What We Do

Work in the Jacobsen Lab focuses on incorporating agroecological practices into intensive horticultural systems, and evaluating the effects on plant productivity, soil quality and nutrient cycling.  Much of our work incorporates systems-level study, and we frequently use interdisciplinary approaches to evaluate economic and ecological tradeoffs in conservation-oriented systems.   Most of Krista and her students’ work is in low external input (LEI) and organic systems, in the field and in controlled environments like high tunnels at the UK High Tunnel Research Facility.

Current Graduate Student Projects

Debendra - Debendra is focusing on the USDA Agriculture and Food Research Initiative (AFRI) awarded to Dr. Jacobsen in Spring 2014.

Rebecca Shelton - Project title, Investigating nitrogen dynamics and loss in conventionally and organically managed conservation agriculture systems with wheat and hairy vetch cover crops

Organic Field with different cover crop treatments established.

Conventional Field with small corn plants growing through the mulch of  terminated cover crops.

Unintentional nitrogen loss from agroecosystems is harmful to downstream environments and costly for farmers; therefore, adoption of conservation agricultural management practices, such as no-till, cover cropping, and inter-cropping, has increased recently among farmers of the United States.  However, the ecosystem consequences of adopting these practices has not been well-studied, and in practice, many different species of cover crop and combinations of these conservation techniques are employed, complicating the quantification of ecosystem benefits that they may provide.  This project examines nitrogen dynamics and loss associated with different agricultural management systems that vary in cover crop species (grass vs. legume), type of cover crop termination (herbicide vs. mowing), type of fertilizer used, and quantity of fertilizer applied.  Specifically, this project investigates nitrogen loss via leaching, volatilization, and denitrification while evaluating the nitrogen dynamics of plant uptake and cover crop decomposition in organic and conventional conservation agricultural corn systems with hairy vetch (a legume) and wheat (a grass)cover crops.  The overall objective of this research is to improve recommendations for best systemic management practices on the farm in order to increase nitrogen use efficiency while decreasing nitrogen loss and environmental impact.  

Former Graduate Student Projects

Kavita - Kavita successfully defended his thesis Spring 2014

Sampling spinach at time of harvest. These samples will be analyzed for leaf petiole nitrate to supplement soil-focused sampling efforts

Spinach just before harvest. The colored pin flags mark the different fertility treatments listed in the project description below.

Project Description: Practices such as movable high tunnels, incorporation of cover crops, and use of amendments to increase soil organic matter content have been suggested to mitigate the effects of intensive production on soils.  This study proposes to examine the effects of the varying environmental conditions, created in two types of tunnel system, movable and stationary, on the flow of nitrogen from amendment to plant and impact on soil quality.

Our chosen fertility treatments are meant to reflect an availability gradient from short to medium to long term availability and are as follows: Harmony, a common organic fertilizer; compost; a combination of Harmony and compost and a suite of inorganic treatments applied concurrently, Chilean Nitrate, KSO4 and CaPO4.  Each plot will be applied with one of the four treatments, randomly assigned in a typical bed.   Soil quality and nutrient availability will be evaluated by measuring a basic set of parameters associated with soil quality and soil microbial community structure.

Alex - Alex successfully defended his thesis entitled Reduced Tillage and Living Mulches in Organic Production Systems in Fall 2013. 

He researched the viability of living mulches and reduced tillage in diversified organic horticulture systems.

Transplanting peppers into tilled strip created by modified strip rototiller for a BCS 853 walk-behind tractor.

Dry beans and Peppers in early summer with  strip till and conventional plots, with living mulch (and weeds!) beginning to emerge between rows.

Project Description: 

Intensive soil tillage and mechanical cultivation are commonplace practices in most successful organic vegetable production systems.  Conservation tillage strategies like strip tillage minimize the spatial extent of soil disturbance and have worked well for many crops and regions.  For organic systems, however, weed suppression by cover crop residue can be inadequate, and high-residue cultivators are often inaccessible to Kentucky's many small-scale vegetable growers.  Living mulches grown between crop rows may improve weed control in conservation tillage systems, while contributing additional benefits to soil health and system diversity.  Competition for resources between a living mulch and the crop may be more readily mediated by equipment used on small farms rather than commercial operations.  My research explores strategies to integrate living mulches and conservation tillage strategies for organic bell pepper and heirloom dry bean production using standard and modified walk-behind tractor-mounted implements.  We are experimenting with variations in living mulch planting date, novel living mulch species, and adjusted fertility rates to identify the most successful combination of practices.  Periodic assessment of the spatial distribution of soil inorganic nitrogen via KCL extraction is combined with regular leaf-petiole nitrate analysis to shed light on crop performance and inform fertigation decisions.  Changes in weed biomass and community composition in the living mulch zone are also monitored throughout the season.  Soil aggregate stability and Permanganate-oxidizable Carbon (Pox-C) are our metrics of soil quality that can detect changes in soil organic matter content expected to occur during the two-year project timeframe.  Our goal is to contribute to a more thorough understanding of the ever-changing dynamics of crop-living mulch-weed interactions and develop proven recommendations to regional farmers interested in adopting conservation tillage or living mulch practices.


Vicky - Vicky successfully defended her thesis entitled Nitrogen Cycling, Plant Growth and Production of Secondary Compounds of Calendula officials in Organic Production Systems in Spring 2013. 

Vicky investigated organic fertility, drought, plant productivity and essential oil production in medicinal plant in organic greenhouse settings.

Calendula Officinalis

Project Description: I am investigating the interrelationship of organic nutrition and drought on the growth and productivity of the medicinal herb Calendula Officinalis L. in a greenhouse setting.  Calendula has been considered a medicinal herb since the time of Virgil and Pliny (and quite possibly before).  Calendula is believed to have a wide range of health benefits such as being anti-inflammatory, antimicrobial and anti-viral, to name only a few.   The medicinal properties are attributed to the essential oil which is distilled from the flowers.  This project observes the fate of nutrients in the soil by periodic extractions of inorganic nitrogen.  These are compared to the nutritional status of the crop by determining the stem nitrate.  Plant growth and development, and especially flowering are critical for the production of essential oil.  The composition of the volatile chemicals from the flowers can be used as an indicator of the overall essential oil composition and are being examined via SPME-GC-FID and GC-MS.  This will indicate how the bioactivity of the essential oil is shifted when plants are grown under nutrient or drought stress. 

In addition I am looking the performance of various organic greenhouse media and fertilizers in the production of ornamental calendula.  This project investigates the interface of media properties and nutrient availability and how this impacts the growth and development of an organic flowering crop.  This will be valuable data for those greenhouse managers who wish to fill a niche market for organically grown herbs or ornamentals.