Value of Functionalized Charcoal for Increasing the Efficiency of Urea N Uptake: Insights into the Functionalization Process and the Physicochemical Characteristics of Charcoal

Paiva, Diogo Mendes de; Guimarães, Gelton Geraldo Fernandes; Teixeira, Breno Cardoso; Cantarutti, Reinaldo Bertola

doi:10.1590/18069657rbcs20180200

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Division – Soil in Space and Time, Commission – Pedometric • Rev. Bras. Ciênc. Solo 43 • 2019 • https://doi.org/10.1590/18069657rbcs20180200 copy

Value of Functionalized Charcoal for Increasing the Efficiency of Urea N Uptake: Insights into the Functionalization Process and the Physicochemical Characteristics of Charcoal

Authorship SCIMAGO INSTITUTIONS RANKINGS

ABSTRACT

Functionalized charcoal (CHox) incorporated into urea is known for its ability to reduce NH₃ volatilization and increase agronomic efficiency. However, it is important to optimize the functionalization process and to elucidate its relationship with the physicochemical properties of CHox for N supply. Thus, charcoal obtained from eucalyptus wood was functionalized with different HNO₃ concentrations and reaction times. Ammonia adsorption by CHox was evaluated in chambers with high NH₃ concentrations. Dry matter yield, N uptake, and apparent N recovery efficiency of corn plants were evaluated after the application of the urea-CHox mixture to soil in a greenhouse experiment. The properties of CHox, such as pH, isoelectric point, and total acidity (carboxylic and phenolics groups) depended on the HNO₃ concentration but were not influenced by the reaction time. The NH₃ adsorption by the functionalized charcoal showed a positive correlation with the quantity of carboxylic and phenolic groups and a negative correlation with the pH value and the isoelectric point. The small differences observed in dry matter yield, N accumulation, and apparent N recovery efficiency among the corn plants from urea mixed with CHox or humic acids derived from charcoal (AH_CH) are not sufficient to determine the higher efficiency of these sources.

biochar; NH₃ adsorption; NH₃ volatilization; efficient fertilization

CHox	HNO₃	Time	C	H	N	O	C/N⁽¹⁾
	mol L^-1	h	------ % ------
1	1.7	1.5	61.87	3.13	2.60	32.40	27.75
2	1.7	6.5	59.79	3.00	2.75	34.46	25.35
3	7.3	1.5	55.81	3.01	3.23	37.95	20.15
4	7.3	6.5	55.90	3.05	3.18	37.87	20.50
5	0.5	4.0	65.88	3.15	2.84	28.13	27.05
6	8.5	4.0	54.70	2.96	3.39	38.95	18.82
7	4.5	0.5	58.60	3.08	3.69	34.63	18.52
8	4.5	7.5	56.17	3.03	3.28	37.52	19.97
9	4.5	4.0	56.39	3.01	3.79	36.81	17.35
Average			58.35	3.05	3.19	35.41	21.72
Confidence level (95 %)			±1.76	±0.03	±0.20	±1.67	±1.90
AH_CH	4.5	4.0	52.80	3.19	2.91	41.62	21.16
CH			78.42	3.71	0.05	17.82	1,829.04

CHox	HNO₃	Time	pH(H₂O)⁽¹⁾	PI⁽²⁾	Carboxylic⁽³⁾	Phenolic⁽³⁾	Total⁽⁴⁾
	mol L^-1	h			------ mmol_c kg^-1 ------
1	1.7	1.5	2.97	1.68	1,671	1,157	2,828
2	1.7	6.5	2.91	1.66	2,216	1,266	3,482
3	7.3	1.5	2.81	1.57	2,970	1,516	4,486
4	7.3	6.5	2.73	1.59	3,381	1,148	4,529
5	0.5	4.0	3.25	2.08	1,263	884	2,147
6	8.5	4.0	2.84	1.62	3,616	1,269	4,885
7	4.5	0.5	2.88	1.67	2,081	1,387	3,468
8	4.5	7.5	2.82	1.62	3,435	1,400	4,835
9	4.5	4.0	2.79	1.64	3,134	1,407	4,541
Average			2.89	1.68	2,641	1,271	3,911
Confidence level (95 %)			±0.12	±0.10	±586	±131	±671
AH_CH			3.56	1.64	3,214	1,008	4,222
CH			5.86	6.06	251	126	377

pH and content of functional groups	Regression equation	R²
pH(H₂O)	ŷ = 3.29 - 0.158*H - 0.011 t + 0.013*H²	0.88
Carboxylic	ŷ = 1531.4 + 257.4***H	0.70
Phenolics	ŷ = 901.3 + 212.4H - 12.2 t - 19.7H²	0.74
Carboxylic + Phenolics	ŷ = 2658.2 + 292.4***H	0.68

CHox	HNO₃	Time	Aromatic or aliphatic C	Carboxylic groups	Phenolic or ether groups	O bound to aromatic C	C=O	N pyrrol pyridine or amines	NO₂ groups/oxidized nitrogen functions
	mol L^-1	h	------ % ------
1	1.7	1.5	76	9	15	55	43	65	35
2	1.7	6.5	54	10	24	39	49	59	41
3	7.3	1.5	68	13	16	49	51	49	51
4	7.3	6.5	66	10	13	48	49	51	49
5	0.5	4.0	68	10	19	37	60	69	31
6	8.5	4.0	70	14	13	48	43	51	49
7	4.5	0.5	73	10	17	48	52	79	21
8	4.5	7.5	63	13	24	50	50	59	41
9	4.5	4.0	71	13	16	50	50	68	32
Average			71.5	16.5	12.0	69.5	30.5	71.5	28.5
Confidence level (95 %)			±0.9	±0.9	±1.9	±38.2	±35.7	±6.8	±5.9
AH_CH			69	15	16	49	51	52	38
CH			80	5	15	74	26	-	-

CHox	HNO₃	Time	N-NH₃ adsorbed
	mol L^-1	h	mg g^-1
1	1.7	1.5	18.50
2	1.7	6.5	19.70
3	7.3	1.5	35.23
4	7.3	6.5	41.87
5	0.5	4.0	5.53
6	8.5	4.0	53.53
7	4.5	0.5	43.23
8	4.5	7.5	55.87
9	4.5	4.0	48.57
AH_CH			36.80
CH			6.17
Average			33.18
Confidence level (95 %)			6.18
Average contrast
C1 = - CH vs (CHox1+CHox2+ ... +CHox9)			26.65*
C2 = - CH vs AH_CH			3.06*
C3 = - CHox vs AH_CH			-0.89^ns
C4 = - CHox5 vs (CHox1+CHox2+ ... +CHox9)			27.69*

Physical-chemical properties	Coefficient
Carboxylic groups	0.88***
Phenolics groups	0.68**
pH	- 0.80***
PI	- 0.70**

Fertilizer	N dose

	90 % of maximum DM yield	80 % of maximum N absorbed
	---- mg dm^-3 ----
NH₄NO₃	122.85	201.93
Urea	165.10	262.77
U-CHox6⁽¹⁾	121.30	280.64
U-CHox9⁽¹⁾	109.40	231.42
U-AH_CH	131.00	242.21

Fertilizer	N dose

	90 mg dm^-3	180 mg dm^-3	270 mg dm^-3	90 mg dm^-3	180 mg dm^-3	270 mg dm^-3

	Dry matter yield			N uptake
	g pot^-1			mg pot^-1
NH₄NO₃	42.34 a	45.20 ab	47.81 a	311.55 a	486.84 a	629.61 b
Urea	39.22 a	41.38 a	50.34 a	273.30 a	400.99 a	517.96 ab
U-CHox6⁽¹⁾	41.30 a	45.72 ab	42.94 a	295.82 a	393.89 a	401.05 a
U-CHox9⁽¹⁾	40.62 a	49.71 b	45.70 a	300.28 a	497.55 a	531.51 ab
U-AH_CH	36.57 a	49.56 b	47.70 a	234.86 a	448.85 a	546.14 ab

Fertilizer	N dose

	90 mg dm^-3	180 mg dm^-3	270 mg dm^-3

	Apparent N recovery
	---- % ----
NH₄NO₃	84.30 A b	81.10 A a	75.22 A a
Urea	67.30 A ab	62.03 A a	58.68 A a
U-CHox6¹	77.31 A ab	60.45 A a	53.21 A a
U-CHox9¹	79.29 A ab	83.48 A a	60.69 A a
U-AH_CH	50.21 A a	72.66 A a	62.85 A a

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[1] * Corresponding author: E-mail: paivadmendes@gmail.com