Evaluation of maize and soybean intercropping on soil quality and nitrogen transformations in the Argentine Pampa

Agricultural intensification to increase food, feed, and fibre production has also resulted in environmental degradation, including poorer soil quality and high emissions of greenhouse gases (GHGs) like nitrous oxide (N2O). Intercropping, an agroecosystem management practice where more than one crop is planted on the same plot of land at the same time, promotes the complementary use of soil nutrients, and may improve soil quality and increase the retention of inorganic nitrogen (N) in the soil, thereby reducing N2O emissions. An experiment was conducted in Balcarce, Argentina to determine the impact of intercropping maize (Zea mays L.) and soybean (Glycine max (L.) Merr.), (either 1:2 or 2:3 rows of maize to soybean) on soil quality and soil N transformations after six cropping seasons. It was found that intercropping significantly improved soil quality over a six year period, as indicated by the soil organic carbon (SOC), soil total nitrogen (TN), soil light fraction organic matter (LF), and soil microbial biomass carbon (SMB-C). However, the soil quality also significantly improved in the sole crops over this time, and in 2012, only SMB-C was significantly (p<0.05) greater in the 2:3 intercrop than in the sole crops. Intercropping resulted in higher rates of gross nitrogen (N) mineralization than the sole crops, and the 2:3 intercrop resulted in higher rates of gross N immobilization than in the other treatments. However, the high rate of gross N mineralization resulted in a low relative NH4+ immobilization in both intercrops, signifying a lower potential for reducing soil NH4+ concentrations than in the sole crop treatments. Net N immobilization occurred in all treatment plots, which was desired at the end of the fallow period to reduce N losses from the soil. The 2:3 intercrop appeared to perform better than the 1:2 intercrop. However, further research needs to be conducted to determine the seasonal variations in N mineralization and immobilization, and to further examine the intercrop spatial arrangements to increase crop residue yield

Technology-assisted education in graduate medical education: a review of the literature

Studies on computer-aided instruction and web-based learning have left many questions unanswered about the most effective use of technology-assisted education in graduate medical education

Changes in soil characteristics after six seasons of cereal–legume intercropping in the Southern Pampa

The Argentine Pampa is one of the most productive agricultural regions in the world, but sole crop management practices have led to soil degradation and losses of soil organic matter. The objective of this study was to evaluate soil organic carbon (SOC) and nitrogen (N) dynamics in 2007 and in 2012 in two intercrop systems [1:2 intercrop (one row of maize (Zea mays L.) and two rows of soybeans (Glycine max L. Merr.)) and 2:3 intercrop (two rows of maize and three rows of soybean)], and in a maize and soybean sole crop. Results showed that C and N input from crop residues was significantly greater (P < 0.05) in the maize sole crop, followed by the intercrops and the soybean sole crop. The land equivalent ratio (LER), based on crop biomass, was significantly greater (P < 0.05) in the 2:3 intercrop. Soil physical and chemical characteristics (bulk density, pH, SOC and N, C/N ratio) were not significantly (P < 0.05) different among treatments and were significantly greater in 2012, except for pH, at all depths. Gross SOC turnover time was significantly longer (P < 0.05) in 2012 compared to 2007 for all treatments and depths, except in the maize sole crop. Soil microbial biomass (SMB) C and N were significantly greater (P < 0.05) in the 2:3 intercrop in both years. To a 40 cm depth, SMB-C turnover time (SMB-CT) was significantly greater (P < 0.05) in the soybean sole crop followed by the intercrops and the maize sole crop in 2007, whereas in 2012, SMB-CT was significantly greater (P < 0.05) in the intercrops followed by the soybean and the maize sole crops. The soil light fraction N (LF-N) was significantly greater (P < 0.05) in the maize sole crop in both years. There was no significant difference (P < 0.05) for LF-C. Our results demonstrated that cereal–legume intercropping is a more sustainable agroecosystem land management practice in the Argentine Pampa, with respect to soil C and N transformations, compared to sole cropping.EEA BalcarceFil: Oelbermann, Maren. University of Waterloo. Department of Environment and Resource Studies; CanadáFil: Regehr, Alison. University of Waterloo. Department of Environment and Resource Studies; CanadáFil: Echarte, Laura. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Balcarce; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Gross Nitrogen Mineralization and Immobilization in Temperate Maize-Soybean Intercrops

Background and aims Reliance on nitrogen (N) fertilizers to maintain crop productivity requires a thorough understanding of the transformation of this nutrient within the soil-plant system. Organic matter input from a mixture of crop residues, such intercrop systems, influence N transformations differently compared to sole crops. We tested the hypothesis that N mineralization and immobilization differ between cereal-legume intercrops and sole crops. Methods A short-term experiment using 15N isotopic pool dilution was conducted in 2007 and 2012 in maize (Zea mays L.) and soybean (Glycine max L. Merr.) sole crops and 1:2 (1 row maize:2 rows soybean) and 2:3 (two rows maize:3 rows soybean) intercrops. Soil characteristics, gross mineralization and immobilization, and net immobilization to a 10 cm depth were quantified. Results Soil characteristics (pH, bulk density, soil organic carbon (C), total N, and C:N) were not significantly different (P < 0.05) among treatments, but differed significantly (P < 0.05) between years (2007 vs. 2012). Soil NH4 +-N was significantly lower (P < 0.05) in the maize sole crop. Gross N mineralization, immobilization and net immobilization, were significantly different (P < 0.05) among treatments and between years. Relative NH4 +-N immobilization was significantly different (P < 0.05) among treatments and between years, showing the lowest values in the intercrops. The amount of NH4 +-N mineralized per day was significantly greater (P < 0.05) in the 2:3 intercrop and was significantly different (P < 0.05) between years in the 2:3 intercrop. Residence time of NH4 +-N was significantly longer (P < 0.05) in the soybean sole crop and 1:2 intercrop followed by the 2:3 intercrop and the maize sole crop. Conclusions Intercropping contributed to the long-term immobilization of N and therefore was a more sustainable land-management practice than sole cropping. The adoption of cereal-legume intercrops will curb our currently growing reliance on N fertilizers.Fil: Regehr, Alison. University of Waterloo; CanadáFil: Oelbermann, Maren. University of Waterloo; CanadáFil: Videla, Cecilia. Universidad Nacional de Mar del Plata; ArgentinaFil: Echarte, Laura. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Instituto Nacional de Tecnología Agropecuaria; Argentin

Estimating soil carbon dynamics in intercrop and sole crop agroecosystems using the century model

Using process-based models to predict changes in carbon (C) stocks enhances our knowledge on the long-term dynamics of soil organic carbon (SOC) in various land management systems. The objective of this study was to apply the Century model to evaluate temporal SOC dynamics in two temperate intercrop systems [1:2 (one row of maize and two rows of soybeans); 2:3 intercrop (two rows of maize and three rows of soybean)] and in a maize and soybean sole crop. Upon initiation of intercropping, SOC increased by 47% after ≈ 100 years, whereas SOC in the maize sole crop increased by 21% and 2% in the soybean sole crop. The quantity of crop residue input was sufficient to increase the active (turnover time of months to years) SOC fraction in the intercrops and the maize sole crop, but not in the soybean sole crop. The slow fraction, with a turnover time of 20 to 50 years, increased in all crop systems and was the major driver of SOC accumulation. A 3 to 15% loss of SOC from the passive fraction, with a turnover time of 400 to 2000 years, in all crop systems showed the long-term impact of land-use conversion from historically undisturbed native grasslands to intensive agricultural production systems. This study provided an example of the potential of process-based models like Century to illustrate possible effects of cereal-legume intercropping on SOC dynamics and that the model was able to predict SOC stocks within -7 to +4% of measured values. We conclude, however that further fine-tuning of the model for application to cereal-legume intercrop systems is required in order to strengthen the relationship between measured and simulated values.Fil: Oelbermann, Maren. University of Waterloo; CanadáFil: Echarte, Laura. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Marroquin, Lisa. Climatecheck; CanadáFil: Morgan, Svenja. University of Waterloo; CanadáFil: Regehr, Alison. Upper Thames River Conservation Authority; CanadáFil: Vachon, Karen E.. University of Waterloo; CanadáFil: Wilton, Meaghan. University of Waterloo; Canad