Progress report for GS24-305
Project Information
Nitrogen (N) is often the limiting nutrient for plant growth in agricultural cropping systems. However, inorganic sources of N are prone to losses through leaching or volatilization, which has contributed to negative environmental effects such as greenhouse gas emissions and nutrient pollution. Identifying stable sources of bioavailable N will be critical to support sustainable intensification of cropping systems while also minimizing environmental impact. Recent discoveries have led to the understanding that plants can take up substantial amounts of N mobilized from generally slow-to-decompose forms of soil organic matter, including mineral-associated organic matter. The goal of this study is to examine the role that agricultural management plays in soil organic matter formation and soil organic N bioavailability. In this study, we will use high-dimensional, complex site-descriptive data from regional small-scale organic vegetables farms to provide information on the relationships between management practices and soil organic N pools and bioavailability. This study will provide an opportunity to form relationships with small-scale growers in the region and develop a survey approach to capture the complexity of agricultural management practices. We will also evaluate the role of organic input (compost, manure, etc.) diversity on soil organic matter formation and N bioavailability in an organic system. We will establish a replicated field study comparing different organic input sources and combinations. Ultimately, information from this study could inform management strategies to build reservoirs of soil organic N for sustainable N management in cropping systems.
- Provide an extension opportunity for small-scale farmers in Virginia to evaluate the influence of their own complex organic cropping systems on SOM formation.
- Develop a surveying approach to capture information on commonly applied organic inputs, crop rotations, and other management practices such as animal integration or tillage in small-scale organic vegetable systems.
- Provide information to participating farmers on how their management practices relate to on-farm variation in SOM amount and N bioavailability.
- Use high-dimensional site-descriptive data to provide a starting point for interpretation of relationships between complex management systems and SOM pools.
- Produce a factsheet reporting emerging patterns between management practices and SOM pool dynamics.
- Evaluate the role of organic input complexity on SOM
formation and N bioavailability in an organic system. For this objective, I hypothesize that overall higher complexity will promote the formation of SOM, and specifically MAOM, due to the potential for more diverse pathways of MAOM formation (Kleber et al., 2015).- Establish a replicated field study that isolates effects on organic input complexity on formation of SOM pools (total, particulate, and mineral-associated) and organic N bioavailability.
- Produce a primary research conference presentation and publication to disseminate findings.
Research
Site Description/Experimental Design
This study will take place throughout the Blacksburg, VA region. The climate in this region is subtropical humid with an average high temperature of 30° C, average low temperature of -5° C and average rainfall of 101 cm. There are 9 farms that have agreed to participate in the study: Virginia Tech Homefield Farm, Cedar Chest Farm, Riverstone Organic Farm, Kat the Farmer, Patchwork Farm, Garden Harvest Farm, Red Fern Farm, Crooked Porch Farm, and Glade Road Growing. We found 1-4 differently managed area at each farm from where we took samples.
Table 1: Farms participating in Objective 1 study.
| Farm | Location | Mapped soil series | Mapped soil order | Mapped A horizon texture |
| Virginia Tech Homefield Farm | Blacksburg, VA | Hayter, 2-7 percent slopes | Alfisol | Loam |
| Cedar Chest Farm | Blacksburg, VA | Guernsey, 2-7 percent slopes | Alfisol | Silt loam |
| Riverstone Organic Farm | Floyd, VA | Elsinboro, 3-8 percent slopes | Ultisol | Silt loam |
| Kat the Farmer | Check, VA | Glenelg, 8-15 percent slopes | Ultisol | Clay loam |
| Glade Road Growing | Blacksburg, VA | Groseclose and Poplimento, 2-7 percent slopes | Alfisol | Loam and silt loam |
| Red Fern Farm | Flyd, VA | Hatboro sandy loam, 0-3 percent slopes | Inceptisol | Silt loam |
| Garden Harvest Farm | Roanoke, VA | Chiswell-Litz-Urban land complex, 2-5 percent slopes | Inceptisol | Silt loam |
| Patchwork Farm | Copper Hill, VA | Watuga-Brownwood complex, 8-15 percent slopes | Ultisol | Loam |
| Crooked Porch Farm | Hillsville, VA | Comus fine sandy loam, floodplain | Inceptisol | Silt loam |
Methods
Farmer Interview: We interviewed each participating farmer to gather information on their cropping systems and management practices. Cropping system information included crop rotation, inclusion/exclusion of animals, tillage practices, and other land-use history. Information on the crop rotation includes how many different crops are grown in a year, the number of years in a rotation, and the species of crop grown. History of the farm will include how many years in production and land use before farm establishment, etc. This interview did not require an Institutional Review Board Approval.
Soil Sampling: Soils will be sampled twice a year. The farmer survey will be used to identify a time in crop rotations toward the end of the summer growing season after a cash crop harvest to do initial sampling and a time late winter to do the second soil sampling before spring planting starts. The goal of this timing is to minimize labile nitrogen that may be in the soil after a fertilizer application or cover crop termination to better understand the more permanent changes from management. Soil was sampled at 2 depths, 0-15 cm and 15-30 cm, within the rooting zone to better understand characteristics of the soil most accessible to plants.
Total C and N Analysis: We will analyze total C and N for the bulk SOM and for each SOM pool to better understand how management influences carbon and nitrogen within each SOM pool.
Bioavailable N: We will conduct a KCl extraction to better understand how much bioavailable N is in the soil.
Statistical Analysis
Multivariate statistic such as non-metric multidimensional scaling will be used to process collected high-dimensional, complex site descriptive data to find potential correlations between management practices (i.e. cover crop inclusion, crop rotational complexity, animal integration, etc.) and soil outcomes. The dependent variables will be SOM, SOM fractions, and total C and N. Briefly, non-metric multidimensional scaling is a multivariate statistical technique that determines similarity among multiple variables and uses the similarity ranking to find correlations (Dexter et al., 2018). We chose this statistical technique for its ability to navigate complex relationships among multiple ecological variables.
Educational & Outreach Activities
Participation Summary:
We conducted interviews with each farmer to better understand their growing practices.
Project Outcomes
I hope this project will contribute to a pool of information pertaining to small organic farmers as well as provide insight on how complexity of growing practices after soil health and soil nutrient availability.
So far, we have conducted interviews which has given me a better idea of the types of growing practices small organic vegetable farmers will use and why. I have also learned about certain challenges that were similar among farmers such as finding a good source for compost on a larger scale.