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Mitigation of greenhouse gases emission affected by no-tillage and winter cover crops in a subtropical paddy rice ecosystem

ABSTRACT

Paddy rice production based on traditional soil management emits large amounts of methane (CH4) into the atmosphere. This study assessed the potential of no-tillage (NT) and winter cover crops (WCC) to mitigate net greenhouse gas (GHG) emissions in a subtropical paddy rice ecosystem. A long-term (20-yrs) experiment was evaluated regarding the effect of NT combined with winter fallow or three WCC (ryegrass, white oat, and birdsfoot trefoil) on seasonal CH4 -C and nitrous oxide (N2O-N) emissions and on soil organic carbon (SOC) stocks in comparison to conventional tillage (CT) under winter fallow in a Gleysol of Southern Brazil. The changes in SOC were used as a proxy for annual net carbon dioxide (CO2) exchanges in the soil-atmosphere, taking the CT treatment as a reference. The GHG balance (summation of CH4 , N2O and CO2 emissions multiplied by their global warming potential of 34, 298, and 1, respectively) and emissions intensity of GHG emissions were calculated. Across winter managements, NT decreased 25 % of GHG emissions in comparison to CT system. This effect was mainly related to the decrease of seasonal CH4 -C emissions (31-113 kg ha-1) and by promoting SOC accumulation (0.45-0.65 Mg ha-1yr-1) in comparison to CT system, since soil N2 O-N emission was not affected by management practices. Increased soil CH4 -C emissions offset the positive effect of WCC on SOC accumulation compared with winter fallow. Based on our findings, NT mitigates net GHG emissions in subtropical paddy rice ecosystems, but no additional effect is observed combining NT with WCC.

nitrous oxide; methane; tillage systems; net balance of GHG; lowland

INTRODUCTION

The improvement of agricultural production systems that allow, at the same time, the production of healthy food and mitigation of greenhouse gas (GHG) emissions, is one of the major challenges facing global warming and climate change ( Princiotta, 2009Princiotta F . Global climate change and the mitigation challenge . J Air Waste Manage Assoc . 2009 ; 59 : 1194 - 211 . https://doi.org/10.3155/1047-3289.59.10.1194
https://doi.org/10.3155/1047-3289.59.10....
; Peters et al., 2013Peters GP , Andrew RM , Boden T , Canadell JG , Ciais P , Le Quéré C , Marland G , Raupach MR , Wilson C . The challenge to keep global warming below 2 °C . Nat Clim Change . 2013 ; 3 : 4 - 6 . https://doi.org/10.1038/nclimate1783
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). Agriculture and land-use change contribute to 25 % of total GHG emissions at the global level ( Smith et al., 2014Smith P , Bustamante M , Ahammad H , Clark H , Dong H , Elsiddig EA , Haberl H , Harper R , House J , Jafari M , Masera O , Mbow C , Ravindranath NH , Rice CW , Robledo Abad C , Romanosvskaya A , Sperling F , Tubiello F . Agriculture, forestry and other land use (AFOLU) . In: Edenhofer O , Pichs-Madruga R , Sokona Y , Farahani E , Kadner S , Seyboth K , Adler A , Baum I , Brunner S , Eickemeier P , Kriemann B , Savolainen J , Schlömer S , von Stechow C , Zwickel T , Minx JC , editors . Climate change 2014: Mitigation of Climate Change Contribution of Working Group III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change . United Kingdom and New York, USA : Cambridge University Press ; 2014 . Available from: https://pure.iiasa.ac.at/id/eprint/11115/1/ipcc_wg3_ar5_chapter11.pdf .
https://pure.iiasa.ac.at/id/eprint/11115...
). In Brazil, this contribution increased to 51 % due to deforestation and large agricultural area ( Brasil, 2016Brasil . Estimativas anuais de emissões de gases de efeito estufa no Brasil . Brasília, DF : Ministério da Ciência, Tecnologia e Inovação (MCTIC) ; 2016 . ).

Agriculture developed in lowlands, more specifically the irrigated rice, has a particular characteristic of high soil methane (CH4 ) emissions, which contribute to approximately 18 % of total GHG emissions from agriculture in southern Brazil (Observatório do Clima, 2019). Since soil CH4 fluxes are driven by the balance between methanogenesis and methanotrophy ( Le Mer and Roger, 2001Le Mer J , Roger P . Production, oxidation, emission and consumption of methane by soils: A review . Eur J Soil Biol . 2001 ; 37 : 25 - 50 . https://doi.org/10.1016/S1164-5563(01)01067-6
https://doi.org/10.1016/S1164-5563(01)01...
), the anoxic soil condition of lowlands favors methanogenesis process and, consequently, CH4 emission. The strong CH4 emissions in the lowlands at this subtropical ecosystem occur by the wide adoption of conventional tillage systems with high soil disturbance by plowing, disking, and leveling, which determine incorporation of weed and crop residues into the soil, providing then C source to the methanogenesis process ( Wang et al., 1998Wang M , Li J , Zhen X . Methane emission and mechanisms of methane production, oxidation and transportation in the rice fields . Sci Atmos Sin . 1998 ; 22 : 600 - 12 . ; Zschornack et al., 2011Zschornack T , Bayer C , Zanatta JA , Vieira FCB , Anghinoni I . Mitigation of methane and nitrous oxide emissions from flood-irrigated rice by no incorporation of winter crops residues into the soil . Rev Bras Cienc Solo . 2011 ; 5 : 623 - 34 . https://doi.org/10.1590/S0100-06832011000200031
https://doi.org/10.1590/S0100-0683201100...
; Bayer et al., 2014Bayer C , Costa FS , Pedroso GM , Zschornack T , Camargo ES , Lima MA , Frigheto RTS , Gomes J , Marcolin E , Macedo VRM . Yield-scale greenhouse gas emissions from flood irrigated rice under long-term conventional tillage and no-till systems in a Humid Subtropical climate . Field Crop Res . 2014 ; 162 : 60 - 9 . https://doi.org/10.1016/j.fcr.2014.03.015
https://doi.org/10.1016/j.fcr.2014.03.01...
).

In addition to CH4 , losses of SOC under conventional tillage combined with low residues input from winter fallow ( Rosa et al., 2011Rosa CM , Castilhos RVM , Pauletto EA , Pillon CN , Leal OA . Conteúdo de carbono orgânico em Planossolo háplico sob sistemas de manejo do arroz irrigado . Rev Bras Cienc Solo . 2011 ; 35 : 1769 - 76 . https://doi.org/10.1590/S0100-06832011000500031
https://doi.org/10.1590/S0100-0683201100...
; Ghimire et al., 2012Ghimire R , Adhikari KR , Chen Z , Shah C , Dahal KR . Soil organic carbon sequestration as affected by tillage, crop residue, and nitrogen application in rice–wheat rotation system . Paddy Water Environ . 2012 ; 10 : 95 - 102 . https://doi.org/10.1007/s10333-011-0268-0
https://doi.org/10.1007/s10333-011-0268-...
) contribute to net emissions of carbon dioxide (CO2 ) to the atmosphere in this subtropical ecosystem. Although not emitted significantly as in uplands ( Bayer et al., 2014Bayer C , Costa FS , Pedroso GM , Zschornack T , Camargo ES , Lima MA , Frigheto RTS , Gomes J , Marcolin E , Macedo VRM . Yield-scale greenhouse gas emissions from flood irrigated rice under long-term conventional tillage and no-till systems in a Humid Subtropical climate . Field Crop Res . 2014 ; 162 : 60 - 9 . https://doi.org/10.1016/j.fcr.2014.03.015
https://doi.org/10.1016/j.fcr.2014.03.01...
, 2016Bayer C , Gomes J , Zanatta JA , Vieira FCB , Dieckow J . Mitigation greenhouse gas emissions from a subtropical Ultisol by using long-term no-tillage in combination with legume cover crops . Soil Till Res . 2016 ; 161 : 86 - 94 . https://doi.org/10.1016/j.still.2016.03.011
https://doi.org/10.1016/j.still.2016.03....
), nitrous oxide (N2 O) emissions in rice fields can be boosted by nitrogen fertilization ( Zhang et al., 2015Zhang Y , Sheng J , Wang Z , Chen L , Zheng J . Nitrous oxide and methane emissions from a Chinese wheat–rice cropping system under different tillage practices during the wheat-growing season . Soil Till Res . 2015 ; 146 : 261 - 9 . https://doi.org/10.1016/j.still.2014.09.019
https://doi.org/10.1016/j.still.2014.09....
; Islam et al., 2018Islam SMM , Gaihre YK , Biswas JC , Singh U , Ahmed MN , Sanabria JMA , Saleque MA . Nitrous oxide and nitric oxide emissions from lowland rice cultivation with urea deep placement and alternate wetting and drying irrigation . Sci Rept . 2018 ; 8 : 17623 . https://doi.org/10.1038/s41598-018-35939-7
https://doi.org/10.1038/s41598-018-35939...
).

A feasible strategy to GHG mitigation is the adoption of no-tillage (NT) by i) decreasing the CH4 emissions maintaining crop residues on soil surface ( Bayer et al., 2014Bayer C , Costa FS , Pedroso GM , Zschornack T , Camargo ES , Lima MA , Frigheto RTS , Gomes J , Marcolin E , Macedo VRM . Yield-scale greenhouse gas emissions from flood irrigated rice under long-term conventional tillage and no-till systems in a Humid Subtropical climate . Field Crop Res . 2014 ; 162 : 60 - 9 . https://doi.org/10.1016/j.fcr.2014.03.015
https://doi.org/10.1016/j.fcr.2014.03.01...
; Hao et al., 2016Hao Q , Jiang C , Chai X , Huang Z , Fan Z , Xie D , He X . Drainage, no-tillage and crop rotation decreases annual cumulative emissions of methane and nitrous oxide from a rice field in Southwest China . Agr Ecosyst Environ . 2016 ; 233 : 270 - 81 . https://doi.org/10.1016/j.agee.2016.09.026
https://doi.org/10.1016/j.agee.2016.09.0...
); ii) retention of atmospheric CO2 -C in soil organic matter in the less oxidative environment of NT soil ( Nascimento et al., 2009Nascimento PC , Bayer C , Silva Netto LF , Vian AC , Viero F , Macedo VRM , Marcolin E . Sistemas de manejo e a matéria orgânica de solo de várzea com cultivo de arroz . Rev Bras Cienc Solo . 2009 ; 33 : 1821 - 7 . https://doi.org/10.1590/S0100-06832009000600030
https://doi.org/10.1590/S0100-0683200900...
; Rui and Zhang, 2010Rui W , Zhang W . Effect size and duration of recommended management practices on carbon sequestration in paddy field in Yangtze Delta Plain of China: A meta-analysis . Agr Ecosyst Environ . 2010 ; 135 : 199 - 205 . https://doi.org/10.1016/j.agee.2009.09.010
https://doi.org/10.1016/j.agee.2009.09.0...
). The combination of winter cover crops (WCC) with NT can booster the potential of SOC sequestration in NT system ( Yagioka et al., 2015Yagioka A , Komatsuzaki M , Kaneko N , Ueno H . Effect of no-tillage with weed cover mulching versus conventional tillage on global warming potential and nitrate leaching . Agr Ecosyst Environ . 2015 ; 200 : 42 - 53 . https://doi.org/10.1016/j.agee.2014.09.011
https://doi.org/10.1016/j.agee.2014.09.0...
; Bayer et al ., 2016), despite an increase in soil CH4 emissions can be also expected due to crop residues represent a labile C source to methanogenesis process in soil ( Zschornack et al., 2011Zschornack T , Bayer C , Zanatta JA , Vieira FCB , Anghinoni I . Mitigation of methane and nitrous oxide emissions from flood-irrigated rice by no incorporation of winter crops residues into the soil . Rev Bras Cienc Solo . 2011 ; 5 : 623 - 34 . https://doi.org/10.1590/S0100-06832011000200031
https://doi.org/10.1590/S0100-0683201100...
; Haque et al., 2013Haque M , Kim SY , Pramanik P , Kim GY , Kim PJ . Optimum application level of winter cover crop biomass as green manure under considering methane emission and rice productivity in paddy soil . Biol Fertil Soils . 2013 ; 49 : 487 - 93 . https://doi.org/10.1007/s00374-012-0766-2
https://doi.org/10.1007/s00374-012-0766-...
; Bayer et al., 2014Bayer C , Costa FS , Pedroso GM , Zschornack T , Camargo ES , Lima MA , Frigheto RTS , Gomes J , Marcolin E , Macedo VRM . Yield-scale greenhouse gas emissions from flood irrigated rice under long-term conventional tillage and no-till systems in a Humid Subtropical climate . Field Crop Res . 2014 ; 162 : 60 - 9 . https://doi.org/10.1016/j.fcr.2014.03.015
https://doi.org/10.1016/j.fcr.2014.03.01...
). Considering legumes as WCC, this impact of legume cover crops on N2 O emissions is partially or totally off-set by SOC sequestration in upland soil ( Bayer et al., 2016Bayer C , Gomes J , Zanatta JA , Vieira FCB , Dieckow J . Mitigation greenhouse gas emissions from a subtropical Ultisol by using long-term no-tillage in combination with legume cover crops . Soil Till Res . 2016 ; 161 : 86 - 94 . https://doi.org/10.1016/j.still.2016.03.011
https://doi.org/10.1016/j.still.2016.03....
), despite some studies showed the increase of soil N2 O emission ( Zschornack et al., 2011Zschornack T , Bayer C , Zanatta JA , Vieira FCB , Anghinoni I . Mitigation of methane and nitrous oxide emissions from flood-irrigated rice by no incorporation of winter crops residues into the soil . Rev Bras Cienc Solo . 2011 ; 5 : 623 - 34 . https://doi.org/10.1590/S0100-06832011000200031
https://doi.org/10.1590/S0100-0683201100...
). For lowland soils, the knowledge on the influence of conservation soil management systems comprising NT and WCC on GHG and SOC sequestration is scant, mainly considering subtropical ecosystems.

Most GHG studies in agricultural systems focused on one of the three GHG and, thus, they are not conclusive regarding the real impact of management practices on net emissions of GHG. However, a full account of the impact of soil management practices must also include the N2 O and CH4 emission from the soil on GHG emissions, expressed in terms of net GHG emission ( Robertson et al., 2000Robertson GP , Paul EA , Harwood RR . Greenhouse gases in intensive agriculture: Contributions of individual gases to the radiative forcing of the atmosphere . Science . 2000 ; 289 : 1922 - 5 . https://doi.org/10.1126/science.289.5486.1922
https://doi.org/10.1126/science.289.5486...
; Mosier et al., 2005Mosier AR , Halvorson AD , Peterson GA , Sherrod L . Measurements of net global warming potential in three agroecosystems . Nutr Cycl Agroecosys . 2005 ; 72 : 67 - 76 . https://doi.org/10.1007/s10705-004-7356-0
https://doi.org/10.1007/s10705-004-7356-...
; Bayer et al., 2016Bayer C , Gomes J , Zanatta JA , Vieira FCB , Dieckow J . Mitigation greenhouse gas emissions from a subtropical Ultisol by using long-term no-tillage in combination with legume cover crops . Soil Till Res . 2016 ; 161 : 86 - 94 . https://doi.org/10.1016/j.still.2016.03.011
https://doi.org/10.1016/j.still.2016.03....
). That full account can be expressed in terms of GHG emission, which adds up SOC changes and soil N2 O and CH4 emissions, taking into account each gas’s respective global warming potential ( Mosier et al., 2005Mosier AR , Halvorson AD , Peterson GA , Sherrod L . Measurements of net global warming potential in three agroecosystems . Nutr Cycl Agroecosys . 2005 ; 72 : 67 - 76 . https://doi.org/10.1007/s10705-004-7356-0
https://doi.org/10.1007/s10705-004-7356-...
). Another useful parameter to measure the impact of soil management systems on GHG emission is the emissions intensity that measures the GHG per unit of grain yield ( Mosier et al., 2006Mosier AR , Halvorson AD , Reule CA , Liu XJJ . Net global warming potential and greenhouse gas intensity in irrigated cropping systems in northeastern Colorado . J Environ Qual . 2006 ; 35 : 1584 - 98 . https://doi.org/10.2134/jeq2005.0232
https://doi.org/10.2134/jeq2005.0232...
).

Our starting hypothesis is that NT and WCC adoption decrease net GHG emissions per area and per unit of yield in subtropical paddy rice ecosystems, possibly related to increased SOC sequestration and mitigation of soil CH4 emission. The main objective of this study was to evaluate the potential of NT and WCC on GHG balance and emissions intensity in paddy rice fields in southern Brazil.

MATERIALS AND METHODS

Site description and experiment design and conduction

The study was based on a long-term field experiment (20 years), established in 1996, conducted in Rice Experimental Station of Rio Grandense Rice Institute, in Cachoeirinha, Rio Grande do Sul State, Southern Brazil (29° 55’ 30” S, 50° 58’ 21” O, 7 m a.s.l). The climate is humid subtropical and classified as Cfa, according to the Köppen classification system, with a mean annual temperature and precipitation of 19.3 °C and 1434 mm, respectively ( Climate data, 2018Climate Data . Dados climáticos para cidades mundiais [ internet ]. Climate-Data. Org ; 2018 . Available from: https://pt.climate-data.org/america-do-sul/brasil/rio-grande-do-sul/cachoeirinha-4501 .
https://pt.climate-data.org/america-do-s...
). The loamy soil is classified as Gleysol (WRB/FAO) ( Gleissolo Háplico Distrófico típico ). The physical and chemical soil properties are described in table 1 .

Table 1
Soil physicochemical characterization before the beginning of the experiment

The experiment started in the 1996/97 crop season to evaluate the adaptation and improvements in soil quality with the long-term use of winter cover crops (WCC) associated with no-tillage (NT). Prior to the establishment of this experiment in the area, experiments were carried out with irrigated rice, under conventional tillage and fallow in the autumn-winter period. Irrigated rice ( Oryza sativa L.) was the summer crop in the whole experiment. Five treatments consisted of different combination of tillage system and cover crops or fallow, as follow: ( i ) conventional tillage (CT) and ( ii ) no-tillage (NT), both combined with winter fallow, and ( iii-v ) NT combined with three winter cover crops (WCC) - ryegrass (Lolium multiflorum L.), white oat (Avena sativa L.), and birdsfoot trefoil ( Lotus corniculatus L.). The treatments were applied in plots of 5 × 8.8 m, and the distribution of four replicates followed a complete randomized block design. The WCC were sowed in April through surface rice crop residues and grown without irrigation. The seed rates for ryegrass, white oat and birdsfoot trefoil were 80, 20 and 8 kg ha-1 , respectively. In treatments with fallow, only weeds developed in the plots.

Conventional tillage and NT systems were applied in spring, usually at the end of September. The CT consisted in plowing and disking at 0.25 and 0.07 m, respectively. These operations buried the harvest residues of rice and weeds into soil. In NT system, soil was not disturbed, and rice, weed and WCC residues were maintained on soil surface. In NT system, weeds control and management of WCC were performed by desiccation with glyphosate (Roundup® 3.5 L p.c. ha-1) about 30 days before rice sowing.

Every year, the rice crop (cultivar IRGA 424 RI) was sowed at a seed rate of 100 kg ha-1 in the first half of October. The mean rates of P2 O5 and K2 O applied at rice sowing were 108 and 68 kg ha-1. Nitrogen fertilization rate was applied at 150 kg ha-1 split in two times, with 66 % applied in V4 and 34 % in R0 stages ( CQFS-RS/SC, 2004Comissão de Química e Fertilidade do Solo - CQFS-RS/SC . Manual de calagem e adubação para os Estados do Rio Grande do Sul e de Santa Catarina . 10 . ed. Porto Alegre : Sociedade Brasileira de Ciência do Solo - Núcleo Regional Sul ; 2004 . ; Sosbai, 2016). Weed control was carried out in the pre-emergence rice period using clomazone herbicide (Gamit® 1.2 L ha-1 ) and glyphosate (Roundup® 2.0 L ha-1 ). Post rice emergence, cyhalophope herbicide (Clincher® 1.7 L ha-1) and penoxulan (Ricer® 0.25 L ha-1 ) were used. Pest control was carried out with neonicotinoid-pyrethroid insecticide (Engeo Pleno® 0.2 L ha-1) in R0. Irrigation by flooding started in V4 developing stage of plants just after the first N application, and a water layer of 0.05-0.07 m was maintained until rice maturation, when the water supply was cut.

Evaluation of biomass addition by cover crops, weeds and rice

Aboveground biomass of WCC and weeds in September (2017) and rice in March (2017/18) at the flowering stage were evaluated by sampling an area of 0.5 m2 per plot at the beginning of the flowering stage. Biomass samples were oven dried (forced air at 50 °C) until constant mass, and the contribution of roots was considered as 30 % of shoot addition by WCC or weeds ( Zanatta et al., 2007Zanatta JA , Bayer C , Dieckow J , Vieira FCB , Mielniczuk J . Soil organic carbon accumulation and carbon costs related to tillage, cropping systems and nitrogen fertilization in a subtropical Acrisol . Soil Till Res . 2007 ; 94 : 510 - 9 . https://doi.org/10.1016/j.still.2006.10.003
https://doi.org/10.1016/j.still.2006.10....
) and rice ( Insalud et al., 2006Insalud N , Bell RW , Colmer TD , Rerkasem B . Morphological and physiological responses of rice ( Oryza sativa ) to limited phosphorus supply in aerated and stagnant solution culture . Ann Bot . 2006 ; 98 : 995 - 1004 . https://doi.org/10.1093/aob/mcl194
https://doi.org/10.1093/aob/mcl194...
). Five subsamples were collected per plot.

Evaluation of rice yield

Rice grain yield evaluation were performed in 2017/2018 crop seasons through a Wintersteiger mechanized harvester and were obtained by extrapolating the yield harvested in the useful area of each plot to one hectare and fitting the grain moisture to 130 g kg-1 .

Evaluation of CH 4 and N 2 O fluxes and calculation of seasonal emissions

Air samplings were conducted on a weekly basis during the flooded rice season (spring–summer) using the static closed chamber method ( Bayer et al., 2014Bayer C , Costa FS , Pedroso GM , Zschornack T , Camargo ES , Lima MA , Frigheto RTS , Gomes J , Marcolin E , Macedo VRM . Yield-scale greenhouse gas emissions from flood irrigated rice under long-term conventional tillage and no-till systems in a Humid Subtropical climate . Field Crop Res . 2014 ; 162 : 60 - 9 . https://doi.org/10.1016/j.fcr.2014.03.015
https://doi.org/10.1016/j.fcr.2014.03.01...
). Each chamber consisted of an aluminum base 0.60 m long × 0.60 m wide × 0.20 m high and an aluminum top of the same size, totaling a volume of 72 L of air per chamber. The bases were driven 0.05 m deep into the soil before permanent flooding in the rice season and after the rice harvest in the non-rice season and left in the soil throughout the seasons.

Each base had an open bottom and sealable channels on the sides to facilitate the free-flowing of irrigation water in the rice season. The latter was sealed during air sampling events. Each base covered three rows of rice plants. In the rice season, additional 0.20 or 0.30 m aluminum extensors were stacked on the bases as the plants grew taller. The chamber volume was considered in estimating all GHG emissions. Each chamber top had a rubber septum sampling port, a stainless-steel thermometer, and a battery operated fan to circulate and homogenize air within the chamber ( Bayer et al., 2014Bayer C , Costa FS , Pedroso GM , Zschornack T , Camargo ES , Lima MA , Frigheto RTS , Gomes J , Marcolin E , Macedo VRM . Yield-scale greenhouse gas emissions from flood irrigated rice under long-term conventional tillage and no-till systems in a Humid Subtropical climate . Field Crop Res . 2014 ; 162 : 60 - 9 . https://doi.org/10.1016/j.fcr.2014.03.015
https://doi.org/10.1016/j.fcr.2014.03.01...
). Chamber closing and initial air sampling were started at 9:00 am and followed by five air samplings 5 min apart ( Minamikawa et al., 2012Minamikawa K , Yagi K , Tokida T , Sander BO , Wassmann R . Appropriate frequency and time of day to measure methane emissions from an irrigated rice paddy in Japan using the manual closed chamber method . Greenh Gas Meas Manag . 2012 ; 2 : 118 - 28 . https://doi.org/10.1080/20430779.2012.729988
https://doi.org/10.1080/20430779.2012.72...
; Bayer et al., 2014Bayer C , Costa FS , Pedroso GM , Zschornack T , Camargo ES , Lima MA , Frigheto RTS , Gomes J , Marcolin E , Macedo VRM . Yield-scale greenhouse gas emissions from flood irrigated rice under long-term conventional tillage and no-till systems in a Humid Subtropical climate . Field Crop Res . 2014 ; 162 : 60 - 9 . https://doi.org/10.1016/j.fcr.2014.03.015
https://doi.org/10.1016/j.fcr.2014.03.01...
). Air samples were withdrawn with polypropylene syringes, transferred to the Biogeochemical Laboratory at UFRGS, and analyzed for CH4 and N2 O on the same day in a gas chromatographer (Shimadzu Corp. 2014) equipped with flame ionization (250 °C) and electron capture (325 °C) detectors. Methane and N2 O fluxes were calculated according to equation 1 .

f = Δ Q Δ t P V R T M A Eq. 1

in which: f is the gas production rate (g m-2 h-1 ); Δ Q/ Δ t is the ratio of the change in gas concentration (mol h-1 ); P is the atmospheric pressure in the chamber (1 atm); V is the chamber volume (L); R is the ideal gas constant (0.0825 atm L mol-1 K-1 ); T is the chamber temperature (K); M is the gas molar mass (g mol-1 ); and A is the chamber basal area (m2 ).

The flux rate of GHG, as estimated from air samples collected from 9:00 to 11:00 am, was used as a measure of mean daily flux ( Costa et al., 2008Costa FS , Bayer C , Zanatta JA , Mielniczuk J . Estoque de carbono orgânico no solo e emissões de dióxido de carbono influenciados por sistemas de manejo no sul do Brasil . Rev Bras Cienc Solo . 2008 ; 32 : 323 - 32 . https://doi.org/10.1590/S0100-0683200800010030
https://doi.org/10.1590/S0100-0683200800...
). Seasonal emissions (rice and non-rice periods) were calculated by trapezoidal interpolation of the daily CH4 and N2 O flux rates throughout each period ( Bayer et al., 2014Bayer C , Costa FS , Pedroso GM , Zschornack T , Camargo ES , Lima MA , Frigheto RTS , Gomes J , Marcolin E , Macedo VRM . Yield-scale greenhouse gas emissions from flood irrigated rice under long-term conventional tillage and no-till systems in a Humid Subtropical climate . Field Crop Res . 2014 ; 162 : 60 - 9 . https://doi.org/10.1016/j.fcr.2014.03.015
https://doi.org/10.1016/j.fcr.2014.03.01...
).

Soil sampling, organic C analysis and calculation of stocks

In September 2015, soil samples of the 0.00-0.025, 0.025-0.05, 0.05-0.075, 0.075-0.10, 0.10-0.15, 0.15-0.20, 0.20-0.30 and 0.30-0.40 m layers were collected before rice sowing the rice (i.e., 18 years after the experiment was started). Trenches were dug manually to allow the assessment of soil bulk density using the volumetric ring method ( Blake and Hartge, 1986Blake GR , Hartge KH . Bulk density . In: Klute A , editor . Methods of soil analysis: Part 1 Physical and mineralogical methods . Madison : SSSA ; 1986 . p. 363 - 75 . https://doi.org/10.2136/sssabookser5.1.2ed.c14
https://doi.org/10.2136/sssabookser5.1.2...
). In the same layers as those sampled for bulk density assessment, soil samples were collected with a spatula and then air-dried and ground to ≤2 mm in a Marconi 330 grinder.

Approximately 20 g of soil was further ground to ≤0.025 mm in an agate mortar and analyzed for C by dry combustion in a Shimadzu VCSH analyzer. Soil organic carbon stocks were calculated for the whole 0.00-0.40 m profile. The annual rate of soil organic C accumulation was calculated as the ratio of the difference between soil organic C stocks in the treatments and the reference system (CT fallow) and the duration time of the experiment when the soil was sampled (18 years).

Net balance of GHG emissions and emissions intensity

The net balance of GHG emissions for each management system was calculated according to equation 2 .

Net balance of GHG = N 2 O × 298 + C H 4 × 34 S O C × 3.67 Eq. 2

in which: N2 O and CH4 are the seasonal emissions of N2 O and CH4 properly converted into CO2 equivalent (CO2 eq ) after considering the global warming potentials (298 for N2 O and 34 for CH4, according to the IPCC (2018)Intergovernmental Panel on Climate Change - IPCC . Global Warming of 1.5°C. An IPCC Special Report on the impacts of global warming of 1.5°C above pre-industrial levels and related global greenhouse gas emission pathways, in the context of strengthening the global response to the threat of climate change, sustainable development, and efforts to eradicate poverty . Genebra : IPCC ; 2018 . Available from: https://www.researchgate.net/profile/Peter-Marcotullio/publication/330090901_Sustainable_development_poverty_eradication_and_reducing_inequalities_In_Global_warming_of_15C_An_IPCC_Special_Report/links/6386062b48124c2bc68128da/Sustainable-development-poverty-eradication-and-reducing-inequalities-In-Global-warming-of-15C-An-IPCC-Special-Report.pdf .
https://www.researchgate.net/profile/Pet...
; Δ SOC x 3.67 is the annual change in soil organic carbon (SOC) stock to 0.40 m depth converted to CO2 amounts ( Mosier et al., 2005Mosier AR , Halvorson AD , Peterson GA , Sherrod L . Measurements of net global warming potential in three agroecosystems . Nutr Cycl Agroecosys . 2005 ; 72 : 67 - 76 . https://doi.org/10.1007/s10705-004-7356-0
https://doi.org/10.1007/s10705-004-7356-...
). Emissions intensity was calculated by the ratio between the balance of net GHG emissions (Mg CO2 eq ha-1 ) and the average grain yield of rice (Mg), aiming to infer the intensity of GHG emission per unit of rice grain yield.

Statistical Analysis

The results were checked for variance normality and homoscedasticity with the Shapiro-Wilk and Oneill & Matthews tests, respectively, and appropriate data transformations were performed when assumptions were violated. Seasonal CH4 -C and N2 O-N emissions, the balance of GHG, rice grain yield and emissions intensity were submitted to analysis of variance. When significant at the 5 % level, the differences among treatments were subjected to Tukey’s post-hoc test at the 5 % significance level. The MIXED procedure was used to compare the effects of soil management in winter on GHG, soil organic C, and rice yield. Statistical procedures used soil winter management as a fixed factor, and blocks and experimental errors as random variables. All analyses were performed with SAS® v. 9.4 (Statistical Analysis System Institute, Cary, NC, USA).

RESULTS

Rice grain yield and annual input of biomass

Rice grain yield was not influenced by tillage systems nor by WCC ( Table 2 ), ranging from 8.2 Mg ha-1 in CT-fallow to 8.7 Mg ha-1 in NT- birdsfoot trefoil ( Table 3 ). A mean rice yield of 8.4 Mg ha-1 was attained across soil management systems ( Table 3 ).

Table 2
Analysis of variance data (values of calculated F and P of analyzed variables) for seasonal emissions of CH4 and N2O, stock and accumulation rate of soil organic carbon (SOC), net balance of GHG (net GHG), rice yield and emissions intensity in a subtropical Gleysol subjected to flooding rice production in Southern Brazil
Table 3
Rice grain yield, biomass input by rice, cover crops and weeds in different winter managements (fallow or cover crops) combined with conventional tillage (CT) or no-tillage (NT) in a subtropical Gleysol subjected to flooding rice production in Southern Brazil

Annual biomass input ranged between 10.4 and 16.8 Mg ha-1 ( Table 3 ). In the winter, biomass input ranged from 0.7 (CT) to 1.6 Mg ha-1 (NT) in the systems under fallow, while in the systems under cover crops the biomass input increased to 5.4 Mg ha-1 on average, ranging from 3.9 to 6.8 Mg ha-1 ( Table 3 ). The highest biomass input was observed for rice, which accounted for 86-93 % of total annual biomass input in fallow systems in CT and NT, and 60-72 % for WCC systems.

Seasonal CH 4 and N 2 O emissions

Seasonal CH4 -C emissions were affected by management systems ( Figure 1 ) and ranged from 359 to 472 kg ha-1 ( Figure 1 ). Greater CH4 -C emission was observed in CT with winter fallow compared to NT with winter fallow (74 kg CH4 -C ha-1 of difference) ( Figure 1a ). Under NT, seasonal soil CH4 -C emission was similar comparing WCC and fallow, with exception of white oat that presented a seasonal soil CH4 -C emission slightly higher (441 kg ha-1 ) in comparison to the others WCC (366 kg ha-1 , on average) ( Figure 1a ).Seasonal soil N2 O-N emissions ranged from 0.25 to 0.87 kg ha-1 , and were not influenced by tillage and WCC (Tables 2 and 3 ; Figure 1b ).

Figure 1
Seasonal emissions of (a) methane (CH4) and (b) nitrous oxide (N2O) in a subtropical Gleysol subjected to different soil winter management (fallow or cover crops) combined with conventional tillage (CT) or no-tillage (NT) in Southern Brazil. Vertical lines denote the mean standard deviation. Different letters on the bars indicate a significant difference between treatments by the Test of Skott-Knott at 5 % level. ns: no significant.

Soil organic C stocks and annual accumulation rates

Soil organic C content was influenced by the management systems ( Table 2 ), mainly in the surface soil layers (0.00-0.025 and 0.025-0.05 m), where NT and WCC favored greater SOC content than CT and winter fallow ( Figure 2a ). Considering 0.00-0.40 m layer, lower SOC stocks were observed in CT (47.0 Mg ha-1 ) than NT (53.3 Mg ha-1 ), both combined with winter fallow ( Figure 2b ). Under NT, the increase in biomass input by WCC did not promote an increase in SOC stocks compared to winter fallow. Compared to CT, NT combined with fallow and WCC presented annual accumulation rates of SOC ranging from 0.45 to 0.65 Mg ha-1 yr-1 ( Table 4 ).

Figure 2
Soil organic C (SOC) contents in soil profile (a) and stocks at 0.00-0.40 m soil layer (b) of a Gleysol subjected to different soil winter managements (fallow or cover crops) combined with conventional tillage (CT) or no-tillage (NT) in southern Brazil. Vertical lines denote the standard deviation. Different letters on the bars indicate a significant difference between treatments by the Test of Skott-Knott at 5 % level. ns: no significant.

Table 4
Seasonal methane (CH4 ) and nitrous oxide (N2O) emissions, annual accumulation rate of SOC, net balance of GHG (net GHG) and emissions intensity in a flooded rice field on a Gleysol subjected to winter managements (fallow or cover crops) combined with conventional tillage (CT) and no-tillage (NT) in Southern Brazil

Net balance of GHG and emissions intensity

Net balance and emissions intensity GWP were influenced by soil tillage and WCC in the long term ( Table 2 ). Considering the three main GHG (CO2 , CH4 and N2 O) emitted from the rice field, total GHG emissions ranged from 14.8 (Ryegrass-NT) to 21.7 (Fallow-CT) Mg CO2 eq ha-1 among soil management systems ( Table 4 ). In comparison to the traditional management system (CT combined with winter fallow), NT adoption decreased GHG emissions by 5.2 Mg CO2 eq ha-1 when combined with winter fallow, and by 3.7-6.8 Mg CO2 eq ha-1 when combined with WCC ( Table 4 ).

Emissions intensity was higher in CT (2.6 Mg CO2 eq Mg-1 grain rice) than in NT (1.9 Mg CO2 eq Mg-1 grain rice), both combined with winter fallow. No effect of WCC was observed on emissions intensity in NT soil, ranging between 1.8 and 2.2 Mg CO2 eq Mg-1 grain rice ( Table 4 ).

DISCUSSION

The positive impact of NT system reduced between 15 and 28 % of soil CH4 emissions in comparison to the traditional CT combined with winter fallow, which is in agreement with previous studies that reported a decrease from 21 % in Southern Brazil ( Bayer et al., 2014Bayer C , Costa FS , Pedroso GM , Zschornack T , Camargo ES , Lima MA , Frigheto RTS , Gomes J , Marcolin E , Macedo VRM . Yield-scale greenhouse gas emissions from flood irrigated rice under long-term conventional tillage and no-till systems in a Humid Subtropical climate . Field Crop Res . 2014 ; 162 : 60 - 9 . https://doi.org/10.1016/j.fcr.2014.03.015
https://doi.org/10.1016/j.fcr.2014.03.01...
) and from 22 to 27 % in China ( Zhang et al., 2015Zhang Y , Sheng J , Wang Z , Chen L , Zheng J . Nitrous oxide and methane emissions from a Chinese wheat–rice cropping system under different tillage practices during the wheat-growing season . Soil Till Res . 2015 ; 146 : 261 - 9 . https://doi.org/10.1016/j.still.2014.09.019
https://doi.org/10.1016/j.still.2014.09....
; Zhao et al. , 2016). This lower CH4 emission in NT has been likely attributed to the no residues incorporation into the soil. These residues are a source of labile C readily available for methanogenic microorganisms that are highly active in subsurface soil layers compared to surface layers ( Wang et al., 1993Wang ZP , Delaune RD , Patrick Jr WH , Masscheleyn PH . Soil redox and pH effects on methane production in a flooded rice soil . Soil Sci Soc Am J . 1993 ; 57 : 382 - 5 . https://doi.org/10.2136/sssaj1993.03615995005700020016x
https://doi.org/10.2136/sssaj1993.036159...
; Silva et al., 2011Silva LS , Griebeler G , Mortele DF , Bayer C , Zschornack T , Pocojeski E . Dinâmica da emissão de metano em solos sob cultivo de arroz irrigado no Sul do Brasil . Rev Bras Cienc Solo . 2011 ; 35 : 473 - 81 . https://doi.org/10.1590/S0100-06832011000200016
https://doi.org/10.1590/S0100-0683201100...
; Zschornack et al., 2011Zschornack T , Bayer C , Zanatta JA , Vieira FCB , Anghinoni I . Mitigation of methane and nitrous oxide emissions from flood-irrigated rice by no incorporation of winter crops residues into the soil . Rev Bras Cienc Solo . 2011 ; 5 : 623 - 34 . https://doi.org/10.1590/S0100-06832011000200031
https://doi.org/10.1590/S0100-0683201100...
). The WCC, when associated with NT, increased the CH4 emission with fallow, since an expressive biomass input was observed (3.9-6.8 vs. 1.6 Mg ha-1 ).

Despite the wide range of soil N2 O-N emissions (0.25-0.86 kg ha-1 ) among soil management systems, the observed difference in seasonal N2 O emissions was not statistically significant (p>0.05) and cannot be attributed to the management systems ( Table 2 ). The magnitude of N2 O emissions is similar to that observed in previous studies conducted in paddy rice fields ( Bayer et al., 2014Bayer C , Costa FS , Pedroso GM , Zschornack T , Camargo ES , Lima MA , Frigheto RTS , Gomes J , Marcolin E , Macedo VRM . Yield-scale greenhouse gas emissions from flood irrigated rice under long-term conventional tillage and no-till systems in a Humid Subtropical climate . Field Crop Res . 2014 ; 162 : 60 - 9 . https://doi.org/10.1016/j.fcr.2014.03.015
https://doi.org/10.1016/j.fcr.2014.03.01...
; Zschornack et al., 2018)Zschornack T , Rosa CM , Reis CES , Pedroso GM , Camargo ES , Santos DC , Boeni M , Bayer C . Soil CH4and N2O emissions from rice paddy fields in Southern Brazil as affected by crop management levels: A three-year fiels study . Rev Bras Cienc Solo . 2018 ; 42 : e0170306 . https://doi.org/10.1590/18069657rbcs20170306
https://doi.org/10.1590/18069657rbcs2017...
, which have been attributed to the temporal and spatial variability that add up to the complex combination of the several soil variables encompassed in soil N2 O production ( Hénault et al., 2012)Hénault C , Grossel A , Mary B , Roussel M , Léonard J . Nitrous oxide emission by agricultural soils: a review of spatial and temporal variability for mitigation . Pedosphere . 2012 ; 22 : 426 - 33 . https://doi.org/10.1016/S1002-0160(12)60029-0
https://doi.org/10.1016/S1002-0160(12)60...
.

No-tillage increased SOC stocks in this lowland soil, a similar tendency observed in previous studies in Southern Brazil ( Nascimento et al., 2009Nascimento PC , Bayer C , Silva Netto LF , Vian AC , Viero F , Macedo VRM , Marcolin E . Sistemas de manejo e a matéria orgânica de solo de várzea com cultivo de arroz . Rev Bras Cienc Solo . 2009 ; 33 : 1821 - 7 . https://doi.org/10.1590/S0100-06832009000600030
https://doi.org/10.1590/S0100-0683200900...
; Rosa et al., 2011Rosa CM , Castilhos RVM , Pauletto EA , Pillon CN , Leal OA . Conteúdo de carbono orgânico em Planossolo háplico sob sistemas de manejo do arroz irrigado . Rev Bras Cienc Solo . 2011 ; 35 : 1769 - 76 . https://doi.org/10.1590/S0100-06832011000500031
https://doi.org/10.1590/S0100-0683201100...
; Carlos et al., 2022Carlos FS , Camargo FAO , Marcolin E , Veloso MG , Fernandes RS , Bayer C . No-tillage promotes C accumulation in soil and a slight increase in yield stability and profitability of rice in subtropical lowland ecosystems . Soil Res . 2022 ; 60 : 601 - 9 . https://doi.org/10.1071/SR21185
https://doi.org/10.1071/SR21185...
), and other countries such as Uruguay ( Terra et al., 2006Terra JA , Garcia-Préchac F , Salvo L , Hernández J . Soil use intensity impacts n total and particulate soil organic matter in no-till crop-pasture rotations under direct grazing . Adv Geo Ecol . 2006 ; 38 : 233 - 41 . ) and China ( Rui and Zhang, 2010Rui W , Zhang W . Effect size and duration of recommended management practices on carbon sequestration in paddy field in Yangtze Delta Plain of China: A meta-analysis . Agr Ecosyst Environ . 2010 ; 135 : 199 - 205 . https://doi.org/10.1016/j.agee.2009.09.010
https://doi.org/10.1016/j.agee.2009.09.0...
). The annual accumulation rates of SOC observed in this study (0.45 to 0.65 Mg ha-1 ) were similar to those observed in upland soils considering the time of NT adoption, clay content and soil depth ( Bayer et al., 2006Bayer C , Martin-Neto L , Mielniczuk J , Pavinato A , Dieckow J . Carbon sequestration in two Braziliam Cerrado soils under no-till . Soil Till Res . 2006 ; 86 : 237 - 45 . https://doi.org/10.1016/j.still.2005.02.023
https://doi.org/10.1016/j.still.2005.02....
; Zanatta et al., 2007Zanatta JA , Bayer C , Dieckow J , Vieira FCB , Mielniczuk J . Soil organic carbon accumulation and carbon costs related to tillage, cropping systems and nitrogen fertilization in a subtropical Acrisol . Soil Till Res . 2007 ; 94 : 510 - 9 . https://doi.org/10.1016/j.still.2006.10.003
https://doi.org/10.1016/j.still.2006.10....
; Veloso et al., 2018Veloso MG , Angers DA , Tiecher T , Giacomini S , Dieckow J , Bayer C . High carbon sequestration in subtropical soil profiles under no-tillage with legume cover crop . Agr Ecosyst Environ . 2018 ; 268 : 15 - 23 . https://doi.org/10.1016/j.agee.2018.08.024
https://doi.org/10.1016/j.agee.2018.08.0...
). Even though these results suggest a similar impact of no soil disturbance on soil organic matter stabilization in lowland and upland soils, the importance of mechanisms encompassed on SOC stabilization may differ. In lowland soils cultivated with irrigated rice, flooding weakens and favors the disruption of aggregates, with a lower impact of NT on the physical protection of SOC ( Nascimento et al., 2009Nascimento PC , Bayer C , Silva Netto LF , Vian AC , Viero F , Macedo VRM , Marcolin E . Sistemas de manejo e a matéria orgânica de solo de várzea com cultivo de arroz . Rev Bras Cienc Solo . 2009 ; 33 : 1821 - 7 . https://doi.org/10.1590/S0100-06832009000600030
https://doi.org/10.1590/S0100-0683200900...
). However, this effect must be partially off-set by the higher magnitude of organo-mineral interactions in flooded soils ( Hanke and Dick, 2017Hanke D , Dick DP . Organic matter stocks and the interactions of humic substances with metals in Araucaria moist forest soil with humic and histic horizons . Rev Bras Cienc Solo . 2017 ; 41 : e0160368 . https://doi.org/10.1590/18069657rbcs20160368
https://doi.org/10.1590/18069657rbcs2016...
). On the other hand, WCC had no effect on SOC stocks in NT soil, despite the higher annual biomass input compared to winter fallow. Annual variability of winter biomass production can help to explain this lack of effect of WCC on SOC stocks, since we have evaluated the residue input during only one year.

The GHG balance in rice production systems is represented by the net GHG, which is the sum of seasonal CH4 and N2 O emissions and CO2 emissions for which annual net change in SOC was used as a proxy ( Piva et al., 2012Piva JT , Dieckow J , Bayer C , Zanatta JA , Moraes A , Pauletti V , Tomazi M , Pergher M . No-till reduces global warming potential in a subtropical Ferralsol . Plant Soil . 2012 ; 361 : 359 - 73 . https://doi.org/10.1007/s11104-012-1244-1
https://doi.org/10.1007/s11104-012-1244-...
). Across winter managements, NT system had lower net GHG than CT combined with winter fallow. These results were mainly related to the decrease of seasonal soil CH4 -C emissions and also to the atmospheric CO2 -C sequestration in soil organic matter. The CH4 -C was the stronger component of net GHG, representing more than 85 % of total GHG emissions, which is widely reported for flooded rice fields ( Kim et al., 2012Kim SY , Lee CH , Gutierrez J , Kim PJ . Contribuition of winter cover crop amendments on global warming potential in rice paddy soil during cultivation . Plant Soil . 2012 ; 366 : 273 - 86 . https://doi.org/10.1007/s11104-012-1403-4
https://doi.org/10.1007/s11104-012-1403-...
; Bayer et al., 2014Bayer C , Costa FS , Pedroso GM , Zschornack T , Camargo ES , Lima MA , Frigheto RTS , Gomes J , Marcolin E , Macedo VRM . Yield-scale greenhouse gas emissions from flood irrigated rice under long-term conventional tillage and no-till systems in a Humid Subtropical climate . Field Crop Res . 2014 ; 162 : 60 - 9 . https://doi.org/10.1016/j.fcr.2014.03.015
https://doi.org/10.1016/j.fcr.2014.03.01...
, 2015Bayer C , Zschornack T , Pedroso GM , Rosa CM , Camargo ES , Boeni M , Marcolin E , Reis CES , Santos DC . A seven-year study on the effects of fall soil tillage on yield-scale greenhouse gas emission from flood irrigated rice in a humid subtropical climate . Soil Till Res . 2015 ; 145 : 118 - 25 . https://doi.org/10.1016/j.still.2014.09.001
https://doi.org/10.1016/j.still.2014.09....
). Across winter cropping systems, SOC accumulation in NT soil was responsible by 12 % of GHG mitigation in comparison to CT soil.

The lack of effect of NT and WCC on rice grain yield has been observed in other studies based on field experiments in Southern Brazil ( Bayer et al., 2014Bayer C , Costa FS , Pedroso GM , Zschornack T , Camargo ES , Lima MA , Frigheto RTS , Gomes J , Marcolin E , Macedo VRM . Yield-scale greenhouse gas emissions from flood irrigated rice under long-term conventional tillage and no-till systems in a Humid Subtropical climate . Field Crop Res . 2014 ; 162 : 60 - 9 . https://doi.org/10.1016/j.fcr.2014.03.015
https://doi.org/10.1016/j.fcr.2014.03.01...
; Zschornack et al., 2016Zschornack T , Rosa CM , Camargo ES , Reis CES , Schoenfeld R , Cimélio Bayer C . Impact of cover crops and soil drainage in CH4and N2O emissions under irrigated rice cultivation . Pesq Agropec Bras . 2016 ; 51 : 1163 - 71 . https://doi.org/10.1590/S0100-204X2016000900016
https://doi.org/10.1590/S0100-204X201600...
) and in other regions of the world ( Bijay-Singh et al., 2008Bijay-Singh , Shan YH , Johnson-Beebout SE , Yadvinder-Singh , Buresh RJ . Crop residue management for lowland rice-based cropping systems in Asia . Adv Agron . 2008 ; 98 : 117 - 99 . https://doi.org/10.1016/S0065-2113(08)00203-4
https://doi.org/10.1016/S0065-2113(08)00...
; Huang et al., 2015Huang M , Zhou X , Cao F , Xia B , Zou Y . No-tillage effect on rice yield in China: A meta-analysis . Field Crop Res . 2015 ; 183 : 126 - 37 . https://doi.org/10.1016/j.fcr.2015.07.022
https://doi.org/10.1016/j.fcr.2015.07.02...
). This is due to the supply of all the demanded nutrients for the crop by fertilization summed to flooding conditions, which reduces the redox potential of the soil and contributes to increasing the content of most nutrients in the soil solution ( Sousa et al., 2021Sousa RO , Carlos FS , Silva LS , Scivittaro WB , Ribeiro PL , Lima CLR . No-tillage for flooded rice in Brazilian subtropical paddy fields: history, challenges, advances and perspectives . Rev Bras Cienc Solo . 2021 ; 45 : e0210102 . https://doi.org/10.36783/18069657rbcs20210102
https://doi.org/10.36783/18069657rbcs202...
), not reflecting the impact of soil management. This is a different result than that observed in uplands, where water availability for crops has been the main variable related to the increase of crop yields in rainfed no-till cropping systems ( Franchini et al., 2012Franchini JC , Debiasi H , Balbinot Junior AA , Tonon BC , Farias JRB , Oliveira MCN , Torres E . Evolution of crop yields in different tillage and cropping systems over two decades in southern Brazil . Field Crop Res . 2012 ; 137 : 178 - 85 . https://doi.org/10.1016/j.fcr.2012.09.003
https://doi.org/10.1016/j.fcr.2012.09.00...
).

Higher emissions intensity under CT with winter fallow than under NT combined with winter cover crops indicated that NT could decrease 26 % of GHG emissions for each 1 Mg of grain rice produced. This result reinforces the NT as a potential tool to increase the sustainability of irrigated rice production in subtropical ecosystems. In general, WCC did not affect net balance of GHG and emissions intensity in NT soil, which is associated to the fact that although favoring SOC sequestration by increasing crop residues input, net GHG and emissions intensity was offset by also favoring CH4 -C emissions. This effect was clearly observed in the system with white oat, where the increase of SOC stock was compensated by the high CH4 -C emissions, compromising the effect of mitigation of NT.

This study observed the importance of adopting no-tillage as a soil management strategy that aims to increase SOC stocks and reduce the intensity of CO2 equivalent emissions, being an important alternative for the production of irrigated rice in subtropical ecosystems like the south of Brazil.

CONCLUSIONS

No-tillage mitigates net GHG emissions compared with conventional tillage in lowland soils cultivated with flooded rice, which is mainly associated with decreased soil CH4 -C emissions and increased SOC sequestration. The decrease of CH4 -C emissions in no-tillage soils is also related to the maintenance of crop residues on soil surface with consequent lower exposure of labile C to the anaerobic environment favoring the reduction of the emission of this potent GHG. Winter cover crops have no clear impact on the net balance of GHG emissions and emissions intensity in NT soil, possibly because the soil C sequestration due to higher aboveground biomass was partially offset by increased CH4 -C emissions.

ACKNOWLEDGEMENTS

This study was funded by the National Institute of Science and Technology for a Low Carbon Agriculture (INCT-Low Carbon Agriculture) sponsored by CNPq (406635/2022-6) and Technological and Inovation Network for a Low Carbon Agriculture in Southern Brazil supported by FAPERGS (22/2551-0000392-3).

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APPENDIX A. SUPPLEMENTARY DATA

Supplementary data to this article can be found online at https://doi.org/10.1016/j.agsy.2018.01.030 .

Edited by

Editors: Carlos Eduardo Pellegrino Cerri 0000-0002-4374-4056 and Maurício Roberto Cherubin 0000-0001-7920-8362.

Publication Dates

  • Publication in this collection
    17 Apr 2023
  • Date of issue
    Mar 2023

History

  • Received
    01 Oct 2022
  • Accepted
    24 Jan 2023
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