Nutrient Management and Control Strategies in the Susquehanna River Basin Towards Meeting Chesapeake Bay TMDL Goals
Open Access
- Author:
- Saha, Arghajeet
- Graduate Program:
- Agricultural and Biological Engineering (PHD)
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- June 20, 2022
- Committee Members:
- Tameria Veith, Major Field Member
Cibin Raj, Chair & Dissertation Advisor
Charlie White, Outside Field Member
Patrick Drohan, Outside Unit & Field Member
Suat Irmak, Program Head/Chair - Keywords:
- Manureshed
SWAT
Nutrient Management
Soil Taxonomy
Manure Timing - Abstract:
- Manure management is a major sustainability challenge in livestock-intensive agricultural regions, a product of the specialization and intensification of modern production systems. Nutrient imbalance and excess application of manure to field crops in the livestock intensive regions of Susquehanna River Basin (SRB) has led to nutrient enrichment in its local waters, as well as in surface waters delivered to the Chesapeake Bay. The delivery of excess nutrients from the SRB is significant in generating hypoxic water conditions in the Bay. Notwithstanding having more than 30 years of research and funding invested in improving the water quality of the Chesapeake Bay, the overall health continues to remain degraded. Restoration of the Bay is essential and requires inventive nutrient management approaches to control the nutrient loadings at various spatial and temporal scales in the SRB. Improving sustainable manure nutrient management in the SRB can play a vital role in reducing excess nitrogen (N) and phosphorus (P) loads delivered to the Bay. The overarching goal of our research was to develop manure nutrient management strategies for SRB and to quantify the potential water quality benefits derived from the strategies through scenario-based simulation modeling analyses. A comprehensive Soil and Water Assessment Tool (SWAT) model was developed for SRB and used for scenario analysis. To aid in model development, we devised a new taxonomically based soil dataset that minimized problems associated with many soil types and misrepresentations of soil identifiers across political borders in SSURGO data. The direct application of SSURGO increases spatial discretization in model which will increase computational cost. The developed taxonomic soil data acted as a suitable alternative since it was computationally efficient, in addition to being comparable to SSURGO in its representation of soil, hydrological and water quality metrics. The SRB SWAT model was developed to represent land use, land management and conservation practices, and fertilizer sources commonly prevalent in the watershed. The comprehensive SWAT model was able to represent over 144,473 spatial simulation units across the watershed. The first set of six manure nutrient management scenarios was based on the ‘manureshed’ concept, developed towards generating sustainable manure balanced systems by connecting crop areas (nutrient sinks) with livestock agriculture (nutrient sources). The manureshed scenarios conceptualized were (i) “Business-as-usual” which assumes manure is not transportable across sub-watershed boundaries and some areas have excess manure application than crop demand, (ii) “Watershed nutrient balance” which assumes excess manure from surplus areas are transportable and applied to crop areas based on nutrient demand, (iii) “Watershed nutrient balance avoiding runoff prone areas” which assumes manure is transportable and applied based on agronomic demand, but not applied in vulnerable landscapes. Manure application rates were calculated considering both N-based and P-based crop nutrient demands, totaling six manure application scenarios. The N-based business-as-usual scenario was considered as the model baseline. The crop N-based manure application applied excess P and P-based application needed supplemental N inorganic fertilizer application to meet crop nutrient demand. The manure redistribution scenarios decreased nutrient loads at the watershed outlet compared to the baseline. The P-based manureshed scenarios reduced manure nutrient (N and P) loadings (3% -25.2%) at the watershed outlet. P-based manuresheds that reallocated manure throughout the SRB based on agronomic P need and avoiding runoff prone areas satisfied agronomic need throughout the SRB and reduced inorganic fertilizer use to supplemental N. The second set of nutrient management scenarios aimed to explore the potential water quality impacts of manure application strategies considering the 4Rs of nutrient stewardship i.e., manure of right quantity applied at the right time and right place. A manure application timing scenario was developed considering antecedent moisture conditions and precipitation potential after manure application. The results compared with the business-as-usual baseline indicated that strategically timed nutrient application considering weather and nutrient demand lowered loading at the SRB outlet by 4% for N and 6% for P. Winter closure for manure having spring only application across the SRB showed an increase in crop nutrient uptake and yield and reduced annual nutrient loads delivered to the Bay from SRB. An incorporation scenario, where manure was applied below 10 mm in the soil, increased nitrate loss through leachate but showed significant reduction (9-53%) in nutrient (N and P) loss through surface runoff compared to the baseline. The practical application of this research would involve the utilization of results by policy planners, working groups, and landowners for developing sustainable nutrient management plans. However, successful implementation of this research will also be dependent of local level cost, science available for successful implementation, and engagement of farming communities.