No-tillage and Adequate N Fertilization Strategies: Key Practices to Enhance Grain Yield and Mitigate Global Warming in Mediterranean Agroecosystems D. Plaza-Bonilla1,2*, J. Álvaro-Fuentes2, J. Lampurlanés3, J. L. Arrúe2, E. Pareja-Sánchez1, S. Franco-Luesma2, C. Cantero-Martínez1 1
Department of Crop and Forest Sciences, Associated Unit to EEAD-CSIC, Agrotecnio, University of Lleida, Av. Rovira Roure 191, 25198 Lleida, Spain 2 Soil and Water Department, Estación Experimental de Aula Dei (EEAD), CSIC, Avda. de Montañana 1005, 50059 Zaragoza, Spain 3 Department of Agricultural and Forest Engineering, Associated Unit to EEAD-CSIC, Agrotecnio, University of Lleida, Av. Rovira Roure 191, 25198 Lleida, Spain * corresponding author:
[email protected] Introduction Mediterranean agriculture under rainfed conditions is characterized by low yields and soil vulnerability to degradation, which can be exacerbated by global warming. Therefore, management practices must be oriented towards a more sustainable approach, dealing with Mediterranean agriculture idiosyncrasy and aiming at mitigating greenhouse gas emissions. In this context, agricultural management practices play a major role. The objective of this work was to study the impact of tillage systems and N fertilization strategies on crop production, greenhouse gas emission and soil carbon under rainfed winter cereal-based cropping systems. Materials and Methods Two field experiments were set up (Agramunt, 41º48’N, 1º07’E, established in 1996; Senés, 41º54’N, 0º30’W, established in 2010) in the Ebro valley (NE Spain), comparing different tillage systems (conventional intensive tillage, CT; no-tillage, NT) and N fertilization strategies (0, 60 and 120 kg N ha-1 of mineral fertilizer in Agramunt, and 0, 75 and 150 kg N ha-1 with mineral fertilizer or pig slurry in Senés). Common characteristics of the field experiments were their statistical design (based on randomized complete blocks with three replications), their size (plots adapted to the use of commercial machinery, with a minimum plot size of 240 m2), and cropping system (winter cereal-based cropping systems, with crop residues maintained, incorporated under CT and spread over the soil surface in NT). Soil water and mineral N dynamics were quantified at key specific dates during the cropping season. Crop productivity as above-ground biomass and grain yield were determined. Soil organic carbon (SOC) was quantified at specific dates over the entire plough layer (i.e. 0-40 cm) with the use of wet oxidation and soil bulk density determination. Soil greenhouse gas emission (nitrous oxide, N2O, and methane, CH4) was quantified during two cropping seasons using non-steady state static chambers (Hutchinson and Mosier, 1981) with intensive samplings during N fertilization applications (i.e. 24 h prior and 3h and 48 h after the application). Gas samples were analyzed with a gas chromatography system equipped with a flame ionization detector to analyze CH4 and an electron capture detector to analyze N2O, and configured to analyze both gases with a unique injection. Ancillary variables such as soil temperature (at 5 cm depth), soil water filled pore space and mineral N (as ammonium and nitrate) were also determined on each gas sampling date. Results and discussion The use of NT led to greater soil water recharge than CT in both sites, increasing the amount of water available to the crop at the beginning of the tillering stage (at the end of January in
our conditions) when crop grows and develops due to greater air temperatures. In Agramunt, as an average of 18 years of experiment, NT increased barley grain yield by a 10, 47 and 53% compared with CT when applying 0, 60 and 120 kg N ha-1, respectively. In Senés, NT showed 1.0, 1.7 and 6.3 times greater grain yield than CT in three of the four cropping seasons analyzed. In Senés, pig slurry application led to the same (in 3 out of 4 years) or higher (in 1 out of 4 years) grain yield than an equivalent rate of mineral N fertilizer. In both sites, crop response to the highest N rate was nil under CT and marginal under NT. Crop response to N fertilizer is highly dependent on soil water availability under rainfed Mediterranean conditions, which explains the greater crop yields under NT when applying increasing N rates, being the response greater on drier years (Cantero-Martínez et al. 2003). The positive impact of NT on crop biomass in most of the years analyzed increased the amount of C inputs returned to the soil as crop residues and led to a significant increase in SOC. Tillage and N fertilization single effects affected significantly N2O emissions in Senés. The impact of tillage on soil N2O emissions differed depending on the site: whereas similar N2O emissions were observed in Agramunt between CT and NT, greater emissions were observed in NT compared with CT in Senés. The increase in N rate independently of the source of N (mineral N or pig slurry) increased N2O emissions, while no differences between N sources were observed for a given N rate. The soil acted as a net sink of CH4 in both sites, showing most sampling dates negative fluxes of this greenhouse gas with the exception of N fertilization applications. Tillage affected differently CH4 fluxes depending on the site: while greater CH4 absorption occurred in Agramunt when using NT the contrary results were observed in Senés. It could be hypothesized that the differential response to tillage of N2O and CH4 in Agramunt and Senés could be the result of soil structure improvement when maintaining NT practices in the long term (Plaza-Bonilla et al., 2013). Regarding to this last point, the maintenance of NT could have enhanced soil porosity (in magnitude and/or continuity) under NT in Agramunt reducing denitrification and enhancing soil methanotrophic (i.e. oxidation of CH4) activity. Conclusion In synthesis, the results we report here point out that the use of NT, maintained over time, and the application of medium rates of N using either synthetic fertilizers or pig slurry are key practices to mitigate greenhouse gas emissions, sequester soil C and enhance winter cereal yields in semiarid rainfed Mediterranean agroecosystems.
References Cantero-Martínez, C., Angas, P., Lampurlanés, J., 2003. Growth, yield and water productivity of barley (Hordeum vulgare L.) affected by tillage and N fertilization in Mediterranean semiarid, rainfed conditions of Spain. Field Crops Res. 84, 341-357. Hutchinson G.L., Mosier A.R., 1981. Improved soil cover method for field measurement of nitrous oxide fluxes. Soil Sci. Soc. Am. J. 45, 311-316. Plaza-Bonilla, D., Cantero-Martínez, C., Viñas, P., Álvaro-Fuentes, J., 2013. Soil aggregation and organic carbon protection in a no-tillage chronosequence under Mediterranean conditions. Geoderma 193-194, 76-82.
