Effet de divers sels alcalins sur la croissance et la nutrition minérale de Lemna minor L

Lemna minor L. was grown in aseptic culture solutions. With sodium chloride or lithium chloride in the solution, the plant increased in yield. Tolerance of Lemna minor to relatively high level of sodium explains the presence of this plant in brackish waters. A low quantity of potassium is required for optimal growth. Sodium was added to nutrient solutions as chloride or sulphate. At equivalent levels the sodium content of the plant was somewhat higher under sulphate salinity.     

Some effects of applied sodium and potassium chloride on yellow rust in winter wheat

In glasshouse experiments with plants in pots, applications of potassium chloride to the soil at 0.5 g/plant, 4 days before inoculation with Puccinia striiformis, decreased the severity of yellow rust on several winter wheat cultivars in comparison with untreated plants. Conversely, yellow rust was encouraged by applications of sodium nitrate. Sodium chloride in solution (8.6 g/l) reduced yellow rust when applied to the soil at the rate of 20 ml/plant but not when it was sprayed on to the leaves. In small-plot field experiments, sodium and potassium chlorides applied to the soil as dry powders in the spring at rates of 376, 1130 or 2260 kg/ha, significantly decreased the severity of yellow rust on most of the winter wheat cvs examined at each rate. The chlorides at these rates did not adversely affect the overall growth or yield in the absence of yellow rust.     

Combination of ammonium nitrate, cerium chloride and potassium chloride salts improves Agrobacterium tumefaciens-mediated transformation of Nicotiana tabacum

The frequency of plant transformation can be improved by addition of various chemical into transformation media. In the past, we showed that exposure of tobacco, wheat and triticale explants to ammonium nitrate, cerium and lantanium chloride and potassium chloride resulted in an increase in the frequency of transformation. Here, we tested whether a combination of increased concentrations of the aforementioned salts yielded a higher transformation frequency. We found that exposure to 61.8 mM ammonium nitrate caused a 5.0-fold increase in transformation frequency, whereas exposure to 1.0 μM cerium chloride or 47.0 mM potassium chloride resulted in 1.2- and 2-fold increases, respectively. Exposure to 61.8 mM ammonium nitrate and 1.0 μM cerium chloride led to a 4.8-fold increase in transformation frequency, whereas exposure to 61.8 mM ammonium nitrate and 47.0 mM potassium chloride let to a 5.2-fold increase. Finally, exposure to 61.8 mM ammonium nitrate, 1.0 μM cerium chloride and 47.0 mM potassium chloride produced a 5.1-fold increase. The analysis of the intactness of T-DNA borders showed that plants exposed to ammonium nitrate and a combination of ammonium nitrate with other salts had the more intact right borders and the less intact left borders. The best results were observed when all three salts (ammonium nitrate, potassium chloride and cerium chloride) were used. Thus, we concluded that the addition of cerium chloride and potassium chloride does not substantially improve the transformation rate beyond the improvement observed upon treatment with 61.8 mM ammonium nitrate, but may slightly improve the intactness of T-DNA borders.     

Exploratory pot experiments on sensitiveness of different crops to sodium: A. Spinach

Summary In orientating pot trials, carried out partly on soil and partly on an artificial soil-mixture, spinach showed a pronounced ability to take up sodium when dressed with sodium nitrate. The crop benefited much by this type of fertilizer both in yield and outward appearance, as compared with controls receiving calcium nitrate.In spinach sodium can replace potassium to a large extent, but it appears that, when receiving an equal supply of sodium and potassium, this plant prefers potassium. The use of sodium, supplied as a secondary constituent of nitrate fertilizers, is found to have economic importance, because it reduces the plant's need of potassium and improves the yields, even in presence of adequate potassium.In pot experiments with soil the dressing of potassium chloride in combination with Chilean nitrate gave negative results. Chilean nitrate alone, however, produced the highest yields of the series. Combined with nitrate of lime, potassium chloride initially depressed the growth, but showed in the end a slight increase of yield. As the water supplying power of this soil was more or less deficient, it is deemed possible that the negative effect of potassium chloride is due to the action of salt-concentration.It is pointed out that the normally grown spinach from the market-gardening centres destined for consumption may contain very high contents of potassium.These experiments were commenced at the Laboratory for Agricultural Chemistry of the Agricultural College at Wageningen, in concert with Prof. Ir. J. Hudig, Director of the Institute. The experiments could not be finished there owing to interference of war conditions.     

Electric Potential Differences and the Donnan Equilibrium in Plant Tissues3

The effect of various factors on the change of the potentialdifference between plant tissues and the external solution ofelectrolyte with change of concentration of the latter is considered.The effect of the presence of calcium ions in the free spacewhen the external electrolyte is potassium chloride is reportedand discussed.     

Some analyses of aquatic plants and their waters

Values are given of chloride, sulphate, phosphate, calcium, sodium, potassium and total nitrogen on aquatic plant material, both water and acid washed, and the corresponding waters.Resumé Ci inclus les resultats de l'analyses de plantes aquatiques sont donnés dont les constituents sont du chlore, du sulfate, du phosphate, du calcium, du potassium, du sodium et du nitrogène.     

Motile activities of Dictyostelium discoideum differ from those in Protista or vertebrate animal cells

Cell movement in the amoebae Dictyostelium discoideum has been examined in media differing in monovalent cation concentration (i.e. Na+ and K+). Under isotonic or even slightly hypertonic conditions, the cells move equally well in solutions in which either potassium or sodium ions dominate. However, in strongly hypertonic solutions the amoebae showed motility in a 2% potassium chloride solution, but remained motionless in a hypertonic 2% sodium chloride solution. This inhibition of D. discoideum amoebae movement in a hypertonic sodium chloride solution was fully reversible. Such behaviour corresponds to that of plant, fungi, and some invertebrate animal cells rather than protozoan or vertebrate cells. These observations suggest that studies using D. discoideum as a model for cell motility in vertebrate animal tissue cells should be considered with caution, and would seem to confirm the classification of cellular slime moulds as related rather to Fungi than to Protista. This also shows that the cell membrane models should consider the asymmetry in sodium/potassium ion concentrations found in vertebrate animal cells as one of various possibilities.     

Effect of aqueous extract of Ipomoea carnea leaf on isolated frog and mouse heart

Ipomoea carnea fam. Convolvulaceae is a poisonous plant and its toxicity is supposed to be due to the cardiac and respiratory failure. The present paper describes the cardiac effect of aqueous extract of the fresh leaves of I. carnea using mouse and frog heart. The aqueous extract produced an initial blockade of isolated frog heart for 5-10 sec followed by dose dependent increase in both amplitude and rate that lasts up to 2 min. Atropine (1 microgram/ml) blocked the initial depressant phase and potentiated the stimulant effect of the aqueous extract. The dose dependent increase in cardiac contractility of aqueous extract was not altered by propranolol or calcium channel blockers like nifedipine or diltiazem. The decrease in sodium chloride concentration or increase in potassium chloride concentration or calcium chloride concentration in physiological salt solution inhibited the responses to aqueous extract while an increase in sodium chloride concentration or decrease in potassium chloride or calcium chloride concentration in physiological salt solution potentiated the responses to the aqueous extract of I. carnea. It may be suggested from the data that aqueous extract of I. carnea produces positive inotropic effect on isolate frog heart possibly by sodium extrusion or release of the intracellular calcium.     

Properties of a halophil nicotinamide–adenine dinucleotide phosphate-specific isocitrate dehydrogenase. Preliminary studies of the salt relations and kinetics of the crude enzyme

The effects of chlorides on NADP-specific isocitrate dehydrogenase from Halobacterium salinarium were investigated. The enzyme is stabilized by potassium chloride and sodium chloride and this effect is discussed in relation to the Hill (1913) equation. Kinetics of the enzyme were studied within a range of concentrations of potassium chloride and sodium chloride. Apparent Michaelis constants for both substrates were affected by salt concentration, the effect being greater in sodium chloride than in potassium chloride. Minimal apparent Michaelis constants for both substrates were similar to the corresponding constants reported for yeast isocitrate dehydrogenase. V(max.) was maximal in each salt at a concentration of about 1m. The maximum was higher in sodium chloride than in potassium chloride. At salt concentrations above about 2.3m, the apparent V(max.) was lower in sodium chloride than in potassium chloride, and at salt concentrations below 0.75-1.0m, each salt behaved as a linear activator of the enzyme. Within this concentration range salt and NADP(+) acted competitively; the activation by salt was overcome at finite concentrations of NADP(+). At concentrations above about 1m, potassium chloride was a linear non-competitive inhibitor of the enzyme. Within the range 1.0-2.5m, sodium chloride was also a linear non-competitive inhibitor, but above 2.5m it caused more pronounced inhibition.     

THE EFFECTS OF SODIUM CHLORIDE ON HIGHER PLANTS

(1) This review concentrates on the effect of sodium chloride on the growth of higher plants, being primarily concerned with relatively high concentrations i.e. 50 mmol 1^-1 and above, though something is also said about those instances when sodium acts as a micronutrient. Emphasis is placed on particular species or genera for which enough information is available to discuss possible mechanisms. (2) Trace amounts of sodium are required for the growth of plants using the C₄ pathway of carbon fixation and may also be important in plants with Crassulacean acid metabolism. (3) The increased growth of Beta vulgaris brought about by sodium chloride can in part be explained by a sparing effect on potassium. However, growth is still increased when sufficient potassium is available. Complementary studies with rubidium indicate that the hormone balance in the plant may be changed. Sodium chloride also increases the level of sucrose in storage roots and allows beet plants to withstand water stress more readily, possibly by increased turgor pressure. (4) Sodium chloride increases production of dry matter in C₄ species of Atriplex under conditions of low relative humidity because water loss is reduced and photo-synthesis hardly affected. (5) Succulence in many plants is stimulated by salinity. The essential basis of the phenomenon is an increased water potential gradient between the leaf and the external medium. In some instances, it is the accumulation of chloride which is important; in others it is the accumulation of cations, when potassium can be as effective as sodium. (6) Salinity reduces the final area achieved by growing leaves. Most of the studies have been made on Phaseolus vulgaris and an important early event is the reduction in the rate of expansion of the epidermal cells and this may be accompanied by a decrease in their number. Reduction of epidermal cell size is a result of water stress; sodium chloride may directly affect cell division, though water stress cannot be ruled out. Whether salinity brings about inhibition of cell division depends upon the calcium content of the medium – a high content is accompanied solely by a reduction in epidermal cell size. (7) Hormones, as yet unspecified, may play an important part in response of a growing leaf to salinity. However, there is no evidence that sodium chloride per se has an effect on hormone balance within the plant. So far, any measured changes in levels of specific hormones can be ascribed to the osmotic effects of the saline medium. (8) Two estimates by flux analysis of cytoplasmic concentration of sodium in plants growing in conditions of high salinity give a value of around 150 mmol 1^-1. There is no similar information for chloride. Other techniques (histochemistry and X-ray micro-probe analysis) give questionable information. (9) There is now extensive information to show that enzymes of halophytes (other than ATPases) do not differ significantly from those of other higher plants with respect to their sensitivity in vitro to sodium chloride. There is a need for further work with respect to the activity of enzymes in the presence of those metabolites which have the highest cytoplasmic concentration. (10) Sodium-stimulated ATPases have been isolated from plant cells but their distribution amongst higher plants is restricted. (11) There are a number of reports of changed metabolism brought about by saline treatments but it is not clear how far the effects of sodium chloride and water stress are confounded. (12) Sodium appears to increase the sucrose levels in sugar beet by an inhibitory effect on product starch-granule-bound ADP-glucose starch synthase. (13) Reversal of a sodium pump located at the plasmalemma might have an effect on cell turgor. (14) Sodium (like other monovalent cations) causes loss of materials from plant cells, possibly through an effect on carrier proteins; calcium prevents this from happening. Calcium also allows plants to grow better in saline conditions by a depression of sodium uptake by and transport within the plant. The properties and composition of the membranes of mesophytes and halophytes need to be compared. (15) A saline medium exerts a major effect on plant growth through water stress to which a halophyte must adapt. As well as this, the cytoplasmic concentration of sodium chloride must be kept lower than the total cellular concentration of the salt. Unless this happens, it is likely that enzymic activity will be reduced due, in some instances, to an unspecific effect of a high concentration of monovalent cations and/or chloride and in other instances to competition between sodium and other cations, specifically potassium, for activation sites on enzymes, e.g. pyruvate kinase. (16) Further work is required to separate the osmotic effects from the specific effect of sodium chloride after it has entered the plant. As well as this, it has become clear that more information is needed about the mineral nutrition of halophytes.     

Effect of various chloride salts on the utilization of phosphorus, calcium, and magnesium

Only part of the effect of dietary protein on urinary calcium excretion can be ascribed to sulfur amino acids. We hypothesized that chloride, another factor often associated with isolated proteins, and another amino acid, lysine, affect utilization of calcium. The effects of supplemental dietary chloride, inorganic or organic, on calcium, phosphorus, and magnesium utilization were studied in two rat studies. Weanling Sprague-Dawley rats were fed semi-purified diets that contained moderate (1.8 mg Cl/g diet) or supplemental (15.5 mg Cl/g diet) chloride as sodium chloride, potassium chloride, or lysine monohydrochloride with or without calcium carbonate for 56 or 119 days. Rats fed supplemental sodium chloride or potassium chloride had higher urinary phosphorus excretion, more efficient phosphorus absorption, but unchanged tissue phosphorus levels after 7 and 16 weeks of dietary treatment as compared to rats fed moderate chloride. Rats fed supplemental sodium chloride or potassium chloride excreted more calcium in urine at 7 weeks and absorbed calcium less efficiently at 16 weeks. Tissue calcium concentrations were unaffected, but total tibia magnesium and plasma magnesium concentrations were lower in rats fed supplemental sodium chloride or potassium chloride than those fed moderate chloride. Lysine chloride with or without additional calcium elevated urinary calcium excretion even more than sodium chloride and potassium chloride ingestion. Rats fed lysine chloride with supplemental calcium had smaller apparent absorption and urinary losses of phosphorus and magnesium after 16 weeks and lower tibia and plasma magnesium concentrations than rats fed lysine chloride.     

Contribution of NaCl excretion to salt resistance of Aeluropus littoralis (Willd) Parl

Aeluropus littoralis is a perennial halophyte, native to coastal zones. Although it is usually exposed to high saline, this plant grows normally without toxicity symptoms. In order to assess leaf salt excretion, different growth parameters, Na(+), K(+), Ca(2+), Mg(2+) and Cl(-) concentrations, as well as excreted ions were examined in plants grown for 2 months in the presence of various salinity levels (0-800 mM NaCl). In addition, salt crystals, salt glands and other leaf epidermal structures were investigated. Results showed that total plant growth decreased linearly with increase to medium salinity. This reduction concerns mainly shoot growth. In addition, this species was able to maintain its shoot water content at nearly 50% of the control even when subjected to 800 mM NaCl. Root water content seemed to be unaffected by salt. Sodium and chloride ion contents in shoots and in roots increased with salinity concentrations, in contrast to our observation for potassium. However, calcium and magnesium contents were not greatly affected by salinity. Excreted salts in A. littoralis leaves were in favor of sodium and chloride, but against potassium, calcium and magnesium which were retained in plants. Sodium and chloride were excreted from special salt glands, which were scattered on the both leaf surfaces. In addition to salt glands, papillae were the most frequent epidermal structure found on A. littoralis leaves, and are likely involved in A. littoralis salt resistance.     

Electrophysiology of bull spermatozoa : Correlations with motility

The bioelectric characterization of bull spermatozoa was based on the establishment of a standard, for comparison with cells subjected to manipulation of the ionic environment. In addition to potassium and sodium, chloride concentration was also found to have an effect on bull spermatozoa membrane potential and motility. The chloride effect on potential was similar in magnitude to that of sodium but smaller than that of potassium. Potential difference in potassium, sodium and chloride supplemented media was related to the amplitude of the flagellar wave.     

Alteration of Ion Channels in the Plasmalemma of Nitella flexilisCells during Long-Term Hyperthermia

The conventional microelectrode technique was applied to study changes in conductance and activation characteristics of potassium and chloride channels in the plasmalemma of characean alga Nitella flexilis(L.) Agardz. during long-term heat treatment. Measurements were conducted at 18–20°C after preliminary exposure of cells to 33°C for 1–25 days. The conductance of outward- and inward-rectifying potassium channels, as well as the currents of excitable chloride channels, decreased after 2–3 days of heat treatment. By the 15th–17th days, the conductance of potassium channels was reduced by a factor of 3–5, whereas the peak values of the chloride current, associated with the action potential, was reduced by a factor of 8–10. These heat-induced changes were long lasting: the restoration of the initial parameters of transport systems after transferring cells to chilling or room temperature occurred within several days. Moreover, the recovery at chilling temperatures (8–10°C) proceeded nearly two times longer than at room temperature. Prolonged hyperthermia accelerated activation and deactivation of outward-rectifying potassium channels and caused the shift of their activation curve towards positive potentials by 35–40 mV. Analysis of current–voltage relations showed that the inward current in inward- and outward-rectifying potassium channels was reduced to a greater extent than the outward current. At the same time, both inward and outward currents of chloride channels were reduced to an equal extent. It is assumed that the changes observed are involved in thermal adaptation and account for the decrease in the intracellular concentrations of potassium and other cations and anions, which represents a nonspecific response of plant cells to stress.     

Comparative effect of potassium chloride and potassium sulfate on the yield and protein content of wheat in three different rotations

Comparative effects of potassium chloride and potassium sulfate at various levels of potassium on the performance of ARZ variety of wheat were studied at Agriculture Research Station Dera Ismail Khan, N.W.F.P., Pakistan. The experiment was laid out in three different rotationsviz, rice-wheat, maize-wheat and fallow-wheat. Potassic fertilizers were applied at the rate of 0, 37, 74, 111 and 148 kg k/ha alongwith the basal dose of 135 kgN plus 44 kg P/ha. Wheat yield data showed that the application of 37 kg K/ha of potassium chloride was found better in case of rice-wheat and fallow-wheat rotation and 37 kg K/ha of potassium sulfate for maize-wheat rotation. On the average of the three rotations, potassium sulfate at the rate of 74 kg K/ha (90 kg K₂O/ha) was found better and economical. Both the sources were almost equally effective but potassium sulfate out-yielded potassium chloride. Protein content of grains was significantly increased due to K application irrespective of the source and potassium sulfate was found with significantly higher protein content than potassium chloride.     

Nitric oxide and potassium chloride-facilitated striatal dopamine efflux in vivo: role of calcium-dependent release mechanisms

Previous studies investigating the calcium-dependency of nitric oxide-facilitated striatal dopamine efflux have produced conflicting results. In the current study, we have investigated the role of extracellular calcium in nitric oxide and potassium chloride-evoked striatal dopamine efflux in vivo using microdialysis. Dialysis probes were implanted in the anterior dorsal striatum of chloral hydrate-anesthetized rats. Intrastriatal infusion (20 min fraction) of the nitric oxide generators sodium nitroprusside (200 μM, 500 μM, or 1 mM) and 3-morpholinosydnonimine (1 mM) increased extracellular dopamine levels. The facilitatory effects of 3-morpholinosydnonimine and potassium chloride on dopamine efflux were attenuated following pretreatment (100 min) and co-infusion of calcium free artificial cerebral spinal fluid containing magnesium chloride. Local potassium chloride infusion (100 mM) administered alone elevated striatal dopamine efflux to a similar degree as potassium chloride (100 mM) delivered 60 min after 3-morpholinosydnonimine infusion. These results demonstrate that like potassium chloride, nitric oxide facilitates striatal dopamine efflux in vivo via a mechanism largely dependent on extracellular calcium. Also, as intrastriatal potassium chloride infusion evoked similar increases in extracellular dopamine levels in controls and subjects receiving pretreatment with the NO-generator 3-morpholinosydnonimine, it is unlikely that the functional integrity of DA nerve terminals is compromised via a neurotoxic disruption of plasma membrane potential following enhanced striatal NO production. © 1999 Elsevier Science Ltd. All rights reserved.     

Role of prostanoids in the control of renal function in normal potassium balance and in acute experimental potassium depletion. 4. Relation of extrarenal parameters, renal function parameters and urinary excretion of prostanoids

The renal function has been evaluated by clearance (cl.) method during hypotonic polyuria and successive moderate antidiuresis induced by a low dose of lysine-8-vasopressin; four 15 min and two 60 min cl. periods were performed, respectively. Glomerular filtration rate was estimated by creatinine cl.; the osmotic cl. (Cosm, CH2O), the absolute and fractional excretions of water, sodium, potassium and chloride were determined by usual methods. The urinary concentrations of PGE2, 6-keto-PGF1 alpha (6KPGF) and TxB2 were measured by RIA. The study protocol was applied in normal potassium balance and experimental potassium balance (KD), both in absence and presence of indomethacin. In KD groups with a potassium cumulative deficit of 198.4 +/- 22.2 meq (D3; n = 6) during polyuria significant correlations are consistent with the hypothesis that the lower the plasma potassium concentration is the higher the urinary chloride excretion and the inhibition of distal fractional chloride reabsorption. Moreover, by utilizing the polyuria and antidiuresis data pool, the effects of urine flow rate changes on PGE2 and 6KPGF urinary excretions are blunted as compared to normal potassium balance (n = 14). After indomethacin treatment (D3.I) the following functional relationships are disclosed: a) the lower the kaliemia is the lower the urinary chloride and potassium excretions and the higher the fractional isosmotic reabsorption; b) the lower the urinary potassium excretion is the lower the urinary chloride excretion. In both D3 and D3.I experimental groups the positive correlation between urinary chloride excretion and urinary potassium excretion is significant.     

Growth and mineral content of coriander (<Emphasis Type="Italic">Coriandrum sativum</Emphasis> L.) plants under mild salinity with different salts

Soil salinity is a complex issue in which various anions and cations contribute to have a general adverse effect on plant growth. In the present study, effects of salinity from various salts including sodium chloride (NaCl), potassium chloride?+?sodium chloride?+?calcium chloride (KCl?+?NaCl?+?CaCl₂), potassium sulfate?+?magnesium nitrate (K₂SO₄?+?Mg(NO₃)₂) at two electric conductivities (EC) of 2 and 4 dS m^?1 of irrigation water, and a distilled water control were evaluated on coriander plants (Coriandrum sativum L.). At EC?=?2, all salts increased plant yield (shoot fresh weight) than control. Most growth traits including plant height, shoot fresh and dry weight, leaf SPAD value and vitamin C, leaf K, Mg and P concentrations were increased by K₂SO₄?+?MgNO₃, and remained unchanged by KCl?+?NaCl?+?CaCl₂ treatment (except reduced plant height). Leaf’s zinc concentration reduced by either treatment. Even sodium chloride at EC?=?2 showed some beneficial effects on leaf chlorophyll index, root fresh weight, leaf’s calcium and phosphorus concentration; however, most traits remained unchanged than control. Treatment of plants with NaCl or KCl?+?NaCl?+?CaCl₂ at either EC increased the number of flowered shoots and leaf proline content than control. Most growth and quality traits including leaf minerals and vitamin C content were reduced by NaCl at EC?=?4; however, shoot fresh and dry weights remained unchanged than control. Plant root fresh weight increased by NaCl at EC?=?2 and decreased at EC?=?4 than control. At EC?=?4, shoot dry weight was increased and leaf Ca, P, Zn and Mn were decreased by KCl?+?NaCl?+?CaCl₂, whereas shoot dry weight, leaf SPAD value and vitamin C content, leaf Mg and P were increased and leaf Zn was decreased by K₂SO₄?+?MgNO₃ than control. The results indicate that in contrast to sodium chloride, the salinity effects of other salts can not be detrimental on coriander plant growth.     

Moderate potassium chloride supplementation in essential hypertension: is it additive to moderate sodium restriction?

Twenty patients with mild or moderate essential hypertension and not receiving any drug treatment, who had been moderately restricting their sodium intake to around 70 mmol(mEq) a day for at least one month and whose mean blood pressure was then 163/103 mm Hg, were entered into a double blind, randomised crossover study to compare one month''s treatment with slow release potassium chloride tablets (64 mmol potassium chloride a day) with one month''s treatment with a matching placebo. Mean (SEM) urinary sodium excretion on entry to the study was 68 (6.8) mmol/24 h. Mean urinary potassium excretion increased from 67 (6.9) mmol(mEq)/24 h with placebo to 117 (4.6) mmol/24 h with potassium chloride. Supine and standing systolic and diastolic blood pressures did not change significantly with potassium chloride supplementation when compared with pressures while receiving placebo or before randomisation. In patients who are able moderately to restrict their sodium intake doubling potassium as a chloride salt has little or no effect on blood pressure.     

Studies on fertilization of field-grown irrigated alfalfa

Alfalfa (Medicago sativa L.) yields of 20–25 ton/ha are obtainable in a Mediterranean climate, with 8–9 harvests each year. These high yields demand a large supply of potassium from the soil. Plant uptake of potassium reached 540 kg K ha, the majority being derived from the exchangeable form. A safety level of 2.5% K in the whole plant is needed to prevent yield declines. Fertilization with potassium chloride gave higher yields than with potassium sulfate. Splitting the K application over period of two cuts is recommended for sandy loam soils with a low cation exchange capacity.Contribution from the Agricultura Research Organization, The Volcani Center, Bet Dagan, Israel. 1975 Series, No.186-E.