Formation of aggregates and carbon sequestration in ameliorated tepetates in the Rio Texcoco basin, Mexico

In many states of central Mexico, hardened volcanic materials called tepetate (hardened layers from tuff) cover large proportions of the land surface, and are therefore of economic and social importance. Under natural conditions, tepetates are unproductive due to their hardness and low porosity, but they can be used agriculturally after the hardened layer is broken up and fertilizer and organic matter are added Just broken up tepetate consists of angular clods of the original consolidated material of various sizes and they are devoided of aggregate. Because of the scarce presence of organic matter these fragmented tepetates present low availability of N and P, limited water infiltration, and small water holding capacity Additions of manure and cultivation of Leguminosae aim to improve the physical properties of tepetates and particularly to promote the formation of aggregates. Such ameliorated tepetates alleviate the demand for agricultural land. The aim of this study was to evaluate the formation of aggregates from initially broken zip and fragmented tepetates, their dry and wet stability, and the distribution of organic carbon in aggregates and fragments of different sizes in tepetates cultivated between 1 and 100 years. The tepetates were were arbitrarily classified as (I) recently broken up; (II) affected by severe erosion: (III) cultivated mostly under monoculture: (IV) cultivated with Leguminosae for at least 20 years and receiving approximately 2 Mg.ha(-1) of farm yard manure (FYM) per year; (V) cultivated under no-tillage and few external inputs; (VI) cultivated with cereals and Leguminosae and receiving more than Mg.ha(-1) per year of FYM; (VII) Used as greenhouse bed; (VIII) cultivated with no-tillage and approximately 5 to 10 Mg.ha(-1) of FYM; (IX) used as greenhouse bed and addition of approximately 2 Mg.ha(-1) of composted wood residues per year In addition to the above mentioned tepetates, two agricultural soils: one managed with traditional tillage (A) and a second with no tillage (IX) were included as checks. We collected 97 samples of tepetates and four soils in the Basin of the Rio Texcoco and neighboring communities. The aggregate stability test overestimated stable aggregates due to the presence of remaining hard fragments of tepetates of different size; the hardness of the latter was one to three times greater than that of the aggregates. The relative amount of stable aggregates increased with the time of cultivation, approaching 80% after 100 years. The recently broken zip tepetates contained only little of C, whereas stable aggregates showed one to three times larger concentration. The accumulation of C with time in tepetate fragments was small, in contrast to the aggregates formed in the same period. The accumulation of organic C was larger in smaller aggregate particles and followed logarithmic or potential models. The results of this study show that ameliorated tepetates have the potential to store carbon. However the accumulated amount of C depend on the aggregate formation, which in turn is related with the agricultural management. Classes VII, VIII y IX produced more stable aggregates and thus aecumulated more carbon

Formation of aggregates and carbon sequestration in ameliorated tepetates in the Rio Texcoco basin, Mexico

In many states of central Mexico, hardened volcanic materials called tepetate (hardened layers from tuff) cover large proportions of the land surface, and are therefore of economic and social importance. Under natural conditions, tepetates are unproductive due to their hardness and low porosity, but they can be used agriculturally after the hardened layer is broken up and fertilizer and organic matter are added Just broken up tepetate consists of angular clods of the original consolidated material of various sizes and they are devoided of aggregate. Because of the scarce presence of organic matter these fragmented tepetates present low availability of N and P, limited water infiltration, and small water holding capacity Additions of manure and cultivation of Leguminosae aim to improve the physical properties of tepetates and particularly to promote the formation of aggregates. Such ameliorated tepetates alleviate the demand for agricultural land. The aim of this study was to evaluate the formation of aggregates from initially broken zip and fragmented tepetates, their dry and wet stability, and the distribution of organic carbon in aggregates and fragments of different sizes in tepetates cultivated between 1 and 100 years. The tepetates were were arbitrarily classified as (I) recently broken up; (II) affected by severe erosion: (III) cultivated mostly under monoculture: (IV) cultivated with Leguminosae for at least 20 years and receiving approximately 2 Mg.ha(-1) of farm yard manure (FYM) per year; (V) cultivated under no-tillage and few external inputs; (VI) cultivated with cereals and Leguminosae and receiving more than Mg.ha(-1) per year of FYM; (VII) Used as greenhouse bed; (VIII) cultivated with no-tillage and approximately 5 to 10 Mg.ha(-1) of FYM; (IX) used as greenhouse bed and addition of approximately 2 Mg.ha(-1) of composted wood residues per year In addition to the above mentioned tepetates, two agricultural soils: one managed with traditional tillage (A) and a second with no tillage (IX) were included as checks. We collected 97 samples of tepetates and four soils in the Basin of the Rio Texcoco and neighboring communities. The aggregate stability test overestimated stable aggregates due to the presence of remaining hard fragments of tepetates of different size; the hardness of the latter was one to three times greater than that of the aggregates. The relative amount of stable aggregates increased with the time of cultivation, approaching 80% after 100 years. The recently broken zip tepetates contained only little of C, whereas stable aggregates showed one to three times larger concentration. The accumulation of C with time in tepetate fragments was small, in contrast to the aggregates formed in the same period. The accumulation of organic C was larger in smaller aggregate particles and followed logarithmic or potential models. The results of this study show that ameliorated tepetates have the potential to store carbon. However the accumulated amount of C depend on the aggregate formation, which in turn is related with the agricultural management. Classes VII, VIII y IX produced more stable aggregates and thus aecumulated more carbon

Glomalin and carbon sequestration in cultivated tepetates = Glomalina secuestro de carbono en tepetates cultivados

The tepetates are hardened volcanic tuffs that outcrop on the surface due to erosive processes; some of them can be ameliorated for agriculture and thus sequester carbon (C). This element accumulates in fragile aggregates that are formed as part of their developing physical structure after being cultivated, but the mechanism by which it is sequestered in the mineral fraction in these volcanic substrates is unknown. It is assumed that the biological activity contributes to the stabilization of the organic C (COS), specifically that of the arbuscular mycorrhizal fungi (AMF). It has been postulated that glomalin (a glycoprotein produced by the AMP) influences both processes. To contribute to the comprehension of this phenomenon, the present study was made with the following objectives: 1) to evaluate the accumulation of COS, glomalin and glomalin carbon (GC) in cultivated tepetates; 2) to measure the contribution of C made by the glomalin to the COS; and 3) to evaluate the tendency of accumulation of GC with years of cultivation. Based on interviews with producers of the Texcoco River basin, 83 plots were selected with 10 to 20 years of cultivation, and 10 classes of agronomic management were defined (I to X). As reference four Phaesozem soils of the region were used, grouped in two classes of management. Another 21 plots of tepetate had from 4 to over 100 years of cultivation. Tepetate samples were collected (0-20 cm) and COS, glomalin and GC were determined. The relationship between COS and the latter variables was close (R>0.91). The agronomic management had significant influence (p <= 0.05) on the accumulation of COS, glomalin and GC. As function of the maximum concentration of COS observed, it was calculated that the tepetates ameliorated for agricultural production after two decades of cultivation, with an agronomic management with constant incorporation of organic residues, have capacity for storing approximately 90 t ha(-1) of C in the first 20 cm of depth, with a contribution of 15 % of stabilized C from glomalin (p <= 0.05). The accumulation of GC as a function of time followed a logarithmic tendency

Probability of mortality by fire damage of young Pinus hartwegii Lindl. trees in the Izta-Popo National Park

A nivel mundial se realizan grandes esfuerzos para determinar el efecto del fuego en la mortalidad de especies arbóreas como las del género Pinus . En este trabajo se evaluó la inf luencia del fuego en la probabilidad de mortalidad del arbolado joven de Pinus hartwegii en el Parque Nacional Izta-Popo, área natural protegida del centro de México. Los efectos de un incendio de mediana a alta intensidad ocurrido en marzo del 2013, una quema prescrita de baja intensidad realizada en abril del mismo año y un área testigo sin presencia de fuego reciente se valoraron y compararon. Los resultados mostraron que 18 meses después de aplicados los tratamientos, la mortalidad del arbolado en el área con quema prescrita fue de 13 %, mientras que en el área incendiada y testigo fue de 28 y 4 %, respectivamente. Se obtuvieron seis modelos logísticos para predecir la mortalidad; el porcentaje de copa dañada, la altura de cicatriz y el diámetro normal con corteza fueron las variables significativas ( P < 0.05) de predicción. Los resultados sugieren que la disminución en la capacidad fotosintética y en el transporte de nutrimentos, asociados al daño de la copa y al cámbium, están estrechamente ligados con la probabilidad de mortalidad