Recycling of phosphorus from dredged lake sediment: Importance of iron-bound phosphates for plant growth

Figures & data

Table 1. Total P and Fe concentrations, molar Fe:P ratio, OM %, applied dosages and abbreviation of the tested P fertilization treatments. *P dosage in % of 30 kg P ha⁻¹ year⁻¹ (yearly maximum allowed P load according to the Danish Agricultural Agency)

Treatment	TP (mg g DW^−1)	TFe (mg g DW^−1)	OM (%)	Molar Fe:P	P dosage (%)*	Abbreviation	Material use kg ha^−1
TSP (granulate)	206.7 ± 2.1	1.38 ± 0.00	–	0.0037	50	TSP50	72.6
					100	TSP100	145.1
					150	TSP150	217.7
Fresh lake sediment (sludge)	3.5 ± 0.00	28.8 ± 0.3	41.5	4.5	100	Sed100	148479.8
					150	Sed150	222719.7
Sediment with Fe-P removed (slurry)	2.04 ± 0.02	26.9 ± 1.21	40.9	7.7	100	Sedno-FeP100	142961.3
					150	Sedno-FeP150	214494.0
Synthetic amorphous Fe-P (slurry)	30.2 ± 0.2	483.1 ± 5.8	–	8.9	100	FeP100	16451.5
					150	FeP150	24677.2
Vivianite (magnetically extracted from sewage sludge; slurry)	125.5 ± 14.1	262.8 ± 32.8	36.1	1.2	100	Viv100	1021.4
					150	Viv150	1532.2

Table 2. Parameters of the soil used for the plant growth and column diffusion experiment. Soil analyses were performed by a commercial laboratory (OK Laboratorium for Jordbrug, Viborg, Denmark, 2021) according to Sørensen and Bülow-Olsen (1994)

Soil parameters (no sand dilution)
TP (mg kg DW^−1)	440
TFe (mg kg DW^−1)	13931
Texture	70.4 % sand, 15.4 % silt, 14.2 % loam
pH (CaCl2)	6.8
Bicarbonate-extractable P (mg kg DW^−1)	18
Ammonium-acetate exchangeable K (mg kg DW^−1)	90
Ammonium-acetate exchangeable Mg (mg kg DW^−1)	51
Humus (%)	4.0
Total C (%)	1.36
Total N (%)	0.12

Figure 1. Growth stage evaluation after Zadoks’ decimal code (Zadoks et al., 1974). The number of fully unfolded leaves (A) and developed tillers (B) per plant was averaged per pot and plotted over time. Color intensity increases with leave and tiller number.

Figure 2. Dry biomass yield and P uptake by barley shoots (A, C) and roots (B, D) in response to the alternative P fertilizer treatments. Treatments with the same letter are not significantly different. The dosage levels 50, 100, and 150 correspond to 50, 100, and 150 % of the Danish maximum yearly P load of 30 kg ha⁻¹. Mean ± SE, n = 5.

Table 3. Final total P, Fe, Cu, Cd, and Zn content in the barley shoots (mg g DW⁻¹) and total C and N (weight %). For total K, Mg, Mn, and Ca content of barley shoots see supplementary material (SI Table E1). Mean ± SE, n = 5. Values with the same footnote letter are not significantly different (one-way ANOVA). Star signs: * p = 0.045, ** p = 0.036, (*) p = 0.017, *** p = 0.005, (***) p = 0.002 (Kruskal–Wallis test)

Treatment	TP (mg g DW^−1)	TFe (mg g DW^−1)	Cu (µg g DW^−1)	Cd (µg g DW^−1)	Zn (mg g DW^−1)	C (weight %)	N (weight %)
0-Control	1.7 ± 0.01^a	0.34 ± 0.08^a	7.4 ± 0.18^a	0.15 ± 0.01^a	0.05 ± 0.002^b	39.0 ± 0.33	4.5 ± 0.07^bcd
TSP50	1.6 ± 0.11 ^a	0.10 ± 0.004^ab	6.6 ± 0.36^ab	0.15 ± 0.01^a	0.03 ± 0.001^c	40.3 ± 0.16**	4.3 ± 0.08^cd
TSP100	1.5 ± 0.06 ^a	0.09 ± 0.01^b	5.5 ± 0.09^c	0.13 ± 0.02^a	0.02 ± 0.001^d	41.1 ± 0.10	4.7 ± 0.21^abc
TSP150	1.3 ± 0.11^a	0.08 ± 0.004^b	4.0 ± 0.23^d	0.13 ± 0.01^a	0.01 ± 0.001^d	41.3 ± 0.14	4.7 ± 0.06^abc
Sed100	1.4 ± 0.08^a	0.11 ± 0.01^ab	6.7 ± 0.17^ab	0.08 ± 0.01^a	0.05 ± 0.001^b	40.6 ± 0.09	5.2 ± 0.15^a
Sed150	1.3 ± 0.03^a	0.095 ± 0.01^ab	6.3 ± 0.20^bc	0.09 ± 0.003^a	0.05 ± 0.001^b	41.0 ± 0.13	4.0 ± 0.08^d
Sedno-FeP100	1.6 ± 0.03^a	0.12 ± 0.01^ab	7.1 ± 0.12^ab	0.16 ± 0.01^a	0.08 ± 0.001^a	40.4 ± 0.19	4.6 ± 0.08^abcd
Sedno-FeP150	1.5 ± 0.09^a	0.09 ± 0.002^ab	6.5 ± 0.03^abc	0.11 ± 0.02^a	0.07 ± 0.001^a	41.3 ± 0.22	4.3 ± 0.15^cd
FeP100	1.5 ± 0.06^a	0.11 ± 0.02^ab	6.4 ± 0.05^abc	0.07 ± 0.01^b	0.03 ± 0.001^c	41.9 ± 0.13^(***)	4.9 ± 0.22^abc
FeP150	1.5 ± 0.11^a	0.12 ± 0.006^ab	6.2 ± 0.25^bc	0.09 ± 0.01^a	0.03 ± 0.001^c	41.6 ± 0.11^(*)	5.3 ± 0.12^a
Viv100	1.5 ± 0.06^a	0.16 ± 0.004^ab	6.4 ± 0.22^abc	0.09 ± 0.01^a	0.04 ± 0.001^c	41.5 ± 0.08*	5.1 ± 0.08^ab
Viv150	1.4 ± 0.08^a	0.14 ± 0.03^ab	5.5 ± 0.21^c	0.09 ± 0.02^a	0.03 ± 0.002^c	42.0 ± 0.43***	4.4 ± 0.12^cd

Table 4. Soil EC, pH, OM %, water extractable P (WEP), and DGT SRP-flux in the soil with and without barley at 56 DAS (harvest day). Mean ± SE. Treatments with the same letter are not significantly different

	With barley (n = 5)			Without barley (n = 3)
Treatment	EC (dS m^−1)	pH (CaCl2)	SOM %	EC (dS m^−1)	pH (CaCl2)	SOM %	WEP (mg kg DW^−1)	DGT SRP-flux (mg m^−2 d^−1)
0-Control	0.46 ± 0.02	6.94 ± 0.05	2.61 ± 0.03^d	0.66 ± 0.04^a	6.40 ± 0.05	2.56 ± 0.02^b	7.4 ± 0.26^bc	0.85 ± 0.11^a
TSP50	0.37 ± 0.02	7.17 ± 0.02	2.61 ± 0.04^d
TSP100	0.37 ± 0.01	7.20 ± 0.04	2.62 ± 0.04^d	0.58 ± 0.03^ab	6.28 ± 0.02	2.75 ± 0.04^ab	9.1 ± 0.43^ab	0.81 ± 0.14^a
TSP150	0.38 ± 0.02	7.16 ± 0.03	2.54 ± 0.04^d
Sed100	0.45 ± 0.01	7.31 ± 0.05	2.93 ± 0.01^abc	0.66 ± 0.09^a(*^)	6.17 ± 0.23	2.99 ± 0.08^a	6.6 ± 0.37^c	0.94 ± 0.24^a
Sed150	0.43 ± 0.01	7.26 ± 0.01	3.05 ± 0.04^ab
Sedno-FeP100	0.63 ± 0.03	6.92 ± 0.03	2.98 ± 0.07^ab	0.59 ± 0.03^ab	6.16 ± 0.08	2.93 ± 0.08^a	7.7 ± 0.17^bc	1.34 ± 0.13^a
Sedno-FeP150	0.70 ± 0.01	6.64 ± 0.01	3.11 ± 0.05^ab
FeP100	0.36 ± 0.02	7.32 ± 0.04	2.67 ± 0.10^d	0.35 ± 0.03^c(*^)	6.40 ± 0.06	2.61 ± 0.09^b	11.1 ± 0.64^a	0.75 ± 0.07^a
FeP150	0.40 ± 0.02	7.30 ± 0.003	2.70 ± 0.03^cd
Viv100	0.33 ± 0.02	7.48 ± 0.01	2.59 ± 0.05^d	0.38 ± 0.02^bc	6.55 ± 0.02	2.70 ± 0.06^ab	9.3 ± 0.54^ab	0.93 ± 0.15^a
Viv150	0.34 ± 0.03	7.54 ± 0.02	2.79 ± 0.01^bcd

*Coefficient of variation (CV) > 15 %.

Figure 3. Phosphorus diffusion patterns from the tested substrates presented as soil WEP concentration as a function of distance from the substrate. Mean ± SE, n = 5.

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Data availability statement

The data that support the findings of this study are available from the corresponding author, S. Haasler, upon reasonable request.