Initial Soil Research Articles

Specific power or droplet shear stress: Which is the primary cause of soil erosion under low-pressure sprinklers?

Specific power and droplet shear stress are generally considered to be the most critical indicators of soil erosion in sprinkler irrigation, but there is controversy about which indicator has a greater impact. This creates uncertainty in the optimization design of low-pressure sprinkler irrigation systems. In this study, a commonly used low-pressure sprinkler, i.e., Nelson D3000, was used to carry out in soil box experiments, to study the effects of specific power and average droplet shear stress at the end of a spray jet on soil erosion during sprinkler irrigation under three nozzle diameters (3.97, 5.95, and 7.94 mm), two operating pressures (103 and 138 kPa), and two soil textures (loamy sand and silty loam). Overall, the larger specific power or average droplet shear stress resulted in higher initial and steady runoff rates and a shorter time until runoff occurs and stabilizes. Enlarging the specific power or average droplet shear stress could significantly increase the initial infiltration rate, sediment yield, and surface soil bulk density, but the infiltration depth prior to runoff and surface soil porosity decreased. Furthermore, the specific power was observed to have greater correlations than average droplet shear stress with the surface runoff rate, initial infiltration rate, and increase in the soil bulk density and decrease in the soil porosity after irrigation. However, it was weakly related to the infiltration depth prior to runoff and sediment yield, indicating that the specific power could more accurately reflect the soil erosion with respect to the shear stress. To minimize the risk of soil erosion, a small operating pressure (103 kPa) is recommended in the design of center pivot irrigation systems, especially for the overhang of the system with large nozzle diameters. This research can provide the technical support for soil erosion prevention under low-pressure sprinkler irrigation.

Nitrogen addition impacts on soil phosphorus transformations depending upon its influences on soil organic carbon and microbial biomass in temperate larch forests across northern China

Globally increasing atmospheric nitrogen (N) deposition can affect soil phosphorus (P) transformations, yet the pathways and underlying mechanisms are largely unclear. Here, we sampled soils from five larch stands along a soil fertility gradient in northern China that have experienced long-term N addition (>5 years), and measured soil P fractions and biochemical properties. We found that the magnitude and direction of N addition effects on soil inorganic P and organic P fractions significantly varied with initial soil C:N ratio. Specifically, N addition significantly reduced almost all soil inorganic P fractions in the larch stand with the highest soil C:N ratio (18.35). In contrast, N addition significantly elevated NaOH-extractable organic P and total organic P in the larch stand with the highest soil C:N ratio while reduced labile organic P and total organic P in the stand with the lower soil C:N ratio (11.74). N addition-induced changes in inorganic P fractions were significantly correlated with that of soil organic C. Moreover, N addition-induced changes in organic P fractions were significantly correlated with those of microbial biomass and acid phosphatase activity. Taken together, our results indicate that N addition influenced soil P availability and fractions mainly by affecting soil organic C and microbial properties, which can improve our understanding of mechanisms of changes in soil P availability under the context of increasing N deposition.

Positive effects of crop rotation on soil aggregation and associated organic carbon are mainly controlled by climate and initial soil carbon content: A meta-analysis

Understanding the global patterns and controls on soil aggregation and associated organic carbon (OC) is essential to improve soil carbon storage and mitigate climate warming. Crop rotation is an important feature of sustainable agricultural management and influences multiple soil properties. However, the effects of crop rotation on soil aggregation and associated OC remain poorly understood. We conducted a meta-analysis of 2199 paired observations from 53 studies to quantitatively analyze crop rotation-induced changes in soil aggregation and associated OC and elucidate optimal climatic, edaphic, and agronomic factors. Overall, crop rotation improved the proportions of macroaggregates (> 0.25 mm) by 7–14%, aggregate stability by 7–9%, and OC contents in all sizes of aggregates by 7–8% relative to continuous monoculture. Crop rotation increased soil aggregation and associated OC mainly in regions with mean annual temperature between 8 and 15℃, mean annual precipitation between 600 and 1000 mm, and also in topsoil (0–20 cm) with loamy textures and medium levels of initial soil OC (10–15 g kg−1), total nitrogen (0.75–1.50 g kg−1), and pH (6−8). Greater increases in soil aggregation and associated OC induced by crop rotation were associated with sub-soiling, no-till, straw retention, combined manure-inorganic fertilizers, and a lower nitrogen fertilization input rate with more rotation cycles and longer rotation length. Crop rotation effects were especially strong when the previously cultivated crop was soybean. The variance partitioning analysis revealed that variations in crop rotation-induced changes in soil aggregation and associated OC were mainly explained by climate (26–35%) and soil properties (17–34%). The random forest model indicated that climate (mean annual temperature and precipitation) and initial soil OC were the predominant controls on the effects of crop rotation. Overall, these findings suggest that the use of crop rotation can help sequester carbon by improving soil aggregation and associated OC, and highlight the importance of climate and initial soil OC in site-specific crop rotation systems to the sustainability of agroecosystems.

Nine‐year organic fertilization enhances poorly crystalline iron hydroxide formation and phosphorus availability in a temperate rice–wheat cropping system

AbstractPhosphorus (P) is typically associated with iron (Fe) hydroxides in paddy soils. Our study investigated the impact of different fertilization treatments on the availability of P regulated by Fe redox transformation in a rice (Oryza sativa L.)–wheat (Triticum aestivum L.) cropping system in the mid‐low reaches of the Yangtze River. Five fertilization treatments were examined: control (CK), chemical fertilizer (CF), 35% CF (P) plus pig manure compost (CFM), 100% CF (P) plus straw (CFS), and 35% CF (P) plus pig manure compost and straw (CFMS). Nine‐year rice–wheat rotations increased the oxalate‐extractable poorly crystalline Fe hydroxides (i.e., Feo) by 33%–87% compared with the initial soil, while fertilization further accelerated this process. Compost application increased the proportion of labile P by 75%–108% and decreased the proportion of non‐labile P by 14%–22% compared with the single chemical fertilization treatment. Furthermore, organic fertilization increased the mass proportions of macroaggregates and macroaggregate‐associated labile P. The Feo was positively correlated with the content of labile P but negatively correlated with the proportion of non‐labile P. Moreover, the reductive dissolution of Fe hydroxides was accompanied by the transformation of P from NaOH‐extractable to NaHCO3‐ and H2O‐extractable phases. These results indicate that seasonal alternation of drying and wetting can progressively drive the redox transformation of Fe hydroxides and promote the formation of Feo, thereby affecting the availability of P. Therefore, we suggested that P fertilizer should be reduced in the rice season due to the reduction of Fe hydroxides, particularly in the compost‐amended soils in the temperate rice–wheat cropping system.

Possibility of exogenous organic carbon input to increase global soil nitrogen supply potential: A meta-analysis

Soil nitrogen (N) mineralization is regulated by the input of exogenous organic carbon (C, ExoC) substrate via changing C availability. Although ExoC input occurs widely among global terrestrial ecosystems, it is still not clear how ExoC input affects soil gross N mineralization (GNM). Here, 265 observations from 63 peer-reviewed publications were collected for a global meta-analysis to investigate the effect and the drivers of ExoC input upon soil GNM. The results showed that ExoC input significantly increased GNM by 40.8%, and the influence depended on the types of ExoC substrate. The input of complex ExoC substrate (straw, animal manure, cellulose, etc.) increased soil GNM by 44.8%, while simple ExoC substrate (glucose, amino acids, oxalic, etc.) had no significant effect on GNM. Only in cropland the ExoC input promote the rate of soil GNM, with no significant effect found in either forest or grassland. Furthermore, the results revealed that the application rate of ExoC was the paramount factor affecting soil GNM, given their significant positive correlations. This study also emphasized that initial soil pH (i.e. soil pH before ExoC input) and pH of ExoC, rather than the change of bulk soil pH, played an important role in regulating soil GNM after the ExoC input, and both were significantly negatively correlated with GNM. In addition, soil GNM was also negatively correlated with mean annual temperature but positively related with soil total N and mean annual precipitation. The findings of this meta-analysis contribute to a comprehensive understanding of how soil N availability and cycling respond to ExoC input on a global scale. That means the factors related to rate of ExoC, soil total N, initial soil pH, the pH of ExoC, and climate factors and the interaction among above factors may affect global soil N supplying potential.

Understanding the dynamics of evaporation from stony soils via laboratory experiments and numerical modeling

Stones and rock fragments are typically found within soil profiles across various landscapes. However, knowledge on, and understanding of, their impact on hydraulic functions and processes are still lacking. Specifically, the presence of stones within the soil profile may increase water storage and availability to vegetation and reduce plant mortality in drylands. However, physically-based testing of stones effect on soil water budget components is overlooked. Experiments under laboratory conditions from soil columns, with two volume content t levels and two sizes of stones, were carried out in this research. Our results reveal that stoniness reduces the duration of stage-1 evaporation (S1) and consequently the overall cumulative evaporation, proportionally to their volumetric content and to the initial soil water content. The effect of stone size on evaporation was minor during S1 but was more pronounced during stage-2 (S2) — when the evaporation front migrates downward — with smaller stones reducing evaporation more than the larger ones. A recent evaporation model, assuming that transient evaporation is a succession of steady state solutions, was applied to explain the 2-phases evaporation process in a stony profile. The model results indicate that apart from changing the effective porosity of the soil profile by replacing a soil volume by stones, stoniness affects mainly the hydraulic conductivity function but practically not the water retention curve. Stoniness induced an increase in the tortuosity-related parameters compared with those of the stone-free soil. This observation was strengthened by the fact that both measured and modelled data reveal that stoniness has not affected the downward movement of the water table level during drying. Although we tested two stone sizes only and further experiments are required for a broader understanding, we suggest that the outcoming insights may improve estimates of water budget components in stony soil profiles and their response to global climatic changes.

Repeated falling-head method for in situ measurements of saturated hydraulic conductivity using a single cylinder

A simple, repeated falling-head (RFH) method, which uses an inexpensive portable cylinder to quickly determine field-saturated hydraulic conductivity (Kfs), is presented. A cylinder of radius r, inserted vertically from the soil surface to a depth d, is used as a water supply tank, through which water infiltrates into the soil. The falling-head test is repeated without allowing the cylinder to be drained entirely to eliminate the effects of the initial soil moisture conditions. Either change in the water level (H) in the water supply cylinder or strong linearity between the infiltration flux (qs) and H can be used to determine Kfs directly or by multiplying the slope with an empirical ring-installation scaling length, Lg; thus, no soil-dependent variable is necessary. To obtain the Lg value for various conditions, we carried out numerical experiments using HYDRUS (2D/3D) with a recently implemented reservoir boundary condition for six different soil textures, ranging from coarse soil (e.g., sand) to fine soil (e.g., silty clay loam), and two different ranges of water levels, 15 ≤ H ≤ 25 cm and 2 ≤ H ≤ 6 cm. Numerical results showed that the Lg has a strong linear dependence on d and r, where Lg increases as d and r increase. We propose a new linear model to determine Lg with optimized coefficients for each H range. Numerical results showed no significant differences in the estimated Kfs after the second repetition, confirming that repeating the falling head test twice is sufficient. The newly obtained Lg values were then applied to the experimental data obtained at multiple fields having different soil textures. The Kfs values determined using the RFH method agreed well with those measured using the field two-ponding depths steady-state method and/or the FH method in the lab. These results demonstrate the reliability of the proposed RFH method.

Estimating biomass and soil carbon change at the level of forest stands using repeated forest surveys assisted by airborne laser scanner data

BackgroundUnder the growing pressure to implement mitigation actions, the focus of forest management is shifting from a traditional resource centric view to incorporate more forest ecosystem services objectives such as carbon sequestration. Estimating the above-ground biomass in forests using airborne laser scanning (ALS) is now an operational practice in Northern Europe and is being adopted in many parts of the world. In the boreal forests, however, most of the carbon (85%) is stored in the soil organic (SO) matter. While this very important carbon pool is “invisible” to ALS, it is closely connected and feeds from the growing forest stocks. We propose an integrated methodology to estimate the changes in forest carbon pools at the level of forest stands by combining field measurements and ALS data.ResultsALS-based models of dominant height, mean diameter, and biomass were fitted using the field observations and were used to predict mean tree biophysical properties across the entire study area (50 km2) which was in turn used to estimate the biomass carbon stocks and the litter production that feeds into the soil. For the soil carbon pool estimation, we used the Yasso15 model. The methodology was based on (1) approximating the initial soil carbon stocks using simulations; (2) predicting the annual litter input based on the predicted growing stocks in each cell; (3) predicting the soil carbon dynamics of the annual litter using the Yasso15 soil carbon model. The estimated total carbon change (standard errors in parenthesis) for the entire area was 0.741 (0.14) Mg ha−1 yr−1. The biomass carbon change was 0.405 (0.13) Mg ha−1 yr−1, the litter carbon change (e.g., deadwood and leaves) was 0.346 (0.027) Mg ha−1 yr−1, and the change in SO carbon was − 0.01 (0.003) Mg ha−1 yr−1.ConclusionsOur results show that ALS data can be used indirectly through a chain of models to estimate soil carbon changes in addition to changes in biomass at the primary level of forest management, namely the forest stands. Having control of the errors contributed by each model, the stand-level uncertainty can be estimated under a model-based inferential approach.

Correlations between moisture content and color spectrum of sandy soils

It is a well-known phenomenon that the color of sand changes due to moisture. As the moisture content increases, the sand will typically become darker. In our research, we are looking for the answer to the exact function according to which this darkening process changes and what relationship there may be between the different, initial (dry) soil colors and how this relationship can influence the evolution of the darkening process. Using the suitably chosen range of the color spectrum, we created a color parameter to characterize the color of the measured sandy soil, and then, in addition to determining the moisture content, we also looked for other uses of the color spectrum for sandy soil. Thus, based on the color spectrum and other input parameters, not only the moisture content can be calculated, but in the case of two components, the grain composition can also be determined.

Short-term Effects of Applying Olive Mill Waste on Turfgrass

The reuse of wastes in agriculture and landscape is often viewed as one way to conserve existing resources. Among the organic waste materials produced by agricultural activities, olive mill wastes derived from the olive oil extraction process may represent a suitable soil amendment. This study evaluated the effect of olive mill wastewater (OMW) application on turfgrass growth and quality and on soil electrical conductivity and pH. Olive mill wastewater at different doses (0, 3.0, and 6.0 L/m2) was applied on a sodded turfgrass grown in clay loamy soil, identically irrigated with fresh water, and without any chemical fertilizer application. The results revealed that OMW application had a positive effect on the tested turfgrass, improving visual quality and increasing the dry weight of the clipping yield, in proportion to doses applied. An increase in electrical conductivity was observed in wastewater-irrigated soil while OMW did not remarkably change the initial soil pH.

Aeolian sand cover affects the soil hydrothermal state and permafrost degradation on the Qinghai-Tibet Plateau

Aeolian sand significantly affects permafrost degradation, but the effect of the aeolian sand on the permafrost on the Qinghai-Tibet Plateau remains unknown. The sand layer thickness is critical to its role. However, little quantitative research has been conducted on the effect of the sand layer thickness on its role. In this study, using CoupModel, we investigated the differences in the impact of the aeolian sand cover on the hydrothermal state of permafrost with 20 different sand layer thicknesses (10 ∼ 200 cm, 10 cm increment) and analyzed the mechanisms that explain the different impacts. The results reveal that the active layer is where the aeolian sand has the most impact on the permafrost. The aeolian sand layer accumulates precipitation into the soil below the sand, thereby significantly drying the shallow soil layer of the current stratum. Moreover, the thicker the sand layer, the more water accumulates in the underlying soil layer. In the middle-upper active layer, the initial soil heat storage, soil heat flow interception, and liquid water and ice contents govern the soil temperatures that increase in cold seasons and decrease in warm seasons as the sand layer thickens. Near the bottom of the active layer, the initial soil heat storage and soil heat flow interception control the soil temperatures that increase in cold seasons but fluctuate between sand layer thicknesses of 50 cm, 70 cm, and 120 cm in warm seasons as the sand layer thickens. Permafrost degradation is enhanced by sand layers thinner than 150 cm and retarded by sand layers thicker than 150 cm, respectively. The thermal state, soil properties, and accumulation process of the aeolian sand also contribute to this effect of the aeolian sand on the permafrost. In the plateau aeolian deserts, the sparse vegetation promotes permafrost degradation and the thinner seasonal snow cover protects permafrost. Moreover, under the different climate during the geological history period, the island or discontinuous permafrost might be formed due to the pluvial-radiation talik caused by the thicker sand layer or dunes.

Comparative study on changes in biochemical constituents, yield and quality of lemongrass (Cymbopogon flexuosus) grown under different soil types

ABSTRACT Lemongrass (Cymbopogon flexuosus) is a perennial aromatic grass suitable for cultivation on a wide range of soils. This study aims to evaluate the feasibility of lemongrass for utilizing alkaline lands and to examine the biochemical, yield and quality response of lemongrass cultivars on different soils. In this experiment, soils with different soil texture, i.e. S1- Clay loam soil; S2- Loamy sand soil; S3- Sandy loam soil; S4- Loam soil, were taken from different geographical locations. Physico-chemical properties, initial soil status of selected soil types were tested. Growth parameters, biochemical enzymes, yield and quality parameters of lemongrass varieties were determined. Post-harvest status of soils was also analyzed. Soil calcareousness and other soil characteristics like cation exchange capacity significantly impacted lemongrass varieties on biochemical properties such as proline content, lipid peroxidation, nitrate reductase activity, herb and oil yields, and constituents of essential oil. The herbage and oil yield of lemongrass significantly decreased with an upsurge in soil calcareousness. The total citral content in the essential oil was highest for the variety ‘Krishna’ (85.33%) grown in clay loam soil and lowest in ‘CIM-Shikhar’ variety (65.09%) grown in sandy loam soil. Post-harvest data of soils showed significant impact on soil ameliorating potential of lemongrass.

Changes in Soil Nitrogen Availability as Influenced by Direct Seeded Rice and Transplanted Rice Ecosystem, Nutritional Approaches and Slow-release Nitrogen Sources

An experiment was conducted on nutrient management approaches using RDF, SSNM, STCR and nutrient expert under different rice ecosystem using slow release nitrogen sources viz., neem coated urea and urea supergranules. The initial and final soil N content was analyzed at active tillering, panicle initiation, milking stages and at harvest of direct seeded and transplanted rice. The three-way interaction (M x N x S) proved that a significantly higher value of available N content in soil was noticed in SSNM (6 t ha-1) treated plot with neem coated urea in transplanted rice (M2N3S2) at active tillering stage (245.96 kg ha-1) and at harvest (213.46 kg ha-1), respectively, while application of NCU through SSNM approach (7 t ha-1) in direct seeded rice (M1N4S2) obtained maximum available N content at panicle initiation stage (229.18 kg ha-1) and application of NCU through STCR approach for the yield target of 7 t ha-1 in direct seeded rice (M1N2S2) at milking stage (218.15 kg ha-1).

Calcium Oxalates in Soils within Disturbed Landscapes and Rock on the Territory of Yakutia (Russia), Formation Conditions in a Sharply Continental Cryoarid Climate

The formation of oxalates in soils and rocks under conditions of cryoarid climate, permafrost and taiga vegetation was studied. Whewellite and weddellite were found in four areas associated with the mining industry: on the kimberlite deposit of the Daldyn territory, in the lower reaches of the Markha River of the Central Yakut Plain, and on the coastal outcrop of the Allah-Yun Sellah-Khotun ore cluster. Whewellite was found in the upper organic horizon of Skeletic Cryosol (Thixotropic) (sample 151) and as a film on the surface of plant remains of Humic Fluvisols (sample 1663). Weddellite was found as an extensive encrustation on the surface of the soil and vegetation cover of Stagnic Cryosols Reductaquic (sample 984) and on a siltstone outcrop (sample KM-6-21). Calcium oxalates were identified by X-ray phase analysis, photographs of the samples were taken on a polarizing microscope, and the crystal morphology was studied on a scanning electron microscope. To determine the chemical composition of soils and rocks, the classical wet-chemical method was used; the physical properties of the studied samples were studied using a pH meter, the photoelectric colorimetric method, and a synchrotron thermal analysis device. The source of calcium for the formation of salts is the parent layers of the studied soils, represented by carbonate and carbonate clastic rocks, which cause neutral and slightly alkaline environments. High humidity, which is provided by the seasonal thawing of the permafrost, has a key role in the formation of the studied oxalates in Yakutia with a sharply continental cryoarid climate. Based on the studies, it was found that the first two samples are the products of lichen activity, and the third and fourth are at the stage of initial soil formation by micromycetes. In addition, the formation of these oxalates, in our opinion, is the result of the protective function of vegetation, in the first two cases, with a sharp increase in the load on lichens under technogenic impact, and in the second and third cases, when favorable conditions arise for initial soil formation, but under conditions of toxic content of heavy metals and arsenic.

EVALUATION OF DIFFERENT RATES OF COMPOST MINERAL FERTILIZER ON THE GROWTH AND YIELD OF TOMATO

Compost – mineral fertilizer has dual effects; improving soil nutrient status and organic matter content which results to increase in yield of cultivated crops. A field experiment was carried out at the Ambrose Alli University Teaching and Research Farm, Ekpoma, Edo State, Nigeria to evaluate the effect of different rates of compost-mineral fertilizer and compost on the growth and yield of tomato. The experimental design was a Randomized Complete Block Design (RCBD) with seven treatments replicated thrice. The treatments were; control, recommended 10 tonnes of compost, 1, 2, 4, 6 and 8 tonnes/hectare (t/ha) of compost-mineral fertilizer. The initial soil analysis showed low nutrients status and the application of fertilizer was necessary to boost its fertility. Parameters taken were; plant height, stem girth, number of branches, number of flowers at 50% flowering, number of fruits and fresh weight of fruits. From the results, the application of 4, 6 and 8t/ha compost-mineral fertilizer significantly (p< 0.05) increased the growth and yield of tomato compared to other treatments. The yield of tomato obtained from the application of 4, 6 and 8 tonnes of compost- mineral fertilizer (252.50, 272.00 and 294.50 t / ha) were not significantly (p< 0.05) different from each other but significantly (p< 0.05) higher compared to other treatments. Therefore, the application of 6 t / ha of compost-mineral fertilizer can be adopted by farmers for tomato production in the study area.

Asystasia intrusa: Cover crop and water balance dynamics in oil palm plantation

Cultivation of A. intrusa as cover crops in oil palm plantation plays a role in reducing water deficit as much as 90% on condition of higher water deficit occurred. The present study aimed to examine the roles of A. intrusa as land cover crop on water balance in oil palm plantation in Bireuen Regency, Aceh Province, Indonesia during the year of 2020. The initial soil moisture content during the experiment were measured at various depths and conducted using a sensor connected to multimeter. The hydrological variables observed were included rainfall, interception of oil palm plants, water interception of A. intrusa, A. intrusa evapotranspiration, initial soil water content, soil water content during the experiment at each predetermined soil depth and percolation. This study showed that with A. intrusa as cover crop, positively affected soil water content especially during dry season and on months when rainfall are moderate. A. intrusa as cover crops in oil palm plantation played an important role in affecting water balance by reducing ground water deficit during dry season or months with lower rainfall.

105 Botanical composition, yield, horse preference, and forage and soil nutrient values of grass pastures treated with different soil amendments

Forage is the foundation of a horse's diet, therefore, pasture management is critical to improve horse health and pasture productivity. The objective of this study was to evaluate botanical composition, horse preference, yield, and forage and soil nutrient values of pasture treated with horse manure, horse compost, commercial urea fertilizer, and a no amendment control. Researchers hypothesized soil amendments would increase soil nutrients and yield with minimal effects on botanical composition, preference and forage nutrient value. Replicated (n = 3) plots of established cool-season mixed grass pasture were 3 × 6 m and located in St. Paul, Minnesota. The soil was a Waukegan silt loam with a pH of 6.4 and 47 g kg–1 organic matter. Urea was applied based on initial soil test recommendations, 0.64 cm of compost was applied based on common recommendations, and manure was applied at a rate to represent horse manure deposition in May 2022. Sample collection and grazing periods occurred in May, June, July, August, and October 2022, each over a 2-d period. Botanical composition, average forage height and maturity, soil samples, forage samples, and forage yield were taken immediately before grazing. Horses were allowed to graze all plots for 4 h with preference visuallyassessed at 2- and 4 h post-grazing based on percent removal. Data were analyzed as a randomized complete block design using PROC MIXED in SAS with significance set at P ≤ 0.05. Season-long yield ranged from 2,690 to 3,363 kg DM ha-1 and did not differ across treatments (P > 0.05). Botanical composition differed across treatments with the control having the most weeds (32%) and the least amount of grass (62%) while manure treatments resulted in the most bare ground (11%; P ≤ 0.05). The soil nutrients magnesium and phosphate were highest in compost-treated plots and nitrate-nitrogen and sodium were highest in manure-treated plots (P ≤ 0.05). Forage nutrient content did not differ across treatments (P > 0.05). Horses did not prefer pasture treated with manure and only 15 and 33% of forage was consumed after 2 and 4 h, respectively (P ≤ 0.001). All other treatments averaged 53 and 78% removal after 2 and 4 h, respectively. Based on differences observed in botanical composition and horse preference, commercial fertilizer and compost appear to be the most beneficial soil amendments for horse pastures.

Linking soil organic carbon dynamics to microbial community and enzyme activities in degraded soil remediation by reductive soil disinfestation

Reductive soil disinfestation (RSD) is a widely practiced strategy for remediating soil degradation that seriously threatens crop production and sustainable agriculture. However, the soil organic carbon (SOC) dynamics and its underlying mechanisms induced by RSD remain unknown. To clarify this problem, a field experiment explored the SOC dynamics under degraded soils (C3) remediated with CK (untreated) and RSD (combination of added maize straw (C4), water flooding, and plastic mulch). The relationships of SOC dynamics with microbial community composition and activities of C-related hydrolase were also disentangled using structural equation model (SEM) and variation partitioning analysis (VPA). Results indicated that the SOC concentration under CK treatment decreased by 0.96 g C kg−1 compared with that in the initial soil, while the SOC concentration under RSD treatment increased by 1.26 g C kg−1 because of old SOC loss (0.56 g C kg−1) and new SOC formation (1.82 g C kg−1). Compared to the CK, the RSD increased the soil dissolved organic C (DOC), but decreased the microbial biomass C (MBC) and abundances of bacteria and fungi. The soil microbial community shifted from Proteobacteria and Actinobacteria to Firmicutes and Ascomycota after RSD treatment, and the activities of C-related hydrolase were also enhanced, such as β-glucosidase, cellobiohydrolase, β-xylosidase, and invertase. The SEM and VPA suggested that the new SOC formation and the reduced old SOC loss under RSD treatment were collaboratively driven by soil properties (i.e., redox potential, DOC, and MBC), microbial taxa (i.e., Arthobacter, Symbiobacterium) and hydrolase activities (i.e., BG and CBH). Meanwhile, the RSD doubled the yield of subsequent tomato by mitigating soil degradation (i.e., salinization and Fusarium oxysporum) and increasing the SOC concentration. In summary, RSD, as a remediation strategy for soil degradation, can increase SOC concentration by modifying microbial community and C-related hydrolase activities.

ASSESSMENT OF DROUGHT INDICES AND WATER AVAILABILITY USING STATISTICAL Z-SCORE AND MOCK MODEL

The phenomenon of drought and water scarcity due to climate change is a major problem in many countries. Assessing drought conditions and water availability in a watershed helps the government and communities implement sustainable watershed management. The study was conducted in Krueng Jreue Sub Watershed, Krueng Aceh Watershed, Aceh Province, Indonesia. The meteorological and hydrological indices in the watershed were analyzed using statistical Z-Score for Precipitation (ZSP) and Discharges (ZSD). Discharges originated from Mock model was used to examine the water availability in a watershed. The results showed the ZSP and ZSD indices from 2008 to 2017 were almost categorized as normal. In certain months, drought indices with the criteria of extreme wet (EW), very wet (VW), and severe drought (SD) also occurred. In general, the ZSP and ZSD indices were consistent, but for certain months (April 2008, November 2010, and March 2017) inconsistencies were found due to differences in signs and index classes. The Mock model parameters for the proportion of surface soil uncovered by vegetation (m), infiltration factor (IF), initial soil moisture (ISM), and flow reduction coefficient (Rc) were 20 %, 0.4, 200 mm month-1, and 0.6, respectively. The average monthly discharge during the period of 2008-2017 ranged from 3.16-31.18 m3s-1. The total water needs of 5.041 m3 s-1 per month. The water availability per month was surplus in the rainy season (October-April), but deficit in the dry season (May-September). This research not only contributes to enriching references for similar research in Krueng Aceh Watershed, Indonesia but can also be applied to other watersheds according to the current conditions of watershed characteristics.

Assessment of GPM Satellite Precipitation Performance after Bias Correction, for Hydrological Modeling in a Semi-Arid Watershed (High Atlas Mountain, Morocco)

Due to its important spatiotemporal variability, accurate rainfall monitoring is one of the most difficult issues in semi-arid mountainous environments. Moreover, due to the inconsistent distribution of gauge measurement, the availability of precipitation data is not always secured and totally reliable at the instantaneous time step. As a result, earth observation of precipitation estimations could be an alternative for overcoming this restriction. The current study presents a framework for either the hydro-statistical evaluation and bias correction of the Global Precipitation Measurement (GPM) Integrated Multi-SatellitE Retrievals version 06 Early (IMERG-E), Late (IMERG-L), and Final (IMERG-F) products. On a sub-daily duration, from the Taferiat rain gauge-based station, which was used as a benchmark from 1 September 2014 to 31 August 2018. Statistical analysis was performed to examine each precipitation product’s performance. The results showed that all Post_Real_Time and Real_Time IMERG had a high level of awareness accuracy. The IMERG-L results were statistically similar to the gauge data, succeeded by the IMERG-F and IMERG-E. The Cumulative Distribution Function (CDF) has been employed to adjust the precipitation values of the three IMERG products in order to decrease bias estimation. The three products were then integrated into the “HEC-HMS” hydrological model to assess their dependability in flow modeling. Six flood occurrences were calibrated and validated for each product at 30-minute time steps. With a mean Nash-Sutcliffe coefficient of NSE 0.82, the calibration findings demonstrate that IMERG-F provides satisfactory hydrological performance. With an NSE = 0.80, IMERG-L displayed good hydrological utility, slightly better than IMERG-E with an NSE = 0.77. However, when the flood events were validated using the initial soil conditions, IMERG F and IMERG E overestimated the discharge by 13% and 10%, respectively. While IMERG L passed the validation phase with an average score of NSE = 0.69.