25th European Biomass Conference and Exhibition, 12-15 June 2017, Stockholm, Sweden
ASSESSING THE EFFECTS OF DIFFERENT AMOUNTS OF SUGARCANE STRAW ON TEMPORAL VARIABILITY OF SOIL MOISTURE CONTENT AND TEMPERATURE S. T. R. Corrêa – CTBE/CNPEM, Brazilian Bioethanol Science and Technology Laboratory, P.O. Box 6170, CEP 13083970, Campinas-SP, Brazil. Phone: + 55 (19) 3518-3130,
[email protected] J. L. N. Carvalho – CTBE/CNPEM, Brazilian Bioethanol Science and Technology Laboratory,
[email protected] T. A. D. Hernandes – CTBE/CNPEM, Brazilian Bioethanol Science and Technology Laboratory,
[email protected] L. C. Barbosa – CTBE/CNPEM, Brazilian Bioethanol Science and Technology Laboratory,
[email protected] L. M. S. Menandro – CTBE/CNPEM, Brazilian Bioethanol Science and Technology Laboratory,
[email protected] M. R. L.V. Leal – CTBE/CNPEM, Brazilian Bioethanol Science and Technology Laboratory,
[email protected]
ABSTRACT: Since the Brazilian Sugarcane Mills have adopted the practice of mechanized harvesting, the large amounts of straw mulching on the soil surface have become an important issue to be investigated. This residue represents a valuable feedstock for 2nd generation ethanol production and bioelectricity cogeneration while could be left in the field for agronomic purposes. In the present study, we assess the temporal variability of moisture content, soil temperature and sugarcane yield in response to different amounts of straw mulching (SM), along two seasons (2014/2015 and 2015/2016) in three important locations of sugarcane expansion areas in Brazil. The treatments were bare soil, 50% and 100% straw mulch(SM) and dielectric sensors MPS-2 measured soil water potential and temperature every 6 hours at a depth of 0.20 m.SM suppressed soil temperature during the initial crop development (regrowth); water storage was improved by SM and enhanced the soil moisture maintenance, which in dry periods (early harvest) is essential to the crop establishment; sugarcane yield increased in response to 100 SM in clayey soils, with amounts above 14.9 Mg ha-1of SM; no increase in sugarcane yield was observed in sandy soil with amounts below 9.2 Mg ha 1of SM. Keywords: agricultural residues, biomass, sugar crops, straw mulching, soil management
1
INTRODUCTION
In terms of environmental issues, straw mulching is essential to sugarcane crop development since it affects the radiation balance due to modifications in thermal conductivities and reflection coefficient interfering with all energy balance components [7]. Thus, straw mulching results in higher fraction of the incident sunlight that the surface reflects and lower thermal conductivity than the bare soil, which reduces the solar radiation reaching the soil and, therefore, the increasing soil temperature [8, 9]. Soil temperature is one of the most important factors that influence soil properties processes involved in plant growth. It controls the rate of evaporation and aeration [10,11], the soil physical, chemical and biological processes [12], the rate of organic matter decomposition and the mineralization of different organic materials [13], as well as the soil nutrient availability and recycling [14]. Soil moisture content is one of the most sensitive parameters to crops residues maintenance, thus, one of the most important factors affecting plant growth and development [15]. Crop residues improves soil water storage by increasing infiltration rate and decreasing runoff losses, reducing evaporation and abrupt fluctuations in soil surface temperature as well as increasing soil organic matter, which increases the soil water retention capacity [8,16]. In the climatic conditions of the south-central region of Brazil, characterized by rainy summers and dry winters, the straw mulching is an important practice for conserving soil moisture and, consequently, result in better water conservation and increased water-use efficiency [6]. The effects of straw mulching on sugarcane productivity are very complex once it can increase, decrease, or have no net effect on sugarcane yields and factors such as annual weather and soil conditions, crop variety and harvest period are more important to determine yield [4]. Despite the effects of crops residues maintenance
Brazil is the largest global producer of sugarcane and has one of the cleanest and diversified energy matrix in the world, with renewable energy which grew from 39.4% in 2014 to 41.24% in 2015 [1]. Ethanol and bioelectricity (from sugarcane bagasse) comprised the largest share of renewable sources of energy, reaching 16.9%, followed by energy produced by hydroelectric power (11.3%), wood and charcoal (8.2%), biodiesel and others (4.7%) [1]. Since 2008, ethanol consumption has surpassed gasoline representing over 50% by volume of the liquid fuel used by light commercial vehicles in Brazil [2] while bagasse, i.e., the principal sugarcane residue for bioenergy production, is practically all consumed in the mill boilers to provide all the mill energy demand. On the other hand, the sugarcane straw (also called trash), which represents about one third of the total primary energy of sugarcane in the field, has shown an incipient usage [3]. Due to environmental and economic reasons, the Brazilian sugarcane areas have recently adopted the practice of mechanized harvesting (green cane management without previous burning). Federal Law No. 2661 of July 8, 1998 and São Paulo State Law No. 11241 of September 19, 2002 have established a time schedule to cane burning phase out [4], resulting in a deposition of large amounts of sugarcane straw on the fields, creating a mulching on the soil surface. Thus, while sugarcane straw represents a valuable feedstock for 2nd generation ethanol production and bioelectricity cogeneration, enabling new opportunities for the Brazilian sugarcane industry, this residue could be left on the field for agronomic purposes, such as weed control, protection against soil erosion, increasing soil biodiversity, favoring water infiltration, soil moisture content and temperature maintenance [5, 6].
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25th European Biomass Conference and Exhibition, 12-15 June 2017, Stockholm, Sweden
on soil temperature [17,18,19,20,21] and on soil moisture [22,23,24] have been widely documented, there are only few researches for sugarcane in Brazil [7, 9, 25,26]. Hence, there is an increasing need for understanding the response of sugarcane straw mulching on soil moisture content and temperature dynamic. In the present study we aimed to analyze the temporal variability of soil water content and water storage, the variation in soil temperature and sugarcane yield in response to different amounts of straw mulching, along two crop seasons in three important locations of sugarcane expansion areas in Brazil.
Table I: Experiments description Description
Locations
São Paulo
Chapadão do Céu Goiás
Soil texture
sand
clay
clay
Limestone1
2
2
2
1
1
1
June 2014
June 2014
June 2014
Location
Quatá
State
Gypsum
1
Plant cane harvest
2
Straw mulching
METHODOLOGY
1, 4
2,3
Fertilizing
2.1 Study locations and field experimental design The experiments were conducted in representative sugarcane growing locationS and were chosen to provide different edaphoclimatic conditions. (Figure 1).
1st ratoon harvest Straw mulching
1, 4
2,3
Fertilizing
2nd ratoon harvest
Quirinópolis Goiás
9.2
14.9
16.5
120 N 120 K
120 N 120 K
120 N 120 K
June 2015
July 2015
July 2015
12.6
15.9
17.2
120 N 120 K
120 N 120 K
120 N 120 K
June 2016
July 2016
May 2016
1Limestone,
gypsum and straw mulching in Mg ha-1; inkg ha-1,3N (ammonium nitrate) and K(potassium chloride),4dry matter base. 2Ferilizing
Before the establishment of the field experiments in 2013, soil samples were collected for chemical and physical properties analysis according to Raij et al., (2001) and EMBRAPA (2011) [29,30] (Table 2). 2.2Soil water content, storage and temperature measurements Two basic parameters describe the state of water in soil: soil water content (WC) and soil water potential (WP). WC is useful when trying to describe the water balance of a soil while water potential determines how water moves in a soil profile or from the soil to the plant. In order to obtain the soil water retention curve (SWRC), i.e., the relationship between the WP(ψ, kpa), and the corresponding values of soil WC (θ, m3m3)undisturbed samples were collected using volumetric rings from four center trenches at depths of 0-0.10, 0.10-0.20, and 0.20-0.40 m. The soil samples were saturated and then subjected to tensions of 2, 6, 10, 33 (tension tables)300, 500, 700 and 1500 kpa (in Richards extraction chambers). After the equilibrium of the samples at the respective tensions, they were dried in an oven at 105oC for 48h to constant dry mass. The soil bulk density (Mg m-3) and gravimetric moisture (g g-1) were calculated [30] and, subsequently, it was calculated the volumetric WC (θ, cm3 cm-3) corresponding to each potential. Dielectric sensors MPS-2 (Matrix Potential Sensor) calibrated and connected to an Em50 data logger (both from Decagon Dev. Inc. Pullman, WA), were used to record and store soil WP and temperature every 6 hours at a depth of 0.20m, representing the soil layer 0-0.40m, since most of the roots are found at this depth. The sensor present a surface-mounted thermistor to take temperature readings.
Figure 1: Coordinates, altitude, soil and climate characteristics for Chapadão do Céu-GO, QuirinópolisGO and Quatá-SP locations.(1Brazilian classification [27]; 2USDA Soil Taxonomy [28]; 3According to Köppen´s classification). The experiments with straw mulching (SM)were established in June 2014 after plant cane harvesting, The plots were composed by ten- sugarcane rows spaced 1.5m and with 9 m in long. In all locations, the established treatments were: i. bare soil (0SM); ii. 50% of straw mulch (50SM) and; iii. 100% of straw mulch (100SM). The adjustment of these quantities was performed manually after harvesting. More information about location description are presented in Table 1.
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25th European Biomass Conference and Exhibition, 12-15 June 2017, Stockholm, Sweden
Table II: Chemical and physical properties of the soil at the sugarcane fields Layer
pH
m
SOM
P
g dm³
dm-³
mg
K Ca Mg H+Al CEC BS mmol
dm-³
Sand
%
Silt g
Clay
kg-1
BD Mg m-3
Macro Micro m3 m-3
Quatá 0-0.10
5.1
12
24
1
16
6
13
36
23
853
60
87
1.7
0.09
0.27
0.11-0.20
4.7
11
16
0
10
3
17
31
13
832
60
108
1.84
0.11
0.22
0.21-0.40
4.6
10
8
0
10
3
16
30
13
801
57
142
1.76
0.08
0.24
0.41-0.60
4.5
12
7
0
8
2
18
28
10
783
73
144
1.68
0.10
0.24
0.61-1.00
4.5
7
6
0
7
2
18
28
10
763
78
159
1.67
0.12
0.25
Chapadão do Céu 0-0.10
5.1
33
15
3
33
12
27
76
49
218
161
621
1.15
0.17
0.37
0.11-0.20
5.2
24
12
2
28
9
28
67
39
208
150
642
1.15
0.16
0.37
0.21-0.40
4.8
24
6
1
16
5
37
58
22
200
145
655
1.15
0.15
0.36
0.41-0.60
4.8
20
5
1
13
3
31
47
17
181
138
681
1.14
0.16
0.35
0.61-1.00
4.8
17
5
1
12
3
27
42
16
177
104
719
1.14
0.15
0.3
Quirinópolis 0-0.10
5.5
32
10
6
44
16
23
89
66
267
186
547
1.37
0.13
0.45
0.11-0.20
5.5
27
8
4
43
12
23
82
59
249
190
561
1.29
0.15
0.46
0.21-0.40
5.5
22
7
3
34
8
21
66
45
225
195
580
1.23
0.20
0.43
0.41-0.60
5.6
18
7
1
28
6
20
55
35
226
175
599
1.2
0.18
0.45
0.61-1.00 5.7 30 6 1 22 7 18 48 30 234 171 595 1.19 0.20 0.44 * SOM = soil organic matter; CEC = cation exchange capacity; BS =base saturation; BD = bulk density; Macro = Macropores and Micro = Micropores.
Thus, aiming to adjust the WC at any WP, the van Genuchten (1980)[31] parameters, provided from RETEC [32] program, was used. Water storage (hz) during both crop seasons in the soil profile at the 0-0.40 m depth was calculated by the integral: L
hz ( Z )dz
TSH is tons of stalk per hectare; SW is the stalk weights average obtained in the four rows of each plot, in Mg, and 9 and 1.5 representing long and row spacing, respectively. Sugarcane yield data was submitted to the variance analysis (F- test) and a Tukey test was used for mean comparison (p < 0.05). Both analysis was performed using STATISTICA software (Dell Inc.) [34].
(1)
0
Where θ is the WCand Z is the soil depth. This integral was based on the trapezoid rule of numerical integration [33]. An average h was calculated for the entire sugarcane development cycle, separated in 4 stages with 3-months each, starting after harvest. A daily variation in water storage∆h was also estimated during the initial crop estabilishment, acording to equation 2: (2) h Z ( i i 1 )
2.4Climate description In general,annual rainfall annual distribution is quite uneven with a marked wet period during the summer months (December - March) and a dry period from May to late September. December and January are the wettest months representing respectively 33%, 36% and 31% of the total rainfall in the year, for Chapadão do Céu, Quirinópolis and Quatá. July is the driest month in Quirinópolis and Chapadão do Céu with an average of 8 and 13 mm respectively, while in Quatá the driest month is August (38 mm). The minimum monthly temperature is recorded in May, on average 15-16°C for all locations, while the maximum monthly temperature occurs in September-October, ranging from 32°C in Quatá (October), 33°C in Chapadão do Céu and 34°C in Quirinópolis. Figure 2 presents the water balance and temperature (maximum and minimum) pattern based on Thornthwaite and Mather (1955) [35]for plant cane and the analyzed crop seasons (1st and 2ndratoon) in Quatá, Chapadão do Céu and Quirinópolis locations.
A two-sample t-test was carried out to indicate whether two treatments (bare soil vs. SM) are different. 2.3 Sugarcane yield At the end of each cycle, the plots were mechanically harvested to determine sugarcane yield in tons of stalk per hectare (TSH). The total stalk biomass of four central rows of each plot was automatically transferred upon cutting to an instrumented truck containing a load cell specifically designed for weighing biomass. The TSH was calculated by the equation:
TSH = ((SW/ 9) * (10000/ 1.5))/1000
(3)
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Figure 2: Water Balance (surplus and deficiency, mm) and temperature (maximum and minimum, °C) pattern for QuatáChapadão do Céu and Quirinópolislocations during the plant cane (2013/2014), first (2014/2015) and second ratoon (2015/2016) seasons (Tmean is the mean temperature along crop cycle; ETP and ETR the potential and real evapotranspiration).
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25th European Biomass Conference and Exhibition, 12-15 June 2017, Stockholm, Sweden
3
RESULTS AND DISCUSSION
and 100 SM), respectively, 15.4% and 12.2%. As sandy soils are more prone to drought and deplete of their available water capacity when evaporation and evapotranspiration rates are high, SM seems to act as a barrier to prevent oscillation in daily water storage avoiding abrupt fluctuations in soil moisture content. This can be observed in the Fig 4, mainly during the stage 2 in the 2014/2015 season. This period was marked by the delayed onset of the rainy season, which commonly occurs in mid-September, in addition to the high temperatures, typical of the spring months in the Southern hemisphere (see Fig 2). Thus, the great oscillation in daily water storage in the bare sand soil is evident when compared to the mulched treatments, i.e., high losses of water due to the evaporation from soil and fast infiltration rates deplete of the available water supply to the plants. The year of 2015/2016 was extremely rainy at this region, and sugarcane experienced water surplus throughout the full crop cycle, thus the oscillation among treatments were less pronounced than 2014/2015 season.
The effects of SM on the temporal variability of soil moisture content, soil temperature dynamic and sugarcane yield are presented in the following topics, separated by location. 3.1 Quatá The results for Quatá (sandy soil) indicates a clear difference in the temporal variability of WC in response to straw maintenance in 2014/2015, highlighting a lower pattern on bare soil treatment (0 SM) compared to the others. The next season (2015/2016) presented lessmarked variation in WC pattern (Fig 3). In the 2014/2015 season, 50 SM and 100 SM stored respectively 7.3% and 8.7% more water than the bare soils (average for the full cycle) (Table 3). Considering the period from 18 September to 17 December2014, denoted here as stage 2corresponding to a 3-6 months’ sugarcane in maximum growth rates, the greatest difference in water storage were reported in the mulched treatments (50 SM
Figure 3: Temporal variability of water content (θ, m3 m-3) for Quatá under different management of straw mulch (SM) during the first (2014/2015) and second ratoon (2015/2016), and the corresponding rain (mm) distribution
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25th European Biomass Conference and Exhibition, 12-15 June 2017, Stockholm, Sweden
Table III: Average water storage, h (mm) for the layer 0-0.40 m and the percentage of variation (0SMvs.50SM; 0SMvs.100SM; 50SMvs.100SM) separated by stages (3-months each) in Quatá. Average h 2014/2015 Stages 0SM 50SM 100SM 1 19 June -17 Sept 43.0 46.1 46.7 2 18 Sept - 17 Dec 39.0 45.0 43.8 3 18 Dec - 17 March 44.4 48.2 47.6 4 18 March - 17 June 49.1 50.2 50.4 Average 43.9 47.4 47.1 2015/2016 1 28 July* - 15 Sept 45.3 45.9 46.8 2 16 Sept - 15Dec 47.1 47.1 49.7 3 16 Dec - 15 March 47.5 48.6 48.2 4 16 March - 8 June 48.5 50.1 47.8 Average 47.1 47.9 48.1 *Missing data; ns not significant difference within 2-sample t-test, p
