Exchangeable Sodium Content Research Articles

Interactive effects of exchangeable sodium and water content on soil modulus of rupture

The interactive effect between exchangeable sodium (sodium adsorption ratio, SAR = 1, 7, 15, 30 and 50) and water content (water saturated and field capacity) on soil hardsetting behaviour was investigated in a loamy topsoil of a Typic Natraquoll. Hardsetting was evaluated by the modulus of rupture (MOR) of dry aggregates, previously subjected to a static pressure simulating that imposed by an adult cow (400 kPa). A control receiving no pressure was included. In both control and water saturated treatments, MOR increased steadily (from 6.5 to 10.4 MPa) with SAR. This indicates that the effect of exchangeable sodium prevailed over that of water content when the soil was stressed at saturation. Exchangeable sodium and water content interacted significantly (F ratio = 4.56; α < 0.002) during the applied pressure, but this interaction was not synergistic. Soil stressing at field capacity prevented MOR increases above a threshold of SAR ≥ 7. As a consequence, an attenuation of hardsetting behaviour can be expected when the studied soil is trampled in moist field conditions.

The effects of soil sodicity on emergence, growth, development and yield of oilseed rape (Brassica napus)

SUMMARYThe effects of exchangeable sodium on emergence, growth, development and yield composition of oilseed rape were investigated at Buenos Aires, Argentina in 1992. A pot experiment was performed using five exchangeable sodium levels, expressed as Sodium Adsorption Ratio (SAR: 12, 20, 27, 34 and 44). Soil with nine different exchangeable sodium contents (SAR from 0·5 to 50) and seven different particle size distributions (from sandy loam to clay) were used in a parallel trial to study the effect of soil crusting on oilseed rape emergence. Soil crusts were made using a rainfall simulator after seeds were sown. Both experiments showed that the direct effect of sodium on emergence occurred with SAR values higher than those which caused clay dispersion (SAR &gt; 20). Oilseed rape seedlings could penetrate crusts having a resistance of &lt; 230 kPa. At SAR values &gt; 20, main stem growth and yield decreased significantly (P &lt; 0·05). These reductions were counterbalanced by an increase in the number of secondary stems. At SAR levels &gt; 34, stem number, grain number per pod on the main stem, as well as pod number on both main stem and secondary stems, were reduced, leading to a marked reduction in total yield. The most important agronomic effect of soil sodium on oilseed rape would be at emergence stage, due to soil crusting.

Univalent Cation Fluxes in Human Erythrocytes from Individuals with Low or Normal Sodium Intake

High salt intake is a risk factor for essential hypertension in man. There is evidence that, in hypertension, intracellular sodium content and univalent cation transport across erythrocyte membranes are changed. It has been proposed that a low-sodium diet has an antihypertensive effect; this may be related to changes in cation fluxes across plasma membranes. Sodium and potassium fluxes and the composition of fatty acids were studied in the erythrocytes of people who had eaten a low-sodium vegan diet for many years (n = 9) and in those of controls who had consumed a mixed diet (n = 11) to investigate the dependence of these variables on dietary factors. Both systolic and diastolic blood pressures were lower in vegans than in controls. The passive permeability to sodium (P < 0.05) ,Na+,K+ cotransport (P < .001) and the intracellular content of exchangeable sodium (P = 0.076) were decreased in the erythrocytes of those who had consumed the low-sodium diet compared with the controls. The activity of the Na+-K+ pump, Na+-H+ exchange and the passive permeability to potassium were unaltered. Swelling-induced K+,C1- cotransport was increased in the erythrocytes of those who had eaten the low-sodium vegan diet compared with controls (P < 0.01). The proportion of linoleic acid was increased (P < 0.01) at the expense of eicosapentaenoic and docosahexaenoic acids (P < 0.001) in the erythrocyte membranes of the vegans. Our results show that levels of intracellular sodium and Na+,K+ cotransport activity, which increase in patients with hypertension, decreased in those consuming a low-sodium vegan diet. This suggests that the risk of essential hypertension was diminished in the vegan participants, confirming our observation that systolic and diastolic blood pressures were lower in the strict vegans than in the controls.

Sodic soils in Western Australia

Sodic soils are common throughout Western Australia, particularly in the south-west agricultural area where they occur mainly as duplex or gradational profiles. Soils with sodic properties are dominant in 26% of the state; saline-sodic sediments and soils in intermittent streams, lakes and estuarine plains occupy a further 5%. Sodic soils are moderately common throughout the south and western portion of the rangeland areas (38% of the state). The south-west coastal sands and the desert and rangeland soils to the north and east of the state are rarely sodic. Although sodicity has been recognized as a discrete problem in W.A. soils since the 1920s, the extent and severity of sodicity has been satisfactorily described only for small areas of the state and most land managers are unaware of the role sodicity plays in limiting the productivity of their soils. Sodicity is implicated in a diversity of problems for both agricultural and non-agricultural uses of Western Australian soils. Subsoil impermeability is probably the most widespread of these, but no comprehensive, quantitative assessment of the influence of exchangeable sodium on subsoil properties has been undertaken. Topsoil sodicity is much less extensive but can severely restrict land productivity, particularly on sandy loam and finer textured soils which set hard when dry. The physical behaviour of Western Australian topsoils cannot usefully be predicted from measurements of exchangeable sodium alone because soils differ so greatly in their response to changing exchangeable sodium. Some remain structurally stable at ESP values &gt;15 while others are so 'sodium-sensitive' that they exhibit highly dispersive behaviour at ESP values as low as 2%. Land values over much of the dryland farming and pastoral areas of W.A. do not justify sustained use of amendments which would reduce soil exchangeable sodium contents. Efficient management of sodic soils in these areas must rely on the prevention of degradation and the use of biological and physical means to maintain adequate soil physical properties. Effective restoration of degraded sodic soils, however, often does require application of inorganic amendments in combination with tillage to initiate structural recovery. Sodicity is currently not considered to be a problem at any of the three main irrigation areas in W.A., but all have sodic soil within their potentially irrigable lands, which may limit their future expansion.

Hypertension Secondary to Early-Stage Kidney Disease: The Pathogenetic Role of Altered Cytosolic Calcium (Ca2+) Homeostasis of Vascular Smooth Muscle Cells

We have examined cardiovascular pressor responsiveness to infused norepinephrine (NE) as related to endogenous plasma NE and plasma renin and to platelet free cytosolic (Ca2+) in 36 patients with early-stage kidney disease and 27 matched normal subjects. The 27 hypertensive patients and the normal subjects did not differ in blood volume, plasma renin, and NE; however, the hypertensive patients had a higher exchangeable body sodium content. Basal plasma NE levels, the relationship between plasma NE measured during NE infusion and the corresponding NE infusion rate, as well as the total plasma clearance for NE did also not differ significantly between the two study groups. In contrast, the threshold or pressor doses of infused NE significantly decreased in the patients with kidney disease. Antihypertensive pharmacotherapy with (Ca2+) channel blockers and/or loop diuretics normalized blood pressure and cardiovascular NE hyperresponsiveness and reduced blood volume, exchangeable body sodium, and platelet free cytosolic (Ca2+). In contrast, experimental digitalisation as a model for in vivo sodium/potassium adenosine triphosphatase inhibition augmented NE responsiveness and raised platelet free cytosolic (Ca2+). Incubation of platelets from normal subjects with plasma ultrafiltrate from hypertensive patients gave evidence for an endogenous factor capable to raise free cytosolic (Ca2+) and to act synergistically with digoxin. Hypertension secondary to early-stage kidney disease is related to an impairment of sodium excretion leading to an expansion of blood volume and exchangeable body sodium. This may result in increased secretion of endogenous factors, leading to alterations of cytosolic (Ca2+) homeostasis of vascular smooth muscle cells followed by elevated peripheral resistance and thus blood pressure.

Physico-Chemical Effect on Compressibility of Tropical Soils

The paper examines the role of physico-chemical factors in the consistency limits and compressibility behavior of kaolinitic soils and montmorillonitic soils of residual origin. The liquid limit, equilibrium void ratio at a given load (in the oedometer test) and compression index values of the kaolinitic soils in the remolded state correlate well with the shrinkage limit values, which in turn are a function of the clay fabric. The corresponding engineering properties of the remolded montmorillonitic soils correlate well with the exchangeable sodium content that reflects a soil’s potential to develop diffuse ion layer. Oedometer tests with undisturbed samples highlight the role of clay mineralogy in the engineering behavior of residual soils; on inundation with water under a nominal pressure, the kaolinitic soils exhibit no volume change while the montmorillonitic soils exhibit a notable swell. Oedometer tests with undisturbed samples also showed that besides the physico-chemical factors, the in-situ moisture content, density and degree of saturation have an important bearing on the void ratio sustained by the soils at a given stress level.

Effect of Pulp and Paper Mill Effluent Irrigation on Carbon‐di‐oxide Evolution in Soils

AbstractPulp and paper mill waste water irrigation increased pH, EC, organic carbon and exchangeable sodium content of soils. The increase in organic matter content of soils accelerated microbial activity and hence accelerated substrate decomposition with the release of CO2. There exhibited a peak followed by a steady‐decline in the rate of CO2 evolution in effluent irrigated soils. The irrigation of pulp and paper mill combined effluent to soils did not affect microbial activity.

Changes in the renin-angiotensin system, exchangeable body sodium, and plasma and atrial content of atrial natriuretic factor during evolution of chronic renal failure in the rat.

The remnant kidney model of progressive renal failure in the rat was used to assess the relationships between the renin-angiotensin system, exchangeable body sodium, and both plasma concentration and atrial content of atrial natriuretic factor (ANF) measured sequentially over 4 weeks. Following subtotal nephrectomy plasma creatinine (mumol/L) rose from 40 +/- 6 (sham) to 107 +/- 24 (P less than 0.05) at 1 week, and rose further to 124 +/- 20 (P less than 0.05) by 4 weeks. Plasma renin activity (nanograms of angiotensin I/mL/min) rose from 4.5 +/- 0.5 to 11.8 +/- 2.8 (P less than 0.05) at 1 week, but was suppressed by 4 weeks to 2.2 +/- 0.3 (P less than 0.001). Plasma angiotensin II (pg/mL) was 52 +/- 2 (sham), 117 +/- 20 at 1 week (P less than 0.05) and 51.3 at 4 weeks. Exchangeable sodium (mmol/kg) rose progressively from 43.2 +/- 5 (before surgery) to 48.6 +/- 0.9 at 1 week and 50.8 +/- 2.2 at 4 weeks. Plasma atrial natriuretic factor (ANF) (pg/mL) rose progressively from 114 +/- 6 (sham) to 248 +/- 31 (P less than 0.01) at 1 week and 456 +/- 78 at 4 weeks (P less than 0.01). Atrial ANF content fell as the plasma concentration rose. In the remnant kidney model of progressive renal failure there was a progressive increase in exchangeable body sodium and plasma atrial natriuretic factor, with reciprocal changes in atrial ANF content suggesting that ANF secretion rate was increased. Initially the renin-angiotensin system was stimulated, but later it was suppressed.

Effects of chlorpromazine on Na+-K+-ATPase pumping and solute transport in rat hepatocytes

Inhibition of Na+-K+-ATPase and sodium-dependent bile acid transport has been suggested as a mechanism for the cholestasis produced by certain drugs such as chlorpromazine. We examined the effects of chlorpromazine (and in selected studies, two of its metabolites) on Na+-K+-ATPase cation pumping (ouabain-suppressible 86Rb uptake), exchangeable intracellular sodium content, membrane potential (assessed by 36Cl- distribution), and sodium-dependent transport of taurocholate and alanine in primary cultures of rat hepatocytes. Chlorpromazine (10-300 microM), 7,8-dihydroxychlorpromazine (10-300 microM), and ouabain (0.1-2 mM), but not chlorpromazine sulfoxide, produced a concentration-dependent decrease in Na+-K+-ATPase cation pumping and an increase in intracellular sodium content. Chlorpromazine (100 microM) and ouabain (0.75 mM) also modestly decreased hepatocyte membrane potential. In further studies, chlorpromazine (75 and 100 microM) and ouabain (0.1, 0.5, and 0.75 mM) decreased initial sodium-dependent uptake rates of taurocholate and alanine by 18-63%. Although the steady-state intracellular content of alanine was decreased 25-53% by both agents, chlorpromazine increased the steady-state content of taurocholate by 171% and decreased taurocholate efflux, apparently related to partitioning of taurocholate into a large, slowly turning over intracellular pool. These studies provide direct evidence that chlorpromazine inhibits Na+-K+-ATPase cation pumping in intact cells and that partial inhibition of Na+-K+-ATPase cation pumping is associated with a reduction of both the electrochemical sodium gradient and sodium-dependent solute transport. These effects of chlorpromazine may contribute to chlorpromazine-induced cholestasis in animals and humans.

A rapid method to determine cation exchange capacity and exchangeable bases in calcareous, gypsiferous, saline and sodic soils

Summary A simple, single‐step extraction with LiEDTA for the estimation of CEC and exchangeable bases in soils has been developed. Multivalent cations are stripped from the soil adsorption sites by the strongly chelating agent EDTA, and are replaced by Li. In soils without CaCO3 or water soluble salts, exchangeable divalent cations (Ca, Mg) are chelated by EDTA and exchangeable monovalent cations (Na, K) are replaced in a single extraction step using 0.25–2.5 g of soil and 10.0 ml of extractant. In calcareous soils the CEC can be determined in the same way, but for the extraction of exchangeable Ca and Mg, another separate extraction is needed because dissolution of calcite by EDTA is unavoidable. This extraction is done with as much NaEDTA as needed to extract only exchangeable Ca and Mg in a 1:2 (m/V) soil/alkaline‐50% (V/V) aethanolic solution to minimize dissolution of calcite. In gypsiferous soils gypsum is transformed into insoluble BaSO4 and soluble CaEDTA by LiBaEDTA thus avoiding interference of Ca from dissolution of gypsum, which renders the traditional methods for determining CEC unsuitable for such soils. To determine exchangeable Ca and Mg, Na4EDTA is used as for calcareous soils. In saline/sodic soils replacement of Na by Li is incomplete but the Na/Li‐ratio at the complex after extraction is proportional to the molar Na/Li‐ratio in the extracts, so that the CEC and original exchangeable sodium (ESP) content can be calculated. Additional analysis of Cl and, if necessary, SO4 in the extracts of saline soils can be used to correct for the effect of dissolution of the salts on the sum of exchangeable cations. This new method is as convenient as the recently developed AgTU (silverthiourea), but is better suitable for calcareous and gypsiferous soils.

Effect of Iron Pyrites, Organic Materials and Micronutrients on Yield of Rice and Wheat and on Amelioration of Sodic Soil

SUMMARYThe effects of iron pyrites, organic materials and micronutrients on the yield of rice and wheat and on the amelioration of saline sodic soil were studied at Kanpur. The grain yield of the first crop of rice increased from 1.37 to 2.97 t ha−1 following application of pyrites at 50% of the estimated gypsum requirement. The grain yield of succeeding wheat and rice crops also increased significantly with pyrites treatment. These increases were associated with marked decreases in pH, electrical conductivity, exchangeable and soluble sodium content and bulk density of the soil and with an increase in its hydraulic conductivity. The beneficial effect of pyrites was increased with the application of rice straw, Sesbania as green manure and micronutrients, the pyrites plus Sesbania green manure treatment being the most effective.

Inhibition by somatostatin of bovine growth hormone secretion following sodium channel activation.

1. Growth hormone secretion, exchangeable cellular sodium and calcium concentrations measured by 22Na and 45Ca incorporation, and efflux of 45Ca were studied in dispersed bovine anterior pituitary cells. 2. Addition of veratridine (100 microM), an activator of sodium channels, increased exchangeable sodium and calcium concentrations in the cells, the efflux of 45Ca from prelabelled cells, and caused a biphasic stimulation of the rate of growth hormone secretion. Secretion of growth hormone was not stimulated when the extracellular calcium was decreased below 0.1 mM. 3. The increases in growth hormone secretion, exchangeable calcium concentration and 45Ca efflux from prelabelled cells caused by veratridine were abolished by addition of the calcium antagonist verapamil (20 microM). Verapamil also reduced the rise in exchangeable sodium caused by veratridine and increased the resting exchangeable sodium concentrations. 4. The peptide somatostatin (1 micrograms/ml) prevented veratridine-stimulated growth hormone secretion but did not inhibit the increases in exchangeable sodium and calcium caused by veratridine. The peptide itself elicited a transient increase in 45Ca efflux and subsequently partially inhibited veratridine-stimulated 45Ca efflux. 5. The data suggest that anterior pituitary cells possess voltage-sensitive sodium channels. Activation of these channels by veratridine may lead to depolarization and increased entry of calcium via potential-dependent calcium channels, which contributes to a rise in cytoplasmic calcium concentration and the subsequent stimulation of growth hormone secretion. We conclude that the calcium antagonist verapamil may also interact with sodium channels, and that the peptide somatostatin may act on growth-hormone-secreting cells either to prevent the rise in cytoplasmic calcium by hyperpolarizing the cells or to decrease the affinity of a population of calcium binding sites in the cells.

Transport of sodium, chloride, and taurocholate by cultured rat hepatocytes.

Transport of sodium, chloride, and taurocholate was studied in primary cultures of adult rat hepatocytes incubated in a balanced electrolyte solution containing 150 mM NaCl, various concentrations of taurocholate, and (22)Na, (36)Cl, [(3)H]taurocholate, and 3-O-[(3)H]methyl-D-glucose. Lithium chloride, choline chloride, or Na(2)SO(4) and mannitol were substituted isotonically for NaCl in selected studies. The steady-state intracellular concentrations of exchangeable sodium and chloride averaged 6.5 mM and 30.1 mM, respectively. Ouabain reversibly increased intracellular sodium concentration. Chloride entry rate was about double that of sodium. Unlike sodium entry, chloride entry rate increased nonlinearly with increasing extracellular concentration. Taurocholate entry exhibited both saturable and nonsaturable components; the former accounting for virtually all taurocholate uptake at concentrations comparable to those found in vivo. Taurocholate was actively concentrated by the cultured cells, with the steady-state intracellular-to-extracellular concentration ratio decreasing from over 50 to about 1 as extracellular taurocholate concentration was increased from 10 muM to 4 mM. Both the saturable uptake component and concentrative taurocholate transport were virtually abolished by substitution of choline or lithium for sodium or by addition of ouabain. Taurocholate entry rate first increased in a sigmoid fashion and then decreased as extracellular sodium concentration was increased from 0 to 150 mM. Sodium entry rate increased in the presence of added taurocholate with an average of one sodium ion accompanying each taurocholate molecule into the cell. These findings indicate that sodium and chloride differ strikingly in their mechanism and rate of entry into cultured rat hepatocytes and in their intracellular concentration. Moreover, hepatocytes concentrate taurocholate by a sodium-coupled mechanism with an apparently equimolar transport stoichiometry.

Irrigation Water Requirement for Dissolution of Gypsum in Sodic Soil

AbstractLaboratory studies were conducted to determine the effect of exchangeable sodium content of the soil and the particle size of gypsum on the irrigation water needs for dissolving gypsum mixed in sodic soils. Gypsum dissolution increased with an increase in the exchangeable Na content of the soil. About 4 cm of water was sufficient to dissolve all the agricultural grade gypsum of &lt;0.26‐mm size. The amount of water required to dissolve the added gypsum and to reclaim a sodic soil did not increase with the amount of gypsum added, provided it equalled the gypsum requirement.The effect of particle size of gypsum on its dissolution and the applicability of the equal‐reduction hypothesis were examined. The dissolution of gypsum was approximately predicted by a dissolution equation based on particle surface area if the initial particle sizes were neither very coarse (&lt;0.5 mm) nor very fine (&gt;0.1 mm). The water required for complete dissolution of gypsum computed from a dissolution equation, increased from 2.8 cm to 15.9 cm as gypsum particle size increased from &lt; 0.1 mm to 0.5–2.0 mm.

The Ionic and Water Relations of Embryos of Lymnaea Stagnalis, A Freshwater Pulmonate Mollusc

ABSTRACT From cleavage to hatching Lymnaea stagnalis (L.) embryos exhibit net uptakes of radioactive sodium, potassium and calcium greater than the amounts of these ions initially present in the capsular fluid, implying the early development of mechanisms for ion uptake from the dilute external water. The rates of net uptake increase very rapidly during trochophore to veliger stages when the main volume increase and shell formation takes place. 22Na influx increases dramatically at first cleavage from 0·03 to 0·04 pmol min−1 in the hour before cleavage to 0·23 pmol min−1. A further increase occurs in early cleavage and for decapsulated morula to gastrula stages the influx is estimated to be 2·75 pmol min−1. 22Na efflux rates are also high in decapsulated morulae, blastulae and gastrulae (minimal estimates 1·40–3·35 pmol min−1) indicating a rapid exchange of sodium between the embryos and the medium. In sodium-free medium the 22Na efflux from decapsulated blastulae is 0–5 pmol min−1, suggesting that exchange diffusion is a large component of the fluxes. The characteristics of 22Na efflux indicate that sodium does not exchange with the medium as a single compartment. Expansion of the’recurrent’ cleavage cavity of early stages is accompanied by a rise in exchangeable sodium content from 5 pmol in embryos without cavities to 11-19 pmol in embryos with normally expanded cavities. Experimental expansions of the blastocoel of morula-blastula stages produced by cyanide are also accompanied by great increases in embryo exchangeable sodium content. A general model is proposed for the movements of sodium and water in the embryos and this provides a mechanism for hyperosmotic regulation by the embryos.

Relative significance of electrolyte and cation exchange effects when gypsum Is applied to a sodic clay soil

The hydraulic conductivity of disturbed samples of a sodic clay taken from a field experiment at Benerembah, in the Riverina of New South Wales, was increased markedly by the addition of gypsum (at 12.5 t ha-1). This initial response is considered to result mainly from an electrolyte effect rather than from cation exchange. After three seasons of irrigation of cotton, essentially all the gypsum had dissolved and the response had declined very considerably. Residual cation exchange accounted for an increase of about 10% in exchangeable calcium, and a decrease of 20 % and 5 % in exchangeable sodium and magnesium contents respectively, in the top 30-40 cm. The exchange involved 40-50% of the calcium applied and represented, in terms of exchangeable sodium lost, a replacement efficiency of some 20-30%. Below 60 cm the situation was reversed with an apparent loss of exchangeable calcium and an increase in exchangeable sodium. Leaching of soluble calcium, magnesium and sodium chlorides, somewhat greater than that in normally tilled soil, occurred especially from between 40 and 120 cm in the gypsum treated-deep tilled soil. Soluble sulphate, on the other hand, was retained in the profile above 130 cm, in amounts about equal to that applied as gypsum. The soluble chlorides accumulated below 130 cm, including apparently the unaccounted applied calcium and exchangeable calcium lost from depths below 60 cm. Deep tillage alone enhanced leaching of soluble calcium and sodium in the upper 80 cm to a similar degree to that when combined with gypsum treatment.

The distribution of sodium in aortic walls from spontaneously hypertensive and normotensive rats.

The contents of exchangeable sodium, bound sodium and total water and the extracellular space of thoracic aortas from normotensive and spontaneously hypertensive rats were measured. The aortas from the hypertensive rats contained more sodium than those from the normotensive animals while the total water content and extracellular space in the two groups were the same. The capacity to bind sodium in an osmotically inactive form was greater in the aortas from the hypertensives than in those from the normotensives. The difference in binding capacity was of the same order of magnitude as the difference in sodium content, indicating that the excess sodium in the thoracic aortas from the hypertensive rats was osmotically inactive and thus unable to cause water logging.

Substrate freezing and thawing as a factor in the mineral nutrient status of mire ecosystems

The effect of freezing and thawing on the release of sodium, potassium, calcium, magnesium, iron, and aluminium directly into the sample water and into a dilute acid extractant was investigated using peat samples collected from three different mire sites. In most cases exchangeable sodium, potassium, calcium, magnesium, and iron content of the treated samples was greater than in the untreated controls. Changes in aluminium content are more probably related to drying and re-wetting of the samples than to freezing and thawing. The role of freezing and thawing in the nutrient status of mires is discussed.

Plasma volume, extracellular fluid volume and exchangeable sodium concentrations in the New Zealand strain of genetically hypertensive rat.

1. Rats of the New Zealand strain with genetic hypertension (GH rats) were found to have lower plasma volume in relation to body weight than rats of the normotensive parent strain (N rats). GH rats had higher venous packed-cell volume percentage than N rats, but total erythrocyte volume was similar in the two strains of rats. Extracellular fluid volume and exchangeable sodium concentrations were lower in the GH rats. Plasma sodium concentration was not altered; plasma potassium concentration was slightly higher in the GH rats. 2. These results indicate that hypersecretion of a sodium-retaining hormone is unlikely to be a primary factor causing hypertension in the GH rats. Cardiac output has not been measured: if an increased cardiac output is a factor in the maintenance of the hypertension, it is evidently not secondary to an increased blood volume. 3. The lower exchangeable sodium concentrations and body fluid volumes found in the GH rats may be due to lower aldosterone activity secondary to a decrease in the activity of the renin-angiotensin system, or to the effects of the elevated blood pressure on the renal handling of sodium, or to both factors.

Prediction of the fertiliser needs of sugar‐beet grown on fen peat soils

AbstractThe fertiliser requirements of sugar‐beet grown on fen soils were tested in 52 experiments from 1963 to 1969. In some fields, N.P.K and Na and, especially N and P, greatly increased yields, but the average responses obtained with the four elements were small. To help to predict where and how much fertiliser was needed for sugar‐beet, soils were grouped according to soil analysis and classified by loss on ignition. Sugar‐beet grown on soils with less than 20 μg/ml P (extracted with sodium bicarbonate) needed 1·20 cwt/acre P2O5, with 21–45 μg/ml P, 0·75 cwt/acre P2O5, and with more than 45 μg/ml P no fertiliser was required. Most soils contained high concentrations of K; with less than 100 μg/ml K (extracted with ammonium nitrate), 2·00 cwt/acre P2O was probably justified; with 100–250 μg/ml, 1·00 cwt/acre K2O was needed. Most of the responses to agricultural salt were by crops on soils with exchangeable sodium concentrations of less than 30 μg/ml Na. Loss on ignition was related to response to N fertiliser; when the loss was 14–25%, N increased yield by 6 cwt/acre sugar and 1·2 cwt/acre N fertiliser was Heeded and when the loss was 26–35%, the yield was increased by 3·5 cwt/acre and 0·6 cwt/acre N was needed. With greater losses there was little response.