Soil Macroporosity Research Articles

Of macropores and tillage: influence of biomass incorporation on cover crop decomposition and soil respiration

AbstractCarbon sequestration in agricultural soils may help to reduce global greenhouse gas concentrations, but building up soil carbon levels requires accumulating organic matter faster than it is lost via heterotrophic respiration. Using field and laboratory studies, this study sought to elucidate how tillage, the below‐ground incorporation of cover crop residue, and soil macroporosity affect soil respiration and residue decomposition rates. In the field, residue from a cover crop mixture of barley (Hordeum vulgare) and crimson clover (Trifolium incarnatum) was placed into litter bags that were left on the surface versus incorporated into the soil at three depths (4, 8 or 12 cm), while the laboratory study compared surface‐placed versus incorporated litter (8 cm depth). To assess tillage effects on cover crop decomposition, the field study simulated no‐till and conventional tillage treatments, while the laboratory and field studies both included treatments in which artificial soil macropores were created. The field study showed that conventional tillage and the presence of macropores enhanced soil respiration, while in the laboratory study, incorporating cover crop residue resulted in higher soil respiration and faster litter decomposition rates. Additionally, the laboratory measurements showed that macropores increased soil respiration in wet conditions, likely by enhancing oxygen diffusion. Thus, organic matter incorporation and macropores may represent important factors that affect soil respiration and carbon dynamics.

Soil macroinvertebrates community and its temporal variation in a well-drained savannah of the Venezuelan Llanos

In the well-drained savannahs of Venezuelan Llanos, intensive agricultural activities could be causing damage to the soil, with negative consequences for the ecosystem. In order to avoid this problem, some agroecological alternatives are needed. Consequently, it is necessary to know the biologic dimension in this ecosystem, and within this, the soil macroinvertebrate community. The purpose of this work was to characterize this community in the natural savannah: its structure and diversity, its time variation and its relationship with the physical-chemical properties of the soil. A total of 72 samples were taken in different season along a period of time of 1405 days. The results revealed that the soil macrofauna had an average density of 243.5 ± 183.6 ind·m−2, distributed in 32 families of 11 orders, with a diversity of N1 = 4.5 ± 2.8 families. Coleoptera, Hymenoptera and Isoptera was the most dominants orders. The density, richness and diversity of families showed a temporal variation (r ≥ −0.5; p < 0,05). Additionally, the structure of the soil macroinvertebrate community showed a vertical variation. The relationship with soil properties differed according families: Lampyridae, Aphodiidae and Formicidae had a positive correlation with soil macro-porosity (radius of the pores > 15 μm); Tenthredinidae and Tenebrionidae had a positive correlation with the micro-porosity (pores ≤ 15 μm). The community in general, correlated positively with soil porosity and negatively with bulk density. This suggests that these soil properties need to be considered when designing agroecological technics in this area.

New molecular evidence for surface and sub-surface soil erosion controls on the composition of stream DOM during storm events

Abstract. Storm events are responsible for more than 60 % of the export of dissolved organic matter (DOM) from headwater catchments due to an increase in both the discharge and concentration. The latter was attributed to changing water pathways inducing the mobilization of DOM from the surface soil horizons. Recent molecular investigations have challenged this view and hypothesized (i) a contribution of an in-stream partition of organic matter (OM) between eroded particles and the dissolved fraction and (ii) the modification of the composition of soil DOM during storm events. To investigate these assumptions, soil solutions in the macropores, surface runoff and stream outlet were sampled at high frequency during three storm events in the Kervidy–Naizin catchment, part of the French critical zone observatory AgrHyS. The molecular composition of the DOM was analysed by thermally assisted hydrolysis and methylation (THM) with tetramethylammonium hydroxide (TMAH) coupled to a gas chromatograph and a quadrupole mass spectrometer. These analyses highlighted a modification of the DOM composition in soil solution controlled by the water-table dynamic and pre-event hydrological conditions. These findings fit with the mechanism of colloidal and particulate destabilization in the soil macroporosity. The different behaviour observed for lignins, carbohydrates and fatty acids highlights a potential chemical segregation based on their hydrophobicity. The composition of surface runoff DOM is similar to the DOM composition in soil solution and could be generated by the same mechanism. The DOM composition in both soil solution and surface runoff corresponds to the stream DOM composition observed during storm events. On the basis of these results, modifications of the stream DOM composition during storm events seem to be due to surface and sub-surface soil erosion rather than in-stream production.

Inorganic Fertilization Effects on the Structure of a Calcareous Silt Loam Soil

Core Ideas Long‐term inorganic fertilization decreased aggregate stability. Long‐term inorganic fertilization decreased soil macroporosity. Long‐term inorganic fertilization did not change soil organic C content. Soil water‐holding capacity was not affected by inorganic fertilization. Swine manure combined with inorganic fertilizers improved soil structure. Inorganic fertilizers have been intensely used in the North China Plain (NCP) to maintain or increase crop yields, but their effects on soil physical properties, especially soil structure, are unclear. The objective of this study was to evaluate the effects of 12 yr of successive application of inorganic fertilization on soil aggregate stability, pore structure, and hydraulic properties of a calcareous silt loam soil. A long‐term field experiment (2001–2013) was established at Luancheng Ecosystem Station, NCP. The experiment included three fertilization treatments: (i) inorganic fertilizer, NPK; (ii) inorganic fertilizer and organic manure, NPKOM; and (iii) a control treatment with no fertilizer, CK. Results showed plots receiving long‐term NPK and NPKOM had significantly greater wheat (Triticum aestivum L.) (275 and 307%, respectively) and maize (Zea mays L.) yields (59 and 107%, respectively) than the control. However, the application of inorganic fertilizer significantly decreased aggregate stability and macroporosity, by 55.3 and 36.1%, respectively, relative to the control. No differences in soil organic carbon (SOC), bulk density (BD), saturated conductivity (Ks), and water‐holding capacity were found between the NPK and the CK treatments. On the other hand, the addition of organic manure with inorganic fertilizers increased SOC, total porosity, and saturated conductivity by 38.5, 5.2, and 75%, respectively, compared with the CK treatment. This study indicated inorganic fertilization alone could not improve soil structure of the calcareous silt loam, although it maintained high yields. Use of organic amendments along with inorganic fertilizers can improve soil structure and crop yields.

English

The system of intercropping maize with other plant species has been a common practice for several years, but its use has been increasingly mainly to improve the quality of soil physical properties of no-tillage system. The objective of this study was to investigate the effect of intercropping using different cover plants on the physical properties of soil and the productivity of maize. Field experiments were conducted on the property of Mr. Arno Paulo Deimling, located in Linha S&atilde;o Jo&atilde;o, in the municipality of Quatro Pontes-PR. The experiment was carried out using a randomized complete block design, with four treatments and five repetitions. The treatments were winter maize intercropped with Urochloa brizantha, Urochloa ruziziensis or black oats (Avena strigosa), and maize sown in monoculture. In winter period, the production of maize used for silage and the production of dry matter from cover crops were assessed. The physical properties of soil samples were also investigated. Cover crops did not influence the productivity of winter maize used for silage, but it promoted improvements in soil macroporosity. The cover crops promoted improvements in the macroporosity of the soil and reduction at soil penetration resistance, particularly in the area planted with U. brisantha, demonstrating its potential in improving water infiltration and soil aeration. &nbsp; Key words: Direct seeding system, green manures, macroporosity, soil penetration resistance, conservationist system.

Computed tomography and soil physical measurements of compaction behaviour under strip tillage, mulch tillage and no tillage

In recent years, there has been an increased application of conservation-oriented tillage techniques, where instead of being turned the soil is only loosened or not tilled at all. Strip tillage, a special form of conservation tillage, results in small-scale structural differences, since tillage is performed only within the seed row, while the soil between seed rows is not tilled. However, tillage always impacts upon physical soil properties and processes.A combined application of conventional soil mechanical methods and X-ray computed tomography (X-ray CT) is employed here in order to investigate small-scale structural differences in a chernozem (texture 0–30 cm: silt loam) located in central Germany under strip tillage (within and between seed rows) compared to no tillage and mulch tillage. Apart from recording changes over time (years: 2012, 2014, 2015) to dry bulk density and saturated conductivity at soil depths 2–8 and 12–18 cm, stress-strain tests were conducted to map mechanical behaviour for a load range of 5–550kPa at a soil depth of 12–18cm (year 2015). Mechanical precompression stress was determined from the stress-dry bulk density curves. In addition, computed tomography scans were created followed by quantitative image analysis of the morphometric parameters mean macropore diameter, macroporosity, connectivity and anisotropy of the same soil samples.For strip tillage between seed rows and no tillage, a significant increase in dry bulk density was observed over time compared to strip tillage within the seed row and mulch tillage. This was more pronounced at a soil depth of 2–8cm than at 12–18cm. Despite higher dry bulk density, strip tillage between the seed row displayed also an increasing saturated conductivity compared to strip tillage within the seed row and mulch tillage. The computed tomography scans showed that the macropores became more compressed and soil aggregates were pushed together as mechanical stress increased, with the aggregate arrangement being transformed down into a coherent soil mass. The soil mechanical and morphometric parameters supported each other in terms of what they revealed about the mechanical properties of the soil structures. For instance, in the strip tillage between seed rows and no tillage treatments, the lack of soil tillage not only resulted in higher dry bulk densities, but also higher aggregate densities, mechanical precompression stress values, mean macropore diameters as well as lower macroporosity and connectivity values compared to mulch tillage and strip tillage within the seed row. The computed tomography parameters are therefore highly suitable for providing Supplementary information about the compaction process. Overall, this study showed that strip tillage combines the advantages of no tillage and a deeper, soil conservation-oriented primary tillage because, on a small scale, it creates two distinct soil structures which are beneficial in terms of optimal plant growth as well as mechanical resistance by driving over the soil.

Exclosure on CT-measured soil macropore characteristics in the Inner Mongolia grassland of northern China

Grassland exclosure is a widely-used option to prevent from grazing in degraded grasslands for restoration. However, the influence of exclosure on soil macropore of grassland remain scarce. The objective of this study was to quantify the pore architecture of grassland soils under exclosure. Two treatments, 9E (grassland enclosed for 9 years) and 5E (grassland enclosed for 5 years), were designed, with grazing as a control in the experiment. Nine soil columns (0–50 cm deep) were taken at the three sites with three replicates. At each site, three soil columns were from the grassland, and cores were scanned with a Philips Brilliance ICT Medical Scanner. Numbers of macropores, macroporosity, network density, length density, and node density within the 50-cm soil profile were interpreted from X-ray computed tomography to analyze soil pore architecture. The results indicated that exclosure significantly influenced CT-measured soil macroporosity in the Inner Mongolia grassland of northern China. Soils under enclosed grassland had greater macroporosity, length density, total volume, and node density than that of under freely grazed grassland. Macroporosity increased as the enclosure age increased. For soils under enclosed grassland, macropores were concentrated at 0–300-mm soil layers, and macropores were mainly present at 0–100-mm soil depth under freely grazed grassland. The large number of macropores found in soil under enclosed grassland can be attributed to greater root development. Exclosure increases soil macroporosity and improve soil structure.

Soil faunal and structural responses to the settlement of a semi-sedentary earthworm Lumbricus terrestris in an arable clay field

We studied the soil community and habitat consequences of introducing a deep-burrowing, sedentary life-style earthworm, Lumbricus terrestris (dew-worm) into arable zero-till clay. Seventeen years after introduction, which was originally aimed at improving the macroporosity and permeability of the heavy clay soil, we returned to the gradient of L. terrestris dispersal (well established, more recent and no settlement) and investigated the temporal development of the ecosystem engineering impacts on different faunal groups (earthworms, enchytraeids and nematodes) and soil porosity. The faunal responses were examined both at L. terrestris midden scale (individual living site) and field scale. We found that L. terrestris middens sustained elevated densities of all three faunal groups. In the case of earthworms, there was evidence for temporal development of the engineering impact as the difference between the midden and non-midden areas was more pronounced in the well-established areas than close to the leading edge of dispersal. The earthworm community composition was not altered at L. terrestris midden sites. The settlement of L. terrestris had no discernible effects on field-scale earthworm and nematode abundances, but enchytraeids were practically absent beyond the leading edge of the dispersal. This effect might, however, be partly explained by a gradient of increasing clay content. Soil macroporosity at L. terrestris midden sites did not increase with the age of L. terrestris settlement. Our results suggest that L. terrestris settlement in a clay soil can significantly increase the spatial patchiness of soil fauna, but may not, except in the case of enchytraeids, affect their field-scale abundances or the macroporosity of the soil in the vicinity of L. terrestris living sites.

Transport of 3,5,6-trichloro-2-pyrdionl (a main pesticide degradation product) in purple soil: Experimental and modeling

Purple soil, a loamy entisol dominating the hilly central Sichuan basin in the upper reaches of Yangtze River, is low in organic matter content and abundant in macropores that form the rapid transport network for water and solutes including pesticides. However, effects of soil's macroporosity on transport of pesticides has not been quantitatively explored and simulated at the column scale. In this study, we explore the transport of 3,5,6-trichloro-2-pyrdionl (TCP), a main pesticide degradation product, in purple soil through experiments and simulations on typical farmland categories, including rice-rape and vegetable farmland. Soil water retention characteristics (SWRCs) and physical properties are measured to learn the hydraulic parameters and porous structures of the soil. Batch experiments are conducted to obtain the adsorption coefficient of TCP on soil, and breakthrough curves of Br− (a conservative tracer) in undisturbed soil columns are applied to evaluate the hydrodynamics of TCP transport. The two-region model is used to simulate the transport processes, and the parameters are obtained by inversion simulation. It is found that TCP transport in purple soil exhibited complex patterns and is strongly affected by both chemical and physical non-equilibrium. A higher pollution risk on water body of rice-rape field is due to the stronger preferential flow and better pore connectivity despite the larger macroporosity observed in vegetable field. These results can provide useful data and modeling approach for evaluating the risk of pesticide leaching toward groundwater.

Surfactant-enhanced flushing enhances colloid transport and alters macroporosity in diesel-contaminated soil

Soil contamination by diesel has been often reported as a result of accidental spillage, leakage and inappropriate use. Surfactant-enhanced soil flushing is a common remediation technique for soils contaminated by hydrophobic organic chemicals. In this study, soil flushing with linear alkylbenzene sulfonates (LAS, an anionic surfactant) was conducted for intact columns (15cm in diameter and 12cm in length) of diesel-contaminated farmland purple soil aged for one year in the field. Dynamics of colloid concentration in column outflow during flushing, diesel removal rate and resulting soil macroporosity change by flushing were analyzed. Removal rate of n-alkanes (representing the diesel) varied with the depth of the topsoil in the range of 14%–96% while the n-alkanes present at low concentrations in the subsoil were completely removed by LAS-enhanced flushing. Much higher colloid concentrations and larger colloid sizes were observed during LAS flushing in column outflow compared to water flushing. The X-ray micro-computed tomography analysis of flushed and unflushed soil cores showed that the proportion of fine macropores (30–250μm in diameter) was reduced significantly by LAS flushing treatment. This phenomenon can be attributed to enhanced clogging of fine macropores by colloids which exhibited higher concentration due to better dispersion by LAS. It can be inferred from this study that the application of LAS-enhanced flushing technique in the purple soil region should be cautious regarding the possibility of rapid colloid-associated contaminant transport via preferential pathways in the subsurface and the clogging of water-conducting soil pores.

English

An experiment was conducted at the Agronomic Institute of Parana – IAPAR, at the Experimental Station of the municipality of Santa Tereza do Oeste – PR, in Hapludox of clayey soil. Studies with the use of plants cover crops with vigorous root system in different systems of soil management systems are needed, in order to have a diversity of species capable of producing different amounts of crop residues which by decomposing, can alter the physical attributes and consequently, the productivity of the successor culture. The objective of this study was to evaluate the effect of crambe crop and plant cover crops in succession on the physical characteristics of a Haplortox under no-tillage system. The experimental area has been cultivated under no-tillage system for 18 years. The experimental area consisted of 15 plots, each plot with 20x25 m. In 12 plots, plant cover crops were planted, six species of summer and six of winter and the last three consisted of plots with no-tillage system with gypsum application, no-tillage system with scarification and traditional no-tillage (control) in a completely randomized design. The physical attributes of this soil were soil density (DS), total porosity (PT), microporosity (Micro), macroporosity (Macro) and saturated hydraulic conductivity (Ksat) of the soil in the periods of 2014 (initial characterization of the soil) and 2015 (after crambe culture). The microporosity (0.0-0.1 m layer) and Ksat (all soil layers) presented significant differences between treatments in the period of 2015. Microporosity was lower in the pigeon pea coverage (PP) (36.08%), while the largest occurred in the coverage of crambe C5 (45.38%). The Ksat was higher in the dwarf pigeon pea (DPP) (298.20 mm h-1) and sunn hemp (SH) (163.39 mm h-1) coverage in the 0.0-0.1 m layer. The highest Ksat was observed for crambe C9 (96.81 mm h-1), C8 (74.13 mm h-1), velvet bean (70.95 mm h-1) and C5 (53.94 mm h-1) respectively, in the soil layer of 0.1-0.2 m. Key words: Soil management, soil structure, residues.

Preferential flow characteristics of reclaimed mine soils in a surface coal mine dump

There are a large number of macropores/tubular channels of a few centimeters and plant roots in reclaimed dump soils, which are the main reasons for the formation of soil macropores and soil preferential flow. To systematically study the morphological characteristics and variation of soil preferential flow for different reclaimed vegetations in a dump, a dye-staining experiment and physical and chemical analysis were carried out to investigate the formation mechanism and influencing factors of soil preferential flow in the vegetation restoration process. The results indicate that there were differences in the soil water breakthrough curves for different plots. The macropore effluent rate generally increased at first and then tended to stabilize. The soil steady effluent rate decreased with increasing soil depth, which reached the maximum and minimum values at the depths of 0∼5cm (0.0193∼0.0315mms-1) and 50∼60cm (0.0028∼0.0035mms-1), respectively. Furthermore, the radius of soil macropores under different types of reclaimed vegetation ranged from 0.03 to 4.71mm, most of which ranged from 0.11 to 2.36mm. The soil macroporosity of different reclaimed vegetation types ranged from 0.03 to 16.58%, which was significantly greater than 5%. The soil macroporosity determined 65% of the variation in the steady effluent rate and 42% of the variation in the saturated hydraulic conductivity. Furthermore, the dye coverage ratio decreased as the soil layer depth increased in different plots, and there were some differences in each plot. The maximum dye coverage ratio occurred in the 0∼5cm soil layer, which reached 90.37%. The dye coverage ratio at a depth of 0∼60cm in six plots followed the order of Robinia pseudoacacia (26.48%)>Ulmus pumila (20.12%)>mixed forest (17.32%)>farmland (15.06%)>shrub (13.97%)>weeds (10.07%). The soil preferential flow mostly occurred in the 0∼40cm soil depth layer, which occupied more than 93% of the total soil profile (0∼60cm). Moreover, a Pearson correlation was used to analyze the relationship between environmental factors (soil, water, and plant factors) and the dye coverage ratio. The dye coverage ratio of soil preferential flow under different reclamation vegetations was very significantly or significantly positively correlated with the gravel content, mean radius of soil macropores, soil saturated hydraulic conductivity, root weight density, and root length density, which promoted the formation and development of soil preferential flow. This study will provide a scientific basis for understanding the formation mechanism and perfecting the research system of soil preferential flow, vegetation restoration, and reconstruction in a dump; furthermore, this research offers significance guidance in the construction of green mines and the development of regional economics.

Dynamic of soil drying close to saturation: What can we learn from a comparison between X-ray computed microtomography and the evaporation method?

The soil water retention curve (SWRC) is a unique relationship between water content and soil water potential. SWRC in near saturation gives the dimension of soil macroporosity which plays an important role in water translocation into soil. Thus, the accurate measurement of SWRC is crucial. The aim of this study is to compare SWRC obtained through two different methods: X-ray computed microtomography (X-ray CT) and evaporation method by HYPROP device. Three different depths (0–10, 25–30 and 45–60cm) are considered for soil sampling. The results showed significant differences in SWRC between the techniques. The SWRC from X-ray CT showed more volumetric water content at 25–30cm (0.044) and 45–60cm (0.024) than evaporation at saturation (0kPa) in cases where the macroporosity was higher. Macropores may have connections with neighbouring pores of smaller sizes. Hence we assume that these pores can be observed through X-ray CT but cannot be evaluated by evaporation. As macropores with narrow opening do not evaporate at very low tension. These pores therefore got empty at relatively higher tension. Consequently, SWRC near saturation appeared rather flatter with the evaporation method where the X-ray CT presented deviation. Accordingly, interpretation of macro pores from SWRC through evaporation method would give comparatively smaller volume of macropores than they really are. Pore morphology and other hydraulic functions of soil, for example, mean connection surface of pores, hydraulic conductivity, and the efficiency of water conducting macropores also support the X-ray CT findings.

Yield and diseases of potato as affected by deep soil tillage and crop succession with grass types

Yield and disease incidence were evaluated in potato ( Solanum tuberosum cv. Atlantic) after six years of cultivation in succession with corn ( Zea mays cv. ‘AG 6080’) under conventional tillage (CT, depth of tillage: 0.20 m) or in succession with three grass types [Guinea grass ( Panicum maximum cv. Tanzânia), Palisade grass ( Brachiaria brizantha cv. Marandu) and corn] under deep tillage (DT, depth of tillage: 0.70 m). Total tuber yield was higher in DT in average 36% the value obtained in CT (17.76 t ha -1 ), with no effect of the grass type. Common scab ( Streptomyces scabies ) incidence was influenced by treatments, the highest (16.9%) and the lowest (9.5%) values being obtained in succession with corn and Guinea grass ( Panicum maximum cv. Tanzania), respectively, both under DT. The lowest incidence of tuber greening at field (2.58%) was also recorded in Guinea DT, significantly lower than obtained in Corn CT (6.33%), possibly due to a more efficient ridging operation. Grass types showed different values of aboveground dry matter production. Guinea grass (26.56 Mg ha -1 ) was the most and Corn under CT and DT (5.72 and 5.56 Mg.ha -1 , respectively, without ears) were the least productive ones. Soil density, macroporosity and resistance to penetration indices were significantly better with DT, the grass type affecting them in a minor degree. The deep tillage system is therefore recommended for potato cultivation regardless the grass type used for crop sucesssion.

Soil compaction management and soybean yields with cover crops under no-till and occasional chiseling

Abstract The introduction of cover crops in agricultural systems under no-till is important in soil structuring and remediation. However, there is a lack of studies exploring the effects of cover crops compared with other soil compaction control tools, such as chiseling, in the long term, mainly under tropical climates. This study aimed to evaluate soil physical properties by cover crops and chiseling in a compacted soil, as well as its effects on soybean yields. The experiment was conducted in Botucatu, Brazil, under no-till. Three crops were grown per year. Soybean [ Glycine max (L.) Merrill] was cropped as summer crop in rotation with triticale (X Triticosecale Wittmack) or sunflower [ Helianthus annuus (L.)] as fall/winter crop. In spring, three different cover crops were grown, pearl millet [ Pennisetum glaucum (L.) R. Brown], forage sorghum [ Sorghum bicolor (L.) Moench] and sunn hemp [ Crotalaria juncea (L.)], compared to a fallow treatment, which was chiseled in 2003, 2009 and 2013 only, always in October and down to 0.60 m depth. The first chiseling increased soil macroporosity and soybean yields in the immediate cropping season (2003/2004). However, these benefits were short-lived and in two years the use of cover crops resulted in higher yields. In the long-term, cover crops improve soil structure, with equal or better results than those obtained by occasional chiseling, as an increase in soil macroporosity by sunn hemp up to 0.20 m depth and a decrease in soil bulk density by sunn hemp and pearl millet in the 0.40–0.60 m layer. Among the cover crops, sunn hemp is particularly interesting, because it increases macroporosity in clay soils otherwise with limited aeration and increases the soybean yield.

Variability of physical properties of soil and rice grown under cover crops in crop-livestock integrated system

ABSTRACT The production systems of upland rice culture in Mato Grosso are not consolidated yet while the effects of soil physical properties and their correlation with rice yield in crop-livestock integrated systems are not defined as well. Therefore, this study determined the spatial variability of physical properties of soil and rice cultivated in no-tillage system under different cover crops, using principal components analysis and geostatistics. The experiment was conducted in Santa Carmen, northern Mato Grosso. A regular grid with 100 sample points distributed in an area of 26,400 m2 was installed. Soil and rice samples were collected to determine rice variables and soil physical properties. The average rice yield was 1.70 Mg∙ha−1, ranging from 0.70 to 3.12 Mg∙ha−1. The highest yields were observed in consortium with cowpea and brachiaria and were associated with lower incidence of grain spots, despite higher soil density and penetration resistance. The consortium with brachiaria, crotalaria, and sudangrass had lower yields, which was associated with higher incidence of grain spots, despite higher soil macroporosity and total porosity.

Soil macropore characteristics following conversion of native desert soils to irrigated croplands in a desert-oasis ecotone, Northwest China

Sustainable use of cultivated desert soils is important for agricultural productivity in desert-oasis ecosystems. However, how soil macropore characteristics may change as a result of agricultural exploitation remains unclear. The objective of this study was to quantify and compare soil properties and macropore characteristics in an old oasis field (>50years of cultivation, OOF), young oasis field (20 years, YOF), and adjacent uncultivated sandy land (0year, USL) in Northwest China. Three replicated soil samples were collected from each site to investigate soil properties. Meanwhile, twelve (four replicates by three sites) intact soil core columns, 15cm in diameter and 30cm in height, were taken to analyze soil structure. Each soil column was scanned with a helical medical X-ray computed tomography (CT) at a voxel resolution of 0.469mm×0.469mm×0.600mm. The results indicated that soil properties and macropore features improved after cultivation. Silt and clay content and dry mean weight diameter (DMWD) of aggregates increased with cultivation time, whereas bulk density decreased. Soil organic carbon and total nitrogen were 7.3 times and 6.7 times greater in soils at the OOF site than USL site, respectively. The increase in silt and clay content and aggregates formation likely resulted from irrigation with silt-laden river water, which in turn impacted soil nutrient accumulation. Soils at the OOF and YOF sites had greater macroporosity compared with soil at USL, and macroporosity also increased with cultivation time. X-ray CT revealed that soil macroporosity was 8.7–18.9 times greater in irrigated croplands than native desert. Soil macropores were mainly distributed at soil depths of 0–200mm at the OOF and YOF sites, while smaller and less continuous macropores were randomly distributed across soil depths at the USL site. The larger number of macropores at the cultivated sites can be attributed to greater soil organic carbon, tillage-induced soil horizons, and alternate wetting and drying processes. Few soil macropores at the USL site may be associated with wind erosion and soil fauna burrows. Conversion of native desert soils to irrigated croplands had a positive effect on soil pore development in the desert-oasis ecotone.

Temporal dynamics of earthworm-related macroporosity in tilled and non-tilled cropping systems

Tillage influences first soil structure and then soil organisms such as earthworms, which are highly involved in the creation of soil macroporosity. This study assessed the temporal dynamics of earthworm-related macroporosity in two ploughed and one unploughed cropping systems. Three sampling dates were chosen: one month before ploughing, and one and five months after the event. Earthworm communities, able to rebuild the macroporosity, were sampled one and five months after ploughing. Before ploughing, the burrow continuity, i.e., the number of burrows with a vertical length greater than 5 cm, was not significantly different in the three systems. It was stable between the three sampling dates in the unploughed system but it decreased by 65% and 46% after ploughing (i.e., in two months) in the organic and the conventional systems, respectively. Five months after ploughing, the burrow continuity remained between two and four times lower than in the unploughed living mulch cropping system. Earthworm biomass was higher and burrow system characteristics (i.e. burrow volume and continuity) were more stable over time in the non-tilled with a living mulch cropping system than in the tilled systems. Earthworm-produced macroporosity was thus substantially decreased after ploughing in conventional and organic systems and had still not totally recovered 5 months later. This can lead to large functional consequences on soil structure and thus on air and water fluxes in the soil.

English

In order to provide an adequate usage to agricultural soils it is crucial to comprehend the soil physical attributes and their spatial variability. The variability of soil attributes is dependent on several formation processes and interactions. To properly describe such complex variability, the statistical methods used must incorporate the spatial and temporal influences. In this context, the present study was developed with the objective of evaluating the spatial variability of physical and hydraulic soil attributes, such as sand, clay and silt contents, soil macroporosity (Ma), soil microporosity (Mi), soil total porosity (TP), soil bulk density (BD), hydraulic conductivity (K), water contents at field capacity (tension of 10 kPa) and permanent wilting point (tension of 1500 kPa) (&theta;Fc and &theta;PWP), in a watershed, located in the Sul-Rio-Grandense Shield, in the South of Brazil, through the geoestatistics analysis based on Ordinary Kriging. It was found a better performance of exponential model for the semivariograms of most physical and hydraulic soil attribute in the 0-0.15 and 0.15 to 0.25 m layers. Spatial dependence was observed for all the soil physical and hydraulic attributes studied, classifying as high for the variables macroporosity (0 to 0.15 m) and clay (0.15 to 0.25 m), with the other variables classified as moderate spatial dependence. Besides, the variables K and macroporosity presented a high heterogeneity in relation to the average, with K in the surface layer and the variables clay, Ma, K and qPWP in the subsurface layer not presenting normality according to Shapiro and Wilk test (p &le; 0.05). &nbsp; Key words: Ordinary kriging, semivariogram, physical and hydraulic soil attributes, Shapiro and Wilk test, exponential.

Enmiendas orgánicas y sus efectos en las propiedades físicas y biológicas de un suelo San Antón

Se utilizaron varias prácticas de enmiendas orgánicas en un suelo de la serie San Antón (Mollisol) y se cuantificaron los cambios respectivos en la capacidad física y biológica de este suelo. Al conjunto de estas prácticas le dimos el nombre de manejo de ciclos de tratamiento de suelo (en inglés, soil treatment management cycles o STMC). Cada STMC duró 60 días y consistía en incorporar 5% de materia orgánica proveniente de composta de pulpa de café, la plantación, crecimiento e incorporación de cuatro especies como abono verde y la aplicación de micorrizas, además de té de composta. Los tratamientos fueron: CL0, CL1, CL2 y CL3; donde CL0 fue el control, CL1 tuvo un STMC, CL2 y CL3 tuvieron dos- y tres-STMC, respectivamente. Los STMC se efectuaron con el propósito de asimilar el efecto conjunto de un sistema agrícola sustentable y no con el propósito de medir los efectos individuales de cada práctica. Todos los tratamientos (CL1, CL2 y CL3) resultaron en un aumento en la materia orgánica del suelo (p≤0.05). La conductividad hidráulica saturada aumentó y la densidad del suelo se redujo al compararlo con el CL0 control. La macroporosidad del suelo aumentó significativamente en CL2 y CL3. La estabilidad de agregados del suelo aumentó en CL1, CL2 y CL3. La biomasa microbiana C aumentó en CL3 y la biomasa microbiana N aumentó por CL2 y CL3. La producción de agregados estables del suelo se correlacionó con el contenido de ácidos húmicos y tuvo efectos positivos en todos los demás parámetros físicos observados en este estudio. Los STMC impactaron las propiedades del suelo cambiando la cantidad de materia orgánica, así como la cantidad de ácidos húmicos. La macroporosidad del suelo, definida como la porosidad de radio &gt; 38 µm, incrementó significativamente para los tratamientos CL2 y CL3. Todas las fracciones de materia orgánica, incluyendo la materia orgánica total, contenido de ácidos húmicos, biomasa microbiana C y biomasa microbiana N fueron significativamente superiores con uno o más STMC.