ERI_Grid_UMESCombining Electrical Resistivity Imaging and Conservative Tracers to Characterize Subsurface Phosphorus Losses from Drained Soils.

Funding agency: Delmarva Land Grant Universities Seed Grant Program; USDA Agricultural Food and Research Initiative (AFRI) Foundational Program

Project cooperators: A. Buda, R. Bryant (USDA-ARS); L. Slater, J. Robinson, D. Ntalgliannis (Rutgers – Newark); A. Allen, A. Collick (Univ. Maryland Eastern Shore)

Long-term application of poultry litter application to agricultural soils on Delmarva has led to a build-up of soil test P to levels and an increased risk of P losses to sensitive waterbodies. Subsurface lateral flow pathways can deliver significant P loads from high P agricultural soils in artificially ditch-drained agricultural soils with high soil test P. However, the mechanisms of subsurface P transport are poorly understood. Electrical resistivity imaging is paired with a conservative salt tracer to track subsurface water flow towards agricultural ditches. Results will provide information about how and when P moves in subsurface lateral flow, which can be used to more accurately assess risk for subsurface P transport in the Delaware P Index and improve management of legacy P.


Developing best management practices to reduce nonpoint source pollution through effective ditch management.

Funding agency: Delaware Department of Natural Resources and Environmental Control

Evaluation of Seeding Rate and Method on Establishment of Cover Crops in Delaware.

Funding Agency: USDA Natural Resources Conservation Service.

Quantifying the effects of irrigation and fertigation on nutrient use efficiency in corn.Irrigation Collage_shober research

Funding agency: Delaware Department of Natural Resources and Environmental Control

Final Report

Inefficient use of nitrogen (N) in agronomic crop production can lead to water quality concerns and reduced yields for growers. Nitrogen fertilizer left in the soil after harvest is highly mobile and can leach to groundwater or is subject to gaseous loss. Split applications of N can better match N fertilizer applications with corn N uptake needs and improve N use efficiency. The objective of this study was to quantify the effect of N rate, timing, and application method under central pivot and subsurface drip irrigation on corn grain yield and N use efficiency in Delaware. All plots (with exception of the 0 N control) received pre-plant manure (94 kg/ha plant available N) and starter N fertilizer (N rate = 34 kg/ha). Additional plots received in-season N fertilizer applications below, at, or above current Delaware N recommendations for a realistic goal of 16 Mg/ha.

Grain yield was determined for each treatment using a weigh wagon. Pre-plant soil, post-harvest grain and residue were collected then analyzed for total N to determine N use efficiency by difference and mass balance methods. In 2014, plots receiving in-season applications of N out yielded plots receiving only manure and starter N (17 vs. 15 Mg ha-1 grain for yield goal of 16 Mg ha-1). Timing and rate of N application in-season did not affect yield. Exceptional growing conditions pushed N efficiency values over 100% for most treatments, suggesting mineralization of manure N was adequate to sustain high yields.

Refining and harmonizing phosphorus indices in the Chesapeake Bay region to improve critical source area identification and to address nutrient management priorities.

This three-year multistate project was initiated in 2012 in the six states within the Chesapeake Bay Watershed (DE, MD, PA, NY, VA, WV). The project seeks to 1) evaluate current Phosphorus Index tools in the upper Nanticoke subwatershed (and other selected subwatersheds) using a watershed model, 2) refine P indices regional, and 3) validate the revised tool. This project will result in an updated P index tool, which will be used to improve agricultural P management in Delaware. I serve as a Co-PI on this project with responsibility for collecting data to input into the model from growers and state agencies. Within Delaware, I work cooperatively with Dr. Tom Sims (Co-PI), Jennifer Volk, and Kathryn Clark (M.S. student under my supervision). We work regionally with scientist from all six Chesapeake Bay states.

The project is currently supported by the United States Department of Agriculture Natural Resources Conservation Service ($138,397 UD subaward; $801,535 total award) through the nationally competitive Conservation Innovation Grant program. Dr. Doug Beegle and Dr. Peter Kleinman serves as project PIs on the main award.

Targeted Conservation Contracts to Enhance Agricultural Best Management Practices: Incorporating Heterogeneity and Predicting Additionality

Funding agency: USDA Agricultural Food and Research Initiative (AFRI) Foundational Program.

Trends in Soil Test Phosphorous and Sorption Capacity following Long-term Application of Poultry Litter and Commercial Fertilizers.

Funding agency: Maryland Grain Producers Utilization Board

The risk for dissolved and particulate losses is increased from agricultural soils with excessive STP concentrations (Sims, 1998; Sims et al., 2000). However, we do not fully understand how soil P cycling is influenced under P build-up (repeated manure or fertilizer applications) or draw-down (crop removal once P applications are stopped). Recent research suggests that the equilibrium among soil P pools may shift as STP increases, leading to a redistribution of P among the soluble (plant available) and more resistant pools (plant unavailable) of P (J. McGrath, personal communication; Binford et al., unpublished data). Significant shifts in soil P equilibrium may restrict the amount of soluble soil P available to growing crops should applications of manure or fertilizer to high P soils cease.

As such, the use of agronomic STP (Mehlich 3) as an estimation of P risk may overestimate the risk at sites with soil test P values in the excessive soil test range. We hypothesize that repeated application of manure/fertilizer will reduce capacity of soil to adsorb P and lead to a shift of soluble P to more recalcitrant pools (plant unavailable). Selected historical soil samples from long-term (15+ year) P research field sites maintained by researchers at UD (build-up) and University of Maryland (draw-down) will be analyzed for water extractable P (Self-Davis et al., 2009) to track changes in soluble P over time. Phosphorus fractionation (modified Hedley fractionation; Welsh et al., 2009) will be used to elucidate changes in distribution of P among different operational soil pools. We will also determine soil sorption/desorption characteristics (Graetz and Nair, 2000) to estimate the potential for these soils to sorb additional P. Phosphorus dynamics will be compared under build-up and draw-down scenarios to better guide management of legacy P soils.

Using Silicon Fertilizers to Improve Soil Phosphorus Availability and Uptake by Winter Wheat in High Phosphorus Soils.

Funding agency: Northeast SARE Graduate Student Grant (awarded to Z. Qin)

Many farmers (and results of some regional research) tout the benefits of starter P fertilizers to winter wheat grown on excessive STP soils to combat early season P deficiency and ensure good fall tillering, which is vital for maximizing yield (Alley et al., 2009). Early season P deficiency is related to cool soil temperatures at the time winter wheat is planted and the fact that that significantly amount of P are strongly bonded with iron (Fe) and aluminum (Al) in acid legacy P soils. However, applications of P fertilizer to legacy P soils are often considered taboo because they may further enrich soils with P. Silicon (Si) fertilization is promising as a BMP that can help enhance crop P uptake, eliminate fall starter-P applications for small grains, and improve small grain yields (Heckman, 2012).

Previous researchers reported increased concentrations of P in plant tissue for corn (Owino-Gerroh and Gascho, 2004), grass species (Eneji et al., 2008), and wheat (Heckman, 2012) following Si fertilization. However, other studies reported decreased plant P uptake following application of Si to rice (Ma and Takahashi, 1990) and corn (Gao et al., 2004). In light of contradicting reports of the effects of Si on crop P uptake, we suggest that more research is needed to evaluate the effect of Si addition on soil P dynamics and P uptake of winter wheat (commonly grown in Delmarva as part of a corn-soybean-small grain rotation), especially for acid soils with excessive STP concentrations. We hypothesize that Si addition will increase soil P availability by replacing adsorbed P on the soil exchange complex (Koski-Vahala et al., 2001) and enhance P uptake by winter wheat in high P soils. We propose to conduct a pot study designed to determine the effects of soil STP concentration (100 – 1000 FIV Mehlich 3), Si fertilizer sources (calcium silicate, silica gel, silicic acid) and Si rate (three rates based on initial soil pH) on soil P dynamics, wheat P uptake, and wheat yield. Soil samples will be analyzed for water extractable P and acetic acid Si periodically. In addition, P fractionation (Welsh et al., 2009) and P isotherms (Graetz and Nair, 2000) will be used to study Si effects on P dynamics. Wheat tissue samples will be analyzed for total Si and P (Seyfferth and Fendorf, 2012) to evaluate plant P uptake after Si addition. A corresponding field trial will extend the pot study determine the utility of applying locally available Si sources (e.g., calcium silicate) to winter wheat under field conditions. Results from this project will help to develop a novel BMP that can help farmers reduce the environmental risks associated with legacy P soils, increase crop uptake of P to speed draw down of soil test P levels, and enhance winter wheat yields.
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