Agronomic Effectiveness of Granulated and Powdered P-Exchanged

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Agronomic effectiveness of granulated and powdered P-exchanged Mg-Al LDH relative to struvite and MAP Maarten Everaert, Fien Degryse, Mike J. McLaughlin, Dirk E. De Vos, and Erik Smolders J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.7b01031 • Publication Date (Web): 21 Jul 2017 Downloaded from http://pubs.acs.org on July 22, 2017

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Journal of Agricultural and Food Chemistry

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Agronomic effectiveness of granulated and powdered P-

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exchanged Mg-Al LDH relative to struvite and MAP

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Maarten Everaert*a, Fien Degryseb, Mike J. McLaughlinbc, Dirk De Vosd, Erik

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Smoldersa

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a

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Science, KU Leuven, Kasteelpark Arenberg 20, B-3001 Heverlee, Belgium

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b

Division of Soil and Water Management, Department of Earth and Environmental

Fertilizer Technology Research Centre, School of Agriculture, Food & Wine,

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University of Adelaide, Waite Campus, PMB1, Glen Osmond SA 5064, Australia

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c

CSIRO Land and Water, Locked Bag 2, Glen Osmond SA 5064, Australia

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d

Centre for Surface Chemistry and Catalysis, Department of Microbial and Molecular

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Systems, KU Leuven, Celestijnenlaan 200F – 02461, B-3001 Heverlee, Belgium

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*Corresponding author: Maarten Everaert

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E-mail address: [email protected]

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Phone: +32 (0)16 37 91 16

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Abstract

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Layered double hydroxides (LDHs) used to recover P from wastewater have recently

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been proposed as new slow-release fertilizers. Here, the use of P-exchanged Mg-Al

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LDHs as powdered or granulated fertilizer is explored and compared with mono-

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ammonium phosphate (MAP), a fully water-soluble fertilizer, and with struvite, a

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recycled phosphate fertilizer with lower solubility. First, these three fertilizers were

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compared in a 100-day incubation experiment using P diffusion visualization and

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chemical analysis to assess P release from either granules or powdered fertilizer in

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three different soils. By the end of the incubation, 74-90% of P remained within the

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LDH granule, confirming a slow release. Second, a pot experiment was performed

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with wheat (Triticum aestivum) in an acid and a calcareous soil. The granular

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treatment resulted in a considerable higher P uptake for MAP compared to LDH and

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struvite. For the powder treatments, the P uptake was less than for granular MAP

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and was largely unaffected by the chemical form. The LDHs and struvite showed a

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lower agronomic effectiveness than granular MAP, but the benefits of their use in P

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recycling, potential residual value and environmental benefits may render these

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slow-release fertilizers attractive.

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Keywords

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Agronomic effectiveness, Fertilizer granulation, Layered double hydroxides,

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Phosphorus, Slow-release fertilizer, Struvite 2 ACS Paragon Plus Environment

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Introduction

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The phosphorus (P) fertilizer market experienced several price-peak events during

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the last decennia, highlighting the importance of efficient P use in agriculture.1

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Currently, the majority of the commercial P fertilizers, such as mono-ammonium

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phosphate (MAP) or triple superphosphate (TSP), contain P in water-soluble form. In

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soils which sorb P strongly, such as acid weathered soils and calcareous soils, the

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soluble P derived from such fertilizers is readily fixed by irreversible adsorption or

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precipitation, leading to low agronomic effectiveness.2,3 The use of slow-release

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fertilizers (SRFs) has recently been proposed to increase this agronomic

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effectiveness. It has been suggested that a gradual release of P from SRF granules

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reduces P fixation by supplying the P gradually to the rhizosphere, thereby limiting

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fixation on soil particles and matching the plants’ P requirements later in the growing

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season.4 Furthermore, slow-release of P from the fertilizer might reduce off-site P

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movement from soils.5–7

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The current SRFs for P can be divided into polymer-coated soluble P forms8,9 and

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materials with intrinsic slow-release properties. The latter group contains struvite

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(NH4MgPO4.6H2O), a recovery product from waste streams with slow-release

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properties associated with poor material solubility.10 The precipitation of struvite from

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different P-rich waste streams,11 as well as its P release characteristics12,13 and

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fertilization efficiency in different soil environments14–18 have been thoroughly

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investigated during the last decade. Very recently, P-exchanged layered double

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hydroxides (LDHs) have also been proposed as SRF materials. Layered double

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hydroxides are inorganic anion exchangers, typically consisting of layered

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hydroxides of divalent (M2+) and trivalent (M3+) cations, holding anionic species in the

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interlayer galleries and at the outer surface of the crystallites by competitive 3 ACS Paragon Plus Environment


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electrostatic interactions.19 Due to their high selectivity towards HPO42- anions, these

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materials have been studied as P adsorbents to isolate P from waste streams,20–23

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and the recovered product of this process, a P-exchanged LDH, has been proposed

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as a SRF.24–26 In a neutral or alkaline soil, the slow-release of P from LDHs can be

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related to the ion-exchange reaction between intercalated or surface bound HPO42-

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anions on the one hand and HCO3- or organic anions from the soil solution on the

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other hand. In an acid soil environment, this ion-exchange driven P release can be

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accompanied by a release of P caused by LDH dissolution.27 Recently, we studied

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the slow-release of P from LDHs in powder form under conditions mimicking the

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rhizosphere and we assessed the agronomic effectiveness of Mg-Al P-LDH powders

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mixed in an acid and a calcareous soil.28 In the acid soil, the P uptake by barley from

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the LDH powder treatment was up to 4.5 times higher than from the soluble KH2PO4

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treatment, likely related to the liming effect of the LDH, whereas in the calcareous

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soil the LDH was inferior to KH2PO4 at the higher P rates and similar at low P rates.

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Benício et al. assessed the P response of maize in two acid soils amended with a

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comparable P-LDH powder material.29 They also found that the P-LDH had higher

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agronomic effectiveness than a soluble fertilizer (TSP) and hypothesized that this

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may be related to the liming effect associated with LDH dissolution, resulting in a

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decrease in P adsorption capacity of the soil.

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Commercial fertilizers are commonly applied in granular form rather than as

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powders. The effect of granulation of struvite material on P release kinetics and P

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availability has recently been assessed by Degryse et al.13 They found that the

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uptake of P by wheat was similar for MAP and struvite when applied in powder form

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in both an acid and a calcareous soil. However, when applied in granular form in the

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same soils, P uptake was considerably greater for MAP than for struvite. This 4 ACS Paragon Plus Environment

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difference between granular and powdered treatments was attributed to the much

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slower dissolution of a struvite granule compared to powdered material.

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The effectiveness of P-LDH has been assessed when in powdered form, but not in

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granular form. Powdered fertilizers are generally impractical for application, given

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current fertilizer delivery systems, and hence granulation or pelletization of P-LDH

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powders would be required to make them suitable for conventional agricultural

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practice. The objective of this study was to explore the use of P-exchanged Mg-Al

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LDH as a granulated fertilizer and to compare this with its powder form and with

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commercial fertilizers struvite and mono-ammonium phosphate (MAP). First, an

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incubation experiment was established with granules and powder fertilizers

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incubated in different soils, and visualization and chemical analysis were used to

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assess the P release. This chemical approach was subsequently complemented with

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a pot trial in which powdered and granulated LDH, struvite and MAP were used as a

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P source for wheat growth.

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Material and Methods

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Soils

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The surface (0-20 cm) horizons of four Australian soils with contrasting soil

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properties were collected, air dried and sieved to 8 mm from the fertilizer

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application point. In the MAP treatment for the Kingaroy soil, less P from the MAP

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granule had diffused to >8 mm from the application than for the Monarto soil due to

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the strong P sorption in this soil. At >8 mm from the application point, the P solution

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concentration was below the instrumental detection limit, so no distinction between

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labile and non-labile P could be made. In the Streaky Bay soil, the amount of non-

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labile P in the inner circle of the MAP treatment was higher than in other soils. For

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the struvite treatments, relatively large amounts of labile P were measured in the

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inner circle of the soil samples, which, as discussed further on, can be attributed to

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dissolution of remaining struvite as a result of the high liquid:solid ratio during

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extraction. The struvite granule could not be recovered from the soil as it

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disintegrated upon retrieval, but there was still a considerable amount of residue that

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had not dissolved. In the Monarto soil, around half of the struvite-derived P had

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diffused to the outer circle, and this P was still partly labile after 100-days incubation. 11 ACS Paragon Plus Environment


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In the two other, more P-fixing soils, no labile P could be detected in the outer circle

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for the struvite treatments. In all three soils, but especially in Kingaroy, a significant

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pH increase was observed in the < 8 mm area around the application point of the

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struvite granules (Table 2). For the P-LDH treatments, the granule could still be

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recovered at the end of the incubation and was analysed separately. This analysis

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showed that 74−90% of the added P was still in the granule at the end of the

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incubation, resulting in overall small amounts of labile P in the LDH treatments. In

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the Kingaroy soil, all the released LDH-derived P in the inner circle was in an

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isotopically exchangeable form (Figure 3).

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The LDH granules retrieved from the soil were examined with XRD and compared to

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the original granule (Figure 4). From the diffraction pattern of the as-synthesized

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LDH material, we concluded that a mixed interlayer anion population was present.

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The high-intensity 003 and 006 reflections could be attributed to a NO3--exchanged

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LDH phase, associated with intercalated NO3- anions which remained in the material

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after loading it with HPO42- in the anion-exchange reaction. Based on these

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reflections, the interlayer spacing of the NO3- intercalated LDH phase was

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determined as 2.9 Å. The 003 reflection of the HPO42- intercalated LDH phase

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largely overlapped with that of NO3- intercalated phase. Also for the 006 reflection,

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there was overlap, but the position of the HPO42- intercalated LDH phase could be

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placed at around a 2θ value of 20.0°, corresponding to an interlayer spacing of 4.0 Å.

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In the incubated LDH samples, however, the presence of the 003 reflection of the

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HPO42- intercalated LDH phase was clearly less pronounced, in line with a significant

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P release.

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Release of P from powdered fertilizers: incubation experiment


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In soils incubated with the fertilizer powders, differences in soil P availability between

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the three fertilizer treatments were small compared to the differences between the

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granular treatments (Table 2). In the Kingaroy soil, the LDH powder significantly

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increased soluble P compared to the other fertilizers.

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Fertilizer use efficiency: pot trial

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Plant yield and P uptake clearly responded to P addition in a dose related matter in

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both soils (Figure S4). With increasing granular MAP dose, the shoot P

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concentrations increased from deficient values (1020 mg P kg-1 for Kingaroy; 1010

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mg P kg-1 for Black Point) to adequate values, reaching concentrations up to 1730

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mg/kg in the Kingaroy soil and up to 3690 mg/kg in the Black Point soil. Also the dry

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matter increased significantly, proving that both soils were P deficient.40

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In the Kingaroy soil, clear visual symptoms of P deficiency could be observed in the

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leaves for most treatments. This was not the case for the granular MAP treatment,

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which performed by far the best in terms of P uptake and dry matter yield (DMY)

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(Figure 5 left). The total P uptake and the uptake of Pdff from both granulated LDH

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and struvite fertilizers were much lower. In the Kingaroy soil mixed with the powder

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fertilizers, there was little difference between the three fertilizer treatments and the

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uptake was much less than for the granular MAP. The LDH powder treatment

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yielded a significantly higher P uptake compared to the other powder fertilizer

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treatments.

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In the Black Point soil, the P uptake and the DMY in the different treatments were

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much higher compared to corresponding treatments in the Kingaroy soil (Figure 5,

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right). Again, the highest yield, P uptake and Pdff values were obtained for the

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granulated MAP fertilizer, while the granular treatments of the slow-release fertilizers



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showed much lower yield and P availability. For the MAP fertilizer, the uptake in the

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powdered treatment was slightly lower than in the granular treatment. For the struvite

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and LDH fertilizers, the uptake and Pdff in the powdered treatments was much

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higher than in the corresponding granular treatments. As in the Kingaroy soil, there

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was little difference between the fertilizer treatments for the powders.

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Discussion

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Release of P from granulated fertilizers: incubation experiment

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The Freundlich isotherms show that the P sorption in these soils ranks Kingaroy >

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Streaky Bay >> Monarto (Table 1), explaining the faster diffusion of P in the Monarto

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soil (Figure 2). The decrease over time of the diameter of the diffusion zone for the

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MAP treatment, which is due to a decrease in color intensity of the visualized P

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diffusion zone, could be attributed to a decrease in solution concentrations due to the

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ongoing diffusion and fixation reactions.35 This decrease in diameter of the high P

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zone was not observed for LDH and struvite granules (Figure 2), which could be

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attributed to the slow and sustained P release from these granules. This difference in

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release kinetics among the fertilizers was most pronounced in the most strongly

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sorbing Kingaroy soil. The counteracting effects of release and fixation resulted in

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only small and inconsistent differences in the diffusion diameters between the

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granular fertilizer treatments after 100 days (Figure 2), despite the clearly different

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release behavior of MAP compared to the slow-release fertilizers.

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The E-values (also termed labile P) and total P analysis also showed that P from

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MAP was able to diffuse further from the application point during the course of the

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experiment (Figure 3), in agreement with the visualization results. This was a result 14 ACS Paragon Plus Environment

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of the high MAP solubility and fast initial P release. Despite the high solubility of

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MAP, most P was transformed to non-labile P by the end of the experiment in the

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Streaky Bay and Monarto soils, pointing to fixation reactions, e.g. precipitation of Ca

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phosphates.

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The diffusion of P from struvite granules was much less than for the MAP granules,

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as evident from the visualization results (Figure 2) and the much lower recovery of

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fertilizer P in the outer soil section (Figure 3), suggesting that the struvite did not fully

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dissolve during the incubation experiment. However, high amounts of labile P were

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found in the inner soil section for the struvite treatments. This suggests that the

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undissolved residues of the struvite granules, which were included in the analysis of

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the inner section, dissolved during the E value determination. Under in situ

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conditions, dissolution is likely limited due to the granular fertilizer form, but the

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grinding step after incubation, as well as the high liquid:solid ratio and full mixing in

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solution under the conditions of the E value measurement would have promoted

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struvite dissolution.35 This also explains the high P concentrations in the CaCl2

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extract from the inner circle soil samples in the Kingaroy and the Monarto soil (Table

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2). The significant pH increase observed in the < 8 mm area around the application

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point of the struvite granules can be explained by the consumption of protons during

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struvite dissolution.13

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A complete P desorption from the LDH granules was not expected since a complete

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ion-exchange based desorption from P-exchanged powder LDH material is not even

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achieved in NaHCO3, NaOH or NaCl solutions.28,41 This is explained either by the

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relative comparable dimensions of HPO42-, HCO3-, and Cl- anions, which could limit

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the diffusion of HPO42- in the interlayer gallery and prevent desorption,42 or by

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complexation/precipitation of HPO42- anions with LDH derived Mg2+ or Al3+.43 15 ACS Paragon Plus Environment


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However, while 50% of P was desorbed within 1600 h in a mixed 2 mM HCO3-

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solution28, only 10-26% of P was released from the granule into the soil at the end of

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the 100-d incubation experiment. The difference in P release between this granule

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incubation experiment and previous desorption tests in solution can be attributed to

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interparticular diffusion limitations and non-mixing conditions. With XRD, the identity

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of a mixed HPO42- and NO3- intercalated LDH phase in the as-synthesized P-

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exchanged LDH fertilizer was confirmed. Comparable values for the measured

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interlayer spacings have been observed in previous research.19,28 The comparison of

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the patterns from an original LDH granule and the LDH granules retrieved from the

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soil demonstrated the release of intercalated HPO42-, and proved P release by anion-

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exchange during incubation of the LDH granule. In the acid Kingaroy soil, the P

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release by anion-exchange may have been accompanied by P release due to

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material dissolution. The large increase in pH in the inner circle soil samples

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surrounding the LDH granule supports this hypothesis (Table 2). In the Monarto soil,

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LDH dissolution may have occurred as well, while it was likely absent in the Streaky

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Bay soil due to the higher stability of LDH material in alkaline conditions.44 This may

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explain the very limited effect of the LDH granule on the soil pH for the inner circle,

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although this may also be related to a high pH buffering capacity of the Streaky Bay

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soil.

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Release of P from powdered fertilizers: incubation experiment

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The differences in soil P availability among the three fertilizers were rather small

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compared to the differences observed between the granular treatments, which could

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be attributed to the higher interaction area between soil and material facilitating

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dissolution and ion-exchange processes. The higher P availability for the LDH

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powder in the Kingaroy soil in comparison with the other fertilizers may be primarily 16 ACS Paragon Plus Environment

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related to the liming effect of this material (Table 2). In this acid soil, the LDH powder

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partially dissolved thereby releasing structural metal cations and OH- anions.28 This

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higher pH might have resulted in less adsorption of P by oxides, and hence higher

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solution concentrations. Due to a better LDH stability in neutral/alkaline conditions,

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and possibly due to a higher soil pH buffer capacity, this pH increase was less

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pronounced in the Monarto and Streaky Bay soils.

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Fertilizer use efficiency: pot trial

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In the pot trial, the dry matter yield, total P uptake and P uptake from the fertilizer

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(Pdff) all showed the same trends across treatments and were highly correlated with

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each other, since the treatment effects on yield and uptake were due to the addition

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of fertilizer P. In the Kingaroy soil, the treatment with granular MAP showed much

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higher uptake and yield than any other treatment (Figure 5). The P uptake from both

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granulated LDH and struvite fertilizers was much lower, indicating that granular slow

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P release led to lower, not higher, agronomic effectiveness than with readily soluble

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forms in the strongly P fixing acid Kingaroy soil. The superior agronomic

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effectiveness of MAP in comparison with other granules is likely related to the

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creation of local ‘hot spots’ with high soluble P concentrations: the soil around the

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granules was saturated with P due to the fast P release from the MAP granule. This

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resulted in a spot with relatively high soluble P concentrations from which plant roots

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can readily tap P, the well-known “banding effect”.45 The situation was different for

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the slow-release granules. The P content in the SRF granules was lower, and the P

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release from LDH and struvite granules was much slower (as observed in the

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visualization study). As a result, the released P was bound more strongly to P

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sorption sites in the soil. Moreover, a substantial amount of P was not released from

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the LDH granules by the end of the 100-d incubation experiment (Figure 3), and 17 ACS Paragon Plus Environment


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would likely not have been released during the pot trial either. The low uptake of

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fertilizer P from the granular struvite treatment supports our interpretation that the

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larger labile P near granulated struvite in the incubation experiment was an artefact

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caused by the high liquid:solid ratio during the E value measurement, causing

414

dissolution of struvite, whereas the dissolution in situ likely proceeded much more

415

slowly.

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The higher soil:fertilizer contact for the powdered forms promotes P dissolution for

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the SRFs through better pH buffering and a greater surface area of soil to sorb

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dissolution products, resulting in little difference with the soluble fertilizer. However,

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this high contact with the soil results in a strong fixation of released P, as indicated

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by the low P uptake by the plants for all powder treatments compared to the granular

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MAP (Figure 5). The slight advantage of LDH powder compared to the other powder

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fertilizers was likely related to the liming effect, thereby increasing soluble P as

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observed in the incubation experiment (Table 2) and indirectly increasing plant

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growth due to overcoming effects of soil acidity. This result was in line with previous

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findings, where an advantage of a powder LDH fertilizer in comparison with

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dissolved KH2PO4 or powdered TSP was observed in acid soils.28,29

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The very large difference between granular and powdered MAP in the Kingaroy soil

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is remarkable. While the benefit of banding P close to the seed, particularly in

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Oxisols, has been generally well recognized (e.g. by Stanford and Nelson45), there

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are only a few studies that compared powdered to granular sources. Most studies on

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the effect of fertilizer placement compared banded granules with broadcast granules.

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However, the difference between granules and ground fertilizer is likely to be much

433

more pronounced, particularly in soils rich in oxides and with a low P status.

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Wiseman et al. described similar effects of granular vs powdered treatments in 18 ACS Paragon Plus Environment

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Oxisols as the ones observed here.46 The plant response was greater for granular

436

than for powdered SSP, particularly in the soil with the highest sorption capacity,

437

while there was no effect of granulation for a sparingly soluble source (rock

438

phosphate). Unfortunately, it is often overlooked that granulation can have large

439

effects on the effectiveness of fertilizer, and many laboratory trials are performed

440

using ground fertilizers, even though commercial fertilizers are rarely in a powdered

441

form.13

442

In the Black Point soil, P uptake and yield in the different treatments were much

443

higher compared to corresponding treatments in the Kingaroy soil (Figure 5, right),

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as P-fixation generally is stronger in acid oxide-rich soils compared to calcareous

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soils.47 For the struvite and LDH fertilizers, P uptake in the powdered treatments was

446

much higher than for the granular treatments, which is most likely due to the slow

447

dissolution of the granules, particularly in alkaline conditions,44,48 as also indicated by

448

the visualization results. For the MAP treatments, there was less difference between

449

the granule and the powder, and in contrast with the SRFs the P uptake was higher

450

for the granule than for the powder treatment, likely due to the better placement of

451

the granule (close to the seed). In calcareous soils, banding may sometimes have a

452

negative effect, due to higher P concentrations around the granules resulting in

453

enhanced formation of poorly soluble calcium-phosphates,7 but no such negative

454

effect was observed here, which may be related to the fact that this soil had no

455

detectable free calcite (Table 1). As in the Kingaroy soil, there was little difference

456

between the fertilizer treatments for the powders, indicating that even in the alkaline

457

soil, the dissolution or P-exchange proceeded quickly when the ground fertilizer was

458

mixed through soil, as also confirmed by the chemical analysis.



459

In summary, this study did not find a higher agronomic effectiveness for granulated

460

LDH and struvite as SRFs than for a common soluble P fertilizer (MAP) in two soils

461

that strongly sorbed soluble P. In both soils, the granular SRFs performed much

462

worse than granular MAP, due to slow dissolution or P release from the SRF

463

granules. When added as a powder, there were only small differences between the

464

fertilizers: in the Oxisol, the LDH performed slightly better than struvite and MAP,

465

probably due to a liming effect, while in the alkaline soil, LDH and struvite performed

466

slightly worse than MAP. However, all powdered treatments performed worse than

467

granular MAP, particularly in the Oxisol. This study highlights the importance of

468

taking into account the physical form of the fertilizer when assessing the value of

469

SRFs.

470

It is obvious that these pot trial data need confirmation with longer term field data

471

where the long-term effects may potentially render the residual values of the SRF

472

fertilizer higher than that of soluble fertilizers in multiple cropping years. In addition,

473

struvite and LDHs can be used to recycle P from waste streams and SRFs may also

474

have advantages over soluble fertilizers in minimizing P losses and associated

475

environmental concerns in high rainfall areas.


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477

Abbreviations Used

478

DMY

Dry matter yield

479

LDH

Layered double hydroxide

480

MAP

Mono-ammonium phosphate

481

SRF

Slow-release fertilizer

482

TSP

Triple superphosphate

483

XRD

X-ray diffraction

484

485

Acknowledgements

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We are grateful to the agency for Innovation by Science and Technology for granting

487

a PhD fellowship to the corresponding author. We also thank Colin Rivers, Ashleigh

488

Broadbent and Bogumila Tomczak for their technical assistance during the

489

experiments, and Peter Self for the XRD measurements.

490

491

Supporting Information Description

492

Additional details on the particle size distribution of the P-LDH powder, the

493

visualization technique and the pot trial are provided.

494 495



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lability of phosphorus from granular and fluid monoammonium phosphate differs in a

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calcareous soil. Soil Sci. Soc. Am. J. 2004, 68, 682–689.

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Figure captions Figure 1: Graphical presentation of the soil sampling from the Petri dish after 100 days of granule incubation. Figure 2: The diameter of the P diffusion zone as a function of time for the granular LDH, struvite and MAP fertilizer treatments, in the three different soils. The error bars present the standard error of the mean (n=3). Figure 3: Percentage of added P recovered in soil sampled at 8 mm from the fertilizer application point at 100 days after its application. The labile P was determined by isotope dilution and non-labile P as the difference between total and labile P. Due to detection limit limitations, this distinction could not be made for P that diffused to the outer circle in the Kingaroy soil. Only the LDH granules were retrieved from the soils, as the other granules disintegrated and are therefore analyzed together with the soil. Error bars present the standard error of the mean (n=3). Figure 4: The XRD patterns of as synthesized LDH granule and of the granules that were recovered from the soil at the end of the 100-days incubation. The patterns are presented as if measured with Cu Kα1 radiation. Figure 5: The dry matter yield (top), the P concentration in the shoot (middle) and the P uptake by the plants (bottom) as affected by the fertilizer type and application form (powder -pwd- or granule -gran) in the acid Kingaroy (left) and alkaline Black Point (right) soil. The unamended control soil is denoted as ctr. The total P uptake for a specific treatment is equal to the sum of the contributions of P derived from the fertilizer (Pdff), P derived from the soil (Pdfsoil) and P derived from the seed (Pdfseed), as determined by isotope dilution (see methods). Error bars on the total P uptake present the standard error of the mean (n=4). Different letters indicate 27 ACS Paragon Plus Environment


statistical (P ≤ 0.05) differences between powder or control treatments (capital letters) or between granular or control treatments (lowercase). Significant differences between the powdered and granulated application for each fertilizer are indicated by asterisks above the pair of bars (* P ≤ 0.05; ** P ≤ 0.01; *** P ≤ 0.001; ns: not significant). Where needed, the data were log-transformed prior to analysis to homogenize variance.


Page 28 of 36

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Tables Table 1: Selected properties of soils. Location

pH (CaCl2)

Organic C

CEC

Clay

CaCO3

%

cmolc kg

%

%

mg kg

16

41

na

2560

-1

Feox

Alox -1

Total P -1

-1

E value a

kb

nb

250

0.50

-1

mg kg

mg kg

mg kg

2350

310

50

Kingaroy

5.1

1.8

Monarto

6.2

1.0

8

8

8mm

Solution P (mg L-1)

< 8 mm

b

> 8mm

0.016

b

0.009 a

6.6 a

0.019 a

5.9

Struvite

6.0 a

5.3 a

1.209 a

0.007 a

5.4 b

0.011 b

MAP

5.3 b

5.1 a

0.297 b

0.007 a

5.3 b

0.010 b

**

ns

*

ns

***

***

a

5.1

a

pH

LDH

Fert Monarto

< 8 mm

Powder -1

LDH

6.6

a

6.1

a

0.400

Struvite

6.5

a

6.1

a

12.906

MAP

6.0

b

6.0

a

0.985

Ferta

*

ns a

b

a

*** a

7.0

a

0.635

a

0.067

b

6.3

b

0.698

a

0.172

a

6.1

c

0.571

a

** a

0.091

*** a

7.9

ns a

0.259 a

7.9

Struvite

8.0 a

7.8 ab

0.686 a

0.094 a

7.8 b

0.235 b

MAP

7.8 b

7.7 b

0.651 a

0.097 a

7.8 b

0.229 b

**

*

ns

ns

**

**

a

0.216

0.030

b

LDH

Fert

7.9

b

a

: Statistical significance of fertilizer treatment, defined as ns: not significant; * P ≤ 0.05; ** P ≤ 0.01; *** P ≤ 0.001. Different letters within the column indicate significant differences (P ≤ 0.05) between the different fertilizer treatments for each soil. b The residual LDH granule was removed from the soil sampled at 8 mm < 8 mm > 8 mm < 8 mm > 8 mm

granule labile labile / non-lab

0 < 8 mm > 8 mm < 8 mm > 8 mm < 8 mm > 8 mm LDH

Struvite

MAP

Figure 3

33

ACS Paragon Plus Environment

< 8 mm > 8 mm < 8 mm > 8 mm < 8 mm > 8 mm LDH

Struvite

MAP

110 113

018

015

009

006

Relative intensity

003


LDH Streaky Bay

LDH Monarto

LDH Kingaroy

As synthesized LDH

0

10

20

30

40

50

60

70

2θ (°)

Figure 4


Page 34 of 36

Page 35 of 36


Kingaroy 2.0

ns

Black Point 8

ns

***

***

***

***

a a

6 DMY (g/pot)

DMY (g/pot)

1.5

1.0

0.5

b

A

B

A

AB

B

2

b

AB

4

b

b

Cc

Cc

0.0

0 pwd gran pwd gran pwd gran LDH

struvite

MAP

**

ns

*

2.0

pwd gran pwd gran pwd gran ctr

LDH

struvite

MAP

ns

***

**

2.0

1.5

A

P in shoot (mg kg-1)

P in shoot (g kg-1)

a a B

ab

b

BC

Cb

1.0

0.5

0.0 struvite

MAP

ns

ns

***

2.5

P uptake (mg/pot)

P uptake (mg/pot)

Pdff b

B

Cc

0.0

LDH

struvite

MAP

***

***

***

ctr

struvite

MAP

a

8 6

A B

B

4 Pdff

Pdfsoil

2

Pdfseed

0

b

b Cc

pwd gran pwd gran pwd gran LDH

0.5

10

1.0

B

Ab

pwd gran pwd gran pwd gran

1.5

A

A

12

2.0

0.5

a A

1.0

ctr

a

b

b

A

0.0


1.5

ctr

Pdfseed pwd gran pwd gran pwd gran

ctr

Pdfsoil

LDH

Figure 5


struvite

MAP

ctr


Calcareous soil

Acid soil 2.0

ns

Page 36 of 36

8

ns

***

***

***

***

a a

6 DMY (g/pot)

DMY (g/pot)

1.5

1.0

0.5 A

b AB

4

2

b B

A

AB

B

b

b

Cc

Cc

0.0

0


struvite

MAP

pwd gran pwd gran pwd gran

ctr

LDH

Table of Contents Graphic


struvite

MAP

ctr

Agronomic Effectiveness of Granulated and Powdered P-Exchanged

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