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Fluid Journal : Fall 2015
13 The Fluid Journal Fall 2015 with the fertilizer (TSP, 15% Ca). In this soil exchangeable Ca (1.5 cmolc kg-1) was very close to the minimum level (1 cmolc, kg-1) recommended for adequate plant growth. In this experiment, Ca was not added in the basal fertilization to avoid opportunities of Ca-P precipitation that could hinder the results. In the Redvale soil, TSP performed much worse than the ammoniated sources. In our previous study, we found that significantly less P remained labile when calcium phosphate fertilizers were applied in the Redvale soil. We hypothesized that the lower P availability may be due to Ca-P precipitation at the relatively high pH of this soil. P effect. In the Andisols and Oxisols the addition of P fertilizer significantly increased tissue P concentration with respect to the control (Figure 2). However, the concentration of P in the shoots was still deficient in many of the amended treatments where the measured shoot P concentrations were below the critical level of 3 mg g-1 . In the calcareous Port Kenny soil, P concentration did not statistically differ between the control and the fertilizer treatments. The seed P contribution needs to be taken into account to distinguish between uptake from soil and fertilizer applied P. Several studies have used the assumption of 50 percent of total seed P translocation to the shoots. However, the uptake of P in the control treatments of the Oxisols and Andisols was very low and in some cases even less than 50 percent of total seed P. Hydroponic experiments were conducted with labeled P to determine the seed P contribution and showed that the translocation of seed P to the shoot increased with increasing P supply. Most literature studies have shown good correspondence between E and L values, except for some species known to mobilize P (e.g. white lupin). Therefore, to estimate the seed contribution, we assumed the E values that were previously determined (data not shown) equaled the L values: R L value = _____________________ 33Pshoot ______________________ Pshoot - Pdfseed Fig. 2. Shoot P concentration (mg g-1) for wheat grown in soils with granular (TSP, MAP, DAP) or fluid (flMAP) fertilizer. A control treatment (nil P) was included for each soil. Bars appended with different letters are statistically different at P ≤ 0.05. Fig. 3. Distribution of P in the plant shoots derived from fertilizer, soil, and seed. Granular fertil- izers (TSP, MAP, and DAP), fluid fertilizer (flMAP), and control (nil P). R (above) is the applied 33P dose. This allowed estimating the P seed contribution for all control treatment replicates. Translocation of seed P to shoot increased with increasing P uptake in the shoot and the relation could be well described with an exponential equation: Pdfseed = Ax(1–exp(BxPshoot)) A and B are fitted parameters. This equation was used to estimate the seed P contribution in the fertilizer treatments. Note that the estimate of seed P contribution was less crucial for the fertilizer treatments, as the relative contribution of seed P to shoot P uptake was smaller. The contribution of P from the fertilizer, soil, and seed to the total P uptake of the plants is shown in Figure 3. For the Andisols and Oxisols, the highest contribution to P uptake came from the fertilizers with an average value of 75 percent (average of all treatments). In “Fluid P fertilizers were highly effective in calcareous soils.”