I need to understand the proper time for measuring the solution phosphorus (P)concentration that can give an estimate to have significant effect on plant P concentration.
Actually I'm reading some old devised extraction techniques for measuring soil test P, K, Zn, Ca and Na for effectiveness of using different extractants to extract soil adsorbed P. Then this question comes into my mind that either only initial soil testing is sufficient or we have to calculate during crop growth aslo for proper calibration of equations for solution phosphorous (P) concentration for crop uptake and P needs??
Soil P concentration is not necessarily correlated with crop plant tissue P concentration as up take depends also on the P/N ratio and the way P is bound in the soil (see attached).
Article Nitrogen and phosphorus limited production of cereals and se...
Mr.Saeed,Soil solution P is estimated normally using water or 0.01M CaCl2 as extractants. A water extraction is used as an estimate of plant-available soil solution P in some countries like Netherlands and Germany.Water-soluble P may give response in terms of crop growth and plant P concentration in soils having high amounts of P accumulated over years due to continuous application of fertilizers and manures ,especially poultry or swine /pig manure.In P accumulated soils ,soil solution P may show good correlation with dissolved reactive P in run off water.When soil solution P is high,there is no need to test it during different crop growth stages and only initial soil testing for P before crop sowing may be adequate.Under conditions of low fertilizer or manure application the soil anion exchange sites may not be saturated with P and soil solution P concentrations may very low.Using P adsorption isotherms one can determine the optimum soil solution P(also called external P) P,fertilizer P requirement and optimum internal P(plant P).The following references may be consulted.
Determination of water-and/or dilute salt-extractable phosphorus.In methods of phosphorus analysis for soils,sediments,residuals,an...32/110 edited by Pierzymski.
pss.okstate.edu/people/faculty-1/..../Methods_of_P_Analysis_2000pdf
Influence of different intensities of phosphorus fertilizing on available phosphorus contents in soils and uptake by plants. by Kulhanek etal. Plant Soil Environment,53(9)382-387 (2007)
www.agricultureljournals.cz/publicFiles/00330.pdf
Soil tests www.agvita.com.au/pdf/expresssoil/Soil_P_tests.pdf
Sir Hein Van Gils ! I'm grateful to you for your guidance and helping material.
Sir Annangi Subba Rao ! Your answers and helping material are always more than my expectations. Thank you very much Sir !
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