BACKGROUND AND AIMS: The duration of soil organic carbon (SOC) sequestration in agricultural soils varies according to soil management, land-use history and soil and climate conditions. Despite ...several experiments have reported SOC sequestration with the adoption of no-tillage (NT) in Mediterranean dryland agroecosystems scarce information exists about the duration and magnitude of the sequestration process. For this reason, 20 years ago we established in northeast Spain a NT chronosequence experiment to evaluate SOC sequestration duration under Mediterranean dryland conditions. METHODS: In July 2010 we sampled five chronosequence phases with different years under NT (i.e., 1, 4, 11, and 20 years) and a continuous conventional tillage (CT) field, in which management prevailed unchanged during decades. Soil samples were taken at four depths: 0–5, 5–10, 10–20 and 20–30 cm. The SOC stocks were calculated from the SOC concentration and soil bulk density. Furthermore, we applied the Century ecosystem model to the different stages of the chronosequence to better understand the factors controlling SOC sequestration with NT adoption. RESULTS: Differences in SOC stocks were only found in the upper 5 cm soil layer in which 4, 11 and 20 years under NT showed greater SOC stocks compared with 1 year under NT and the CT phase. Despite no significant differences were found in the total SOC stock (0–30 cm soil layer) there was a noteworthy difference of 5.7 Mg ha⁻¹ between the phase with the longest NT duration and the phase under conventional tillage. The maximum annual SOC sequestration occurred after 5 years of NT adoption with almost 50% change in the annual rate of SOC sequestration. NT sequestered SOC over the 20 years following the change in management. However, more than 75% of the total SOC sequestered was gained during the first 11 years after NT adoption. The Century model predicted reasonably well SOC stocks over the NT chronosequence. CONCLUSIONS: In Mediterranean agroecosystems, despite the continuous use of NT has limited capacity for SOC sequestration, other environmental and agronomic benefits associated to this technique may justify the maintenance of NT over the long-term.
In semi-arid Mediterranean areas, studies of the performance of conservation tillage systems have largely demonstrated advantages in crop yield, soil water storage and soil protection against wind ...and water erosion. However, little attention has been given to interactions between soil biochemical properties under different tillage practices. Biochemical properties are useful tools to assess changes caused by different soil tillage systems in long-term field experiments. This study deals with the effect of long-term tillage practices (reduced tillage and no-tillage vs. traditional tillage) on soil chemical properties and microbial functions in three different sites of Spain (two of them located in the Northeast and one in the Southwest) under semi-arid Mediterranean conditions. Soil biological status, as index of soil quality, was evaluated by measuring microbial biomass carbon (MBC) and dehydrogenase (an oxidoreductase) and protease (a hydrolase) activities at three soil depths (0–5, 5–10 and 10–25
cm). In the three experimental areas, increases in soil organic matter content, MBC and enzymatic activities were found at the superficial layers of soil under conservation tillage (reduced tillage and no-tillage) in comparison with traditional tillage. Values of the stratification ratio of some biochemical properties were significantly correlated with yield production in Northeast sites.
Conservation tillage has proven to be an effective strategy to improve soil quality and fertility in Mediterranean areas of Spain.
Under semiarid conditions, soil quality and productivity can be improved by enhancing soil organic matter content by means of alternative management practices. In this study, we evaluated the ...feasibility of no-till (NT) and cropping intensification as alternative soil practices to increase soil organic C (SOC). At the same time, we studied the influence of these management practices on two SOC fractions (particulate organic matter C, POM-C, and the mineral-associated C, Min-C), in semiarid agroecosystems of the Ebro River valley. Soil samples were collected from five soil layers (0-5-, 5-10-, 10-20-, 20-30-, 30-40-cm depth) during July 2005 at three long-term tillage experiments located at different sites in the Ebro River valley (northeast Spain). Soil bulk density, SOC concentration and content, SOC stratification ratio, POM-C, and Min-C were measured. Higher soil bulk density was observed under NT than under reduced tillage (RT), subsoil tillage (ST), or conventional tillage (CT). At the soil surface (0-5-cm depth), the highest total SOC concentration, POM-C, and Min-C were measured under NT, followed by RT, ST, and CT, respectively. In the whole soil profile (0-40 cm), similarly, slightly greater SOC content was measured under NT than under CT with the exception of the Selvanera site, where deep subsoil tillage combined with moldboard plowing accumulated more SOC than NT. In semiarid Mediterranean agroecosystems where CT consists in moldboard plowing, NT is a viable management practice to increase SOC.
► Long-term effects of tillage and N fertilization on soil biochemical properties were evaluated in Mediterranean conditions. ► Greater SOC and soil biochemical properties in no-tillage were only ...observed in the soil surface. ► Nitrogen fertilization did not significantly affect soil dehydrogenase and protease activities.
Tillage and N fertilization practices contribute to the balance between soil C inputs and outputs. Thus, the impacts of both practices and their interactions on soil organic C (SOC) dynamics must be studied. The main objective of this study was to determine long-term effects of tillage and N fertilization on soil biochemical properties in a long-term experiment established in 1996 on a dryland Typic Xerofluvent soil cropped with barley (Hordeum vulgare L.) in NE Spain. The response of SOC concentration, soil microbial biomass carbon (SMBC) and soil enzyme activities (DHA, dehydrogenase, and PRA, protease) to different tillage (no-tillage, NT; reduced tillage, RT; and conventional tillage, CT) and N treatments (zero, 0kg Nha−1; medium, 60kg Nha−1; and high, 120kg Nha−1) were measured in 2008 at four soil depths (i.e., 0–5, 5–10, 10–25 and 25–50cm). All the soil biochemical properties studied showed significant differences for tillage, depth and the interaction between tillage and soil depth. However, N fertilization rates only affected the SMBC content, which was greater under 120kg Nha−1 than under 0kg Nha−1 in the 10–25cm soil layer. In the soil surface layer (0–5cm), SOC, SMBC and DHA levels in CT were about 50% of the levels in the NT plots. However, in the 10–25cm soil layer, a greater SOC concentration in CT compared with NT and RT was also accompanied by SMBC and DHA values 30% higher in CT. Below 25cm soil depth, similar values of soil biochemical properties were found among tillage systems. There was a significant correlation among almost all the parameters studied, with the greatest correlations between SOC and SMBC and between SOC and DHA. In semiarid Mediterranean conditions, after 12 years of experiment, tillage impacted soil biochemical properties in a greater extent compared with N fertilization even though this effect was only limited to the upper soil layers.
In semiarid agroecosystems of the Ebro valley (NE Spain) soils are characterized by low soil organic matter (SOM) and a weak structure. In this study we investigated the individual and combined ...effect of tillage system (no‐tillage, NT; reduced tillage, RT; conventional tillage, CT) and cropping system (barley–fallow rotation at the Peñaflor site, PN‐BF and continuous barley at the Peñaflor site, PN‐BB) on soil organic carbon (SOC) storage as well as the physical protection of SOM fractions by soil aggregates in three long‐term experimental sites. In both cropping systems, total SOC content was more than 30% higher in NT compared with CT in the 0‐ to 5‐cm depth. The suppression of fallowing in the PN‐BB cropping system led to a greater SOC stabilization only in NT. In all the three sites, greater proportion of water‐stable macroaggregates (>250 μm) was found under NT than under CT in the 0‐ to 5‐cm depth. Macroaggregate organic C concentration (250–2000 μm) was greater in NT compared with CT in the BB cropping system, but did not differ with tillage treatment in the PN‐BF rotation. Greater proportion of microaggregates within macroaggregates in NT compared with CT was only found in the Agramunt site (AG). However, greater C stabilized inside these microaggregates was observed in AG, Selvanera site (SV), and PN‐BB in the 0‐ to 5‐cm depth. The results of this study demonstrate that in the semiarid Mediterranean agroecosystems of the Ebro valley, the adoption of NT together with the suppression of long‐fallowing period can significantly increase the amount of SOC stabilized in the soil surface and improve soil structure and aggregation.
There is limited information on the effects of tillage practices on soil hydraulic properties, especially changes with time. The objective of this study was to evaluate on a long-term field ...experiment the influence of conventional tillage (CT), reduced tillage (RT) and no-tillage (NT) on the dynamics of soil hydraulic properties over 3 consecutive 16–18 month fallow periods. Surface measurements of soil dry bulk density (
ρ
b), soil hydraulic conductivity (
K(
ψ)) at −14, −4, −1 and 0
cm pressure heads using a tension disc infiltrometer, and derived hydraulic parameters (pore size, number of pores per unit of area and water-transmission porosity) calculated using the Poiseuille's Law were taken on four different dates over the fallow period, namely, before and immediately after primary tillage, after post-tillage rains and at the end of fallow. Under consolidated structured soil conditions, NT plots presented the most compacted topsoil layer when compared with CT and RT. Soil hydraulic conductivity under NT was, for the entire range of pressure head applied, significantly lower (
P
<
0.05) than that measured for CT and RT. However, NT showed the largest mean macropore size (0.99, 0.95 and 2.08
mm for CT, RT and NT, respectively;
P
<
0.05) but the significantly lowest number of water-conducting pores per unit area (74.1, 118.5 and 1.4
macropores per m
2 for CT, RT and NT, respectively;
P
<
0.05). Overall, water flow was mainly regulated by macropores even though they represented a small fraction of total soil porosity. No significant differences in hydraulic properties were found between CT and RT. In the short term, tillage operations significantly increased
K (
P
<
0.05) for the entire range of pressure head applied, which was likely a result of an increase in water-conducting mesopores despite a decrease in estimated mesopore diameter. Soil reconsolidation following post-tillage rains reduced
K at a rate that increased with the intensity of the rainfall events.
Carbon sequestration in agricultural soils can contribute to offsetting CO
2 anthropogenic emissions and also to enhance soil fertility, soil water retention and crop production. In this experiment, ...our main objective was to validate the Century model for Mediterranean semiarid agroecosystems and to investigate management effects on soil organic carbon (SOC) dynamics in these areas. Data from a long-term experiment in NE Spain comparing three tillage systems (no-tillage, NT; reduced tillage, RT; conventional tillage, CT) and two cropping systems (barley-fallow rotation, BF and continuous barley system, CB) was used to simulate SOC with the Century model in the 0–30
cm soil depth. The model was able to accurately simulate SOC and above-ground C inputs under different tillage systems although it over-estimated C inputs in some growing seasons (e.g. 2000). Simulated and measured C inputs showed a significant relationship (
P
<
0.001;
R
2
=
0.83) and both tended to decrease as tillage intensity decreases but differences were not statistically significant. However, SOC content was greater under NT than under CT and RT. Also, intensification of cropping systems (i.e. eliminating bare fallow) led to greater SOC in all tillage treatments. Consequently, SOC sequestration rates were greatest in NT followed by RT and CT in the CB system with 0.46, 0.24 and 0.18
Mg
C
ha
−1
yr
−1, respectively. In the BF rotation lower SOC sequestration rates were found with values ranged from 0.15 to −0.004
Mg
C
ha
−1
yr
−1 in NT and CT, respectively. Both simulation and measured values showed that reduction in tillage intensity and an intensification of the cropping system are promising strategies to increase SOC sequestration under semiarid Mediterranean conditions. The Century model is a useful tool to simulate tillage and cropping system effects on SOC dynamics in semiarid Mediterranean agroecosystems.
Losses of soil organic carbon (SOC) have contributed to CO2 emissions from soils to the atmosphere and to global climate change. We hypothesized that in semiarid agroecosystems of the Mediterranean ...region, a shift from the traditional management system (including conventional tillage CT and a cereal-fallow rotation) to a more conservative system, including no-till (NT) and continuous cropping, could reduce CO2 emissions during the cropping season. Thus, in this study, we studied the effects of tillage and cropping systems on C inputs and soil CO2 fluxes during three cropping seasons at three different sites in the Ebro River valley (northeast Spain). Carbon inputs ranged from 650 to 6000 kg ha-1 and seasonal average CO2 flux ranged from 0.10 to 1.76 g CO2 m-2 h-1. Differences in rainfall led to marked differences in C inputs and soil fluxes among growing seasons. Although differences among tillage treatments were weak, CO2 fluxes under NT were always lower. Intensification of cropping systems led to an increase in C input. A move from CT to NT together with cropping intensification is suitable to increase C inputs and to reduce soil CO2 fluxes in semiarid Mediterranean agroecosystems.
The co-ordinated European research project Wind Erosion and Loss of SOil Nutrients in semiarid Spain (WELSONS) was carried out from 1996 to 1999 to understand and predict the potential impacts of ...land-use change and management on soil degradation by wind erosion on agricultural land in Central Aragon, a semiarid desertification-threatened region in NE Spain. This paper gives a description of the project's experimental approach and an overview of the main results regarding the effects of agricultural practices (i.e. conventional, CT, versus reduced tillage, RT) on surface conditions affecting wind erosion, the mobilisation of soil particles in the saltation layer and the atmospheric emission of fine dust into the suspension layer. The characterisation of the soil surface showed that soil erodibility by wind under RT was lower than that under CT. Though strong
Cierzo wind events occurred during the experimental period, only a limited amount of material was available for wind erosion mainly due to soil crusting, a common feature in the area. In spite of this, saltation transport flux was measured at CT plots for different erosion episodes. Also, significant vertical emission of dust was observed only in the CT plot. Finally, the sandblasting efficiency calculated in the present experiment could be interpreted as the result of a higher binding energy for the particles of the silt loam experimental soil compared to soils with a lighter texture.
Knowledge of soil water conductive porosity is of paramount importance for understanding the water and solute movement in soil. The objective of this study was to describe and evaluate an alternative ...pore index, i.e., the representative mean pore radius for two consecutive soil water tensions (lambda delta psi), for characterizing the water-transmitting macro- and mesoporosity of soil. The hydraulic conductivity (K) and related hydraulic parameters were measured using a tension disk infiltrometer at -14, -4, -1, and 0 cm water pressure heads at a soil depth of 2 cm on a long-term conservation tillage experiment (after 9 yr of trial) under conventional tillage (CT), reduced tillage (RT), and no-tillage (NT) treatments. The soil was loam (Xerollic Calciorthid). The measurements were performed within the first half of a 16- to 18-mo-long fallow period. Unlike the model based on the classical capillary rise theory, which assumes no differences between measurement sites (e.g., tillage treatments) for the corresponding equivalent pore radius (C₀) for macro- and mesopores, significant differences in lambda delta psi values for macro- and mesopores were found between the three tillage systems tested. The number of water-transmitting macro- and mesopores per unit area estimated by means of the capillary rise approach was significantly greater than that calculated using the lambda delta psi pore index. Although significantly higher values of lambda delta psi for both macro- and mesopores were observed under NT, a significantly lower near-saturation K was found under NT than CT and RT treatments due to the lower density of water-transmitting macro- and mesopores.
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