The mutual interference of spruce canopy structural elements

The drag force on fourteen three-prong spruce shoots (Picea rubens) has been measured in a wind tunnel in velocities ranging from 0.4 to 4.5 m s^?1. The influence of wind velocity and shoot needle density on momentum transfer and the mutual interference to momentum transfer are evaluated.The influence of the shoot needle density (ranging from 0.6 to 1.7) on momentum transfer is velocity dependent. The shoot needle density does not influence the momentum transfer to the shoot when the wind velocity is less than about 1.5 m s^?1. However, a slight trend of increased momentum transfer to the shoot with decreased shoot needle density was found for wind velocities between 1.5 and 4.5 m s^?1. This trend is not statistically significant.The shelter factor, a measure of the mutual interference to momentum transfer to the shoot structure, is shown to be dependent on the model used to describe the flow around and through the shoot. This suggests that any apparent velocity dependence of the shelter factor may actually be due to a change in flow conditions. It is concluded that: (1) the needles are the vegetative component involved in mutual interference within the shoot for wind speeds between 0.4 and 1.5 ms^?1, and (2) the shoots themselves are the vegetative component involved in mutual interference within a shoot array for wind speeds between 1.5 and 4.5 ms^?1. The shelter factor at the low wind speeds is estimated to be 2.1 The shelter factor at the higher wind speeds should be based on interference between shoots and not between needles within a single shoot.     

Modelization of the mercury fluxes at the air-sea interface

Aqueous and atmospheric Hg° concentrations for remote marine areas such as the equatorial Pacific Ocean and for coastal seas such as the North Sea and the Scheldt Estuary are discussed. Biological processes seem to be at the origin of the supersaturated Hg° concentrations in the water. On the other hand, transfer velocities across the air-sea interface were calculated with a classical shear turbulence model and with a wave breaking model. With these data, Hg° fluxes from the sea to the atmosphere were calculated: in the Pacific Ocean they range from 0.43 to 6.5 μg g Hg.m^?2. yr^?1 at a wind speed of 2.8 m.s^?1 and from 10.3 to 156 μg Hg.m^?2 yr^?1 at a wind speed of 54 m.s^?1, but they are still higher when wave breaking is considered (from 11 to 168 μg Hg.m^?2.yr^?1). These transfer fluxes are an order of magnitude higher in the Scheldt Estuary.     

Light intensity selectively influences the distribution and further redistribution of macro- and micronutrients in hydroponically grown wheat (Triticum aestivum L.)

Investigations were focused on light effects on allocation of root-borne macronutrients (calcium, magnesium and potassium) and micronutrients (iron, manganese, zinc and copper) in roots, shoots and harvested grains of wheat (Triticum aestivum L.). Plants were exposed to low (100 μmol photons m^?2 s^?1) or high light (380 μmol photons m^?2 s^?1). High light stimulated both root and shoot growth. While the total contents per plant of some nutrients were markedly higher (calcium and potassium) or lower (copper) under high light, no major differences were observed for other nutrients. The distribution of nutrients and the further redistribution within the shoot were influenced by the light intensity in an element-specific manner. Nutrients were selectively directed to the leaves of the main shoot (low light) or to the tillers (high light). The quality of the harvested grains was also affected by the light intensity.     

Effectiveness of Fly Ash and Polyacrylamide as a Sand-Fixing Agent for Wind Erosion Control

Searching for an effective and economical sand stabilization measure has an important significance in wind erosion control. Wind tunnel experiments were conducted to evaluate the sand-fixing effect of fly ash (FA) at three different application rates (10, 20, and 30?% (w/w) soil). The additional effect of polyacrylamide (PAM) was also studied under two different application rates (0.05 and 0.1?% (w/w) soil) on the basis of the optimum FA usage. The results indicated that the utilization of FA increased the threshold wind speed of the treated soil significantly, which was further increased by the addition of PAM. The soil treated with 20?% FA could most effectively withstand the pure wind with a wind speed of 8?m?s^?1 for 10?min, while only the slightest wind erosion occurred after exposure to the sand-carrying wind with a wind speed of 8?m?s^?1 for 10?min. However, moderate wind erosion occurred after exposure to both the pure wind and the sand-carrying wind with a wind speed of 14?m?s^?1 for 10?min, respectively, and there was a decline in the wind erosion rate with the increase of FA application rate. The soil treated with 20?% FA and 0.05 or 0.1?% PAM could effectively withstand the pure wind with a wind speed of 14?m?s^?1 for 30?min, while only the slightest wind erosion occurred after exposure to the sand-carrying wind with a wind speed of 14?m?s^?1 for 30?min. The combination of a 20?% FA and 0.05?% PAM application rate is recommended to give effective and economical wind erosion protection.     

Adjustment of mineral ratio and composition in rice genotypes under varied salinity regimes

A study of the salinity effect on mineral content in rice genotypes differing in salt tolerance was conducted in a factorial Completely Randomized Design experiment. The results indicated that the genotypes developed differently by mutation conventional breeding. NS15 represented as salt-sensitive, Pokkali was included as an internationally salt-tolerant check and Iratom24 was moderately tolerant. The content of Na⁺, Ca²⁺, Mg²⁺ and Cl^? followed an increasing pattern in roots and shoots of all the rice genotypes due to increasing salinity levels except Ca²⁺ and Mg²⁺ in the root. However, the concentration of K⁺ showed more or less an increasing pattern in root and a decreasing pattern in shoot. The concentration of Na⁺ and Ca²⁺ sharply increased with increasing the salinity levels in both the roots and shoots of NS15. The concentration of K⁺ sharply decreased in shoot and increased in the root of susceptible genotype NS15 with increasing salinity over 6 dS m^?1 salinity levels, where the transformation of K⁺ from root to shoot was disrupted by Na⁺. The Cl^? content sharply increased with increasing salinity in the root of NS15 as compared to shoot. The effect of different salinity levels on Na⁺/K⁺ ratio in the shoots of the selected rice genotypes sharply increased in susceptible genotype NS15 as compared to the other genotypes.     

Measurement of ammonia emission after liquid manure application: II. Comparison of the wind tunnel and the IHF method under field conditions

A wind tunnel was constructed for measurement of NH₃^? N volatilization after application of liquid manure. It combines the advantages of micrometeorological field methods with those of customary wind tunnel methods. The wind tunnel, as specified in part I (Braschkat et al., 1993), is characterized by:

• -the same (or higher) reliability of results as in field measurement by the IHF method (Integrated Horizontal Flux, also known as Mass Balance)

• -universal applicability independent of topographical conditions

• -a higher temporal and spatial density of experiments compared to micrometeorological methods

The reliability of the NH₃^? N measurements obtained by the wind tunnel was tested under controlled conditions in a greenhouse (calibration) as well as under field conditions by direct comparison with the IHF method. The rate of recovery of NH₃^? N inserted into the wind tunnel is almost 100 % (± 3 %). In field experiments, no differences between the measurements of the wind tunnel and the IHF method were observed under standard conditions. The higher precision in the determination of the NH₃^? N background concentration with the wind tunnel resulted in a higher accuracy in measurements of the time course of NH₃^? N emissions. Intensity and timing of precipitation may cause an overestimation of NH₃^? N volatilization by the wind tunnel. In contrast to the IHF method. NH₃^? N emissions can be measured with the wind tunnel at wind speeds below 1 m s^?1 at 2 m height. No reliable data were obtained with the wind tunnel at wind speeds below 0.3 m s^?1 in 0.3 m height.     

用气象数据估算固定和半固定沙地的起沙速率

Taibus County, Inner Mongolia, China, lies in a farming-pastoral ecotone, where severe wind erosion and various aeolian sand hazards are prevalent and fixed and semi-fixed sand dunes occur frequently. This study was conducted to investigate the relationships between sand transportation rate and wind speed for the fixed and semi-fixed sand dunes based on field measurements. The annual quantity of soil erosion by wind was estimated using meteorological wind data. The results indicated that the sand transportation rate in Taibus County in 2000 was 57.38 kg cm-1 year-1 for the semi-fixed dunes and 4.56 kg cm-1 year-1 for the fixed dunes. The total duration of erosive winds covered 12.5% of the time of the year, and spring posed the highest potential of sand transportation. Wind with low speed (≤17 m s-1) and high frequency plays a dominant role in sand transportation, while strong wind (≥17 m s-1) with low frequency significantly enhanced the sand transportation. Erosive wind speed, directions, and frequency were three crucial dynamic factors influencing sand hazards in the farming-pastoral ecotone. The dominant factors intensifying sand and dust storms in Taibus County might be related to the favorable wind condition in combination with the durable drought, which led to land desertification and vegetation degradation.     

Effect of particle-size distribution on wind erosion rate and soil erodibility

Wind erosion is a serious problem, especially in arid and semi-arid regions. This study was conducted to assess the effects of wind speed as well as soil particle-size distribution on erosion rate (ER) using a wind tunnel. For this purpose, two clay loam soil samples (C2 and C10) in addition to a sandy clay loam (S2) were exposed to different wind velocities of 2, 9 and 18 m s^?1. The result showed that erosion rate increased significantly with increasing wind speeds. In addition, a critical diameter of 0.84 mm for soil particles was supported; for larger particles the changes in erosion rate were negligible. Furthermore, soil erodibility (K) was determined, which for S2, C2 and C10 was 57.73, 10.27 and 1.43, respectively. To predict soil erodibility, a power relationship as K = 3.382 MWD^?1.732 (R ² = 0.99) was established. The results indicated with increasing wind speed, the sensitivity of S2 remained constant, whereas C2 and C10 resisted wind speed. The finding of this research indicates the importance of particle-size distribution on wind erosion rate as well as soil erodibility.     

INTERACTION OF MOLYBDENUM AND PHOSPHORUS SUPPLY ON UPTAKE AND TRANSLOCATION OF PHOSPHORUS AND MOLYBDENUM BY BRASSICA NAPUS

A hydroponic trial was conducted to assess interaction of molybdenum (Mo) and phosphorus (P) on uptake and translocation of P and Mo by Brassica napus. Molybdenum was applied at four rates (0, 0.01, 0.1 and 1 mg L^?1) and P at three rates (1, 30, and 90 mg L^?1) in nutrient solution. The results indicated that P increased shoot growth and 0.01 mg L^?1 Mo improved the growth of shoots and roots. Molybdenum increased shoot P uptake and root P concentration and uptake when higher P was provided, and had a stimulating effect on P translocation from shoots to roots. P increased shoot Mo concentration and uptake, decreased those in roots, and enhanced Mo transport from roots to shoots. These results implied that both Mo and P had beneficial effects on Mo and P absorption and translocation and co-application of them were necessary to promote growth and utilization of Mo and P for Brassica napus.     

Effects of three N strategies on tillering and yield of low shoot density winter wheat

Abstract

Application of nitrogen (N) in early spring is often recommended for low shoot density winter wheat in northern temperate areas such as Sweden. Regional N-strategy field trials in such areas generally show no relationship between early N and grain yield but the effects on shoot numbers and other yield components are seldom investigated. This study quantified the effect of three N fertilization strategies on the number of tillers at GS30-31 and the grain yield of winter wheat with low shoot density in early spring, in order to evaluate the importance of early N application. The investigations were carried out from 1999–2002 in four annual field experiments on a clay soil in south-west Sweden using winter wheat (cvs. Kosack and Tarso) with shoot densities in early spring ranging from 360–850 shoots m^?2. A positive relationship between time of first N application as number of days before GS30 and increase in number of shoots from GS20-21 to GS30-31 was observed. The relationship was strongest in experiments with the lowest shoot density in early spring (360–560 shoots m^?2) and the additional increase with each day of earlier availability of N before GS30 was 11 shoots m^?2. In wheat with this low shoot density in early spring, N was needed before GS30 to avoid yield reductions. Whether N was applied and available 24 or 13 days before GS30 did not affect yield, despite significantly more shoots being present at GS30-31 with earlier N application.     

Transitions of water‐drop impact behaviour on hydrophobic and hydrophilic particles

Extreme soil water repellency can have substantial implications for soil hydrology, plant growth and erosion, including enhanced splash erosion caused by raindrop impact. Previous studies of water droplet impact behaviour on man‐made super‐hydrophobic surfaces, with which water‐repellent soil shares similar characteristics, revealed three distinct modes of splash behaviour (rebound, pinning and fragmentation) distinguished by two transition velocities: rebound‐to‐pinning (v_min) and pinning‐to‐fragmentation (v*). By using high‐speed videography of single water droplet impacts we show that splash behaviour is influenced by the hydrophobicity of immobile particles, with hydrophobic glass spheres exhibiting all three modes of splash behaviour in the hydrophobic state but hydrophilic spheres exhibiting solely pinning behaviour. We found that increasing the particle size of fixed glass spheres increases v_min. A study of droplet impact on hydrophobic sand shows that the increased roughness of the immobile particles makes impacting droplets more likely to fragment at slower impact velocities. The mobility of the particles influenced droplet impact behaviour, with loose, hydrophobic particles displaying significantly greater v_min values than their fixed analogues. The surface tension of the water droplet also lifted loose, hydrophobic particles from the surface, forming highly mobile ‘liquid marbles'. Water‐repellent soil was also shown to form ‘liquid marbles' at both the slow (approximately 0.3–2.1 m s^?1) and fast (about 7 m s^?1) droplet impact velocities studied. The observation of very mobile liquid marbles upon water droplet impact on water‐repellent soil is significant as this provided a mechanism that may enhance erosion rates of water‐repellent soil.     

风速对盆栽苋菜蒸腾及物质积累的影响

通过温室盆栽试验,研究了2.0 m·s-1、1.0 m·s-1、0.4 m·s-1、0.0 m·s-1风速下风速气象因子对苋菜蒸腾耗水及生长的影响.结果表明:温室内盆栽苋菜的蒸腾速率及日蒸腾量受不同风速影响的表现相似,差异不显著,整体看来,蒸腾速率和日蒸腾量以1.0 m·s-1风速处理最大,0.4 m·s-1风速处理和对照次之,最大风速2.0 m·s-1处理最小.采用逐步回归分析了不同风速处理下盆栽苋菜的蒸腾速率、日蒸腾量与气象因子的相关关系,发现不同风速处理蒸腾速率与光照强度的正相关性最强,2.0 m·s-1风速处理的蒸腾速率与温度的正相关性次之,而其他处理的蒸腾速率与相对湿度呈显著负相关;日平均温度是影响各处理日蒸腾量的主要因素.盆栽苋菜的物质积累曲线表明,风速1.0 m·s-1处理的物质积累量最大,2.0 m·s-1处理最小.风速处理对温室盆栽苋菜的地上部鲜重、地下部鲜重以及根冠比均有极显著影响,且1.0m·s-1与2.0m·s-1风速间差异极显著.干物质重受风速影响显著,1.0 m·s-1处理干重最大.风速处理对盆栽耗水量和水分利用效率的影响未达显著水平,但1.0m·s-1风速处理的水分利用效率最大.     

Effect of cadmium toxicity on micronutrient concentration,uptake and partitioning in seven rice cultivars

Heavy metal uptake, translocation and partitioning differ greatly among plant cultivars and plant parts. A pot experiment was conducted to determine the effect of cadmium (Cd) levels (0, 45 and 90 mg kg^?1 soil) on dry matter yield, and concentration, uptake and translocation of Cd, Fe, Zn, Mn and Cu in seven rice cultivars. Application of 45 mg Cd kg^?1 soil decreased root and shoot dry weight. On average, shoot and root Cd concentrations and uptake increased in all cultivars, but micronutrients uptake decreased following the application of 45 mg Cd kg^?1. No significant differences were observed between 45 and 90 mg kg^?1 Cd levels. On average, Cd treatments resulted in a decrease in Zn, Fe and Mn concentrations in shoots and Zn, Cu and Mn concentrations in roots. Differences were observed in Cd and micronutrient concentrations and uptake among rice cultivars. Translocation factor, defined as the shoot/root concentration ratio indicated that Cu and Fe contents in roots were higher than in shoots. The Mn concentration was much higher in shoots. Zinc concentrations were almost similar in the two organs of rice at 0 and 45 mg Cd kg^?1. A higher Cd level, however, led to a decrease in the Zn concentration in shoots.     

INTERACTIVE EFFECTS OF SALINITY AND PHOSPHORUS NUTRITION ON PHYSIOLOGICAL RESPONSES OF TWO BARLEY SPECIES

Salinity is one of the most important agricultural problems in Iran. The effect of different levels of salinity and phosphorus on shoot length, root and shoot fresh and dry weight, nutrient elements (sodium (Na⁺), potassium (K⁺), phosphorus (P) and chloride (Cl^?), proline and soluble sugar contents of barley were investigated. Two cultivars of barley, Hordeum murinum (wild resistant germplasm) and Hordeum vulgar, variety Afzal were treated in vegetative stage under hydroponics condition in a factorial arrangement based on completely randomized block (CRB) design with four levels of salinity [0, 100, 200 and 300 mM sodium chloride (NaCl)] and three levels of phosphorus (15, 30 and 55 μm L^?1) with three replications. By increasing salinity, all the measured parameters, except sodium (Na⁺) content were reduced. Furthermore, with increased in phosphorus levels from 15 to 55 μm, Na⁺ content of the plant shoots decreased, but length, fresh and dry weights of roots and shoots and K⁺, P, Cl^?, proline, and soluble sugars content of the shoots increased. The results indicated that accumulation of mineral ions for osmotic adjustment and restriction of Na⁺ accumulation in shoots were involved in phosphorus enhancement of the salt tolerance of barley. Thus, it seems that in saline soils, where there is no possibility for soil leaching and amending, application of phosphorus fertilizers can lead to a satisfactory growth and production in barely yield.     

Dry deposition to snow in an urban area

Ambient particle and gas concentrations, wet deposition and dry deposition were measured in Warren, MI between December 18, 1983 and April 6, 1984. Dry deposition was measured to various surfaces in a cutoff bucket, including a snow surface, a snow/water surface during melting and a deionized water surface. Dry deposition velocities were calculated for various species from the ratio of the dry flux to the ambient concentrations. The dry deposition velocities measured to a snow surface were 0.082 cm s^?1 SO₂ 2.0 for HNO₃, 0.083 for NH₄ ⁺, 2.0 for Ca⁺⁺ and 4.3 for Cl^?. The values were not significantly different for a snow/water surface during melting compared to a snow surface. However, higher values of 0.69 cm s^?1 for SO₂, 6.2 for HNO₃, 0.33 for NH₄ ⁺, and 4.2 for Ca⁺⁺ were found to a deionized water surface in the spring. These higher values could be due to the higher air temperature, the pH of the liquid or to increased atmospheric mixing during this period.     

Identification of Rice Varieties with High Tolerance or Sensitivity to Copper

ABSTRACT

To study tolerance of rice (Oryza sativa L.) to excessive copper (Cu), 167 varieties were screened for Cu tolerance or sensitivity. Based on the elongation of the root, No. 1139 and No. 1195 were chosen as Cu-tolerant and Cu-sensitive variety. Compared with the control (0.32 μ mol L^{? 1} Cu), treatments with 5 and 8 μ mol L^{? 1} Cu for 10 days had no significant effect on the root and shoot dry masses of Cu-tolerant variety No. 1139, but significantly decreased root and shoot dry masses of variety No. 1195. Copper at 5 and 8 μ mol L^{? 1} also significantly decreased contents of chlorophyll and carotenoid and the ratio of variable to maximal chlorophyll fluorescence (Fv/Fm) in the leaves of the Cu-sensitive variety No. 1195. Roots and shoots of variety No. 1139 contained significantly higher the concentration of Cu than variety No. 1195 exposed to 5 and 8 μ mol L^{? 1} Cu. However, variety No. 1139 had higher Cu proportions on the cell walls in shoots and roots than variety No. 1195.     

Bioaccumulation of Copper by Zea mays: Impact on Root, Shoot and Leaf Growth

In the present study, the growth and the Cu²⁺accumulation by roots, shoots and leaves of Zea mays were examined using copper sulphate in the range of 10^?4 to 10^?2 M. Plants of Z. mays did not show inhibition of growth in the presence of 10^?4 to 10^?2 M Cu²⁺; however, it was observed growth effects on root when different Cu²⁺ solution concentrations were used. Only the seedlings exposed to 10^?2 M exhibited substantial root growth reduction, yielding only 56% of length with respect to the control. Seedlings exposed to 10^?4 M Cu²⁺ exhibited 16% and 42% growth increase in shoots and leaves, respectively, when compared with the controls. The seedlings treated with 10^?3 and 10^?2 M Cu²⁺ were inhibited in shoot and leaf growth. The fresh weights in roots, shoots and leaves significantly decreased at 10^?2 M Cu²⁺. The tolerance index, based on root length, was not significantly different for the three different treatments with copper. However, the total accumulation rate was very low at 10^?4 and 10^?3 M compared to 10^?2 Cu treatments. The capacity of copper accumulation by roots, shoots and leaves of Z. mays plants increased concomitant to the copper concentration, arriving to 382 times more in roots, 157 in shoots and only 16 in leaves, all compared to the controls. Cu could be accumulated by roots, shoots and leaves when the initial concentrations were 10^?3 and 10^?4 M. However, when it was 10^?2 M, the metal could not be accumulated by leaf and shoot levels; the roots could increase their copper accumulation capacity three times compared to the control. Z. mays has potential ability to accumulate Cu without being overly sensitive to Cu toxicity.     

Alleviation of cadmium phytotoxicity by magnesium in Japanese mustard spinach

Abstract

To clarify the mechanism of Magnesium (Mg) in alleviating cadmium (Cd) phytotoxicity, Japanese mustard spinach (Brassica rapa L. var. pervirdis) was grown for 10 days after treatment in hydroponics in a growth chamber under natural light. The treatments were: (1) nutrient solution alone (Control), (2) 10 mmol L^?1 Mg (High-Mg), (3) 2.5 µmol L^?1 Cd (Cd-toxic), (4) 2.5 µmol L^?1 Cd plus 10 mmol L^?1 Mg (Mg-alleviated). The Cd-toxic treatment showed substantial growth retardation and chlorosis of young leaves, such symptoms were not observed in Mg-alleviated plants. Magnesium-alleviated plants showed higher shoot growth, more than twofold, and decreased shoot Cd concentration, approximately 40%, compared with Cd-toxic plants. This increase in shoot growth and simultaneous decrease in shoot Cd concentration may explain the alleviation of Cd toxicity with Mg in Japanese mustard spinach. In Cd-toxic plants, concentrations of K in shoots and Zn in both shoots and roots increased compared with the other three treatments. Concentrations and accumulations of Fe and Mn in shoots decreased significantly in the Cd-treated (Cd-toxic and Mg-alleviated) plants compared with the control and High-Mg plants. Thus, the application of high amounts of Mg in the nutrient solution can alleviate Cd toxicity in plants.     

Assessment of the potential for dredged material dispersal from dumping sites in the Gulf of Gdańsk

Purpose

Environment-friendly management of sites used for disposal of locally generated sedimentary material involves designation of an optimal dumping site location which will render the dredged material re-usable for beneficial purposes. The objective of this research was to determine whether wind, waves, and currents can induce transport of sediment from offshore dumping sites located at intermediate depths in the southern Baltic.

Materials and methods

The problem was addressed by exploring potential sediment transport from two sites located in the Gulf of Gdańsk at depths of about 20 m. A total of 29 combinations of hydrodynamic variables, representing the most extreme possible situations in the area, including eight theoretical uniform wind fields over the entire Baltic Sea from the W, NW, N, NE, E, SE, S, and SW sectors, the wind speed of 30 m s^?1, as well as 21 historical extreme storms, retrieved from the HIPOCAS project database, were used.

Results and discussion

The bottom velocities resulting from waves and currents at the dumping sites considered were computed using wave models (WAM, SWAN) and the M3D hydrodynamic model (based on the POM model). To estimate the velocities critical for bedload transport, formulae developed by Soulsby (1997) and Sawamoto and Yamashita (Proc Coastal Sediments 87:415–423, 1987) were used. The volumetric bedload transport was computed based on Meyer-Peter and Müller (1948). The model simulations demonstrated that, for the storm conditions analyzed, the current velocity in the area of the two dumping sites would be so low that it would practically not affect the magnitude of the bottom sediment transport. Thus, the resultant volume of bedload transported would be equal to that generated by the wave action. For the heaviest historical storm, the maximum transport is about 3?×?10^?5 m² s^?1.

Conclusions

Under conditions of theoretical storms, the bottom orbital velocities would be higher and the resultant sediment transport would reach almost 7?×?10^?5 m² s^?1 for northerly winds. However, this value is still very low compared with the volume of sediment being dumped. The findings of this study may prove useful in designation of future dumping sites.

     

Comparison between the seminal and nodal root systems of winter wheat in their activity for N and K uptake

The activity of seminal and nodal root systems of winter wheat (cv. Avalon) in taking up NO₃^? and K⁺ has been measured in solution culture using a split root technique. Plants in the tillering phase of growth (36 days old) were used for the experiment which lasted 20 days. During this time plant dry weights increased by a factor of 20, whilst root: shoot ratios and nutrient compositions remained constant. Inflows (uptake rate per unit root length) were 2–6 times higher for the nodal roots than for the seminal roots, with values varying between 1 and 9 pmol cm^?1 s^?1 for N and between 0.5 and 4 pmol cm^?1 s^?1 for K. When uptake was expressed on the basis of unit fresh weight of roots, values ranged from 1 to 2.3 pmol mg^?1 s^?1 for N and from 0.4 to 1.0 pmol mg^?1 s^?1 for K, and there were only very small differences in uptake efficiency between the nodal and seminal roots. Uptake rate per unit root decreased with plant age. This was caused by a decline in shoot demand due to the reduction of the relative growth rate. When either the nodal or seminal root system alone was supplied with nutrients, uptake rate per unit root increased and nutrient uptake per plant reached 72–92% of the control.