Critical Phosphorus Concentration Research Articles

Effects of phosphorus application on carbohydrate metabolism in cottonseed kernel during the key development period provided a new insight for phosphorus management in cotton production

Cottonseed provides abundant and high-quality raw materials for biodiesel, fine chemical, and other industries due to its rich oil, but phosphorus-deficient farmland and finite phosphate resource hinder its production. Cottonseed development is based on its carbohydrate, and exploring the response of cottonseed carbohydrate metabolism to phosphorus could contribute to optimizing phosphorus management in cotton production and continuously obtaining high-quality cottonseed. Here, the experiment on phosphorus rates [0 (phosphorus deficient), 100 (phosphorus critical), and 200 (phosphorus excess) kg P2O5 ha−1] was conducted using Lu 54 (low-phosphorus sensitive) and Yuzaomian 9110 (low-phosphorus tolerant) in a field containing 16.9 mg kg−1 available phosphorus to assess the effects of phosphorus on cottonseed yield, cottonseed total phosphorus, ash, and oil contents, carbohydrate metabolism related carbohydrate contents, and enzymes activities. The results showed that phosphorus application increased cottonseed yield and oil content by 32.4%−54.2% and 14.8%−20.1% on average, respectively, which could be attributed to the improvements in sucrose transport and hydrolysis in cottonseed kernel during 18–26 days post anthesis induced by higher total phosphorus content (17.1%−26.7%). During the key development period of cottonseed kernel, phosphorus application increased sucrose content (13.0%−19.4%) by increasing the expression of sucrose transporter genes, and promoted sucrose hydrolysis by elevating enzymes activities, especially sucrose synthase (11.2%−19.1%) in cottonseed kernel. Consequently, phosphorus application increased hexose levels in cottonseed kernel and thus provided more substrates for its development, which promoted the formation of cottonseed kernel biomass (6.2%−10.6%), cottonseed and oil yields. Additionally, carbohydrate metabolism in Lu 54 was more sensitive to phosphorus than Yuzaomian 9110 during the key development period, resulting in greater increases in cottonseed kernel biomass, cottonseed yield, and oil content for Lu 54. Notably, the increments generated by unit phosphate fertilizer on the above indicators attenuated markedly with phosphorus application. Based on sucrose content, the key substance, the critical phosphorus concentration in the subtending leaf to cotton boll (LPC) needed by the efficient operation of the key carbohydrate metabolic pathway was 0.38% for Lu 54 versus 0.34% for Yuzaomian 9110. This report first unveiled the key carbohydrate metabolic pathway regulated by phosphorus for cottonseed and oil yield formation and its demand for LPC during the key development period, providing a new insight for diagnosing and regulating phosphorus in cotton production.

Validation and use of critical phosphorus concentration in maize

Abstract Plant-based indicators may have the potential to improve fertilizer phosphorus (P) recommendations for maize (Zea mays L.). Our objectives were (i) to validate existing models of critical P concentration (Pc) in maize shoot biomass during vegetative growth and (ii) to evaluate on farm the ability of the P nutrition index (PNI), a plant-based indicator derived from Pc, to predict a positive response to P fertilization. Existing models of Pc for maize were validated in a 3-yr experiment in which mineral fertilizer P was band-applied at planting at four rates (0, 10, 20, and 40 kg P ha−1) on a clay soil with a low to medium-low available-P content based on the soil P saturation index (PM-III/AlM-III). Fertilizer P generally did not affect shoot growth from the V6 to VT stages and grain yield, indicating that nonlimiting P conditions were achieved with no applied P. Critical P concentration under those nonlimiting P conditions was described by a linear function of shoot N concentration (Pc = 0.82 + 0.097 × N, R2 = 0.90), which was close to that previously reported in the same region (Pc = 1.00 + 0.094 × N). The on-farm PNI evaluation was conducted on eight farm sites varying in soil PM-III/AlM-III (0.021−0.308). Five P rates (0, 4.5, 9.0, 17.5, and 35.0 kg P ha−1) were applied on fields where the PNI had been measured the year before. The PNI at the V12 stage measured the year before was a better predictor of the relative grain yield with no P applied than the soil PM-III/AlM-III measured prior to planting. A critical PNI value of 0.9 was established below which a positive response to P fertilization is expected. This plant-based diagnostic approach therefore appears to be a valuable alternative or a complement to the currently used soil P test to decide whether fertilizer P is needed or not for maize production.

Mehlich 3 extractant used for the evaluation of wheat-available phosphorus and zinc in calcareous soils

Relation between wheat (Triticum aestivum) nutritional status determined at the beginning of stem elongation and during anthesis, respectively, and available content of phosphorus (P-M3) and zinc (Zn-M3) determined by the Mehlich 3 extractant was studied. Both one-year pot experiment with spring wheat and two-year on-farm trials with winter wheat were run on various calcareous soils (pH values of 7.18–7.94, median 7.80, P-M3 1–289 ppm, median 54, and Zn-M3 2–14 ppm, median 4), in the Czech Republic (Central Europe). Phosphorus nutrition index (ratio of phosphorus concentration in shoot biomass to critical phosphorus concentration – P<sub>c</sub>) was calculated using the Belanger et al.’s model: P<sub>c</sub> = –0.677 + 0.221N – 0.00292N(2), where both phosphorus and nitrogen concentrations were expressed in g/kg shoot dry matter. Unlike phosphorus concentration in shoot biomass, phosphorus nutrition index significantly correlated with P-M3 content in soil. Optimal values of the phosphorus nutrition index were recorded if P-M3 was 51–68 ppm. Zinc concentration in shoot biomass more strongly correlated with P:Zn ratio (M3) in soil compared to Zn-M3 content in soil. P:Zn ratio in shoot biomass of 130:1 did not lead to phosphorus deficiency and corresponded to P:Zn (M3) ratio in soil of 9.3:1–14.3:1.

Determination of Critical Tissue Phosphorus Concentration in Mungbean and Urdbean for Plant Diagnostics

A pot experiment was conducted to study the effect of phosphorus (P) nutrition on mungbean and urdbean genotypes and to determine the critical concentration of tissue phosphorus at different growth stages for plant diagonostic and P management. There were eight treatments consisting of different levels of P added in the form of monopotassium phosphate (KH2PO4). Destructive plant samples were taken to determine tissue P concentration and plant dry matter at different growth stages. Plant tissue P concentration was found highly correlated with dry matter production in mungbean (r2 = 0.84–0.98) and urdbean (r2 = 0.98–0.998) at corresponding sampling period throughout the growth stages. Considerable variation was observed in critical P concentration with genotypes and leaf position in mungbean and urdbean. Critical P concentration varied between 0.45–0.49 in mungbean and 0.45 to 0.57 in urdbean at early stages of crop growth, and these values declined sharply with advancement in crop growth.

Impurity Concentration Dependence of Optical Absorption for Phosphorus-Doped Anatase TiO2

The efficient absorption of visible light is crucial for improving the photocatalytic activity of foreign species-doped TiO2. With first-principles calculations, we explore the effects of phosphorus doping on mediating the photocatalytic activity of anatase. It is found that the P impurity tends to occupy the cation site in TiO2; more importantly, there exists a critical phosphorus concentration of about 0.7% for maximizing the absorption of solar light. The optical energy gap is narrowed by ∼0.3 eV at the low doping concentration of 0.7%, whereas it increases with P concentration at the higher P concentration region of 0.7−3.1 atm. %. These results suggest that the dopant concentration dependence might be responsible for numerous seeming controversies of optical absorption observed in experiments. This finding points to a possibility of tailoring the optical absorption of TiO2 by varying the dopant content.

Solid-phase epitaxial regrowth of amorphous layers in Si(100) created by low-energy, high-fluence phosphorus implantation

Medium energy ion scattering has been used to study the kinetics of solid-phase epitaxial regrowth (SPEG) of ultrathin amorphous layers formed by room-temperature implantation of 5keV energy phosphorus ions into Si (100). The implants create P distributions with peak concentrations up to ∼7×1021cm−3. SPEG has been driven by rapid thermal annealing, 475°C⩽TA⩽600°C, for times up to 2000s. At each temperature, the regrowth velocity is enhanced in the early stages due to the presence of phosphorus but then slows sharply to a value more than an order of magnitude below the intrinsic rate. The critical phosphorus concentration at the transition point for TA=475°C regrowth is ∼6×1020cm−3 and increases steadily with anneal temperature. Time-of-flight secondary ion mass spectroscopy profiles confirm the onset of phosphorus push out, where the advancing recrystallization front enters the transition region. Supplementary cross-sectional transmission electron microscopy evidence confirms the existence of a local strain field.

Critical Phosphorus Concentrations for Oats, Barley, Triticale, and Narrow‐Leaf Lupin

Diagnostic critical phosphorus (P), which is the P concentration in tissue that was related to 90% of the maximum, P nonlimiting yield measured at the time of sampling, was determined for dried whole shoots and seed (grain) of oats (Avena sativa L.), barley (Hordeum vulgare L.), triticale (xTriticosecale L.), and narrow‐leaf lupins (Lupinus angustifolius L.). For all species, diagnostic critical P in dried whole shoots generally decreased with increasing plant age and was larger for grain than dried whole shoots near maturity. For dried whole shoots, diagnostic critical P ranges (%P, dry weight basis) [days from sowing (DAS)] were oats, 0.72 (30 DAS)–0.23 (105 DAS); barley, 1.09 (30 DAS)–0.24 (203 DAS); triticale, 1.2 (30 DAS)–0.11 (120 DAS); and lupin, 0.60 (66 DAS)–0.21 (163 DAS). For grain, mean diagnostic critical P (range) was oats, 0.27 (0.18–0.39); barley, 0.32 (0.23–0.35); triticale, 0.22 (0.19–0.25); and lupin, 0.31 (0.25–0.41). In addition, we related the P concentration in dried whole shoots to grain yield measured at the end of that growing season (prognostic critical P). For dried whole shoots of each of the four plant species, the decrease in both diagnostic and prognostic critical P concentration as the plants matured was very similar, so both procedures predicted similar grain yields at the end of that growing season.

PHOSPHORUS LEVELS IN SHOOTS OF BAMBARA GROUNDNUT IN BOTSWANA SOILS

ABSTRACT The critical phosphorus (P) concentration and range of bambara groundnut (Vigna subterranea) plants were determined from a sand culture experiment at Botswana College of Agriculture. Twelve P levels (0.207–159 mg P pot−1) were used for growing the plants for 78 days (early podding stage) and the shoot P concentrations determined. The critical P concentration was used for assessing the P nutritional status of bambara groundnut plants grown in farmers fields in Botswana. Plants from 10 farmers' fields were sampled at 78 days after sowing and analyzed for P. The critical shoot P concentration and range for bambara groundnut determined visually from graphs were 0.15% and 0.15–0.20%, respectively. In 80% of the farms, plants showed shoot P concentrations between 0.10% and 0.13% which correspond with moderate to severe P deficiency. Therefore, most of bambara groundnut farmers in Botswana grow the crop under limiting P conditions.

Response of winter-sown carrots (Daucus carota L.) to rate and timing of phosphorus application on Joel sands

The response of winter-sown carrots to rate and timing of phosphorus application on Joel sands was investigated at 2 commercial vegetable property sites on the Swan Coastal Plain in 1996. Phosphorus was applied at rates from 0 to 160 kg/ha at 2 times of application either 100% broadcast to the soil surface and incorporated before sowing (BS) or 25% broadcast and incorporated before sowing with 75% broadcast to the soil surface (not incorporated) after sowing in 5 equal-sized applications of 15% every 3 weeks, commencing 3 weeks after sowing (BS + AS ). There was a significant increase in total yield in response to rate and time of application of phosphorus at both sites. Total yield was 3–10% higher in the BA + AS than in the BS treatment at site 1 and 10–35% higher at site 2. Marketable yield was 21% higher at site 2 in the BS + AS compared with the BS treatment. Total and marketable yields were maximised at 40–80 kg/ha applied P at both sites. The concentration of phosphorus (%DW) in the youngest mature leaves at mid-growth was up to 30–35% higher in the BS + AS than in the BS treatment. Consequently, the percentage of phosphorus corresponding to the rate of applied phosphorus necessary for maximum yield was higher in the BS + AS than in the BS treatment. Thus, critical concentrations of phosphorus in the youngest mature leaves required for maximum yield of carrots should take account of timing of phosphorus application. Exponential regressions best described the relationship of phosphorus uptake (phosphorus concentration yield) by roots or whole plants to rate and timing of applied phosphorus. Phosphorus uptake by roots and whole plants increased with rate of applied phosphorus and was higher in the BS + AS than in the BS treatment. Recovery efficiency of fertiliser phosphorus by whole plants was 2.0–3.0-fold higher in the BS + AS treatment than in the BS treatment at 40–80 kg P/ha.

Critical nutrient concentrations and antagonistic and synergistic relationships among the nutrients of NFT‐grown young tomato plants

Critical concentrations of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), iron (Fe), zinc (Zn), and manganese (Mn) with respect to dry matter yield end antagonistic and synergistic relationships among these nutrients were studied in which tomato (Lycopersicon esculentum L.) was grown in recirculating nutrient solution (NFT). Increments of nutrient elements in the nutrient solution increased the proportional rate of the corresponding nutrient elements. Increasing levels of N negatively correlated with plant P and positively correlated with Ca, Fe, and Zn. Iron and Mn contents of the plants were increased and N, K, Ca, and Mg were decreased as a function of P applied. Increases in K in the nutrient solution caused increases in the concentrations of K, N, P, and Zn, and decreases in the concentration of Ca and Fe. Applied Ca increased the concentrations of Ca and N, and decreased the concentrations of P, Mg, Fe, Zn, and Mn. Potassium, Ca, and Fe contents of the plants were decreased and Zn increased, while N, P, and Mn were not affected by the increasing levels of external Mg. Iron suppressed the plant Mg, Zn, and Mn contents. Synergism between Zn and Fe was seen, while P, K, Ca, Mg, and Mn contents were not affected by Zn levels. Potassium, Ca, Mg, and Fe were not responsive to applied Mn, however, N and P contents of the plants were decreased at the highest levels of Mn.

Critical phosphorus concentrations in potato plant parts at two growth stages

Adequately evaluating the phosphorus (P) nutritional status of a potato crop is dependent upon sampling the appropriate plant part at a defined growth stage. To establish P critical concentration levels in various potato plant parts (leaves, stems, tubers, leaflets, and petioles) at two growth stages [20 and 50 days after plant emergence (DAE)], an experiment under Brazilian climatic and soil conditions was conducted using seven P treatment levels (0, 40, 80, 160, 320, 640, and 1,280 kg P2O5 ha‐1) applied in a randomized complete block design with four replications. ‘Baraka’ potato tubers were seeded at a spacing of 0.80 x 0.30 m following agronomic cultural practices recommended for this crop. Phosphorus concentrations in all the potato plant parts were significantly affected by the P fertilizer rates applied. The highest correlation between the P concentration in the various plant parts and marketable yield and optimum profit yield was obtained for the petiole taken 20 days DAE. Critical P levels associated with optimum profit yield were lower than those for maximum marketable tuber yield, and they were, 0.41, 0.39,0.39,0.57, and 0.57 g P 100 mg‐1 DM in the leaf, stem, tuber, petiole, and leaflet, respectively.

Thermal diffusivity and conductivity measurements for Si:P near the metal - insulator transition

Silicon doped with phosphorus undergoes a metal - insulator transition (MIT) at a critical phosphorus concentration. We present here data for the thermal diffusivity D of an insulating sample of Si:P very near the MIT. We describe briefly our method for measuring the dependence on the magnetic field (H) of D at very low temperatures ( mK). We present also data for the magnetoresistivity and the thermal conductivity of the same sample, and the calculated specific heat . We compare with earlier direct measurements, and we try to explain the behaviour of D, , and taking into account the complex situation in Si:P. We show that the measurement of D at very low temperatures and under a magnetic field can be a fruitful way of extracting information about the physics of doped semiconductors.

Critical plant and seed concentrations of phosphorus and zinc for predicting response of faba beans (Vicia faba)

Faba beans (Vicia faba cv. Fiord) were grown in 1 glasshouse and 3 field experiments to calibrate the critical concentrations of phosphorus (P) and zinc (Zn) in selected plant tissues for vegetative and grain yields. In the field experiments, responses in grain yield to soil-applied P were between 0.5 and 0.8 t/ha (20-25%) at sites with extractable Colwell soil P concentrations of 20 and 23 mg/kg. Similarly, grain yields were increased by 0.6-1.2 t/ha (20-30%) from the application of either soil-applied or foliar Zn. These field responses to Zn only occurred if P fertiliser was applied at sowing. Maximum yields were obtained by either applying about 2 kg Zn/ha to the soil at sowing, or 500 g Zn/ha as a foliar spray, 8 weeks after sowing. In field experiments, critical P concentrations in the youngest open leaf during vegetative growth for prediction of maximum grain yield in the field, remained constant over a 10-week growing period. A critical nutrient range of 0.40-0.41% is proposed. However, critical concentrations of P in whole top for maximum grain yield, declined from 0.40 to 0.27% over the same growing period. For bean seed collected at harvest, a critical concentration of 0.36% P for maximum grain yield was derived. Critical concentrations of Zn during vegetative growth for prediction of maximum grain yield, derived in both glasshouse and field experiments, were very similar in youngest open leaf and whole top, and no significant decline with plant age was observed; a critical nutrient range of 19-24 mg/kg is proposed. For seed collected at harvest, a critical nutrient range for diagnosis of Zn deficiency of 13-15 mg/kg is suggested.

Critical phosphorus concentrations for subterranean clover in the high rainfall areas of South‐Western Australia

Abstract The relationship between yield and phosphorus (P) concentration of dried subterranean clover (Trifolium subterraneum) herbage has been measured in many long‐term field experiments in the greater than 800 mm annual average rainfall areas of south‐western Australia. In the experiments, seven levels of different P fertilizers (single superphosphate, rock phosphates, partially acidulated rock phosphates) were applied to the surface, either annually, or once only to new plots in different years. Yields and P concentration in dried herbage were measured whenever possible in each growing season (April to November near the south coast, May to October near the west coast) for several successive years. Critical P, the P concentration in dried herbage related to 90% of the maximum yield, was calculated. At each harvest, critical P was similar for different fertilizers. However, critical P was different when measured for samples collected at about the same time in different years at the same site or differen...

Critical phosphorus concentrations for burr medic, yellow serradella, subterranean clover, and wheat

Abstract The relationship between plant yield and the phosphorus (P) concentration in dried tops and seed of burr medic (Medicago polymorpha), yellow Serradella (Ornithopus compressus), subterranean clover (Trifolium subterraneum), and wheat (Triticum aestivum) was determined, and critical P, which is the P concentration in tissue that is related to 90% of the maximum yield of each species at each harvest, was interpolated. Critical P data are limited for subterranean clover and wheat, which are widely grown in south‐western Australia. There are no critical P data for burr medic and yellow senadella, two new pasture legumes. For each species, critical P varied, often markedly, for different experiments. For all species, (i) critical P in dried tops generally decreased with increasing maturity, (ii) critical P was larger for seed than dried tops near maturity.

Comparison of Methods for Determining Critical Concentrations of Soil Test Phosphorus for Corn

AbstractCritical concentrations of soil‐test P (STP) are used to identify soils where response to P fertilization should be expected. There is, however, little agreement concerning the methods that should be used to identify critical STP concentrations. This study compares the efficacy of critical STP concentrations generated by using various methods. Twenty‐five P fertilization trials with corn (Zea mays L.) were established in Iowa. Available soil P at each site was estimated by the Bray‐P1, Mehlich‐3, and Olsen extractants. Corn yield response was expressed in both absolute and relative terms and then related to STP values by using various statistical models (Cate‐Nelson split, linearplateau and quadratic‐plateau segmented polynomials, the quadratic polynomial, an exponential Mitscherlich‐type equation, and a multivariate polynomial). The use of various combinations of the extractants, expressions of yield response, and models resulted in a wide variety of critical STP concentrations. Comparisons of the ability of each critical concentration to generate economic returns when used to guide fertilization across the 25 sites showed that selection of the model was much more important than selection of the extractant or the expression of yield response. The best model was the Cate‐Nelson, which identified critical concentrations of 13 rag kg−1 for the Bray‐P1, 12 mg kg−1 for the Mehlich‐3, and 5 mg kg−1 for the Olsen extractants. Overall, the results of this study demonstrate that selection of the most appropriate critical STP concentration can be a major factor affecting the profitability of fertilization in areas having an abundance of soils testing high in P.

Critical phosphorus concentrations in oilseed rape (Brassica napus) and Indian mustard (Brassica juncea) as affected by nitrogen and plant age

Oilseed rape and Indian mustard were grown in sand culture experiments in a glasshouse to derive values for a tissue test for the diagnosis of phosphorus (P) deficiency. Seven rates of P, combined factorially with 3 rates of nitrogen (N), were used to determine critical P concentrations. Suitable tissues to sample for a diagnostic test were the whole shoot of both species at any stage, or the youngest fully expanded leaf of rape and leaves 4-6 of mustard at the rosette stage. Critical P concentrations depended on both plant age and N supply. The critical values reported here for rape agreed closely with critical values found previously in tissues of field-grown crops of similar phenological age. Critical P levels in whole rape shoots adequately supplied with N decreased from 0.29% at the early rosette stage to 0.21% at the late rosette or yellow bud stage, while critical values in mustard fell from 0.25% at the early rosette stage to 0.18% at stem elongation to full flower. Critical P concentrations for prediction of seed yield were slightly higher (0.05% higher at the rosette stage). A nutrient supply with high P and high N reduced the seed oil concentration of both species; a low P and high N supply reduced the oil concentration in rape seed but increased it in mustard seed.

The Nutritional Eco-physiology of Chaetomorpha linum and Ulva rigida in Peel Inlet, Western Australia

The uptake rates and critical tissue concentrations of nitrogen and phosphorus were determined for Chaetomorpha linum and Ulva rigida , the dominant algae in Peel Inlet, Western Australia. Both species had rate-saturating mechanisms of phosphate uptake described by Michaelis-menten type functions; C. linum had the faster uptake rate (667 c.f. 272 mu g P g/dwt/h) although U. rigida had a lower half-saturation value. Both species displayed linear relationships between ammonium uptake rates and substrate concentrations with C. linum having the greater slope (4.4 c.f. 1.7). Chaetomorpha linum also had a linear increase in uptake rate with increasing concentration of nitrate, but U. rigida showed rate-saturating kinetics; below 750 mu g/L, U. rigida had the higher rate of uptake. Ulva rigida had critical tissue nitrogen and phosphorus concentrations of 20 and 0.25 mg g/dwt respectively. Corresponding concentrations for C. linum were 12 and 0.5 mg g/dwt. Ulva is frequently nitrogen limited during spring in Peel Inlet, reflecting the high nitrogen requirements of this plant compared to Chaetomorpha as well as the reduced ability of Ulva to store nutrients over winter.

Ecological studies on Potamogeton pectinatus L. V. Nutritional ecology, in vitro uptake of nutrients and growth limitation

The growth of Potamogeton pectinatus L. at different concentrations of bicarbonate, phosphate and nitrate was studied during long-term culture experiments in aquaria. The uptake of bicarbonate, phosphate, nitrate and ammonium by the shoots or the root system was studied during short-term experiments in 2-compartment chambers. When P. pectinatus was cultured without a phosphorus source, the tubers were able to supply phosphorus and enable growth for about 5 weeks before the plants died. Depletion of nitrate or dissolved inorganic carbon (DIC) caused a rapid death of plants. Potamogeton pectinatus takes up phosphorus and nitrogen with the shoots and the root system, bicarbonate can only be taken up by the shoots. The nutrient contents of plants indicated luxury consumption of phosphorus at high external phosphate concentrations. Critical phosphorus concentrations for plant growth according to biomass production in cultures at different external phosphate concentrations are supposed to be between 1.5 and 14 μmol 1 −1 phosphate. Analysis of plant tissue shows that the critical phosphorus content is 0.15%, which corresponds with a stock phosphate concentration between 3 and 4 μmol PO 4 3− l −1. It is argued that phosphate and nitrate are probably not limiting growth of P. pectinatus in the Veluwemeer study site (The Netherlands), but DIC might well be.

Comparison of the use of total phosphorus concentration and acetic acid soluble phosphorus concentration in petioles for assessing the phosphorus status of potato crops

We studied the effect of rate of applied phosphorus on total phosphorus concentration (17 sites) and acetic acid soluble phosphorus concentration (12 sites) in petioles of youngest fully expanded leaves of potatoes (cvv. Kennebec, Coliban and Exton) when their largest tubers were 5-10 mm long. We showed that the internal requirements for phosphorus are similar for the cvv. Kennebec and Coliban. Taken over all sites, mean total phosphorus concentrations and acetic acid soluble phosphorus concentrations ranged from 0.22 to 0.84% and 0.10 to 0.63%, respectively depending on phosphorus supply. For each site a coefficient of determination (r2) was calculated based on the mean total phosphorus concentration versus acetic acid soluble phosphorus concentration data for all treatments. The r2 values varied from 0.969 (site 14) to 0.997 (site 17). On the pooled data for all sites, the Cate-Nelson separation and the Mitscherlich and Smith-Dolby bent-hyperbola models were used to investigate the correlations between relative yield [(mean treatment yields/maximum treatment yie1d)x 100] and total phosphorus concentration (n = 16 1, 17 sites) and acetic acid soluble phosphorus concentration (n = 112, 12 sites) and to calculate the critical values. Depending on the model fitted the critical total phosphorus concentrations varied from 0.41 (r2 = 0.62) to 0.53% (r2 = 0.72). The critical acetic acid soluble phosphorus concentrations varied from 0.29 (r2 = 0.62) to 0.52% (r2 = 0.72). Critical concentration ranges of 0.41-0-53% for total phosphorus and 0.29-0.52% for acetic acid soluble phosphorus have been proposed to assist in the assessment of the phosphorus status of irrigated potato crops in South Australia. Based on sensitivity, reproducibility and sharpness of the transition zone between adequacy and deficiency we found no advantage in determining acetic acid soluble phosphorus concentration rather than total phosphorus concentration to assess the phosphorus status of potato plants.