Sumit Sen

Nutrient Loss in Leachate and Surface Runoff from Surface-Broadcast and Subsurface-Banded Broiler Litter

Subsurface band application of poultry litter has been shown to reduce the transport of nutrients from fields in surface runoff compared with conventional surface broadcast application. Little research has been conducted to determine the effects of surface broadcast application and subsurface banding of litter on nutrients in leachate. Therefore, a field experiment was conducted to determine the effects of subsurface band application and surface broadcast application of poultry litter on nutrient losses in leachate. Zero-tension pan and passive capillary fiberglass wick lysimeters were installed in situ 50 cm beneath the soil surface of an established tall fescue ( Schreb.) pasture on a sandy loam soil. The treatments were surface broadcast and subsurface-banded poultry litter at 5 Mg ha and an unfertilized control. Results of the rainfall simulations showed that the concentrations of PO-P and total phosphorus (TP) in leachate were reduced by 96 and 37%, respectively, in subsurface-banded litter treatment compared with the surface-applied litter treatment. There was no significant difference in PO-P concentration between control and subsurface-banded litter treatment in leachate. The trend in the loading of nutrients in leachate was similar to the trend in concentration. Concentration and loading of the nutrients (TP, PO-P, NH-N, and NO-N) in runoff from the subsurface-banded treatment were significantly less than for the surface-applied treatment and were similar to those from control plots. These results show that, compared with conventional surface broadcast application of litter, subsurface band application of litter can greatly reduce loss of P in surface runoff and leachate.

Watershed-level comparison of predictability and sensitivity of two phosphorus models.

Buildup of phosphorus (P) in agricultural soils and transport of P to nearby surface waters due to excessive, long-term application of poultry litter is an environmental concern in many poultry-producing states. Watershed models are often used to quantify soil and water quality impacts of poultry litter applications. However, depending on how P transport is simulated in watershed models, the anticipated impact could be quite different. The objective of this study was to determine the predictability and sensitivity of the Soil and Water Assessment Tool (SWAT) P model and a newly developed, state-of-the-art manure P model called SurPhos in a poultry litter-applied pasture watershed. A small, predominantly agricultural watershed in Randolph County, Alabama was used for this study. The SWAT model, calibrated for surface runoff and total stream flows (Nash-Sutcliffe coefficient of 0.70 for both), was used to provide runoff inputs to the SurPhos model. Total dissolved P (TDP) exports simulated by the SWAT P and SurPhos models from the hay hydrological response units of the watershed were compared for different poultry litter application rates and different initial soil Solution P levels. Both models showed sensitivity to poultry litter application rates, with SWAT simulating linear and SurPhos simulating nonlinear increases in TDP exports with increase in poultry litter application rates. SWAT showed greater sensitivity to initial soil Solution P levels, which can lead to overestimation of TDP exports, especially at low poultry litter application rates. As opposed to the SurPhos model simulations and contrary to recent studies, SWAT simulated excessive accumulation of Solution P in the top 10 mm of soil. Because SurPhos appears to simulate P transport and build-up processes from manure-applied areas more accurately, this study suggests that SWAT be replaced by SurPhos to more accurately determine watershed-level effectiveness of P management measures.

Surface Transport of Nutrients from Surface-Broadcast and Subsurface-Banded Broiler Litter

Nutrient buildup, mainly phosphorus (P), and loss from fields fertilized with poultry (broiler) litter contribute to eutrophication of surface waters. In the U.S., broiler litter is typically surface-applied, but recently, to reduce surface transport of P and other nutrients, subsurface-banding of broiler litter has been promoted as a new manure application method. The objective of this study was to evaluate differences in nutrient transport between subsurface-banded and surface-applied broiler litter in a tall fescue pasture. Treatments were surface-applied and subsurface-banded broiler litter at a rate of 5.0 Mg ha-1, and no application of litter (control). Results showed that runoff concentrations and loadings of total P (TP), ortho-P (PO4-P), nitrate-nitrogen (NO3-N), and ammonium-N (NH4-N) were reduced by 83%, 88%, 74%, and 80%, respectively, for the subsurface-banded litter as compared to the surface-applied litter. Concentrations and loadings of all nutrients in surface runoff from the subsurface-banded treatment were similar to those from the control. This study showed that subsurface banding of broiler litter can substantially reduce nutrient losses in surface runoff. However, since less than 10% of the simulated rainfall contributed to surface runoff (more than 90% rainfall infiltrated), subsurface transport of nutrients from surface-applied and subsurface-banded litter needs to be studied in field research.

Analysis of Spring Discharge in the Lesser Himalayas: A Case Study of Mathamali Spring, Aglar Watershed, Uttarakhand

In a hilly terrain, water from spring is one of the main sources of domestic water supply. There is a huge concern in relation to spring discharge, i.e. drying up or becoming seasonal in this region. For better understanding of spring discharge behaviour, this study applied various methods of recession curve and time series. Specific objectives of this study are (i) to compare recession curves using simple exponential, hyperbola and least square methods, (ii) to develop the autocorrelation of spring discharge and rainfall series and (iii) to analyse the flow duration curve using mean daily spring discharge data. A fracture- and contact-type spring located in the Aglar watershed of the Yamuna River basin has been instrumented for collection of continuous discharge data (Feb 2014–July 2015). Recession curve analysis using the method of least square found to be more accurate than exponential and hyperbola for six selected events with NSE (0.82–0.94) and RMSE (0.14–1.08). Flow duration curve analysis reveals that 90% of measured data is less than 23 lpm which can be taken as the characteristic value for minimum spring flow. Results of this study will be useful for conserving the spring discharge during the monsoon period and for various watershed management practices, such as developing a sustainable irrigation system.

Understanding plot-scale hydrology of Lesser Himalayan watershed-A field study and HYDRUS-2D modelling approach

Department of Hydrology, Indian Institute of Technology Roorkee, Roorkee, Uttarakhand 247667, India Scientist‐E, National Institute of Hydrology, Roorkee, Uttarakhand 247667, India Correspondence Sumit Sen, Department of Hydrology, Indian Institute of Technology Roorkee, Roorkee 247667, Uttarakhand, India. Email: ssenhfhy@iitr.ac.in Funding information Indian Institute of Technology Roorkee, Grant/Award Numbers: FIG#100582, Grant F. I.G‐100582; Science and Engineering Research Board, Grant/Award Number: SER‐776 Grant SER‐776; Department of Science and Technology

Spatial-Temporal Variability and Hydrologic Connectivity of Runoff Generation Areas in Sand Mountain Region of Alabama

This study delineated spatially- and temporally-variable runoff generation areas in the Sand Mountain region of North Alabama under natural rainfall conditions and demonstrated that hydrologic connectivity is important for generating hillslope response when infiltration-excess runoff mechanism dominates. Data from four rainfall events (rainfall amounts 1.4 – 3.2 cm) on an intensively-instrumented pasture hillslope (0.12 ha) were analyzed. Two of these rainfall events occurred in the summer months, while the two others occurred in the winter months. Analysis of data from surface runoff sensors, tipping bucket rain gauge, and HS-flume demonstrated spatial and temporal variability in runoff generation areas. Results showed that the maximum runoff generation area, which contributed to runoff at the outlet of the hillslope varied between 87 to 100%. Furthermore, because infiltration-excess was the main runoff generation mechanism on the hillslope, the data showed that, as the rainfall intensity changed during a rainfall event, the runoff generation areas expanded or contracted. During rainfall events with high-intensity short- to medium-duration, 4 to 8% of total rainfall was converted to runoff at the outlet. Rainfall events with medium- to low-intensity, medium duration were found less likely to generate runoff at the outlet. In situ soil hydraulic conductivity (k) measured and interpolated across the hillslope confirmed hydrologic connectivity of the runoff generation areas. Combined surface runoff sensor and ln(k) interpolated data clearly showed that during a rainfall event, lower k areas start generating runoff first, and then, depending on rainfall intensity during the event, runoff at the outlet is generated by hydrologically connected areas. It was concluded that in infiltration-excess runoff dominated areas, rainfall intensity and soil hydraulic conductivity can explain hydrologic response. The study demonstrated that only hydrologically connected areas of low hydraulic conductivity generate surface runoff during high intensity rainfall events. Quantification of these areas would serve as an important foundation for controlling nonpoint source pollution.

Runoff Generation Mechanism in the Appalachian Plateau Region of Alabama – A Field Investigation

Alabama is one of the largest poultry producing state in the country. However, excessive land application of litter to pastures in Alabama has resulted in buildup of phosphorus (P) in soils of major poultry producing counties located in the Appalachian Plateau region in North Alabama. Alabama has developed P-index to alleviate water quality impacts of P loss from soils. Alabamas P-index is based on agronomic soil P thresholds and treats an entire field as the surface runoff (and P) contributing area. This approach often leads to over application of litter to areas with high probability of P loss via surface runoff and an improper and incomplete assessment of fields for litter application. Since the primary mechanism of P transport is surface runoff, it is important to identify hydrologically active areas (HAAs) and the surface runoff generation mechanisms within a field. Through an intensively-instrumented field study we are identifying HAAs. Specific objective of this study is to delineate spatial and temporal distribution of HAAs and identify surface runoff generation mechanism (infiltration excess vs. saturation excess) using distributed sensors. Results from two events showed that the surface runoff generation mechanism is mostly infiltration excess. During intense storm (e.g., Event 1) surface runoff was observed from fairly large areas within the field. For these events, the surface runoff generation areas originated at the same location and expanded and contracted depending on the rainfall and other hydrologic characteristics. Certain hydrologic characteristics (e.g., rainfall intensity, antecedent soil moisture conditions, saturated hydraulic conductivity and presence of sandstone layer) seem to play dominant role in surface runoff generation in this region. Thus, this study demonstrates that spatial and temporal distribution of HAAs can be characterized. If spatial and temporal distribution of HAAs can be predicted by a few key variables, it will have a huge impact on the management of P from land-applied poultry litter. Hence, this study will greatly contribute to science-based decision making and will increase the acceptability of Federal and State regulations that are based on sound science.