I want to measure the PBC and sorption/desorption characteristics of paddy soils, under long term fertilization. Kindly suggest some convenient and time saving protocols that i should follow.
Phosphorus Buffering Capacity Indices as Related to Soil Properties and Plant Uptake( Journal Journal of Plant Nutrition ,Volume 28, 2005 - Issue 3)
Abstract: Evaluation of the plant-available phosphorus (P) in calcareous soils is commonly performed by removing a portion of solid phase P using chemical extractants. Critical soil test values, however, may be affected by variation in sorption and buffering behavior of different soils. The objective of this study was to evaluate the importance of buffering capacity indices to predict P uptake by wheat (Triticum aestivum). Eleven surface soil samples were assayed for a number of P intensity (CaCl2-P) and quantity (Olsen-P, Colwell-P, and Resin-P) factors. Some phosphorus buffering indices were obtained from P sorption equations. A single-point index of buffering was also determined experimentally. In a greenhouse experiment, wheat was grown for 35 and 70 days on the same soils and P uptake was determined. Nonlinear and linear equations described the P sorption data (P < 0.001). Buffering indices derived from these equations were highly correlated with single-point index of capacity. Clay content was the most important soil property affecting the buffering capacity factor. The phosphorus intensity index (CaCl2-P) was weakly related to P uptake (P < 0.05). Among the quantity factors only Resin-P was significantly correlated with P uptake. Buffering indices showed significant but inverse relationships with P uptake only at 70 days harvest (r = −0.69 to −0.71; P < 0.05). Combination of intensity or quantity factors with buffering capacity indices, such as intensity/capacity or quantity/capacity indicators, improved considerably the ability to account for variations in P uptake by wheat.
Effects of phosphate buffer capacity of soil on the phosphate requirements of plants ( Plant and Soil, October 1976, Volume 45, Issue 2, pp 433–444)
Abstract: Plant-uptake and yield data for ryegrass in a greenhouse experiment are used to estimate the theoretical fertilizer phosphate requirement (Pf) of 24 Sherborne soils. Pf is shown to be a function of three parameters: (i) quantity of P required by the plant (Pr) for optimum yield; (ii) quantity of soil P (Qr) required to maintain a non-limiting soil solution concentration (Ir); (iii) quantity of labile soil P (Q). Because of its large effect on Qr and Ir, the phosphate buffer capacity has an important effect on Pf. However Pf cannot be directly related to phosphate buffer capacity if Q is ignored. On soils of similar Q, increasing buffer capacity will always have a positive effect on Pf, but on soils of the same I, it may have a positive or negative effect on Pf. Consequently, Pf can only be simply, but inversely, related to Q or I on a group of soils of similar phosphate buffer capacity
Phosphorus Buffering Capacity Indices as Related to Soil Properties and Plant Uptake( Journal Journal of Plant Nutrition ,Volume 28, 2005 - Issue 3)
Abstract: Evaluation of the plant-available phosphorus (P) in calcareous soils is commonly performed by removing a portion of solid phase P using chemical extractants. Critical soil test values, however, may be affected by variation in sorption and buffering behavior of different soils. The objective of this study was to evaluate the importance of buffering capacity indices to predict P uptake by wheat (Triticum aestivum). Eleven surface soil samples were assayed for a number of P intensity (CaCl2-P) and quantity (Olsen-P, Colwell-P, and Resin-P) factors. Some phosphorus buffering indices were obtained from P sorption equations. A single-point index of buffering was also determined experimentally. In a greenhouse experiment, wheat was grown for 35 and 70 days on the same soils and P uptake was determined. Nonlinear and linear equations described the P sorption data (P < 0.001). Buffering indices derived from these equations were highly correlated with single-point index of capacity. Clay content was the most important soil property affecting the buffering capacity factor. The phosphorus intensity index (CaCl2-P) was weakly related to P uptake (P < 0.05). Among the quantity factors only Resin-P was significantly correlated with P uptake. Buffering indices showed significant but inverse relationships with P uptake only at 70 days harvest (r = −0.69 to −0.71; P < 0.05). Combination of intensity or quantity factors with buffering capacity indices, such as intensity/capacity or quantity/capacity indicators, improved considerably the ability to account for variations in P uptake by wheat.
Effects of phosphate buffer capacity of soil on the phosphate requirements of plants ( Plant and Soil, October 1976, Volume 45, Issue 2, pp 433–444)
Abstract: Plant-uptake and yield data for ryegrass in a greenhouse experiment are used to estimate the theoretical fertilizer phosphate requirement (Pf) of 24 Sherborne soils. Pf is shown to be a function of three parameters: (i) quantity of P required by the plant (Pr) for optimum yield; (ii) quantity of soil P (Qr) required to maintain a non-limiting soil solution concentration (Ir); (iii) quantity of labile soil P (Q). Because of its large effect on Qr and Ir, the phosphate buffer capacity has an important effect on Pf. However Pf cannot be directly related to phosphate buffer capacity if Q is ignored. On soils of similar Q, increasing buffer capacity will always have a positive effect on Pf, but on soils of the same I, it may have a positive or negative effect on Pf. Consequently, Pf can only be simply, but inversely, related to Q or I on a group of soils of similar phosphate buffer capacity
There are no shortcuts. You need to do multiple point sorption measurements and fit a regression model to smooth out the experimental variation. Then you can estimate the slope (buffer capacity) at different residual concentrations in solution, typically most useful around the solution requirement that satisfies the maximum growth potential. In the absence of appreciable pre-sorbed P, log/log sorption relations (Freundlich) are usually close to linear over orders of magnitude, which makes the stats simple. The presorbed P is what Anoop describes as Q. In our work we find that Q, estimated from 32P exchange, does not account for the apparent effect of presorbed P.
Each soil exert specific P buffer capacity due to physico-chemical properties such as soil texture, clay mineralogy, oxide content and mineralogy, organic matter content, and pH. Therefore it is required to be accurately determined by sorption/desorption experiment by considering the targetted soil solution concentration. The capacity may change as a function of initial P concentration and time as well. Because P can be removed readily available sorption sites and time-dependent sites. Therefore the buffer capacity is relatively higher in sort-term than the longer one.The buffer capacity may be influenced by irrigation practices or long-term water regime of a soil. i.e. drying and wetting cycles can even be effective in relation redox potential of soil.
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