DOI: 10.4226/47/587dab89314f1
title: Novel applications for Oxalate-Phosphate-Amine Metal-Organic-Frameworks (OPA-MOFs): Can an iron-based OPA-MOF be used as slow-release fertilizer

description: A novel hybrid material developed at Southern Cross University was investigated as fertiliser and soil modifying agent to address problems associated with acidification of agricultural soils. The compound, containing phosphorus, nitrogen and oxalate as structural elements, was tested in extended pot trials using wheat cv. Dollarbird. Its degradation, controlled by oxalate solubility and consumption by bacteria using it as carbon source to biomineralise carbonate, enables slow release of enclosed nutrients. Research objectives were met as trial results include increases in grain yield, protein content and micronutrient uptake, and presence of active oxalate degrading bacteria was confirmed.
description: Data Processing: All statistical analyses were performed GENSTAT 16.1 software, 2-way ANOVA and Duncan's Tests.
description: Soil from the top 150mm horizon of a Pdeficient rhodic Ferralsol [24] was collected at New South Wales Department of Primary Industries Wollongbar Agricultural Institute (28°50′S, 153°25′E) in northeastern NSW, Australia. Soil was airdried to ~ 25% moisture and sieved to 4 mm. A subsample was dried at 65°C for 3 days and analysed for physicochemical properties and soil nutrient status. Analyses for Bray I and II, nitrateN, ammoniumN, K, Mg and Ca, DTPAextractable micronutrients, ECEC, electrical conductivity and soil pH were undertaken using standard methods at the NATA accredited Environmental Analysis Laboratory (EAL) at Southern Cross University (SCU), Lismore, NSW, Australia. Briefly, soil pH was measured in water (1:5), and total N and C were measured by combustion using a LECO TruMAC CNS analyzer. Extractable cations were quantified using inductively coupled plasma optical emission spectroscopy (ICPOES 4300D, Perkin Elmer, USA). Concentrations of extracted nitrate and ammoniumN were quantified using a flow injection analyser (FIA) after KCl extraction.
Fertilizer combination treatments were made from commercially available agricultural fertilizers with urea as the N source and triple superphosphate as the P source in a pelletised form. Commercially available calcium oxalate was used as an oxalate source (Ox). The oxalate-phosphate-amine-metal-organic-framework mineral (OPAMOF) was synthesised from commercially available chemicals. Briefly, a homogenized starter solution made from ferric chloride, orthophosphoric acid, oxalic acid, urea, and water, mixed to a molar ratio of 1:6:1:3:100, respectively, was filled into Teflon coated polypropylene (PP) flasks and locked into steel pressure-digestion vessels. The hydrothermal reaction took place at 100°C over 24 hours, and precipitated the crystalline OPAMOF mineral. After filtering and drying to constant weight the mineral was ground to a powder using an agate mortar and pestle, and passed through a 0.5 mm sieve before application. In all there were eight fertilizer treatments and a nil fertilizer control. The eight fertilizer treatments were applied at two rates, high and low, where the dose rates were 120 kg Nha and 40 kg Nha , respectively, on the basis of N concentration of the synthesised OPAMOF (3.1%). The required amounts for the two rates of N application were calculated for OPAMOF, and then the required amounts of urea, superphosphate and oxalate back-calculated on the basis of the respective mineral concentrations in OPAMOF (12.5% P; 14.5% Ox).