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Agricultural challenge today is to maximize crop production reducing negative environmental impacts by efficiently use of resources and inputs. Objectives: i) to evaluate N2O emissions during a soybean-barley-maize rotation and their respective interperiods -chemical fallows (ChF) and cover crops (CC)-, and ii) to understand the relationships between N2O flow rates with soil mineral N content (Nmin), water-filled porous space (WFPS), and soil temperature (ST). N2O emissions were evaluated weekly under two management systems, ecological intensification (EI) and farmer current practices (FP). EI included higher N rates than FP, split N application, a cover crop (CC) after barley, among other management practices. Simultaneously to N2O emissions, Nmin, WFPS and ST were determined. The N2O fluxes were highest during crop periods (9-43, 6-61 and 4-104 µg N2O-N m-2 h-1, for soybean, barley and maize, respectively), intermediate during barley-maize interperiod (2-47 and 3-35 µg N2O-N m-2 h-1, for CC and ChF, respectively) and lowest during ChF of maize-soybean and soybean-barley interperiods (1-26 and 5-22 µg N2O-N m-2 h-1, respectively). Regression tree provided threshold splits for the effect of soil variables on emission rates: 7.4 mg N kg-1 for Nmin; 10.35 or 8.7°C for ST, depending on Nmin and WPFS values; 39.6 and 55.4 % for WPFS, both with high N. There were no significant differences in accumulated N2O emissions between management systems for the complete sequence (3050 and 3380 g N2O-N ha-1, for EI and FP, respectively). Yield-based N2O emissions for the complete sequence were lower for EI than for FP. EI decreased yield-scaled N2O emissions by 29% for soybean (p<0.05) and barley (ns) and by 30% for maize (p<0.05) compared with FP. In conclusion for the complete sequence, the EI system did not increase N2O emissions per unit area and reduced emissions per unit yield despite utilizing higher N rates and including a CC. [ABSTRACT FROM AUTHOR]

Soil biological activity (i.e. mineralized carbon (C) (Cmin)) is a crucial property to evaluate soil health and its changes due to soil use. In the southeastern Buenos Aires province (SEB) there is scarce information about how agriculture ecological intensification (IEA) affects soil global biological activity and the potentially mineralized C (C0) to improve the comprehension of the mechanisms that regulate soil C dynamics. It would be relevant to determine the adequate incubation time at which the determination of Cmin can predict C0 in soils from the SEB. Moreover, the Cmin determined in early incubation days has been proposed as a quick alternative to estimate C0. It has been hypothesized that it is necessary to run longer incubations to correctly evaluate C0 of soils of the SEB and that the CO2 emitted during short incubation periods is a good estimator of C0. Soil samples were taken (0-5 and 5-20 cm) from a long-term experiment on crop-pasture rotations on Mollisols at Balcarce with different levels of IEA under conventional tillage and no-tillage (SD). Total (COT), particulate (COP) and associated organic C were determined, as it was the Cmin from aerobic incubations under controlled conditions at 2, 4, 6, 10, 16, 22, 28, and 63 days. The C0 was estimated from the Cmin at 22, 28, and 63 days. The Cmin and C0 showed similar patterns among cropping systems. The estimations of C0 from the Cmin at 63 days were the most trustable (mean of C0 466,9 and 517,8 mg C kg-1 from Cmin(28) and Cmin(63), respectively). Furthermore, the Cmin at a few days of incubation showed high correlation coefficients with C0 (r between 0.68 and 0.92 at 0-20 cm for 2 to 10 incubation days) and therefore short incubations would be promising to estimate C0. [ABSTRACT FROM AUTHOR]

Changes in land use modify soil C and N dynamics. Our objectives were (1) to study C and N variations in the organic matter and its granulometric fractions (MOP and MOAM), and (2) to evaluate how these variations affect the potentially mineralizable N (Nan) under different land uses. Analyzed land uses were: grassland (PN), agriculture (AGR), forestation with pines (MP), and thinned strips in MP: secondary grassland (PS). We determined the lowest total organic carbon (COT), total N (Nt), C and N in granulometric fractions, and Nan values at AGR, evidencing soil degradation. The COT values at MP and PS (63,3 and 53,5 g kg-1, respectively) were greater than at PN (50,4 g kg-1 soil), due to an increase in C associated with minerals (C-MOAM). We observed more Nt, C-MOP and N-MOP at PN than at MP and P. This explained the fact that Nan was 100 mg Kg-1 greater at PN than at MP and PS. The N-MOP was the variable that best explained Nan variability (R² = 0,859). The C and N distribution in the MO and its fractions reflected changes in land use, but it is necessary to better study C and N dynamics under forest vegetation. [ABSTRACT FROM AUTHOR]

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