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Repeated broiler litter application on agricultural lands can cause nutrient enrichment of subsurface effluent, especially with the existence of preferential flow through soil macropores. Previous studies quantifying soil macropores have not attempted to establish a connection of soil macropore characteristics with the subsurface nutrient (nitrogen [N] and phosphorus [P]) losses, across different topographical locations in the field. This study investigated the effect of broiler litter application and preferential flow on subsurface nutrient transport (N and P) at different topographical positions (upslope, midslope, and downslope) in a no‐till pasture field located in Alabama, USA. Twelve intact soil columns (150 mm id and 500 mm length) were used, and the nutrient leaching measurements from laboratory experiments were linked to soil macropore characteristics quantified using X‐ray computed tomography image analysis and solute transport modeling. Treatments included surface broadcast broiler litter (5 Mg ha−1, on dry basis) and unamended control. Leachates were analyzed for dissolved reactive P (DRP), total P (TP), and nitrate + nitrite‐N (NO3− + NO2−–N). The bromide breakthrough curves provided evidence of preferential flow in all columns. Litter application significantly increased leachate P concentrations, and average TP and DRP concentrations were significantly higher in the leachate from upslope columns compared to those at downslope location. The NO3−–N concentrations in leachate exceeded the US EPA drinking water standard of 10 mg L−1 in all the treatment columns. The highest flow‐weighted mean concentrations of TP and DRP, at 2.7 and 2.5 mg L−1, respectively, were recorded in the upslope columns. Soil physicochemical properties and nutrient leaching losses varied substantially across topographical positions, indicating a need for variable litter application rates to reduce P build‐up and subsequent leaching in vulnerable locations within the field. The relevance of the effect of topographic position on nutrient leaching found in this study should be further tested by investigating a wider range of slopes and soil types in pastures. Core Ideas: Phosphorus and nitrogen concentrations in the leachate varied as a function of slope position.Breakthrough curves and X‐ray computed tomography (CT) analysis provided evidence of preferential flow.Solute transport was well‐fitted by the two‐region physical nonequilibrium model.Broiler litter application significantly increased phosphorus leaching under saturated conditions. [ABSTRACT FROM AUTHOR]

Sediment fingerprinting is an extensively used approach for investigating sediment sources by linking in-stream sediment mixtures with watershed source materials. The overall goal of this research was to estimate the relative source contributions of stream banks and construction sites to the stream bed sediment in an urbanized watershed (Alabama, USA) using a fingerprinting technique established on composite fingerprints selected by two different machine learning techniques at a sub-watershed scale. The two statistical approaches employed to select the subset of fingerprinting properties were: (1) the Random Forest algorithm (RF) with Gini importance ranking of variables; and (2) logistic regression with the least absolute shrinkage and selection operator (LASSO). A Bayesian mixing model was then used to estimate the distribution of mixing proportions along with the associated uncertainty. The models were built based on the composite fingerprints selected using the two machine learning methods. Overall, using the subset of fingerprints selected by RF and LASSO, the relative contribution of stream banks ranged from 14±9% to 97±2% and from 24±18% to 94±5%, respectively, throughout the watershed. The stream bank contributions were compared with a previous study conducted in the watershed that utilized a two-step statistical procedure (which involved a Mann-Whitney U-test as the first step and discriminant function analysis (DFA) as the second step) to select the composite of fingerprinting properties and a frequentist mixing model to calculate the source apportionments. The relative contributions of stream banks to stream bed sediment in the previous study reported ranged from 9±8% to 100±1%. Therefore, the study demonstrated the dependence of source attributions on the statistical procedures used to select the optimum composite fingerprints for sediment fingerprinting applications. Furthermore, the results underscored the importance of using different mixing model structures to obtain reliable estimates of source contributions. [ABSTRACT FROM AUTHOR]

Use of broiler litter (BL) for agronomic purposes requires balancing the amount of nitrogen (N) needed to maximize crop yield while reducing environmental N footprints. This 2‐yr study (2018–2019) compared the effects of N source (BL or urea), application rate [0, 168, and 336 kg total N ha–1), and application timing (single or split) on corn (Zea mays L.) yield and environmental nitrogen loss (ENL) on three Alabama soil types. A field‐scale partial N budget was developed by accounting for known N inputs and outputs. The difference between the input and output in the partial N budget was considered as ENL, which comprised of N losses via runoff, leaching, volatilization, and denitrification. Application of BL increased corn yield relative to urea at only one site. At the responsive site, BL application rate had no significant effect on corn yield, but pre‐plant single application of BL produced 52% greater corn yield compared with split application. At other two sites where yield was lower for corn receiving BL, corn yield increased significantly with increasing BL application rate. Total N loss to the environment ranged between 32 and 52% of the N input. The influence of N source on ENL varied by site however losses increased with increasing N fertilization rates. Application timing did not influence ENL at two of three sites. This study showed that a lower application rate (168 kg ha–1) of BL prior to planting was a better management strategy for increasing corn yield, while reducing environmental N loss. Core Ideas: Broiler litter increased corn yield relative to urea only where soil N was nonlimiting.Split applications of broiler litter produced lower corn yield than single pre‐plant applications.Total N loss to the environment ranged from 32 to 52% of the N input.Nitrogen losses to the environment increased with increasing N application rate. [ABSTRACT FROM AUTHOR]