(1) Background: Coffee agroforestry systems (CAFS) in Veracruz, Mexico, are being displaced by avocado monocultures due to their high economic value. This change can generate alterations in the type of organic residues produced and soil biological activity (SBA) which is sensitive to climatic variations, changes in floristic composition, and agronomic management. It can be evaluated through soil respiration and macrofauna, both related to soil carbon (C) and nitrogen (N) dynamics. The objective was to: (1) Analyze the variation of SBA as well as the C and N dynamics in modified coffee agroforestry systems; (2) Methods: Three CAFS (renewed, intensive pruning, and with the introduction of avocados) and an avocado plantation were compared. The evaluations were conducted during the period 2017–2019. Soil parameters (respiration, macrofauna, C and N contents) and C content of plant biomass were measured in plots of 25 × 25 m2 from three soil depths in triplicate. Spearman’s test and a principal component analysis were performed to determine the structural dependence on C and N dynamics; (3) Results: The introduction of avocado showed the lowest soil respiration values (with 193 g CO2 ha−1 h−1 at 0–10 cm depth), this system did not display soil macrofauna and increased soil organic carbon content. The soil C/N ratio was sensitive to the introduction of avocado. Correlation between soil respiration and litter-related parameters was positive, but it was negatively correlated with soil organic matter and total soil nitrogen, explaining 67.7% of the variation; (4) Conclusions: Modification of CAFS generated variations in the SBA and soil C and N contents.

La agricultura sustentable promueve la reducción de fertilizantes químicos con residuos orgánicos, e incrementa la fertilidad del suelo. Con la incorporación de residuos orgánicos, un efecto poco evaluado es la emisión de CO2 el cual resultaría un indicador de la mineralización del carbono y la liberación de nutrientes para los cultivos. El objetivo del presente estudio fue evaluar la incorporación de tres abonos orgánicos: estiércol caprino (EC), estiércol bovino (EB) y gallinaza (EG), con dos dosis de 4.5 y 9.0 kg m-2, para determinar la liberación y acumulación de C-CO2 en condiciones de laboratorio por 95 días. Las aplicaciones de EB incrementaron el pH, conductividad eléctrica, carbono orgánico, nitrógeno total, emisión y liberación de CO2en comparación con los otros abonos. Se observaron mayores efectos por los abonos orgánicos a la profundidad de 0 a 15 cm en todas las variables de estudio. La acumulación de CO2 se relaciona con la mineralización del carbono, esta fue mayor en EB seguido de EG y EC. La adición de EB al suelo es una opción para incrementar la mineralización del carbono y mantener la productividad de los cultivos de manera sustentable.

<p>Calcareous soils are characterized by containing a greater amount inorganic carbon (SIC) than organic carbon (SOC), and both contribute to CO<sub>2</sub> emissions to the atmosphere. SOC mineralization and SIC dissolution are related to soil moisture content, but their effect on CO2 emissions from calcareous soils is unclear. This investigation aimed to evaluate the effect of moisture content on CO<sub>2</sub> emission of a calcareous soil in the Comarca Lagunera, Mexico.</p> <p>Calcareous soil samples were taken from a cropland and shrubland of Comarca Lagunera, Mexico and their physical and chemical properties were determined. For a 30-day period, 100g of soil were incubated in closed-jars and two moisture treatments, related to field capacity (FC) and permanent wilting point (PWP) values were applied. The CO<sub>2</sub> emission assessment was performed every two days using an infrared gas analyzer (IRGA, PP Systems, UK).</p> <p>For cropland, the FC, PWP, SIC and SOC values were 27.2 %, 14.6 %, 7.3 % (140.4 Mg ha<sup>-1</sup>) and 0.23 % (4.4 Mg ha<sup>-1</sup>), while for shrubland, the values were 27 %, 11 %, 7.6 % (152.8 Mg ha<sup>-1</sup>) and 0.08 % (1.6 Mg ha<sup>-1</sup>), respectively. Average emission of CO<sub>2</sub>, every two days, from cropland soil was 2.1 g CO<sub>2</sub> m<sup>-2</sup> h<sup>-1</sup> for moisture at FC, while to PWP was 1.7 g CO<sub>2</sub> m<sup>-2</sup> h<sup>-1</sup>, and for shrubland soil was 1.8 g CO<sub>2</sub> m<sup>-2</sup> h<sup>-1</sup> for moisture at FC, while to PWP was 1.6 g CO<sub>2</sub> m<sup>-2</sup> h<sup>-1</sup>.</p> <p>In both cases, cumulative CO<sub>2</sub> emissions were significantly higher in FC compared to PWP. For cropland, cumulative CO<sub>2</sub> emissions were 23.4 g CO<sub>2</sub> m<sup>-2</sup> h<sup>-1</sup> and 29.4 g CO<sub>2</sub> m<sup>-2</sup> h<sup>-1</sup>, but for shrubland were 21.7 g CO<sub>2</sub> m<sup>-2</sup> h<sup>-1</sup> and 25.3 g CO<sub>2</sub> m<sup>-2</sup> h<sup>-1</sup>. Cumulative CO<sub>2</sub> emissions for moisture content at FC were equivalent to a soil carbon (C) loss of 1.9 Mg ha<sup>-1</sup> and 1.7 Mg ha<sup>-1</sup> for cropland and shrubland, respectively. This result implies the loss of 43.2% (1.9 Mg C ha<sup>-1</sup> / 4.4 Mg SOC ha<sup>-1</sup>) of the SOC content in the cropland, but for the shrubland it suggests the total loss of the SOC (1.6 Mg C ha<sup>-1</sup> / 1.6 Mg SOC ha<sup>-1</sup>) and a part of the SIC content (0.1 Mg C ha<sup>-1 </sup>/ 152.8 Mg SIC ha<sup>-1</sup>).</p> <p>Our study shows that soil moisture content has a significant effect on CO<sub>2</sub> emissions from calcareous soils, such as Comarca Lagunera, where an increase in soil moisture corresponds to increases in CO<sub>2</sub> emissions into the atmosphere, where SIC and SOC reserves are involved.</p>

Soil CO 2 emissions are formed from biotic and abiotic processes related to organic carbon (SOC) and inorganic carbon (SIC), respectively. Calcareous soil has a high amount of SIC and occurs mainly in arid areas, and little is known about CO 2 emissions from aggregates of this soil. This study aims to evaluate the emission of CO 2 of aggregates from calcareous soil in the Comarca Lagunera, Mexico. Soil samples were taken from the layers of 0.00-0.15 and 0.15-0.30 m, and soil physical and chemical properties were determined. Aggregates distribution was obtained using the dry-sieving method. Macro (0.25-0.149 mm), meso (0.149-0.074 mm) and microaggregates (<0.074 mm) were selected for incubation in a dynamic closed system for 30 days under two moisture contents (15 and 30 %, dry weight basis). The CO 2 emissions were quantified using a non-dispersive infrared gas analyzer (IRGA). From total carbon measured, 97 % were found to be SIC. Soil texture is a sandy clay loam with a field capacity and a permanent wilting point of 27 and 17 %, respectively. From whole soil aggregates, 60 % were distributed in fractions lower than 0.25 mm diameter, which are highly erodible by the wind. Soil moisture content had a significant effect on the emission of CO 2 . The highest accumulated CO 2 emission was registered in the superficial layer (0.00-0.15 m) within 0.25 mm aggregates (29.4 g m -2 h -1 ), which turned out higher than reported for similar areas. The CO 2 emissions were attributed to the dissolution -reprecipitation process of high concentrations of SIC present in soil, involving a considerable contribution of CO 2 to the atmosphere.

Los sustratos representan un componente importante en los sistemas hidropónicos. El objetivo del estudio fue evaluar la adición de composta y mezcla mineral de zeolita-dolomita que permitieran mejorar las características químicas y físicas de los sustratos utilizados para la producción de Capsicum pubescens. Se utilizaron dos sustratos: 1) tezontle y aserrín (1:2) y 2) tezontle, aserrín y composta (1:2:2), dos concentraciones de K en Solución Steiner (50 y 100%) y tres niveles de mezcla mineral (0, 40 y 80 cm3 L‑1) generando 12 tratamientos (2×2×3) establecidos en parcelas subdivididas: la parcela grande correspondió a la concentración de K, la parcela mediana comprendió los dos sustratos y la parcela chica se conformó con los aportes de mezcla mineral. Se evaluó el efecto en las propiedades de densidad aparente, humedad, diámetro de partículas, porosidades, pH, CE, contenido de MO y CO, relación C/N, CIC y contenido nutrimental foliar. La densidad aparente, humedad y porosidades no se vieron afectadas significativamente. La granulometría, aunque hubo diferencias entre tratamientos, los diámetros se ajustaron a los establecidos (<2.50 mm). El pH no fue afectado por los tratamientos, la CE incrementó significativamente (1 dS m-1) por la composta; el contenido de MO fue <30% en los sustratos con la mezcla mineral. La relación C/N de los sustratos con composta fue <19 debido a la descomposición y liberación de N. La CIC fue >8 en los tratamientos con composta, favoreciendo la retención de nutrientes en el sustrato y el incremento de los mismos en el tejido vegetal. Los resultados señalan que, en sustratos sin composta, la CE y la Dap fueron menores cuando se aplicó el 50% de K, sin embargo, las propiedades físicas se asemejaron a las óptimas, siendo el tratamiento testigo el que menor calidad presentó. La adición de composta aumentó el contenido de N, P, Ca y la CIC en los sustratos.