Validation of body surface colonic mapping (BSCM) against high resolution colonic manometry for evaluation of colonic motility

Abnormal cyclic motor pattern (CMP) activity is implicated in colonic dysfunction, but the only tool to evaluate CMP activity, high-resolution colonic manometry (HRCM), remains expensive and not widely accessible. This study aimed to validate body surface colonic mapping (BSCM) through direct correlation with HRCM. Synchronous meal-test recordings were performed in asymptomatic participants with intact colons. A signal processing method for BSCM was developed to detect CMPs. Quantitative temporal analysis was performed comparing the meal responses and motility indices (MI). Spatial heat maps were also compared. Post-study questionnaires evaluated participants' preference and comfort/distress experienced from either test. 11 participants were recruited and 7 had successful synchronous recordings (5 females/2 males; median age: 50 years [range 38-63]). The best-correlating MI temporal analyses achieved a high degree of agreement (median Pearson correlation coefficient (Rp) value: 0.69; range 0.47-0.77). HRCM and BSCM meal response start and end times (Rp = 0.998 and 0.83; both p < 0.05) and durations (Rp = 0.85; p = 0.03) were similar. Heat maps demonstrated good spatial agreement. BSCM is the first non-invasive method to be validated by demonstrating a direct spatio-temporal correlation to manometry in evaluating colonic motility.

Childhood-Onset Lupus Nephritis in the Childhood Arthritis and Rheumatology Research Alliance Registry: Short-Term Kidney Status and Variation in Care

OBJECTIVE

The goal was to characterize short-term kidney status and describe variation in early care utilization in a multicenter cohort of patients with childhood-onset systemic lupus erythematosus (cSLE) and nephritis.

METHODS

We analyzed previously collected prospective data from North American patients with cSLE with kidney biopsy-proven nephritis enrolled in the Childhood Arthritis and Rheumatology Research Alliance (CARRA) Registry from March 2017 through December 2019. We determined the proportion of patients with abnormal kidney status at the most recent registry visit and applied generalized linear mixed models to identify associated factors. We also calculated frequency of medication use, both during induction and ever recorded.

RESULTS

We identified 222 patients with kidney biopsy-proven nephritis, with 64% class III/IV nephritis on initial biopsy. At the most recent registry visit at median (interquartile range) of 17 (8-29) months from initial kidney biopsy, 58 of 106 patients (55%) with available data had abnormal kidney status. This finding was associated with male sex (odds ratio [OR] 3.88, 95% confidence interval [95% CI] 1.21-12.46) and age at cSLE diagnosis (OR 1.23, 95% CI 1.01-1.49). Patients with class IV nephritis were more likely than class III to receive cyclophosphamide and rituximab during induction. There was substantial variation in mycophenolate, cyclophosphamide, and rituximab ever use patterns across rheumatology centers.

CONCLUSION

In this cohort with predominately class III/IV nephritis, male sex and older age at cSLE diagnosis were associated with abnormal short-term kidney status. We also observed substantial variation in contemporary medication use for pediatric lupus nephritis between pediatric rheumatology centers. Additional studies are needed to better understand the impact of this variation on long-term kidney outcomes.

Intraarticular steroids as DMARD-sparing agents for juvenile idiopathic arthritis flares: Analysis of the Childhood Arthritis and Rheumatology Research Alliance Registry

BACKGROUND

Children with juvenile idiopathic arthritis (JIA) who achieve a drug free remission often experience a flare of their disease requiring either intraarticular steroids (IAS) or systemic treatment with disease modifying anti-rheumatic drugs (DMARDs). IAS offer an opportunity to recapture disease control and avoid exposure to side effects from systemic immunosuppression. We examined a cohort of patients treated with IAS after drug free remission and report the probability of restarting systemic treatment within 12 months.

METHODS

We analyzed a cohort of patients from the Childhood Arthritis and Rheumatology Research Alliance (CARRA) Registry who received IAS for a flare after a period of drug free remission. Historical factors and clinical characteristics and of the patients including data obtained at the time of treatment were analyzed.

RESULTS

We identified 46 patients who met the inclusion criteria. Of those with follow up data available 49% had restarted systemic treatment 6 months after IAS injection and 70% had restarted systemic treatment at 12 months. The proportion of patients with prior use of a biologic DMARD was the only factor that differed between patients who restarted systemic treatment those who did not, both at 6 months (79% vs 35%, p < 0.01) and 12 months (81% vs 33%, p < 0.05).

CONCLUSION

While IAS are an option for all patients who flare after drug free remission, it may not prevent the need to restart systemic treatment. Prior use of a biologic DMARD may predict lack of success for IAS. Those who previously received methotrexate only, on the other hand, are excellent candidates for IAS.

Social determinants of health influence disease activity and functional disability in Polyarticular Juvenile Idiopathic Arthritis

BACKGROUND

Social determinants of health (SDH) greatly influence outcomes during the first year of treatment in rheumatoid arthritis, a disease similar to polyarticular juvenile idiopathic arthritis (pJIA). We investigated the correlation of community poverty level and other SDH with the persistence of moderate to severe disease activity and functional disability over the first year of treatment in pJIA patients enrolled in the Childhood Arthritis and Rheumatology Research Alliance Registry.

METHODS

In this cohort study, unadjusted and adjusted generalized linear mixed effects models analyzed the effect of community poverty and other SDH on disease activity, using the clinical Juvenile Arthritis Disease Activity Score-10, and disability, using the Child Health Assessment Questionnaire, measured at baseline, 6, and 12 months.

RESULTS

One thousand six hundred eighty-four patients were identified. High community poverty (≥20% living below the federal poverty level) was associated with increased odds of functional disability (OR 1.82, 95% CI 1.28-2.60) but was not statistically significant after adjustment (aOR 1.23, 95% CI 0.81-1.86) and was not associated with increased disease activity. Non-white race/ethnicity was associated with higher disease activity (aOR 2.48, 95% CI: 1.41-4.36). Lower self-reported household income was associated with higher disease activity and persistent functional disability. Public insurance (aOR 1.56, 95% CI 1.06-2.29) and low family education (aOR 1.89, 95% CI 1.14-3.12) was associated with persistent functional disability.

CONCLUSION

High community poverty level was associated with persistent functional disability in unadjusted analysis but not with persistent moderate to high disease activity. Race/ethnicity and other SDH were associated with persistent disease activity and functional disability.

The effects of 4 weeks normobaric hypoxia training on microvascular responses in the forearm flexor

Intermittent exposure to hypoxia can lead to improved endurance performance. Currently, it is unclear whether peripheral adaptions play a role in improving oxygen delivery and utilization following both training and detraining. This study aimed to characterize skeletal muscle blood flow (mBF), oxygen consumption (mV̇O₂), and perfusion adaptations to i) 4-weeks handgrip training in hypoxic and normoxic conditions, and ii) following 4-weeks detraining. Using a randomised crossover design, 9 males completed 30-min handgrip training four times a week in hypoxic (14% FiO₂ ~ 3250m altitude) and normoxic conditions. mBF, mV̇O₂ and perfusion were assessed pre, post 4-weeks training, and following 4-weeks detraining. Hierarchical linear modelling found that mV̇O₂ increased at a significantly faster rate (58%) with hypoxic training (0.09 mlO₂·min^-1 · 100g^-1 per week); perfusion increased at a significantly (69%) faster rate with hypoxic training (3.72 μM per week). mBF did not significantly change for the normoxic condition, but there was a significant increase of 0.38 ml· min^-1 · 100ml^-1 per week (95% CI: 0.35, 0.40) for the hypoxic condition. During 4-weeks detraining, mV̇O₂ and perfusion significantly declined at similar rates for both conditions, whereas mBF decreased significantly faster following hypoxic training. Four weeks hypoxic training increases the delivery and utilisation of oxygen in the periphery.

Differences in forearm strength, endurance, and hemodynamic kinetics between male boulderers and lead rock climbers

This study examined differences in the oxygenation kinetics and strength and endurance characteristics of boulderers and lead sport climbers. Using near infrared spectroscopy, 13-boulderers, 10-lead climbers, and 10-controls completed assessments of oxidative capacity index and muscle oxygen consumption (m⩒O₂) in the flexor digitorum profundus (FDP), and extensor digitorum communis (EDC). Additionally, forearm strength (maximal volitional contraction MVC), endurance (force-time integral FTI at 40% MVC), and forearm volume (FAV and ΔFAV) was assessed. MVC was significantly greater in boulderers compared to lead climbers (mean difference = 9.6, 95% CI 5.2-14 kg). FDP and EDC oxidative capacity indexes were significantly greater (p = .041 and .013, respectively) in lead climbers and boulderers compared to controls (mean difference = -1.166, 95% CI (-3.264 to 0.931 s) and mean difference = -1.120, 95% CI (-3.316 to 1.075 s), respectively) with no differences between climbing disciplines. Climbers had a significantly greater FTI compared to controls (mean difference = 2205, 95% CI= 1114-3296 and mean difference = 1716, 95% CI = 553-2880, respectively) but not between disciplines. There were no significant group differences in ΔFAV or m⩒O₂. The greater MVC in boulderers may be due to neural adaptation and not hypertrophy. A greater oxidative capacity index in both climbing groups suggests that irrespective of climbing discipline, trainers, coaches, and practitioners should consider forearm specific aerobic training to aid performance.

Haemodynamic kinetics and intermittent finger flexor performance in rock climbers

Currently it is unclear whether blood flow (BF) or muscle oxidative capacity best governs performance during intermittent contractions to failure. The aim of this study was to determine oxygenation kinetics and BF responses during intermittent (10 s contraction: 3 s release) contractions at 40% of MVC in rock climbers of different ability (N=38). Total forearm BF, as well as de-oxygenation and re-oxygenation of the flexor digitorum profundus (FDP) and the flexor carpi radialis (FCR) were assessed. Compared to the control, intermediate and advanced groups, the elite climbers had a significantly (p<0.05) greater force time integral (FTI), MVC and MVC/kg. Furthermore, the elite climbers de-oxygenated the FDP significantly more during the first (7.8, 11.9, 12.4 vs. 15.7 O2%) and middle (7.3, 8.8, 10.4 vs.15.3 O2%) phases of contractions as well as for the FCR during the first phase only (8.3, 7, 11.7 vs. 13.3 O2%). They also had a significantly higher BF upon release of the contractions (656, 701, 764 vs. 971 mL ∙ min(-1)). The higher FTI seen in elite climbers may be attributable to a greater blood delivery, and an enhanced O2 recovery during the 3 s release periods, as well as a superior muscle oxidative capacity associated with the greater de-oxygenation during the 10 s contractions.

Sport-specific power assessment for rock climbing

AIM

The popularity of rock climbing has resulted in a growing research base for the sport. However, at present there is a lack of sport-specific measures of performance in the field. The aim of this study was to examine the use of the powerslap test as a sport specific power measure.

METHODS

The participants in this study were categorised into four different ability groups (novice, intermediate, advanced and elite) based on self reported lead grade. Two separate experiments were conducted to determine validity and reliability. The powerslap test was conducted on a revolution board with two variations - wide and narrow grip, for both sides of the body. The test started with the climber hanging at full extension from two holds from which a pull up movement was made releasing one hand to slap a scaled score board above.

RESULTS

There was a significant relationship between powerslap scores and climbing ability (Left Wide: r=0.7, P<0.0005; right wide: r=0.69, P<0.0005; left narrow: r=0.73, P<0.0005; right narrow: r =0.72, P<0.0005). Further to this, scores on the powerslap narrow test were significantly differentiated by climber ability (LEFT: F(3,37)=15.74, P<0.0005; right: F(3,37)=12.16, P<0.0005). Limits of agreement and intra-class correlation indicated that the powerslap test is a reliable performance measure.

CONCLUSION

According to the present findings the narrow grip variation of the powerslap test is a useful sport-specific power test that is related to climbing performance.

Comparison of lactate sampling sites for rock climbing

Comparisons of capillary blood lactate concentrations pre and post climb have featured in the protocols of many rock climbing studies, with most researchers obtaining samples from the fingertip. The nature of rock climbing, however, places a comparatively high physiological loading on the foreaand fingertips. Indeed, the fingertips are continually required for gripping and this makes pre-climb sampling at this site problematic. The purpose of our study was to examine differences in capillary blood lactate concentrations from samples taken at the fingertip and first (big) toe in a rock climbing context. 10 participants (9 males and 1 female) completed climbing bouts at 3 different angles (91°, 100° and 110°). Capillary blood samples were taken simultaneously from the fingertip and first toe pre and post climb. A limit of agreement plot revealed all data points to be well within the upper and lower bounds of the 95% population confidence interval. Subsequent regression analysis revealed a strong relationship (R (2)=0.94, y=0.940x + 0.208) between fingertip and first toe capillary blood lactate concentrations. Findings from our study suggest that the toe offers a valid alternative site for capillary blood lactate concentration analysis in a rock climbing context.

Walking for fitness: is it enough to maintain both heart and bone health?

Exercising at levels of whole body accelerations exceeding 3.6 g has been shown to have positive effects on cardiovascular fitness, bone density and balance. This pilot research project evaluated the whole body accelerations and cardiovascular challenge provided by selected walks in the Canberra region of Australia to determine if walks could be ranked according to potential level of impact on both cardiovascular fitness and bone health. Nine participants, who described themselves as walking at least 3 km, three times per week, wore a data logging device recording heart rate, acceleration and GPS position while walking three outdoor tracks: (1) the running track of an athletics stadium; (2) on a hill climb path through bushland; and (3) on a route through suburban streets. There was a significant difference (P < 0.05) for heart rate, distribution of whole body accelerations and average walking speed between track 2 and tracks 1 and 3. There was a significant difference for heart rate, distribution of whole body accelerations and average walking speed between the walks. The running track and the suburban walk provide a moderate exercise challenge, with the hill climb walk providing progressively greater vertical height challenge, resulting in an increased cardiovascular exercise challenge. No participant effectively exceeded the threshold for achieving a positive impact on bone density (100 or more accelerations/day >3.6 g) on track 1, and only two of the nine participants intermittently achieved this threshold on tracks 2 and 3.

Does group B streptococcal infection contribute significantly to neonatal sepsis in Antigua and Barbuda?

Group B streptococcus is the most common cause of neonatal sepsis in the United States of America (USA). This study was undertaken to determine the contribution of group B streptococcus to neonatal septicaemia in Antigua and Barbuda. From 1994 to 2002, there were about 12,000 births, with 2500 Special Care Nursery admissions, 1100 (44%) with potential neonatal septicaemia. Blood cultures were done in 433/1100 (39%) and cerebrospinal fluid cultures in 52/1100 (5%). Positive cultures were seen in 41/433 (9.5%) with group B streptococcus in 1/41 (2.4%), streptococcus "species" in 3/41 (7.4%) and positive cerebrospinal fluid cultures were seen in 2/52 (one group B streptococcus) giving 5 per 12,000 or 0.4 cases per 1000 babies. Vaginal cultures from 1994 to 2002 revealed group B streptococcus in 14/163 (8.6%) of positive bacterial cultures. A sample of pregnant women from a private office had positive culture for group B streptococcus in 2/120 (1.7%). The prevalence rate of carriage (15 to 40%) and infection (1.7 to 4 per 1000 babies) was much higher in the USA in the same period Universal screening of mothers for group B streptococcus may not be as necessary or cost-effective in Antigua and Barbuda.

Adverse effects of left ventricular hypertrophy in the reduction of endpoints in NIDDM with the angiotensin II antagonist losartan (RENAAL) study

AIMS/HYPOTHESIS

We explored the impact of baseline left ventricular hypertrophy (LVH) and losartan treatment on renal and cardiovascular (CV) events in 1,513 patients from the Reduction of Endpoints in NIDDM with the Angiotensin II Antagonist Losartan (RENAAL) trial, which studied the effects of losartan on the progression of renal disease and/or death in patients with type 2 diabetes and nephropathy.

MATERIALS AND METHODS

LVH was assessed using ECG criteria (Cornell product and/or Sokolow-Lyon voltage). The risk of renal or CV events was determined by a proportional hazards model fit with treatment allocation and presence of LVH. Covariates at baseline included age, sex, systolic BP, mean arterial pressure, pulse, proteinuria, serum creatinine, albumin and haemoglobin.

RESULTS

A total of 187 subjects (12%) had LVH at baseline. Treatment with losartan resulted in a significant decrease in the Cornell product (-6.2%) and Sokolow-Lyon voltage (-6.3%). LVH was shown to be significantly associated with the primary endpoint, which was a composite of doubling of serum creatinine (DSCR), endstage renal disease (ESRD) or death (hazard ratio [HR]=1.44, p=0.011), as well as with the composite renal endpoint of DSCR/ESRD (HR=1.42, p=0.031) and CV events (HR=1.68, p=0.001). Losartan treatment of patients with LVH decreased the CV as well as renal risk to a level similar to that of patients without LVH.

CONCLUSIONS/INTERPRETATION

In patients with type 2 diabetes and nephropathy, LVH is associated with significantly increased risk of CV events and the progression of kidney disease. Importantly, in patients with LVH, losartan reduced the CV as well as the renal risk to a level similar to that seen in subjects without LVH.

Response of field-grown maize to applied magnesium in acidic soils in north-eastern Australia

Split-plot field experiments, with main plots consisting of various rates of calcitic lime and single rates of dolomite, gypsum, and calcium silicate, were conducted at each of 4 sites to determine the effect of band-applied magnesium (Mg) on maize yield. The sites were acidic with pH values of 4.5, 4.9, 5.0, and 6.1 and exchangeable Mg levels of 0.16, 0.10, 6.0, and 2.0 cmol(+)/kg, respectively. Magnesium significantly (P < 0.05) increased grain yield at the 2 low-Mg sites, both of which were strongly acidic and responsive to lime application, but the nature of the Mg × lime interaction was different at each of the 2 responsive sites. The absence of a response to Mg at lime rates ≥1 t/ha at one responsive site was attributed to the presence of small amounts of Mg in the calcitic lime and/or an improved root environment enabling better exploitation of the soil Mg. Supplying a readily soluble source of Mg in the fertiliser band also resulted in increased grain yield in the gypsum, dolomite, and calcium silicate treatments at the 2 Mg-responsive sites. When the initial soil pH was strongly acidic, exchangeable Mg levels increased with increasing lime rate, suggesting that the small quantities of Mg that occur in the majority of liming materials may be of importance with respect to Mg nutrition. In contrast, gypsum application exacerbated the Mg deficiency at one site. The relationship between grain yield response and soil Mg level across all sites indicated that above an exchangeable Mg level of 0.27 cmol(+)/kg there would be little likelihood of a response to applied Mg.

Field amelioration of acidic soils in south-east Queensland. I. Effect of amendments on soil properties

Replicated field trials with rates of lime ranging up to 8 t/ha were conducted at each of 27 sites in south-east Queensland. At 16 of these sites, single rates (2 t/ha) of gypsum or phosphogypsum were also applied. Soil samples (0-10 cm) were collected from each plot and analysed for pH in both water (pHw) and 0·01 M CaCl2 (pHCa), for electrical conductivity, exchangeable cations, and extractable Al and Mn. Gypsum application resulted in either a general trend for, or significant (P < 0·05), reductions in pHw but had no significant effect on pHCa. The relationship between rate of applied lime and soil pH at each site permitted the calculation of pH buffer capacity for a wide range of soil types and properties. The pH increase per t applied lime ranged from 0·14 to 0·82 and from 0·16 to 0·63 for pH measured in water and 0·01 M CaCl2, respectively, reflecting the range in pH buffer capacity which was significantly correlated with organic carbon. Multiple regression indicated that organic carbon and clay significantly contributed to the variation in pH buffer capacity but only around 40% of the variation could be accounted for. The pH values at which Al saturation was reduced to 10% ranged from 4·82 to 6·02 (pHw) and from 4·26 to 4·93 (pHCa) and indicated that if neutralising exchangeable Al is the basis for liming, then no single target pH value will be appropriate for all soils. However, the target pH at which Al saturation would be reduced to 10% could be predicted from the initial pH and initial Al saturation. The effective cation exchange capacity (ECEC) was increased by liming at all sites and the additional exchange capacity was occupied by Ca. This increased Ca saturation was not necessarily at the expense of exchangeable K and Mg, which were significantly (P < 0·05) reduced at only a few sites. The increase in ECEC for a unit increase in pH ranged from 0·5 to 9 cmol(+)/kg and at some sites represented a doubling of the soil"s cation exchange capacity.

Field amelioration of acidic soils in south-east Queensland. III. Relationships of maize yield response to lime and unamended soil properties

Maize (Zea mays) grain yield responses to rates of lime were measured at 19 sites onseveral soil types in south-east Queensland. At some sites, one rate of gypsum or phosphogypsum was also applied. Relative grain yield (100 mean yield of nil lime treatment/maximum yield) was correlated with each of soil pH (1 : 5 water and 1 : 5 0·01 M CaCl2), soil solution pH, exchangeable (1 M KCl) Al, exchangeable (1 M NH4Cl) Ca, Al saturation of the effective cation exchange capacity (ECEC), Ca saturation of the ECEC, and 0·01 M CaCl2 extractable Mn and Al. Across all soil types, Mitscherlich fits indicated that most of the variation in relative grain yield was accounted for by either Ca saturation (R2 = 0·62) or soil solution pH (R2 = 0·61), although soil pH(water) (R2 =0·53), Al saturation (R2 = 0·46), exchangeable Ca (R2 = 0·42), soil pH(CaCl2) (R2 = 0·40), and CaCl2-extractable Mn (R2 = 0·33) also accounted for significant (P < 0·05) amounts of variation. These results demonstrate that one or both of Al and Mn toxicities were having an impact on yieldat different sites. The contrast between the lack of responses to gypsum/phosphogypsum at mostlime responsive sites and the observation that Ca saturation was well correlated with relative grainyield suggested an ameliorating effect of Ca on Al toxicity. This effect was captured by an index,Al saturation/Ca saturation, which was well correlated with relative grain yield (R2 = 0·66 for a Mitscherlich fit). A step-up regression approach indicated that most variation in relative grain yield (RY) could beaccounted for by the following equation: The assessment of factors likely to limit yield on strongly acidic soils of the region will therefore needto include indices of Al and Mn toxicities as well as Ca status. Soil pH integrated the effects of these factors on yield, and as a single index, was shown to bean effective diagnostic tool. Relative grain yields of 90% were associated with pH values in the soil solution, 1 : 5 water and 1 : 5 0·01 M CaCl2 of 4·5, 5·2, and 4·4, respectively.

Prediction of nitrogen fertiliser requirements of maize in subtropical Queensland

Sixteen field experiments were conducted at 9 sites in the South Burnett region of subtropical Queensland, to determine grain yield response of maize to fertiliser nitrogen (N) and to assess soil mineral N levels at sowing for predicting N requirement. At 6 sites, areas were either winter-cropped or bare-allowed, resulting in different cropping histories immediately prior to summer maize. In each experiment, 4 rates of N (0, 38, 76, and 152 kg/ha) were applied, with an additional rate (304 kg/ha) at 3 sites that received supplementary irrigation. Immediately prior to sowing, soil samples for mineral N and moisture were taken from each 10-cm increment to a depth of 120 cm. Soil nitrate-N levels (0-120 cm) before sowing were 16-100 kg N/ha (winter-cropped) and 65-167 kg N/ha (bare-fallowed). Application of N significantly (P<.05) increased grain yield in 14 of the 16 experiments. Maximum grain yields in non-irrigated experiments ranged from 2.08 to 5.61 t/ha and reflected profile available water at sowing and rainfall during the growing season. Maximum yields in irrigated experiments ranged from 4.44 to 6.95 t/ha. The magnitude of the response was greater at winter-cropped sites (relative yields 33-89%) than at fallow sites (82-100%). Relative grain yield was well correlated with nitrate-N in the 0-60 cm profile ( R2 = 0.74). There was also a good relationship between relative grain yield and nitrate-N at 0-10 cm depth ( R2= 0.64).

Synchronously pumped, femtosecond dye laser insensitive to cavity-length variations of up to 15 microm

A synchronously pumped, hybridly mode-locked, antiresonant-ring dye laser that is insensitive to cavity-length variations of up to 15 microm is described. At a cavity length that is 70-80 microm shorter than the synchronous cavity length this laser generates stable pulses as short as 55 fsec, with a pulse width of 65 fsec being typical (assuming a sech(2) pulse shape). No evidence for colliding-pulse mode-locking effects is observed.

Mineral nutrition of soybeans grown in the South Burnett region of south eastern Queensland. 2. Prediction of grain yield response to phosphorus with soil tests

Grain yield response of soybean (Glycine max cv. Bragg) to applied phosphorus was measured at 19 experimental sites in the South Burnett region. The soil phosphorus supply factors of quantity, intensity, buffer capacity and rate were estimated by various soil chemical tests, and relative yield [(yield at nil applied phosphorus/maximum yield) x 100] regressed against these tests. The equilibrium phosphorus concentration-the intensity measure-accounted for the greatest percentage variation in relative yield (80%) and at 90% maximum yield was 0.014 �g P/ml. Phosphorus extracted by 0.01 M CaCl2 was highly correlated with the equilibrium phosphorus concentration (r2=0.93) and accounted for 73% of the variation in relative yield. Soil levels of calcium chloride-extractable phosphorus were interpreted as follows: < 0.044 �g P/g, response to phosphorus probable; 0.044 �g P/g to 0.058 �g P/g, response uncertain; > 0.058 �g P/g, response unlikely