Aims This study aims to (i) determine the effects of incorporating 47 Mg ha⁻¹ acacia green waste biochar on soil physical properties and water relations, and (ii) to explore the different mechanisms by which biochar influences soil porosity. Methods The pore size distribution of the biochar was determined by scanning electron microscope and mercury porosimetry. Soil physical properties and water relations were determined by in situ tension infiltrometers, desorption and evaporative flux on intact cores, pressure chamber analysis at -1,500 kPa, and wet aggregate sieving. Results Thirty months after incorporation, biochar application had no significant effect on soil moisture content, drainable porosity between -1.0 and -10 kPa, field capacity, plant available water capacity, the van Genuchten soil water retention parameters, aggregate stability, nor the permanent wilting point. However, the biochar-amended soil had significantly higher nearsaturated hydraulic conductivity, soil water content at -0.1 kPa, and significantly lower bulk density than the unamended control. Differences were attributed to the formation of large macropores (>1,200 μm) resulting from greater earthworm burrowing in the biocharamended soil. Conclusion We found no evidence to suggest application of biochar influenced soil porosity by either direct pore contribution, creation of accommodation pores, or improved aggregate stability.
Soil erosion is extreme in Mediterranean orchards due to management impact, high rainfall intensities, steep slopes and erodible parent material. Vall d'Albaida is a traditional fruit production area which, due to the Mediterranean climate and marly soils, produces sweet fruits. However, these highly productive soils are left bare under the prevailing land management and marly soils are vulnerable to soil water erosion when left bare. In this paper we study the impact of different agricultural land management strategies on soil properties (bulk density, soil organic matter, soil moisture), soil water erosion and runoff, by means of simulated rainfall experiments and soil analyses. Three representative land managements (tillage/herbicide/covered with vegetation) were selected, where 20 paired plots (60 plots) were established to determine soil losses and runoff. The simulated rainfall was carried out at 55 mm h in the summer of 2013 (< 8% soil moisture) for one hour on 0.25 m circular plots. The results showed that vegetation cover, soil moisture and organic matter were significantly higher in covered plots than in tilled and herbicide treated plots. However, runoff coefficient, total runoff, sediment yield and soil erosion were significantly higher in herbicide treated plots compared to the others. Runoff sediment concentration was significantly higher in tilled plots. The lowest values were identified in covered plots. Overall, tillage, but especially herbicide treatment, decreased vegetation cover, soil moisture, soil organic matter, and increased bulk density, runoff coefficient, total runoff, sediment yield and soil erosion. Soil erosion was extremely high in herbicide plots with 0.91 Mg ha h of soil lost; in the tilled fields erosion rates were lower with 0.51 Mg ha h . Covered soil showed an erosion rate of 0.02 Mg ha h . These results showed that agricultural management influenced water and sediment dynamics and that tillage and herbicide treatment should be avoided.
Soil water erosion on cultivated lands represents a severe threat to soil resources in the world, and especially in Mediterranean areas, due to their topographic, edaphic and climatic conditions. Among the cultivated lands, vineyards deserve a particular attention because, aside representing one of the most important crops in terms of income and employment, they also have proven to be the form of agricultural use that causes one of the highest soil losses. Although the topic of soil water erosion on vineyards has been studied, it still raises uncertainties, due to the high variability of procedures for data acquisition, which consists into different scales of analysis and measurement methods. There is still a great gap in knowledge about the effect of triggering factors on soil water erosion and, so far, an effort to quantify this effect on the Mediterranean viticulture has not been made yet. Therefore, this paper review aims to (i) develop a documented database on splash, sheet and rill erosion rates in Mediterranean vineyards, (ii) identify and, if possible, quantify the effect of triggering factors such as topography, soil properties, rainfall characteristics and soil conservation techniques on soil water erosion, and (iii) provide suggestions for a more sustainable viticulture. Although the large variability of data, some general trends between erosion rates and triggering factors could be found, as long as data were categorized according to the same measurement method. However, no general rule upon which to consider one triggering factor always predominant over the others came out. This paper review supports the importance of monitoring soil water erosion by field measurements to better understand the relationship between the factors. However, protocols should be established for standardizing the procedure of collecting data and reporting results to enable data comparison among different study areas.
RationaleThe ability to recover the isotopic signature of water added to soil samples that have previously been oven-dried decreases with the increasing presence of silt and clay. The effects on the isotopic signature of water associated with physicochemical soil properties are not yet fully understood, for either hydration or dehydration of soil samples. MethodsThe soil sample chemistry and the crystallinity of minerals were measured by X-ray fluorescence and X-ray diffraction. The organic carbon and the cation-exchange capacity were also determined. Water of known isotopic signature was used to spike an oven-dried substrate and subsequently extracted by cryogenic vacuum extraction at a temperature of 105 degrees C. In addition, the soils were oven-dried at 205 degrees C and water extractions were also performed at 205 degrees C. The isotopic signatures of the water samples were determined by cavity-ring-down spectrometry. ResultsThe isotope effects caused by the cryogenic vacuum extraction method applied to soils with elevated clay content were reduced. First, by increasing the extraction temperature to 205 degrees C, we improved the precision of the cryogenic vacuum extraction method and the recovery of the known isotopic signature of the spike water. Secondly, the post-correction of data based on the physicochemical soil properties and a common extraction temperature of 105 degrees C improved the measurement trueness. ConclusionsThe isotopic signature of soil water is influenced by mineral-water interaction. During the hydration of clay, different minerals deplete free water in heavy isotopes. The extracted soil water (dehydration water) gathered from clay-rich soils is generally more depleted in the heavy isotopes than the spike water, making results obtained for different soil types difficult to compare. Isotope effects observed at the mineral-water interface highlight potential explanations for eco-hydrological separation of water pools. Copyright (c) 2016 John Wiley & Sons, Ltd.
Among the soil conservation practices that are used, mulching has been successfully applied to reduce soil and water losses in different contexts, such as agricultural lands, fire-affected areas, rangelands and anthropic sites. In these contexts, soil erosion by water is a serious problem, especially in semi-arid and semi-humid areas of the world. Although the beneficial effects of mulching are known, further research is needed to quantify them, especially in areas where soil erosion by water represents a severe threat. In the literature, there are still some uncertainties about how to maximize the effectiveness of mulching to reduce the soil and water loss rates. Given the seriousness of soil erosion by water and the uncertainties that are still associated with the correct use of mulching, this study review aims to (i) develop a documented and global database on the use of mulching with vegetative residues; (ii) quantify the effects of mulching on soil and water losses based on different measurement methods and, consequently, different spatial scales; (iii) evaluate the effects of different types of mulches on soil and water losses based on different measurement methods; and (iv) provide suggestions for more sustainable soil management. The data published in the literature have been collected. The results showed the beneficial effects of mulching in combating soil erosion by water in all of the environments considered here, with reduction rates in the average sediment concentration, soil loss and runoff volume that, in some cases, exceeded 90%. However, the economic feasibility of mulching application was not readily available in the literature. Therefore, more research should be performed to help both farmers and land managers by providing them with evidence-based means for implementing more sustainable soil management practices.
Water flow from soil to plants depends on the properties of the soil next to roots, the rhizosphere. Although several studies showed that the rhizosphere has different properties than the bulk soil, effects of the rhizosphere on root water uptake are commonly neglected. To investigate the rhizosphere's properties we used neutron radiography to image water content distributions in soil samples planted with lupins during drying and subsequent rewetting. During drying, the water content in the rhizosphere was 0.05 larger than in the bulk soil. Immediately after rewetting, the picture reversed and the rhizosphere remained markedly dry. During the following days the water content of the rhizosphere increased and after 60 h it exceeded that of the bulk soil. The rhizosphere's thickness was approximately 1.5 mm. Based on the observed dynamics, we derived the distinct, hysteretic and time-dependent water retention curve of the rhizosphere. Our hypothesis is that the rhizosphere's water retention curve was determined by mucilage exuded by roots. The rhizosphere properties reduce water depletion around roots and weaken the drop of water potential towards roots, therefore favoring water uptake under dry conditions, as demonstrated by means of analytical calculation of water flow to a single root.
Many studies report that, under some circumstances, amending soil with biochar can improve field capacity and plant-available water. However, little is known about the mechanisms that control these improvements, making it challenging to predict when biochar will improve soil water properties. To develop a conceptual model explaining biochar's effects on soil hydrologic processes, we conducted a series of well constrained laboratory experiments using a sand matrix to test the effects of biochar particle size and porosity on soil water retention curves. We showed that biochar particle size affects soil water storage through changing pore space between particles (interpores) and by adding pores that are part of the biochar (intrapores). We used these experimental results to better understand how biochar intrapores and biochar particle shape control the observed changes in water retention when capillary pressure is the main component of soil water potential. We propose that biochar's intrapores increase water content of biochar-sand mixtures when soils are drier. When biochar-sand mixtures are wetter, biochar particles' elongated shape disrupts the packing of grains in the sandy matrix, increasing the volume between grains (interpores) available for water storage. These results imply that biochars with a high intraporosity and irregular shapes will most effectively increase water storage in coarse soils.
Aims Stable isotopes of oxygen and hydrogen are often used to determine plant water uptake depths. We investigated whether and to what extend soil moisture, clay content, and soil calcium carbonate influences the water isotopic composition. Methods In the laboratory, dried soil samples varying in clay content were rewetted with different amounts of water of known isotopic composition. Further, we removed soil carbonate from a subset of samples prior to rewetting. Water was extracted from samples via cryogenic vacuum extraction and analysed by mass spectrometry. Results The isotopic composition of extracted soil water was similarly depleted in both ¹⁸O and ²H with decreasing soil moisture and increasing clay and carbonate content. Soil carbonate changed the δ¹⁸O composition while δ²H was not affected. Conclusions Our results indicate that soil carbonate can cause artifacts for ¹⁸O isotopic composition of soil water. At low soil moisture and high carbonate content this could lead to conflicting results for δ¹⁸O and δ²H in plant water uptake studies.
Drought is a major cause of limited agricultural productivity and of crop yield uncertainty throughout the world. For that reason, agricultural drought research and monitoring are of increasing interest. Although soil moisture is the main variable to define and identify agricultural drought, the actual soil water content is rarely taken into account because this type of drought is commonly studied using methodologies based on either climatological data or hydrological modeling. Currently, it is possible to use remote sensing to obtain global and frequent soil moisture data that could be directly used for agricultural drought monitoring everywhere. For example, the SMOS (Soil Moisture and Ocean Salinity) satellite was launched in 2009 and provides global soil moisture maps every 1–2 days. In this work, the Soil Water Deficit Index (SWDI) was calculated using the SMOS L2 soil moisture series in the REMEDHUS (Soil Moisture Measurement Stations Network) area (Spain) during the period 2010–2014. The satellite index was thus calculated using several approaches to obtain the soil water parameters and was compared with the SWDI obtained from data. One approach was based directly on SMOS soil moisture time series (using the 5th percentile as an estimator for wilting point and the 95th percentile and the minimum of the maximum value during the growing season as estimators for field capacity). In this case, the results of the comparison were good, but the temporal distribution and the range of the index data were unrealistic. Other approaches were based on data parameters and pedotransfer functions estimation. In this case, the results were better, and the satellite index was able to adequately identify the drought dynamics. Therefore, the final choice to apply the index in one particular site will depend on the availability of data. Finally, a comparison analysis was made with the SMOS SWDI and two indices (Crop Moisture Index, CMI, and Atmospheric Water Deficit, AWD) commonly used for agricultural drought monitoring and assessment. In both cases, the agreement was very good, and it was proven that SMOS SWDI reproduces well the soil water balance dynamics and is able to appropriately track agricultural drought.