Ap1 Horizon Research Articles

Dynamics of soluble soil organic matter in Mediterranean maize-based forage system under organic and mineral fertilization

In Nitrate Vulnerable Zones (NVZ), the impact of animal effluent management on soil fertility is essential. A three-year study was carried out in a NVZ (Arborea, Central-western Sardinia, Italy), aiming to analyze the effect of different fertilization systems on soluble and total soil organic matter (SOM) within a silage maize-hay crop cropping system on sandy soil (Oxyaquic Xeropsamment). Four types of fertilization systems were compared: (i) cattle manure; (ii) cattle slurry; (iii) mineral; (iv) slurry + mineral. The water-extractable C and N content (WEC and WEN) from the topsoil (0–20 cm layer, the Ap1 horizon), the dissolved carbon (DC) and the dissolved nitrogen (DN) of the soil solution collected by disk lysimeters placed along the soil profiles, and the C content at the beginning and at the end of the experiment were determined.The seasonal dynamics of WEC in the topsoil seemed mainly associated with the timing of the fertilizer distribution. In the topsoil, WEC was larger under slurry than under mineral treatment. The DC was rather low in the deeper soil layers and did not show any variation due to the fluctuations of fertilizer distribution that were seemingly influenced by the groundwater table. The fertilization systems influenced the soil C inputs and, in turn, the SOM content. Manure promoted a higher C stock in the deeper soil layers among the organic fertilizers. However, the hay crop added with manure and slurry showed lower crop residues and, thus, C input than that added with mineral fertilizer. This result suggests that the management of these organic fertilizers should carefully consider their impact on the overall productivity of the studied cropping system in Mediterranean NVZ to avoid a potential limitation for soil C accumulation in the long term.

Effects of liming on oxic and anoxic N2O and CO2 production in different horizons of boreal acid sulfate soil and non-acid soil under controlled conditions

In acid sulfate (AS) soils, organic rich topsoil and subsoil horizons with highly variable acidity and moisture conditions and interconnected reactions of sulfur and nitrogen make them potential sources of greenhouse gases (GHGs). Subsoil liming can reduce the acidification of sulfidic subsoils in the field. However, the mitigation of GHG production in AS subsoils by liming, and the mechanisms involved, are still poorly known. We limed samples from different horizons of AS and non-AS soils to study the effects of liming on the N2O and CO2 production during a 56-day oxic and subsequent 72-h anoxic incubation. Liming to pH ≥ 7 decreased oxic N2O production by 97–98 % in the Ap1 horizon, 38–50 % in the Bg1 horizon, and 34–36 % in the BC horizon, but increased it by 136–208 % in the C horizon, respectively. Liming decreased anoxic N2O production by 86–94 % and 78–91 % in Ap1 and Bg1 horizons, but increased it by 100–500 % and 50–162 % in BC and C horizons, respectively. Liming decreased N2O/(N2O + N2) in anoxic denitrification in most horizons of both AS and non-AS soils. Liming significantly increased the cumulative oxic and anoxic CO2 production in AS soil, but less so in non-AS soil due to the initial high soil pH. Higher carbon and nitrogen contents in AS soil compared to non-AS soil agreed with the respectively higher cumulative oxic N2O production in all horizons, and the higher CO2 production in the subsoil horizons of all lime treatments. Overall, liming reduced the proportion of N2O in the GHGs produced in most soil horizons under oxic and anoxic conditions but reduced the total GHG production (as CO2 equivalents) only in the Ap1 horizon of both soils. The results suggest that liming of subsoils may not always effectively mitigate GHG emissions due to concurrently increased CO2 production and denitrification.

Soil functions are affected by transition from conventional to organic mulch-based cropping system

Soil ecosystem services depend on soil properties and their interactions, which are mostly influenced by soil use and management. The main objective of the present study was to evaluate, through a multidisciplinary approach, the effect of different cropping systems on food provisioning, soil chemical features, size and structure of soil microbial community, soil invertebrate biodiversity and habitat provision (trophic interactions). The systems were: conventional integrated (INT); traditional organic with cover crops and conventional tillage (ORG); and organic coupled with conservation agriculture (cover crop mulching and no-tillage, ORG+). During 2016, we conducted soil and field samplings and collected data relative to the crop yield, C and N content in the agroecosystem, chemical and microbial soil properties and soil invertebrate abundance and trophic interactions. The INT system showed the highest crop yield (similar to ORG and three-fold higher than ORG+). Nevertheless, the INT system showed the greatest amount of N lost with drainage water (six-fold higher than the other systems), the lowest soil total PLFA abundance (around two-fold lower than ORG and ORG+ in the Ap1 horizon of soil). Additionally, INT system was characterized by the lowest invertebrate biodiversity (e.g., two-fold and ten-fold lower than ORG and ORG+ respectively for ground-dwelling predator abundance). By contrast, the ORG+ system had the lowest crop yield, but it showed the highest soil total organic C concentration and microbial biomass in the Ap1 horizon, supported higher invertebrate biodiversity and a slightly wider prey-spectrum for ground beetle predators. The ORG system had an intermediate behaviour between INT and ORG+. The results of this study demonstrate that, despite the reduction of crop yield, the conversion from INT to ORG or ORG+ possibly enhances important soil functions like nutrient cycling and storage, biodiversity and habitat provisioning. However, management optimization for improving crop yield would be required to make ORG+ a viable system.

Cover crops and pruning in Bobal and Tempranillo vineyards have little influence on grapevine nutrition

Cover crops may improve vineyard soil properties, grapevine nutrient status and berry composition, however, factors such as cover crop type, annual rainfall, climate and irrigation may change their effects on vineyards. From 2008 to 2011, the effects of a non-permanent cover crop and two pruning techniques on soil as well as vine nutrients and grapevine performance of two vineyards (cv. Tempranillo and cv. Bobal) were evaluated. For that purpose, two legumes were sown in inter-rows of hand-pruned vines in February and were tilled at flowering. Soil tillage, or cover cropping, was combined with either light pruning or severe pruning to study foliar nutrient variations. Soil N, P, K and total organic carbon (TOC) were determined in samples taken from the Ap1 horizon in January prior to vine pruning. Foliar N, P, K contents were measured in leaves sampled upon grape veraison. The differences between vineyards with cover cropping and bare soils suggest that legumes positively affected soil N (1.55 vs. 1.68 g kg−1 and 1.49 vs. 1.76 g kg−1 in Bobal and Tempranillo vineyards, respectively) and soil organic matter (SOM) (12.5 vs. 15.5 g kg−1 and 12.9 vs. 17.2 g kg−1 in Bobal and Tempranillo vineyards, respectively). The use of cover crops did not affect grapevine yields nor quality of Bobal and Tempranillo berry . Cover crops, or light pruning, did not alter the foliar N, P, K contents of both cultivars since their concentrations were similar to those found in the leaves from vineyards with soil tillage or severe pruning.

Soil particle accumulation in termite (Macrotermes bellicosus) mounds and the implications for soil particle dynamics in a tropical savanna Ultisol

AbstractThis study investigated the influence of mound‐building termites on soil particle dynamics on the land surface and in soil‐forming processes by examining the amount of soil particles in mound structures of Macrotermes bellicosus in a highly weathered Ultisol of tropical savanna. Soil particle turnover via the mounds was estimated using particle stock data and soil turnover data from previous studies. A 4‐ha study plot with six mounds of relatively uniform shape and size was investigated. Soil mass constituting the mounds was 6,166 ± 1,581 kg mound−1 within which the mound wall and nest body accounted for 5,002 ± 1,289 and 1,164 ± 293 kg, respectively. The mound wall contained a significantly larger amount of clay (252 ± 9.97 g kg−1) balanced with a lower sand content (676 ± 26.5 g kg−1) than in the adjacent surface (Ap1) horizon, (46.4 ± 12.8 g clay kg−1; 866 ± 83.2 g sand kg−1); the nest body had much higher clay content (559 ± 51.0 g kg−1) but less sand (285 ± 79.2 g kg−1) than the mound wall. As a result, the mounds of M. bellicosus accumulated clay of 2,874 ± 781 kg ha−1 (corresponding to 2.52% of clay stock in the Ap1 horizon) along with an estimated clay turnover rate of 169 kg ha−1 year−1. These findings suggest a positive feedback effect from termite mound‐building activity on soil particle dynamics in tropical savanna ecosystems: M. bellicosus preferentially use subsoil material for mound construction, resulting in relocation of illuvial clay in the subsoil to the land surface where clay eluviation from the surface soil and its illuviation in the subsoil are major soil‐forming processes.

Nutrient storage in termite (Macrotermes bellicosus) mounds and the implications for nutrient dynamics in a tropical savanna Ultisol

The role of mounds of the fungus-growing termite Macrotermes bellicosus (Smeathman) in nutrient recycling in a highly weathered and nutrient-depleted tropical red earth (Ultisol) of the Nigerian savanna was examined by measuring stored amounts of selected nutrients and estimating their rates of turnover via the mounds. A study plot (4 ha) with a representative termite population density (1.5 mounds ha−1) and size (3.7 ± 0.4 m in height, 2.4 ± 0.2 m in basal diameter) of M. bellicosus mounds was selected. The mounds were found to contain soil mass of 9249 ± 2371 kg ha−1, composed of 7502 ± 1934 kg ha−1 of mound wall and 1747 ± 440 kg ha−1 of nest body. Significant nutrient enrichment, compared to the neighboring topmost soil (Ap1 horizon: 0–16 cm), was observed in the nest body for total nitrogen (N) and exchangeable calcium (Ca), magnesium (Mg) and potassium (K), and in the mound wall for exchangeable K only. In contrast, available (Bray-1) phosphorus (P) content was found to be lower in both the mound wall and the nest body than in the adjacent topmost soil horizon. Consequently, the mounds formed by M. bellicosus contained 1.71 ± 0.62 kg ha−1 of total N, 0.004 ± 0.003 kg ha−1 of available P, 3.23 ± 0.81 kg ha−1 of exchangeable Ca, 1.11 ± 0.22 kg ha−1 of exchangeable Mg and 0.79 ± 0.21 kg ha−1 of exchangeable K. However, with the exception of exchangeable K (1.2%), these nutrients amounted to less than 0.5% of those found in the topmost soil horizon. The soil nutrient turnover rate via M. bellicosus mounds was indeed limited, being estimated at 1.72 kg ha−1 for organic carbon (C), 0.15 kg ha−1 for total N, 0.0004 kg ha−1 for available P, 0.15 kg ha−1 for exchangeable Ca, 0.05 kg ha−1 for exchangeable Mg, and 0.06 kg ha−1 for exchangeable K per annum. These findings suggest that the mounds of M. bellicosus, while being enriched with some nutrients to create hot spots of soil nutrients in the vicinity of the mounds, are not a significant reservoir of soil nutrients and are therefore of minor importance for nutrient cycling at the ecosystem scale in the tropical savanna.

Hydropedological processes and their implications for nitrogen availability to corn

Hydropedological processes affect soil water and nutrient transport and cycling. This study evaluated the impact of hydropedological properties on soil N availability and corn ( Zea mays L.) growth in three areas within the same field representing distinguishing but typical mid-Atlantic (USA) landforms. These areas included: a depressional area (Site A), a steep (14%) slope area (Site B), and a flood plain area with 1% slope (Site C); different soil types (Hagerstown, Opequon, and Melvin series, respectively); and varying hydrological features (soil water content, matric potential, and subsurface flow) in a Ridge and Valley agricultural landscape. A small-plot replicated study was conducted in each of these three areas, including four blocks of two N treatments (NH 4NO 3) applied to corn at planting (0 and 150 kg N ha − 1 ). Soil and above-ground plant biomass samples were collected during the growing season and grain yield was determined at harvest. Site A had the greatest mean grain yield (fertilized: 8.5 Mg ha − 1 ; control: 4.5 Mg ha − 1 ) and above-ground plant biomass (at physiological maturity or PM, fertilized: 11.7 Mg ha − 1 ; control: 7.1 Mg ha − 1 ), probably due to the fine-textured (> 19% clay) and low saturated hydraulic conductivity (Ksat < 0.3 cm min − 1 ) soil with good water and N holding capacity. In contrast, Site B had the smallest grain yield (fertilized: 6.9 Mg ha − 1 ; control: 3.5 Mg ha − 1 ), which corresponded to the smallest inorganic soil N content due to its thin Ap1 (10 cm) and Ap2 (21 cm) horizons, greater Ap1 horizon Ksat (1.61 cm min − 1 ), and shallow lateral subsurface flow at the steep soil–bedrock interface (0.4 m below the surface). Despite the greater inorganic soil N content at Site C, the above-ground plant biomass (at PM, fertilized: 7.0 Mg ha − 1 ; control: 6.2 Mg ha − 1 ) and grain yield (fertilized: 7.1 Mg ha − 1 ; control: 4.5 Mg ha − 1 ) were less than observed at Site A and probably resulted from the low soil water content during the growing season, which also corresponded to greater solar radiation (564 kw h m − 2 ), coarser texture (> 20% sand), and deep subsurface lateral convergent flow (0.7 m below the surface). Understanding these types of relationships between corn response to N fertilizer and hydropedological features will improve N management decisions for corn production.

Quantifying Soil Structure and Preferential Flow in Intact Soil Using X‐ray Computed Tomography

Computed tomography (CT) provides a nondestructive means of observing soil structure and monitoring solute breakthrough in real time. We investigated an intact soil column 10 cm in diameter and 30 cm in length using industrial CT with a resolution of 105.5 by 105.5 by 125.25 μm. The satiated soil column was scanned to obtain overall soil structure. Then 60 g L−1KI solution was injected at 6.6 mL min−1for about 23 h and solute transport was monitored in real time by scanning two critical positions in the column and taking digital radiographs. At the end of the experiment, the whole column was scanned again to obtain the overall solute mass distribution. The voxel‐based soil porosity and solute concentration were quantified. The three‐dimensional visualization of the pore network and solute distribution with time showed that both the pore network and the flow pattern varied considerably with soil depth, in part due to the soil horizonation and different macropores involved. Although the macroporosity below the Ap1 horizon was much lower, macropores were more continuous and less tortuous as a result of limited agricultural disturbance and more earthworm activities. Only part of the macropores at the subsurface were effective, however, in transporting the solute. The results revealed a sequential initialization of the transport process from the macropore domain to the matrix domain and a decreased degree of interaction between the two domains with soil depth. Point‐specific breakthrough curves were obtained from real‐time point‐specific solute concentration and porosity, from which point‐specific pore velocity was determined. Preferential flow pathways in this intact structured soil consist of a complex network of earthworm burrows, root channels, interaggregate macropores, and mesopores or even micropores in the soil matrix. Modeling of this flow network and its dynamics requires a new approach different from the classical continuous‐domain approach.

Sistema de porosidade do solo numa topossequência Luvissolo-Solonetz no Sul de Portugal

Soils with stagnic properties occurring in Alentejo commonly have low porosity. The study of a typical soil toposequence, showed that soil pore features were significantly different amongst summit and foot/toe slope pedons. In the summit pedon the Ap1 horizon was more porous than the Ap2, both exhibiting similar void distribution patterns. Conversely, the Ap1 and Ap2 horizons of the footslope pedon had a similar pore space volume, but pores with diameter larger than 500 µm were less important in the later. Pore space volume of Bt horizons was low whatever the slope position of pedons. However, they differ significantly in terms of void type and orientation patterns. No preferred orientation patterns were found in soil voids that could be related with soil compaction, being their low porosity, namely their low “conductive” porosity, not attributable to soil compaction. Those features can instead be due to the sodicity and/or the low organic C of these soils.

Direct and indirect exogenous contamination by pesticides of rice-farming soils in a Mediterranean wetland.

It is known that the sources of soil contamination can be endogenous or exogenous and that exogenous contamination may be direct or indirect. In this work, an environmental pesticide fate study was conducted in soil profiles collected from 23 rice field sites in an important Mediterranean wetland (Albufera Natural Park, Valencia, Spain) from April 1996 to November 1997. Temporal and spatial distribution of 44 pesticide residues in an alluvial Mediterranean soil (gleyic-calcaric Fluvisol, Fluvaquent) were monitored. During this period, the levels of pesticide residues in different soil horizons (Ap1 0-12 cm, Ap2 12-30 cm, ApCg 30-50 cm, C1gr 50-76 cm, and C2r 76-100 cm) were investigated. In addition, information was collected on agricultural pesticide application practices and soil characteristics. Distribution throughout the soil profile showed that pesticide concentrations were always higher in the topsoil (Ap1 horizon), in the autumn season, and in the border with citrus-vegetable orchard soils (calcaric Fluvisol, Xerofluvent). Chlorpyrifos (organophosphorus), endosulfan (organochlorine), and pyridaphenthion (organophosphorus) insecticides were, respectively, the most detected of all the pesticides investigated. These results were associated with processes, such as nonleaching, transport by movement into surface waters, retention, volatilization, and chemical and biological degradation in the topsoil, as well as with direct and indirect exogenous contamination sources.

SOIL TEMPERATURE DYNAMICS AND HEAT TRANSFER IN A SOIL CROPPED TO RICE

Soil temperature distribution and heat transfer affect crop development as well as water and solute transfers in the vadose zone. The objective of this study was to characterize seasonal soil temperature distribution throughout a rice-growing season in an eastern Arkansas soil typically cropped to rice. Soil temperature (T) measurements and climatic parameters were taken every 30 min throughout the season. T was measured in a layered calloway silt loam (fine-silty, mixed, thermic, Aquic Fragiudalfs) at nine different depths from the soil surface to 1 m. Results indicated that average daily soil T varied throughout the season at all recording depths (e.g., from 14.2 °C to 29.3 °C at 0.14 m and from 13 °C to 24.9 °C at 1 m). Diurnal soil T amplitude was reduced, and T phase shift increased by an additional 3 h at 0.05 m and by 5 h at 0.14 m and 0.26 m (when compared with air temperatures) on field flooding and increased canopy cover. Heat transfer was modeled using the onedimensional Fourier equation, solved using the finite element method of the mathematical software MATLAB. Predicted T (Tp) were in close agreement with measured T (Tm) at all depths in the soil profile when two constant values of thermal diffusivity (α) were used for the soil profile: α = 4.58E-7 m2 s−1 in the Ap1 horizon and α = 4.86E-7 m2 s−1 in the rest of the soil profile. Differences between Tp and Tm were always lower than 1.04 °;C for all periods considered.

MACRONUTRIENT, SOIL ORGANIC CARBON, AND EARTHWORM DISTRIBUTION IN SUBTROPICAL PASTURES ON AN ANDISOL WITH AND WITHOUT LONG-TERM FERTILIZATION

Pasture fertilization affects plant growth and animal production, and it may influence the redistribution and cycling of nutrients excreted in dung and urine. Kikuyugrass (Pennisetum clandestinum Hochst. ex Chiov.) pastures on a high organic carbon (C) Typic Hydrudand soil with and without (control) annual nitrogen (N) and periodic phosphorus (P) and potassium (K) fertilizations were stocked with Hereford and crossbred cattle (Bos taurus) for 33 years. The pastures were divided into 1.2-ha paddocks for rotational stocking after the 15th year. Selected fertilized paddocks that were uniformly managed over the years were paired with control paddocks to determine management effects on soil organic C; soil and plant N, P, and K; and earthworm distribution. Responses were assessed using a zonal sampling procedure based on distance from the waterer because the paddocks lacked shade. Soil organic C, organic N, and organic P did not statistically differ between managements or zones in any horizon. Relative to the control, however, an apparent recovery of 25% of the total N applied to the fertilized paddocks was obtained as soil organic N within the 80 cm profile depth examined. Inorganic N (NH4-N + NO3-N) was greater in the Ap1 and Bw1 horizons of fertilized paddocks, and there was a trend in the Ap1 horizon toward greater concentrations within 15 m of the waterer. Additionally, substantial inorganic P accumulated within 30 m of the waterers in the Ap1 and Bw1 horizons of fertilized paddocks while minimal P accumulation occurred within 15 m of the waterer in control paddocks. The magnitude of K accumulation near waterers was also considerably greater in the Ap1 horizon of fertilized paddocks. It is suggested that fertilization increases the magnitude of P and K accumulation near waterers due to the combination of increased forage P and K concentrations and pasture carrying capacity. Management and zone effects for forage N, P, and K tended to follow patterns relatively similar to the soil Ap1 horizon data for the inorganic forms of these nutrients. Earthworm populations did not differ among zones, but populations in fertilized paddocks were double those of control paddocks.

Impact of Grazing Management on Soil Nitrogen, Phosphorus, Potassium, and Sulfur Distribution.

Little information is available directly comparing soil nutrient distribution under different defoliation managements. During 1990 (116 d) and 1991 (141 d), 'Callie' bermudagrass (Cynodon dactylon var. aridus Harlan et de Wet) pastures grazed by Holstein heifers (Bos taurus) were used to determine the effects of two rotational stocking methods and continuous stocking on lateral and vertical distribution of extractable N, P, K, and S. A hay management also was included to compare soil responses under grazing and clipping. Nutrient distribution and concentration in the Ap1 horizon (0- to 15-cm soil depth) did not differ among grazing methods, but N, P, and K accumulated in the third of the pastures closest to shade, water sources, and supplement feeders (lounging areas where cattle tend to congregate or rest). Similar observations were made with K in the Ap2 horizon (15- to 30-cm soil depth). Nutrient concentrations were lower or tended to be lower in the Ap1 horizon of the hay management than in grazed pastures because of nutrient removal in harvested herbage. Across defoliation managements, greater extractable N, P, and K concentrations were observed in the Ap1 horizon in 1991 than in 1990. For N and K, this was attributed to fertilizer inputs in all managements and partially to supplemental feed inputs in grazed pastures. Increases in extractable P appeared to be associated primarily with flooding of the experimental site in late 1991. This study suggests that grazing method of well-managed pastures may have little effect on short-term (2 yr) soil nutrient distribution, especially when grazing occurs during months when temperatures are high.

Shortleaf Pine Site‐Index Relationships in the Ozark Highlands

AbstractBy carefully limiting the area of application and the soils included in individual analyses, practical equations were developed for predicting shortleaf pine (Pinus echinata Mill.) growth on major soils in the Ozark Highlands. Large pits were dug to adequately classify the soils, and soil properties were determined by standard techniques. Shortleaf pine site index at age 50 was correlated with aspect, slope shape, loss‐on‐ignition of the A1 and Ap1 horizons, depth to fragipan, and latitude. Regression equations developed for limestone and dolomite soils, sandstone soils, and fragipan soils predicted site indexes within an average of 0.6 m (2 feet) on confirmatory plots.