Sign up for email alerts of new Fluid Journal issues!
Fluid Journal : Winter 2014
9 The Fluid Journal Winter 2014 Can Soil Chemical Changes Influence Plant Growth? What about mobility and lability of various P fertilizers on high P-fixing soils? The Fluid Journal • Official Journal of the Fluid Fertilizer Foundation • Winter 2014 • Vol. 22, No. 1, Issue #83 It has long been recognized that interactions between phosphorus (P) and soils result in a reduction in the availability of P for crop growth over time. This necessitates additional or excessive applications of P to maintain crop productivity, which can be costly and can result in environmental problems. In many areas of the world, extensive weathering or a unique mineralogy have produced agricultural soils that are deficient in plant-available P. As a result, when P fertilizer is added it rapidly undergoes chemical transformations that make P unavailable for plant uptake. Direct information from literature on high P-fixing soils and the associated mechanisms reducing P availability to plants is limited. A deeper understanding of these processes may help in developing improved management strategies and/or efficient fertilizer formulations leading to higher productivity on these soils. The objectives of this research were to: • Investigate the mobility and ability of various P fertilizers on two high-P fixing soils • Identify the P reaction products formed within and around the point of fertilizer application. Methodology Site. The five-week laboratory incubation- based experiment consisted of two different soils: • An Oxisol collected from Rondonopolis, Brazil • A calcareous Inceptisol soil collected from southwest Idaho. Neither of the soils had a history of being fertilized, though the soil from Brazil had been under cultivation. Sources. There were three P fertilizer sources used in the study: • Monoammonium phosphate (MAP) • Diammonium phosphate (DAP) • Ammonium polyphosphate (APP). MAP and DAP were added as granules and APP was added as a fluid. Application. MAP, DAP, and APP were each applied to the center of a petri dish filled with soil at a moisture content equivalent to 60 percent of its maximum water-holding capacity. Each P source added approximately 9.8 mg P/plate for a total of four treatments, including a control treatment not receiving P. The nitrogen (N) was balanced using urea. Five replicates of each treatment on both soils were covered and incubated in petri dishes for five weeks at 25oC. Sampling. At the end of the incubation period, concentric rings of soil surrounding the fertilizer application point were removed corresponding to 0-7.5 mm, 7.5 -13.75 mm, 13.75-25 mm and 25-43.5 mm from the point of P application. Soil samples were analyzed for soil pH, total P, and resin extractable P. Ms. Joy Pierzynski, Dr. Ganga Hettiarachchi, & Mr. Raju Khatiwada Summary: There was evidence of fertilizer P diffusion to the second section with Brazil soil and up to the third section with Idaho soil. We found no differences in P diffusion away from the point of application between the three P sources (MAP, DAP, and APP) for either soil. Percent resin P results for Brazil soil indicated there was no statistical difference between the three P sources. Results for Idaho soil were different from Brazil soil. There was significantly greater percent resin P in the center section with the APP as compared with either MAP or DAP. Speciation results indicated that the addition of P induced the formation of P solid phases, including adsorbed as well as secondary P minerals. In calcareous soil, low pH and formation of less Ca-P species in the APP-treated soils may have been the reason for observed high-resin extractable P concentrations. ▼ DOWNLOAD