Impact of single biochar application on maize growth and water-fertilizer productivity under different irrigation regimes.

The improvement of soil water and nutrient availability through soil management practices are crucial in promoting crop growth and obtaining high water-fertilizer productivity under limited irrigation. In this study, a 2×4 fully randomized factorial design with two drip-irrigation regimes and four biochar rates was performed during maize crop growing seasons for a semiarid region of China in 2015 and 2016. Irrigation regimes was applied on the basis of the water lower limit of -15 kPa soil matric potential as W15 and -35 kPa as W35. Maize straw-derived biochar application rate of 0 (B0), 15 (B15), 30 (B30), and 45 (B45) t ha-1 was once applied to sandy loam soil in the first growing season. Our results showed that the W15 and W35 regimes generally increased soil nutrient availability and organic matter content under all biochar treatment rates for the entire growth period. In comparison, the B45-induced increase in available P and K was higher in the W15 regime than in the W35 regime during the second growing season. Furthermore, biochar treatment improved the comprehensive fertility index (CFI), leaf area index, and yield of maize. Within the same biochar treatment, the CFI value was higher in the W15 regime than in the W35 regime during the first growing season. However, the opposite was observed in the second growing season. The average irrigation water productivity (IWP) increased by 11.6%, 8.8%, and 7.8% in the W35 regime and by 15.2%, 12.9%, and 10.2% in the W15 regime for the B15, B30, and B45 treatments, respectively. Moreover, biochar treatment enhanced maize grain yield and partial fertilizer productivity (PFP) of synthetic N, P, and K fertilizers under both irrigation regimes. The highest PFP values were observed in the B15 treatment under W15. In general, a one-time application of biochar treatment at a rate of 15 t ha-1 in the first growing season is recommended in terms of increasing the availability of N, P, K, and organic matter in sandy loam and also improve water-fertilizer productivity under irrigation water lower limit of -15 kPa soil matric potential.

Application of the US-EPA's HAWQS model to predict future climate impacts on hydrological processes.

Climate change could add a variety of uncertainties to hydrological processes and water resources. Very limited efforts have been devoted to applying the US-EPA (Environmental Protection Agency)'s Hydrologic and Water Quality System (HAWQS) model for predicting climate change impacts on hydrological processes at basin scale. Here we applied the model to project the next 50 years' (from 2021 to 2070) hydrological processes at the Yazoo River basin in Mississippi, USA. Simulations showed that over the next 50 years, there are no significant trends in monthly precipitation, ET, runoff, and discharge; only 2% of the annual precipitation percolated into the deep aquifer; and dry seasons become dryer and wet seasons become wetter. These findings provide very useful information to stakeholders for water resource management. Our study further suggests that the HAWQS model is a user friendly and time-saving tool for basin scale hydrological modeling.

Impact of climate change on groundwater resource in a region with a fast depletion rate: the Mississippi Embayment.

Mississippi Embayment (ME) is one of the fastest groundwater depletion regions around the world, while the impacts of climate change on groundwater resources in the region are complex and basically unknown. Using the U.S. Geological Survey's Mississippi Embayment Regional Aquifer Study (MERAS) model, such a challenge was addressed through the base, wet, and dry simulation scenarios. Over the 137-year simulation period from 1870 to 2007, the cumulative aquifer storage depletions were 1.70 × 1011, 1.73 × 1011, and 1.67 × 1011 m3, respectively, for the base, dry, and wet scenarios. As compared with that of the base scenario, the aquifer storage depletions were only 1.76% more for the dry scenario and 1.8% less for the wet scenario. A multiple regression analysis showed that the aquifer storage depletion rate was controlled more by the groundwater pumping and stream leakage rates and less by the groundwater net recharge rate. Groundwater table variation in the forest land was much smaller than in the crop land. Results suggested that groundwater pumping rather than climate change was a key driving force of groundwater depletion in the ME. Our findings provide a useful reference to water resource managers, foresters, and farmers in the ME and around the world when developing their groundwater supply strategies.

Decomposition of poultry litter organic matter co-applied with industrial and agricultural products/by-products.

Increasing soil organic matter (SOM) is one purpose of applying manures to soils, but soil-applied manures decompose and disappear in a short time, leaving very little trace as SOM. The objective of this study was to test and identify agricultural and industrial products and by-products (PBPs) that reduce the speed of manure decomposition and, potentially, increase SOM. Raw poultry litter (PL) was amended with selected PBPs (15% fresh weight) and incubated for 1-3 mo. Unamended PL lost an average of 19% of its dry weight after 1 mo incubation and 24% of its dry weight after 3 mo. Monitoring the CO2 release during a 1-mo incubation revealed that decomposition and weight loss of unamended PL is greatest in the first 2 d. Amending PL with Al2 (SO4 )3 · 18H2 O and CaO reduced cumulative CO2 release and final dry biomass loss during the incubation period of 1-3 mo. Amending PL with Al2 (SO4 )3 · 18H2 O reduced PL temperature by up to 14 °C and pH by ∼4.0, whereas CaO elevated its temperature by up to 24 °C and pH by ∼4.0. Both products suppressed total culturable bacteria and reduced dehydrogenase activity soon after mixing. Amending PL with flue gas desulfurization gypsum, CaCO3 , cement kiln dust, or biochar either enhanced or had no effect on suppressing litter decomposition. Our results overall show that the decomposition of PL and possibly other manures may be slowed and that the soil-residence life of manure C may be increased using PBPs that raise or lower manure pH and temperature.

A century of precipitation trends in forest lands of the Lower Mississippi River Alluvial Valley.

Variations in long-term precipitation trends due to climate forcings have been observed in many parts of the world, exacerbating hydrological uncertainties to predicting droughts, floods, water resource availability, and ecosystem services. The Lower Mississippi River Alluvial Valley (LMRAV) is an important economic region of the midsouth USA, which is prone to natural disasters from extreme climate events and is known historically for cyclic flooding events and, within the last 20 years, for groundwater level declines. However, our knowledge of long-term precipitation trends in this region is fragmented. Using 100-year historic daily precipitation data from six stations of forest lands along with multivariate statistical analysis, we found that there were significant increasing trends (p ≤ 0.05) in annual precipitation near the south coastal area of the LMRAV and only marginally increasing trends in the northern area. Spatial variation in seasonality was observed at the decadal scale with increasing trends in fall near the coastal area and in spring around the north area. In addition to becoming wetter, the coastal area also experienced higher precipitation intensity with shorter return period over the past 100 years. These findings are useful to water resource managers for adapting to changing climate conditions in the LMRAV.

Impact of biochar on greenhouse gas emissions and soil carbon sequestration in corn grown under drip irrigation with mulching.

Biochar is widely used as a soil amendment to challenge climate change through restraining greenhouse gas production and increasing soil C sink in cropland soils, yet its effect was not studied well under drip irrigation with mulch. A two-year field experiment was conducted to investigate the impact of corn residue-derived biochar amendments on greenhouse gases (GHG), soil organic carbon (SOC), and global warming potential (GWP) on sandy loam soil in Inner Mongolia, China. Biochar application rates of 0 (B0, control), 15 (B15), 30 (B30), and 45 (B45) t ha-1 were broadcasted onto the soil surface, and then mixed into 30-cm soil depth at the first crop growing season to a film-mulched and drip-irrigated corn production. Soil emissions of CO2, N2O, and CH4 were measured using a closed static chamber approach. Compared to control plots, biochar amendments reduced total CO2 emission by 18-25% at the first growing season, and 19-41% at the second growing season. The highest and lowest CH4 emissions were from B45 and B15 in the first year, and B45 and B30 in the second year, respectively. Relative to the control, B15 and B30 reduced CH4 emission by 124% and 132% as averaged over 2-yr. With biochar amendments, total N2O emission was decreased by 71-110% and 39-47% in the first and second year. Among these biochar amendments, B30 was the best amendment limiting the GWP of N2O and CH4 in any of the two years. B30 and B45 significantly increased SOC sequestration in the top 15-cm depth by 19% and 37% in the first growing season, respectively, and by 12% and 15% in the second growing season. Biochar amendment B30 also significantly increased corn yields. Biochar shows the greatest potential to mitigate greenhouse gas emissions and increase soil C sequestration. The greatest reductions with biochar application 30 t ha-1 in corn.

The influence of chlorination timing and concentration on microbial communities in labyrinth channels: implications for biofilm removal.

Chlorination is an effective method to control biofilm formation in enclosed pipelines. To date, very little is known about how to control biofilms at the mesoscale in complex pipelines through chlorination. In this study, the dynamic of microbial communities was examined under different residual chlorine concentrations on the biofilms attached to labyrinth channels for drip irrigation using reclaimed water. The results indicated that the microbial phospholipid fatty acids, extracellular polymeric substances, microbial dynamics, and the ace and Shannon microbial diversity indices showed a gradual decrease after chlorination. However, chlorination increased microbial activity by 0.5-19.2%. The increase in the relative abundances of chloride-resistant bacteria (Acinetobacter and Thermomonas) could lead to a potential risk of chlorine resistance. Thus, keeping a low chlorine concentration (0.83 mg l-1 for 3 h) is effective for controlling biofilm formation in the labyrinth channels.

Application of Climate Assessment Tool (CAT) to Estimate Climate Variability Impacts on Nutrient Loading from Local Watersheds.

A vast amount of future climate scenario datasets, created by climate models such as general circulation models (GCMs), have been used in conjunction with watershed models to project future climate variability impact on hydrological processes and water quality. However, these low spatial-temporal resolution datasets are often difficult to downscale spatially and disaggregate temporarily, and they may not be accurate for local watersheds (i.e., state level or smaller watersheds). This study applied the US-EPA (Environmental Protection Agency)'s Climate Assessment Tool (CAT) to create future climate variability scenarios based on historical measured data for local watersheds. As a case demonstration, CAT was employed in conjunction with HSPF (Hydrological Simulation Program-FORTRAN) model to assess the impacts of the potential future extreme rainfall events and air temperature increases upon nitrate-nitrogen (NO3-N) and orthophosphate (PO4) loads in the Lower Yazoo River Watershed (LYRW), a local watershed in Mississippi, USA. Results showed that the 10 and 20% increases in rainfall rate, respectively, increased NO3-N load by 9.1 and 18% and PO4 load by 12 and 24% over a 10-year simulation period. In contrast, simultaneous increases in air temperature by 1.0 oC and rainfall rate by 10% as well as air temperature by 2.0 oC and rainfall rate by 20% increased NO3-N load by 12% and 20%%, and PO4 load by 14 and 26 %, respectively. A summer extreme rainfall scenario was created if a 10% increase in rainfall rate increased the total volume of rainwater for that summer by 10% or more. When this event occurred, it could increase the monthly loads of NO3-N and PO4, by 31 and 41%, respectively, for that summer. Therefore, the extreme rainfall events had tremendous impacts on the NO3-N and PO4 loads. It is apparent that CAT is a flexible and useful tool to modify historical rainfall and air temperature data to predict climate variability impacts on water quality for local watersheds.

Assessment of Surface Water Quality in the Big Sunflower River Watershed of Mississippi Delta Using Nonparametric Analysis.

Assessment of surface water quality in the Mississippi Delta is essential to quantify the eutrophication of the Gulf of Mexico. This study estimated the characteristics and variations of surface water quality at three study sites in the Big Sunflower River Watershed (BSRW) within the Mississippi Delta using Kruskal-Wallis, Dunn, Mann-Kendall, and Pettitt tests. In general, contents of some water quality constituents such as nitrate-nitrogen (NO 3 - N) and total phosphorus (TP) in the BSRW varied from site to site each year, whereas variations of other constituents such as pH and dissolved oxygen (DO) each year were basically not significant. The highest median concentrations were found in spring for NO 3 - Nand total nitrogen (TN); in summer for specific conductance (SC), Na, and Cl; and in winter for DO. Mann-Kendall trend analysis revealed that there was an increasing annual trend at Leland but a decreasing annual trend at Merigold for NO 3 - Nconcentrations even though such changes were very small, whereas there was no annual trend for TP at any of the three study sites. Pettitt's test further identified that the NO 3 - N concentrations had an abrupt increase in February 2009 at the median value of 0.44 mg L-1 in Leland and an abrupt decrease in June 2012 at the median value of 3.65 mg L-1 in Merigold. A very good linear correlation exited between total dissolved solid (TDS) and magnesium (Mg) in the BSRW, which could be used to estimate TDS from Mg concentrations for this watershed when the data for TDS are absent.

Identify temporal trend of air temperature and its impact on forest stream flow in Lower Mississippi River Alluvial Valley using wavelet analysis.

Characterization of stream flow is essential to water resource management, water supply planning, environmental protection, and ecological restoration; while air temperature variation due to climate change can exacerbate stream flow and add instability to the flow. In this study, the wavelet analysis technique was employed to identify temporal trend of air temperature and its impact upon forest stream flows in Lower Mississippi River Alluvial Valley (LMRAV). Four surface water monitoring stations, which locate near the headwater areas with very few land use disturbances and the long-term data records (60-90 years) in the LMRAV, were selected to obtain stream discharge and air temperature data. The wavelet analysis showed that air temperature had an increasing temporal trend around its mean value during the past several decades in the LMRAV, whereas stream flow had a decreasing temporal trend around its average value at the same time period in the same region. Results of this study demonstrated that the climate in the LMRAV did get warmer as time elapsed and the streams were drier as a result of warmer air temperature. This study further revealed that the best way to estimate the temporal trends of air temperature and stream flow was to perform the wavelet transformation around their mean values.

Influence of land use and land cover on the spatial variability of dissolved organic matter in multiple aquatic environments.

Water quality of lakes, estuaries, and coastal areas serves as an indicator of the overall health of aquatic ecosystems as well as the health of the terrestrial ecosystem that drains to the water body. Land use and land cover plays not only a significant role in controlling the quantity of the exported dissolved organic matter (DOM) but also influences the quality of DOM via various biogeochemical and biodegradation processes. We examined the characteristics and spatial distribution of DOM in five major lakes, in an estuary, and in the coastal waters of the Mississippi, USA, and investigated the influence of the land use and land cover of their watersheds on the DOM composition. We employed absorption and fluorescence spectroscopy including excitation-emission matrix (EEM) combined with parallel factor (PARAFAC) analysis modeling techniques to determine optical properties of DOM and its characteristics in this study. We developed a site-specific PARAFAC model to evaluate DOM characteristics resulting in five diverse DOM compositions that included two terrestrial humic-like (C1 and C3), two microbial humic-like (C2 and C5), and one protein-like (C4) DOM. Our results showed elevated fluorescence levels of microbial humic-like or protein-like DOM in the lakes and coastal waters, while the estuarine waters showed relatively high fluorescence levels of terrestrial humic-like DOM. The results also showed that percent forest and wetland coverage explained 68 and 82% variability, respectively, in terrestrial humic-like DOM exports, while 87% variability in microbially derived humiclike DOM was explained by percent agricultural lands. Strong correlations between microbial humic-like DOM and fluorescence-derived DOM indices such as biological index (BIX) and fluorescence index (FI) indicated autochthonous characteristics in the lakes, while the estuary showed largely allochthonous DOM of terrestrial origin. We also observed higher concentrations of total dissolved phosphorous (TDP) and ammonium nitrogen (NH4-N) in coastal waters potentially due to photodegradation of refractory DOM derived from the sediment-bound organic matter in the coastal wetlands. This study highlights the relationships between the DOM compositions in the water and the land use and land cover in the watershed. The spatial variability of DOM in three different types of aquatic environments enhances the understanding of the role of land use and land cover in carbon cycling through export of organic matter to the aquatic ecosystems..

Broiler Litter × Industrial By-Products Reduce Nutrients and Microbial Losses in Surface Runoff When Applied to Forages.

The inability to incorporate broiler litter (BL) into permanent hayfields and pastures leads to nutrient accumulation near the soil surface and increases the potential transport of nutrients in runoff. This study was conducted on Marietta silt loam soil to determine the effect of flue gas desulfurization (FGD) gypsum and lignite on P, N, C, and microbial concentrations in runoff. Treatments were (i) control (unfertilized) and (ii) BL at 13.4 Mg ha alone or (iii) treated with either FGD gypsum or lignite applied at 20% (w/w) (2.68 Mg ha). Rainfall simulators were used to produce a 5.6 cm h storm event sufficient in duration to cause 15 min of continuous runoff. Repeated rains were applied at 3-d intervals to determine how long FGD gypsum and lignite are effective in reducing loss of litter-derived N, P, and C from soil. Application of BL increased N, P, and C concentrations in runoff as compared to the control. Addition of FGD gypsum reduced ( < 0.05) water-soluble P and dissolved organic C concentrations in runoff by 39 and 16%, respectively, as compared to BL alone. Lignite reduced runoff total N and NH-N concentrations by 38 and 70%, respectively, as compared to BL alone. Addition of FGD gypsum or lignite failed to significantly reduce microbial loads in runoff, although both treatments reduced microbial concentration by >20%. Thus, BL treated with FGD and lignite can be considered as cost-effective management practices in the mitigation of P, N, and C and possibly microbial concentration in runoff.

Is there a common control mechanism for anti-saccades and reading eye movements? Evidence from distributional analyses.

In the saccadic literature, the voluntary control of eye movement involves inhibiting automatic saccadic plans. In contrast, the dominant view in reading is that linguistic processes trigger saccade planning. The present study explores the possibility of a common control mechanism, in which cognitively driven responses compete to inhibit automatic, perceptually driven saccade plans. A probabilistic model is developed to account for empirical distributions of saccadic response time in anti-saccade tasks (Studies 1 and 2) and fixation duration in reading and reading-like tasks (Studies 3 and 4). In all cases the distributions can be decomposed into a perceptually based component and a component sensitive to cognitive demands. Parametric similarities among the models strongly suggest a shared cognitive control mechanism between reading and other voluntary saccadic tasks.

Orthography and the development of reading processes: an eye-movement study of Chinese and English.

As children become proficient readers, there are substantial changes in the eye movements that subserve reading. Some of these changes reflect universal developmental factors while others may be specific to a particular writing system. This study attempts to disentangle effects of universal and script-dependent factors by comparing the development of eye movements of English and Chinese speakers. Third-grade (English: mean age = 9.1 years, n = 23; Chinese: mean age = 9.4 years, n = 25), fifth-grade (English: mean age = 11.2 years, n = 30; Chinese: mean age = 11.4, n = 25), and undergraduate students (English: n = 26; Chinese: n = 30) read stories in their native language while their eye movements were recorded. Results show a mixture of orthography-dependent factors with others that are remarkably parallel across these two very different writing systems. Orthographic effects are also more pronounced for children than for skilled adult readers. Implications for theories of reading eye movements and reading development are discussed.