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Fluid Journal : Fall 2015
11 The Fluid Journal Fall 2015 The Fluid Journal • Official Journal of the Fluid Fertilizer Foundation • Fall 2015 • Vol. 23, No. 4, Issue #90 By Drs. Daniela Montalvo, Fien Degryse, and Mike J. McLaughlin Summary: Our study demonstrated that in acidic and oxide-rich soils, where the availability of phosphorus (P) is restricted by strong adsorption reactions, P fluid fertilizers did not provide any additional advantage to plant growth over the granular sources. In contrast, fluid P fertilizer was highly effective in calcareous soil. Chemical properties of the soils need to be considered prior to the selection of P fertilizers as they play a vital role in the fate of P in soils. Andisols and Oxisols are rich in P-sorbing minerals, such as Al/ Fe oxyhydroxides or allophone. Management of P nutrition in these soils is often very challenging. To overcome P deficiency and to increase the bio- available P pool in soil, the application of fertilizer P is necessary. In these soils, a substantial quantity of fertilizer P is required to achieve economically acceptable yields; however, over- fertilization can result in environmental problems and accumulation of P in the soil. Phosphate fertilizers come from a finite resource and recently there has been speculation of exhaustion (in the next few centuries) of the more accessible sources, which may lead to an increase of the already high fertilizer prices. Phosphorus fertilizers are commonly applied in the form of granules, but the use of fluid P is also a viable alterative. The selection of fertilizer type (granular vs. fluid) should be made, taking into consideration the chemical properties of the soils. It has been shown that there is more bio-available P in calcareous soils fertilized with fluid P than with granular P fertilizers. However, our previous work has indicated this is not the case for Andisols and Oxisols. A greater percentage (34%) of added P with granular fertilizer remained in a labile form (potentially plant available) than with fluid fertilizer (24% labile). These results indicated that when adsorption (not precipitation) reactions reduce the availability of fertilizer P, the use of fluid sources may not provide any agronomic advantage over the conventional granular formulations. Objective This study aimed to investigate the relative effectiveness of fluid and granular P fertilizers for wheat grown in acidic, strongly P-sorbing soils under glasshouse conditions. Also a calcareous soil was included for comparison. Methodology Materials. Surface soil samples (0 to 10 cm depth) of two Andisols from Chile and New Zealand (North), two Oxisols from Australia (Greenwood and Redvale), and a calcareous Inceptisol from Australia (Port Kenny) were used for this pot experiment. Soils. All soils were characterized by low soil test P level and high capacity to fix P. Selected soil chemical properties are presented in Table 1. Fertilizers. The P fertilizers evaluated were: • Granular triple super-phosphate (TSP, 20% P) Management of P Nutrition in Andisols, Oxisols Challenging ▼ DOWNLOAD • Mono-ammonium-phosphate (MAP, 22% P) • Di-ammonium-phosphate (DAP 20% P) • Fluid mono-ammonium-phosphate (flMAP, 26% P). Rates. Fertilizer rates were 150 mg kg-1 for Chile, North, Greenwood, and Redvale soils, and 40 mg kg-1 for Port Kenny soil. Higher P rates were used for the Andisols and Oxisols because of their very high P sorption capacity. Also a control (no fertilizer) treatment was included for each soil. Each treatment was replicated four times. Soils. A total of 260 cm3 of dried- air and 2-mm sieved soil (weight of soil calculated based on the soil bulk density) was used in each pot. The soils were placed in double plastic bags and –basal macro- (100 mg N, 33 mg K, 21mgMg,28mgSperkg)andmicro- (0.83 mg Fe, Mn, Zn, Cu, 0.083 mg Co, Mo, B per kg) nutrients were added as a solution. Consequently, soils were uniformly labeled with 500 kBq kg-1 of carrier-free 33P-orthophosphate and watered to field capacity. Application. Three days after soil labeling and basal nutrient application, the P fertilizer treatments (granular and fluid) were applied at equidistant points around the pot and at 3 cm depth. One While fluids did not excel over granular here in plant growth, they did in calcareous soils.