ABSTRACT Global warming potential (GWP) of rice paddies depends on straw management. This study evaluated methane (CH4) and nitrous oxide (N2O) emissions and soil C stocks to determine GWP and yield-scaled GWP under different strategies and intensities of rice straw management in a subtropical climate. We hypothesized that decreasing soil management intensity and straw incorporation in the soil would reduce GWP. Methane fluxes were substantially higher during the rice growing season than in the off-season, while the opposite was observed for N2O fluxes. The cumulative emissions of CH4 during the growing season among the straw management strategies evaluated ranged from 165.8 to 586.0 kg ha-1. Annual CH4 emissions were lower when soil and straw received some type of management compared to no-tillage. Daily N2O fluxes ranged from -2.8 to 201.7 g ha-1 day-1; cumulative N2O emissions during the off-season ranged from 455.2 to 2816.5 g ha-1. During the off-season, strategies to reduce N2O emissions include post-harvest straw incorporation using a disc harrow, winter straw removal, and ryegrass cropping. Soil organic C stocks ranged from 35.96 to 38.36 Mg ha-1. Straw management using a disc harrow reduced soil organic C stocks, with more adverse effects than straw removal. Soil and rice straw management did not affect rice grain yield, with an average of 10.4 Mg ha-1. Methane emissions were the main component of GWP in all straw management systems. The contribution of N2O emissions to GWP was small and mostly (>85 %) determined by off-season emissions. Yield-scaled GWP ranged from 0.64 to 1.06 Mg CO2eq Mg-1 yield and was lower when soil and straw management systems occurred shortly after the rice harvest. Our results indicate that soil and straw management immediately after rice harvest reduces CH4 emissions, GWP, and yield-scaled GWP. (GWP CH (CH4 NO N O (N2O yieldscaled scaled climate offseason, offseason off season, 1658 165 8 165. 5860 586 0 586. ha1. ha1 ha 1. 1 notillage. notillage no tillage. tillage no-tillage 2.8 28 2 -2. 2017 201 7 201. ha- day1 day day-1 4552 455 455. 28165 2816 5 2816. postharvest post removal cropping 3596 35 96 35.9 3836 38 36 38.3 104 10 4 10. >85 85 (>8 % Yieldscaled Yield 064 64 0.6 106 06 1.0 COeq CO eq Mg1 Mg- (CH 16 58 2. -2 20 day- 45 281 359 3 9 35. 383 38. >8 (> 6 0. - > (

ABSTRACT Irrigated rice cultivation is an important source of greenhouse gas emissions. Among the main greenhouse gases, there are carbon dioxide, methane, and nitrous oxide, with the emission of each gas varying according to the management of the crop, cultivar and irrigation management. In this context, the present study aimed to quantify the partial global warming potential (pGWP) measured by CH4 and N2O emissions in conventional and hybrid cultivars under two irrigation management, as well as the relation with grain yield (pGWP/Y). For this, a field experiment was conducted during the 2016/17 and 2017/18 crop seasons, with an experimental design of randomized blocks in a factorial arrangement (2×4), with four replications using water and rice cultivars. The water was managed through permanent and intermittent irrigation, with one conventional cultivar (IRGA 424 RI) and three hybrid cultivars (XP 113, Titan CL and Lexus CL). The pGWP can be reduced by up to 18% depending on the cultivar used and 11.8% through the adoption of intermittent irrigation management. More than 90% of the pGWP is due to methane emission, and the management actions of the rice crop should be directed towards the mitigation of this gas. In relation to the pGWP/Y index, the cultivar XP 113 had presented the best results.

RESUMO: A decomposição de resíduos culturais é controlada pela composição química do tecido vegetal. O objetivo deste estudo foi avaliar as alterações que ocorrem nos componentes do tecido vegetal, separados pelo fracionamento de Van Soest, durante a decomposição de plantas de cobertura. A fração solúvel foi a primeira a ser liberada dos resíduos culturais, seguida pela celulose e hemicelulose. A lignina foi o componente dos resíduos culturais de menor degradação, sendo que em alguns resíduos culturais não foi possível detectar a degradação deste componente. A degradação dos principais componentes dos resíduos culturais (fração solúvel, celulose, hemicelulose e lignina) é determinada pela composição química e estrutural de cada uma destas frações.

ABSTRACT: Crop residues decomposition are controlled by chemical tissue components. This study evaluated changes on plant tissue components, separated by the Van Soest partitioning method, during cover crop decomposition. The Van Soest soluble fraction was the first to be released from the crop residues, followed by cellulose and hemicellulose. Lignin was the crop residue component that suffered the least degradation, and for certain crop residue types, lignin degradation was not detected. The degradation of the main components of crop residues (soluble fraction, cellulose, hemicellulose and lignin) is determined by the chemical and structural composition of each fraction.

Resumo: O objetivo deste trabalho foi avaliar a mineralização de carbono e nitrogênio no solo após a aplicação de compostos produzidos numa planta de compostagem automatizada, tendo-se utilizado dejetos líquidos de suínos (DLS), com e sem a adição de xisto retortado (XR) e dicianodiamida (DCD) durante a compostagem. Estudos laboratoriais foram conduzidos durante 180 dias, em dois solos com características contrastantes: Argissolo franco-arenoso e Latossolo argiloso, que foram manejados por mais de 10 anos em sistema plantio direto. Os compostos foram completamente misturados com os solos. A mineralização do C e do N do composto foi avaliada pela medição contínua do CO2 emitido e periódica do conteúdo de N mineral (NH4+ + NO3-) dos solos, respectivamente. A mineralização do C do composto sem a adição de XR e DCD foi maior no solo franco-arenoso (20.5%) do que no argiloso (13.9%). Similarmente, 19.4% do N total do composto foi mineralizado no solo franco-arenoso e 10.9% no solo argiloso. A presença do XR no composto reduziu a mineralização do C em 54%, comparado ao tratamento sem aditivos, no solo franco-arenoso e causou imobilização líquida de N em ambos os solos durante a incubação. A adição de DCD durante a compostagem dos DLS não afetou a mineralização do C e do N do composto em ambos os solos. A adição de XR durante a compostagem dos DLS favorece a retenção do C do composto no solo, principalmente no franco-arenoso, porém resulta em imobilização líquida de N.

Abstract: The objective of this work was to evaluate carbon and nitrogen mineralization in the soil after the application of composts produced in an automated composting plant, using pig slurry (PS) with and without the addition of retorted oil shale (ROS) and dicyandiamide (DCD) during composting. Laboratory studies were carried out for 180 days on two soils with contrasting characteristics: sandy-loam Typic Paludalf and clay Rhodic Hapludox, which were managed for more than 10 years under a no-tillage system. The composts were thoroughly mixed with the soils. The mineralization of the C and N from the compost was evaluated by measuring continuously CO2 emissions and periodically mineral N (NH4+ + NO3-) content in the soils, respectively. The mineralization of the C from the compost without ROS and DCD was higher in the sandy-loam soil (20.5%) than in the clay soil (13.9%). Similarly, 19.4% of the total N from the compost was mineralized in the sandy-loam soil and 10.9% in the clay soil. The presence of ROS in the compost reduced C mineralization by 54%, compared with the treatment without additives, in the sandy-loam soil and caused net N immobilization in both soils during incubation. The addition of DCD during PS composting did not affect the mineralization of the C and N from the compost in both soils. The addition of ROS during the composting of PS favors the retention of the C from the compost in the soil, especially in the sandy-loam one, but results in a net N immobilization.

ABSTRACT Little is known about the interaction between the inoculation of diazotrophic bacteria, the variety, and the substrate used in inoculated sugarcane seedling production. Bearing this in mind, the aim of this study was to evaluate the effects of diazotrophic bacteria inoculation, four sugarcane varieties and four different substrates on the growth and nitrogen accumulation of sugarcane seedlings. Parameters related to sprouting, height, and root growth, as well as nitrogen accumulation, were evaluated. The results indicate that inoculating sugarcane seedlings belonging to the following varieties: RB867515, RB92579, RB966928 and RB975932 with bacteria may increase sprouting speed index, height, root length, fresh and dry matter weight, as well as nitrogen accumulation, which has resulted in a more uniform stem diameter. However, the responses to inoculation differ from variety to variety and are also dependent on the substrate used with better results observed in the commercial substrate and the substrate mixtures containing a higher proportion of organic compost. Understanding the interaction between the variety and the substrate with the bacterial inoculation is essential to the success of the production of inoculated sugarcane seedlings.

RESUMO O objetivo do estudo foi avaliara dinâmica de decomposição de resíduos de culturas num pomar de pereiras no Brasil. Resíduos de aveia, nabo forrageiro, azevém e vegetação espontânea foram adicionados em sacos de decomposição depositados à superfície do solo nas linhas de cultivo das pereiras. Após 0, 21, 36, 56 e 136 dias, a matéria seca e os teores de carbono, lignina, celulose, componentes não estruturais e nitrogênio (N), fósforo (P), potássio (K), cálcio (Ca) e magnésio (Mg) foram determinados. Os resíduos de vegetação espontânea apresentaram o maior tempo de semi-vida em comparação com as culturas de cobertura cultivadas, enquanto os resíduos de aveia apresentaram as taxas de decomposição da matéria seca mais rápidas (2-3 vezes maior). O nabo forrageiro e o azevém apresentaram os maiores teores de matéria seca remanescente (26-36%) e a maior liberação de nutrientes. Os resíduos de nabo forrageiro e azevém liberaram 85 kg N ha-1, 67 kg P ha-1, 48 kg K ha-1, 16 kg Ca ha-1 e 9 kg Mg ha-1. O nabo forrageiro poderá beneficiar a nutrição mineral de fruteiras, enquanto a vegetação espontânea poderá contribuir para proteger o solo da erosão e para aumentar o teor de carbono orgânico acumulado no solo num longo prazo.

ABSTRACT Our objective was to evaluate the dynamics of decomposition of crop residues in a pear orchard in Brazil. Residues of oat, oilseed radish, ryegrass and spontaneous vegetation were placed in litter bags and deposited at surface soil in the inter-row spacing of pear trees. After 0, 21, 36, 56 and 136 days, the dry matter, carbon, lignin, cellulose, non-structural components, and nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) concentrations were determined. Spontaneous vegetation residues had the longest half residence time compared to the introduced cover crops, while oat residues presented faster dry matter decomposition rates (2-3 fold higher). Oilseed radish and ryegrass showed the highest final remaining dry matter (26-36%), and the largest nutrients release. Oilseed radish and ryegrass residues released 85 kg N ha-1, 67 kg P ha-1, 48 kg K ha-1, 16 kg Ca ha-1, and 9 kg Mg ha-1. Oilseed radish can potentially benefit mineral nutrition of fruit trees, whereas the spontaneous vegetation is recommended to protect the soil agains the erosion and to contribute to the soil organic carbon stock in the long term.

Resumo: O objetivo deste trabalho foi quantificar o efeito da inoculação de Azospirillum brasilense (estirpes Ab-V5 e Ab-V6) na produção de forragem, na fixação biológica de nitrogênio (FBN) e na recuperação de 15N-ureia pela gramínea forrageira 'Coastcross-1'. O experimento foi feito em arranjo fatorial 2 (com e sem inoculação) × 2 (sem fertilização nitrogenada e com 100 kg ha-1 de N por ano, na forma de ureia) × 7 (cortes). O método da abundância natural de 15N foi utilizado para determinar a FBN; para a recuperação de N-ureia, aplicou-se 15N-ureia marcada em microparcelas. As produções de forragem foram maiores nas gramíneas com inoculação, com 7,4 Mg ha-1 de matéria seca por ano, no tratamento sem N fertilizante, e 8,0 Mg ha-1 de matéria seca por ano no tratamento com 100 kg ha-1 de N por ano, o que mostra o efeito aditivo da inoculação e da fertilização nitrogenada. A contribuição da FBN foi de 23,0 e 53,8 kg ha-1 por ano para o tratamento sem fertilização de N, tanto nas plantas sem inoculação como naquelas com inoculação, respectivamente. A recuperação de 15N-ureia foi de 13,7 e 16,5 kg ha-1 por ano, para os tratamentos sem e com inoculação, respectivamente, o que corresponde a 13,7 e 16,5% do N-ureia aplicado. A inoculação com A. brasilense aumenta a produção de forragem e a contribuição da FBN para a nutrição nitrogenada de 'Coastcross-1', assim como a recuperação de N-ureia pela gramínea.

Abstract: The objective of this work was to quantify the inoculation effect of Azospirillum brasilense (Ab-V5 and Ab-V6 strains) on the forage yield, biological nitrogen fixation (BNF), and urea-15N recovery of the forage grass 'Coastcross-1'. The experiment was carried out in a 2 (with or without inoculation) × 2 (without N fertilizer and with 100 kg ha-1 N per year as urea) × 7 (cuts) factorial arrangement. The natural 15N abundance method was used to determine BNF; to determine urea-N recovery, 15N-labeled urea was applied in microplots. Forage yield was higher in grasses subjected to inoculation, with 7.4 Mg ha-1 dry matter per year, for the treatment without N fertilizer, and 8.0 Mg ha-1 dry matter per year for the treatment with 100 kg ha-1 N per year, respectively, which shows an additive effect of inoculation and N fertilization. The contribution of BNF was 23.0 and 53.8 kg ha-1 per year for the unfertilized treatment, both in uninoculated and inoculated plants, respectively. Urea-15N recovery was 13.7 and 16.5 kg ha-1 per year for uninoculated and inoculated treatments, respectively, corresponding to 13.7 and 16.5% of the urea-N applied. Inoculation with A. brasilense increases forage yield and the contribution of BNF to grass nutrition with N, as well as urea-N recovery by the forage grass.

ABSTRACT One of the challenges in rice areas is the sustainable post-harvest system, which involves using rice straw management and cover crop species. In this context, this study aimed to evaluate the emission of methane (CH4) and nitrous oxide (N2O) with the use of different post-harvest management of rice straw as well as with the combined use of ryegrass. A field experiment was conducted during the 2016 off-season and 2016/17 rice crop season with different post-harvest rice straw management: maintaining rice straw on the soil surface (No-tillage); incorporating straw into dry soil with a disc (Disc); incorporating straw into flooded soil with a roller crimper (Roller Crimper); maintaining rice straw on the soil surface with subsequent rolling of the soil with a roller (Roller). In each straw management, treatments with and without ryegrass were established. The results demonstrate that incorporating rice straw in flooded soil with a roller crimper increases CH4 emissions in the off-season, and used in combination with ryegrass, proved to be the most significant contributor to partial global warming potential. Most annual N2O emissions occur in the off-season for all management treatments, especially for the no-tillage treatment, which showed increased emissions when combined with the use of ryegrass. However, as global warming potential is influenced mainly by emissions of CH4, the no-tillage system showed the best mitigation potential on greenhouse gas emissions.

RESUMO O estudo foi desenvolvido para avaliar o fornecimento de nitrogênio (N) à rúcula através de compostos obtidos por compostagem automatizada de dejetos líquidos de suínos (DLS). Durante a compostagem, xisto retortado (XR) e dicianodiamida (DCD) foram adicionados aos DLS para mitigar as perdas gasosas de N. O estudo foi realizado em casa de vegetação, com quatro tratamentos, sendo três com aplicação dos compostos (composto DLS, composto DLS + XR e composto DLS + XR + DCD) e um sem aplicação de composto (testemunha), em dois solos contrastantes . O melhor resultado foi obtido com o composto sem aditivos (composto DLS), o qual aumentou a produção de matéria seca da rúcula em 2,2 vezes no Latossolo e 6,1 vezes no Argissolo, comparado ao tratamento testemunha. A presença do XR nos compostos reduziu a produção de rúcula em 27% no Latossolo e em 35% no Argissolo, enquanto a presença de DCD não afetou a produção de matéria seca da rúcula. Os resultados deste estudo indicam que a adição de XR aos DLS durante a compostagem diminui o fornecimento de N à rúcula, tanto no efeito imediato (1º corte) quanto residual (2º corte).

ABSTRACT This study was developed to evaluate nitrogen (N) supply to arugula from composts produced by automated composting of pig slurry (PS). During the composting process, retorted oil shale (ROS) and dicyandiamide (DCD) were added to PS to mitigate gaseous N losses. The study was developed in a greenhouse where four treatments were evaluated, three with compost addition (PS compost, PS compost + ROS, and PS compost + ROS + DCD) and one without compost (control) in two contrasting soils (clayey and sandy-loam). The best result was obtained with the compost without additives (PS compost), which increased the arugula dry matter yield 2.2 times in clayey soil and 6.1 times in sandy-loam soil compared to the control treatment. The presence of ROS in composts reduced arugula dry matter yield in 27% in clayey soil and 35% in sandy-loam, while DCD did not affect arugula dry matter yield. The results of this study show that the addition of ROS to PS during composting reduces N supply to arugula, both in the immediate (first cut) and residual effect (second cut).

RESUMO: O Rio Grande do Sul possui cerca de 20% da área total de solos de terras baixas, propícias para o cultivo do arroz (Oryza sativa) irrigado por inundação. Buscando mitigar danos ocasionados com o monocultivo de arroz, novas culturas, como o sorgo (Sorghum bicolor) e a soja (Glycine max), têm sido cultivadas nestas áreas. Com diferentes qualidades de resíduos culturais, espera-se uma alteração na dinâmica da matéria orgânica do solo (MOS) e, consequentemente, do nitrogênio (N). O objetivo deste estudo foi avaliar a influência de resíduos culturais de arroz, soja e sorgo na quantidade de N em frações físicas da MOS de dois solos de terras baixas, utilizando a técnica de marcação isotópica de 15N das culturas e uma incubação por um ciclo de 180 dias em condição aeróbica e mais 180 dias em condição anaeróbica. Aos 30, 180 e 360 dias de incubação foi quantificado o N remanescente dos resíduos vegetais e destino do N proveniente dos resíduos nos dois solos em frações físicas da MOS >250 μm, 250-53 μm e <53 μm. O solo com maior quantidade de argila+silte recebeu maior quantidade de 15N dos resíduos, enquanto que o alagamento do solo após 180 dias de incubação ocasionou uma perda do N adicionado ao solo pelos resíduos de soja e sorgo. De maneira geral, foram encontradas maiores quantidades de 15N na fração <53 μm, associado aos argilominerais. As perdas de N devem ser consideradas na adubação nitrogenada para as culturas sequentes nos sistemas de rotação de culturas com arroz irrigado.

ABSTRACT: The state of Rio Grande do Sul has about 20% of the total area as lowland soils, suitable for flooded rice (Oryza sativa). In order to mitigate damage caused by rice monoculture, new crops such as sorghum (Sorghum bicolor) and soybean (Glycine max) have been cultivated in these areas. With different qualities of crop residues, it is expected a change in soil organic matter (SOM) dynamics and consequently, nitrogen (N) availability. The objective of this study was to evaluate the influence of rice, soybean and sorghum crop residues on the N present in physical fractions of SOM of two lowland soils, using labeled 15N technique, under incubation for 180 days in aerobic condition and more 180 days in anaerobic condition. At 30, 180 and 360 days of incubation the remaining N of the plant residues and N destination from the residues in both soils were quantified in the physical fractions of SOM >250 μm, 250-53 μm and <53 μm. The soil with higher amount of clay+silt received a larger quantity of 15N from residues, while flooding of the soil after 180 days caused a loss of N added to the soil by the soybean and sorghum residues. In general, larger amounts of 15N were reported in the fraction <53 μm, associated with clay minerals, throughout the incubation period. These N losses should be considered in N fertilization for the following crops in rotation with flooded rice.

ABSTRACT Methane (CH4) is the second major greenhouse gas after CO2, exerting a significant influence on the climate and the chemistry of the atmosphere. In lowland soil, acetate and H2/CO2 are the most important precursors of CH4 and formed from organic matter fermentation in an anaerobic environment, giving rise to short-chain organic acids (ethanoic, propanoic, and butanoic), depending on the type of crop residue and the soil management system. Ethanoic acid can be directly converted to CH4 by methanogenic microorganisms, but propanoic and butanoic acids must be converted to acetate before being converted to CH4. This study aimed to quantify, in isolation, the dynamics and CH4 emission potential of the three short-chain organic acids found in flooded lowland soils with rice crops. The study was carried out in a controlled environment using four standard carbon doses (0, 90, 180, and 270 mg kg−1) of ethanoic, propanoic, and butanoic acids. The dynamics and the potential emission of CH4 from soil were investigated when the acids were applied to flooded soil previously incubated for 20 days. The CH4 emission dynamics were altered with the application of the three short-chain organic acids to the soil, even using an equal amount of carbon. The faster and more intense emission was achieved with the ethanoic acid application in relation to the other two acids application, while butanoic acid presents slower, delayed, and prolonged dynamics of CH4 emission. Propanoic acid resulted in the lowest CH4 emission due to its own stoichiometry and the temperature condition in which the experiment was conducted, which were unfavorable to the hydrogenotrophic bacteria. The addition of short-chain organic acids promoted a priming effect in the soil with conversion values of C to CH4 above the calculated theoretical values.

ABSTRACT Cover crops have numerous benefits when used in a no-till system. Understanding the processes of decomposition and N release of summer cover crops (SCC) may help select species and management to be used in cropping systems. This study aimed to evaluate C and N loss of SCC shoots. Six SCCs were evaluated: velvet bean (Mucuna aterrima), pearl millet (Pennisetum americanum), dwarf pigeon pea (Cajanus cajan), sunn hemp (Crotalaria juncea), showy rattlebox (Crotalaria spectabilis), and jack bean (Canavalia ensiformis). The experiment was conducted for two years under no-till in soil classified as Typic Hapludalf (Argissolo). The C and N remaining of crop shoots were evaluated for 140 days using litter bags and the results were fitted with a simple nonlinear regression model. Elevated air temperature and rainfall volume accelerated C and N loss in the first year. Carbon and N loss was characterized by a rapid initial phase followed by a slower one. Jack bean had the highest C loss rates, while the lowest rates were found in pearl millet. Velvet bean and pearl millet had the lowest N loss rates in the first year, together with showy rattlebox in the second year. The rates of C (kC) and N (kN) loss were positively correlated with total N and water-soluble C and N in crop shoots. During the 35 days after cover crop termination, SCCs released 35 to 137 kg ha-1 N in 2010 and 5 to 66 kg ha-1 N in 2011. Velvet bean and showy rattlebox showed more gradual N release, which may favor the synchronization between N release and N uptake by the succeeding crop. The sunn hemp was the legume species that combined higher remaining residues on the soil surface, releasing less N but preventing soil erosion.

ABSTRACT The use of cover crops and poultry manure (PM) is an alternative to reduce the use of synthetic inputs and can contribute to the nutrient cycling in onions ( Allium cepa L.) grown under a no-tillage system. However, this management practice may contribute to an increase in N2O emissions to the atmosphere. The aims of this study were to evaluate the immediate effect on N2O emissions of adding PM onto cover crop residues and to verify the effect of different no-tillage systems on N2O emissions. Two studies (laboratory and field) were conducted with the addition of oilseed radish (OR), black oat (BO), and weed (WD) residues with and without PM under a no-tillage (NT) system. Emission of N2O (kg ha-1) was influenced by the different residue-management systems and was higher in treatments with OR residues (2.96 ± 0.67 kg ha-1 for OR and 5.28 ± 1.04 kg ha-1 for OR + PM). The other treatments behaved similarly with emissions of approximately 1.91 ± 0.17 kg ha-1 of N-N2O. The highest N2O emissions in the field study were found within the first 15 days and represented 50.3 % of the average emissions. Poultry manure showed high emissions when the cover crop was OR, but not when it was BO and WD.

ABSTRACT Isotopic labeling of plants is useful in tracking the fate of carbon (C) from different plant parts in a soil-plant system when these parts decompose simultaneously. Pulse labeling is a relatively simple technique and is amenable for use in the field. Therefore, we evaluated a 13CO2 pulse-labeling method to label crop plants under subtropical field conditions for simultaneous root and shoot decomposition studies. Wheat (Triticum aestivum L.), pea (Pisum sativum L.), and vetch (Vicia sativa L.) plants were grown inside polyvinyl chloride (PVC) cylinders and pulse labeled once a week for a total of 11 times. After harvest, “paired” treatments were designed by combining 13C-labeled shoots with unlabeled roots and unlabeled shoots with 13C-labeled roots, resulting in six treatments (2 combinations × 3 species), plus an unamended control treatment. The 13C enrichment of plant parts, chemical fractions, 13C recovery, and distribution in roots, shoots, and soil were determined. Soil CO2 emissions were measured continuously by the alkaline trap method for 180 days. Plant dry matter production and chemical composition were not modified by 13C labeling. The maximum level of 13C enrichment (δ13C) in plants was +495 %o in wheat, +426 %o in pea, and +378 ‰ in vetch plants. All three crops showed similar patterns of 13C distribution in the following order: shoots > roots > soil. On average, 81 to 89 % of the recovered 13C was in the shoots, 7 to 14 % was in the roots, and 2.7 to 4.3 % was in the soil. The rate of C mineralization and cumulative C mineralization were not different between “paired” treatments of the three crops, showing that the paired treatments were equally degradable. The pulse-labeling technique used under field conditions allowed for production of sufficiently labeled wheat, pea, and vetch plants. Therefore, it is a practical approach with respect to resource demand (tracer and labor costs), and it is suitable for in situ labeling.

ABSTRACT: The impact on nitrous oxide (N2O) emissions caused by combining dairy slurry (DS) and urea to supply crops with nitrogen (N) is still not well characterized. The main objective of this study was to compare the differences between N2O emissions in the cases of exclusive use of urea and the combined use of DS and urea as N sources to no-tillage wheat and corn. We also compared N2O emissions between two DS application methods (surface-broadcast vs. injection), as well as the addition of dicyandiamide (DCD) to DS. The experiment was conducted under no-tillage and six treatments were applied at sowing as follows: no fertilization (control), surface-broadcast urea (urea-N), surface-broadcast DS (DSs), surface-broadcast DS with DCD (DSs + DCD), shallow-injected DS (DSi), and shallow-injected DS with DCD (DSi + DCD). Urea was applied at side-dressing in all treatments with DS and urea-N. The N2O emissions were evaluated from the application of the treatments to wheat until 22 days after corn harvest, resulting in a total of 364 days. The partial supply of the N demand of wheat and corn, by DS application at sowing, and the posterior complement of N demand by side-dressing urea increased the annual N2O emissions only when DS was shallow-injected without DCD (DSi). Although the amount of N2O-N emitted from the DSi treatment was 1.04 kg ha-1 (91.2 %) higher than from DSs in corn, the annual N2O-N emissions did not differ between the two methods of DS application to the soil. The emission factors of N2O-N were low, ranging from 0.49 % (DSi + DCD) to 1.27 % (DSi). The results of this study suggest that the combined use of DS with urea in N fertilization of no-tillage wheat and corn (DS applied at sowing and urea at side-dressing) caused no changes in the annual N2O-N emissions compared to crops fertilized exclusively with urea (1/3 at sowing + 2/3 at side-dressing). However, DCD should be added if DS is shallow-injected.