Protection from wintertime rainfall reduces nutrient losses and greenhouse gas emissions during the decomposition of poultry and horse manure-based amendments

Figures & data

Table 1. Weather conditions during the experimental period, including cumulative rainfall computed for the 2015–2016 winter and 10-yr averages for both temperature and rainfall.

	August	September	October	November	December	January	February
Weather condition	Month 0	Month 1	Month 2	Month 3	Month 4	Month 5	Month 6
Temperature (°C)
2015–2016	18.4	14.2	12.6	6.0	5.5	5.7	7.3
Average	19.3	16.4	11.1	7.3	4.3	4.2	5.0
Precipitation (mm)
2015–2016	59	41	110	178	240	183	144
Average	31	59	120	180	151	164	95
Cumulative precipitation
2015–2016	59	100	210	388	628	811	955
Average	31	90	210	390	541	705	800

Note. Refer to Figure S1 for daily values.

Table 2. Statistical results for two-way ANOVAs and Tukey post hoc tests computed on total nutrient concentrations and ratios.

Variable	Month	Factor	P value		Broiler	Turkey	Horse
Nitrogen	0	Cover	0.709
		Amendment	<0.001	C & U	a	b	c
		Interaction	0.945
	3	Cover	0.681
		Amendment	<0.001	C & U	a	b	c
		Interaction	0.214
	6	Cover	0.001		C > U	C > U	C ≈ U
		Amendment	<0.001	C	f	g	h
				U	x	y	y
		Interaction	0.095
Phosphorus	0	Cover	0.74
		Amendment	<0.001	C & U	a	b	c
		Interaction	0.95
	3	Cover	0.008		C < U	C < U	C ≈ U
		Amendment	<0.001	C & U	a	a	b
		Interaction	0.032
	6	Cover	0.011		C ≈ U	C > U	C > U
		Amendment	<0.001	C	f	f	g
				U	x	y	z
		Interaction	0.024
Potassium	0	Cover	0.267
		Amendment	0.973
		Interaction	0.646
	3	Cover	<0.001		C ≈ U	C > U	C > U
		Amendment	0.015	C	f	f	f
				U	x	y	y
		Interaction	<0.001
	6	Cover	<0.001		C > U	C > U	C > U
		Amendment	0.143
		Interaction	0.992
C:N	0	Cover	0.160
		Amendment	<0.001	C & U	b	b	a
		Interaction	0.200
	6	Cover	<0.001		C ≈ U	C < U	C ≈ U
		Amendment	<0.001	C	g	g	f
				U	z	y	x
		Interaction	0.090
N:P	0	Cover	0.820
		Amendment	0.152
		Interaction	0.717
	6	Cover	0.005		C ≈ U	C ≈ U	C < U
		Amendment	<0.001	C	f	f	f
				U	y	y	x
		Interaction	<0.001

Note. Significant interactions (P<0.1) are highlighted in bold, and different letters refer to statistical differences among amendments in covered piles only (C; f, g, h), uncovered piles only (U; x, y, z), or both storage conditions (C & U; a, b, c). If the interaction term is significant (P < 0.1) but the relationship among amendments is identical in both covered and uncovered conditions, values are reported only once as “C & U.” Significant differences (P < 0.05) between covered (C) and uncovered (U) piles for a specific amendment at a specific time are indicated by > or <, whereas ≈ indicates that the effect of cover was not significant (P > 0.05).

Table 3. Variations in C:N and N:P ratios (mean ± standard deviation) at the beginning and end of the experiment.

Variable	Month	Cover	Broiler	Turkey	Horse
C:N	0	All	9 ± 0	12 ± 2	36 ± 4
	6	Covered	9 ± 1	14 ± 3	25 ± 3
		Uncovered	12 ± 2	22 ± 1	29 ± 2
N:P	0	All	3.9 ± 0.2	3.6 ± 0.5	3.5 ± 0.2
	6	Covered	3.4 ± 0.6	2.9 ± 0.2	4.3 ± 0.5
		Uncovered	2.4 ± 0.4	2.8 ± 0.3	8.5 ± 1.2

Note. Refer to Table 2 for details on statistical results for ANOVAs and post hoc Tukey tests.

Figure 1. Variations in amendment total nitrogen, phosphorus, and potassium concentrations (mean ± standard deviation), reported on a dry-matter basis. Refer to Table 2 for details on statistical results for ANOVAs and post hoc Tukey tests.

Table 4. Statistical results for two-way ANOVAs and Tukey post hoc tests computed on ammonium (NH₄⁺-N) and nitrate (NO₃⁻-N) concentrations.

Variable	Month	Factor	P value		Broiler	Turkey	Horse
NH4^+-N	0	Cover	0.139
		Amendment	<0.001	C & U	b	a	c
		Interaction	0.320
	1	Cover	0.001		C < U	C < U	C ≈ U
		Amendment	<0.001	C & U	a	a	b
		Interaction	0.051
	2	Cover	<0.001		C < U	C < U	C ≈ U
		Amendment	<0.001	C & U	a	a	b
		Interaction	<0.001
	3	Cover	0.479		C ≈ U	C > U	C ≈ U
		Amendment	<0.001	C	f	f	g
				U	x	y	z
		Interaction	0.002
	4	Cover	0.673		C < U	C > U	C ≈ U
		Amendment	<0.001	C & U	a	b	c
		Interaction	<0.001
	5	Cover	<0.001		C ≈ U	C > U	C ≈ U
		Amendment	<0.001	C	f	f	g
				U	x	y	z
		Interaction	0.007
	6	Cover	<0.001		C > U	C > U	C ≈ U
		Amendment	<0.001	C	f	f	g
				U	x	y	y
		Interaction	0.002
NO3^—N	0	Cover	0.555
		Amendment	0.021		b	b	a
		Interaction	0.925
	1	Cover	<0.001		C < U	C < U	C ≈ U
		Amendment	<0.001	C & U	b	b	a
		Interaction	0.010
	2	Cover	0.748
		Amendment	<0.001	C & U	b	b	a
		Interaction	0.059
	3	Cover	0.019		C ≈ U	C < U	C > U
		Amendment	<0.001	C	g	g	f
				U	z	x	y
		Interaction	<0.001
	4	Cover	0.015		C ≈ U	C ≈ U	C > U
		Amendment	0.006	C	g	g	f
		Interaction	0.043	U	x	x	x
	5	Cover	0.001		C > U	C < U	C > U
		Amendment	0.002	C	g	g	f
				U	y	x	y
		Interaction	<0.001
	6	Cover	0.079		C ≈ U	C < U	C > U
		Amendment	0.003	C	g	g	f
				U	y	x	y
		Interaction	<0.001

Note. Significant interactions (P<0.1) are highlighted in bold, and different letters refer to statistical differences among amendments in covered piles only (C; f, g, h), uncovered piles only (U; x, y, z), or both storage conditions (C & U; a, b, c). If the interaction term is significant (P < 0.1) but the relationship among amendments is identical in both covered and uncovered conditions, values are reported only once as “C & U.” Significant differences (P < 0.05) between covered (C) and uncovered (U) piles for a specific amendment at a specific time are indicated by > or <, whereas ≈ indicates that the effect of cover was not significant (P > 0.05).

Figure 2. Variations in amendment ammonium (NH₄⁺-N) and nitrate (NO₃⁻-N) concentrations (mean ± standard deviation), reported on a dry-matter basis. Refer to Table 4 for details on statistical results for ANOVAs and post hoc Tukey tests.

Figure 3. Variations in fluxes (mean ± standard deviation) of nitrous oxide (N₂O), carbon dioxide (CO₂), and methane (CH₄), expressed as daily fluxes (left) or cumulative fluxes after 6 months (right). For ANOVA terms: ***P < 0.001; **P < 0.01; *P < 0.05. Colored plus signs (+) indicate a statistically significant difference (P < 0.05) between covered and uncovered piles for that specific amendment. Letters indicate a statistically significant difference among amendments, regardless of rainfall exposure (i.e., interaction terms were not significant).

Figure 4. Cumulative fluxes (mean ± standard deviation) of nitrous oxide (N₂O), carbon dioxide (CO₂), and methane (CH₄) expressed as CO₂-equivalents after 1, 3, and 6 months in covered (Cov) and uncovered (Unc) conditions. For ANOVA terms: **P < 0.01; *P < 0.1. Colored plus signs (+) indicate a statistically significant difference (P < 0.05) between covered and uncovered piles for that specific amendment. Letters indicate a statistically significant difference among amendments at that specific time, where solid letters are used if there is no interaction (i.e., after 6 months) and white-centered letters are used when differences are found only in uncovered piles (i.e., after 3 months).