Soil gaseous N2O and CH4 emissions and carbon pool due to integrated crop-livestock in a subtropical Ferralsol

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Soil gaseous N2 O and CH4 emissions and carbon pool due to integrated crop-livestock in a subtropical Ferralsol Jonatas Thiago Piva a,1 , Jeferson Dieckow a,∗ , Cimélio Bayer b , Josiléia Acordi Zanatta c , Anibal de Moraes d , Michely Tomazi b,2 , Volnei Pauletti a , Gabriel Barth e , Marisa de Cassia Piccolo f a Departamento de Solos e Engenharia Agrícola/Programa de Pós-Graduac¸ão em Ciência do Solo, Universidade Federal do Paraná, Rua dos Funcionários 1540, Bairro Cabral, 80035-050 Curitiba, PR, Brazil b Departamento de Solos, Universidade Federal do Rio Grande do Sul, 91540-000 Porto Alegre, RS, Brazil c Empresa Brasileira de Pesquisa Agropecuária (EMBRAPA), Centro Nacional de Pesquisa em Floresta, 83411-000 Colombo, PR, Brazil d Departamento de Fitotecnia e Fitossanitarismo, Universidade Federal do Paraná, Rua dos Funcionarios 1540, Bairro Cabral, 80035-050 Curitiba, PR, Brazil e Fundac¸ão ABC para Assistência e Divulgac¸ão Técnica Agropecuária, P.O. Box 1003, CEP 84166-990 Castro, PR, Brazil f Centro de Energia Nuclear na Agricultura, Universidade de São Paulo, Av. Centenário 303, 13416-970 Piracicaba, SP, Brazil

a r t i c l e

i n f o

Article history: Available online xxx Keywords: Global warming mitigation Dairy livestock Grazing Subtropical soil Fertiliser-N Static chamber

a b s t r a c t We assessed the impact of integrated crop-livestock (CL), with silage maize (Zea mays L.) in summer and grazed annual-ryegrass (Lolium multiflorum Lam.) in winter, and continuous crop (CC), with annualryegrass used only as cover-crop, on net greenhouse gas emission from soil (NetGHG-S) in a subtropical Ferralsol of a 3.5-year-old experiment in Brazil. Emissions from animal excreta in CL were estimated. Soil N2 O fluxes after N application to maize were higher in CL (max. 181 ␮g N2 O-N m−2 h−1 ) than in CC (max. 132 ␮g N2 O-N m−2 h−1 ). The cumulative annual N2 O emission from soil in CL surpassed that in CC by more than three-times (4.26 vs. 1.26 kg N2 O-N ha−1 , p < 0.01), possibly because of supplementary N application to grazed ryegrass in CL (N was not applied in cover-crop ryegrass of CC) and a certain degree of soil compaction visually observed in the first few centimetres after grazing. The estimated annual N2 O emission from excreta in CL was 2.35 kg N2 O-N ha−1 . Cumulative annual CH4 emission was not affected significantly (1.65 in CL vs. 1.08 kg CH4 -C ha−1 in CC, p = 0.27). Soil organic carbon (OC) stocks were not affected by soil use systems, neither in 0–20-cm (67.88 in CL vs. 67.20 Mg ha−1 in CC, p = 0.62) or 0–100cm (234.74 in CL vs. 234.61 Mg ha−1 in CC, p = 0.97). The NetGHG-S was 0.652 Mg CO2 -Ceq ha−1 year−1 higher in CL than in CC. Crop-livestock emitted more N2 O than CC and no soil OC sequestration occurred to offset that emission. Management of fertiliser- and excreta-N must be focused as a strategy to mitigate N2 O fluxes in CL. © 2013 Elsevier B.V. All rights reserved.

1. Introduction Integrated crop-livestock (CL) is characterized by the rotation of crop and pasture in the same area over time. Crop-livestock associated with no-tillage farming is recently gaining importance as an innovative soil use system in Brazil that improves food production (grain, milk and beef) and economical income of farmers.

∗ Corresponding author at: Rua dos Funcionarios 1540, CEP 80035-050 Curitiba, PR, Brazil. Tel.: +55 41 33505608; fax: +55 41 3350 5673. E-mail addresses: [email protected], [email protected] (J. Dieckow). 1 Current address: Universidade Federal de Santa Catarina, Campus Curitibanos, 89520-000 Curitibanos, SC, Brazil. 2 Current address: Empresa Brasileira de Pesquisa Agropecuária (EMBRAPA), Centro de Pesquisa Agropecuária do Oeste, P.O. Box 449, 79804-970 Dourados, MS, Brazil.

Successful experiences on CL have also been reported for temperate and other subtropical environments (Studdert et al., 1997; Russelle et al., 2007; Franzluebbers and Stuedemann, 2008). Considering the potential of CL to expand area in Brazil and worldwide, it is important to obtain information on how this system affects soil organic carbon (OC) stock, soil nitrous oxide (N2 O) and methane (CH4 ) emissions, and thus global warming contribution or mitigation. In CL, nitrogen (N) inputs are fertiliser application to crop or pasture, biological fixation by legumes, and animal excreta deposition (urine and dung). Nitrous oxide emissions from pastoral soils after fertiliser-N application may be associated with nitrification, mainly if N is applied as urea or NH4 + form, and denitrification (Dalal et al., 2003). Nitrogen fertilization has been reported to increase N2 O emissions up to three-fold in pastures of the Great Plains of USA (Liebig et al., 2006) and significantly in European grasslands (Velthof and Oenema, 1995). Concerning excreta, Yamulki

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and Jarvis (1997) found that N2 O emission averaged 0.77 kg N2 ON ha−1 year−1 in humid temperate grasslands with urine the main contributor (0.61 kg N2 O-N ha−1 year−1 ). Pastoral soils may also become source of CH4 , mainly when water saturation creates anaerobic conditions favourable for methanogenesis (Saggar et al., 2008). However, most pastoral soils in tropical and subtropical free-drained Ferralsols function as CH4 sinks because they remain under aerobic conditions that favour the oxidation of CH4 into CO2 by methanotroph organisms (Saggar et al., 2008). Grazing has shown benefits in terms of soil OC accumulation (Salton, 2005; Jantalia et al., 2006; Carvalho et al., 2010), with rates of 0.68 Mg ha−1 year−1 (Salton, 2005) and 0.36 Mg ha−1 year−1 (Jantalia et al., 2006) being reported for brachiaria (Brachiaria sp.) pasturelands in Brazil. For CL in Amazonia or Cerrado, OC accumulation has ranged from 0.82 to 2.58 Mg ha−1 year−1 (Carvalho et al., 2010), while in temperate lands of Argentina it reached 1.35 Mg ha−1 year−1 (Studdert et al., 1997). In a twoyear study encompassing nine sites in Europe, Soussana et al. (2007) found an OC increase of 1.04 Mg ha−1 year−1 in grassland ecosystems. Differently, Marchão et al. (2009) reported decreases of OC stocks in a Cerrado soil after 13 years of continuous pasture or CL relative to continuous crop. A worldwide compilation by Milchunas and Lauenroth (1993) comparing grazed versus ungrazed pasturelands indicated that in 40% of the studies grazing increased soil OC, while grazing maintained or decreased in the rest. Impacts of soil use and management systems on mitigation or contribution of global warming can be measured by the net GHG emission approach, after counting N2 O and CH4 emissions and changes in soil OC stock (which represents the net CO2 balance) (Robertson and Grace, 2004). A practice that reduces the emission of one gas might eventually increase the emission of another. Approaches to calculate net GHG emission have been adopted to assess soil tillage (Robertson et al., 2000; Six et al., 2004), soil use (Mosier et al., 2005) and bioenergy production systems (Robertson et al., 2011), all based on a balance of emitted and mitigated amount of GHG and eventually costs of agronomic practices (Lal, 2004). The assessment can be further refined by using the GHG intensity approach (GHGI) (Mosier et al., 2006), where net GHG emission is divided by the crop yield of the system, so that instead of expressing emission on land area basis it is on yield basis. This study aimed at assessing the impact of integrated croplivestock system, based on no-tillage succession of maize and annual-ryegrass pasture, over N2 O and CH4 emissions and OC stock in a subtropical Umbric Ferralsol, and thus over the net GHG emission from soil, including animal excreta, relative to a continuous crop system.

2. Materials and methods 2.1. Field experiment The study was conducted in an experiment located in Castro, Paraná State, southern Brazil (24◦ 47 53 S, 49◦ 57 42 W and elevation of 996 m). Soil type was an Umbric Ferralsol (IUSS System) or Latossolo Bruno (Brazilian System), with clayey texture in 0–20-cm (439 g kg−1 of clay, 177 g kg−1 of silt and 384 g kg−1 of sand). Climate is humid subtropical (Cfb, Köppen), with mean temperature of 23 ◦ C in the warmest month (January) and 13 ◦ C in the coldest (July); mean annual precipitation was about 1400 mm (Caviglione et al., 2000). Treatments included three soil use systems, set in main plots of 70-m × 10-m, and seven tillage systems, set in subplots of

10-m × 10-m, arranged in a split-plot randomized complete block with four replicates. However, for this study we selected only two soil use systems and only in no-tillage subplots: (i) Integrated crop-livestock (CL), with annual-ryegrass (Lolium multiflorum Lam.) being grazed in three to four grazing cycles per winter by Holstein or Jersey cows (Bos taurus). Each grazing cycle started when annual-ryegrass was 20-cm high and finished two or three days later, when annual-ryegrass was 10cm high. The standing residue left after the last grazing cycle was desiccated with glyphosate herbicide (1200 g a.i. ha−1 ). In summer, maize (Zea mays L.) was cropped for silage. (ii) Continuous crop (CC), with annual-ryegrass not being grazed but used as winter cover-crop, which was desiccated with glyphosate herbicide at flowering (plants about 40 cm high). Maize was also cropped for silage in summer. Maize was planted in October, and a total of 165 kg N ha−1 was split in two applications: 40 kg N ha−1 (15-30-00) at planting, incorporated into about 5-cm depth aside seed rows, and 125 kg urea-N ha−1 (25-00-25) at sidedress, not incorporated, when maize had four expanded leafs. Maize was mechanically harvested for silage in February and then the plot was left fallow until the sowing of annual-ryegrass in April. Urea-N, at a rate of 60 kg ha−1 , was applied to the grazed ryegrass of CL, 15 days after emergence, but not in cover-crop ryegrass of CC. Air temperature and precipitation during the study period were measured at a meteorological station within 10 km of the experimental site. 2.2. Measurement of N2 O and CH4 emissions from soil Soil N2 O and CH4 fluxes were measured during 1-year period, which included one maize cropping in summer and one ryegrass cropping in the following winter, in the 4th year of the experiment. Measurements included 30 air sampling events, from 26 September 2008 to 16 September 2009, being 15 samplings during maize growing in spring (September–November 2008) and 15 during ryegrass cycle in autumn/winter (April–September 2009), at intervals varying from 1 to 22 days, depending on how far from sowing or N application operations. From December 2008 to March 2009, measurements could not be carried out (problems in the chromatograph equipment), and based on previous studies (Gomes et al., 2009; Petersen et al., 2011) reporting background fluxes (close to zero) for this period of summer crops (no fertilization or tillage done, and N intensely taken up by maize), we assumed background fluxes as well for this interval. Air samples were collected from static PVC chambers of 20-cm height and 25-cm diameter deployed on aluminium-bases (three bases and chambers per plot) previously installed in a delimited mini-plot of 2.4-m × 2.4-m inside plots of CC and CL. Bases were inserted 5 cm into the soil 48 h before the first sampling and kept continuously, except for sowing and silage harvesting. During the two or three days of each grazing, a metal cage was used to avoid the approximation of cows and urination and defecation into the mini-plots. Ryegrass plants in the mini-plots were cut to 10-cm high as to simulate grazing. Each air sampling session began at 9.00 am, the time that represents the mean flux of the day (Jantalia et al., 2008). Air subsamples were taken with 20-mL polypropylene syringes every 15 min after chamber deployment (0, 15, 30 and 45 min). The basechamber sealing was made with water in a gutter surrounding the base. Headspace temperature during deployment was monitored. Internal air mixing was provided by a 12 V fan installed at the upper part of the chamber. Samples were analyzed within 24–36 h after sampling, in a Shimadzu 2014 Chromatograph equipped with

Please cite this article in press as: Piva, J.T., et al., Soil gaseous N2 O and CH4 emissions and carbon pool due to integrated crop-livestock in a subtropical Ferralsol. Agric. Ecosyst. Environ. (2013), http://dx.doi.org/10.1016/j.agee.2013.09.008

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flame ionization detector (FID) and electron capture detector (ECD). Fluxes were estimated from the slope of the linear model fitted to describe the gas concentration increase in headspace over the 45min deployment (Gomes et al., 2009). Fluxes were averaged across the three chambers per plot. The cumulative annual emissions of N2 O and CH4 were calculated by integrating the hourly emission fluxes measured during the 30 sampling events. From December 2008 to March 2009, fluxes considered background. 2.3. Estimation of N2 O emitted from animal excreta The emission of N2 O from excreta deposition (dung plus urine) during the ryegrass cycle in CL was estimated after considering that 2% of the excreted N was lost as N2 O (emission factor of 2%) (IPCC, 2006) and that 84.2% of the ingested N by cows was excreted, according to a compilation from several studies made by Haynes and Williams (1993). The ingested N was calculated by considering the ryegrass forage yield (data collected since the beginning of the experiment). The N concentration of aboveground ryegrass at grazing was assumed as being 28.2 g N kg−1 , according to a compilation of studies conducted in the same region (Pauletti, 2004). 2.4. Organic carbon stocks and other soil parameters

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sequestration rate of each system. Data of N2 O and CH4 cumulative annual emission were converted into CO2 -Ceq ha−1 year−1 , considering the global warming potential of N2 O (298) and CH4 (25) relative to CO2 in a 100-year time horizon (IPCC, 2007). The GHG intensity was calculated by dividing NetGHG-S by the mean annual fodder yield in each system (Mosier et al., 2006). The fodder yield in CL was the ryegrass forage plus maize silage and in CC only maize silage, because ryegrass was not grazed. Information on ryegrass forage yield was collected since the beginning of the experiment and on silage yield over four crop seasons (June 2005 to September 2008). Those data are from historic files of the experiment. 2.6. Statistical analysis Results of N2 O and CH4 emission rates of each sampling, the annual cumulative emission of N2 O and CH4 , the soil OC concentration of each layer and the soil OC stocks in 0–20 and 0–100-cm layers were submitted to analysis of variance (ANOVA). The p-value of the Fisher F-test was used to assess the significance of the effects from the two soil use systems (CC and CL) with Statistical Analysis Software. Although the experimental design was a split-plot randomized complete block, with main plots as soil use systems and subplots as tillage systems, we performed statistical analysis as a complete randomized block design, because tillage system was not a variable of this portion of the study. We assessed CC and CL only under no-tillage plots.

Soil samples were collected for OC assessment in the 0–5, 5–10, 10–20, 20–40, 40–60, 60–80 and 80–100-cm layers in December 2008 (experiment was 3.5 year old), at two points per plot. Samples of the upper three layers were collected with spatula and below 20-cm with a Dutch auger type. Samples were air dried at ambient temperature, crushed with a wood roll and stored in plastic pots. About 20 g were further crushed in a mortar, to pass 0.50-mm mesh, and 400 mg were analyzed by dry combustion in a Shimadzu TOCVCSH analyser to determine the OC concentration. To estimate OC stocks, soil bulk density was assessed in undisturbed cores samples, collected in cylinders of 5.6-cm diameter and 3.1-cm height that were introduced vertically until the middle of each of the three upper layers. We assumed that soil bulk density in layers below 20-cm depth was the same of that in 10–20-cm layer. The opening of a trench to assess bulk density up to 1-m depth would cause severe damage to the experimental plots. Organic carbon stocks were calculated in equivalent soil mass, considering CC as the reference of soil mass. The annual OC sequestration rate in CL relative to CC was calculated by the difference of OC stock between those two systems divided by 3.5 years of experimental duration (June 2005 to December 2008). This is referred as a relative sequestration rate and not absolute because it does not consider the OC stock at the beginning of the experiment, which was not available. Annual OC sequestration was calculated for both 0–20 and 0–100-cm layers. Soil cores were also used for macro and microporosity evaluation. Saturated samples were submitted to a tension of 6 kPa (48 h). Microporosity was equivalent to the volume of water contained in the sample after 6 kPa tension. Macroporosity was the difference between total porosity and microporosity. Total porosity was calculated from bulk and particle density (2.65 kg dm3 ). Inorganic N forms (NH4 + and NO3 − ) and water filled pore space (WFPS) were monitored in the 0–5 cm layer at each gas sampling. Soil moisture, used to calculate WFPS, was measured gravimetrically (105 ◦ C). The NH4 + and NO3 − forms were determined by steam-distillation method (Mulvaney, 1996).

The N2 O fluxes from seven days before to 21 days after maize planting (samplings 1 to 10) were in general similar in CL and CC and averaged 14 ␮g N2 O-N m2 h−1 (Fig. 2). Emission increased sharply three days after sidedress urea-N application to maize (sampling 11), so that the average flux across CL and CC increased about seven-fold and reached 108 ␮g N2 O-N m2 h−1 . In CL the emission continued to increase, reaching 181 ␮g N2 O-N m2 h−1 at sampling 15, and differed (p = 0.04) from the 96 ␮g N2 O-N m2 h−1 flux in CC. In general, N2 O fluxes during the 21-day period following N application (samplings 11–15) were an average of 53% greater in CL than CC (Fig. 2). During the ryegrass cycle in autumn–winter, N2 O fluxes in CC were almost negligible and averaged a background value of 5 ␮g N m2 h−1 (Fig. 2). Before urea-N application (samplings 16–21), the N2 O fluxes were similar between CL and CC (except of a negative flux in CL at sampling 17), but then the application of 60 kg ureaN ha−1 to grazed ryegrass in CL increased N2 O-N flux to 33 ␮g m2 h−1 seven days later (sampling 22) and to 83 ␮g m2 h−1 120 days later (sampling 30). Based on those fluxes, the cumulative annual N2 O emission from soil reached 4.26 kg N2 O-N ha−1 in CL and 1.26 kg N2 O-N ha−1 in CC (p < 0.01) (Fig. 3). Methane influxes occurred in most of the assessment period, either in CL or CC (Fig. 4), but a great emission occurred in April and May and reached an average flux of 194 ␮g CH4 -C m2 h−1 at sampling 21. Total CH4 emission was not affected by land use system, averaging 1.65 vs. 1.08 kg CH4 -C ha−1 year−1 (p = 0.27) in CL and CC, respectively (data not shown). The mean ryegrass forage yield was 4.94 Mg DM ha−1 year−1 (Table 1) and considering the N concentration of 28.2 g N kg−1 of DM (Pauletti, 2004), the estimated amount of ingested N was 139 kg ha−1 . Assuming that 84.2% of that N was excreted (Haynes and Williams, 1993), this would be 117 kg N ha−1 . Applying the IPCC emission factor of 2% (IPCC, 2006) leads to an emission of 2.35 kg N2 ON ha−1 year−1 (Fig. 3), which is equivalent to 0.300 Mg CO2 -Ceq ha−1 year−1 (Table 1).

2.5. Net GHG emission from soil and GHG intensity

3.3. Soil organic carbon

The net GHG emission from soil (NetGHG-S) was calculated after counting the soil N2 O and CH4 emissions, the estimated N2 O emission from animal excreta deposition in CL and the soil OC

Soil OC concentration within the 100-cm depth did not change significantly between CL and CC (Fig. 5), hence the similar OC stocks in 0–20 cm (67.9 Mg ha−1 in CL and 67.2 Mg ha−1 in CC, p = 0.62) and 0–100 cm layers (234.7 Mg ha−1 in CL and 234.6 Mg ha−1 in CC, p = 0.97) (data not shown). Accordingly, the calculated

3. Results 3.1. Temperature and precipitation The annual precipitation during the study year was 1740 mm, and monthly precipitation was below normal in April 2009 (21 vs. 88 mm) and above in July 2009 (315 vs. 112 mm) (Fig. 1). June was the coldest month (mean temperature of 11.7 ◦ C) and February the warmest (20.8 ◦ C, a little below the normal of 23.0 ◦ C). 3.2. N2 O and CH4 emissions

Please cite this article in press as: Piva, J.T., et al., Soil gaseous N2 O and CH4 emissions and carbon pool due to integrated crop-livestock in a subtropical Ferralsol. Agric. Ecosyst. Environ. (2013), http://dx.doi.org/10.1016/j.agee.2013.09.008

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25

80 Last sampling

Temperature Precipitation

20

Precipitation (mm)

60

15 40 10 20

Temperature (oC)

1st sampling

5

0

0 8 00 -2

09 20 pSe 09 20 gAu 9 00 l-2 Ju 09 20 nJu 09 20 yMa 9 00 r-2 Ap 9 00 r-2 Ma 09 20 bFe 09 20 nJa 08 20 cDe 08 20 vNo 8 00 t-2 Oc

p Se

Fig. 1. Mean daily precipitation (vertical bars) and mean air temperature (continuous line) in the experimental site from September 2008 to September 2009.

**

**

0

25

***

***

30

Oct

Nov

Apr

200 -2 -1 CH4 (µ µg CH4-C m h )

10

1

***

***

*** 20

15

5

Sep

***

Ryegrass planting

Maize planting

50

-50

N application to grazed ryegrass in crop-livestock ***

N application to maize

*** ***

100

250 CC: continuous crop CL: crop-livestock

***

150

***

200

*** ***

-2 -1 N2O (µ µg N2O-N m h )

250

150 100 50

Jun

Jul

Aug

Sep

Fig. 2. Nitrous oxide flux from a Ferralsol subjected to no-tillage integrated croplivestock (CL) or continuous crop (CC). Numbers denote the sampling identification. The asterisks *, ** and *** denote significance between cropping system treatments at p ≤ 0.10, p ≤ 0.05 and p ≤ 0.01, respectively, according to F-test. The lack of asterisk means not significant. Vertical bars denote standard deviation.

OC sequestration rates in CL relative to CC in 0–20 cm (0.194 Mg ha−1 year−1 ) or 0–100 cm layers (0.037 Mg ha−1 year−1 ) were also regarded as not significant (Table 1). 3.4. Net GHG emission from soil and GHG intensity

-50

1

15

10

25

30

N application to grazed ryegrass in crop-livestock

-150 Oct

Sep

Nov

Apr

May

Jun

Jul

Aug

Sep

Fig. 4. Methane fluxes from a Ferralsol subjected to no-tillage integrated croplivestock (CL) or continuous crop (CC). Numbers denote the sampling identification. For all sampling times, the difference between crop-livestock and annual crop was not significant (p > 0.10) according to F-test. Vertical bars denote standard deviation.

the 0–100-cm layer, the NetGHG-S (0.822 Mg CO2 -Ceq ha−1 year−1 ) was about five-fold greater than in CC, mainly because of measured N2 O emitted from soil (0.544 Mg CO2 -Ceq ha−1 year−1 ) and estimated N2 O from excreta deposition (0.300 Mg CO2 -Ceq ha−1 year−1 ). The total fodder yield was greater in CL (23.5 Mg DM ha−1 year−1 ) than in CC (17.3 Mg DM ha−1 year−1 ) because ryegrass was not fertilized and grazed in CC and

Organic carbon (g kg-1 soil) 0 12

16

20

24

28

32

36

0 ns p=0.65 ns p=0.87

***

4

4.26

p<0.01

20

3 2.35

2

1.26 From excreta

From soil

CC

CL

Fig. 3. Total nitrous oxide emission from a Ferralsol subjected to no-tillage integrated crop-livestock (CL) or continuous crop (CC), and estimated emission from excreta in CL. The p value refers to the significance of difference for soil N2 O emission between CC and CL (excreta not included), according to F-test. Vertical bars denote standard deviation.

Depth (cm)

N2O emission (kg N2O-N/ha/yr)

5

-100

5

0

20

Maize planting

The NetGHG-S in CC was 0.170 Mg CO2 -Ceq ha−1 year−1 and derived mainly from N2 O emission (0.160 Mg CO2 -Ceq ha−1 year−1 ) (Table 1). In CL and considering

1

Ryegrass planting

0

-200

May

CC: continuous crop CL: crop-livestock

N application to maize

ns p=0.50 ns p=0.89

40

60

80

100

ns p=0.69

ns p=0.17

ns p=0.25

CC: continuous crop CL: crop-livestock

Fig. 5. Organic carbon concentration in a Ferralsol subjected to no-tillage integrated crop-livestock (CL) or continuous crop (CC) at the end of 3.5 years (p values refer to the significance level of the difference, according to F-test). Horizontal bars denote standard deviation.

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Table 1 Net greenhouse gas emission from soil (NetGHG-S), ryegrass forage and maize silage yield, and greenhouse gas intensity (GHGI) in a no-tillage Ferralsol subjected to integrated crop-livestock (CL) or continuous crop (CC). Organic carbon sequestration rates, NetGHG-S and GHGI are presented for 0–20 and 0–100-cm layers. Parameter

CC

−1

Net GHG emission parameters (Mg CO2 -Ceq ha N2 O emission from soil N2 O emission from excreta (estimated)a Total N2 O emission, including excreta CH4 emission OC sequestrationb NetGHG-Sc Greenhouse gas intensity parameters Ryegrass forage yield (Mg DM ha−1 year−1 )d Maize silage yield (Mg DM ha−1 year−1 )e Total fodder yield (Mg DM ha−1 year−1 ) GHGI (kg CO2 -Ceq Mg−1 DM forage)f

−1

year

 (CL–CC)

CL

0–20

0–100

0–20

0–100

0–20

0–100

−0.037 (p = 0.97) 0.822

0.384 (p < 0.01) 0.300 0.684 0.005 (p=0.27) −0.194 (p = 0.62) −0.037 (p = 0.97) 0.495 0.652

) 0.544 0.300 0.844 0.015

0.160 0.000 0.160 0.010 0.000 0.170

0.000 0.170

−0.194 (p = 0.62) 0.665

0.00 17.33 17.33 9.81

4.94 18.57 23.51 9.81

15.52

22.20

4.94 1.24 6.18 12.39

5.71 −1

The estimated N2 O emission from excreta was calculated considering the ryegrass forage production (4.94 Mg DM ha ), the N concentration of ryegrass (28.2 g N kg−1 DM (Pauletti, 2004)), the percentage of excreted N over ingested N (84.2% (Haynes and Williams, 1993)), and the IPCC emission factor for excreted N in pasture soils of 2% (IPCC, 2006). b The OC sequestration rates in CL were calculated considering the 3.5 years of experimental duration.  c NetGHG-S = (N2 O emission + CH4 emission + N2 O emission from excreta + OC sequestration). a

d e f

Ryegrass forage production: average of 5 years since the beginning of the experiment (2005–2009). Maize silage production: the average of four crop seasons (June 2005–September 2008). GHGI = greenhouse gas intensity = NetGHG-S/total fodder yield.

Table 2 Physical properties of a subtropical Ferralsol subjected to no-tillage integrated crop-livestock (CL) or continuous crop (CC) system at the end of 3.5 years. Soil use system

Soil bulk density (kg dm3 )

0–5 cm CC CL

1.17 1.16

nsa

0.55 0.56

ns

0.10 0.10

ns

0.45 0.46

ns

5–10 cm CC CL

1.23 1.19

ns

0.54 0.55

ns

0.11 0.13

ns

0.43 0.42

ns

10–20-cm CC CL

1.24 1.17

ns

0.53 0.56

ns

0.12 0.15

ns

0.41 0.41

ns

a

Total porosity (m3 m3 )

Macro-porosity (m3 m3 )

Micro-porosity (m3 m3 )

Difference not significant between means in the same column and in the same layer according to F-test (p ≤ 0.10).

4.1. N2 O and CH4 emissions Before application of urea to maize, the N2 O fluxes in CL and CC were similar and close to background (samplings 1–10). We would have expected this trend to continue if N had not been applied. Nitrous oxide flux rose sharply after urea application to maize in both systems, but more in CL (Fig. 2). During the ryegrass cycle (autumn-winter), the high N2 O flux observed in CL was also induced by N application, since fluxes before application were low and similar to those of CC, which did not receive N (Fig. 2). The overall indication is that N application was the primary factor that triggered high N2 O fluxes, while the effect of CL was secondary that further increased those fluxes.

-1

+

-1

N-NH4 (mg kg )

4. Discussion

250

-

Soil bulk density, macroporosity and microporosity were not affected by soil use systems (Table 2). The concentration of inorganic N forms of NH4 + and NO3 − were also similar in CL and CC (Fig. 6a and b), with increase after urea application to maize. After urea application to ryegrass in CL, N concentration did not increase as expected. The WFPS was similar between CC and CL and was higher in July 2009, when precipitation exceeded normal. No significant correlation was observed between NH4 + , NO3 − or WFPS and N2 O fluxes (data not shown).

250

a

200

CC: continuous crop CL: crop livestock

150 100 50 0

200 150

b

N application to grazed ryegrass in crop-livestock

N application to maize

Maize planting

Ryegrass planting

100 50 0 100

WFPS (% )

3.5. Soil physical attributes and inorganic N

N-NO3 (mg kg )

maize silage yield tended to be greater in CL (Table 1). Considering NetGHG-S and fodder yield, the GHG intensity was 9.8 and 22.2 kg CO2 -Ceq Mg−1 DM in CC and CL, respectively.

15

80 60

5

40

c

20

25

10

30

1

20 0

Sep

Oct

Nov

Apr

May

Jun

Jul

Aug

Sep

Fig. 6. Concentrations of NH4 + -N (a) and NO3 − -N (b) and water filled pore space (WFPS) (c) in the 0–5 cm layer of a Ferralsol subjected to no-tillage integrated croplivestock (CL) or continuous crop (CC). Numbers denote the sampling identification.

Please cite this article in press as: Piva, J.T., et al., Soil gaseous N2 O and CH4 emissions and carbon pool due to integrated crop-livestock in a subtropical Ferralsol. Agric. Ecosyst. Environ. (2013), http://dx.doi.org/10.1016/j.agee.2013.09.008

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The effect of fertiliser-N in increasing N2 O emission is widely reported (Baggs et al., 2003; Zanatta et al., 2010) and attributed to nitrification and denitrification processes induced by increase of inorganic N (NH4 + or NO3 − ) in soil (Velthof and Oenema, 1995). Such as the increase that was observed mainly after urea application to maize (Fig. 6a and b). Liebig et al. (2006) reported that N fertilization increased N2 O emissions by three-fold in pastures of the Great Plains, although enhancing deep storage of soil OC. The higher N2 O fluxes after urea-N application in the CL relative to CC might be related to more anaerobic soil conditions favouring denitrification as a consequence of soil surface compaction due to animal treading (Velthof and Oenema, 1995; Oenema et al., 1997). The non-differing results of soil bulk density and macroporosity between CL and CC, especially in the 0–5 cm layer, could not confirm this hypothesis (Table 2). However, that might be related to the method of collecting core samples by vertically inserting the 3.1-cm-hight cylinder into the middle of the 0–5 cm layer (aiming at later core trimming) and so not including the top centimetre layer, which was visually more compacted in CL and could eventually contain more anaerobic micro-sites for denitrification. More localized assessments of bulk density and macroporosity in the first few centimetres (1 or 2 cm) of the soil surface should be employed to assess the effects of animal treading. Considering that N fertilization was the primary factor controlling N2 O fluxes in CL, its management should be a priority in mitigation plans. That includes, for example, splitting the total N dosage into more than one dressing application (either to maize or ryegrass), choosing appropriate N sources (e.g., ammonium-N sources emit less N2 O than nitrate N sources) and using urease and nitrification inhibitors (e.g., dicyandiamide) (Di and Cameron, 2002; Zanatta et al., 2010). Management of animal grazing, however, is equally important, especially with respect to adequate stocking rates and avoiding grazing when soil is wet (de Klein and Ledgard, 2005), although this is not always possible in practical terms. As a consequence of the greater soil N2 O fluxes and emission from excreta, the accumulated annual N2 O emission was five-fold higher in CL (4.26 from soil + 2.35 from excreta = 6.61 kg N2 ON ha−1 year−1 ) relative to CC (1.26 kg N2 O-N ha−1 year−1 ). In spite of that, the annual emission in CL still remained at the lower part of the range of 6–12 kg N2 O-N ha−1 year−1 reported for dairy pasture soils in Australia and New Zealand (Dalal et al., 2003; Saggar et al., 2008), and lower than the average of 13.4 kg N ha−1 year−1 reported by Velthof et al. (1996) in a clayey Fluvisol under grassland in Europe. In a two year study in nine European grasslands, Soussana et al. (2007) obtained an average N2 O emission of 1.10 kg N2 O-N ha−1 year−1 , but in one site N2 O emission reached 6.8 kg N2 O-N ha−1 year−1 , close to our findings in CL. With respect to CH4 fluxes, during most of the time soils in CL or CC acted as CH4 sinks. This result is logical assuming that the aerated condition of those soils would have favoured methanotrophic oxidation of CH4 into CO2 (Saggar et al., 2008). However, to the unexpected increase in CH4 flux observed in April and May (Fig. 4), no plausible explanation could be given. Further research is needed to verify that netGHG-S are consistent and of similar magnitude with our observations during one year of evaluation under grazed CL and ungrazed CC management systems. Further studies should encompass different environmental regions than the subtropics and experiments longer than the 3–4 years.

significant changes in OC stock (0–10 cm) (Souza et al., 2008), but another one conducted by Nicoloso (2009) showed that OC stock increased when maize was introduced in the rotation scheme and winter grazing intervals were longer. In southeast USA, CL system did not change OC stock significantly after three years compared to annual crop system, but microbial biomass did increase in 0–6 cm (Franzluebbers and Stuedemann, 2008). The lack of significant change in OC stock in CL might be attributed to two reasons. First, the experimental duration was short and not enough for CL to express its effects on OC. In the longterm, however, expectations are that grazing would increase stocks significantly (Franzluebbers et al., 2000; Jantalia et al., 2006). Longterm results from Brazilian Cerrado showed that CL with brachiaria pasture increased OC stocks at rates of 0.68 Mg ha−1 year−1 (Salton, 2005) and 0.36 Mg ha−1 year−1 (Jantalia et al., 2006) after 9 and 11 years, respectively. The second reason is the initially high OC stock of the Umbric Ferralsol in which the study was conducted, which averaged 67 and 234 Mg ha−1 in 0–20 and 0–100-cm, respectively. Soil OC sequestration in high C-content soil is a rather difficult process, as shown by Campbell et al. (1991) in a thick black Chernozem after 31 years of various management practices.

4.2. Soil organic carbon

Nitrous oxide emission was primarily induced by N fertilization, but in crop-livestock it was further increased possibly because of the effects of soil surface compaction caused by animal treading. Additional N2 O emission in crop-livestock was derived from excreta.

Organic carbon concentration (Fig. 5) and stocks were not significantly affected by CL compared to CC. A previous study in a Ferralsol of southern Brazil managed under CL also showed no

4.3. Net GHG emission from soil and GHG intensity Crop-livestock was considered a net source of soil GHG relative to CC (Table 1). The major contributor was N2 O emitted from soil, driven mainly by N application, and from excreta depositions. Expectations were that soil OC sequestration in CL would offset these emissions, since there were reports of significant sequestration in CL soils elsewhere (Salton, 2005; Jantalia et al., 2006), but this balancing of processes was not observed. However, the large contribution of N2 O emission from excreta may be arguable based on the generic emission factor of 2% for N-N2 O (IPCC, 2006), which is shown to be overestimated for some situations (de Klein et al., 2003; van der Weerden et al., 2011). Further research in this area is needed. On the other hand, the CH4 emission derived from enteric fermentation of ruminants was not considered in our study (our objective was focused on soil emissions), which would have certainly increased the emission figure in CL. On the other hand, the higher GHG emission in CL was partially compensated by a higher fodder production. When considering only the NetGHG-S on a per hectare basis, GHG emission was about five-fold higher in CL than CC (0.822 vs. 0.170 Mg CO2 Ceq ha−1 year−1 ). However, by normalizing emissions to fodder yield to obtain the GHG intensity, GHG emission was about two-fold higher in CL than in CC (22.2 vs. 9.8 kg CO2 -Ceq Mg−1 DM). More studies related to GHG in CL systems must be carried out in distinct climatic and edaphic conditions. Crop-liestock has better economic returns and crop yields, less soil erosion, lower risks related to excess nutrient concentrations (as in intensive livestock), a potential for biological pest control and other benefits (Moraes et al., 2007; Russelle et al., 2007). Hence, a full life-cycle approach should be included in future studies to assess GHG emissions comparatively to the many beneficial ecosystem services provided by CL.

5. Conclusions

Please cite this article in press as: Piva, J.T., et al., Soil gaseous N2 O and CH4 emissions and carbon pool due to integrated crop-livestock in a subtropical Ferralsol. Agric. Ecosyst. Environ. (2013), http://dx.doi.org/10.1016/j.agee.2013.09.008

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Please cite this article in press as: Piva, J.T., et al., Soil gaseous N2 O and CH4 emissions and carbon pool due to integrated crop-livestock in a subtropical Ferralsol. Agric. Ecosyst. Environ. (2013), http://dx.doi.org/10.1016/j.agee.2013.09.008