Concentration In Corn Research Articles

Distribution and Plant Availability of Soil Boron Fractions

AbstractThe fractionation of soil B and the plant availability of each fraction have not been examined extensively. This laboratory and greenhouse research was conducted to study the distribution and plant availability of B in different soil fractions. Total B in the 14 soils under study ranged from 21.5 to 96.3 mg kg−1. A trace to 0.34% of the total B was in a water‐soluble form; ≤0.23% was 0.02 M CaCl2 extractable (nonspecifically adsorbed B); from 0.05 to 0.30% was mannitol exchangeable (specifically adsorbed B); and from 0.23 to 1.52% was acidified NH2OH·HCl extractable (B occluded in Mn oxyhydroxides). Ammonium oxalate solution (pH 3.25) extracted from 2.8 to 34.4% of the total soil B in the dark (B occluded in noncrystalline Al and Fe oxyhydroxides) and from 17.5 to 73.9% under ultraviolet (UV) light (B occluded in crystalline Al and Fe oxyhydroxides). Residue B, which was considered to be in association with soil silicates, accounted for 2.4 to 79.2% of the total B. Boron concentration in corn (Zea mays L.) tissue correlated positively (α = ≤0.05) with water‐soluble B, CaCl2 extractable B, mannitol exchangeable B, and acidified NH2OH·HCl extractable B. The sum of these four fractions, which were related to B availability, accounted for only 0.4 to 2.0% of the total B in the 14 soils. Boron concentration in corn tissue was unrelated (α = 0.05) to NH4‐oxalate extractable B (either in the dark or under UV light) and to the residue B fraction. These relationships indicate that B in noncrystalline and crystalline Al and Fe oxyhydroxides and in silicates was relatively unavailable for plant uptake.

Nitrogen Contribution to Succeeding Corn from Alfalfa and Red Clover1

AbstractThe use of leguminous crops as plowdown has stimulated interest in their contribution to soil fertility. The contribution of N from single‐year plowdown to a succeeding corn (Zea mays L.) crop was evaluated in two field experiments located at Elora, Ontario, on a Guelph‐London loam series Grey‐Brown Luvisolic (Typic Hapludalf) soil. In Experiment 1, 20 cultivars of alfalfa (Medicago sativa L.) and 10 cultivars of red clover (Trifolium pratense L.) were compared. Experiment 2 included two cultivars each of alfalfa and red clover under three management treatments. Nitrogen yield of plowdown legumes was considered in relation to the yield and wholeplant N concentration of the succeeding corn crop. In both experiments, whole‐plant N concentration of corn was significantly higher following alfalfa than following red clover. This suggested that alfalfa N was more readily mineralized than that of red clover, as predicted by a decomposability index based on the C/N ratio and lignin concentration of the plowdown material. However, corn yield following alfalfa plowdown was not always greater than that following red clover. Factors other than N‐supply may have influenced corn yield response to legume plowdown. Although significant cultivar variation in plowdown N yield was observed, there appeared to be no association with succeeding corn yield and N concentration. In general, legume plowdown supported corn yields equivalent to those achieved with 90 to 125 kg ha−1 of fertilizer N.

Plant Availability of Phosphorus in Sewage Sludge Compost

AbstractField and greenhouse studies were conducted to compare the effectiveness of Blue Plains sewage sludge compost (BLU), Parkway sewage sludge compost (PAR), and triple superphosphate (TSP) as sources of P for corn. These amendments were applied to a Sassafras sandy loam (Typic Hapludults) in a field study and to the Sassafras soil and a Christiana silty clay loam (Typic Paleudults) in a greenhouse study. First‐year application rates in the field study ranged from 0 to 1500 kg total P/ha. Plots were split the second year with one‐half receiving no additional P and one‐half receiving P equal to 1st‐yr rates. Nitrogen as NH4NO3 was applied at variable rates to plots so that the total assumed available N equaled 180 and 219 kg N/ha for the 1st and 2nd yr, respectively. Dry matter yield and P uptake were measured at the eight‐leaf stage (V8) and at maturity. Below the 100 kg P/ha rate, there were no significant differences in P uptake or yield among the different sources and rates of P. Above the 100 kg P/ha rate, TSP but not the composts, significantly increased growth and P uptake by corn in both field and greenhouse studies. The TSP was approximately four to seven times more effective than either compost in raising tissue P concentration in corn (Zea mays L) ear leaves. A maximum of 2.05 and 11.2% of the P applied as compost and TSP, respectively, was taken up by the corn. Soil P extracted by the dilute double acid (0.5 M HCl and 0.0125 M H2SO4) and 0.5 M NaHCO3 methods increased with increasing P application from all sources. Extractable soil P by both methods correlated well with total P uptake from TSP but did not correlate well with P uptake from the composts. A P fractionation indicated that most of the compost P was associated with Fe and Al and only 2 to 5% was in organic forms. The Fe‐bound P fraction of the amended soils increased with increasing P application from all sources. Two factors appeared to control the P uptake response of corn: the treatment of the wastewater to remove P at the sewage treatment plant, and the P fixing capcity of the soil.

Extractability and Plant Availability of Molybdenum from Inorganic and Sewage Sludge Sources

AbstractA greenhouse experiment was conducted to evaluate the influence of soil pH on the plant uptake and extractability of Mo applied to a soil as an inorganic salt and as a Mo‐enriched sewage sludge. Molybdenum additions of 30, 60, and 120 mg/kg soil from Na2MoO4·2H2O and 20, 44, and 94 mg/kg soil from an anaerobically digested sewage sludge significantly increased Mo concentrations in corn (Zea mays L.), soybeans [Glycine max (L.) Merr.], and alfalfa (Medicago sativa L.) grown on a sandy loam soil. Increases in soil pH significantly increased Mo accumulation in the three crops from both Mo sources. Molybdenum extracted with Tamm's acid ammonium oxalate was not significantly influenced by soil pH, while Mo extracted from sludge treated soils with the ammonium bicarbonate‐DTPA (AB‐DTPA) extractant was significantly increased with increasing soil pH. Multiple regressions between Mo concentrations in the crops and extractable Mo and soil pH indicated that soil pH was a significant variable in 17 of 24 prediction equations. The AB‐DTPA extractant was more effective in predicting Mo concentrations in plant tissue than Tamm's acid ammonium oxalate with sludge Mo additions and is more effective with sludge source Mo as compared to inorganic source Mo. Whether AB‐DTPA will predict Mo uptake by plants grown on soils receiving Mo additions needs to be tested by field evaluation with a large number of soil types.

Interaction of Combined Nitrogen with the Expression of Root-Associated Nitrogenase Activity in Grasses and with the Development of N2 Fixation in Soybean (Glycine max L. Merr.)

Soluble root N concentrations of corn, sorghum, pearl millet, rice, wild rice, and soybeans were determined and related to measurements of nitrogenase activity and changes in availability of combined N to plants. In corn, sorghum, and pearl millet, applications of fertilizer N increased soluble root N concentrations, but root-associated nitrogenase activity was negligible in control and treated plants. Applications of NH(4)NO(3) to rice increased the water soluble root N concentrations and inhibited root-associated nitrogenase activity. In wild rice, root-associated nitrogenase activity was absent during vegetative growth and developed at the reproductive growth stage. The soluble root N concentration decreased progressively as wild rice grew indicating that the availability of combined N in the root environment declined. Therefore, development of nitrogenase activity in wild rice is associated with the change in availability of combined N in the root environment. The development of nitrogenase activity in wild rice was probably not due to colonization of roots by N(2)-fixing bacteria because most probable numbers of recovery did not significantly vary throughout the plants' growth cycle. In field-grown soybeans with or without fertilizer N application, we also observed a relationship between a decrease in soluble root N concentration and the development of nitrogenase activity.

Association of Low Levels of Aflatoxin in Feed with Productivity Losses in Commercial Broiler Operations , ,

Six growers from each of five broiler companies were classified into equal numbers of good, mediocre, and poor growers based on a productivity index. Feed samples were collected weekly during the growout period of a flock from each grower and from the mill where the feed was produced. Samples of corn from which the feed was made were also collected. Aflatoxin, moisture contents, and bacterial, coliform, and fungal counts of the samples were determined. On the same weekly basis, the temperature and relative humidity of the chicken houses were measured and the age of the feed samples ascertained. Aflatoxin concentration in feed of good growers was 6.1 ppb with an 18.0% frequency of contamination while the values for poor growers were 14.0 ppb and 31.3%. Mean aflatoxin concentration in corn of 1.2 ppb increased to 8.8 ppb in feed from the farms. Optimum conditions for aflatoxin formation were 19 to 27 C, 79 to 89% relative humidity, and 10 to 13% moisture. Increasing age of feed was associated with low moisture and high aflatoxin. High aflatoxin was associated with high relative humidity but not with fungal, bacterial, or coliform counts. These data suggest that aflatoxin is produced during and after feed manufacture in apparently normal operations, that low levels of aflatoxin are associated with productivity losses in apparently healthy broilers, and that the aflatoxin formation is associated with high relative humidity in houses and with long residence time of the feed in the house. Because relative humidity and residence time in houses can be altered, aflatoxin formation might be limited by controlling these two factors.

High Pressure Liquid Chromatographic Determination of Penicillic Acid in Chicken Tissues

Penicillic acid (PA) is a mycotoxin with reported cytotoxic, cardiotoxic, and carcinogenic activity and it can occur in high concentrations in corn. The occurrence of PA in contaminated poultry feed represents a potential public health hazard. A reverse phase high pressure liquid chromatographic (HPLC) method is proposed for determining PA residues in chicken tissues. Optimization of chromatography was achieved for PA using a mobile phase consisting of acetonitrile:H2O. PA was detected by ultraviolet absorption at 254 nm, identified by retention time, and quantitated by peak area integration. Blood, parenchymal tissues, muscle, and alimentary tract contents were homogenized, sonicated, and acid treated followed by extraction with ethyl acetate and analysis by HPLC. Acute oral dosing of chickens with PA over a range of 50 to 550 mg/kg body weight resulted in detectable levels of the mycotoxin (confirmed by gas liquid chromatography) in gizzard muscle and contents, liver, kidney, heart, and intestinal contents. This method should prove useful both for the rapid and sensitive detection of PA residues in poultry and in further studies on the distribution and metabolism of this mycotoxin.

Distribution of T‐2 Toxin in Wet‐Milled Corn Products

ABSTRACTThe distribution of T‐2 toxin in wet‐milled corn products was studied by processing contaminated corn with bench scale wet‐milling equipment. Approximately two‐thirds of the T‐2 toxin initially present was removed by the steep and process water, 4% was found in starch and the remainder was distributed between germ, gluten, and fiber. The toxin concentration in germ ranged from 163–194% of the toxin concentration in the corn from which it was derived, while the T‐2 toxin concentration in starch was 6.6—8.8% of the concentration in corn. The steep water concentration was related to the concentration of T‐2 toxin in the original corn and the human consumption products. This may provide a convenient substrate for toxin assay.

Aflatoxin Concentration in Corn as Influenced by Kernel Development Stage and Postinoculation Temperature in Controlled Environments1

Developing kernels of two cultivars of corn (Zea mays L.), ‘Gaspe Flint’ (Gaspe) and ‘W103 ✕ Gaspe,’ were inoculated with Aspergillus flavus Link ex Fr. at three kernel‐development stages (early‐dough, medium‐dough, and late hard‐dough) and grown in four post inoculation temperature regimes of 9.5, 12.5, 14.5, and 17.5 C thermal units/day (mean daily temperature minus 10 C) in controlled environments. Kernels were assayed for aflatoxin B1 after plants were grown for about 365 cumulative thermal units after inoculation. The highest toxin levels (48,641 and 31,046 ppb for Gaspe and W103 ✕ Gaspe, respectively) were observed hi kernels inoculated at the latest kernel‐development stage (late hard‐dough) and grown at the highest postinoculation temperature regime (17.5 C thermal units/day, i.e., day/night temperatures and times of 30/26 C and 9/15 hours, respectively). Toxin levels were low hi kernels inoculated at earlier development stages and grown at lower temperatures. Longer postinoculation growth at lower temperatures did not raise aflatoxin concentrations to levels observed with shorter postinoculation growth at higher temperatures.

Land Application of Chemically Treated Sewage Sludge: III. Effects on Soil and Plant Heavy Metal Content

AbstractAnaerobically digested sewage sludges resulting from treatment of sewage with Ca(OH)2, Al2(SO4)3, or FeCl3 for phosphorus precipitation were applied to corn (Zea mays L.) and bromegruss (Bromus inermis Leyess) grown on a soil having an initial pH of 7.3. Rates of sludge supplied 200, 400, 800, and 1,600 kg N/ha each year for 5 years. Treatments with NH4NO3 supplying 0, 100, 200, and 400 kg N/ha were included for comparison. Plant tissue was analyzed for Cu, Zn, Mn, Cd, Ni, Cr, and Pb. No toxicity or deficiency symptoms were noted. Soil Zn, Cd, and Ni extracted by NTA (nitrilotriacetic acid) were increased by continued sludge application. The NTA‐extractable Zn and Cd were positively correlated with the Zn and Cd concentrations in corn stover. Soil pH was reduced by the Fe‐sludge application, slightly affected by the Al‐sludge, and increased by the Ca‐sludge. Increases in Cu concentrations in bromegrass and corn stover were associated with increases in the N content rather than the source of N, and plant Cu concentrations remained relatively constant across years. Sewage sludge application increased Zn, Cd, and Ni concentrations in bromegrass and corn stover, and Zn and Ni concentrations in corn grain, particularly at the higher metal loadings from sludge application. Zinc and Cd concentrations, especially in corn stover, increased with continued sludge application during the 5‐year period. The inclusion of soil pH as a factor, in addition to cumulative amounts of Zn or Cd added as a constituent of sludge, improved the regression equations predicting Zn or Cd uptake. Manganese concentrutions in bromegrass were reduced by the sludges used in this study, but did not change from one year to the next. Chromium and Pb concentrations in corn and bromegrass were not significantly increased by the application of 680 kg Cr/ha and 310 kg Pb/ha from sludge.

Evaluation of Penicillic Acid for Toxicity in Broiler Chickens ,

Penicillic acid is a mycotoxin produced by various fungi. It may occur in high concentrations in corn and can also be produced concomitantly with other mycotoxins in poultry feed. This mycotoxin was evaluated for its toxicity in broiler chickens by feeding graded concentrations (0, 100, 200, and 400 μg/g of diet) to 4 groups of 10 birds per treatment. No significant (P>.05) effects were measured on growth rate, feed conversion, relative size of pancreas, spleen, liver, heart, bursa, or kidney or on hemoglobin, packed cell volume, liver lipid, plasma protein, or glucose. The only significant effects were a slight reduction in the size of the proventriculus and gizzard at dose levels of 200 and 400 μg/g. Neither the salt nor lactone forms of penicillic acid had any detectable effect. The acute oral LD50 for the sodium salt form was 92 ± 9 mg/kg. These data suggest that penicillic acid by itself has little toxicity (less than 1% of that of aflatoxin) in chickens.

Effect of Limestone Variables on Amendment of Acid Soils and Production of Corn and Coastal Bermudagrass

AbstractThree particle size ranges of calcitic and dolomitic limestones were applied at 4.5, 9, and 13.5 metric tons/ha. Evaluations were designed to determine the most efficient treatment for neutralizing soil acidity, and increasing crop production in Katy fine sandy loam (pH 5.2) and Boy loamy fine sand (pH 5.4). Liming effects were evaluated by soil and plant analyses. Efficiency rating (ER) was used to describe the limestone particle size ranges. Finer limestone particles were assigned higher relative efficiency values. The sum of the products of particle size percentage ranges multiplied by the relative efficiency assigned those ranges, times the neutralizing value of that limestone is the ER.Increases in soil pH were proportional to limestone ER and application rate. Calcitic limestone neutralized soil acidity more rapidly than did dolomitic. We found a statistically significant increase in calcium (Ca) in the 30‐ to 46‐cm depth of Boy loamy fine sand at the 13.5 metric ton/ha rate of ER 110 calcitic limestone. This was probably due to 689 kg of N/ha applied as NH4NO3 the first year following limestone treatment. Magnesium (Mg) increased in the 30‐ to 46‐cm depth due to all dolomitic treatments.Limestone did not increase the yield of corn (Zea mays L.) or Coastal bermudagrass (Cynodon Dactylon L. Pers.) in the harvest year.All treatments of calcitic limestone significantly increased the Ca percentage in corn. All dolomitic limestone treatments except the ER 26 material applied at 4.5 metric tons/ha increased Mg concentration in corn leaves and Coastal bermuda‐grass. Manganese toxicity occurred in corn plants growing in nonlimed plots the third season following treatment. Soil acidity and reducing conditions contributed to the toxicity.

Comparative performance of polyphosphate fertilizers for row crops

Abstract Field and growth chamber studies comparing polyphosphate and orthophosphate fertilizers were conducted with soils of pH 7.2 ‐8.0. Applied P frequently increased grain yields in the field and plant dry matter production in the growth chamber along with P concentrations in the plants. Yield differences between poly‐ and orthophosphate P carriers were not significant. In one growth chamber study, ammonium polyphosphate (APP) produced significantly higher zinc concentrations in corn (Zea mays L.) than did ammonium orthophosphate (AOP) applications. In one field study, APP also produced significantly higher P concentration in grain sorghum (Sorghum bicolor) leaves than did AOP and potassium polyphosphate (KPP). Soil Zn applications usually increased plant Zn concentrations in the field and growth chamber.

Portland Cement as a Soil Amendent for Corn and Soybeans1

AbstractIn the corn belt there are many areas of imperfectly drained soils, often adjacent to well‐drained soils in the same fields. Tile drainage of these imperfectly drained soils helps remove excess water within the profile. Slow movement of water into and through the Ap horizon of these soils is thought to contribute to reduced crop yields in wet years. Since application of Portland cement (the binding material in concrete) to soil in a laboratory experiment increased water‐stable soil aggregate size as well as hydraulic conductivity of a soil, it was assumed that cement would act similarly in the field and increased crop yields, particularly under wet conditions.Two experiments were conducted to determine whether the application of portland cement (the binding material in concrete) would increase crop yields or change selected chemical and physical properties of soil. The first experiment was on two silt loam soils—a fine silty, mixed mesic Typic Hapludalf (Russell) and a fine silty mixed mesic Aquiac Arqiudall (Raub) in 1970. Cement was incorporated at 0, 560, 1,120, 2,240, and 4,480 kg/ha in a randomized complete block design with four replications per soil. At the end of the 1970 cropping year each plot was split, and the same rates were again applied on one of the two subunits. Corn (Zea mays L.) was grown in 1970 and 1971, and soybeans (Glycine max L. Merr.) in 1972 and 1973. The second experiment was on two other silt loam soils, a fine illitic mesic Typic Hapludalf (Morley) and a fine illitic mesic, Aerie Ochraqualf (Blount), at a different location. Cement was incorporated in 1971, at 0, 3,920, and 19,600 kg/ ha, each rate with 0 and 122 kg/ha of P, with three replications per soil. Corn was grown in 1971 and 1972, and soybeans in 1973. Corn yield increased H.9%, mean weight diameter (MWD) of water‐stable soil aggregates increased 54.5%, and soil pH increased 24.6%, with the 19,600 kg/ha rate on Blount soil in 1971. Multiple regression analyses for that soil showed an influence of cement on corn yield not accounted for by MWD and/ or pH, either singly or together. There were no other crop‐yield increases related to cement application, but there were increases in Ca and decreases in z concentration in corn or soybean leaves in selected years. In summary, crop yield increases occurred in one out of six applications of cement and were not economical when they did occur.

Solubility and Plant Uptake of Cadmium in Soils Amended with Cadmium and Sewage Sludge

AbstractAdsorption and precipitation of Cd2+ in soil suspensions were investigated as possible factors controlling Cd2+ levels in soils. Both adsorption of Cd2+ onto soils surfaces and possibly precipitation of cadmium minerals were evident in this study. At low cadmium levels solubility relationships in soils are best described by adsorption and fit the empirical Freundlich adsorption isotherm. Based on current thermodynamic data the solid phases CdCO3 (log Ksp = −12.07) and Cd3(PO4)2 (log Ksp = −32.61) most likely limit Cd2+ activities in soils. Under alkaline conditions, Cd2+ activity decreased approximately 100‐fold for each unit increase in pH. In this study, CdCO3 precipitated in sandy soils, having low cation exchange capacity (CEC), low organic matter, and pH values >7.0.DTPA‐extractable cadmium levels in soils were highly correlated (r = 0.96) with Cd concentrations in corn (Zea mays L.) seedlings grown on soils amended with Cd solutions, sewage sludge, or Cd‐spiked sewage sludge. Increasing Cd additions to the soil increased plant Cd regardless of the form of Cd added. Addition of inorganic Cd to the soil increased the Cd concentration of corn seedlings more than equivalent Cd additions in the form of sewage sludge or Cd‐spiked sludge.

SHORT-TERM FLOODING OF SOIL: ITS EFFECT ON THE COMPOSITION OF GAS AND WATER PHASES OF SOIL AND ON PHOSPHORUS UPTAKE OF CORN

A laboratory procedure and apparatus design are described for the sampling of the soil solution and dissolved gases below the surface of a flooded soil without disturbance of the soil or the normal diffusion process. Ethylene and CO2 concentration increased in the dissolved gases of a flooded Maryhill loam (Ortho Humic Gleysol) as the duration of flooding increased from zero to 17 days and the redox potential (Eh) decreased. Soluble Fe and Mn slowly increased as the Eh decreased. The addition of NO3-N depressed ethylene formation and the release of soluble Fe and Mn. The addition of sucrose rapidly eliminated NO3-N from the soil solution, reduced the Eh to −330 mV, stimulated ethylene and CO2 formation, and further solubilized Fe and Mn. The accumulation of dry weight, total P and fertilizer P concentrations in corn were reduced by flooding soil for periods up to 12 days. The measurement of Eh, gases and Fe and Mn in the soil solution suggest that ethylene accumulation and O2 depletion were involved in the reduction of fertilizer P uptake.

Nutrient concentration of corn as effected by poultry manure

Abstract The elemental composition of corn was evaluated during the 1973 growing season in an experiment with various rates of poultry manure. In general, the nutrient concentration of plant tissue reflected poultry manure applications with the exception of Mg which declined and Ca, Fe and Na which appeared to be largely unaffected. The elemental concentrations in the corn tissue were not in a toxic range however, the nutrient balance was changed by poultry manure application. Sampling of corn early in the growing season can be quite valuable with respect to predicting nutrient concentration of more mature corn for Mg, Mn, B and Zn, but it leaves much to be desired for the other elements tested.

Nutrient Dilution—Antagonism Effects in Corn and Snap Beans in Relation to Rate and Source of Applied Potassium

AbstractGreenhouse pot experiments were conducted to compare responses of corn (Zea mays L.) and snap beans (Phaseolus vulgaris L.) to 0 to 1,600 mg of K/pot as KNO3, KCl, and K2SO4 on K‐deficient soils (3 kg of soil/pot). Marked responses were obtained to applied K, which were similar among sources, except for a toxic salt effect of 1,600 mg of K as KCl. Marked reciprocal K‐N, K‐P, K‐Ca, and K‐Mg relationships with yield response to rates of applied K were attributed to both dilution and ion antagonism. The latter was most pronounced at higher K rates giving little or no additional yield response and resulting in decreased Ca, Mg, or P uptake. There was a close relationship between total N and total cation concentrations in corn leaves but not in bean leaves. This difference is attributed to absorption of much of the N as NO3‐N by corn and as biologically fixed NH2‐N by snap beans.

Mineral element concentrations in corn leaves by position on the plant and age

Abstract Leaves from corn (Zea mays L.) plants, grown in nutrient solutions, were harvested regularly from seedlings to maturity by position on the plant and analyzed for P, K, Ca, Mg, Mn, Fe, B, Cu, and Zn. Concentrations of the mineral elements were higher in seedling leaves, decreasing with position up the plant. Macronutrients decreased more rapidly than micronutrients. Except for decreased P and K, concentrations of the mineral elements increased in the leaves with age. Increases were relatively large for Ca, Mg, Mn, and B and slight for Fe, Cu, and Zn. Corn leaves varied markedly in mineral element concentration with leaf position and age. If available, roots can provide adequate minerals for kernel development independent of leaves.

Phosphate Absorption Rates and Adenosine 5′-Triphosphate Concentrations in Corn Root Tissue

The correlations between ATP concentration in corn (Zea mays) root tissue and the rate of phosphate absorption by the tissue have been examined. Experimental variation was secured with 2,4-dinitrophenol, oligomycin, mersalyl, l-ethionine, 2-deoxyglucose, N(2) gassing and inhibition of protein synthesis. It is concluded that ATP could be the energy source for potassium phosphate absorption, but only if the transport mechanism possesses certain properties: oligomycin-sensitivity; creation of a proton gradient susceptible to collapse by uncouplers; phosphate transport via a mersalyl-sensitive Pi(-)-OH(-) transporter; good activity at energy charge as low as 0.4; short enzymatic half-life for the ATPase or phosphate transporter; a linked mechanism for K(+)-H(+) exchange transport, possibly electrogenic.