Improve Soil Water Retention Research Articles

Effect of Replacing Mineral Fertilizer with Manure on Soil Water Retention Capacity in a Semi-Arid Region

The long-term and excessive use of mineral fertilizers in a semi-arid region with severe water shortage will lead to soil compaction and poor water-holding capacity. The fertilization method of manure instead of mineral fertilizer has attracted wide attention. It has adverse consequences for the growth and development of crops. Hence, the objective of this study was to determine how replacing mineral fertilizer with manure affects the soil water retention curve, soil water constant, soil water availability, and soil equivalent pore size distribution, and to seek the best scheme of applying manure in semi-arid area and provide theoretical a basis for improving soil water retention capacity. Here, 0% (CK), 25% (M25), 50% (M50), 75% (M75), and 100% (M100) of 225 kg ha−1 nitrogen from mineral fertilizer were replaced with equivalent nitrogen from manure in the Loess Plateau of China under semi-arid conditions. The centrifuge method was used to determine the soil volumetric water content under different water suction levels, and the Gardner model was used to fit and draw its soil water retention curve, and then calculate the soil water constant and equivalent pore size distribution. The results showed that the Gardner model fitted well. The soil saturated water content with the M100 treatment was the highest, whereas the specific water capacity, water availability, and soil porosity with the M75 treatment were the highest. The soil saturated water content showed a downward trend with the increase in nitrogen from manure instead of nitrogen from mineral fertilizer in the partial replacement treatments. This downward trend slowed down over time. The M75 treatment increased field capacity. The M100 treatment increased soil capillary porosity, soil available water porosity, and soil water availability compared with CK from the fifth fertilization. Replacement treatments increased the specific water capacity, soil saturated water content, soil water availability, soil porosity, and reduced the wilting point over time. In the replacement treatments, specific soil water capacity, soil water availability, and soil porosity first rose and then declined with the increase in nitrogen provided by manure replacing that provided by mineral fertilizer. Therefore, the soil water holding capacity and water supply capacity with the M75 treatment were the best.

No-tillage and rye cover crop systems improve soil water retention by increasing soil organic carbon in Andosols under humid subtropical climate

No-tillage (NT) combined with a cover crop is a climate-smart agricultural practice that eliminates nearly all physical disturbance of the soil surface and increases soil aggregation and soil organic carbon (SOC); however, the response of SOC and soil water retention (SWR) to long-term NT and cover crops systems in the volcanic ash Andosol soil of Japan has not been well addressed. This study aimed to evaluate the effect of NT and moldboard plow (MP) tillage systems combined with rye (RY) and fallow (FA) cover crop treatments on SOC, active carbon (AC), water-stable aggregates, aggregate stability index, mean weight diameter (MWD), bulk density, aggregate-associated carbon, and SWR. NT significantly increased the > 4 and 2 mm aggregates, aggregate-associated C at the 0–2.5 and 2.5–5 cm depths, field capacity, and SWR between 0 and 15 cm. RY cover crops significantly increased aggregate-associated carbon at the 2.5–5 and 5–10 cm depths in both NT and MP and SWR at the 10–15 cm depth. NT combined with RY significantly increased SOC and AC in the surface layer and volumetric water content at all soil depths. Path analysis revealed that SOC and MWD were correlated with easily plant-available water (EPAW) and field capacity under the NT system and is the primary reason for the observed increase in SWR. Thus, the NT system increased plant residue, reduced soil evaporation, increased SOC content and SWR, and bonded soil microaggregates into macroaggregates better than the MP system. The use of an RY-based NT system is an effective climate-smart agriculture practice that reduces the drought effects brought on by climate change.

Enhancing rhizosphere soil water retention in wheat through colonization with endophytic fungus Serendipita indica

Effect of S. indica colonization of wheat (Triticum aestivum) on water retention and physical quality of the rhizosphere soil was investigated in a greenhouse study. Colonized and uncolonized seedlings of four wheat cultivars (i.e., Roshan, Ghods, Pishtaz, and Kavir) were grown in rhizoboxes. Plants were harvested and intact samples were taken from the rhizosphere to measure soil organic carbon (SOC), hot-water soluble carbohydrates (HWSC), and soil water retention curve (SWRC). Water contents at field capacity (θFC) and permanent wilting point (θPWP), and plant available water (PAW) were obtained from the measured SWRC data. The integral energy (EI(PAW)) and integral water storage (WI(PAW)), two alternative indices of soil water availability and physical quality, were computed by integration of SWRCs over the PAW range with respect to water content and matric potential, respectively. Low EI(PAW) and high WI(PAW) indicate improved soil physical quality and better soil water availability to plant. The results showed that the SOC storage and HWSC of the wheat rhizosphere were approximately 146 and 83% greater than those of unplanted soils, respectively. Moreover, compared with the uncolonized counterparts, S. indica colonization significantly increased the SOC and HWSC by 76 and 134%, respectively. The presence of plant roots and S. indica colonization improved soil water retention by increasing SOC and HWSC and subsequently enhancing portion of structural porosity (i.e., pore space between the soil aggregates in the size range of 0.5–500 μm, mainly includingmacropores and mesopores). Despite having the same PAW, colonized soil samples had lower EI(PAW) (≈ 133 J kg−1) compared to uncolonized counterparts (≈ 153 J kg−1). This finding implies that plant roots take up water from the colonized wheat-planted soils easier than from the uncolonized counterparts. Compared to uncolonized samples, an increase of 50% in S1 (Dexter's index of soil physical quality) of the colonized Kavir cultivar [with the lowest root extension, SOC (i.e., 0.97 g kg−1), and HWSC (i.e., 0.059 g kg−1)] showed that S. indica can improve soil physical quality due to greater structural pores. Among the four wheat cultivars, the rhizosphere of Roshan (≈ 1.60 g kg−1) and Ghods (1.61 g kg−1) had the highest SOC values. Higher HWSC (i.e., 0.138 g kg−1) and more extensive root distribution for Roshan, especially upon co-cultivation with S. indica, led to greater contribution of structural pores in water retention in the rhizosphere soil when compared with three other cultivars. To conclude, S. indica colonization not only in the presence of plant roots and by increasing SOC and HWSC improves the physical quality of the rhizosphere soil but also the fungus by itself enhances soil physical quality due to enhancing portion of structural porosity involving in water transition and storage.

Engineering and slow‐release properties of lignin‐based double‐layer coated fertilizer

AbstractChemical fertilizer has become a necessary condition for increasing the production and income of agricultural products in modern agriculture. However, excessive fertilization and fertilizer leakage could cause environmental pollution. To improve the utilization rate of agricultural fertilizers and reduce environmental pollution, the degradability of slow‐release fertilizers (SRFs) has become a research hotspot. In this work, a double‐layer coating material of slow‐release fertilizer was fabricated using low‐cost polyvinyl alcohol (PVA) and methylcellulose (MC) as the inner coating materials, and attapulgite was doped into super absorbent polymer poly acrylic acid (PAA) and polyacrylamide (PAM) grafted natural biodegradable lignin as the outer coating materials. We investigated the chemical structures, mechanical properties, hydrophilic properties, and water retention properties of the double‐layer coating material coated on the surface of urea particles, and optimized the synthesis parameters to obtain the best water absorption properties of the outer layer water absorbent. Simultaneously, urea release was evaluated in dissolution experiments. The results show that at the PVA concentration of 5 wt% and the MC addition amount of 2.0 g, the performance indicators of the inner coating liquid were better than other contents. At the same time, more urea molecules (>30 days) were released in the single‐layer and double‐coated fertilizers, and the cumulative release rates of urea molecules were 92.36% and 85.10%, respectively. Therefore, this work provides research ideas for the preparation of double‐coated slow‐release fertilizers, which can improve soil water retention and fertilizer utilization.

Alkali Lignin-Based Hydrogel: Synthesis, Characterization, and Impact on Soil Water Retention From Near Saturation to Dryness

Highlights A lignin-based hydrogel was synthesized and shown to possess a swelling ratio of 2013%. The hydrogel contained important hydrophilic hydroxyl groups and macropores for water retention. The hydrogel improved soil water retention in silt loam soil at high matric potentials and in the dry soil range. Increasing hydrogel concentration increased water retention in a loamy fine sand soil at high and low matric potentials. Abstract. Superabsorbent polymers (hydrogels) have been proposed as soil amendments to increase the amount of plant-available water in the soil. Synthetic hydrogels have been widely investigated for use in agriculture. Due to increasing environmental concerns related to synthetic hydrogels, naturally sourced hydrogels are of interest because of their potential for increased biodegradability and biocompatibility. A lignin-based hydrogel was synthesized for this study, and its swelling properties and water absorption capacity were determined. The hydrogel was characterized using scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and gas pycnometry. A hanging water column, pressure plate apparatus, and dew point potentiometer were used to measure the soil water retention curve from saturation to oven-dryness for silt loam and loamy fine sand soils after amendment with the lignin-based hydrogel. Results showed a maximum swelling ratio in deionized water of 2013% of the hydrogel’s original mass, 1092% in tap water, and 825% in a 0.9% NaCl solution. The FTIR spectra of the hydrogel showed the presence of O-H bonds from the lignin structure, which renders the hydrogel reactive to a crosslinker and forms insoluble bonds, thereby allowing the hydrogel to swell when exposed to water. SEM images of the lignin hydrogels indicate large macropores, which allowed for water absorption. Applying hydrogels significantly increased the soil's water-holding capacity at 0.3% (w/w) treatment. Hydrogel treatment significantly increased water retention at saturation or near saturation by 0.12 cm3 cm-3 and at field capacity by 0.08 cm3 cm-3 for silt loam soil at 1% (w/w) treatment compared to the control treatment with no added lignin hydrogel. Hydrogel application increased water retention over the range of the soil water retention curve from -3 to -15,000 cm for the loamy fine sand soil at 1% (w/w) treatment. However, the application of lignin-based hydrogel did not affect plant available water capacity (PAWC) in either soil tested. These results serve as preliminary evidence upon which further lignin-based hydrogel amendment studies could be built by testing higher concentrations of hydrogel in the soil. Keywords: Lignin, Soil water retention curve, Super absorbent polymers, Swelling capacity, Water retention.

Macroalgal-Derived Alginate Soil Amendments for Water Retention, Nutrient Release Rate Reduction, and Soil pH Control.

There is a need to develop sustainably sourced products that can address the needs for improved water retention in soils, slow the release rate of fertilizers (to prevent leaching and downstream eutrophication), and control soil pH for use in agriculture. This article investigates the use of industrial kelp solid waste extracted alginate (IW) slurries to produce soil amendment beads, potentially improving soil water retention, acting as slow-release fertilizers (SRFs), and combined with limestone controls soil pH levels. Alginate extracted from the IW was determined to have a lower guluronic (G) to mannuronic (M) acid ratio than pure laboratory-grade (LG) alginate (0.36 vs. 0.53). Hydrogels produced from the IW alginate achieved significantly higher equilibrium swelling ratios (1 wt% IW = 1.80) than LG hydrogels with similar concentrations (1 wt% LG = 0.61). Hydrogel beads were impregnated with ammonium nitrate and potassium chloride to produce potential SRFs. The release rates of K+ and NO3− nutrients from the produced SRFs into deionised water were decreased by one order of magnitude compared to pure salts. The nutrient release rates of the IW-based SRFs were shown to be similar to SRFs produced from LG alginate. Hydrogel beads were impregnated with limestone, and it was determined that the alginate-based hydrogels could significantly decrease the nutrient release rate. Using industrial kelp solid waste extracted alginate slurries shows potential for soil amendments production. This report emphasises, for the first time, the use of a crude alginate product in soil amendment formation. Further, it demonstrates slower release rates and soil pH control.

Improvements in soil physical properties after long-term manure addition depend on soil and crop type

Manure application and crop rotation are common agricultural practices that can alter soil physical properties and affect soil functions. In this study, we assessed the effect of long-term manure fertilization (24 to 126 years) and crop type on soil hydraulic, aggregate and pore structural properties. Samples were collected from three long-term experiments (LTEs) in Sweden (silty clay, SiC), Germany (silt loam, SiL) and Denmark (sandy loam, SL). Measurements included water retention, air permeability and gas diffusivity measured at five matric potentials −3, −5, −10, −30 and −50 kPa, saturated hydraulic conductivity (Ksat), bulk density (ρb), and water-stable aggregates (WSA). The treatments at the three LTEs included various manure rates and crop sequences (winter wheat, maize, spring barley, and grass/clover). Results showed that long-term manure addition reduced ρb by an average of 3–6% for all three sites, and improved soil water retention, plant available water and WSA for most investigated plots. However, increasing manure rates for the SiL and SL sites did not result in further improvements in soil water retention, ρb and water-stable aggregates. The effect of manure on soil pore size distribution, gas transport, and Ksat varied with soil and crop type. Manure increased the porosity of pores < 30 µm in the two fine-textured sites and increased the porosity of pores > 30 µm for wheat and maize plots in the SL site. Manure improved gas transport and Ksat in the wheat plots and decreased these properties in the barley plots regardless of soil texture. The maize plots in the SL site had well developed pore structure, while the pore structure in the SiL site was relatively poor. Grass plots had poorer gas transport than maize plots in the SL site despite the manure addition. The study shows that improvements in soil physical and chemical properties arising from manure application largely depend on the crops grown and the soil texture.

The preparation of slow-release fertilizers with biomass ash and water/waste acid solutions from desulfurization and denitrification of flue gas.

In this study, a method of preparing fertilizers with the fly ash from biomass power plants and the waste acid solution from flue gas desulfurization and denitrification was disclosed. In addition, the study also explored the effects of added fine particles, unburned biochar, and other commercial fertilizers on soil water retention and slow-release effect of fertilizers. The analysis was done by comparing the aggregation degrees of crystalline salt and the variations of the chemical bonds. The experimental results showed that the added fine particles could effectively increase the water absorption of fertilizers, which helped to improve soil water retention. Meanwhile, the fine particles could strengthen the special adsorption of basic compounds containing N, P, and other nutrients by biochar and enhance the slow-release effect of fertilizers. Although adding part commercial fertilizers weakened the water absorption of fertilizers slightly, it had only a relatively small effect on the aggregation of water-soluble crystalline salt on the surfaces of fine particles and biochar. Furthermore, the microwave was applied to promote the absorption of N by unburned biochar, during which only small amounts of volatile were released and lost. The experiments had confirmed that microwave irradiation could promote the agglomeration of biochar on crystalline salt effectively, thus enhancing the slow-release effect of crystalline salt in fertilizers. Finally, pot experiments demonstrated that the self-prepared fertilizer improved plant growth by its better water absorption and slow-release properties during the whole growth period, which had promising application potential as the slow-release fertilizer in the plant growth field.

Biochar from food waste: a sustainable amendment to reduce water stress and improve the growth of chickpea plants

The application of biochar in agriculture is a developing means to improve soil water retention, fertility, and crop yield. The present work focuses on biochar preparation from mixed vegetable and fruit wastes, using cauliflower, cabbage, banana peels, corn leaves, and corn cobs. The biochar produced at 400 °C was applied to the soil as an amendment to observe the qualitative changes of soil quality, plant growth, and water retention capacity of the soil based on screening in a previous study. Pot experiments were conducted at a laboratory scale having 0%, 2%, and 6% biochar mixed with sand. Each pot was sown with seeds of chickpeas (Cicer arietinum L.) and monitored over 60 days. Two biochar application rates improved soil quality by increasing soil porosity from 49.3 to ≥ 53.4%, more than doubling cation exchange capacity to ≥ 21.1 cmolc.kg−1, providing a small reduction in bulk density of approximately 10% and decreasing electrical conductivity of the extract by at least 40% in comparison to control condition. The biochar application also increased key soil nutrients K, Mn, S, and P by a factor of 2–9 times. Application of biochar at 2% and 6% improved water retention from 55 to 77 and 91 mL respectively over the study and, more importantly, more than doubled the biomass yield for the same water application. The lower biochar application rate of 2% led to more germinated seeds (p = 0.0001), leaves (p = 0.0001), flowers, and fruiting chickpeas than the control condition. The 6% biochar application rate slightly improved plant height (p = 0.01) and provided a small reduction in water loss compared with the 2% biochar. Both biochar loadings increased the root and shoot biomass (p = 0.005) and nutrient content of the shoot and root biomass, particularly K, P, and S (p = 0.0001). This study demonstrates that biochar application at 2–6% is an effective means to increase chickpea yield and reduce water stress. Given small differences in performance within this application range, 2% application is recommended. The study establishes valorization of cellulose rich food waste in the form of biochar as a potential method for positive soil management and increased agricultural productivity in arid environments.

Interactive Effects of Honeysuckle Planting and Biochar Amendment on Soil Structure and Hydraulic Properties of Hillslope Farmland

Plant roots and biochar amendment cause changes in soil structure and hydraulic properties; however, their interactive influences are still inadequately understood. A six-year field study was conducted on hillslope farmland in the Sichuan basin, China, to evaluate how honeysuckle planting and biochar application affect soil structure and hydraulic properties. Various parameters related to soil structure (soil organic matter (SOM), soil aggregate stability, bulk density were obtained in the laboratory) and hydraulic (hydraulic conductivity, and soil water retention characteristics by single porosity of van Genuchten 1980 and dual porosity bi-exponential model) properties were determined. The results showed that honeysuckle planting alone increased (SOM) content, honeysuckle planting following biochar amendment could not only enhance SOM content to a greater magnitude in top 20 cm soil but also markedly increase the SOM content in deeper soil layers (20–30 and 30–40 cm), while the application of biochar alone enhanced the SOM content in top 20 cm soil. The combination of honeysuckle planting and biochar amendment could increase soil aggregate stability. Furthermore, It was found that soil pores with size r &gt; 125 µm were the dominant macropores in all treatments. Honeysuckle planting increased saturated soil hydraulic conductivity (Ks) significantly (p &lt; 0.05). Biochar amendment also significantly increased Ks directly or indirectly through enhancement of SOM content. Results also showed that honeysuckle planting and biochar amendment could lead to a greater increase in saturated soil water content than saturated soil hydraulic conductivity. However, SOM showed lower value in bare land plots suggesting that both honeysuckle planting and biochar could increase SOM in soil, hence improving soil quality. Therefore, our field study demonstrated that the practice of honeysuckle planting and biochar amendment jointly in sloping farmland of purple soil could effectively strengthen soil structure and improve soil water retention.

A Bio-Based Hydrogel Derived from Moldy Steamed Bread as Urea-Formaldehyde Loading for Slow-Release and Water-Retention Fertilizers.

In this work, a novel slow-release and water-retention nitrogen (N) fertilizer (SRWRNF) was prepared using moldy steamed bread-based starch-g-poly(acrylic acid-co-acrylic amide) (SBS-g-P(AA/AM)) as the skeleton and urea-formaldehyde oligomers (UF) incorporated as the slow-release N source by semi-interpenetrating methods. Various analysis technologies including scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, and differential scanning calorimetry were used to characterize the structure and properties of SRWRNFs. Swelling measurements indicated that the maximum water absorbency of SBS-g-P(AA/AM)-UF samples was 104.2 g/g in distilled water. The water-retention study showed that the SBS-g-P(AA/AM)-UF improved the maximum soil water content by 15.3–17.6% while improving soil water-retention capacity. N release experiments confirmed that SBS-g-P(AA/AM)-UF enabling offered a gradual N supply in soil. In comparison to conventional urea and UF fertilizers, the maize yield of SBS-g-P(AA/AM)-UF was increased by 20.3 and 9.7%, respectively. This study implies that the SRWRNFs provide a promising feasibility for large-scale applications in agriculture.

RETRACTED: Biochar and compost amendment impacts on soil water and pore size distribution of a loamy sand soil

AbstractSoil structure, which refers to aggregates and pore characteristics, reflects the spatial arrangement of soil particles and is a key component for crop yield and soil health. Well‐formed soil structure has favorable pore size distribution, which supports soil water flow and retention and healthy plant growth. Compost and biochar, important organic amendments, have a potential to influence soil structure, but their effects on specific soil types and soil properties have not been fully investigated. The main objective of this study was to investigate the impact of the additions of compost and/or date palm biochar on selected soil water indicators and pore size distribution of a loamy sand soil using disturbed soil samples. Statistical parameters of pore size distribution properties such as SD, kurtosis, skewness, modal diameter (dmode), median diameter (dmedian), and mean diameter (dmean) as well as plant available water capacity (PAWC), available soil water capacity (ASWC), saturated soil water content, and measured saturated hydraulic conductivity (Ksat) were measured and evaluated. The results showed that the dmode, dmedian, dmean, SD, skewness, and kurtosis values for untreated soil (control) were 31.6 μm, 25.8 μm, 23.5 μm, 3.3, −0.16, and 1.14, respectively. Biochar, compost, and a mixture of biochar–compost additions to a loamy sand soil significantly reduced dmode, dmedian, and dmean values in comparison with nonamended soil. Application of these amendments increased PAWC and ASWC and reduced Ksat of the loamy sand soil, significantly. Biochar–compost mixture has the most significant effect on improving soil water retention and PAWC.

Hydro‐physical soil properties as influenced by short and long‐term integrated crop–livestock agroecosystems

AbstractIntegration of cover crops and livestock (ICLS) in an existing corn (Zea mays L.)–soybean [Glycine max (L.) Merr.] cropping system can be an effective strategy to improve soil physical and hydrological properties. Three on‐farm long‐term (≥30 yr) sites (Sites 1, 2 and 3) and one short‐term (3 yr) experimental site (Site 4) with a randomized block design in eastern South Dakota were selected to evaluate the impacts of ICLS on soil physical and hydrological properties. At Sites 1, 2, and 3, the following long‐term management systems were compared: ICLS (corn/grazing–soybean/grazing–cover crop/grazing), control (CNT, corn–soybean with no cover crop and no grazing), and a grazed pasture (GP). At Site 4, the treatments included ICLS (corn/grazing–soybean/grazing–oat [Avena sativa L.]–cover crop/grazing], cover crop (corn–soybean–oat–cover crop with no grazing), CNT (corn–soybean–oat without cover crop and grazing), and GP. Data showed that soil organic carbon (SOC) was higher by 20–26% and bulk density was lower by 18–37% in long‐term ICLS compared with CNT. Long‐term ICLS also improved soil water retention, macroporosity, infiltration rate, and total porosity compared with the CNT. However, these properties were not affected by short‐term ICLS at Site 4. The GP had the lower soil bulk density and higher SOC and infiltration rate compared with ICLS and the CNT except at Site 4. This study showed that long‐term integration of cover crops and livestock grazing under ICLS can be beneficial in enhancing soil physical and hydrological properties. However, whether such integration improves other soil quality parameters and crop yield requires further investigation.

Critical source areas' identification for non-point source pollution related to nitrogen and phosphorus in an agricultural watershed based on SWAT model.

Water eutrophication caused by the extensive expansion of slope farming has caused the high attention of the Chinese government. We choose Lake Tianmu basin as the study area because it can represent vast majority of basins plagued by water eutrophication derived from slope tillage in southern China. The water ecosystem in the reservoir Daxi and Shahe within the basin has been seriously threatened by multiple pollution sources related to many intricate human activities especially agricultural production. For the first time, we identified the critical source areas (CSAs) within the basin based on nutrient load and nutrient load intensity (NLI), and on this basis, we further excavated the main causes of pollution and proposed pertinent remediation measures. The results based on the calibrated Soil and Water Assessment Tool model indicated that the TN load of each reservoir remarkably exceeded their respective water environmental capacity from 2014 to 2018. Accordingly, six main tributaries with great nutrient contributions and their corresponding sub-basins were then identified. Overall, tea and rice plantations appear to be the major nutrient contributors to reservoir Daxi. And the main nutrient sources for reservoir Shahe are tea plantations, orchards, farmland, forestland, and point sources. Regarding the CSAs identified only by nutrient load, agronomic measures such as reducing fertilizer amount, biochar application, straw incorporation, and plastic mulch coverage can be employed to improve soil water retention and curb soil erosion. Regarding the CSAs identified by nutrient load intensity (NLI), the CSAs with narrow areas should be turned directly into forestland. For the CSAs with large areas, engineering measures such as constructing ecological riparian zone, filtration, and sedimentation tank can be employed to prevent pollutants from entering downstream reaches. Overall, the present results can provide the decision-making support for the safe and efficient management of watershed land use in southern China.

Soil organic matter protects US maize yields and lowers crop insurance payouts under drought

Higher levels of soil organic matter improve soil water retention, meaning they could mitigate agricultural yield losses from drought. Yet evidence to support such claims is mixed and incomplete. Using data from 12 376 county-years in the United States of America, we show that counties with higher soil organic matter are associated with greater yields, lower yield losses, and lower rates of crop insurance payouts under drought. Under severe drought, an increase of 1% soil organic matter was associated with a yield increase of 2.2 ± 0.33 Mg ha−1 (32.7 bu ac−1) and a 36 ± 4.76% reduction in the mean proportion of liabilities paid. Similar, yet smaller, effects were found for less severe levels of drought and this effect was reduced as soil clay content increased. Confirmatory pathway analyses indicate that this positive association of soil organic matter and yields under drought is partially explained by positive effects of soil organic matter on available water capacity and cation exchange capacity, but that soil organic matter may be imparting yield protection via mechanisms not fully captured by those metrics. Overall, our results suggest soil organic matter predicts yield resilience at regional scales in the United States. We argue that data on soil organic matter should be used in agricultural policy and financial planning, with our analyses providing quantitative evidence of the co-benefits of soil organic matter believed fundamental to advancing soil health and carbon sequestration initiatives.

Influence of the physical properties of pumice and biochar amendments on the soil’s mobile and immobile water: implications for use in saline environments

Context Biochar and pumice have potential to improve soil water retention and mitigate salinity. However, little is known about their effect on salt transport in sandy soils. Aims We investigated the influence of the porosity and pore size distribution of soil amendments with pumice and biochar on the mobile water content of a New Zealand sandy soil. Methods Pumice and biochar (1.5-cm, 3-cm and 6-cm in diameter, Ø) were characterised using scanning electron microscope technology. The fraction of mobile water present in these amendments, previously added to a sandy soil at different application rates and particle sizes, was determined using a tracer (Na+) technique. Key results (1) Pumice exhibited a wider pore-size span than biochar; and (2) both materials had a predominance of pores with Ø &lt; 30 μm; but (3) the total porosity in pumice and biochar was not significantly different; (4) pumice had a significantly larger (P &lt; 0.05) mean absolute micro-scale porosity than biochar; and (5) a significantly greater (P &lt; 0.05) relative resident Na+ concentration than biochar, irrespective of the particle size. Conclusions These results reflect a larger fraction of the mobile water in pumice than that of biochar under near-saturated conditions, irrespective of the biochar particle size; and this increased as the pumice particle size increased. Implications While both materials are expected to contribute to water retention and thus might alleviate salt-stress by diluting salt concentration, pumice may perform better than this specific biochar on improving the retention of plant-available water.

An environmental friendly superabsorbent composite based on rice husk as soil amendment to improve plant growth and water productivity under deficit irrigation conditions

An environmental friendly superabsorbent composite (SAC) based on rice, (Oriza sativa L.), husk was created by the scientific group at Faculty of Science, Tanta University, and City of Scientific Research and Technological Applications (SRTA-City), Egypt. SAC was tested for its ability to improve soil water retention, control the release of urea, and its biodegradability in soil. The effect of SAC on sweet pepper, Capsicum annuum, productivity under severe deficit irrigation conditions was studied. Doses of irrigation water representing percentage ∼16.7, 11.9, 7.1, and 2.4 of the actual crop water requirements (CWR) were tested in soil treated with 0.25, 0.50, 0.75, and 1.00 wt% SAC. The tested SAC lost ∼60% of its weight in 150 days. Soil water retention and urea release rates were improved plant growth in response to the addition of SAC. Application of ∼11.9% of CWR with 1.00 wt% SAC resulted in significantly better crop production than other treatments without SAC. This could annually save about 154.44 million cubic meters (MCM) to be directed for horizontal expansion and improve food security.

Transformation of non-water sorbing fly ash to a water sorbing material for drought management

Securing water in the soil through suitable amendments is one of the methods for drought management in arid regions. In this study, a poor water sorbing fly ash was transformed into a high water-absorbing material for improving soil water retention during the drought period. The fly ash water absorbent (FAWA) exhibited high water-absorbing capacity (WAC) of 310 g/g at par with commercially available superabsorbent hydrogel (SAH). The FAWA showed excellent re-swelling behavior for more than eight alternate wetting–drying cycles. The WAC of FAWA was sensitive to salt type, pH, and ionic strength of the solution. At maximum salinity level permitted for plant growth, the WAC of FAWA was 80 g/g indicating its suitability for drought management. There was only a marginal WAC variation in the range of pH (5.5–7.5) considered most suitable for plant growth. The drying characteristics of FAWA amended soil exhibited an increase in desaturation time by 3.3, 2.2, and 1.5 times for fine sand, silt loam, and clay loam, respectively. The study demonstrates the success of using a low rate of FAWA for drought management with the advantage of offering a non-toxic and eco-friendly solution to mass utilization of industrial solid waste for agricultural applications.

Effect of co-composting municipal solid waste with Mg-modified zeolite on soil water balance components using HYDRUS-1D

Application of organic and inorganic amendments is an excellent technique for enhancing available water content in the soils. In this study, municipal waste compost containing three different amounts (i.e., 5%, 10%, and 15% on a wet weight basis) of natural and Mg-modified zeolites were added to a loamy sand soil improving soil water retention. During the plant growth period, the volume of drainage water (DW) and soil water content were measured after each irrigation event and every other day, respectively. HYDRUS-1D was used to simulate the following treatment effects on DW, soil water content distribution and evapotranspiration under corn cultivation: unamended soil (Ctrl), soil amended with compost without zeolite (SC) and soil amendment with composts containing natural zeolite- and Mg-modified zeolites (SCNZ and SCMZ, respectively). Cumulative drainage content was 35.68%, 16.41%, 11.74%, and 10.95% of total applied water in Ctrl, SC, SCNZ and SCMZ treatments, respectively. In the topsoil, the soil water content increased by 4.67%, 5.51% and 9.08% in SC, SCNZ, and SCMZ treatments, respectively as compared to Ctrl treatment. This indicates that water losses decreased in treatments containing zeolite (specially the modified form) relative to Ctrl and SC treatments. The HYDRUS-1D model was effective at simulating DW at different irrigation events (R2 = 0.95–0.99, NRMSE = 0.06–0.16). Simulated soil water content statistically matched those measured using a SM150 soil moisture sensor. Statistical measures (R2 = 0.57–0.92, NRMSE = 0.07–0.19) indicated a close match between measured and simulated soil water content. The SCNZ and SCMZ treatments decreased the hydraulic conductivity and DW value and increased the water content in the upper layer (where the compost applied).

Predicting water retention of biochar-amended soil from independent measurements of biochar and soil properties

Biochar is black carbon produced from pyrolysis of biomass and may be added to soil to sequester carbon and improve soil water retention. To date models to predict changes in soil water retention with biochar amendment are still missing and therefore direct measurements are required for every biochar/soil combination, which can be time-consuming. Here, a predictive model for biochar's effect on soil water retention was developed and tested that includes water retained in biochar intrapores and biochar's impact on interpores between particles. The independently measured parameters needed for the model are the particle size distributions (PSDs) and particle densities for biochar and soil, water retention data for biochar-free soil, biochar intrapore volume distribution from mercury porosimetry, amount of biochar added, bulk density of the biochar/soil mixture, and dew point potentiometer measurements of biochar. The model was tested using poultry litter and wood biochars amended to two soils (sand and sandy loam) at 2 and 7% mass fraction. The model predicted changes in the soil water characteristic well for the biochar amendment, with RMSE decreasing by ~50% when the full model was used. Model predictions of the change in available water capacity with biochar amendment for eight biochar/soil combinations had an average absolute error of 0.017 ± 0.006 and an average relative error of 10¯0 ± 40%. The model correctly predicted the increase in available water content when sandy loam was amended with wood biochar, and the decrease if amended with poultry litter biochar. The model provides an improved understanding of the mechanisms by which biochar alters water retention, and a means to estimate the initial change in available water capacity for a particular biochar/soil combination if necessary biochar and soil properties are measured.