Water Holding Capacity Treatments Research Articles

Soil type and wetting intensity control the enhancement extent of N2O efflux in soil with drought and rewetting cycles

Climate change alters the intensity and frequency of drought and rewetting (D/W) events; however, the influence patterns of D/W on soil N2O efflux in the water-limited area were not fully understood. Therefore, the impacts of D/W cycles varying in different extent of rewetting and frequency to N2O efflux in two kinds of soil on the Loess Plateau were investigated. The incubation conditions consisted of 1) D/W treatments with four 7-day cycles from 10% water holding capacity (WHC) to 60%WHC or 90%WHC, 2) constant moisture of 60%WHC and 90%WHC. The pulse of N2O efflux rate under 10−60%WHC treatment was higher than that under 10−90%WHC treatment in calcic cambisols, while opposite trend was observed in earth-cumuli-orthic anthrosols. Meanwhile, the pulse of N2O efflux rate decreased as cycle number increased for different wetting intensities and soil types. The direct N2O efflux under 10−60%WHC and 10−90%WHC treatments were 5.49 and 1.89 μg N2O–N g−1 soil in calcic cambisols, with those being 1.92 and 10.85 μg N2O–N g−1 soil in earth-cumuli-orthic anthrosols, respectively. The N loss in earth-cumuli-orthic anthrosols was approximately 5.74 times greater than that in calcic cambisols under 10−90%WHC treatment, whereas the N loss under 10−60%WHC treatment was about 2.86 times greater in calcic cambisols than that in earth-cumuli-orthic anthrosols. This study suggested that extreme rainfall events can enhance the N2O efflux and N loss in agricultural soils on the Loess Plateau in terms of soil type and wetting intensity, which should not be ignored in the N fertilizer management.

Drying-rewetting cycles reduce bacterial diversity and carbon loss in soil on the Loess Plateau of China

Soil drying-rewetting (DRW) events became intensified and occurred frequently on the Loess Plateau with the global climate change. However, the extent to which the DRW cycles with different intensity and number alter microbial community and respiration is rarely understood. Therefore, indoor DRW treatments on the soil samples obtained from Loess Plateau involving soil moisture that accounted for 10% water holding capacity (WHC) increasing to 60% WHC and 90% WHC (i.e., 10%–60% WHC and 10%–90% WHC) with 1 or 4 cycles, respectively, were implemented. Constant soil moistures of 10%, 60% and 90% WHC were set as control. Results showed that the bacterial diversity and richness were decreased and those of fungi remained unchanged under DRW treatments compared to those under constant moisture conditions. At the bacterial and fungal phylum level, Actinobacteriota and Ascomycota were the most dominant in all the different moisture treatments, respectively. The bacterial network was more complex than fungi, indicating that the bacteria had a greater potential for interaction and niche-sharing under DRW treatment. The pulse of respiration rate was declined as DRW cycle was increased under 10%−60% WHC treatment, but remained similarly in different cycles under 10%−90% WHC treatment. Moreover, the DRW treatments could reduce the overall carbon loss and the direct carbon release under 10%−60% WHC treatment was larger than that under 10%−90% WHC treatment. The cumulative CO2 emission after four cycles were positively correlated with microbial biomass carbon (MBC) and negatively correlated with fungal Chao 1 richness with great significances.

End water content determines the magnitude of N2O pulse from nitrifier denitrification after rewetting a fluvo-aquic soil

Large nitrous oxide (N2O) emissions pulses have been observed after rewetting dry soil. However, few studies have uncoupled the effects of drought severity from the degree to which the soil is saturated. In this study, we conducted three aerobic incubation experiments to investigate the effects of soil rewetting on N2O emissions from a dryland soil. The results showed that, at constant soil moisture, total N2O emissions in soil with 90% water-holding capacity (WHC) were significantly higher than those in 30%, 45%, 60% and 75% WHC treatments. In the dry–wet group, the soil moisture content was adjusted from 30%, 45% and 60% WHC to the end content of 75% and 90% WHC, respectively; the cumulative N2O emissions in the 30–90%, 45–90% and 60–90% WHC nitrogen (N) treatments were significantly higher than those in the 30–75%, 45–75% and 60–75% WHC N treatments. Regarding fertilizer N types, there was no significant difference in N2O emissions from soil at 90% WHC when (NH4)2SO4 or urea was applied. Nitrification inhibitor significantly reduced N2O emissions in soil applied with NH4+-N fertilizer, indicating that nitrification played a major role in N2O emissions from soils. The contribution of denitrification was negligible, according to the low emission rate of soils with only NO3− additions. High N2O emissions occurred in soil treated with NO2−, accounting for about 83.6% of those of the NH4+ treatment. Therefore, in this study we concluded that the end water content of soil was more important than the role of drought severity in the dry-wet process and that nitrifier denitrification was probably the main pathway of N2O production under the condition of 90% WHC moisture after rewetting soil.

Effect of Water Regimes on Pb and Cd Immobilization by Biochar in Contaminated Paddy Soil

An incubation experiment was conducted to explore the influence of 30% water holding capacity (WHC), flooding, and alternate dry-wet conditions on changes in heavy metal fractions with 1% rice straw biochar in Pb and Cd co-contaminated paddy soils, to provide a scientific basis for a water regime of biochar remediation on heavy metal contaminated paddy soil. Results showed that flooding and alternating wet-dry conditions could significantly increase soil pH, the contents of dissolved organic carbon (DOC), and amorphous iron oxide (Feo) after adding biochar. Compared with a 30% WHC treatment, when the soil is flooded and alternating wet-dry conditions, the content of the TCLP extractable Pb decreased by 31.87% and 20.33%, respectively, and the content of the TCLP extraction Cd decreased by 25.29% and 16.07%, respectively. Under flooding, the acid soluble Pb and Cd content decreased by 24.78% and 20.14%, respectively, and the acid soluble Cd content decreased over time. The decreasing order of available Pb and Cd content was flooding > alternating dry-wet > 30% WHC. Correlation analysis results showed that soil pH and Feo have significant negative correlation with available heavy metals, which means flooding with biochar could effectively immobilize Pb and Cd by increasing soil pH and Feo content. Flooding and biochar have a synergistic interaction on promoting the transformation of Pb and Cd to more stable fractions in acidic co-contaminated heavy metal polluted paddy soil.

Accumulation and translocation of phenanthrene, anthracene and pyrene in winter wheat affected by soil water content

Polycyclic aromatic hydrocarbons (PAHs) are universal organic pollutants in the agro ecosystems in China, therefore, it is important to understand the uptake and accumulation of PAHs in crops growing on PAHs contaminated soils for human health risk assessments. Water management is a common practice to maintain high grain yields during wheat production. However, the effects of soil water content on the accumulation and translocation of PAHs in wheat are still not clear. The main objectives of the present study were to investigate the effects of soil water content on the accumulation of three selected PAHs (Σ3PAHs, phenanthrene, anthracene and pyrene) in wheat during whole plant growth stage and on translocation or remobilization of Σ3PAHs from vegetative tissues to wheat grains. Winter wheat (Triticum aestivum cv. Xiaoyan22) were grown on Σ3PAHs spiked soils maintaining 80%, 60% or 40% water-holding capacity during the whole plant growth stage. Plant samplings were performed at jointing, anthesis or maturity stage, respectively. The present study showed that grain yield and biomass of the crop increased with soil water content increasing. Transpiration rate of wheat leaf under 80% and 60% water-holding capacity treatments was significantly (p < 0.05) higher than that under 40% water-holding capacity treatment at both anthesis and filling stage. Soil water content and plant growth stage had significant (p < 0.0001) effects on concentrations of phenanthrene, anthracene and pyrene in winter wheat. When exposed to 0, 15, 60, and 150 mg kg−1 Σ3PAHs in soils, Σ3PAHs concentrations in the grains under 60% water-holding capacity treatment were 46.6%, 69.9%, 89.5% and 81.7% of those under 80% water-holding capacity treatment, respectively. The highest concentrations of Σ3PAHs in the crop were recorded at anthesis stage. The distribution of PAHs in different tissues of wheat varied among different soil water treatments and plant growth stages. The present study indicated that optimizing soil water content during winter wheat production could apparently reduce concentrations of Σ3PAHs in grains via influence root uptake of Σ3PAHs and translocation of Σ3PAHs from stem or leaf into grain, suggesting the potential of water management to cope with PAHs contamination in crops growing on PAHs contaminated soils.

Influence of soil moisture regimes on growth, photosynthetic capacity, leaf biochemistry and reproductive capabilities of the invasive agronomic weed; Lactuca serriola.

Global temperatures are predicted to increase by 1.5–5.9°C during this century, and this change is likely to impact average rainfall, with predictions that water deficit will perhaps be the most severe threat to sustainable agriculture. In this respect, invasive weeds, which have traits better adapted to drought stress than crops, add to concerns regarding crop sustainability. Lactuca serriola, an aggressive agronomic weed is thought to be a successful weed because of its ability to maintain high water use efficiency under drought conditions. In this study, experiments were conducted to examine the influence of different soil moisture regimes (100%, 75%, 50% and 25% water holding capacity (WHC)) on growth, photosynthetic capacity, leaf biochemistry and reproduction of this species. Soil moisture significantly affected plant’s height, stem diameter, number of leaves and biomass. The highest plant height (115.14 cm ± 11.64), shoot diameter (9.4 mm ± 0.18), leaf area (1206.5 mm2 ± 73.29), plant fresh weight (83.1 ± 3.98) and dry weight (22.38 ± 1.24) were recorded at 75% soil moisture content. A fundamental adaptation to drought was observed as plants in the 25% WHC treatment had the highest root: shoot ratio. Soluble sugars and total phenolic content were highest in the 25% WHC treatment and significantly different to 100% WHC which was a response to soil moisture stress to ameliorate the damaging effects of reactive oxygen species produced under stress conditions. Results also indicate that L. serriola can survive and produce seeds under water stress as more than 6000 seeds were produced per plant in all WHC treatments. In this study, there was no significant difference in the seed weight, number of seeds produced and their germination ability. This can have a huge impact on agricultural systems as the species can survive both under low and high soil moisture conditions. We therefore suggest that the demonstrated ability of L. serriola to complete its life cycle and produce biomass and seeds under water stressed conditions leads to the introduction of strategies that minimize weed survival while maximizing irrigation efficiency for the crop. A clear understanding of the ecological and biological characteristics of this weed will help land managers take appropriate control measures to mitigate the effect of this species on economic crop productivity.

Effects of Cyclical Temperature Fluctuations on Organic Carbon Mineralization in Purple Soil

In the natural state, the soil temperature changes periodically throughout the day, but there is no unified opinion on whether the daily variation of soil temperature affects the mineralization of soil organic carbon. Therefore, the effect of cyclical temperature fluctuations on organic carbon mineralization of purple soil, widely distributed in southwest China, was studied by an incubation experiment in the laboratory. These soils were incubated at three constant temperatures (15, 20, and 25℃) with cyclically fluctuating temperatures (the range was within 15/25℃) and two moisture levels (70% water holding capacity (WHC) and submerged condition). In the entire incubation period (66 d), aerobic and submerged condition, variable temperature (15/25℃) cultivation of purple soil, SOC cumulative mineralization and the mineralization intensity had no obvious differences with constant temperature of 20℃. This indicated that the periodic variable temperature treatment (15/25℃) of SOC mineralization of purple soil with the same accumulated temperature of constant temperature processing (20℃). In addition, except for constant temperature of 15℃, the temperature processing of submerged condition of purple soil SOC cumulative mineralization was significantly higher than 70% WHC treatment (P<0.05). During the entire incubation period, soil microorganism carbon content could not reflect the SOC mineralization differences under constant temperature and cyclically fluctuating temperature. According to two-pool first-order model, the submerged condition can effectively increase the labile SOC pool size of purple soil, but the cyclically fluctuating temperature cannot effectively affect the labile SOC pool size of purple soil.

Degree of short-term drying before rewetting regulates the bicarbonate-extractable and enzymatically hydrolyzable soil phosphorus fractions

Soil drying-rewetting can remarkably affect phosphorus (P) transformation, and thus, alter P distribution among P pools; however, little is known about the effect of the degree of drying before rewetting on labile P fractions and the bioavailability of organic P (Po). In this study, soils with distinct physico-chemical properties were allowed to desiccate to 5%, 10%, 20%, 30%, and 40% water holding capacity (WHC), and soils maintained at 50% WHC were used as controls, and the bicarbonate-extractable P and hydrolyzable Po fractions were analyzed after 5h of rewetting. Bicarbonate-extractable Po accounted for 33.3–56.4% of extractable total P, and hydrolyzable Po constituted 34.4–79.7% of extractable Po. For extractable Po, 7.7–29.9% was labile monoester P, 6.5–14.9% was diester P, and 17.8–36.5% was phytate-like P. Bicarbonate-extractable inorganic P and Po contents were not affected by 20–40% WHC treatments, but increased by 26.3–48.1% and 5.7–52.9%, respectively, when the soils were dried to 5% WHC. Similarly, labile monoester, diester, and phytate-like P contents increased by 12.5–89.8%, 0–65.2%, and 24.6–65.6%, respectively, in 5% WHC soils. Pearson's correlation analyses showed that the relative increases in bicarbonate-extractable inorganic P and phytate-like P, following extreme drought, were positively correlated with soil organic carbon, oxalate-extractable aluminum (Al), and iron (Fe), suggesting regulatory roles of organic matter and Al/Fe oxides in P transformation during soil drying-rewetting. Taken together, our results suggest that extreme drought events before rainfall or irrigation facilitate an increase in the level of labile P, including considerable proportions of hydrolyzable Po fractions, potentially posing a substantial threat to water bodies in the context of climate change.

Mechanical insights into the effect of fluctuation in soil moisture on nitrous oxide emissions from paddy soil

Paddy fields are subjected to fluctuating water regimes as a result of the alternate drying and wetting water management, which often incurs a sensitive change in N2O emissions from paddy soils. However, how the soil moisture regulates the emission of N2O from paddy soil remains uncertain. In this study, three incubation experiments were designed to study the effects of constant and fluctuating soil moisture on N2O emission and the sources of N2O emission from paddy soil. Results showed that the N2O emission from paddy soil at 100 % WHC (water-holding capacity) was higher than that at 40, 65, 80, 120, and 160 % WHC, indicating that 100 % WHC was the optimum soil moisture content for N2O emission under the incubation experiment. Small peak of N2O flux appeared when the soil moisture content from 250 % WHC decreased near to 100 % WHC, lower than that triggered by nitrogen (N) fertilization, which was mainly owing to the low NH4 + concentration at this period. Nitrification dominated the emissions of N2O from paddy soil at 250 % WHC (54.96 %), higher than that of nitrification-coupled denitrification (6.74 %) and denitrification (38.3 %). The contribution of denitrification to N2O emissions (44.10 %) was equivalent to that of nitrification (44.45 %) in soil at 100 % WHC, which was higher than that of 250 % WHC treatment. In conclusion, the finding suggested that the peak of N2O in paddy soils during midseason aeration could be attributed to the occurrence of optimum soil moisture under sufficient N availability, favorable for the production and accumulation of N2O.

Effects of Soil Moisture and Temperature Variations on Organic Carbon Mineralization of Purple Soil in the Hydro-fluctuation Belt of the Three Gorges Reservoir

Soil sampling in the field and an incubation experiment in the laboratory was conducted to investigate the effects of soil moisture and temperature on soil organic carbon (SOC) mineralization of purple soil in the hydro-fluctuation belt of the Three Gorges Reservoir. Three incubation temperatures (10, 20 and 30℃) and four moisture levels (40% water holding capacity (WHC), 70% WHC, 100% WHC and submerged condition) were used in the experiment. In the entire incubation period (66 d), the SOC cumulative mineralization reached the maximum at 100% WHC, but there was no significant difference between 100% WHC and submerged condition (P>0.05). At 10℃ and 20℃, the SOC cumulative mineralization at 100% WHC and under submerged condition was not significantly different from that at 70% WHC treatment, but significantly higher than that at 40% WHC treatment. While the cumulative mineralization of organic carbon at 100% WHC and under submerged condition was significantly higher than that at 70% WHC and 40% WHC when the temperature was 30℃ (P<0.05). The results indicated that compared with 70% WHC treatment, the higher moisture content (100% WHC and submerged condition) had no negative effects but rather promotion effects on the mineralization of SOC at high temperature (30℃). Under the same soil moisture conditions, the SOC cumulative mineralization of purple soil in the hydro-fluctuation belt increased as temperature increased. Moreover, the analysis of variance showed that SOC cumulative mineralization was significantly affected by temperature and soil moisture, and there was a significant interaction with temperature and soil moisture (P<0.05). Fitting of two-pool first-order model was performed to indicate that temperature and soil moisture influenced the contents of labile SOC fraction and the mineralization rates of recalcitrant SOC fraction, which led to the differences of SOC cumulative mineralization under the different treatments. With the increasing temperature, the temperature sensitivity was significantly decreased in the 40% WHC treatment, but there was no obvious difference when the soil moisture content was not less than 70% WHC.

Short-Term Responses of Nitrogen Mineralization and Microbial Community to Moisture Regimes in Greenhouse Vegetable Soils

Soil drying and wetting impose significant influences on soil nitrogen (N) dynamics and microbial communities. However, effects of drying-wetting cycles, while common in vegetable soils, especially under greenhouse conditions, have not been well studied. In this study, two greenhouse vegetable soils, which were collected from Xinji (XJ) and Hangzhou (HZ), China, were maintained at 30% and 75% water-holding capacity (WHC), or five cycles of 75% WHC followed by a 7-day dry-down to 30% WHC (DW). Soil inorganic N content increased during incubation. Net N mineralization (Nmin), microbial activity, and microbial biomass were significantly higher in the DW treatment than in the 30% and 75% WHC treatments. The higher water content (75% WHC) treatment had higher Nmin, microbial activity, and microbial biomass than the lower water content treatment (30% WHC). Multivariate analyses of community-level physiological profile (CLPP) and phospholipid fatty acid (PLFA) data indicated that soil moisture regime had a significant effect on soil microbial community substrate utilization pattern and microbial community composition. The significant positive correlation between Nmin and microbial substrate utilization or PLFAs suggested that soil N mineralization had a close relationship with microbial community.

Effect of temperature and moisture on rates of carbon mineralization in a Mediterranean oak forest soil under controlled and field conditions

SummaryWe examined the relationship between carbon mineralization (Cmin), moisture and temperature in a Mediterranean forest soil under controlled and field conditions. We studied the following.1 The temperature sensitivity at three soil depths: soil samples were incubated at 4, 10, 20 and 30°C at optimal water content of 60% of water holding capacity (WHC). Values ofCminof the top layer were more than 12 times faster than those measured in deeper layers. We found a temperature sensitivity factor (Q10) of 3.3, 2.7 and 2.2 for the 0–5 cm, 5–10 cm and 10–20 cm layers, respectively.2 The relationship betweenCmin, moisture and temperature (top layer). The sensitivity ofCminto fluctuating moisture depended on temperature. However, theQ10was not significantly affected by soil moisture. We fitted a multiple polynomial model that predictedCminas a multiplicative function of temperature and moisture (R2 &gt; 0.99).3 The response ofCminof soil to rewetting after 1 and 24 hours. In all cases, the response was rapid. The soil incubated at 60% WHC or less responded positively to a sudden increase in water content, with the largest increase in the 20% WHC treatment. The model predictedCminin the field well when rewetting effects were taken into account (R2 &gt; 0.81).These results indicate that sudden changes in soil moisture can lead to increased carbon mineralization during the dry summer. It is necessary to include such responses in models as they may represent a substantial loss of carbon in the overall carbon balance of Mediterranean ecosystems.

Nitrous oxide and dinitrogen emissions from soil under different water regimes and straw amendment

In a laboratory study, soil amended with and without wheat straw (2.8 g kg −1 soil) was incubated under 70% water holding capacity (WHC), continuously flooded and flooded/drained cycle conditions at 30°C for 51 days. Dinitrogen and N 2O evolution and ammonia volatilisation were measured during the incubation. Extractable NH 4 +-N and NO 3 −-N were determined at the end of the incubation. Entrapped N 2, N 2O, and dissolved NH 4 +-N and NO 3 −-N in drainage water were measured in the flooded/drained cycle treatment when the floodwater was drained. The results indicated that N loss through ammonia volatilisation was undetected in all treatments due to the low soil pH value (pH H 2O =5.87) and no air movement. The recovery of urea- 15N as N 2 was lowest in the continuously flooded treatments (0.75% and 0.96% with and without straw amendment, respectively), highest in the 70% WHC treatments (5.65% and 4.41%, respectively), and intermediate in the flooded/drained cycle treatments (1.79% and 2.65%, respectively). The recovery of urea- 15N as N 2O was in the same order as that of N 2, negligible in the continuously flooded treatments, 0.01% and 0.07% in the flooded/drained cycle treatments, and 1.29% and 2.23% in the 70% WHC treatments, respectively. Peak N 2O evolution rates were observed after the floodwater was drained but no substantial evolution was found after the soil was re-flooded following drained periods. However, peak N 2 evolution rates were observed after the onset of both drainage and re-flooding. Considerable quantities of N 2 but no detectable N 2O were entrapped in the flooded soil.