Simulating soil carbon and nitrogen trends under an integrated system in the Brazilian Cerrado

Vogado, Renato Falconeres; Souza, Henrique Antunes de; Althoff, Tiago Diniz; Menezes, Rômulo Simões Cezar; Gualberto, Adriano Veniciús Santana; Cunha, João Rodrigues da; Leite, Luiz Fernando Carvalho

doi:10.4025/actasciagron.v46i1.62574

ABSTRACT.

Management systems that include trees tend to provide higher amounts of plant biomass to the soil, contributing to the increase in carbon (C) and nitrogen (N) stocks. This study simulated C and N stocks and their compartments in a crop-livestock-forest integration system in the edafoclimatic conditions of the Maranhão Cerrado using the Century 4.5 model. The evaluated areas were native Cerrado vegetation (NV) and crop-livestock-forest integration (CLFI). The calibration process gradually modified the model parameters to better fit the simulated and observed soil C and N stocks. The best fit between the data was obtained after changes in the main parameters (DEC3(2), DEC4, and DEC5) that controlled the rate of decomposition of soil organic matter. C and N stocks increased by 14% and 15%, respectively, over 14 years after replacing NV with CLFI. The slow compartment of C presented greater sensitivity to changes in management, with an increase of 47% compared with that of NV. The active compartment increased by 31% and the passive compartment remained constant for over 14 years. Future scenarios, where pasture was maintained between the eucalyptus trees and the scenario that allowed the soybean, corn, and Brachiaria rotation between the trees, were more effective, accumulating approximately 37 Mg C ha^-1. The continuous contribution of residues from the trees and pasture increased C and N stocks in the long-term in the slow fraction, where the total organic carbon increased from 32 to 36 Mg ha^-1 when NV was replaced with CLFI. The model predicted the C and N stocks with accuracies ranging from 1 to 11% of the observed values.

Keywords:
soil organic matter; Century 4.5 model; carbon stocks; nitrogen stock.

[1] * Author for correspondence. E-mail: renatoagro86@hotmail.com

Variables	Values
Sand (g g^-1)	0.451
Silt (g g^-1)	0.097
Clay (g g^-1)	0.452
Soil density (g cm^-3)	1.22
pH (CaCl₂)	4.57
Monthly precipitation⁽¹⁾	20.2, 17.1, 19.6, 11.7, 4.4, 0.5, 0.2, 0.3, 2.6, 8.3, 14.1, 17.3
Maximum monthly average T °C⁽²⁾	28.5, 26.3, 26.6, 32.5, 30, 31.9, 32.6, 34.1, 33.7, 31.7, 29.7, 30.2
Minimum monthly average T °C⁽²⁾	22, 19.7, 20.7, 22.3, 21.2, 20.5, 18.9, 20.2, 21.5, 21.1, 18.2, 19.8

Parameter	Description	Code	Value
SITE.100	Number of soil layers	nlayer	8
	Number of soil layers in the top-level	nlaypg	8
	Soil sand	sand	0.451
	Soil silt	silt	0.097
	Soil clay	clay	0.452
	Soil pH	pH	4.54
	Effect of annual precipitation on atmospheric N fixation	epnfa	0.00445
	Effect of annual precipitation on non-symbiotic soil N fixation	epnfs	0.01080
FIX.100	Maximum decomposition rate of soil organic matter with active turnover	dec3(2)	15
	Maximum decomposition rate of soil organic matter with slow turnover	dec4	0.009
	Maximum decomposition rate of soil organic matter with intermediate turnover	dec5	0.8
	Minimum C/N ratio for material entering active pool	varat1(2,1)	8
	Minimum C/N ratio for material entering slow pool	varat2(2,1)	15
TREE.100	C allocation fraction of new production for mature forest leaves	fcfrac(1,2)	0.02
	C allocation fraction of new production for mature forest fine roots	fcfrac(2,2)	0.09
	C allocation fraction of new production for mature forest fine branches	fcfrac(3,2)	0.06
	C allocation fraction of new production for mature forest coarse roots	fcfrac(5,2)	0.08
CROP.100	Potential aboveground monthly production for crops	prdx(1)	1.8 (soy); 1.7 (rice); 0.5 (pasture)
	Plant growth type: 1 - perennial plant (grass, dynamic carbon allocation); 2 - annual plant (crop, dynamic carbon allocation)	frtcindx	2.0 (soy); 2.0 (rice); 1 (pasture)
	Fraction of C allocated to roots at planting, with no water or nutrient stress.	frtc(1)	0.65 (soy); 0.45 (rice); 0 (pasture)
	Final fraction of C allocated to roots	frtc(2)	1 (rice); 0 (pasture)
	Time after planting (months with soil temperature greater than rtdtmp) at which the final value is reached	frtc(3)	3 (soy); 3 (rice)
	Maximum fraction of C allocated to roots under maximum nutrient stress	cfrtcn(1)	0 (soy); 0 (rice); 3 (pasture)
	Minimum fraction of C allocated to roots with no nutrient stress	cfrtcn(2)	0 (soy); 0 (rice)
	Maximum fraction of C allocated to roots under maximum water stress	cfrtcw(1)	0 (soy); 0 (rice); 0.4 (pasture)
	Minimum fraction of C allocated to roots with no water stress	cfrtcw(2)	0 (soy); 0 (rice); 1 (pasture)
	Harvest index maximum (fraction of aboveground live C in grain)	himax	0.45 (soy); 0.4 (rice); 0.5 (pasture)
	Symbiotic N fixation maximum for grass/crop	snfxmx(1)	0.05 (soy); 0.005 (rice)
	Number of soil layers used to determine water and mineral N, P, and S that are available for grass/crop growth	claypg	8 (soy); 8 (rice); 8 (pasture)
GRAZ.100	Fraction of live shoots removed by a grazing event	flgrem	0.15
	Fraction of standing dead removed by a grazing event	fdgrem	0.01

Management system	C Stock (Mg ha^-1)		Error C (%)	N Stock (Mg ha^-1)		Error N (%)	C/N Ratio		Error C/N (%)
Management system	Obs.¹	Sim.²		Obs.¹	Sim.²		Obs.	Sim.
NV	32.00	32.32	1.00	2.20	1.95	11.40	14.54	16.60	14.17
CLFI	36.38	37.43	2.90	2.53	2.42	4.35	14.38	15.47	7.58

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Simulating soil carbon and nitrogen trends under an integrated system in the Brazilian Cerrado

ABSTRACT.