Influence of liquid and granular phosphorus fertilizer on soil inorganic phosphorus fractions and fertilizer efficiency in calcareous soil

A large proportion of total P is unavailable to plants in calcareous soil due to rapid fixation of phosphorus into un-soluble form of P, which was not readily accessed by plant. In present study, a field experiment was carried out to compare the effects of different forms of phosphorus fertilizer sources (liquid and granular) on soil inorganic phosphorus fractions using sequence fractionation approach, and on fertilizer efficiency in calcareous soil under drip irrigation. Tomato was used as tested plant. The results showed that soil Ca2-P and Ca8-P content at the top 0-20 cm soil depth decreased statistically with application time. However, Ca10-P increased gradually indicating that P fertilizer was transformed or fixed to the form of Ca10-P after P fertilizer application. Ca2-P content in the topsoil (0-20 cm) was higher throughout the growing period under the treatment of liquid fertilizer topdressing than the others, Relative higher soil Ca8-P content was also observed during the growing stage of tomato. Compared with other treatments, liquid fertilizer application reduced soil P fixation and increased Ca2-P and Ca8-P significantly, and hence improved the P efficiency. It could also increase tomato yield (91725 kg/ha) by 26.7% compared with basal application granular P (CK1) and plant foliar P content. These findings suggest that compared with traditional granular phosphorus fertilizer base application, liquid phosphorus fertilizer have some potential advantage to decrease soil P fixation and enhance soil phosphorus bioavailability. Liquid phosphorus fertilizer was strongly recommended to be applied in calcareous soil under drip irrigation condition.