiment, we evaluated how plant P concentration of Paspalum dilatatum, (a waterlogging-tolerant grass from the Flooding Pampa, Argentina) was affected by waterlogging and P supply and how this related to changes in root-shoot ratio. Under both soil P levels waterlogging reduced root-shoot ratios, but did not reduce P concentration. Thus, uptake of P per unit of root biomass increased under waterlogging. Our second objective was to test three non-exclusive hypotheses about potential mechanisms for this increase in P uptake. We hypothesized that the greater P uptake per unit of root biomass was a consequence of: (1) an increase in soil P availability induced by waterlogging; (2) a change in root morphology, and/or (3) an increase in the intrinsic uptake capacity of each unit of root biomass. To test these hypotheses we evaluated (1) changes in P availability induced by waterlogging; (2) specific root length of waterlogged and control plants, and (3) P uptake kinetics in excised roots from waterlogged and control plants. The results supported the three hypotheses. Soil P avail-ability was higher during waterlogging periods, roots of waterlogged plants showed a morphology more favorable to nutrient uptake (finer roots) and these roots showed a higher physiological capacity to absorb P. The results suggest that both soil and plant mechanisms contributed to compensate, in terms of P nutrition, for the reduction in allocation to root growth. The rapid transformation of the P uptake system is likely an advantage for plants inhabiting frequently flooded environments with low P fertility, like the Flooding Pampa. This advantage would be one of the reasons for the increased relative abundance of P. dilatatum in the community after waterlogging periods. Received: 15 February 1997 / Accepted: 20 May 1997     

A Two-dimensional Model for Water Uptake by Desert Succulents: Implications of Root Distribution

Water uptake by Agave deserti and Ferocatus acanthodes was predictedusing a two-dimensional simulation model in which the soil arounda plant was divided into a series of layers and concentric cylindricalshells. Root lengths in 0.05 m thick soil layers were determinedfor both species in the field, where mean root depths were only0.11 m for A. deserti and 0.10 m for F. acanthodes. For a yearwith average precipitation (159 mm), 42 per cent of the annualprecipitation could be taken up by A. deserti and 25 per centby F. acanthodes. Predicted water uptake by both species wasgreater from the upper soil layers (above 0.15 m) for averageand dry years, but was greater from the deeper layers for awet year. The actual root distribution for both species ledto more water uptake than when all of the roots were in a singlelayer. The large number of days per year when the soil temperaturesexceeded 57 °C (the temperature for 50 per cent inhibitionof uptake of a vital stain by root cells) may exclude rootsfrom the 0.00–0.05 m soil layer, even though water uptakewhen all roots were located there was predicted to be maximal.Therefore, the observed root distribution of A. deserti andF. acanthodes may be limited near the soil surface by high temperaturesand at maximum depths by water availability for all but wetyears. Agave deserti, Ferocactus acanthodes, desert succulents, root system, root distribution, soil temperature, water uptake     

Modelling diverse root density dynamics and deep nitrogen uptake—A simple approach

We present a 2-D model for simulation of root density and plant nitrogen (N) uptake for crops grown in agricultural systems, based on a modification of the root density equation originally proposed by Gerwitz and Page in J Appl Ecol 11:773–781, (1974). A root system form parameter was introduced to describe the distribution of root length vertically and horizontally in the soil profile. The form parameter can vary from 0 where root density is evenly distributed through the soil profile, to 8 where practically all roots are found near the surface. The root model has other components describing root features, such as specific root length and plant N uptake kinetics. The same approach is used to distribute root length horizontally, allowing simulation of root growth and plant N uptake in row crops. The rooting depth penetration rate and depth distribution of root density were found to be the most important parameters controlling crop N uptake from deeper soil layers. The validity of the root distribution model was tested with field data for white cabbage, red beet, and leek. The model was able to simulate very different root distributions, but it was not able to simulate increasing root density with depth as seen in the experimental results for white cabbage. The model was able to simulate N depletion in different soil layers in two field studies. One included vegetable crops with very different rooting depths and the other compared effects of spring wheat and winter wheat. In both experiments variation in spring soil N availability and depth distribution was varied by the use of cover crops. This shows the model sensitivity to the form parameter value and the ability of the model to reproduce N depletion in soil layers. This work shows that the relatively simple root model developed, driven by degree days and simulated crop growth, can be used to simulate crop soil N uptake and depletion appropriately in low N input crop production systems, with a requirement of few measured parameters.     

Ion uptake and respiration of dry bean roots subjected to localized anoxia

Summary Ion uptake by dry bean root systems was examined during a three day treatment period. Three aeration treatments were applied to split root systems where both halves were aerated, both halves were nonaerated and one half aerated and the remaining half nonaerated (localized anoxia). Ion absorption was similar for the aerated control and localized anoxia treatments. The nonaerated control absorbed 2, 40, and 60 percent of the aerated control for K⁺, Ca⁺⁺, and NO₃ ⁻, respectively. Ion absorption by stressed plants appeared to increase directly with root growth in the aerated portions of the localized anoxia treatments. Localized anoxia resulted in greater potassium ion uptake per unit root weight and in greater root respiration rates of the aerated half of the Pinto III cultivar root system. Transpiration rates of Seafarer subjected to localized anoxia were 135% of the aerated control. The additional water use may have contributed to greater ion uptake, by mass flow, in the nonaerated portion of the localized anoxia treatment. Nutrient solutions of the nonaerated controls became more alkaline during stress than did the nonaerated portions of the localized anoxia treatments, indicating a possible direct or indirect effect of the aerated portions of the localized anoxia treatments on the corresponding nonaerated half. Compensation in ion uptake by dry bean roots subjected to localized anoxia appeared to be the result of increased root growth, greater respiration rates, greater transpiration rates and, for Pinto III, an increase in the ion uptake rate per unit root weight. This compensatory uptake of water and nutrients by the root system may be one mechanism by which roots overcome localized stress within a soil profile.     

Capacity of biological soil crusts colonized by the lichen <Emphasis Type="Italic">Diploschistes</Emphasis> to metabolize simple phenols

Background and aims

Soil compaction strongly affects water uptake by roots. The aim of the work was to examine soil—plant interactions with focus on the impact of distribution of compacted soil layers on growth and water uptake by wheat roots.

Methods

The growth-chamber experiment was conducted on wheat growth in soil with compacted soil layers. The system for maintaining constant soil water potential and measurement of daily water uptake from variously compacted soil layers was used.

Results

Layered soil compaction differentiated vertical root distribution to higher extent for root length than root mass. The propagation rate of a water extraction front was the highest through layers of moderately compacted soil. The root water uptake rate was on average 67 % higher from moderately than heavily compacted soil layers. Correlations between water uptake and the length of thick roots were increasing with increasing level of soil compaction.

Conclusions

The study shows that root amount, water uptake, propagation of water extraction and shoot growth strongly depend on the existence of compacted layers within soil profile. The negative effects of heavily compacted subsoil layer on water uptake were partly compensated by increased uptake from looser top soil layers and significant contribution of thicker roots in water uptake.     

A split-pot experiment with sorghum to test a root water uptake partitioning model

Correct modeling of root water uptake partitioning over depth is an important issue in hydrological and crop growth models. Recently a physically based model to describe root water uptake was developed at single root scale and upscaled to the root system scale considering a homogeneous distribution of roots per soil layer. Root water uptake partitioning is calculated over soil layers or compartments as a function of respective soil hydraulic conditions, specifically the soil matric flux potential, root characteristics and a root system efficiency factor to compensate for within-layer root system heterogeneities. The performance of this model was tested in an experiment performed in two-compartment split-pot lysimeters with sorghum plants. The compartments were submitted to different irrigation cycles resulting in contrasting water contents over time. The root system efficiency factor was determined to be about 0.05. Release of water from roots to soil was predicted and observed on several occasions during the experiment; however, model predictions suggested root water release to occur more often and at a higher rate than observed. This may be due to not considering internal root system resistances, thus overestimating the ease with which roots can act as conductors of water. Excluding these erroneous predictions from the dataset, statistical indices show model performance to be of good quality.     

Vertical patterns of fine root biomass, morphology and nitrogen concentration in a subalpine fir-wave forest

To clarify the nutrient acquisition strategies for below-ground resources in a subalpine Abies forest with shallow soils, we examined the vertical patterns of fine root biomass, morphology, nitrogen concentration of fine root tissue and soil chemical characteristics in nine quadrats of sapling, young and mature stands in a subalpine fir-wave forest, central Japan. The community characteristics changed with stand development, but stand development did not influence the vertical pattern of fine root characteristics. Fine root biomass decreased with soil depth. Specific root length did not differ among soil depths, and neither average diameter nor tissue density of fine roots changed vertically. The nitrogen concentration of fine roots differed significantly among soil depths, and was higher in surface soils than in deeper soils. Moreover, soil pH, soil electrical conductivity and soil nitrogen concentration were higher in surface layers than deeper layers. Therefore, we suggest that the subalpine Abies community has a nutrient acquisition strategy that allows uptake of more nutrients near the surface in shallow soils due to the larger investment in biomass and more active metabolism, but not due to phenotypic plasticity in fine root morphology. In addition, we observed that fine root biomass changed with stand development, where specific root length was greater in sapling stands than in older stands.     

Hydraulic lift: Substantial nocturnal water transport between soil layers by Artemisia tridentata roots

Summary Diel soil water potential fluctuations reflected daytime depletion and nocturnal resupply of water in upper soil layers. Transpiration suppression experiments demonstrated that water absorption by roots caused the daytime depletion. The soil water potential data and experimental results suggest that at night water absorbed from moist soil by deeper roots is transported to and lost from roots into drier upper soil layers. The deeper roots appear to absorb and transport water both day and night. Implications for the efficiency of deep roots and water storage, nutrient uptake and water parasitism in upper soil layers are discussed.     

Influence of root density on the critical soil water potential

Estimation of root water uptake in crops is important for making many other agricultural predictions. This estimation often involves two assumptions: (1) that a critical soil water potential exists which is constant for a given combination of soil and crop and which does not depend on root length density, and (2) that the local root water uptake at given soil water potential is proportional to root length density. Recent results of both mathematical modeling and computer tomography show that these assumptions may not be valid when the soil water potential is averaged over a volume of soil containing roots. We tested these assumptions for plants with distinctly different root systems. Root water uptake rates and the critical soil water potential values were determined in several adjacent soil layers for horse bean (Vicia faba) and oat (Avena sativa) grown in lysimeters, and for field-grown cotton (Gossypium L.), maize (Zea mays) and alfalfa (Medicago sativa L.) crops. Root water uptake was calculated from the water balance of each layer in lysimeters. Water uptake rate was proportional to root length density at high soil water potentials, for both horse bean and oat plants, but root water uptake did not depend on root density for horse bean at potentials lower than −25 kPa. We observed a linear dependency of a critical soil water potential on the logarithm of root length density for all plants studied. Soil texture modified the critical water potential values, but not the linearity of the relationship. B E Clothier Section editor     

Microtensiometer technique for in situ measurement of soil matric potential and root water extraction from a sandy soil

The suitability of microtensiometers to measure the spatial variation of soil matric potential and its diurnal change was tested in a pot experiment with pearl millet (Pennisetum americanum [L.] Leeke) in a sandy soil as the soil dried out.The temporal and spatial resolution of this technique allowed precise measurement of soil matric potential and thus estimation of soil water extraction from different compartments as well as from the whole rooting zone. The technique also allowed the measurement of rehydration of plants at night and root water uptake rate per unit soil volume or per unit root length. The precision of determination of root water uptake depended greatly on the accuracy of the estimate of hydraulic conductivity, which was derived from a bare soil and might be different for a cropped soil owing to aggregation induced by the root system. A linear relationship between root length and water uptake was found (r²=0.82), irrespective of variation in soil water content between compartments and despite the variation in root age, xylem differentiation and suberin formation expected to exist between different compartments of the rooting zone. As the experiment was carried out in a range of soil matric potentials between –4 and –30 kPa, drought stress did not occur. Further information at lower soil matric potentials are required, to address questions such as the importance of soil resistance for water uptake, or which portion of the root system has to be stressed to induce hormonal signals to the shoot. The microtensiometer technique can be applied to soil matric potentials up to –80 kPa.     

Use of the root contact concept,an empirical leaf conductance model and pressure-volume curves in simulating crop water relations

A simulation model “DanStress” was developed for studying the integrated effects of soil, crop and climatic conditions on water relations and water use of field grown cereal crops. The root zone was separated into 0.1 m deep layers of topsoil and subsoil. For each layer the water potential at the root surface was calculated by a single root model, and the uptake of water across the root was calculated by a root contact model. Crop transpiration was calculated by Monteith's combination equation for vapour flow. Crop conductance to water vapour transfer for use in Monteith's combination equation was scaled up from an empirical stomatal conductance model used on sunlit and shaded crop surfaces of different crop layers. In the model, transpirational water loss originates from root water uptake and changes in crop water storage. Crop water capacitance, used for describing the water storage, was derived from the slope of pressure-volume (PV) curves of the leaves. PV curves were also used for deriving crop water potential, osmotic potential, and turgor pressure. The model could simulate detailed diurnal soil-crop water relations during a 23-day-drying cycle with time steps of one hour. During the grain filling period in spring barley (Hordeum distichum L.), grown in a sandy soil in the field, measured and predicted values of leaf water and osmotic potential, RWC, and leaf stomatal conductance were compared. Good agreement was obtained between measured and predicted values at different soil water deficits and climatic conditions. In the field, measured and predicted volumetric soil water contents (θ) of topsoil and subsoil layers were also compared during a drying cycle. Predicted and measured θ-values as a function of soil water deficits were similar suggesting that the root contact model approach was valid. From the investigation we concluded: (I) a model, which takes the degree of contact between root surface and soil water into account, can be used in sandy soil for calculation of root water uptake, so that the root conductance during soil water depletion only varies by the degree of contact; (II) crop conductance, used for calculation of crop transpiration, can be scaled up from an empirical single leaf stomatal conductance model controlled by the level of leaf water potential and micrometeorological conditions; (III) PV curves are usable for describing crop water status including crop water storage.     

The effect of the nutrient intensity and buffering power of a soil,and the absorbing power,size and root hairs of a root,on nutrient absorption by diffusion

Summary A portion of a single plant root is treated as an absorbing cylindrical sink to which nutrients move by diffusion. Assuming that the rate of uptake of nutrient is proportional to its concentration at the root surface, and that the nutrient, though reacting with the solid, moves only through the soil solution, standard diffusion equations are used to calculate the effect of soil and plant characteristics on the rate of uptake. The treatment is applicable to phosphorus and potassium. Among soil properties uptake should increase directly with the soil solution concentration. It should also increase, but only slowly, with increasing buffering power. It increases with increasing soil moisture. Among plant characteristics, uptake should increase with the root absorbing power until diffusion through the soil becomes limiting. Absorption by unit surface area of root increases as the root radius decreases. A root hair is shown to interfere quickly with the uptake of adjacent hairs. The hairs increase absorption by the root because they can exploit rapidly the soil between the hairs, and they have the effect of extending the effective root surface to their tips.     

Leaf and root growth dynamics in Eucalyptus globulus seedlings grown in drying soil

Summary Seedlings of Eucalyptus globulus growing in soil columns were subjected to a 24 day soil drying treatment. Water and solute potentials of both young expanding and fully expanded leaves declined under reduced soil water availability, while slightly higher turgor was sustained by the fully expanded leaves. Although leaf area of unwatered seedlings was smaller, the corresponding leaf dry weight was quite similar to that of well-watered seedlings. Soon after rewatering, leaf area of plants experiencing water shortage was comparable to that of well-watered plants. It seems that a difference in wall properties between juvenile and mature leaves allows for an effective pattern of water use by eucalypt plants growing in drying soil. Some stomatal opening is sustained and therefore, presumably, some carbon may be fixed, keeping the carbon balance of the whole plant positive, and allowing a continuous cell division despite the limited water supply. The highest root density of both well-watered and unwatered plants was found in the upper soil layers. However, root growth of unwatered seedlings was gradually increased in the deeper soil layers, where thicker root apices and higher soil water depletion rates per unit root length were recorded. As a consequence, root absorbing surface area was as large in unwatered plants as in well-watered plants.     

Water Movement Through Plant Roots

Mathematical analysis of the hydraulics of water movement throughplant roots, in terms of radial and axial resistances, has ledto equations which provide new insights into the effects ofthe component resistan ces on water uptake by and movement throughindividual roots and root systems. The ratio of axial to radialresistance determines the optimum length of a root and its totalresistance to water movement. The equations permit direct calculationsof the plant water potentials necessary, at the base of theplant, to sustain given flow rates through root systems withgiven characteristics. Lateral spacing and the resistance ofindividual laterals are the dominant factors determining totalflux per unit area into a root. When soil water potential increases with depth (surface layersdrier) root resistance tends to decrease with increasing flowrate; the reverse occurs when the surface is wetter than thelower layers. Calculated patterns of water movement into andthrough roots, in relation to soil water potential and flowrate through the root, indicate efflux from root to soil undercertain conditions. This is considered to reflect reality, althoughthe fluxes are probably transient or intermittent. The equations presented should be combined with equations describingwater movement through soil to define the behaviour of the wholeroot-soil system adequately.     

膜下滴灌下土壤深层水分对棉花根系生理及叶片光合特性的调节效应

在新疆气候生态条件下,以土柱栽培棉花（新陆早13号）为试材,通过人工改变播种前60 cm以下土壤含水量,设计有深层水和无深层水处理,并采用膜下滴灌控制生育期间耕层土壤含水量［分别为田间相对持水量的70%（±5%）和55%（±5%）］,探讨土壤深层水分对棉花根系生理及叶片光合特性的影响.结果表明：深层水增强了棉花根系SOD活性和根系活力,提高了植株对土壤深层水的利用率,提高了叶片水势、叶绿素含量、净光合速率和植株光合物质累积量,最终获得了较高的产量和水分利用效率.在有深层水条件下,棉花生育期间耕层水分为55%处理的中下层根系衰老慢、根系活力增强,在一定程度上弥补了生育期间水分亏缺对叶片光合功能的负面效应,但其产量仍显著低于70%处理,而水分利用效率与70%处理无明显差异.因此,在膜下滴灌棉花水分管理中,播种前应重视冬春储备灌,增加土壤深层的贮水量,并通过协调关键栽培技术、适度减少滴水量或延长滴水周期,充分挖掘膜下滴灌节水增产潜力.     

Growth and morphology of eucalypt seedling-roots, in relation to soil strength arising from compaction

Information on the response of root growth and morphology to soil strength is useful for testing suitability of existing and new tillage methods and/or for selecting plants suitable for a specific site with or without tillage. Although there is extensive published information on the root growth-soil strength relationships for annual agricultural plants, such information is scarce for woody, perennial tree species. The purpose of this study is to examine growth and morphology of the root systems of 17-day-old eucalypt seedlings with respect to variation in soil strength. Soil strength in this study was varied by compaction of a well-aggregated clay soil to bulk densities of 0.7–1.0 Mg m^-3 whilst maintaining adequate water availability and aeration for plant growth. Lengths and tip-diameters of primary and lateral roots were measured on the excavated root systems of seedlings.With increase in bulk density and also soil strength (expressed as penetrometer resistance), total length of primary and lateral roots decreased. There were 71 and 31% reduction in the lengths of primary and lateral roots respectively with an increase in penetrometer resistance from 0.4 to 4.2 MPa. This indicated primary roots to be more sensitive to high soil strength than the lateral roots. Average length of lateral roots and diameters of both primary and lateral root tips increased with an increase in soil strength as well. There was greater abundance of lateral roots (no. of lateral roots per unit length of primary root) and root hairs with increased soil strength. The observed root behaviour to variable soil strength is discussed in the context of compensatory growth of roots and overall growth of plants.