Mineral composition of kenhy tall fescue as affected by nutrient solution concentrations of Mg and K

Four greenhouse sand culture experiments were conducted with Kenhy tall fescue, a Lolium multiflorum X Festuca arundinacea hybrid derivative. These experiments were conducted to characterize mg accumulation and the chemical composition of Kenhy under various combinations of Mg, K, and N solution concentrations. Of primary interest was the shape and magnitude of response of tissue Mg concentration to solution K levels and potential for Mg accumulation that exists in Kenhy under low solution K levels. Analyses were made for Mg, K, Ca, Na, N, and nitrate.

Increased Kg concentrations were observed with increased solution Mg. Increased solution K was in all cases associated with lower concentrations of Mg. Under conditions of low solution K (0.125 mM) and adequate Mg (0.25 mM), Mg accumulation exceeded 1.0%. Increased solution N was associated with decreased Mg concentrations. Both the linear and quadratic components of Mg solution concentration contributed significantly to increased tissue Mg. Hawever, the linear component of K solution concentration was sufficient to account for decreased tissue Mg. The reduction of tissue Mg to solution K was greater at higher concentrations of K.

Potassium accumulation significantly increased with increased solution K. Increased solution Mg was associated with lower tissue K in which the greatest reduction in K accumulation occurred with the first Mg addition.

Calcium accumulation decreased with increased solution K. Higher solution Mg was associated with lower tissue Ca levels while higher levels of N were associated with increased tissue Ca. Sodium accumulation was significantly reduced by increased K concentrations but neither Mg nor N was effective in consistently altering tissue Na concentrations.

From these experiments it is evident that Kenhy tall fescue has the absorptive capability for high levels of Mg under conditions of low levels of solution K. However, even small increments of solution K were shown to be capable of substantially reducing the Mg content, Thus, the selection of forage grasses for Mg absorptive capability must be conducted under conditions of high solution K, if large improvements on present forage materials are to be obtained. In addition, the inverse relationship between Mg and K present in Kenhy seedlings confirms the need to consider K fertilization recommendations in attempting to increase forage Mg durirg the grass tetany period.     

Aluminum effects on uptake and translocation of nitrogen in sorghum (Sorghum bicolor,L. Moench)

The effects of aluminum on the uptake and translocation of N in two hybrid cultivars of sorghum with differential tolerance to aluminum were studied.

Aluminum decreased the amount of N accumulated and the % of N in the aerial parts of the plants. In the roots the amount of N accumulated also decreased but the % of N increased, in both cultivars. Besides an effect on dry matter yield, Al probably reduces the uptake of N and its translocation to the aerial parts of the plant. Apparently, this impairment on N translocation resulted from Al effects on the root pressure.

Aluminum not only reduced the amount of N translocated but also changed the sap composition. The % of NO₃ ‐N decreased while the % of amino acid‐N increased suggesting an Al effect on N uptake and also on protein degradation. Asparagine and glutamine contributed about 80% of the free amino acid fraction; however, their proportions changed in presence of Al. Therefore, Al also interfered with the synthesis and/or interconversion of these amino acids.     

Ammonium (15N) metabolism in cotton under salt stress

Plant growth and metabolism is impaired under stress conditions, resulting in decreased crop yields. The purpose of this investigation was to evaluate the NaCl stress effects on NH⁺ ₄ metabolism in cotton plants at vegetative and reproductive stages of growth.

Cotton (Gossypium hirsutum L.) plants grown in normal (control) and NaCl treated Hoagland solutions were analyzed for distribution of N¹⁵ in NH⁺ ₄ plus amide‐N, free α‐amino‐N, total soluble‐N and protein‐N after the plants were provided ¹⁵NH₄NO₃ in nutrient solutions for 6, 12 and 24 h. The concentration of protein‐¹⁵N was enhanced under a low level of NaCl (‐0.4 MPa osmotic potential) at the vegetative growth stage. The difference between the protein‐¹⁵N concentration of the moderately salinized (‐0.8 MPa) plants and the controls was not significant. A high level of NaCl (‐1.2 MPa) significantly decreased protein‐N content of plants compared with the controls and any other level of salinity. The NaCl increased accumulation of NH₄ ⁺ plus amide‐N, free (α‐amino‐N, and total soluble‐N in cotton shoots, at both stages of growth. Low osmotic potential (high osmotic pressure) of the nutrient solution induced by excessive amounts of NaCl in nutrient solution inhibited NH⁺ ₄ metabolism and decreased protein synthesis, thus resulting in accumulation of soluble N‐compounds. The ionic effect probably contributed also to inhibition of protein synthesis.     

Grain yield increases in wheat and barley to nitrogen applied after transient waterlogging in the high rainfall cropping zone of western Australia

Nitrogen (N) is a major factor limiting grain production in the high rainfall zone (HRZ, 450–700 mm annual average rainfall of southwestern Australia (SWA). Transient waterlogging and leaching of applied N fertilizer are hazards faced in most years by crop producers. The major crops are wheat (Triticum aestivum L.), barley (Hordeum vulgare L.), canola (Brassica napus L.) and lupin (Lupinus angustifiolius L.) grown in rotation. Two series of experiments involving, levels and timing of N fertilizer application and levels of plant population were done. The first series, in 2003–2004, consisted of 3 experiments in 3 growing seasons (early May to late-October) to measure the grain yield (GY) increase (response) of wheat and barley to various methods of N fertilizer application (methods of split N application were compared to N applied at sowing). The aim of the experiments was to determine the optimal N fertilizer application strategy for maximum GY and quality in situations where transient waterlogging was a frequent occurrence. The second series of four experiments, from 2007–2009, measured the GY of wheat sown at three levels of plant population to 4 levels of N applied after transient waterlogging (taken to be rainfall events in which >25 mm of rain was recorded in 24 to 48 hours).

Applying the N fertilizer after high rainfall and transient waterlogging (tactical N application) increased GY and protein percentage of grain compared to applying all of the N fertilizer at sowing. Where transient waterlogging was not frequent, applying the N after waterlogging was not always better than applying part of the N according to growth stage of the crop or according to fixed times after sowing. When the crop was water-logged three or more times, N uptake by the crop at anthesis and apparent fertilizer N recovery in the crop was substantially increased by applying the N after waterlogging compared to applying the entire N at sowing. This study found that a tactical N management strategy for the HRZ of SWA is to apply some N at sowing with subsequent applications made after heavy rainfall that leads to transient waterlogging. Split N fertilizer applied either according to time after sowing or to growth stage of the crop was equally effective for increasing GY in situations where waterlogging was less frequent.

The observation from these experiments, that grain yield increases due to splitting the N dose were associated with increases in ear numbers, lead to a further set of experiments where plant population was increased in conjunction with N applied after waterlogging events. The combined strategy of increased plant population with strategic N application decreased the amount of N required for maximum GY where more than 3 heavy rainfall events occurred in a growing season.

One practical outcome of this research is to indicate that farmers can withhold applications of N fertilizer after sowing in seasons when transient waterlogging does not occur.     

Sulfur nutrition effects on dinitrogen fixation of seedling alfalfa

Greenhouse experiments with alfalfa (Medicago sativa L. cv. ‘Apollo') were performed to evaluate the effect of varied nutrient solution concentrations of S on the yield, nodulation, dinitrogen fixation, N and S concentration, and the partitioning of N and S into shoots and roots.

Sulfur treatments consisted of four levels (0, 1, 2.5, and 25 mg S/L) of added S. The experimental design was a randomized complete block, with three replications. Seeds were inoculated with commercial inoculum, planted in plastic containers of acid‐washed sand, and irrigated with nutrient solution for one minute, at 2 h intervals.

Sulfur application increased the yield of all treatments. The results demonstrated that the addition of 2.5 mg S/L to the nutrient solution, besides providing the highest total dry matter yield (12 g/72 plants), showed the highest percent yield increase (19%), acetylene reduction rate (0.426 umole ethylene/mg nodule dry wt/h), total N content (306 mg/72 plants), percent recovery of S (3.8%), and percent increase in N due to dinitrogen fixation (32%).

N:S ratios obtained were different for shoots and roots, with S application decreasing the N:S ratios. The N:S ratios of 16:1 (shoots), and 9:1 (roots) obtained in the 2.5 mg S/L treatment were found to be adequate for normal growth and development.

These data indicated that the 2.5 mg S/L treatment (2.7 mg total S/L) was optimal for alfalfa seedling development.     

Effects of N‐source,light intensity and temperature on nitrogen metabolism of bahiagrass

Under greenhouse conditions, a study was made on the effects of nitrogen (N) source (N)O₃ or NH₄), mode of application (single vs. split) and nitrification inhibition on the N‐uptake and metabolism, of bahiagrass.

Variations in light and temperature in the greenhouse affected the N‐metabolism of bahiagrass plants. Nitrate fed plants had nitrate reductase activity (NRA) pattern different from that of NH₄‐fed plants. Amino‐N accumulation patterns were similar for plants under both N‐sources, although amino‐N levels in leaves of NH₄‐fed plants were much smaller than that of NO₃ plants. Nitrate accumulation in leaves showed inverse trend to that of roots in plants fed both NO₃ or NH₄. To the sharp peaks in NO₃ levels in roots due to increases in light and temperature corresponds a sharp decrease of its levels in leaves.

For both both NO₃ or NH₄ treatments, soluble‐N accumulated most in the rhizomes of bahiagrass plants, whereas protein N accumulated most in leaves, suggesting that rhizomes had a buffering effect on the NO₃ fluxes to leaves. This presumably resulted in a lag in the NRA response of the NO₃‐fed plants to increases in light and temperature.     

Effect of nitrogen and sulphur fertilizers and seed inoculation with rhizobium phaseoli on the nitrogen‐sulphur relationships of bean (phaseolus vulgaris L.)

A greenhouse experiment with beans (Phaseolus vulgaris L.) was performed in order to investigate the effect of nitrogen and sulphur application and seed inoculation on the yield, leaf area, distribution of different nitrogen and sulphur fractions and N/S ratio in shoot, fruit and root.

Inoculation of plants together with nitrogen or sulphur application produces an increase in the concentration of total nitrogen and a decrease in the accumulation of nitrate‐nitrogen and sulphate‐sulphur in shoot, fruit and root. Leaf area increased more with nitrogen than with sulphur application while the highest amounts of fruit dry matter were obtained with sulphur application.

N: S ratios obtained were different according to the part of the plant tested. Sulphur fertilization decreased the N: S ratios in shoot, fruit and root. The data obtained indicate that and adequate N: S ratio can insure maximum production of yield.     

Tomato growth,nitrogen fraction and mineral composition in response to nitrate and ammonium foliar sprays 1

Tomato plants were grown in sand culture with NO₃ or NH₄ N at two levels of light. Foliar sprays at three levels of N as well as combinations of foliar and root feeding were used.

Shade increased NH₄ toxicity in plants sprayed with NH₄ but decreased the toxicity in plants receiving NH₄ through the roots. NH₄‐N greatly reduced growth and cation uptake when supplied through the roots but not with foliar application. Plants sprayed with NH₄ showed better growth, higher K, Ca, and Mg content and lower free NH₄ in shoot, compared to plants receiving NH₄ through the roots.

The overall free amino acid contents of shoots was higher for NH₄‐fed plants regardless of how the N was applied. Plants sprayed with NH₄ incorporated a greater amount of N into insoluble compounds compared with NO₃ nutrition. The N uptake per unit of leaf area was higher for plants grown under full sun light whereas N content was higher for plants grown under hade. N content in tissue increased with N concentration in foliar spray, although plants supplied with N through the roots had higher levels of free amino acids and total nitrogen.     

Soil temperature affects element uptake by sorghum

The influence of soil temperature on nutrient accumulation in aerial portions of sorghum plants was evaluated in a greenhouse experiment. Plants were grown in 20‐liter containers at cooled and ambient soil temperatures of 20 and 25C, respectively, and were harvested at the 8‐ and 12‐leaf stages of development for yield and nutrient analysis.

At the 8‐leaf stage, sorghum plants subjected to 25C were significantly higher in concentration of N, P, K, Mg, and Cu, but were significantly lower in Ca. Soil temperature did not significantly affect concentration of Zn, Fe, and Mn. At the 12‐leaf stage, sorghum plants grown in the warm soil temperature treatment were lower in concentration of N, K, Ca, Mg, Zn, Fe, Mn, and Cu than plants grown in the cooled‐soil treatment. Phosphorus showed a negative response to increased temperature.

It was concluded that further research relating element uptake and translocation to temperature is needed. Element accumulation in the roots, stems, leaves, and floral and seed portions of the plant should be included. In addition, the interaction between plant age and element concentration should be studied more thoroughly. Both this study and the published literature indicate that this interaction is significant for many of the elements.     

Effect of manganese on concentrations of Zn,K, Ca and Mg in two bush bean cultivars grown in solution culture

Two bush bean cultivars [Phaseolus vulgaris L. cv. ‘Wonder Crop 2’ (WC‐2) and ‘Green Lord’ (GL)], differing in Mn toxicity, were grown in a growth chamber for 12 days in Hoagland No. 2 nutrient solution containing 0.05 to 1 ppm Mn as MnCl₂4H₂O with 1 ppm Fe as Fe‐EDTA, at an initial pH 5.00. Concentrations of Zn, K, Ca and Mg in the tissues of two bush bean cultivars were examined in relation to Mn toxicity.

The concentration of Zn in the leaves of Mn‐sensitive WC‐2 increased significantly with increasing Mn concentration in the solution, but such levels were not toxic to the plants.

The percent distribution of Zn and K in Mn‐sensitive WC‐2 plants (% of total uptake) significantly increased in the tops and decreased in the roots with increasing Mn concentration in the nutrient solution; however, Mn treatment had no effect on distribution of either Ca or Mg in WC‐2. External Mn concentration had little or no effect on the K, Ca, or Mg concentration in the tops of Mn‐tolerant GL.     

Elemental leaf content and deficiency symptoms in rabbiteye blueberries: 1. Nitrogen

Rabbiteye blueberries grown in sand culture were subjected to varying levels of N fertilization (0 ‐ 81 mg N/liter) applied in aqueous solution at the rate of 250 ml/plant daily. Essential elements other than N were kept constant. Shoot growth and leaf concentration of N, P, K, Mg, Ca, Mn, Fe, Cu, B, Zn, Co, and Al were determined. Shoot growth and percent leaf N increased with increased N levels. Shoot growth increased little at N fertilization levels of 0 ‐ 9 mg/ liter but increased rapidly at higher rates. N content in leaves followed a quadratic curve, with % N in leaves increasing more rapidly from 0 to 27 mg N/liter than from 27 to 81 mg N/liter fertilization levels. Leaf concentration of K, Ca, Mg, Mn, B, and Ca decreased linearly as N levels increased. Total content of all elements increased as N fertilization increased. Visual N deficiency became increasingly evident as % N content decreased below 1.4% N.

Nitrogen, the most utilized element in plants, is usually the first to become deficient in sandy soils low in nutrient content (1). Rabbiteye blueberries (Vaccinium ashei Reade) are often grown on acidic, sandy, upland coastal plains soils that are low in cation exchange capacity, organic matter content, and available nutrients. In these acidic soils, NH₄N is more available than in neutral soils (2). The NH₄N source appears to be more suitable for blueberry growth, resulting in greater nutrient uptake, plant growth, and % N of leaf tissue than did the NO₃N sources (5,6).

Nitrogen deficiency symptoms in rabbiteye blueberries are characterized by small, yellow and/or red leaves and stunted plants (3). Since young rabbiteye plants are very sensitive to fertilizer, similar chlorosis symptoms (yellowing or reddening of leaves) can be associated with over‐fertilization, possibly due to root damage (7). Cain (2) found that leaves from healthy container‐grown highbush (V. corymbosum L.) blueberry plants contained about 2% N and higher levels of K and Ca than field‐grown plants. Greenhouse and Field studies indicate that leaf N content in rabbiteye blueberries is usually lower, ranging from about 1.5 to 1.8 (3,7,8). Increased N fertilization decreased the nutrient uptake of other essential elements (Ca and Mg) in rabbiteye blueberries (6). In highbush, Popenoe (4) indicated that a depression of P and K might occur under conditions of high N levels.

This study was initiated to ascertain the effect of NH₄N fertilization levels on uptake patterns of essential elements and to determine the relationships of N fertilization, leaf N content, plant growth, and visible deficiency symptoms.     

The effect of salinity and iron application on growth and mineral uptake of sunflower (helianthus annuus L.)

In a greenhouse experiment, the effect of salinity and Fe chelate on growth and mineral uptake of sunflower (Helianthus annuus L. c.v. Record) was studied.

Sunflower plants were grown in nutrient solution with four levels of salinity (0, 1.5, 3.0 and 4.5 atm), induced by NaCl and four rates of Fe chelate (0, 0.5, 1.0 and 1.5, ppm Fe) as FeEDDHA. The experiment was a completely randomized design with treatment combinations arranged in a factorial manner with three replications.

Dry matter yield, shoot‐root ratio, leaf area, plant height and transpiration decreased as salinity increased, the effect of salinity being depressed by iron applications. Salinity reduced P, K, Ca and Mg uptake by roots as well as that of N, P, K, Ca, Mg by shoots, while Fe applications increased uptake of these elements in roots and shoots. Both salinity and iron applications increased Cl, Na and Fe uptake by roots and shoots, as expected. In most instances salinity reduced uptake of Fe, Mn and Zn by the plants while iron applications improved uptake of these elements.

The sunflower plant used in this experiment was found to be, at least partly, tolerant to salinity and decreased water availability as well as toxicity of ions. Nutritional disorders were the cause of decreased plant growth by increasing salinity of the nutrient solution. The decreased plant growth and mineral uptake, induced by salinity, were partially offset by increased iron levels in the nutrient solution.     

Distribution of magnesium between chlorophyll and other photosynthetic functions in magnesium deficient “sun”; and “shade”; leaves of poplar

Photosynthesis of attached sun and shade grown leaves of poplar (Populus euramericana (Dode) Guinier cv. ‘Robusta') has been measured at 0.03 and 0.5% CO₂ at light limitation and light saturation. Photosynthetic rates were compared for plants grown at normal and low Mg‐supply and related to leaf Mg content.

Photosynthetic rates at high CO₂ level were affected at Mg concentration lower than about 50 μmoles/g dry leaf tissue at both photosynthetic irradiations. This was paralleled by a decrease in chlorophyll concentration. At a low CO₂ level photosynthesis was affected at the same Mg concentration but the degree of the inhibition was higher. This indicates that synthesis of chlorophyll as well as CO₂ fixation are affected at the same “critical”; Mg concentration.

Shade leaves contain more chlorophyll per unit leaf weight than sun leaves but the percentual‐ decrease of chlorophyll in Mg deficient leaves Is similar for sun and shade leaves at the same Mg leaf concentration. As a consequence, in Mg deficient shade leaves extraordinary high portions of leaf Mg are bound to chlorophyll (up to 57%; in contrast: up to 37% in sun leaves).     

Incidence of P,Mn and B deficiencies on the levels of the whole and individual flavonoid groups in tomato leaves

Alterations occur in the normal content of total and individual flavonoids with P, Mn and B deficiencies, in tomato leaves.

P and Mn deficiencies do not alter the total flavonoid level. Nevertheless, these deficiencies lead to different contributions of each flavonoid group (flavonols, flavones and flavanones) to the whole content.

B deficiency produces a very significant increase in total flavonoid content. Compounds that contribute the most to this accumulation are flavones.     

Nitrogen rates in strawberry (Fragaria ananasa) nursery on growth and yield in the field

Strawberry (Fragaria ananassa cv. Aliso) plants were grown under three N‐rates in the nursery: 80, 320 and 640 kg N/ha, and then transplanted to the fruiting field. Plants from each nursery treatment were given 150, 300 and 450 kg N/ha. The fertilizer was given as ammonium sulfate in the nursery and as ammonium nitrate in the field, a part broadcasted before planting and the other part applied as top dressings. Biomass production, plantlets size distribution and N content were restricted by the lowest level of N given in the nursery. Plants grown at 320 kg N/ha in the nursery gave significantly earlier and higher total yields than those grown at the other rates. Fruit yields were not significantly influenced by the N‐application in the field. N fertilization in the early stages of strawberry plant development in the nursery is more important than later field application.

The influence of N fertilization on the growth and yield of strawberry plants has been studied by several workers. In some reports yields were increased when the rate of N applied was increased (1, 2, 3). In other studies no influence was found (4, 5, 6), or even a decrease in yield was reported as the rate of applied N was increased (7). While in some studies detrimental effects of N‐fertilizer on fruit yield were observed at 200–300 kg N/ha (8, 9), in other studies (6, 7) N applications up to 400 kg/ha did not affect yield. In Spain (3), adding up to 680 kg/ha caused an increase in fruit yield.

Even at relatively low applied‐N levels, up to 150 kg N/ha, strawberry response reports are not consistent. Some workers found that increasing N in this range caused an increase in fruit yield (8, 9, 3, 7, 10), while no effect was observed (4, 5, 6, 11) in several other studies. Most of the reported experiments with N‐fertilizer were carried out after plants were transplanted from the nursery to the field. To the best of our knowledge no attempt was made to evaluate the effect of fertilizer applied in the nursery.

The objective of this work was to evaluate the influence of different levels of N‐fertilizer, in both the nursery and the field, on strawberry plant development and composition, earliness, yield level and yield distribution.     

Iron nutrition of sunflower(Helianthus annuus L.) as affected by various levels of p and ZN

The effects of various P and Zn levels on iron nutrition of sunflower (Helianthus annuus L.c.v. Record) were studied in two separate experiments in nutrient solution under greenhouse conditions.

In the first experiment, sunflower was grown in nutrient solutions containing four levels of P(1.5, 2.5, 3.5 and 4.5 mM/l) and three levels of Fe(0.25, 0.75, and 1.5 ppm) as FeCl₃ or FeEDDHA. In the second experiment (following the first experiment), the treatments were three P levels (0.75, 1.50 and 3.00 mM/l), three Fe levels (0.25, 0.75 and 1.5 ppm) as FeEDDHA and three Zn levels (0.1, 0.2 and 0.4 ppm).

The plants receiving Fe‐chelate, except for 0.25 ppm Fe, showed no symptoms of iron chlorosis. With inorganic Fe treatments, iron chlorosis appeared after 7–10 days depending on P level, but except for 0.25 ppm Fe which remained chlorotic, plants recovered completely within 3–4 days thereafter due to pH regulating mechanism of sunflower under iron stress condition. With both sources of Fe, chlorosis was associated with high P:Fe ratio.

Increased P and Fe levels in nutrient solution resulted in general increases in the dry weights of roots and shoots. The Fe concentration of shoots, except in few instances, was not affected by P levels, indicating that the sunflower cultivar used in this experiment could utilize inorganic Fe as well as Fe‐chelate under our experimental conditions.

Increasing P levels caused significant increases in Mn content of the shoots as 0.25 and 0.75 ppm inorganic Fe³⁺. Increased Fe levels increased shoot Mn content with inorganic Fe and decreased it with Fe‐chelate. The effects of P, Fe and Zn on sunflower indicated an antagonistic effect of Zn on 1.5 ppm Fe for all P levels. Increased Zn levels in nutrient solution generally increased Zn content of the shoots without having any marked effect on their Mn content.     

Growth and cation absorption of some fruit‐vegetable crops grown on rockwool as affected by different cation ratios in the nutrient solution

In a series of experiments, cucumber, eggplant and sweet pepper were grown in rockwool with nutrient solutions of different ratios of potassium (K), calcium (Ca) and magnesium (Mg). The ratios between the anions in the nutrient solutions compared were the same. In addition to yield, the concentrations of cations in the root environment and in different plant tissues were determined.

The results show that the yield for eggplant fruits were strongly reduced by a low Mg level, while the yield of cucumbers seemed to be somewhat reduced by a low Ca supply. Sweet pepper yields were not affected among the cation ratios compared.

Relationships between cation contents in the root environment and cation contents in plant tissues were established. The correlation coefficients for these relationships were very high. The equations calculated for the various cations show remarkable differences. Regression coefficients and intercepts strongly depend on crop and plant part sampled. For Mg, it could be established that Ca strongly affected the uptake of Mg.     

Phosphorus uptake rate and growth characteristics of wheat roots 1

Phosphorus uptake by plant roots is influenced by the plant root properties and solution P supply characteristics. These properties included (i) the relation between nutrient concentration and uptake rate, (ii) the change in uptake rate with plant age and with root age.

Information on the size of nutrient flux values and their change with increasing plant age can be used to determine the nutrient levels needed in the soil to supply nutrients rapidly enough to the root surface to minimize deficiencies. The objective of this research was to determine the relation between plant age and P absorption properties and root growth characteristics of wheat (Triticum vulgare L.) cv. Era.

Wheat was grown for periods up to 42 days in solution culture in a controlled climate chamber. Sequential harvests were made and P uptake and root morphology were measured. Shoot growth was exponential with time to 32 days and linear thereafter. Root dry weights increased linearly with time at a slower rate than shoot dry weights. Root length increased logarithmically with time (r² = 0.95; log y = 0.069x + 1.85).

With increasing plant age there was a reduction in average P uptake rate by wheat roots.     

Differential tolerance of bush bean cultivars to excess manganese in solution and sand culture

Nineteen bush bean cultivars were screened for tolerance to excess Mn in nutrient solution and sand culture experiments. Seven‐day‐old seedlings were treated with full strength Hoagland No. 2 nutrient solution containing different Mn concentrations for 12 days in the greenhouse.

Cultivars showing the greatest sensitivity to Mn toxicity were ‘Wonder Crop 1’ and ‘Wonder Crop 2'; those showing the greatest tolerance were ‘Green Lord’, ‘Red Kidney’ and ‘Edogawa Black Seeded’.

Leaf Mn concentration of plants grown in sand culture was higher than that for plants grown in solution culture. The lowest leaf Mn concentration at which Mn toxicity symptoms developed, was higher in tolerant than in sensitive cultivars. The Fe/Mn ratio in the leaves at which Mn toxicity symptoms developed, was higher in the sensitive cultivars than in the tolerant ones.

We concluded that Mn tolerance in certain bush bean cultivars is due to a greater ability to tolerate a high level of Mn accumulation in the leaves.     

Cation exchange capacity of roots: Titration,sum of exchangeable cations,copper adsorption

The cation exchange capacity of roots (CECR) has been measured according to three different methods : titration of H‐roots with NaOH in the presence of CaCl₂, MgCl₂, or NaCl 0.1 N, saturation of roots with mixed Ca‐Mg‐Na solutions of eight different compositions and extraction of the adsorbed cations with copper, saturation of roots with Cu‐ions and extraction with HC1. Two types of roots were studied : roots of ryegrass (Lolium multiflorum Lm.) and roots of clover (Trifolium pratense L.)

The very good coincidence of the results from the three methods tends to prove the reliability of the experimental procedures. The simplicity and the reproducibility of the Cu‐method renders it recommendable in view of possible standardization of the methods in the future.