Plant Available Water Capacity Research Articles

Soil physico-hydraulic properties under organic conilon coffee intercropped with tree and fruit species

Abstract: The objective of this work was to evaluate the cultivation effects of organic conilon coffee (Coffea canephora) intercropped with tree and fruit species on soil physico-hydraulic properties. Conilon coffee managements in the organic system were: T1, full-sun monoculture; T2, T3, T4, and T5, intercropping with peach palm (Bactris gasipae), gliricidia (Gliricidia sepium), banana (Musa sp.), and inga (Inga edulis), respectively; and T6, an area of secondary native forest used as a control. The evaluated soil physico-hydraulic properties were: bulk density, porosity, plant-available water capacity, soil-penetration resistance, soil-water content, soil temperature, and least limiting water range. Conilon coffee intercropped with peach palm and gliricidia resulted in lower soil bulk density and penetration resistance, and in higher total porosity, microporosity, and soil-water content. Organic coffee shaded with peach palm and gliricidia improve the soil physico-hydraulic quality, in comparison with the soil under monoculture in full sun and with the soil of secondary native forest.

Surface and incorporated liming effects on clay dispersion, water availability, and aeration capacity of a Dystrudept soil

ABSTRACT Liming represents a management procedure that can affect the soil structure and its thermodynamic processes. In this context, the aims of this study were to assess (i) the effects of the surface and incorporated liming on the clay dispersion, soil water availability, and aeration capacity; (ii) the influence of soil chemical alterations in its physical attributes. For this, a field experiment was installed in a family farming property, located in the southeastern region of the State of Parana, in a Dystrudept soil. The treatments were 3 application modes (on the surface, incorporated via plowing and incorporated via subsoiling and harrowing), with and without 15 Mg∙ha–1 of lime, aiming to increase the base saturation in the topsoil (0 – 0.20 m) to approximately 70%. Eighteen months after application, undisturbed and disturbed soil samples were collected from the 0 – 0.10 and 0.10 – 0.20 m layers to evaluate the waterdispersed clay (WDC), water content at the field capacity (θFC) and at the permanent wilting point (θPWP), plant available water capacity (PAWC), relative water capacity (RWC), aeration capacity (AC), granulometry and the soil structural and chemical attributes. WDC content in the 0 – 0.10 m layer increased when the soil was revolved and it was influenced exclusively when lime was applied on the soil surface. With surface liming there were increase in θFC, θPWP, PAWC and RWC, and reduction in AC in the 0 – 0.10 m layer. In the 0.10 – 0.20 m layer isolated effects were verified of the modes application and liming on θFC, PAWC and RWC, while θPWP was not influenced by treatments. The soil water availability and aeration capacity alterations were mainly affected by micro and macroporosity increases, pH reduction, Al3+ precipitation, and substitution of this ion in the exchange complex by Ca2+ and Mg2+.

In a native pasture, landscape properties influence soil moisture more than grazing management

It has been proposed that changes to grazing systems, from continuous to rotational grazing, alter the pasture mass and composition, which are reflected in changes to stored soil water. Additionally, in highly variable landscapes, determining whether the variation in soil water is due to the inherent landscape properties rather than the imposed grazing management has long been a contentious argument. To address this question, soil moisture was measured across a highly variable landscape under three differing grazing treatments (1-, 4- and 20-paddock systems). From the soil-water measurements, plant-available water and plant-available water capacity were determined. Different production zones (high, medium and low) were identified in the landscape by visually estimating green herbage mass in late spring. There were no observed differences in the measured plant-available water capacity across the grazing treatments; however, significant differences occurred in plant-available water capacity across the three production zones (high-production zone, 114 mm; medium-production zone, 102 mm; low-production zone, 88 mm) within the study period. There appears to be a trend between the plant-available water capacity and near-surface gravel content as measured in production zones. The high production zones held more plant-available water than did the low production zones, enabling more biomass and longer pasture growth during spring and autumn. The plant-available water in the low production zones significantly decreased with time. In all, 22 of the 50 soil-moisture monitoring locations displayed high temporal stability and were identified as being catchment-average soil water-content monitoring locations. A majority of these locations occurred in the medium production zone, demonstrating that representative soil moisture can be measured in these landscapes.

Measuring and Modeling the Water Balance in Low-Rainfall Cropping Systems

Abstract. In low-rainfall cropping systems, understanding the water balance, and in particular the storage of soil water in the rooting zone for use by crops, is considered critical for devising risk management strategies for grain-based farming. Crop-soil modeling remains a cost-effective option for understanding the interactions between rainfall, soil, and crop growth, from which management options can be derived. The objective of this study was to assess the error in the prediction of soil water content at key decision points in the season against continuous, multi-layer soil water measurements made with frequency domain reflectometry (FDR) probes in long-term experiments in the Mallee region of South Australia and New South Wales. Field estimates of the crop lower limit or drained upper limit were found to be more reliable than laboratory-based estimates, despite the fact that plant-available water capacity (PAWC) did not substantially differ between the methods. Using the Agricultural Production Systems sIMulator (APSIM) to simulate plant-available water over three-year rotations, predicted soil water was within 7 mm (PAWC 64 to 99 mm) of the measured data across all sowing events and rotations. Simulated (n = 46) wheat grain production resulted in a root mean square error (RMSE) of 492 kg ha-1, which is only marginally smaller than that of other field studies that derived soil water limits with less detailed methods. This study shows that using field-derived data of soil water limits and soil-specific settings for parameterization of other properties that determine soil evaporation and water redistribution enables APSIM to be widely applied for managing climate risk in low-rainfall environments. Keywords: APSIM, Climate risk management, Crop models, Decision support, Soil moisture.

Genetic Diversity in Barley and Wheat for Tolerance to Soil Constraints

Surface soil sodicity as well as subsoil salinity, acidity, and phytotoxic concentrations of chloride (Cl) are major soil constraints to crop production in many soils of sub-tropical, north-eastern Australia. The identification of genotypes tolerant to these soil constraints may be an option to maintain and improve productivity on these soils. We evaluated performance of 11 barley and 17 wheat genotypes grown on two sites <0.5 km apart. Compared to the non-sodic site, the sodic site had significantly higher Cl concentration (>800 mg·Cl·kg−1) in the subsoil (0.9–1.3 m soil depth) and higher exchangeable sodium percentage (ESP) (>6%) in the surface and subsoil. Barley grain yield and plant available water capacity (PAWC) were reduced between 5%–25% and 40%–66%, respectively, for different genotypes at the sodic site as compared to the non-sodic site. For wheat genotypes, grain yield was between 8% and 33% lower at the sodic site compared to the non-sodic site and PAWC was between 3% and 37% lower. Most barley and wheat genotypes grown at the sodic site showed calcium (Ca) deficiency symptoms on younger leaves. Analysis of the youngest fully mature leaf (YML) confirmed that genotypes grown at the sodic site with Ca concentration < 0.2% exhibited deficiency symptoms. Grain yields of both barley and wheat genotypes grown on the sodic and non-sodic sites increased significantly with increasing Ca and K in YML and decreased significantly with increasing Na and Cl concentrations in YML. Sodium (Na) concentrations in YML of wheat genotypes grown at the sodic site were 10-fold higher than those from the non-sodic site whereas this increase was only two-fold in barley genotypes. In step-wise regression, the PAWC of barley and wheat genotypes grown on sodic and non-sodic sites was the principal determinant of variability of barley and wheat grain yield. Including the Ca concentration in the YML of wheat genotypes and K:Na ratio in the YML of barley genotypes significantly improved the prediction of grain yield in the regression analysis. Barley genotypes, Mackay and Kaputar, were relatively susceptible while Baronesse and Grout were relatively more tolerant to sodicity. Wheat genotypes Gregory and Stampede were generally relatively more susceptible to sodicity, and genotypes Baxter, Hume, and the experimental line HSF1-255 were relatively more tolerant than the former group.

Effects of crop rotation on properties of a Vietnam clay soil under rice-based cropping systems in small-scale farmers' fields

In tropical deltas, intensive monoculture with three rice crops per year (RRR) has been the standard for decades. However, in recent years some farmers have started rice-based rotations with one or more upland crops per year. The trends for increased grain yields with this new system raises the question as to whether the introduction of upland crops affects properties of alluvial clay paddy soil. This was evaluated in the present study, which was performed at 40 paddy fields in the Vietnamese Mekong Delta under four different cropping systems (10 farms per system) on paddy rice soils: RRR; crop rotation with two rice crops and one upland crop per year (RUR); crop rotation with one rice and two upland crops per year (RUU); and upland crop (UUU). Soil samples were collected at depths of 0–10, 10–20 and 20–30cm. Most soil properties differed significantly between the RRR and the RUR, RUU or UUU. The RUR, RUU and UUU systems alleviated soil compaction, resulting in reduced penetration resistance and bulk density and increased total and macroporosity at 20–30cm depth. In addition, aggregate stability index and plant-available water capacity were higher for RUR, RUU and UUU compared with RRR at the 20–30cm depth. Average soil organic carbon (SOC) stocks ranged from 59.3tha–1 in UUU to 72.3tha–1 in RUR, with SOC stocks in RRR and RUU being intermediate (66.4 and 68.3tha–1) and not significantly different to that of the RUR system. Carbon hydrolysable by HCl (Chydrolysable) was 74–84% greater in the RUR, RUU and UUU than in RRR systems. In conclusion, rice–upland crop systems may alleviate soil degradation resulting from continuous rice monoculture.

Physical quality of Northern Nigeria Savanna Alfisol: Influence of Jatropha curcas L. and other land use systems

AbstractThis study investigated the impact of three adjacent land use systems [land under arable cropping (ARL), cattle grazing fallow (GFL) and Jatropha curcas L. Orchard (JCL)] on selected soil physical quality indicators in a Northern Nigeria Savanna Alfisol. GFL had significantly higher organic carbon content (26.2–32.1% higher) and bulk density (4.5–9.2% higher) than JCL and ARL respectively. Higher bulk density (ρb) in GFL aided by trampling induced compaction resulted in its high relative field capacity (RFC), permanent wilting point (PWP) and micro-pore spaces (PMIC). Continuous tillage in ARL created loose soil in the plough layer (<20 cm) which turn out to its low bulk density (ρb) and high plant-available water capacity (PAWC), total pore spaces (f) and macro-pore spaces (PMAC) over JCL and GFL. Total nitrogen content, dry stability of large macro-aggregate fractions [5–2 mm, (LMag)] and mean weight diameter (MWD) were higher in JCL than GFL and ARL to about 47.2–60.6, 12.5–68.8 and 8.57–44.76%...

Assessment of chemical properties of reclaimed subsidence land by the integrated technology using Yellow River sediment in Jining, China

Land subsidence is one of the most prominent environmental problems in China. Chemical properties of reclaimed subsidence land by the integrated reclamation technology using Yellow River sediment were assessed. Reclamation engineering of mining subsidence land was conducted, and representative soil samples of the reclaimed farmland (SR) and nearby unaltered farmland (CK) were collected from Jining City, Shandong Province. Soil chemical properties, including pH, electrical conductivity (EC), organic carbon (OC), total nitrogen (TN), extractable phosphorus (EP) and potassium (EK), and eight heavy metals were measured. The results indicate that more than 95 % of mining subsidence lands can be restored to farmland, which indicates the integrated reclamation technology with Yellow River sediment was feasible. The soils of SR and CK were alkaline but non-saline. The contents of TN, EP, EK and OC of SR were less than those of CK. Cd and Hg were not detected in any soil, and the contents of Pb, Zn, Cu, Cr, Ni and As of all soil layers of SR and CK were less than the maximum contaminant values of the second level to maintain human health and third level to protect plant normal growth as suggested in the standard for soils of China. Some improved methods of the integrated reclamation technology are suggested, such as draining water after settling of the water–sediment mixture in the reclamation strip for several days (>48 h) to increase deposition of more clay and silt in SR. The return of wheat or maize residue is recommended to improve both the fertility and plant-available water capacity of SR. Conventional tillage of the reclaimed land will likely improve productivity as the sand, silt and clay particles become an integral, living, soil body.

Soil physical quality on conilon coffee intercropping and monoculture

The objective of this study was to evaluate the effects of conilon coffee the unshaded and shaded with tree species on soil physical quality. Six treatments were studied: T1- coffee monoculture; T2, T3, T4 and T5- intercropping coffee with peach palm, gliricidia, banana and inga, respectively; T6- native vegetation in natural regeneration. Soil samples were collected at a depth of 0-0.10 m for determination of soil attributes. Similar values of soil bulk density, total porosity, organic matter and carbon stocks occurred in the coffee monoculture and intercropping managements. T2 and T3 showed a greater plant-available water capacity, with 142 and 135 L m-3, which resulted in higher soil moisture. Lower aeration porosity occurred in T2 and T3. The treatments presented non-limiting S index (S>0.035), with the exception of T4. The treatments presented critical bulk density of 1.32 Mg m-3. The increase in soil organic matter resulted in an increase of the S index. The managements of the conilon coffee plantation with peach palm and gliricidia presented improvements in soil physical quality. The choice of species used in intercropping with conilon coffee must be adjusted to the characteristics of the region and the farmer.

Effects of gasification biochar on plant-available water capacity and plant growth in two contrasting soil types

Gasification biochar (GB) contains recalcitrant carbon that can contribute to soil carbon sequestration and soil quality improvement. However, the impact of GB on plant-available water capacity (AWC) and plant growth in diverse soil types still needs to be explored.A pot experiment with spring barley (Hordeum vulgare L.) was conducted to investigate the effect of soil amendment by 1% straw and wood gasification biochar (SGB and WGB), respectively, on AWC and plant growth responses under two levels of water supply in a temperate sandy loam and a coarse sandy subsoil. In the sandy loam, the reduced water regime significantly affected plant growth and water consumption, whereas the effect was less pronounced in the coarse sand. Irrespective of the soil type, both GBs increased AWC by 17–42%, with the highest absolute effect in the coarse sand. The addition of SGB to coarse sand led to a substantial increase in plant biomass under both water regimes: shoot growth by 40–165% and root growth by 50–57%. However, no positive effects were achieved by the addition of WGB. In the sandy loam, soil application of GB had no or negative effects on plant growth.Our results suggest that SGB has considerable potential for enhancing crop productivity in coarse sandy soils by increasing soil water retention and improving root development.

Prediction of Plant Available Water at Sowing for Winter Wheat in the Southern Great Plains

Sowing plant available water (PAWs) can impact wheat (Triticum aestivum L.) stand establishment, early crop development, and yield. Consequently, PAWs is an essential input in crop simulation models and its estimation can improve agronomic decisions. Our objective was to identify effective methods to predict PAWs in continuous winter wheat by exploring empirical and mechanistic models based on the preceding 4‐mo summer fallow. The mechanistic soil water balance models dual crop coefficient (dual Kc) and simple simulation model (SSM) were calibrated, validated, and tested using soil moisture datasets collected from 2009 to 2013 in Oklahoma totaling 29 site‐years. Additionally, PAWs was predicted using empirical nonlinear models based on cumulative fallow precipitation and the soil's plant available water capacity (PAWC). Both the dual Kc and SSM models resulted in normalized root mean squared error (RMSEn) below 12% (20 mm) for the calibration and validation datasets. Modeled PAWs for the prediction dataset was within ±30% of field observations in 67% of the site‐years for both dual Kc and SSM models, with RMSEn of 27 and 32%. An inverse‐exponential and a logarithmic model of PAWs using cumulative fallow precipitation and PAWC both resulted in RMSEn = 23 and 29% in the calibration and validation datasets. The dual Kc model was slightly superior to empirical models based on nonlinear regression analysis, and was superior to the SSM model. Initializing the dual Kc at the start of the preceding fallow or using empirical relationships allow for acceptable predictions of PAWs, eliminating the need for subjective PAWs values.Core Ideas Wheat is among the most important crops cultivated in the southern Great Plains. Plant‐available water at sowing is a critical input in dynamic crop simulation models. Mechanistic water balance models or empirical models can predict wheat PAW at sowing. Models here shown decrease the need for subjective initial PAW values in crop models.

The impact of soil and climatic factors on forest growth

This preliminary study reveals the relations between the forest growth (annual dendromass increment; ADMinc - as dependent variable) and some important soil factors, which have effect on plant growth, such as: groundwater level (GWL), groundwater composition (GWC), plant available water capacity (PAWC), depth of humus layer, texture (hyi) and pH of the soil, moreover the maximum concentration (MAX) of salt and CaCCb and the depth of its MAX in the soil profile. 17 plantations (Poplar, Common oak and Black locust) are included in the analysis investigated all over the Great Hungarian Plain. Correlation profile of the above parameters was created explaining that two abiotic parameters limit plant growth: if GWL is deeper than 5 m and if HCO3 concentration in groundwater is high (above 15 meq/L). Within the tested range (0.17 - 2.23 mS/cm for electrical conductivity (EC) and 0.5 /sand/ - 4.21 /clay loam/ for hyi), the higher magnitude of EC results in higher ADMinc and the higher hyi (higher proportion of fine soil particles) leads to higher ADMinc The positive relationship of ADMinc with EC suggests good nutrient supply of the soil, while the higher proportion of fine particles refers to better water management properties. Thickness of humus layer is an important soil factor: compared to shallow humus layer, deep one increases ADMinc exponentially. In case of Black locust, PAWC is the substantial factor for growing, unlike Poplar, whose growth depends on groundwater uptake (GWU). This phenomenon originates from the differences between the individual needs of the tree species and differences in root morphology. Merely 4 sampling plots were equipped with meteorological stations, thus the number of climatic parameter data were not enough for statistical analysis. So data for all 17 plots were collected from literature and a general, regionally calculated data were applied (mean rainfall in the vegetation period and aridity index). There was no significant correlation between climatic parameters and ADMinc Further studies and more field investigations are needed in order to clarify the results.

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).

Potential and challenges of conservation agriculture in sequestration of atmospheric CO 2 for enhancing climate-resilience and improving productivity of soil of small landholder farms.

Abstract The projected climate change, caused by emissions from fossil fuel combustion and land use change, may adversely impact the agronomic yields and aggravate food insecurity of small landholder farms. About 500 million small landholder farms have depleted and degraded soils, while having low soil organic carbon (SOC) pools, low plant nutrient reserves, low plant-available water capacity and low agronomic yield, yet high vulnerability to changing and uncertain climate. Projected climate change may reduce rice yield by 10% for every 1°C increase in temperature, and total maize production may decline by 10% by 2050. Agronomic yield of wheat in South Asia may be adversely affected by increase in temperature during spring. Yield of other cereals (sorghum, millet) and root crops (cassava, yam) may be adversely affected by aggravation of other biotic stresses (smut, fungi, viruses, etc.). Thus, climate-resilience may be a key component of sustainable intensification of small landholder agriculture. It is in this context that conservation agriculture (CA) can be an important option. With fine-tuning for adaptation to site-specific conditions, CA has numerous benefits including erosion control, water conservation, SOC sequestration and increase in profitability and farm income. Further, CA can be implemented in synergism with other practices such as forestry and forest plantations (during early stages of tree establishment), and integrated crop-livestock (ley farming). In several farm operations, CA builds upon the traditional systems and indigenous technology. Widespread adoption of CA could sequester 1 Pg C/year globally, which could create another income stream for small landholders. Further, CA fits in with the '4 per Thousand' programme proposed at the COP-21 in Paris.

Temporal effects of food waste compost on soil physical quality and productivity

Reynolds, W. D., Drury, C. F., Tan, C. S. and Yang, X. M. 2015. Temporal effects of food waste compost on soil physical quality and productivity. Can. J. Soil Sci. 95: 251–268. The benefits of compost additions on soil organic carbon content and crop productivity are extant in the literature, but detailed studies of compost effects on soil physical quality (SPQ) are limited. The objective of this study was therefore to describe how one-time additions of compost impact the immediate, mid-term and long-term SPQ and crop yields of an agricultural soil. Food waste compost (FWC) was incorporated once into the top 10 cm of a humid-temperate Brookston clay loam soil at rates of 0 (Control), 75 dry t ha−1 (FWC-75), 150 dry t ha−1 (FWC–150) and 300 dry t ha−1 (FWC-300); measurements of SPQ parameters and corn yield were then made annually over the next 11 yr. The SPQ parameters included bulk density (BD), organic carbon content (OC), air capacity (AC), plant-available water capacity (PAWC), relative field capacity (RFC), and saturated hydraulic conductivity (KS), which were obtained from intact (undisturbed) soil core samples. Prior to compost addition, BD, OC, AC, PAWC, RFC and KS were substantially non-optimal, and BD had increased relative to virgin soil by 46%, while OC, AC and PAWC had decreased relative to virgin soil by 60, 56 and 43%, respectively. Improvements in SPQ 1 yr after compost addition were negligible or small for FWC-75 and FWC-150, but FWC-300 generated optimal values for BD, OC, AC, PAWC and RFC. The SPQ parameters degraded with time, but 11 yr after compost addition, OC and AC under FWC-300 were still within their optimal ranges, as well as significantly (P&lt;0.05) greater than the Control values by 65 and 26%, respectively. Soil cracks and biopores apparently induced substantial annual variation in KS, but average KS nevertheless increased with increasing compost addition rate. Corn grain yield varied substantially among years, which was likely due to weather and compost effects; however, 11-yr cumulative yields from the compost treatments were greater than the Control by 2200–6500 kg ha−1.

Determining the features influencing physical quality of calcareous soils in a semiarid region of Iran using a hybrid PSO-DT algorithm

Soil physical quality indicators (SPQIs) are used to make complex information more accessible to decision makers; however, their site-specific nature may restrict their applicability only to a specific soil type and/or management system. Therefore, it would be advantageous if such indicators could be predicted indirectly from easily available soil properties using inexpensive methods. In this study, we introduce a hybrid algorithm, specifically designed to work with optimized decision tree with particle swarm optimization (PSO-DT), for the prediction of SPQIs (i.e., air capacity, AC; plant-available water capacity, PAWC; and relative field capacity, RFC). The potential power of using the PSO-DT algorithm in setting up a framework for identifying the most determinant parameters affecting the physical quality of agricultural soils in a semiarid region of Iran (Baft plain, 29° 11′ to 29° 13′ N and 56° 34′ to 56° 38′ E) was also investigated. An empirical multiple linear regression (MLR) model was constructed as benchmark for the comparison of performance. In results, a permutation of five input features, including soil organic matter (SOM), electrical conductivity (EC), clay, sand, and bulk density (BD), was introduced by the hybrid PSO-DT algorithm as explanatory variables. Using the PSO-DT method resulted in higher model efficiency and coefficient of determination (R2) than the MLR approach. The obtained R2 values for the constructed PSO-DT model for the AC, PAWC, and RFC predictions were 0.91, 0.90, and 0.96, respectively, whereas they were 0.61, 0.16, and 0.47 for the MLR-model. The SOM, clay, and sand parameters were accounted as the discriminating variables of the models constructed for the prediction of AC, PAWC, and RFC indicators, respectively. This study provides a strong basis for the prediction of SPQIs and identifying the most determinant parameters influencing the physical quality of agricultural soils in semiarid regions of Iran; however, its general analytical framework could be applied to other parts of the world with similar challenges.

Soil physical quality of Mollisols quantified by a global index

Indicators synthesizing the state of the structural quality and the function of the porous system are useful for assessing soil production capacity as well as the way it may serve natural ecosystems. This research aimed (i) to determine indicators of the state and function of the porous system, (ii) to use them to derive a global index to characterize the soil physical quality, and iii) to establish a reference pore-size distribution curve for Mollisols from the province of Santa Fe (Argentina). Sixty water retention curves (WRC) of A and B horizons of Mollisols, with clay varying between 119 and 538 g kg−1, organic matter between 5 and 40 g kg−1, and soil bulk density between 1.09 and 1.49 Mg m−3, were used. The indicators measured were: pore size distribution, macroporosity (PORp), air capacity (ACt) and plant-available water capacity (PAWC) among others. Soils were classified into four groups according to their physical properties and a reference WRC was determined. From this WRC and considering a total porosity of 0.514 m3 m−3, PORp was 0.035 m3 m−3, ACt 0.153 m3 m−3, field capacity 0.361 m3 m−3, permanent wilting point 0.136 m3 m−3 and PAWC 0.225 m3 m−3. Both the high silt content and low organic matter content confer on the soil characteristics with low stability, excess of small pores and low porosity of the macropore domain. Consequently, the capacity to quickly drain the water excess and allow root proliferation was not optimal, possibly due to the high silt or clay content and the low sand content, characteristic of the soil matrix of these Mollisols.

Soil–water relationships in the upper soil layer in a Mediterranean Palexerult as affected by no-tillage under excess water conditions – Influence on crop yield

In Mediterranean regions, the performance of conservation tillage under water-deficit conditions has been widely reported, but conversely there exists a lack of studies investigating its effects during periods of water excess, which are common in these regions between fall and spring. Our experiment was established in 2005 on a degraded Palexerult from a raña, a continental detritic formation, of western Spain to study the influence of soil tillage and Ca amendments on soil quality. During high precipitation periods, perched water tables can be formed in very flat raña surfaces with the upper limit close to soil surface due to the presence of Bt horizons with low permeability. In the 2010–2011 and 2012–2013 campaigns, when perched water tables developed very close to the soil surface between November and March, we studied the effects of no tillage (NT) vs. tillage (T) on selected soil hydraulic properties in the 0–5cm soil layer and on crop yield. We observed the lowest bulk density and the highest soil organic matter content (SOM) for this soil layer under NT. As a result of the higher SOM content and higher total porosity as well as the potential to preserve soil biopores under NT, water content at saturation (SAT), plant-available water capacity (AWC), water infiltration and saturated hydraulic conductivity were also higher in the NT plots compared with those under T. During wet periods, the degree of water saturation (Sr) under T was higher, and sometimes close to saturation. Crop development and yield were strongly affected by near-saturation conditions in the 0–5cm surface layer, resulting in substantial yield losses under T.

Data-driven analysis of soil quality indicators using limited data

The difficult question of which variables to include as a minimum data set of soil quality (SQ) indicators may be simplified by statistical methods, which allow working with databases including categorical and numerical variables commonly used for assessing SQ. The aims of this study were: i) to identify soil structural related parameters that may associate to SQ at different geographic areas and ii) to test the potential power of using decision trees in setting up a framework for SQ assessment, and in determining structural soil properties, visually evaluated, that could be included in the estimation of soil physical properties such as saturated hydraulic conductivity (Ks). SQ was evaluated by visual soil assessment (VSA) in the field and a limited number of physical and chemical soil properties (bulk density (BD), air capacity, plant available water capacity (PAWC), saturated hydraulic conductivity (Ks), water stable aggregates (WSA), particle size distribution, soil organic carbon (SOC) and cation exchange capacity (CEC)) determined in the laboratory. Using categorical and numerical data of those physical, chemical and morphological properties of soils in both tropical and temperate areas, classification trees and model trees were grown. Parameters related to SQ differed between geographic areas. Ks was the strongest variable determining the SQ in ‘tropical’ soils, but WSA, SOC and PAWC were also key variables in determining differences in SQ. For ‘temperate’ soils PAWC was the only variable selected by the tree building algorithm. SOC, clay, and CEC were the discriminating variables of the model constructed from the combined data set. Statistically significant relationships between measured and visual parameters are promising in demonstrating the SQ description required for merging morphological, physical and chemical properties for minimum data set of SQ indicators. Thresholds of different predicting variables could be better established when SQ frameworks involve VSA. We also proved that prediction of KS with a model tree was more accurate when morphological parameters were included as predictor variables, and that in that case the model tree showed a simpler structure compared to the tree built only from chemical and physical soil properties. In conclusion, decision trees are encouraging in the selection of SQ indicators. Moreover, including morphological properties in the prediction of key soil properties such as Ks seems promising. VSA could render morphological response variables for predicting other soil properties and developing SQ frameworks (agricultural interest) more capable of representing structural dynamic.

Impacts of 48 years of consistent cropping, fertilization and land management on the physical quality of a clay loam soil

Reynolds, W. D., Drury, C. F., Yang, X. M., Tan, C. S. and Yang, J. Y. 2014. Impacts of 48 years of consistent cropping, fertilization and land management on the physical quality of a clay loam soil. Can. J. Soil Sci. 94: 403–419. Soil physical quality (SPQ) is often ignored or under-monitored in long-term field studies designed to determine the economic and environmental sustainability of agricultural practices. Accordingly, a suite of complementary soil physical and hydraulic parameters was measured using intact core samples to determine the SPQ of a Brookston clay loam under a long-term (48 yr) cropping, fertilization and land management study at Woodslee, Ontario. The SPQ under virgin woodlot, fertilized monoculture sod and unfertilized monoculture sod treatments was similar, with optimal SPQ occurring in the top 10–20 cm, but severely suboptimal SPQ occurring below 30 cm because bulk density (BD), relative field capacity (RFC) and saturated hydraulic conductivity (KS) were excessive, and because organic carbon (OC), air capacity (AC) and plant-available water capacity (PAWC) were critically low. The SPQ for fertilized and unfertilized monoculture corn under fall moldboard plow tillage was similar and substantially suboptimal throughout the top 40–50 cm due to high or excessive BD and RFC, critically low OC, low or critically low AC and PAWC, and KSthat varied erratically from excessive to critically low. The SPQ under fertilized and unfertilized corn–oat–alfalfa–alfalfa rotations (corn and second-year alfalfa fall plowed) was similar and largely non-optimal below 10 cm, but largely optimal in the top 10 cm due to the ameliorating effects of numerous biopores and crop roots. A bimodal soil water release function fitted to release curve data showed that PAWC was determined by soil matrix porosity (PM), and AC was determined by soil structure porosity (PS). Strong inverse linear correlations between BD vs. PM, BD vs. PSand BD vs. OC provided site-specific estimates of optimal ranges and critical limits for PAWC, AC and OC, respectively. Although SPQ changed substantially among treatments, the changes did not extend below 30-to 40-cm depth, and were largely unaffected by long-term annual fertilization. The SPQ below 30- to 40-cm depth was similarly poor across all treatments, and is likely an inherent characteristic of the soil.