Soil Available Water Capacity Research Articles

Uncertainty assessment of soil available water capacity using error propagation: A test in Languedoc-Roussillon

Soil available water capacity (SAWC) is a key soil indicator that plays a major role in many ecosystem services, such as food production, irrigation management, soil drought, flood control, and climate and gas regulation. Digital soil mapping (DSM) can be used to obtain needed SAWC maps. However, SAWC differs from the usual soil properties considered in DSM in that it involves several soil properties determined at several soil layers. Therefore, a specific approach is required to obtain SAWC maps and the associated uncertainty predictions.The objective of this study was to build a SAWC mapping approach that could predict SAWC values at three maximum rooting depths (60, 100 and 200 cm) and their associated prediction uncertainties.The approach was tested in the Languedoc-Roussillon region (southern France). Elementary available water capacities of each layers (in cm.cm−1) and soil layer thicknesses were first mapped separately at 0–30, 30–60, 60–100 and 100–200 cm and then aggregated to estimate the SAWCs at the three mentioned maximum rooting depths. SAWC uncertainty was estimated with an error propagation model that used a first-order Taylor analysis. This analysis considered the mapping errors of each involved property, which were estimated by the quantile regression forest algorithm. We tested different error propagation models that differently considered the correlations between these mapping errors: no correlation considered, correlations between soil layer thicknesses and elementary water capacities per soil layer only, correlations between soil layers only, or all correlations considered.The performances of both SAWC predictions and their uncertainties were assessed with a 10-fold cross validation that was iterated 20 times. The SAWC predictions showed poor accuracies (percentages of explained variance ranged from 0.12 to 0.13). The uncertainties of SAWC predictions were best estimated when the correlations between the soil layer errors were considered in the error propagation model whereas the uncertainties of SAWC predictions were severely underestimated when these correlations were neglected.In spite of the poor performance in predicting SAWC at the punctual level due to the low density of soil observations (1/19 km2), the SAWC approach appeared promising since it produced maps that agreed with the available pedological knowledge and precisely estimated the uncertainties.

Carbon isotope discrimination as a surrogate for soil available water capacity in rainfed areas: A study in the Languedoc vineyard plain

Soil available water capacity (SAWC) is a key soil function for plant growth. Classical SAWC characterization requires time consuming determinations of bulk density and specific soil moisture contents. Consequently, these data are extremely sparse in existing soil databases. Using surrogates of the vegetal response to characterize SAWC across a great number of sites constitutes a promising perspective. The carbon isotope ratio (δ13C) measured in a plant organ is largely known as an indicator of plant water status. The aim of the paper is to test δ13C as an indicator of SAWC in rainfed vineyard.δ13C values of grapes at harvest time were measured at 21 sites on the Languedoc vineyard plain with contrasting SAWC (33 to 308 mm) for four years (2015 to 2018) with contrasting annual precipitation (from 390 to 715 mm). The relationships between δ13C and SAWC determined using a classical approach (soil description, soil sampling and laboratory methods) were satisfactory for all years (RMSEs from cross validation were between 35 and 61 mm). Better relationships were obtained between δ13C and SAWC for years that showed a full winter recharge of SAWC (2015, 2017 and 2018). Averaging the δ13C measurements over such years provided an even better relationship (R2 = 0.85; RMSE 32 mm), which was successfully validated in distant sites on the Languedoc vineyard plain.This work demonstrated that δ13C can be considered as a simple and inexpensive surrogate for estimating SAWC. In addition to considerably increasing the density of SAWC measurements, the use of δ13C would lead to better consideration of the contribution of deep horizons in the case of perennial plants. Application of this isotopic technique to other agro-systems is required to better define the potential areas of use of δ13C.

Exploring the effect of varying soil organic matter contents on current and future moisture supply capacities of six Italian soils

The Available Soil Water Capacity (AWC) is standard data in most soil databases and expresses soil water contents in the rootzone between field capacity (FC; –33 kPa) and permanent wilting point (WP; −1500 kPa). Literature suggests that increasing the content of soil organic matter (SOM) of a given soil does not significantly increase AWC and this has important implications when estimating soil moisture supply to crops and evaluating the potential for climate mitigation. For most crops, the real FC values vary between −10 and −50 kPa in different soils and WP values between −800 and −1500 kPa. Thus standard values for AWC of FC and WP do not represent field conditions in many soils. When exploring AWC for six Italian soil series, ranging from clay to sandy, AWC values at increasing %SOM were lower in clay soils and higher in sand as compared with actual conditions, which could be explained by considering the shape of the corresponding moisture retention curves. Rather than focus on static AWC values to define moisture supply to plants, real or actual soil moisture supply capacities (MSC) can be obtained by dynamic modeling of the soil-water-atmosphere-plant system, including a “sink-term” indicating a continuous relation between water uptake and negative pressure head of soil water and evaporative demand. Also, only models allow exploration of the effects of future severe IPCC climate scenario RCP 8.5. Thus, studying MSC for the six Italian soil series showed that MSC values were: (i) on average 30% higher than the corresponding AWC; (ii) distinctly different for the six soils; (iii) affected by declines of 1–9% as a result of the effects of future climate scenarios.; (iv) not significantly affected by increases of %SOM when considering climate change, except for the sand. Generalizations as to the effect of future climate scenarios and %SOM on MSC can only be realistic when modeling is performed for soil series in different climate zones.

Hydrogel synthesis based on lignin/sodium alginate and application in agriculture

A new green hydrogel has been synthesized by crosslinking lignosulfonate (L), sodium alginate (SA) and konjaku flour (KJ). We have optimized the ratio of the three synthesized polymers using an orthogonal design of experiments and characterized this hydrogel using SEM, BET and FTIR spectra. We have added the hydrogel into soil and investigated its degradability in soil and its influence on chemical and physical properties of soil, such as maximum water holding capacity, saturated hydraulic conductivity, water retention curve and nutrient retention and evaluated its performance when applied in drought stress tests on tobacco plants. The results show that the maximum water absorption of optimized L/KJ/SA is 41.23 g/g. Adding the L/KJ/SA hydrogel to soil reduces saturated hydraulic conductivity, increases available water capacity of soil and reduces leaching of soil nutrient. The L/KJ/SA hydrogel can improve the photosynthetic capability of tobacco plants under drought stress and the levels of osmotic regulators such as proline and reducing sugar, and could prolong the growth time of tobacco plants up to 14 days, which significantly increases its mass harvest. The L/KJ/SA hydrogel also has good degradability, which can degrade 20% when buried in soil for 120 days.

Adapting the available water capacity indicator to forest soils: An example from the Haut-Languedoc (France)

Soil available water capacity (SAWC) is becoming a crucial issue for forest management in the context of climate change. However, the SAWC indicator, which was created for agricultural soils, needs specific adaptations when it is estimated for forest soils. This study aims to determine the best way to apply the SAWC indicator with regard to its significance for explaining variation in tree fertility across a given region. An extensive investigation with spatial sampling of 100 Douglas fir stand plots was conducted in the Haut Languedoc Regional Nature Parc (Southern France). It involved stand fertility assessments, morphological observations of deep soil pits including the saprolite, quantitative estimations of coarse fragments, texture and organic matter laboratory analysis and water retention and density measurements on a limited sample of horizons (35). Different approaches were used to compute SAWC from the collected data. These approaches differed in the methods i) for estimating the fine earth water retention – national vs local pedotransfer function -, ii) for incorporating coarse fragments – assumed to contribute or not to the water retention of soils- and iii) for estimating soil volumes – variable thicknesses and considerations of rooting. The results showed that the estimate of SAWC that explained the greatest variation in tree fertility over the study area (23% of the variance) was obtained by estimating fine earth water retention from a local pedotransfer function, by considering the water retention of the coarse fraction and by exploring the thickest soil volumes (thicknesses of 200 cm, 300 cm and equal to the depth to bedrock) without explicit consideration of rooting observations. The ranking of SAWC component impact on SAWC values was i) soil volume, ii) coarse fraction water retention and iii) fine earth retention. These results indicate that improvements in estimating coarse fraction water retention and soil volume and, to a lesser extent, fine-earth water retention estimated by a forestsoil-adapted pedotransfer function would greatly benefit the application of the SAWC indicator to forest soils.

Some practical aspects of predicting texture data in digital soil mapping

Soil texture is the most well-known composition in soil science. When separate components of the texture (sand, silt, and clay) are predicted independently in digital soil mapping (DSM), there is no guarantee that the separate estimates will sum to 100%. Log-ratio transformations before DSM modelling are alternatives to guarantee a constant sum of the estimates. Little is known about the effect of non-summing to 100% and transformations of particle-size fractions (PSFs) when DSM products were used to predict soil functional properties using pedotransfer functions (PTFs). Therefore, this study was conducted to investigate the effect of different soil texture modelling methods on the estimation of available soil water capacity (AWC) and the total amount of irrigation water (TIW) required for wheat production on a 4600 ha area in Khuzestan province, southwestern Iran. Specifically, this study aimed i) to assess the performance of random forest models (RF) to predict untransformed (UT) and transformed PSFs using environmental covariates; ii) to study the effects of three widely used log-ratio transformations including additive, centroid and isometric log-ratio transformations (alr, clr, and ilr respectively) on the estimations of AWC and TIW. A total of 150 soil samples were collected from the surface layers (0–30 cm) based on the conditioned Latin hypercube sampling (cLHS) procedure. Results indicated that, in terms of root mean square error (RMSE), RF provided similar accuracies in predicting PSFs for both untransformed and transformed data. However, transformation resulted in biased estimates. In addition, RF prediction based on untransformed data resulted in more correctly soil texture classes allocation when compared to transformed data. The spatial distribution of the sum of the predicted untransformed fractions indicated only small parts of the area conformed to the 100% sum. Almost the same accuracies for estimates of AWC were obtained when both untransformed and transformed predicted texture components were used as the inputs to PTFs. Data transformation can result in biased estimates of AWC. The findings indicated no significant difference between transformation methods in predicting AWC and TIW. The general patterns of the spatial distribution of the predicted AWCs across the whole area were the same for transformed and untransformed data (except for clr transformation).

Assessment of Consumptive use and Water use Efficiency of Okra (abelmoschus esculentus l. Moench) Using Minilysimeters in Makurdi, Benue State, Nigeria

This study was carried out during the 2015 and 2016 dry cropping seasons at the Teaching and Research Farm of the University of Agriculture, Makurdi, Southern Guinea Savanna Agroecology of Nigeria. The objectives were to determine the consumptive use and water use efficiency of okra using the Lysimetric technique. This involved the use of twelve (12) locally fabricated minilysimeters housing three (3) irrigation treatments corresponding to 50, 75 and 100% of the soil available water capacity replicated four (4) times and laid out in a Randomized Complete Block Design (RCBD). The Blaney-Criddle formula which is latitude dependent derives its strength from a 5-year accumulated temperature, data was used to predict the potential evapotranspiration of okra. The crop evapotranspiration is equivalent to the crop water use. Results show that the consumptive use estimated varied from 263.52 – 1,944.90 mm, water use efficiency was from 22.73 – 2.28 kg/ha/mm and crop coefficients of 0.36 – 2.28 corresponding to 50 – 100% (Low to High) soil available water capacity (SAWC) respectively. Okra performed better under low soil available water capacity.

Smart method of agricultural drought regionalization: A winter wheat case study

Abstract The occurrence of drought during flowering (usually from the end of May to the beginning of June) is the most hazardous timing in terms of the possible negative impact of agricultural drought on winter wheat, which is the most cultivated crop in the Czech Republic (about 800000 ha). Lack of water, often accompanied by high temperatures, negatively affects the number of grains in the wheat ear and the tissue development of the developing grain, with consequent impacts on yield and quality of product. With the use of a) long-term time series of agrometeorological data (1961–2010), b) long-term phenological time series of winter wheat (1981–2010), and c) soil conditions data (available water capacity of soils of the Czech Republic) for the arable soil, the ratio of actual evapotranspiration and potential evapotranspiration for the period of 1961–2010, used as an indicator of agricultural drought (lack of water) for wheat, was calculated. The innovative aspect of this categorization of the territory of the Czech Republic according to the risk of occurrence of agricultural drought for winter wheat is considering drought from the aspect of the plant, i.e., evaluation based on the actual consumption of water by the vegetation. This is a very sophisticated procedure. Frequently, water content in soils data, presented as an output of some models, do not fully indicate the possible negative impacts on yield generation because the plants themselves are typically not considered. The method used in this study is universally applicable and allows comparisons of regions at the local, regional, and supra-regional levels. For estimation of the development of agronomic drought in the future, the basic water balances in the growing seasons of 1961–2010 and 2071–2100 were compared using a climate scenario. The forecast indicates a significant deterioration of agricultural drought in the region with probable direct impacts on agricultural production.

Optimizing the bioenergy water footprint by selecting SRC willow canopy phenotypes: regional scenario simulations.

Background and AimsBioenergy is central for the future energy mix to mitigate climate change impacts; however, its intricate link with the water cycle calls for an evaluation of the carbon–water nexus in biomass production. The great challenge is to optimize trade-offs between carbon harvest and water use by choosing cultivars that combine low water use with high productivity.MethodsRegional scenarios were simulated over a range of willow genotype × environment interactions for the major UK soil × climate variations with the process-based model LUCASS. Soil available water capacity (SAWC) ranged from 51 to 251 mm and weather represented the north-west (wet, cool), north-east (dry, cool), south-west (wet, warm) and south-east (dry, warm) of the UK. Scenario simulations were evaluated for small/open narrow-leaf (NL) versus large/closed broad-leaf (BL) willow canopy phenotypes using baseline (1965–89) and warmer recent (1990–2014) weather data.Key ResultsThe low productivity under baseline climate in the north could be compensated by choosing BL cultivars (e.g. ‘Endurance’). Recent warmer climate increased average productivity by 0.5–2.5 t ha−1, especially in the north. The modern NL cultivar ‘Resolution’ had the smallest and most efficient water use. On marginal soils (SAWC <100 mm), yields remained below an economic threshold of 9 t ha−1 more frequently under baseline than recent climate. In the drought-prone south-east, ‘Endurance’ yielded less than ‘Resolution’, which consumed on average 17 mm year−1 less water. Assuming a planting area of 10 000 ha, in droughty years between 1.3 and 4.5 × 106 m3 of water could be saved, with a small yield penalty, for ‘Resolution’.ConclusionsWith an increase in air temperature and occasional water scarcities expected with climate change, high-yielding NL cultivars should be the preferred choice for sustainable use of marginal lands and reduced competition with agricultural food crops.

Soil water storage appears to compensate for climatic aridity at the xeric margin of European tree species distribution

Based on macroecological data, we test the hypothesis whether European tree species of temperate and boreal distribution maintain their water and nutrient supply in the more arid southern margin of their distribution range by shifting to more fertile soils with higher water storage than in their humid core distribution range (cf. soil compensatory effects). To answer this question, we gathered a large dataset with more than 200,000 plots that we related to summer aridity (SA), derived from WorldClim data, as well as soil available water capacity (AWC) and soil nutrient status, derived from the European soil database. The soil compensatory effects on tree species distribution were tested through generalized additive models. The hypothesis of soil compensatory effects on tree species distribution under limiting aridity was supported in terms of statistical significance and plausibility. Compared to a bioclimatic baseline model, inclusion of soil variables systematically improved the models’ goodness of fit. However, the relevance measured as the gain in predictive performance was small, with largest improvements for P. sylvestris, Q. petraea and A. alba. All studied species, except P. sylvestris, preferred high AWC under high SA. For F. sylvatica, P. abies and Q. petraea, the compensatory effect of soil AWC under high SA was even more pronounced on acidic soils. Soil compensatory effects might have decisive implications for tree species redistribution and forest management strategies under anthropogenic climate change. Therefore, soil compensatory effects deserve more intensive investigation, ideally, in studies combining different spatial scales to reduce the uncertainty associated with the precision of soil information.

Limited effect of organic matter on soil available water capacity

SummarySoil water‐holding capacity is an important component of the water and energy balances of the terrestrial biosphere. It controls the rate of evapotranspiration, and is a key to crop production. It is widely accepted that the available water capacity in soil can be improved by increasing organic matter content. However, the increase in amount of water that is available to plants with an increase in organic matter is still uncertain and may be overestimated. To clarify this issue, we carried out a meta‐analysis from 60 published studies and analysed large databases (more than 50 000 measurements globally) to seek relations between organic carbon (OC) and water content at saturation, field capacity, wilting point and available water capacity. We show that the increase in organic carbon in soil has a small effect on soil water content. A 1% mass increase in soil OC (or 10 g C kg−1 soil mineral), on average, increases water content at saturation, field capacity, wilting point and available water capacity by: 2.95, 1.61, 0.17 and 1.16 mm H2O 100 mm soil−1, respectively. The increase is larger in sandy soils, followed by loams and is least in clays. Overall the increase in available water capacity is very small; 75% of the studies reported had values between 0.7 and 2 mm 100 mm−1 with an increase of 10 g C kg−1 soil. Compared with reported annual rates of carbon sequestration after the adoption of conservation agricultural systems, the effect on soil available water is negligible. Thus, arguments for sequestering carbon to increase water storage are questionable. Conversely, global warming may cause losses in soil carbon, but the effects on soil water storage and its consequent impact on hydrological cycling might be less than thought previously.Highlights We investigated how available water capacity can be increased with a 1% increase in soil organic carbon. We analysed data from 60 published studies and global databases with more than 50 000 measurements. The increase in organic carbon in soil has a small effect on soil water retention. A 1% mass increase in soil OC on average increased available water capacity by 1.16%, volumetrically.

Investigating the impact of surface soil moisture assimilation on state and parameter estimation in SWAT model based on the ensemble Kalman filter in upper Huai River basin

AbstractThis paper investigates the impact of surface soil moisture assimilation on the estimation of both parameters and states in the Soil and Water Assessment Tool (SWAT) model using the ensemble Kalman filter (EnKF) method in upper Huai River basin. The investigation is carried out through a series of synthetic experiments and real world tests using a merged soil moisture product (ESA CCI SM) developed by the European Space Agency, and considers both the joint state-parameter updating and only state updating schemes. The synthetic experiments show that with joint state-parameter update, the estimation of model parameter SOL_AWC (the available soil water capacity) and model states (the soil moisture in different depths) can be significantly improved by assimilating the surface soil moisture. Meanwhile, the runoff modeling for the whole catchment is also improved. With only state update, the improvement on runoff modeling shows less significance and robustness. Consistent with the synthetic experiments, the assimilation of the ESA CCI SM with joint state-parameter update shows considerable capability in the estimation of SOL_AWC. Both the joint state-parameter update and the only state update scheme could improve the streamflow modeling although the optimal model and observation error parameters for them are quite different. However, due to the high vegetation coverage of the study basin, and the strong spatial mismatch between the satellite and the model simulated soil moisture, it is still challenging to significantly benefit the runoff estimates by assimilating the ESA CCI SM.

Interacting effects of climate and landscape physiography on piñon pine growth using an individual‐based approach

AbstractForest and woodland ecosystems play a crucial role in the global carbon cycle and may be strongly affected by changing climate. Here, we use an individual‐based approach to model piñon pine (Pinus edulis) radial growth responses to climate across gradients of environmental stress. We sampled piñon pine trees at 24 sites across southwestern Colorado that varied in soil available water capacity (AWC), elevation, and latitude, obtaining a total of 552 piñon pine tree ring series. We used linear mixed‐effect models to assess piñon pine growth responses to climate and site‐level environmental stress (30‐year mean cumulative climatic water deficit [CWD] and soil AWC). Using a similar modeling approach, we also determined long‐term growth trends across our gradients of environmental stress. Piñon pine growth was strongly positively associated with winter precipitation. Summer vapor pressure deficit (VPD) was strongly negatively associated with piñon pine growth during years of low winter precipitation, whereas summer VPD had no effect on piñon pine growth during years of high winter precipitation. The strength of the relationship between the annual climatic variables (winter precipitation and summer VPD) and piñon pine growth was also influenced by site‐level environmental stress, suggesting that the sensitivity of woodland ecosystems to changing climate will vary across the landscape due to differences in local physiographic conditions. Trees at sites with lower CWDs were more responsive to summer VPD, showing greater reductions in growth rates during warmer years. Trees at sites with greater soil AWC were more responsive to winter precipitation, showing higher growth rates during years of high precipitation. Piñon pine growth rates declined moderately over the past century across our study area, suggesting that recent increases in aridity have resulted in long‐term growth declines.

Effects of Biochar Produced From Sugarcane Bagasse at Different Pyrolysis Temperatures on Water Retention of a Calcaric Dark Red Soil

Biochar (BC) is a promising soil amendment that can enhance water retention and plant-available water capacity while mitigating CO2 emissions. We investigated the effect of sugarcane bagasse–derived BC on the water retention properties of a calcaric clay soil amended with 3% (wt/wt) BC produced at three pyrolysis temperatures (400°C, 600°C, and 800°C). For BC pyrolyzed at 800°C (BC800), water retention curves of soil amended at 1%, 5%, and 10% (wt/wt) were also measured. Water retention curves were measured immediately after amending soil with BC (all types and rates) and after a 180-day incubation period for soils amended with 3% BC. The hydrophobicity of BC pyrolyzed at 400°C (B400) was the highest of the three temperatures tested, resulting in the lowest water retained in soil amended with BC400, but only for measurements done before incubation. During incubation, the hydrophobicity of B400 decreased as the aliphatic compounds became exhausted by oxidation of the BC surfaces. The available water capacity of the clay soil increased significantly by more than 60% when amended with BC at rates greater than of 3% wt/wt (P < 0.05).

Does water repellency of pyrochars and hydrochars counter their positive effects on soil hydraulic properties?

Adding carbon-rich solids from pyrolysis (pyrochars) and hydrothermal carbonization (hydrochars) to soils can improve their hydraulic properties and increase the plant available soil water capacity (AWC). However, the effects of the specific char characteristics on soil hydraulic properties are still little understood and thus, difficult to optimize for soil amendment. It is often assumed that the water repellency of chars is an important factor influencing the water retention of soils. In using the evaporation method and saturated conductivity measurements, we investigated how changes of hydraulic properties of a loamy sand with 2% (w/w) char addition depend on (i) production processes, (ii) feedstocks, (iii) particle size, and (iv) wetting properties of added chars. Applied chars comprised pyrochars carbonized at 750°C and hydrochars carbonized at 200°C and 250°C from two different feedstocks (digestate and woodchips) and two particle sizes (<0.5mm and 0.5–1.0mm). The wetting properties of the pure chars and soil–char composites were determined by the sessile drop method. To investigate the impact of the water repellency of chars, pure chars and soil–char composites were saturated by capillary water uptake under atmospheric conditions and by saturation from the bottom under vacuum conditions.The chars showed highly variable wetting properties with the contact angles being strongly correlated to the specific surface area of the chars. The saturated hydraulic conductivity was significantly increased after char addition for both vacuum and capillary saturated samples, while being independent of wettability characteristics. The effects for the unsaturated conductivity were negligible. In contrast to expectation, soil amendments with more water repellent chars caused higher increases of AWC (up to 15%), both after vacuum and capillary saturated conditions. Highest increase of AWC occurred for chars from digestate material, particle size fractions <0.5mm, and chars hydrothermally carbonized at 200°C. The increase of AWC only occurred in the low pressure range (pF1.8 to 2.5), whereas it was decreased in the high pressure range (pF2.5 to 4.2). Our study indicates that water repellency of pyrochars and hydrochars have little counteracting effect on the overall improvement of soil water retention and saturated conductivity, and other factors that also depend on production process and feedstock, such as particle size, intra-particle porosity, shape, and plasticity are more important.

Influence of soil properties on silver fir (Abies alba Mill.) growth in the Dinaric Mountains

Tree growth can be influenced by a wide variety of complex interacting factors. The contribution of soil to site productivity is confounded by the interactions between other site factors and silviculture. The contribution of soil properties to the growth of silver fir (Abies alba Mill.) was studied in the Dinaric Mountains, which are characterised by abundant sinkholes and limestone outcrops, resulting in diverse micro topography and different soil development at small spatial scales. Basal area increment and height growth data were estimated based on stem analysis of dominant silver fir trees (n=65) on a 50m×50m sampling grid, and competition intensity was determined. The soil development around each tree was defined using morphological properties of the genetic horizons based on soil probing (n=65×12). In the study area, the chemical and physical soil characteristics (based on 21 soil profiles) were favourable for plant growth. Soil parameters e.g. soil depth, thickness of genetic soil horizons, share of soil types around each tree and soil associations were the factors controlling tree growth. Tree age and competition intensity were also influential factors in the case of height and radial tree growth respectively. Positive effects on height and radial growth were confirmed also for available water capacity of soil and location of tree in slope position (in the sinkhole, out of the sinkhole). The decrease in specific basal area increment with increasing competition intensity was most evident for trees growing on leached soils. The coefficient of determination and the statistical significance of the relationship between height growth and soil association over the last 100years emphasised the cumulative effect of the soil condition on tree height growth.

Functional Digital Soil Mapping for the Prediction of Available Water Capacity in Nigeria using Legacy Data

Soil information, particularly water storage capacity, is of utmost importance for assessing and managing land resources for sustainable land management. We used digital soil mapping (DSM) and digital soil functional mapping (DSFM) procedures to predict available water capacity (AWC) of soils in Nigeria based on three published Pedotransfer functions (PTFs). We followed the specifications of the GlobalSoilMap.net project to produce predictions at a grid resolution of 100 m using regression tree models applied to a compiled soil point database together with auxiliary environmental predictors. Mean AWC (cm cm−1) estimates for Nigeria using methods published by Hodnett and Tomasella (PTF‐HT), Zacharias and Wessolek (PTF‐ZW), and Minasny and Hartemink (PTF‐MH) PTFs were 0.08, 0.21, and 0.12 cm cm−1 for the 0‐ to 5‐cm depth interval and 0.16, 0.08, and 0.08 for the cumulative depth (0–200 cm). The AWC estimates from the PTFs and from the literature for a number of discrete points and locations generally compared well. Comparison of AWC estimated from predicted soil properties (AWPp) against those estimated directly from profile observations (AWPd) for a number of discrete point locations showed a significant relationship only for PTF‐HT (R2 = 0.24, p &lt; 0.05, for the 0–5 cm depth interval) and PTF‐ZW (R2 = 0.25, p &lt; 0.05, for the cumulative depth). Soil properties predictions using remote sensing environmental covariates alone yielded similar results compared to predictions using a more extensive environmental covariate datasets. Overall, the process adopted for estimating AWC in this study shows promising results, but field measurements are still needed for validation and fine tuning of the process.

Meta‐modeling soil organic carbon sequestration potential and its application at regional scale

Upscaling the results from process-based soil-plant models to assess regional soil organic carbon (SOC) change and sequestration potential is a great challenge due to the lack of detailed spatial information, particularly soil properties. Meta-modeling can be used to simplify and summarize process-based models and significantly reduce the demand for input data and thus could be easily applied on regional scales. We used the pre-validated Agricultural Production Systems sIMulator (APSIM) to simulate the impact of climate, soil, and management on SOC at 613 reference sites across Australia's cereal-growing regions under a continuous wheat system. We then developed a simple meta-model to link the APSIM-modeled SOC change to primary drivers, i.e., the amount of recalcitrant SOC, plant available water capacity of soil, soil pH, and solar radiation, temperature, and rainfall in the growing season. Based on high-resolution soil texture data and 8165 climate data points across the study area, we used the meta-model to assess SOC sequestration potential and the uncertainty associated with the variability of soil characteristics. The meta-model explained 74% of the variation of final SOC content as simulated by APSIM. Applying the meta-model to Australia's cereal-growing regions reveals regional patterns in SOC, with higher SOC stock in cool, wet regions. Overall, the potential SOC stock ranged from 21.14 to 152.71 Mg/ha with a mean of 52.18 Mg/ha. Variation of soil properties induced uncertainty ranging from 12% to 117% with higher uncertainty in warm, wet regions. In general, soils in Australia's cereal-growing regions under continuous wheat production were simulated as a sink of atmospheric carbon dioxide with a mean sequestration potential of 8.17 Mg/ha.

Evaluación de la calidad del suelo tras la implantación de cubiertas permanentes en viñedos de zonas semiáridas. Materia orgánica y propiedades físicas y biológicas del suelo

El establecimiento de cubiertas vegetales permanentes (PGC) en viñedos de zonas semiáridas, con manejo tradicional de suelo desnudo mediante laboreo y aplicación de herbicidas, es controvertido, porque tiene ventajas agronómicas y ambientales, pero puede inducir cambios negativos en la calidad física del suelo. Los objetivos de este trabajo fueron: (i) avanzar en el conocimiento del efecto de la implantación de PGC en la calidad física y biológica del suelo, e (ii) identificar los indicadores de calidad del suelo más apropiados para suelos calizos de viñedo en una zona semiárida. Se determinaron propiedades físicas y biológicas clave en un Calcisol Cámbico con PGC de diferente edad (1 y 5 años), con un control manejado convencionalmente. El análisis de correlaciones mostró una relación directa entre la estabilidad estructural (WSA), la capacidad de retención de agua útil (AWC), la biomasa microbiana y las actividades enzimáticas del suelo bajo PGC. El contenido de C orgánico total (SOC) y lábil (POM-C) estuvo también correlacionado con los parámetros microbianos. Los indicadores de calidad del suelo más sensibles se identificaron mediante análisis factorial por componentes principales (PCA). La actividad de lombrices, AWC, WSA, SOC y POM-C mostraron el mayor peso en los dos factores obtenidos con PCA, por lo que estas propiedades pueden considerarse indicadores adecuados de la calidad del suelo en este agrosistema. Estos resultados indican que tanto los atributos físicos como biológicos del suelo son diferentes bajo PGC, y necesitan ser evaluados al estudiar las consecuencias de su introducción en suelos de viñedo.

Drought response and changing mean sensitivity of European beech close to the dry distribution limit

European beech (Fagus sylvatica L.) covers a large area mainly in the colline and montane ranges in Europe, and a drier and warmer climate, as expected for the coming decades, is likely to alter its distribution. So far, an altitudinal shift has been projected using a variety of modelling approaches. However, we lack knowledge about the climatic and edaphic factors that control the growth and competitive behaviour of beech at its dry distribution limit. We applied and further developed dendroecological methods to study the drought response and sensitivity pattern of beech at sites with different moisture regimes. We compared three pairs of sites from different geographical regions near the dry distribution limit of beech in Switzerland, consisting of a dry and mesic site each. Radial growth differed between mesic and dry sites, in that average ring-width at mesic sites was around double the width at dry sites. For the whole study period (1930–2006), the sites with the lowest available soil water capacity (AWC) were found to respond most sensitively to drought. However, in recent years, sites with higher AWC have shown increasing drought sensitivity, i.e. they have responded even more strongly to drought than the dry sites. This change in sensitivity corresponds to a seasonal shift in drought response at mesic sites, with a change in the months showing significant drought response in all three studied regions compared with the past. Even though dry sites generally displayed a larger number of negative pointer years than mesic sites, it appears that the frequency of pointer years has increased at mesic sites, i.e. they have become more sensitive particularly in the last quarter of the twentieth century. Yet, the frequency of pointer years at the dry sites has remained fairly constant. These results indicate that beech trees near their dry distribution limit are adapted to extreme conditions already, while changes in the growth patterns of beech under mesic conditions have to be expected.