No abstract

No abstract

No abstract

No abstract

Agricultural systems where monoculture prevails are characterized by fertility losses and reduced contribution to ecosystem services. Including cover crops (CC) as part of an agricultural system is a promising choice in sustainable intensification of those demanding systems. We evaluated soil microbial functionality in cash crops in response to the inclusion of CC by analyzing soil microbial functions at two different periods of the agricultural year (cash crop harvest and CC desiccation) during 2013 and 2014. Three plant species were used as CC: oat (Avena sativa L.), vetch (Vicia sativa L.) and radish (Raphanus sativus L.) which were sown in two different mixtures of species: oat and radish mix (CC1) and oat, radish and vetch mix (CC2), with soybean monoculture and soybean/corn being the cash crops. The study of community level physiological profiles showed statistical differences in respiration of specific C sources indicating an improvement of catabolic diversity in CC treatments. Soil enzyme activities were also increased with the inclusion of CC mixtures, with values of dehydrogenase activity and fluorescein diacetate hydrolysis up to 38.1% and 35.3% higher than those of the control treatment, respectively. This research evidenced that CC inclusion promotes soil biological quality through a contribution of soil organic carbon, improving the sustainability of agrosystems. The use of a CC mixture of three plant species including the legume vetch increased soil biological processes and catabolic diversity, with no adverse effects on cash crop grain yield.

R������. Los cambios de vegetación pueden alterar los flujos de agua y nitrógeno (N) de los ecosistemas. La intensificación de las rotaciones con cultivos de cobertura (CC) otoño-invernales reduce el N del suelo y el riesgo de lixiviación durante los excesos hídricos. El objetivo de este trabajo fue contrastar el drenaje profundo y la lixiviación de N en una rotación soja-maíz con y sin CC, utilizando lisímetros. Se cultivó avena antes de soja y avena+vicia antes de maíz. Las precipitaciones fueron 732 y 562 mm durante los períodos intercultivo 2014 y 2015, y 817 y 705 mm durante los cultivos de soja y maíz, respectivamente. La inclusión de CC redujo el drenaje durante los períodos intercultivo (de 41 a 25% y de 22 a 9% de la precipitación durante el primer y segundo período intercultivo, respectivamente) y durante el cultivo de soja (de 18 a 14% de la precipitación). Durante el cultivo de maíz, el drenaje fue similar en las dos rotaciones; representó el 14% de la precipitación. La concentración media de N-NO 3 3 del drenaje fue de 6 y 15 mg/L para la rotación con y sin CC, respectivamente. La inclusión de CC redujo la lixiviación de 35 a 14 y de 17 a 3 kg N/ha durante los períodos intercultivo 2014 y 2015, respectivamente, y de 36 a 3 y de 15 a 6 kg N/ha durante los cultivos de soja y maíz, respectivamente. Estas reducciones, sumadas al aporte adicional de N por fijación biológica de vicia, produjeron balances de N positivos o cercanos a neutro, mientras que la rotación sin CC presentó balances negativos. Además de mejorar la circulación interna de N, las reducciones en el drenaje con CC se pueden traducir en menor recarga del acuífero y contribuir a la regulación de inundaciones durante períodos lluviosos.[Palabras clave: lisímetros de relleno, balance hídrico, balance de nitrógeno, nivel freático] A�������. Deep drainage and nitrogen leaching reduction in crop rotations with cover crops. Ecosystem water and nitrogen (N) fluxes can be altered by vegetation changes. The intensification of crop rotations with fall-winter cover crops (CC) reduces soil N and leaching risk during period of water excess. In this study we used filled-in lysimeters to evaluate the effect of including CC (oats and an oats+vetch mixture) in a soybean-maize rotation on deep drainage and N leaching during a rainy period. Rainfall was 732 and 562 mm during 2014 and 2015 intercropping periods, and 817 and 705 mm during soybean and maize cropping periods, respectively. The introduction of CC reduced drainage during both intercropping periods (from 41 to 25% and from 22 to 9% of rainfall during the first and second intercropping periods, respectively) and during soybean cropping period (from 18 to 14% of rainfall). Drainage represented 14% of the rainfall of maize in both rotations. Mean drainage N-NO3¯ concentration was 6 and 15 mg/L for the rotation with and without CC, respectively, and the introduction of CC reduced leaching from 35 to 14 and from 17 to 3 kg N/ha during 2014 and 2015 intercropping periods, respectively, and from 36 to 3 an...

Cropping diversification with cover crop mixtures combined with low N fertilization represents an ecological alternative that may promote sustainability. Our objective was to evaluate changes on soil organic fractions and structure, cover crop biomass, and main crop yield 5 years after the introduction of two cover crop mixtures, oats+forage radish (CC1) and oats+forage radish+vetch (CC2), in a soybean-soybean and maize-soybean sequence with low N fertilization of maize. After 5 years, the soil from sequences with cover crops had higher concentrations of soil organic carbon (SOC) (23.3 vs 20.1 g kg −1 ), soil organic nitrogen (SON) (2.4 vs 2.0 g kg −1 ), and particulate organic carbon (POC) (4.4 vs 2.9 g kg −1 ) at 0-5 cm depth than the controls without cover crops, in association with C input from cover crops aboveground biomass, which averaged 2.2 and 3.0 Mg ha −1 year −1 for CC1 and CC2, respectively. Soil aggregation at 0-5 cm depth was more stable with than without cover crops (33.4 vs 16.4%), and it was positively related to SOC (R 2 = 0.44, p < 0.01) and POC (R 2 = 0.50, p < 0.01) concentrations. Soil from CC2 had a higher proportion of macropores and mesopores over 300 μm than soil from CC1 and the controls without cover crops at 0-5 and 10-30 cm depth, respectively. Maize yield was affected by rainfall: it was similar among treatments in dry growing seasons (<5.0 Mg ha −1 ) and higher in CC2 and the control without cover crops than in CC1 in more humid seasons (9.2 vs 7.9 Mg ha −1 ). Soybean yield was similar among treatments except after dry cover crop growing seasons, when control treatments yielded more than cover crop treatments (3.4 vs 2.8 Mg ha −1 ). This study demonstrates that summer crop sequences with cover crop mixtures increase ecosystem multifunctionality and that including vetch in the mixture increases its production potential and benefits, especially in the soybean-soybean sequence.

The use of cover crops, combined with low N fertilization and no-tillage, reduces the environmental impacts of agriculture. Legume cover crops provide N to the agroecosystem and allow N fertilization to be reduced without losing productivity, but may also increase nitrous oxide (N2O) emissions. Our main objective was to evaluate the impact of using oats, vetch, and oats+vetch mixture as cover crops on N2O emissions and summer crop yields in a maize–soybean rotation with low N fertilization to maize (32 kg N ha−1) under no-tillage. We also studied how the different cover crops affected soil variables related to N2O emissions. For the treatments that included vetch (vetch and oats+vetch), plots without N fertilization were included to evaluate if N2O emissions and crop yield were increased by low-rate N fertilization after a legume cover crop. We measured N2O emissions using static chambers in a long-term experiment located in the Argentine Pampas. We selected measurement periods in which high N2O fluxes were expected to evaluate the effect of the different cover crops during these hotspots. In the early stages of maize and soybean, the use of vetch as a cover crop increased N2O emissions compared with oats and a control without a cover crop. In those early stages, conditions for high N2O flux occurrence were promoted by the use of cover crops, as they increased soil moisture and, when vetch was the cover crop, nitrate content. Although the oats+vetch mixture reduced soil nitrate availability compared with vetch, this was not reflected lower N2O emissions. The use of oats as a cover crop did reduce N2O emissions compared with vetch and also decreased maize yields by 30.6%. The low-rate N fertilization in treatments that included vetch as a cover crop did not increase N2O emissions or yield significantly. Our study demonstrates that in low-input cropping systems under no-tillage, the use of legume cover crops can favor yields and also increase N2O emissions during the early stages of the following cash crop. Consequently, future work should explore mitigation strategies during this period.