Increased Soil Water Availability Research Articles

Advanced growing-season precipitation peak promotes soil nitrogen mineralization in a semi-arid grassland

Soil nitrogen (N) mineralization is a key process of global N cycling and profoundly regulates plant productivity and soil nutrient pools in the terrestrial biosphere. However, its response to seasonal precipitation redistribution remains largely unexplored. As part of a nine-year (2013–2021) field experiment that simulated advanced and/or delayed growing-season precipitation peaks in a semi-arid grassland on the Mongolian Plateau, this study was conducted for two years (2020–2021) in situ to examine the effects of changing precipitation distributions in the growing seasons on soil mineralization processes. The results showed that advanced precipitation peak (AP) increased soil ammonification (Ramm), nitrification (Rnit), and net mineralization rates (Rmin) by 45.8 %, 26.0 %, and 84.4 %, respectively (all p < 0.001), whereas delayed precipitation peak (DP) enhanced Ramm by 55.7 % (p < 0.001) only, but did not change Rnit or Rmin. The elevated soil N mineralization under the AP treatment could be primarily attributed to the increased soil water availability and microbial biomass N in the early growing season, both of which play essential roles in meditating biological processes in the soil. In addition, the large consumption of soil inorganic N in the early and middle growing seasons may lead to an enhancement of ammonification in September. These observations suggest that advanced rather than delayed growing-season precipitation peak has a stronger influence on soil N dynamics in the growing seasons. Moreover, our findings highlight the positive contributions of altered N transformations to soil respiration and net ecosystem productivity under the AP treatment and imply the crucial roles of intra-annual redistribution of precipitation in regulating ecosystem nutrient and carbon cycling in semi-arid regions.

Seed functional ecology in Brazilian rock outcrop vegetation: an integrative synthesis.

Rock outcrop vegetation is distributed worldwide and hosts a diverse and unique flora that evolved under harsh environmental conditions. Unfortunately, seed ecology in such ecosystems has received little attention, especially regarding seed traits, germination responses to abiotic factors and the potential role of phylogenetic relatedness on such features Here, we provide the first quantitative and phylogenetically-informed synthesis of the seed functional ecology of Brazilian rock outcrop vegetation, with a particular focus on quartzitic and ironstone campo rupestre. Using a database of functional trait data, we calculated the phylogenetic signal of seven seed traits for 371 taxa and tested whether they varied among growth forms, geographic distribution, and microhabitats. We also conducted meta-analyses that included 4,252 germination records for 102 taxa to assess the effects of light, temperature, and fire-related cues on the germination of campo rupestre species and explored how the aforementioned ecological groups and seed traits modulate germination responses. All traits and germination responses showed a moderate-to-strong phylogenetic signal. Campo rupestre species responded positively to light and had maximum germination between 20-25 ºC. The effect of temperatures beyond this range was moderated by growth form, species geographic distribution, and microhabitat. Seeds exposed to heat shocks above 80 °C lost viability, but smoke accelerated germination. We found a moderating effect of seed mass for in responses to light and heat shocks, with larger, dormant seeds tolerating heat better but less sensitive to light. Species from xeric habitats evolved phenological strategies to synchronise germination during periods of increased soil water availability. Phylogenetic relatedness plays a major role in shaping seed ecology of Brazilian rock outcrop vegetation. Nevertheless, seed traits and germination responses varied significantly between growth forms, species geographic distribution and microhabitats, providing support to the regeneration niche hypothesis and the role of functional traits in shaping germination in these ecosystems.

Partitioning urban forest evapotranspiration based on integrating eddy covariance of water vapor and carbon dioxide fluxes

Partitioning of evapotranspiration (ET) in urban forest lands plays a vital role in mitigating ambient temperature and evaluating the effects of urbanization on the urban hydrological cycle. While ET partitioning has been extensively studied in diverse natural ecosystems, there remains a significant paucity of research on urban ecosystems. The flux variance similarity (FVS) theory is used to partition urban forest ET into soil evaporation (E) and vegetation transpiration (T). This involves measurements from eddy covariance of water vapor and carbon dioxide fluxes, along with an estimated leaf-level water use efficiency (WUE) algorithm. The study compares five WUE algorithms in partitioning the average transpiration fraction (T/ET) and validates the results using two years of oxygen isotope observations. Although all five FVS-based WUE algorithms effectively capture the dynamic changes in hourly scale T and E across the four seasons, the algorithm that assumes a constant ratio of intercellular CO2 concentration (ci) to ambient CO2 concentration (ca) provides the most accurate simulation results for the ratio of T/ET. The performance metrics for this specific algorithm include the RMSE of 0.06, R2 of 0.88, the bias of 0.02, and MAPE of 8.9 %, respectively. Comparing urban forests to natural forests, the T/ET in urban areas is approximately 2.4–25.3 % higher, possibly due to the elevated air temperature (Ta), greater leaf area index (LAI), and increased soil water availability. Correlation analysis reveals that the T/ET dynamic is primarily controlled by Ta, LAI, net radiation, ca, and soil water content at half-hourly, daily, and monthly scales. This research provides valuable insights into the performance and applicability of various WUE algorithms in urban forests, contributing significantly to understanding the impact of urbanization on energy, water, and carbon cycles within ecosystems.

Carbon Sequestration Potential of Biomass Production along Highways in China.

In response to climate change, China is making great efforts to increase the green area for carbon sequestration. Road verges, as marginal land with favorable conditions for plant growth and ease of transportation, can be used for biomass production, but the biomass production and carbon sequestration potential have not been assessed. Here, we mapped the biomass production potential of road verges in China by combining a biomass model and Geographic Information System and then evaluated the effect of road runoff and CO2 fertilization on the production according to the runoff coefficient and vehicle emission inventory. Nationwide, road verges can produce 15.86 Mt C yr-1 of biomass. Road runoff contributes to a biomass production of 1.26 Mt C yr-1 through increasing soil water availability, which mainly occurs in arid regions. The CO2 fertilization effect by vehicle emission is considerable in Eastern and Southern China, contributing to a production of 0.09 Mt C yr-1. Life cycle assessment shows that major road verges in China have a carbon sequestration potential of 6.87 Mt C yr-1 currently. Our results revealed that road verges can make a significant contribution to carbon neutrality under proper management.

Soil management considerations for water resiliency in a changing climate

AbstractProviding adequate water for crops is a key consideration for agricultural resiliency. Climate change is expected to exert substantial pressure on crop water supplies through increased rainfall variability and increased evaporative demand. The temporal and spatial variability of these climate change impacts, in combination with many feedbacks, at times operating at different scales, makes identifying specific, yet broadly applicable “one‐size‐fits‐all” soil management solutions challenging. Adaptations that work well in one location may represent a poor management choice in another. Considering the local combinations of climate, soils, and crop production systems is fundamental for identifying appropriate strategies. Nonetheless, some broadly applicable soil management pathways for increasing soil water availability can be identified: (i) maximizing rainfall capture, (ii) maximizing soil water storage capacity (intensity × volume), and (iii) suppressing unproductive evaporative water losses, particularly during intervals when leaf area of the primary crop is low. Selecting climate, soil, and production‐system‐appropriate tillage and surface cover management practices is among the most relevant considerations for improving soil water availability. Maintaining surface cover favors evaporation suppression and increased capture of precipitation. Tillage choices affect internal soil water storage through impacts on soil properties that influence storage intensity and by altering the volume of soil available for root growth, as well as through effects on surface cover. Promoted management practices aimed at improving soil water availability for increased agricultural resiliency must be practically feasible and cost‐effective in order to support their broad adoption, and such constraints should be an important consideration in their development.

Impact of biochar amendments on soil water and plant uptake dynamics under different cropping systems

AbstractApplication of biochar amendments in agricultural systems has received much attention in recent years. In this study, we assess the 5‐year impacts of biochar application on soil water and plant interactions for an irrigated fresh market tomato (Solanum lycopersicum) and a rainfed pasture (Poaceae) cropping system. In particular, we focus on three varieties of locally produced biochar from agricultural waste materials—almond shell, walnut shell, and almond pruning residues that are pyrolyzed using a mobile pyrolysis unit. We used the soil hydrological model HYDRUS‐1D to explicitly track seasonal and annual soil water fluxes through changes in water retention, drainage, evaporation, and plant water uptake under biochar application. Modeling results show that the application of biochar at 5% increased soil water availability within the top 20 cm for a rainfed system, irrespective of biochar amendment type. This is clearly indicative of higher plant water uptake and greater water use efficiency (WUE) under biochar application. In contrast, a similar biochar amendment for the irrigated system did not affect WUE, instead reducing seasonal soil evaporation loss and thereby reducing irrigation demand. In both cropping systems, year‐to‐year variability in precipitation significantly impacted the total amount of water saved under biochar application with certain amendments retaining more water than others. Given that biochar application increased water retention irrespective of cropping systems, we further used a simple approach to determine yield trade‐off, if any, between control and biochar treatments. Our economic balance clearly demonstrates that the water saved by amending soil with biochar does not offset the yield disparity if compensated with carbon credits and therefore, application of biochar should be actively considered for both its direct and indirect benefits to potential greenhouse gas mitigation (e.g., diverting orchard waste from open burning), water savings, and soil health.

Thinning effectively mitigates the decline of aging Mongolian pine plantations by alleviating drought stress and enhancing plant carbon balance

Intensifying drought around the globe poses strong challenges to the growth and survival of trees, emphasizing the urgency of understanding the physiological mechanisms of drought-induced tree decline and mortality and the necessity of using silvicultural approaches to mitigate drought effects on tree growth. We experimentally explored whether thinning enhances tree growth vigor and drought resilience in early aging Mongolian pine (Pinus sylvestris var. mongolica Litv.) plantations in a water-limited area of Northeast China using dendrochronological methods. Meanwhile, we compared plant hydraulic traits, water relations, and non-structural carbohydrate concentrations between trees growing in the thinned and un-thinned stands with the aim of unraveling the physiological mechanisms underlying the density effects on tree growth performance. The results showed that basal area increments of Mongolian pine trees in the high-density plantations started to decline continuously at tree cambium age of around 15 years over about a decade, while thinning effectively reversed their growth decline. Trees in thinned stands exhibited significantly higher predawn leaf water potentials, higher stem hydraulic conductivities, and larger carbon reserves than trees in un-thinned stands. Although trees growing in high-density stands maintained as low risks of xylem hydraulic dysfunction as trees growing in low-density stands, that was at the cost of substantially reducing tree crown size through branch mortality that unavoidably undermined their carbon balance at the whole-plant level. Consistently, trees growing in the thinned low-density stands showed significantly higher levels of non-structural carbohydrate reserve in stems and enhanced growth resilience to extreme drought than trees growing in the high-density reference stands. Our results suggest that thinning can effectively enhance xylem hydraulic transport efficiency and reduce the risk of carbon imbalance by increasing soil water availability and hence mitigates the early aging of Mongolian pine plantations in water-limited environments.

Impact of Nanoparticles from Ball-Milled Date Palm Biochar on the Hydro-Physical Characteristics of Sandy Soils

Water management in sandy soils (Typic Torripsamments) is crucial in sustaining agricultural production. The main goal of this research was to assess the impact of date palm biochar on the physical properties of sandy soil with different particle sizes of biochar (macro and nano). For nano-biochar preparation, stick chips were established into a tubular furnace with nitrogen air and heated to 400–450 °C, which was accompanied by a holding period of 4 h. The ball-milled biochar was inclined via ball grinding in a model number PQN2.110 planetary mill and within jars (500 mL), and the biochar-to-sphere mass ratio was 1:100. The sphere-milling apparatus was processed at a speed of 300 rpm for 13 h. Laboratory experiments were carried out at one rate—biochar 5%—and three depths (0.0–5, 5–10, and 10–15 cm). Applying macro-biochar reduced cumulative evaporation compared to the control by 4%, 24%, and 14% for the macro-biochar particles at soil depths. In contrast, biochar reduced cumulative evaporation compared to the control by 8%, 12%, and 4% for the nano-biochar particles at the soil depths tested. Adding biochar significantly raised the amount of retained water, with the highest level recorded at the 5–10 cm depth, while the variations were significantly lower between the macro and nano-biochar when in the direction of the soil surface (0–5 cm), indicating the significance of mixing biochar with the top 10 cm of the soil to increase its ability to reduce evaporation and increase the amount of water retained in the soils. It could be concluded that applying at the top of the coarse soil can positively impact soil hydro-physical properties and increase soil water availability to plants.

The constancy of chemical weathering intensity on hillslopes in the arid to semiarid Qilian Mountains, NE Tibetan Plateau

Quantifying the relationship between the chemical weathering and denudation rates of active orogenic belts over a range of climates is the key to addressing the controversy over the uplift-weathering hypothesis. However, studies have focused on warm and humid environments and have not examined cold and arid environments. Here, we present a new dataset of the chemical depletion fraction (CDF: ratio of the chemical weathering rate to the total denudation rate) across the arid to semiarid Qilian Mountains on the northeastern Tibetan Plateau, where the uplift-weathering hypothesis has been proposed. We selected 60 points from 12 catchments in the middle Qilian Mountains. At each point, we collected three samples (soil, saprolite, and bedrock samples) and calculated the CDF values based on their Zr concentrations. We found no clear correlation between the CDF and climatic factors (temperature, precipitation, and normalized difference vegetation index (NDVI)), topographic factors (slope and local relief), and denudation rate. The calculated chemical weathering rates, nevertheless, are positively correlated with precipitation, NDVI, and denudation rate, and negatively correlated with temperature. This result indicates that the Qilian Mountains are under supply-limited conditions, even at high denudation rates (>800 t km−2 y−1). We speculate that low temperatures (<0 °C) could intensify near-surface chemical weathering by promoting the physical breakdown of the bedrock and increasing soil water availability. This mechanism causes a compensation effect maintaining the supply-limited conditions in landscapes with high denudation rates. Combing a worldwide dataset regarding the correlations between CDF and climatic factors and denudation rates, we argue that intensified denudation since the late Cenozoic contributed to global cooling.

The roles for branch shelters and sheep manure to accelerate the restoration of degraded grasslands in northern China

New strategies are desperately needed for restoring the millions of hectares of degraded grasslands in arid and semiarid areas of northern China. This study evaluated using different combinations of manure amendments and shrub branch shelters for their impacts on soil moisture, nutrient availability, and plant growth over two growing seasons in a degraded grassland in Ningxia, China. A two-factor experiment was conducted, with three concentrations of 1.2 g m−2, 442 g m−2, and 884 g m−2 native Tan sheep manure as the main plots. Cut caragana (Caragana intermedia) branches were used to create branch shelters covering 0%, 20%, 40%, and 60% of ground area, and these acted as sub-main plots. Soil water storage, soil temperature, manure decomposition, branch decomposition, soil nutrients, and plant growth were monitored for 2 years. Results indicated that soil water storage was significantly increased, and soil temperature decreased, under the 40% and 60% branch shelters. Decomposition rate of manure and shrub branches also increased with increasing soil water availability associated with the higher branch sheltering effects, although soil carbon and nitrogen concentrations were primarily driven by the decomposing manure. The combination of high levels of shrub branch shelter and manure application significantly enhanced plant production, although the bulk of the biomass was concentrated in one species, Artemisia scoparia. In conclusion, our study successfully demonstrated feasible and inexpensive solution for the restoration of degraded grasslands, which takes advantage of resources associated with overgrazing Tan sheep and Caragana shrub encroachment in arid and semiarid areas.

Piñon and juniper tree removal increases available soil water, driving understory response in a sage‐steppe ecosystem

AbstractOver the past century, piñon and juniper trees have encroached into sagebrush steppe lands of the interior United States, and managers have for many years removed trees to stimulate the favored understory. While consistent understory response to tree removal in these semiarid lands suggests that trees outcompete other plants for water, no studies have linked increased soil water to understory response after tree removal. We tested the hypothesis that tree removal at six sagebrush steppe sites increased soil water, leading to increased understory plant cover. Using a structural equation model, we found that before tree removal, trees suppressed shrubs (standardized coefficient [SC] = −0.87), perennial deep‐rooted (SC = −0.50) and shallow‐rooted bunchgrasses (SC = −0.36), but had no influence on cheatgrass. The model explained between 2% (cheatgrass) and 40% (shrubs) of pretreatment cover variation. Measurement of the same plots six years post‐treatment showed that most cover variation was due directly to plant growth, with standardized coefficients between 0.51 (perennial shallow‐rooted grasses) and 0.72 (cheatgrass). Competition between cheatgrass and perennial deep‐rooted grasses was evident, with perennials having twice the influence on cheatgrass than vice‐versa (SC = −0.24 vs. −0.11). Spring soil water (wet‐degree days) increased significantly after tree removal, measured as cumulative over 6 years (SC = 0.30), and in the early Spring of year six (SC = 0.16). Treatment‐induced increase of cumulative Spring wet degree‐days explained variation in shrub cover at year 6 (SC = 0.12) and the increase of early Spring wet degree‐days at year 6 led to increases in perennial deep‐rooted grasses (SC = 0.24) and cheatgrass (SC = 0.23). We detected no influence of Spring wet degree‐days on perennial shallow‐rooted grasses. The post‐treatment model explained between 34% (shallow‐rooted perennial grasses) and 69% (deep‐rooted perennial grasses) of variation in understory cover. Most variation was explained by re‐measurement of the same populations, followed by treatment effects mediated through increased soil water availability, soil factors, and direct effects of the treatment itself. In conclusion, our model is consistent with the a priori hypothesis that additional wet degree‐days due to tree removal is a significant mechanism behind observed increases in understory cover.

Bio-organic fertilizer production from industrial waste and insightful analysis on release kinetics

The present study has been designed to utilize industrial and agricultural solid waste for NPK (Nitrogen–Phosphorus–Potassium) bio-organic fertilizer production and its optimized use. The collagenic material of wet blue leather (WBL) from leather industry was used as nitrogen source, after H3PO4 acid-mediated chromium removal. Chicken meat-bone meal (CMBM) and rice husk ash (RHA) are abundantly available locally, had used as P, K, and Ca sources. The presence of N, P, K, Ca in the produced bio-organic NPK fertilizer were 10.76, 11.03, 3.41, 13.64, respectively as per mixing ratio of ingredients. In this study it was effect on the chili plant (Capsicum annuum L.) growth and revealed 1.15 and 1.03 fold higher plant growth, 1.40 and 1.18 fold higher total chlorophyll content than untreated soil (control), and chemical fertilizer. The liberation of fertilizers components from their source, transport of fertilizer components in the soil, and absorption in plant roots have been studied using mathematical models indicating the optimum fertilizer use for better productivity and to reduce loss of extra fertilizer and eutrophication. The formulation showed excellent water retention capability (3.2 L/kg), which might increase soil water availability to the plants and eventually reduce water demand and labour cost. DNA intercalation study proved there is no harm to use this fertilizer.

Implications of Watershed Management Practices on Water Availability Using Hydrus-1D Model in the Aba Gerima Watershed, Upper Blue Nile Basin, Ethiopia

The main objective of this study was to examine the implications of watershed management (WSM) on hydrological parameters in the Aba Gerima watershed in the Upper Blue Nile Basin. The Hydrus 1D model simulations were conducted in control sites and sites under WSM to estimate various components of the hydrologic cycle, using different soil physical &amp; hydrological data under each category of experimental sites. Results were calibrated with measured soil moisture data through inverse solutions. Thus, Hydrus 1D model was found to be effective in predicting results, with R2 values of 0.73 to 0.853 and RMSE values ranging from 0.015 to 0.04. The cumulative evaporation estimated for 365 days for control sites was 37.6% higher than that of sites under WSM. Surface and bottom fluxes in the sites under WSM were 4.6% and 12.5%, respectively, higher than the control sites. This could be attributed to the increased soil water availability resulting from the implemented WSM practices in Aba Gerima, and the results of this study can be used as empirical evidence of the positive implications of WSM on water availability. Finally, WSM should be strengthened by concerned bodies and development partners in all watersheds, especially where water availability is affected by severe land degradation.

Temperature: A major climatic determinant of cowpea production

Cowpea planting season is crucial for high yield and should comprise the period of the year that warrants the best climatic conditions for cowpea cultivation. Thus, the objective of this study was to evaluate the influence of water availability and temperature on the performance of cowpea cultivars. A greenhouse experiment was conducted using a 4 × 2 × 5 factorial arrangement, with four replications. Factors included four levels of soil moisture (25, 50, 75, and 100% of water holding capacity), two growing seasons (mild and hot), and five cowpea cultivars (Carijó, Itaim, Pujante, Rouxinol, and Tapahium). The number of pods and seeds per plant, seed production, water use efficiency, shoot dry mass, root dry mass, and physiological parameters were evaluated. Seed production was higher during the mild season than during the hot season and increased linearly with increasing soil water availability. Photosynthetic activity and transpiration were higher during the hot season than during the mild season, with their reduction under a water availability of 25% regardless of the growing season. Total chlorophyll content decreased with excess water. Regardless of water availability, temperature was the most limiting climatic factor for cowpea performance. Cultivars Carijó, Itaim, and Tapahium exhibited a lower reduction in productive potential when grown in the hot season.

Root efficiency and water use regulation relating to rooting depth of winter wheat

It is well-recognized that deep roots play a vital role in increasing soil water availability to crop water use, their ability in regulating the allocation of the crop water use during the growing season would also influence crop yield and water productivity. Experiments were conducted using tubes of 0.5, 1.0, 1.5 and 2.0 m in depth (with an inner diameter of 30.5 cm) and irrigation amounts varying from 90 to 500 mm for two seasons of winter wheat (2019–2020 and 2020–2021). The combinations of the different tube depth and irrigation created different situations in terms of maximum rooting depth and soil water availability to assess the functions of deep roots on regulation of soil water availability to crops, and if the deep root growth being economic or not in relating to crop production and water productivity (WP). The results showed that under the same seasonal evapotranspiration (ET), the shallower the root depth was, the lower the yield. Higher WP was achieved with deep root systems. Further analysis showed that higher proportion ET occurred during the reproductive stage for the treatments with deep roots, which increased the leaf photosynthetic rate and the duration of the greenness, resulting in higher harvest index and WP. Deep roots not only increased the soil water availability for crop water use, but also regulated the timing of the soil water use to favor an increased proportion of water use during the reproductive stage. The root: shoot ratio was slightly increased from the 0.5 m tube to 1.0 m tube, but under a sufficient water supply, root: shoot ratio gradually decreased in the 1.5 m and 2.0 m tubes, resulting in less root length corresponding to the unit grain production. The treatments with deep root systems increased the root efficiency. The results indicated that both the total available water and the allocation of the water consumption during the crop growing season influenced the yield and water productivity. Increasing rooting depth was an efficient regulation measure to optimize the allocation of water consumption and increase soil water availability to crops without increasing metabolic input in root growth.

Pre-commercial thinning could mitigate drought stress of black spruce stands

Rising temperatures are likely to increase the risk of drought across the globe over the next century. Boreal forests are particularly vulnerable to drought because temperatures within these biomes are projected to warm the fastest. Warm and dry conditions can reduce tree growth, particularly in regions that are already moisture-limited, which may reduce forest productivity. Forest stand density management, such as pre-commercial thinning (PCT), can reduce moisture stress for residual trees by reducing canopy evaporation and increasing soil water availability. PCT is applied 15–20 years after clearcut and removes smaller stems to increase resource availability to residual trees, thereby increasing diameter growth and wood value. How PCT can mitigate climate change impact in boreal forests is still unclear, partly due to heterogeneity in moisture availability and growth response. This study tests the relative effect of PCT on radial growth of black spruce (Picea mariana (Mill.) B.S.P.) on sites with varying water availability to inform forest managers about PCT’s potential to mitigate anticipated effects of drought on tree growth. Tree discs from PCT and non-thinned plots were harvested from three contrasting site types in eastern Canada (warm-dry, warm-wet and cool wet). Using dendrochronology, the relationship between annual ring width index (RWI) and standardized-evapotranspiration index (SPEI) was explored in the time since PCT and during known climate anomalies. RWI showed a positive growth response to increasing SPEI on warm-dry sites, but a negative growth response on warm-wet and cool-wet sites. PCT provided a greater benefit to radial growth on warm-dry site types in the 15 years since treatment but provided no additional benefits during years of climate anomalies. Results suggest that PCT will remain an important forest management practice on moisture-limited sites in order to maintain black spruce productivity, whereas tree growth may benefit from future warming on relatively wet sites.

Leaf surface traits contributing to wettability, water interception and uptake of above-ground water sources in shrubs of Patagonian arid ecosystems.

The ecohydrological significance of leaf wetting due to atmospheric water in arid and semiarid ecosystems is not well understood. In these environments, the inputs of precipitation or dew formation resulting in leaf wetting have positive effects on plant functioning. However, its impact on plant water relations may depend on the degree of leaf surface wettability. In this study we evaluated leaf wettability and other leaf traits and its effects on foliar water uptake and canopy interception in plant species of a Patagonian steppe. We also studied how leaf traits affecting wettability vary seasonally from growing to dry season. Contact angle of a water droplet with the leaf surface, water adhesion, droplet retention angle, stomatal density, cuticular conductance, canopy interception and maximum foliar water uptake were determined in six dominant shrub species. All species increased leaf wettability during the dry season and most species were considered highly wettable. The leaf surface had very high capacity to store and retain water. We found a negative correlation between foliar water uptake and leaf hydrophilia. Despite the diversity of life forms, including cushion shrubs and tall shrubs, as well as phenological variability, all species converged in similar seasonal changes in leaf traits that favour wettability. Intercepted water by crowns and the extremely high capacity of retention of droplets on leaf surfaces can have a significant impact on eco-hydrological process in water limited ecosystems where most of water sources during the growing and the dry season may be small rainfall events or dew, which do not always increase soil water availability.

Biomaterial amendments combined with ridge–furrow mulching improve soil hydrothermal characteristics and wolfberry (Lycium barbarum L.) growth in the Qaidam Basin of China

Droughts, intense soil evaporation, and poor soil structure with low water holding capacity and nutrients restrict agricultural production in the Qaidam Basin on the Tibetan Plateau. Excessive chemical fertilizers have been applied to increase the yields of wolfberry (Lycium barbarum L.), a significant economic crop in northwest China, which has further degraded soils. Biomaterial amendments and ridge–furrow mulching are effective measures for increasing soil water availability, crop yields, and water use efficiency (WUE). However, the combined effects of biomaterial amendments and ridge–furrow mulching on soil hydrothermal conditions, crop growth, and yield in this area are unknown. A field study was undertaken in 2018 and 2019 to investigate their combined influences on soil moisture and temperature, crop growth, yield characteristics, and WUE on the Tibetan Plateau. The experiment comprised four treatments: flat planting with film mulching (FM), flat planting with film mulching and biomaterial amendment (FMBA), ridge–furrow planting with film mulching (RM), and ridge–furrow planting with film mulching and biomaterial amendment (RMBA). The biomaterial amendment and ridge–furrow mulching treatments increased soil water content in the 0–120 cm soil layer, especially at 0–60 cm soil depth at early growth stages, compared with FM. Furthermore, the ridge–furrow mulching treatments had significantly higher soil temperatures than the FM treatment at the sprout stage. The RMBA treatment produced favorable soil hydrothermal properties, which significantly increased mean plant height, ground diameter, and root length density (RLD). The RMBA treatment also produced the highest crop yield, WUE, and berry quality in both growing seasons. Compared with FM, the RMBA treatment increased mean yield and WUE by 23.0% and 28.6%, respectively, across the two growing seasons. We conclude that the RMBA treatment is an effective and promising cultivation pattern for alleviating water scarcity and improving soil hydrothermal conditions, yield, and WUE on the Tibetan Plateau.

Effect on soil water availability, rather than silicon uptake by plants, explains the beneficial effect of silicon on rice during drought

Various studies showed a decrease of drought stress specific parameters of plants after silicon (Si) fertilization. But all studies differed in soil Si concentration between the control and Si treatments. As amorphous silica (ASi) was recently found to cause a strong increase of water holding capacity and plant available water in soils, a combined effect of soil moisture and plant response due to Si addition was assumed. In this study, the influence of the soil Si content was excluded by using the same Si enriched soil for treatments of two rice lines, lsi1 mutant defective in Si uptake and its wild-type rice. Most plant parameters, such as nutrient contents, biomass, specific leaf area, specific root length, leaf water content and C allocation did not differ significantly between the genotypes neither under flooded conditions, nor under drought conditions. Only photosynthesis and stomatal conductance were slightly higher for the wild type in both drought and flooded treatments. Overall, our data showed that Si accumulation within the plant tissues has only a minor effect on plant performance under drought stress. Hence, existing studies should be reinterpreted in light of the fact that Si additions may increase soil water availability.

Medium-term effect of fertilizer, compost, and dolomite on cocoa soil and productivity in Sulawesi, Indonesia

AbstractIn Indonesia, management practices that reduce soil fertility could be limiting cocoa (Theobroma cacao L.) production. To address this, we investigated the effects of fertilizers and organic amendments comprising different combinations of NPK + urea, dolomite, and manure-based compost on soil properties and cocoa productivity. We extended an existing field experiment in South Sulawesi, Indonesia, to assess these treatments’ effects on cocoa trees from the age of 2.9 years to 7.4 years. The treatments were first applied 5 months after planting and subsequently twice a year. Soil analyses were performed before planting, after 3 years, and finally after 7 years. Productivity was assessed yearly between the age of 3.5 and 7.4 years. The highest yields were obtained from the plots receiving compost, although the yield benefits diminished over time. Inorganic fertilizer alone doubled the yield compared to the control, while the yields with compost and compost + fertilizer were three times that of the control. With dolomite alone, the yield cumulated over 4 years was 41% higher than the control. The positive effect of compost on cocoa yields can potentially be attributed to (1) physical changes increasing soil water availability, (2) the chemical improvement of nutrient availability, and (3) biologically, by promoting the activity of beneficial organisms. The application of dolomite increased soil pH, Ca, and Mg contents. Soil organic carbon greatly declined in the composted treatments, even though 10 kg of compost was applied per tree per year, probably because of the low C:N ratio of the compost. Future studies should assess different fertilizer formulations and combinations with organic inputs and explore the mechanisms by which compost promotes cocoa productivity.