Growth of a root system described as diffusion. II. Numerical model and application

In simulation models for water movement and nutrient transport, uptake of water and nutrients by roots forms an essential part. As roots are spatially distributed, prediction of root growth and root distribution is crucial for modelling water and nutrient uptake. In a preceding paper, De Willigen et al. (2002; Plant and Soil 240, 225–234) presented an analytical solution for describing root length density distribution as a diffusion-type process. In the current paper, we present a numerical model that does the same, but which is more flexible with respect to where root input can occur. We show that the diffusion-type root growth model can describe well observed rooting patterns. We used rooting patterns for different types of crops: maize, gladiolus, eastern white cedar, and tomato. For maize, we used data for two different types of fertiliser application: broadcast and row application. In case of row application, roots extend more vertically than horizontally with respect to the broadcast application situation. This is reflected in a larger ratio of diffusion coefficients in vertical versus horizontal direction. For tomato, we considered tomatoes grown on an artificial rooting medium, i.e. rockwool. We have shown that, in principle, the model can be extended by including reduction functions on the diffusion coefficient in order to account for environmental conditions.     

青杨人工林根系生物量、表面积和根长密度变化

在植物生长季节,采用钻取土芯法对秦岭北坡50年生青杨人工林根径≤2 mm和2～5 mm根系的生物量、表面积和根长密度进行测定.结果表明：在青杨人工林根系(＜5 mm)中,根径≤2 mm根系占总生物量的77.8%,2～5 mm根系仅占22.2%;根径≤2 mm根系表面积和根长密度占根系总量的97%以上,而根径2～5 mm根系不足3%.随着土层的加深,根径≤2 mm根系生物量、表面积和根长密度数量减少,根径2～5 mm根系生物量、表面积和根长密度最小值均分布在20～30 cm土层.≤2 mm根系生物量、表面积和根长密度与土壤有机质、有效氮呈极显著相关,而根径2～5 mm根系的相关性不显著.     

Simulation model of soil compaction and root growth

Soil compaction is a widespread cause of reduced plant productivity. If the effects of soil compaction on plant growth are to be reproduced in simulation models, then the processes through which compaction reduces root elongation must be expressed mathematically and then tested against experimental data. The mathematical theory by which these processes may be represented is given in the accompanying article. In this article, the behavior of a simulation model based on this theory is tested against data for root growth and soil gas concentration recorded from soil columns of which the middle layers were compacted to different bulk densities. The model was able to reproduce the failure of the root system to penetrate the compacted middle layer within the period of the experiment when bulk density exceeded 1.55 Mg m^-3. The model also reproduced decreases in O₂ concentrations, and increases in CO₂ concentrations, in the atmospheres of the compacted layer and of the uncompacted layer below it as bulk density of the compacted layer increased. The simulated time course of O₂ and nutrient uptake and of O₂ concentrations in the compacted layer at different depths is presented and its consistency with experimental findings is examined. As part of a larger ecosystem model, this model will be useful in estimating site-specific effects of soil compaction on carbon cycling in agroecosystems.     

Tillage and N fertilization effects on maize root growth and root:shoot ratio

Two methods for estimating the size of the maize (Zea mays l.) root system from soil cores taken in the field were compared. The spatially weighed block method of estimation accounted for variation in root density by using 18 samples per plant which varied in distance from plant and soil depth. This method was compared to an estimation which averaged all of the 18 samples together. Both methods gave surprisingly similar estimates for total root growth. Increased root growth in the surface soil layers, due to tillage and N fertilization, did not impact on the estimation of total root growth. Total root length remained unchanged or increased with N fertilization, while root weight remained the same or decreased. Root mass per length decreased with N fertilization. The estimated size of the root system was used to calculate root:shoot weight ratios. The largest root:shoot ratio was found in the vegetative stage and decreased throughout the rest of the season. In this field experiment, the estimated size of the root system at 8 weeks after planting was not significantly different from the size at silking or harvest. Nitrogen fertilization significantly decreased the root:shoot weight ratio. However, tillage did not significantly change the ratio.     

Seasonal dynamics of fine root biomass,root length density,specific root length,and soil resource availability in a Larix gmelinii plantation

Fine root tumover is a major pathway for carbon and nutrient cycling in terrestrial ecosystems and is most likely sensitive to many global change factors.Despite the importance of fine root turnover in plant C allocation and nutrient cycling dynamics and the tremendous research efforts in the past,our understanding of it remains limited.This is because the dynamics processes associated with soil resources availability are still poorly understood.Soil moisture,temperature,and available nitrogen are the most important soil characteristics that impact fine root growth and mortality at both the individual root branch and at the ecosystem level.In temperate forest ecosystems,seasonal changes of soil resource availability will alter the pattern of carbon allocation to belowground.Therefore,fine root biomass,root length density(RLD)and specific root length(SRL)vary during the growing season.Studying seasonal changes of fine root biomass,RLD,and SRL associated with soil resource availability will help us understand the mechanistic controls of carbon to fine root longevity and turnover.The objective of this study was to understand whether seasonal variations of fine root biomass,RLD and SRL were associated with soil resource availability,such as moisture,temperature,and nitrogen,and to understand how these soil components impact fine root dynamics in Larix gmelinii plantation.We used a soil coring method to obtain fine root samples(≤2 mm in diameter)every month from Mav to October in 2002 from a 17-year-old L.gmelinii plantation in Maoershan Experiment Station,Northeast Forestry University,China.Seventy-two soil cores(inside diameter 60 mm;depth intervals:0-10 cm,10-20 cm,20-30 cm)were sampled randomly from three replicates 25 m×30 m plots to estimate fine root biomass(live and dead),and calculate RLD and SRL.Soil moisture,temperature,and nitrogen(ammonia and nitrates)at three depth intervals were also analyzed in these plots.Results showed that the average standing fine root biomass(live (32.2 g.m-2.a-1)in the middle(10-20 cm)and deep layer (20-30cm),respectively.Live and dead fine root biomass was the highest from May to July and in September,but lower in August and October.The live fine root biomass decreased and dead biomass increased during the growing soil layer.RLD and SRL in May were the highestthe other months,and RLD was the lowest in Septemberdynamics of fine root biomass,RLD,and SRL showed a close relationship with changes in soil moisture,temperature,and nitrogen availability.To a lesser extent,the temperature could be determined by regression analysis.Fine roots in the upper soil layer have a function of absorbing moisture and nutrients,while the main function of deeper soil may be moisture uptake rather than nutrient acquisition.Therefore,carbon allocation to roots in the upper soil layer and deeper soil layer was different.Multiple regression analysis showed that variation in soil resource availability could explain 71-73% of the seasonal variation of RLD and SRL and 58% of the variation in fine root biomass.These results suggested a greater metabolic activity of fine roots living in soil with higher resource availability,which resulted in an increased allocation of carbohydrate to these roots,but a lower allocation of carbohydrate to those in soil with lower resource availability.     

水曲柳根系生物量、比根长和根长密度的分布格局

采用连续钻取土芯法在生长季内对东北林业大学帽儿山实验林场17年生水曲柳人工林根系取样,研究水曲柳不同直径根系现存生物量、比根长和根长密度及垂直分布状况.结果表明,水曲柳人工林根系总生物量为1 637.6 g·m^-2,其中活根生物量占85%,死根占15%.在活根生物量当中,粗根(直径5～30 mm)占的比例最高（69.95%）,其次为活细根（直径<1 mm,13.53%）,小根(1～2 mm)和中等直径的根(2～5 mm)比例较小（分别为7.21%和9.31%）.直径<1 mm活细根的比根长为32.20 m·g^-1,直径5～30 mm粗根的比根长为0.08 m·g^-1.单位面积上活根的总长度为6 602.54 m·m^-2,其中直径<1 mm的细根占92.43%,其它直径等级则不到活根总长度的8%.直径<1 mm的细根生物量与根长密度具显著线性关系（R²=0.923）,但与比根长无显著相关关系（R²=0.134）.     

滨岸不同植物配置模式的根系空间分布特征

崇明岛位于长江河口,是世界上最大的冲积岛。滨岸植物配置模式对防止侵蚀、坍塌等具有不同的作用。以崇明岛南岸4种不同的植物配置模式:芦苇(Phragmites australis)-海三棱藨草(Scirpus mariqueter)模式(PSM)、池杉(Taxodium ascendens)-芦苇-海三棱藨草模式(TAPSM)、杂交柳(Salix matsudana×alba)-芦苇-海三棱藨草模式(SPSM)及落羽杉(Taxodium distichum)-芦苇-海三棱藨草模式(TDPSM)为对象,对不同植物配置模式在低、中、高3个潮位根系空间分布进行了调查和分析。结果表明:(1)4种模式中0-40cm土层内平均总根长最大的为SPSM模式,其值为137.0cm/cm2,平均总根长最小的为TAPSM模式(91.4cm/cm2);在3种乔木增配模式中,草本植物根长占总根长比例达94.6%-98.1%。(2)除SPSM模式外,其他3种植物配置模式根长密度均随土层加深而减小,这3种模式根长密度最大的土层皆为0-10cm土层,分别为各自最底层根长密度的15.1倍(PSM)、4.9倍(TDPSM)和2.0倍(TAPSM);SPSM模式在10-20cm土层根长密度最大。(3)在所有4种模式中,直径Φ0.1mm的微细根对总根长密度的贡献均为最大,比例从74.7%到81.7%,其次为直径0.1mm≤Φ1mm的细根,直径Φ≥5mm的大根极少。(4)秩和检验显示,4种模式在低、中、高3个潮位根长密度的差异并不一致。根系能够提高土壤抗侵蚀能力,研究4种模式根系空间分布特征,可以为崇明岛滨岸植物配置,建设抗蚀护滩植被带提供科学依据。     

不同林龄胡杨克隆繁殖根系分布特征及其构型

以中龄林和成熟林胡杨为研究对象,采用挖剖面和根窗的方法,研究胡杨繁殖根系分布、根系构型,以及胡杨根蘖与繁殖根系构型之间的关系。结果表明:(1)细根(d<2 mm)的根长密度、根表面积密度,随深度增加呈现指数函数分布;(2)中龄林细根的根长密度、根表面积密度在0—90 cm各层都是显著大于成熟林的对应指标(P<0.05),成熟林的中等粗根(5 mm0.05),且两种林龄的一级侧根数、分枝角度亦无显著差异(P>0.05);(5)对比两种林龄不同根序上的根蘖芽发现,二级根上不定芽个数均是同组一级根上不定芽个数的3—4倍;基于以上对胡杨根系的功能权衡的分析,得出:细根对胡杨根系构型有重要的影响,在胡杨根系功能权衡中扮演重要角色。     

大田期烟草根系构型参数的动态变化

采用“根箱”法研究了大田期烟草根系构型参数在时间、空间上的动态变化.结果表明, 烟草2级侧根总长度的增加明显大于1级侧根,根快速增长期分别出现在移栽后26～40和56～70 d.栽后57 d(打顶)前,烟草根系的分枝密度表现为10～20＞0～10＞20～30＞30～40 cm,此后随土层的加深呈递减趋势.在主根上,以7～21 cm范围内的分枝密度最大.打顶前,比根长随着入土深度的加深而递增;栽后90 d,比根长随土层的加深而递减.1级侧根根长密度在0～10 cm土层内的变化呈“S”型曲线,10～20、20～30和30～40 cm内表现为双峰曲线;2级侧根根长密度随生育期的进程而增加,其中0～10 cm根长密度的变化为“S”曲线,其它层次为单峰曲线.     

Statistical modeling of nitrogen-dependent modulation of root system architecture in Arabidopsis thaliana

Plant root development is strongly affected by nutrient availability. Despite the importance of structure and function of roots in nutrient acquisition,statistical modeling approaches to evaluate dynamic and temporal modulations of root system architecture in response to nutrient availability have remained as widely open and exploratory areas in root biology. In this study,we developed a statistical modeling approach to investigate modulations of root system architecture in response to nitrogen availability. Mathematical models were designed for quantitative assessment of root growth and root branching phenotypes and their dynamic relationships based on hierarchical con figuration of primary and lateral roots formulating the fishbone-shaped root system architecture in Arabidopsis thaliana. Time-series datasets reporting dynamic changes in root developmental traits on different nitrate or ammonium concentrations were generated for statistical analyses. Regression analyses unraveled key parameters associated with:(i) inhibition of primary root growth under nitrogen limitation or on ammonium;(ii) rapid progression of lateral root emergence in response to ammonium; and(iii) inhibition of lateral root elongation in the presence of excess nitrate or ammonium. This study provides a statistical framework for interpreting dynamic modulation of root system architecture,supported by metaanalysis of datasets displaying morphological responses of roots to diverse nitrogen supplies.     

Effect of cyclic wetting and drying of a soil on root hair growth of maize roots

The objective of this study was to investigate the effect of cyclic soil wetting and drying on maize (Zea mays L.) root hair growth. Three soils, Chalmers silty clay loam (Typic Haplaquolls), Raub silt loam (Aquic Argiudolls) and Aubbeenaubbee sandy loam (Aric Ochraqualfs) and two soil moisture contents, −175 (M₀) and −7.5 kPa (M₁), were used to study root hair growth in a controlled-climate chamber. Increasing soil moisture after 7d from M₀ and M₁ resulted in a cessation of root hair growth behind the root cap while drying the soil after 7d from M₁ and M₀ promoted root hair growth on new but not old or existing roots. By maintaining liquid continuity under cyclic wetting and drying of a soil, root hairs may be of far greater significance to the nutrition of the plant than originally thought. Journal Paper No. 11023, Purdue Univ. Agric. Exp. Stn., W. Lafayette, IN 47907. Contribution from the Dep. of Agron.     

Scaling of root length density of maize in the field profile

Root length density is an important parameter in crop growth simulation and in evaluating consequences of root pattern on crop water and nutrient uptake. In this study, a scaling model was presented for estimating the profile distribution of root length density of maize (Zea mays L.). The model inputs are root length data of a reference profile and bulk densities of soil layers, as well as root length data in the first soil layer of a field profile to be investigated. Using the root length data of 10 soil profiles investigated over 2 years, the model was examined. The results show that the proposed scaling approach is effective in estimating the root length density of each layer of soil in the field profile. The relative root mean square error (RRMSE) of the developed scaling model was 25.28%, while that of the traditional exponential model was 39.53%. The scaling approach would facilitate determination of heterogeneous distributions of root length densities in the field.     

Seasonal dynamics of fine root biomass, root length density, specific root length, and soil resource availability in a Larix gmelinii plantation

Fine root turnover is a major pathway for carbon and nutrient cycling in terrestrial ecosystems and is most likely sensitive to many global change factors. Despite the importance of fine root turnover in plant C allocation and nutrient cycling dynamics and the tremendous research efforts in the past, our understanding of it remains limited. This is because the dynamics processes associated with soil resources availability are still poorly understood. Soil moisture, temperature, and available nitrogen are the most important soil characteristics that impact fine root growth and mortality at both the individual root branch and at the ecosystem level. In temperate forest ecosystems, seasonal changes of soil resource availability will alter the pattern of carbon allocation to belowground. Therefore, fine root biomass, root length density (RLD) and specific root length (SRL) vary during the growing season. Studying seasonal changes of fine root biomass, RLD, and SRL associated with soil resource availability will help us understand the mechanistic controls of carbon to fine root longevity and turnover. The objective of this study was to understand whether seasonal variations of fine root biomass, RLD and SRL were associated with soil resource availability, such as moisture, temperature, and nitrogen, and to understand how these soil components impact fine root dynamics in Larix gmelinii plantation. We used a soil coring method to obtain fine root samples (⩽2 mm in diameter) every month from May to October in 2002 from a 17-year-old L. gmelinii plantation in Maoershan Experiment Station, Northeast Forestry University, China. Seventy-two soil cores (inside diameter 60 mm; depth intervals: 0–10 cm, 10–20 cm, 20–30 cm) were sampled randomly from three replicates 25 m × 30 m plots to estimate fine root biomass (live and dead), and calculate RLD and SRL. Soil moisture, temperature, and nitrogen (ammonia and nitrates) at three depth intervals were also analyzed in these plots. Results showed that the average standing fine root biomass (live and dead) was 189.1 g·m⁻²·a⁻¹, 50% (95.4 g·m⁻²·a⁻¹) in the surface soil layer (0–10 cm), 33% (61.5 g·m⁻²·a⁻¹), 17% (32.2 g·m⁻²·a⁻¹) in the middle (10–20 cm) and deep layer (20–30cm), respectively. Live and dead fine root biomass was the highest from May to July and in September, but lower in August and October. The live fine root biomass decreased and dead biomass increased during the growing season. Mean RLD (7,411.56 m·m⁻³·a⁻¹) and SRL (10.83 m·g⁻¹·a⁻¹) in the surface layer were higher than RLD (1 474.68 m·m⁻³·a⁻¹) and SRL (8.56 m·g⁻¹·a⁻¹) in the deep soil layer. RLD and SRL in May were the highest (10 621.45 m·m⁻³ and 14.83m·g⁻¹) compared with those in the other months, and RLD was the lowest in September (2 198.20 m·m⁻³) and SRL in October (3.77 m·g⁻¹). Seasonal dynamics of fine root biomass, RLD, and SRL showed a close relationship with changes in soil moisture, temperature, and nitrogen availability. To a lesser extent, the temperature could be determined by regression analysis. Fine roots in the upper soil layer have a function of absorbing moisture and nutrients, while the main function of deeper soil may be moisture uptake rather than nutrient acquisition. Therefore, carbon allocation to roots in the upper soil layer and deeper soil layer was different. Multiple regression analysis showed that variation in soil resource availability could explain 71–73% of the seasonal variation of RLD and SRL and 58% of the variation in fine root biomass. These results suggested a greater metabolic activity of fine roots living in soil with higher resource availability, which resulted in an increased allocation of carbohydrate to these roots, but a lower allocation of carbohydrate to those in soil with lower resource availability. __________ Translated from Acta Phytoecologica Sinica, 2005, 29(3): 403–410 [译自: 植物生态学报, 2005, 29(3): 403–410]     

Comparison of tomato root distributions by minirhizotron and destructive sampling

Calibration of minirhizotron data against root length density (RLD) was carried out in a field trial where three drip irrigation depths: surface (R0) and subsurface, 0.20 m (RI) and 0.40 m depth (RII) and two processing tomato cultivars: `Brigade' (CI) and `H3044' (CII) were imposed. For each treatment three minirhizotron tubes were located at 10, 37.5 and 75 cm of the way from one plant row to the next. Roots intersecting the minirizotrons walls were expressed as root length intensity (L _a) and number of roots per unit of minirhizotron wall area (N _ra). Root length density (RLD) was calculated from core samples taken for each minirhizotron tube at two locations: near the top of the minirhizotron (BI) and 15 cm apart from it, facing the minirhizotron wall opposite the plant row (BII). Minirhizotron data were regressed against RLD obtained at BI and BII and with their respective means. The results show that for all the situations studied, better correlations were obtained when RLD was regressed with L _a than with N _ra. Also was evident that the relationship between L _a and RLD was strongly influenced by the location of soil coring. RLD was correlated with L _a trough linear and cubic equations, having the last ones higher determination coefficients. For instance at 10 cm from the plant row when values from the top layer (0–40 cm) were analysed separately, L _a was significantly regressed with RLD measured at BII and described by the equations: RLD = 0.5448 + 0.0071 L _a (R ² = 0.51) and RLD = 0.4823 + 0.0074L _a + 8×10^–5 L _a ² – 5×10^–7 L _a ³ (R ² = 0.61). Under the 40 cm depth the highest coefficients of determination for the linear and cubic equations were respectively 0.47 and 0.88, found when L _a was regressed with RLD measured at BI. For minirhizotrons located at 75 cm from the plant row and for location BI it was possible to analyse jointly data from all depths with coefficients of determination of 0.45 and 0.59 for the linear and cubic equations respectively.     

Modelling the branching growth fractal pattern of the maize root system

Using the technique of L-systems, a growth model of the maize root system is developed. From the observation of the root systems developed under various soil density in eight root boxes, a spatial hierarchy of growth rules was extracted. The rules were divided into three categories: a meta-rule for describing features of an entire root system, a branching growth rule and a tip elongation rule. Some variations in the entire features of the root system, such as the outline and the root distribution, were confirmed by observation, and then the respective meta-rules were re-defined. The branching properties of first- and second-order lateral roots were statistically almost equal in the observations, and this lead us to set up a single stochastic branching growth rule. Tip elongation movement was not observed here; its rule had to be assumed by reference to data in the literature. A single set of branching growth and tip elongation rules were coupled with the respective meta-rules corresponding to the root samples observed, where a small scale rule was loosely governed by a large scale rule. Computer simulations offered optimized drawings of the observed root systems, and they also reproduced a typical anisotropic power distribution of roots similar to those observed.     

Significance of temperature and precipitation for maize root distribution in the field

Measurements of maize (Zea mays L.) root distribution with depth in the soil for nine years in a 11-year period revealed significantly different distribution patterns. Weather variations were expected to be related to the amount of roots found in each of the five 15-cm soil layers. The objective of this study was to attempt to explain root distribution in the field on the basis of precipitation and temperature data for the nine growing seasons. Growing degree days (GDD), accumulated in daily increments from planting to silking, were used to describe temperature effects. Correlations were calculated for weekly time increments of GDD versus root length densities at silking in all soil layers. Root length density below 30 cm was correlated (P=0.05) with GDD for two weeks following planting, whereas no relation was found between GDD and root length density in the topsoil. Amount of precipitation was accumulated in weekly increments from silking to planting and correlated with root length density in the soil layers at silking. This procedure evaluated the relation between precipitation and root growth during the vegetative growth period. Root length density in the 0 to 15 cm layer was found to be related significantly (P=0.05) to precipitation. The period 3 weeks prior silking gave the highest correlation coefficient (r=0.79). Journal Paper no. 10,629. Purdue Univ. Agric. Exp. Stn., W. Lafayette, IN 47907. Contribution from the Dep. of Agronomy. The research was supported in part by BARD, United States-Israel Binational Agricultural Research and Development Fund, and Deutsche Forschungsgemeinschaft.     

Nutrient uptake relationship to root characteristics of rice

Data on root parameters and distribution are important for an improved understanding of the factors influencing nutrient uptake by a crop. Therefore, a study was conducted on a Crowley silt loam at the Rice Research and Extension Center near Stuttgart, Arkansas to measure root growth and N, P and K uptake by three rice (Oryza sativa L.) cultivars at active tillering (36 days after emergence (DAE)), maximum tillering (41 DAE), 1.25 cm internode elongation (55 DAE), booting (77 DAE) and heading (88 DAE). Soil-root core samples were taken to a depth of 40 cm after plant samples were removed, sectioned into 5 cm intervals, roots were washed from soil and root lengths, dry weights and radii were measured. Root parameters were significantly affected by the soil depth × growth stage interaction. In addition, only root radius was affected by cultivar. At the 0- to 5-cm soil depth, root length density ranged from 38 to 93 cm cm^-3 throughout the growing season and decreased with depth to about 2 cm cm^-3 in the 35- to 40-cm depth increment. The increase in root length measured with each succeeding growth stage in each soil horizon also resulted in increased root surface area, hence providing more exposed area for nutrient uptake. About 90% of the total root length was found in the 0- to 20-cm soil depth throughout the season. Average root radius measured in the 0- to 5-cm and 35- to 40-cm depth increments ranged from 0.012 to 0.013 cm and 0.004 to 0.005 cm, respectively throughout the season. Total nutrient uptake by rice differed among cultivars only during vegetative growth. Differences in total nutrient uptake among the cultivars in the field appear to be related to absorption kinetics of the cultivars measured in a growth chamber study. Published with permission of the Arkansas Agricultural Experiment Station.     

Root growth and distribution of two short-season rice genotypes

Root growth dynamics of lowland rice (Oryza sativa L.) throughout the growing season are poorly understood. A field experiment was conducted in 1987 to compare root growth and distribution of two rice genotypes at two Arkansas locations on soils with different physical and chemical properties. Two genotypes, Bond and an experimental line (RU8701084), were grown on a Captina silt loam (Typic Fragiudults) at Fayetteville, AR, and on a Crowley silt loam (Typic Albaqualfs) near Stuttgart, Ar. Plots contained minirhizotrons oriented at a 45° angle and extended 55 cm (Captina) and 40 cm (Crowley) vertical to the soil surface. Root measurements were taken several times during the season at specific growth stages. Plant height and tiller number were taken at 9 dates at Fayetteville up to physiological maturity. In general, root length (RL) and root length density (RLD) were greater on the Captina soil. Genotypes at both locations reached maximum root growth rates between active tillering and panicle initiation (PI) and maximum RL by early reproduction. Total RL were similar between genotypes on the Captina. However on the Crowley, the mean RL for Bond between the period of early booting and flood removal was an average of 54% greater than for RU8701084. During early reproductive growth at both locations RL plateaued, but then declined during the grain filling process. There was a trend for RU8701084 to contain a greater percentage of its total RL in the top 20 and 10 cm of soil on the Captina and Crowley, respectively, while Bond tended to be a deeper rooted genotype. Bond had a greater RLD at the 20–30 cm depth increment on the Crowley, which contributed to the greater RL. Less than 15% of the total RL of either genotype was measured below 30 cm on the Crowley. In contrast, nearly 25% of the total RL was found at the 30–40 cm depth increment on the Captina. Results showed that rice root growth varied between soils, that root distribution patterns differed between genotypes, and that patterns of root growth changed with changes in plant development.