Monitoring the availability of phosphorus (P) in soil under continuous cropping facilitates finding deficiency in crops and contributes to improving crop growth and nutrient management models. Soil P ...availability for crops is usually estimated by soil test P (STP), such as Bray‐1. This is widely used in the Americas. The relationship between the decrease of STP Bray‐1 and cumulative removal of P was evaluated in non‐P‐fertilized areas in long‐term studies. This removal was the sum of annual P removal over the study period as P exported in grains/crop outside the soil. The objectives were to: (a) quantify changes in STP as a function of cumulative P removal, (b) assess the relationship between relative decrease rate of STP and soil variables as well as annual removal of P by crops, and (c) develop a model to predict decrease of STP Bray‐1. Exponential decay functions were used to describe annual cumulative removal of P and STP from soil over time for 12 long‐term studies where no addition of P fertilizer was carried out. Changes in the relative rate of decrease of STP, relative to the initial STP Bray‐1 value at the onset of the experiment, were predicted by the ratio of soil organic matter to clay and silt and the average annual P removal by exponential decay (R2adj = 0.64; RMSE = 3.2 mg kg−1). We propose this predictive model as suitable to provide estimates of the relative decrease rate of STP by Bray‐1 and thereby improve management of P for optimizing crop yield.
Highlights
STP Bray‐1 decrease and cumulative P removal were related by exponential decay functions.
Relative decrease rate of STP Bray‐1 was related to SOM/(clay+silt) ratio and annual P removal.
A predictive model of the relative decrease rate of STP Bray‐1 was fitted and validate.
Our model is a useful tool to help predict soil P availability and nutrient management.
Many countries do not have a newborn screening (NBS) program, and immigrants from such countries are at risk for late diagnosis of phenylketonuria (PKU). In this international survey, 52 of 259 ...patients (20%) with late diagnosed PKU were immigrants, and 145 of the 259 (55%) were born before NBS or in a location without NBS.
This study explores the effects on some hematological parameters of a low-dose aspirin regimen (50 mg/day) versus a conventional aspirin treatment with reported antithrombotic efficacy (324 mg/day), ...in patients with acute myocardial infarction. Fifteen patients were randomized into 3 equal groups receiving 50 mg or 324 mg aspirin or placebo, daily for 21 days. Compared with placebo, bleeding time was significantly and similarly prolonged with both aspirin doses (+ 71 +/- 22% and + 69 +/- 20%, mean +/- S.D.). Aspirin 50 mg/day suppressed arachidonate-induced platelet aggregation and secondary phase aggregation after ADP and adrenaline. Collagen aggregation was inhibited by 44 +/- 15%. In no case were differences in the antiplatelet effects of the two doses observed. The effects of 50 mg/day persisted without attenuation during the observation period. Platelet thromboxane B2 generation during arachidonate-induced aggregation was inhibited by 95 +/- 2 and 99 +/- 1% compared to placebo group after 50 and 324 mg/day, respectively (P between doses less than 0.05). No change was observed with any treatment in coagulation time, prothrombin time or plasma thromboplastin time. Thus, in patients with acute myocardial infarction, the antiplatelet effects of aspirin 50 mg/day are stable over time and superimposable on those of 324 mg/day. The antithrombotic efficacy of aspirin 50 mg/day remains to be tested clinically.
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