Sensitivity analysis of the AquaCrop parameters for rainfed corn in the South of Brazil

The objective of this work was to perform a sensitivity analysis of the main input parameters required for the AquaCrop water balance model, using biomass and grain yield data of a rainfed-simulated corn crop, obtained along the climate data series of 1987-2016 in the South of Brazil. The levels of soil-water stress and the depths of maximum effective rooting were the input parameters that most affected the biomass and grain yields simulated by the model, followed by the crop coefficient, water-use efficiency, soil water storage capacity, and contribution of groundwater to water availability in the root zone. The parameters crop cycle duration, plant density, pattern of soil-water extraction, and field surface practices showed little or no impact on the final results. AquaCrop is a robust water balance model, with small or moderate general sensitivity to variations of the main input parameter values, which makes it applicable to situations with field data limitations.

Index terms:
calibration; crop model; drought; simulation; soil-water balance; soil-water stress

Authorship

Luiz Carlos Pittol Martini

Universidade Federal de Santa Catarina, Departamento de Engenharia Rural, Rodovia Admar Gonzaga, no 1.346, CEP 88034-000 Florianópolis, SC, Brazil. E-mail: luiz.martini@ufsc.brUniversidade Federal de Santa CatarinaBrazilFlorianópolis, SC, BrazilUniversidade Federal de Santa Catarina, Departamento de Engenharia Rural, Rodovia Admar Gonzaga, no 1.346, CEP 88034-000 Florianópolis, SC, Brazil. E-mail: luiz.martini@ufsc.br

SCIMAGO INSTITUTIONS RANKINGS

Figures | Tables

Figures (1)
Tables (4)

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Figure 1.
Maize relative biomass depending on root deepening (A), and maize relative biomass depending on water holding capacity of the soil (B), obtained by AquaCrop simulations applied to the 1987-2016 climate data series, in Concórdia SC, Brazil.

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Table 1.
Reference parameterization in the AquaCrop 6.0 software for maize, and parameter ranges used for sensitivity analysis simulations.

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Table 2.
Plant parameter effects on maize mean relative biomass (%) and grain yield (Mg ha^-1 [in brackets]) obtained by AquaCrop simulations applied to the 1987-2016 time series, in Concórdia SC, Brazil. Equal lowercase (relative biomass) and uppercase (grain yield) letters indicate no significant differences by Kruskal-Wallys test (α<0.05).

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Table 3.
Number of years with total failure of maize yield, during the 1987-2016 climate data series, according to the AquaCrop sensitivity analysis performed for some plant, soil, and crop management parameters, in Concórdia, SC, Brazil.

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Table 4.
Soil and crop management effects on maize mean relative biomass (%) and grain yield (Mg ha^-1 [in brackets]) obtained by AquaCrop simulations, applied to the 1987-2016 time series, in Concórdia SC, Brazil. Equal lowercase (relative biomass) and uppercase (grain yield) letters indicate no significant differences by the Kruskal-Wallys test (α<0.05).

Figure 1. Maize relative biomass depending on root deepening (A), and maize relative biomass depending on water holding capacity of the soil (B), obtained by AquaCrop simulations applied to the 1987-2016 climate data series, in Concórdia SC, Brazil.

Table 1. Reference parameterization in the AquaCrop 6.0 software for maize, and parameter ranges used for sensitivity analysis simulations.

Parameter		AquaCrop reference	Parameter range
Plant parameter
	Soil water stress factors - Canopy expansion - Stomatal closure - Early canopy -senescence Aeration stress - Effect on the harvest index during flowering	-Sensitive to water stress -Tolerant to water stress -Moderately tolerant to water stress -Moderately tolerant to waterlogging -Sensitive to water stress	- Water stress response: All factors set in each of the soil water stress levels provided in the software. - Individual factor relative effect: Each individual factor set in to maximum sensitivity to water stress, and the other factors set in to moderately tolerant to water stress.
	Root deepening	- Very deep rooted crops -Maximum effective rooting depth of 2.30 m	- Maximum effective rooting depth of 0.60 m (shallow-medium rooted) - Rooting depth range from 20 to 60 cm in 5 cm increments
	Water extraction pattern in the effective root zone	- Upper ¼ : 40% - Second ¼ : 30% - Third ¼ : 20% - Bottom ¼ : 10%	- patterns from upper to bottom layers: - 40-30-20-10 (default); 35-28-20-10; 30-27-23-20; 25-25-25-25; 20-23-27-30
	Growing cycle (degree-day)	I. Emergence: 80 II. Max. canopy: 705 III. Flowering: 880 IV. Senescence: 1.400 V. Maturity: 1.700	- Degree-day length from I-V stages: - Normal: 78/630/970/1550/1860 Early: 72/555/890/1500/1800 Extra-early: 60/450/770/1160/1470 Ultra-early: 46/355/570/800/1110
	Crop coefficient	- Kc = 1.05	- Kc ranged from 0.80 to 1.25 in 0.05 increments
	Crop water productivity	- WP = 33.7 g m^-2	- WP ranged from 26 to 40 g m^-2.mm^-1 in 2 g m^-2.mm^-1 increments
Soil parameter
	Water holding capacity	- Total available water (TAW) featured by user	- TAW ranged from 70 to 150 mm m^-1 in 10 mm m^-1 increments
	Capillary raise	- Depth groundwater table below soil surface featured by user	- Depth groundwater ranged from 0.5 to 5.0 m in 0.5 m increments
Crop and field management
	Plant density	- 75,000 plants ha^-1	- Plant densities of 40, 50, 55, 62.5, 70 and 75,000 plants ha^-1
	Effects of field surface practices on runoff	- Changes in curve-number (CN) value featured by user	- no effects (CN=65); reduced 10, 20, and 30% (CN 58, 52, and 45); increased 10, 20, and 30% (CN 72, 78 and 85)
	Mulches	- Percent of soil cover by mulches featured by user	- Soil cover with mulches in 0, 25, 50, 75, and 100%

Table 2. Plant parameter effects on maize mean relative biomass (%) and grain yield (Mg ha^-1 [in brackets]) obtained by AquaCrop simulations applied to the 1987-2016 time series, in Concórdia SC, Brazil. Equal lowercase (relative biomass) and uppercase (grain yield) letters indicate no significant differences by Kruskal-Wallys test (α<0.05).

Parameters	Factors, types or ranges
Five plant-soil- water stress factors set to the same level	Extremely sensitive		Sensitive		Moderately sensitive		Moderately tolerant		Tolerant	Extremely tolerant
	30b [2.74B]		42b [3.84B]		56ab [5.21AB]		77a [7.61A]		80a [8.20A]	82a [8.24A]
Relative effect to each of the five plant-soil- water stress factors	Canopy expansion		Stomatal closure		Early canopy senescence		Aeration stress		Effect on Harvest Index during flowering
	51a [4.68A]		53a [5.58A]		30a [2.60A]		56a [5.21A]		56a [5.21A]
Root deepening	20 cm		25 cm	30 cm	35 cm	40 cm	45 cm	50 cm	55 cm	60 cm
	26c [2.03C]		37c [3.42C]	50bc [4.63BC]	68ab [6.83AB]	76ab [7.82AB]	78a [8.31A]	81a [8.79A]	84a [9.12A]	86a [9.36A]
Water extraction pattern in the effective root zone	40-30-20-10		35-28-22-15		30-27-23-20		25-25-25-25		20-23-27-30
	78a [8.31A]		79a [8.39A]		79a [8.41A]		79a [8.44A]		80a [8.49A]
Growing cycle	Normal		Early			Extra-early			Ultra-early
	77b [10.51A]		78b [10.61A]			83ab [9.49A]			89a [7.96B]
Crop coefficient	0.80	0.85	0.90	0.95	1.00	1.05	1.10	1.15	1.20	1.25
	88a [7.06B]	87ab [7.34AB]	85ab [7.58AB]	84ab [7.81AB]	82ab [8.01AB]	80ab [8.18AB]	78ab [8.31AB]	77ab [8.32A]	75ab [8.42A]	73b [8.54A]
Crop water productivity	26 g m^-2 mm		28 g m^-2 mm		30 g m^-2 mm	32 g m^-2 mm	34 g m^-2 mm	36 g m^-2 mm	38 g m^-2 mm	40 g m^-2 mm
	78a [7.21D]		78a [7.76CD]		78a [8.31BCD]	78a [8.85ABCD]	78a [9.40ABC]	78a [9.94AB]	78a [10.48A]	78a [11.02A]

Table 3. Number of years with total failure of maize yield, during the 1987-2016 climate data series, according to the AquaCrop sensitivity analysis performed for some plant, soil, and crop management parameters, in Concórdia, SC, Brazil.

Parameters	Factor or range
Five plant-soil -water stress factors set to the same level	Extremely sensitive		Sensitive		Moderately sensitive		Moderately tolerant		Tolerant	Extremely tolerant
	18/29		14/29		10/29		3/29		0/29	0/29
Relative effect to each of the five plant-soil-water stress factors	Canopy expansion		Stomatal closure		Early canopy senescence		Aeration stress		Effect on the harvest Index during flowering
	10/29		9/29		19/29		10/29		10/29
Root deepening	20 cm		25 cm	30 cm	35 cm	40 cm	45 cm	50 cm	55 cm	60 cm
	17/29		13/29	9/29	3/29	1/29	0/29	0/29	0/29	0/29
Crop coefficient	0.80	0.85	0.90	0.95	1.00	1.05	1.10	1.15	1.20	1.25
	0/29	0/29	0/29	0/29	0/29	0/29	0/29	1/29	1/29	1/29
Water holding capacity of the soil	70mm m^-1		80mm m^-1	90 mm m^-1	100mm m^-1	110mm m^-1	120mm m^-1	130mm m^-1	140mm m^-1	150mm m^-1
	5/29		4/29	3/29	1/29	0/29	0/29	0/29	0/29	0/29
Effect of field surface practices on runoff (CN: curve-number)	CN=45 Reduced 30%		CN=52 Reduced 20%		CN=58 Reduced 10%		CN=65 No effects	CN=72 Increased 10%	CN=78 Increased 20%	CN=85 Increased 30%
	0/29		0/29		0/29		0/29	0/29	1/29	1/29

Table 4. Soil and crop management effects on maize mean relative biomass (%) and grain yield (Mg ha^-1 [in brackets]) obtained by AquaCrop simulations, applied to the 1987-2016 time series, in Concórdia SC, Brazil. Equal lowercase (relative biomass) and uppercase (grain yield) letters indicate no significant differences by the Kruskal-Wallys test (α<0.05).

Parameter	Range
Water holding capacity of the soil	70 mm m^-1		80 mm m^-1	90 mm m^-1	100 mm m^-1	110 mm m^-1	120 mm m^-1	130 mm m^-1	140 mm m^-1	150 mm m^-1
	58b [5.32C]		64ab [6.15BC]	68ab [6.75BC]	75ab [7.67BC]	77ab [8.06BC]	78ab [8.31BC]	80a [8.62AB]	81a [8.78AB]	82a [8.93A]
Water table depth effect on capillary raise	0.5 m	1.0 m	1.5 m	2.0 m	2.5 m	3.0 m	3.5 m	4.0 m	4.5 m	5.0 m
	59c [6.37C]	100a [10.93A]	100a [10.94A]	100a [10.92A]	93b [10.36AB]	89b [9.91B]	89b [9.84B]	88b [9.78B]	78bc [8.31BC]	78bc [8.31BC]
Plant density	40.000 ha^-1		45.000 ha^-1		50.000 ha^-1		55.000 ha^-1	62.500 ha^-1	70.000 ha^-1	75.000 ha^-1
	78a [8.16A]		78a [8.18A]		78a [8.23A]		78a [8.26A]	78a [8.31A]	78a [8.31A]	78a [8.37A]
Effect of field surface practices on runoff (CN: curve-number)	CN=45 Reduced 30%		CN=52 Reduced 20%		CN=58 Reduced 10%		CN=65 No effects	CN=72 Increased 10%	CN=78 Increased 20%	CN=85 Increased 30%
	79a [8.41A]		79a [8.39A]		79a [8.36A]		78a [8.31AB]	77ab [8.18AB]	75ab [7.77AB]	64b [6.21B]
Mulches	None (0%)		Sparse (25%)		About half (50%)		Significant (75%)		Complete (100%)
	77a [8.15A]		78a [8.31A]		81a [8.69A]		82a [8.90A]		84a [9.07A]

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Sensitivity analysis of the AquaCrop parameters for rainfed corn in the South of Brazil

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