Pot experiments on the agronomic efficiency of rock phosphates. IV. Effect of rock phosphates on the shoot yield and P uptake of spring barley at tillering

摘要

A pot experiment was set up using acidic sandy soil from Nyirlugos (N) and acidic clay loam soil from Ragaly (R) to investigate the effects of 5 types of rock phosphates (RP; from Algeria, Florida, North Carolina, Senegal and Morocco) and hyperphosphate (HP) on the shoot yield, P concentration and uptake of spring barley at tillering. Superphosphate (SP) was used as the standard P source. The effect of applying CaCO3 in combination with SP was also examined in a separate treatment. On the average, the shoot yield was almost twice as high on the colloid-rich clay loam soil from R (3.69 g/pot) as on the colloid-poor sandy soil from N (1.90 g/pot). The P uptake was only 25% higher on the clay loam soil (13.0 mg/pot) as on the sandy soil (10.4 mg/pot). This could be attributed to the fact that on the N soil, the P concentration of the shoots was almost 0.1% higher on average in the RP treatments and 0.2-03% higher in the SP and SP+CaCO3 treatments. Diverse P effects were observed on both soils when total P2O5 rates of 0-100-400-1600 mg/kg, adjusted on the principle of active agent equivalence, were applied using the different RP types. The differences between the P effects manifested as yield surpluses and P uptake exhibited a close correlation with differences in the P solubility of the different RPs. On both soils, the Algerian RP, which had excellent natural solubility, gave the highest yield surpluses and P uptake. The HP and RPs from Morocco and North Carolina were also efficient. The other extreme was represented by the RPs from Senegal and to a certain extent, from Florida, which had low specific surface area, poor P solubility and low CaCO3 content. The differences between the RPs can also be described in terms of relative agronomic efficiency (RAE%), when the effect of the RP is compared with that of a water-soluble P fertilizer, in the present case SP. Averaged over the 2 soils and over RAE% values calculated in terms of shoot yield or P uptake, the ranking of the RPs based on RAE was the same as that based on their solubility in neutral ammonium citrate (NAC). When correlations were analysed between the solubility of RP and the shoot yield or P uptake at tillering, the loosest correlations on both soils were observed when the P rates applied were given in terms of total P content and the closest when the quantities were expressed as the P fraction soluble in NAC. Together with the ranking of the RPs on the basis of RAE, this suggests that under conditions similar to those of the present experiments the best extracting agent for determining the P solubility of RPs is NAC. When the effects of the individual RPs on the P uptake were examined separately, the differences in P effects were found to exhibit a close correlation with differences in the various properties of the RPs (P solubility, specific surface, CaCO3 content) on both soils..