In agricultural activities, the main greenhouse gases (GHG) are those related to C and N global cycles. The impact of agriculture on GHG emissions has become a key issue, especially when considering that natural C and N cycles are influenced by agricultural development. This review focuses on CO2 and N2O soil emissions in terrestrial ecosystems, with emphasis in Chilean and similar agro-ecosystems around the world. The influence of land use and crop management practices on CO2 and N2O emissions is analyzed; some mitigation measures to reduce such emissions are also discussed here. More knowledge on the biological processes that promote of GHG emissions from soil will allow creating opportunities for agricultural development under friendly-environmental conditions, where soil can act as a reservoir and/or emitter of GHG, depending on the balance of inputs and outputs.

Old-growth forests of southern Chile represent an important reserve of temperate (rain) forests in the world. Wetter and colder forest ecosystems appear to be more efficient in conserving and recycling N such that mostly non-plant available N species are lost, which could be indicated by more depleted δ¹⁵N values of the soil and plants. Hydrological N loss from the old-growth forests in southern Chile occurs mainly via dissolved organic nitrogen and not via dissolved inorganic N. Forest disturbances (e.g. fire, clear-cutting or enhanced N deposition) cause (abrupt) changes in ecosystem N-cycling processes. In this study, we hypothesized that δ¹⁵N signatures of soil profiles under old-growth forests could be used as an integrator for ecosystem N-cycling, and changes of these δ¹⁵N profiles could be valuable to assess ecosystem resilience towards disturbances. Six old-growth forests were selected in the phytogeographical region of the Valdivian rain forest in southern Chile. One of the sites has been partly burned in February 2002. First, we observed that ecosystems with higher mean annual precipitation and lower mean annual temperature were relatively more depleted in ¹⁵N. Secondly, we found that a forest fire caused a 100-fold increase of the nitrate export and induced an enrichment of the soil δ¹⁵N signal in the upper 20 cm.

The use of phosphate solubilizing bacteria (PSB) is an ecological strategy that allows for increasing the availability of phosphorus (P) in soil. The objective of this study was to evaluate P availability in wheat, in soils derived from volcanic ash (Andisol and Ultisol,) and inoculated with phosphate-solubilizing Bacillus thuringiensis, the experiment was conducted in pots under greenhouse conditions using a completely randomized design. Wheat plants were inoculated and re-inoculated at 20 and 46 days after sowing (DAS), respectively, with B. thuringiensis; and, soil and plant sampling was performed after 46, 66, and 87 days based on the Zadoks growth scale (Z). The inoculation resulted in an 11% increase in P of the rhizosphere at Z46 (Ultisol), P also increased 34% and 67% in aerial tissues at Z46 (Andisol and Ultisol), respectively, while an increase of 75% was observed in root tissues at Z87 (Ultisol). Similarly, the inoculation resulted in increases in acid phosphatase activity (Andisol), soil microbial biomass (Andisol and Ultisol), and root biomass in plants (Ultisol), without achieving increase of the aerial biomass of the plants. The phosphate solubilizing B. thuringiensis strain showed some positive, but also negative effects in soils and plants, depending on the soil.