Authored By:

Miguel Castillo – Extension Forage & Grassland Management Specialist, Dept. of Crop & Soil

Owen Duckworth – Soil & Environmental Biogeochemistry, Dept. of Crop & Soil Sciences

Luke Gatiboni – Extension Soil Fertility Specialist, Dept. of Crop & Soil Sciences

Steph Kulesza – Extension Nutrient Management & Animal Waste, Dept. of Crop & Soil Sciences

Ekrem Ozlu – Extension Soil Management Specialist, Dept. of Crop & Soil Sciences

Austin Menker – Conservation Agriculture Extension Associate, Dept. of Crop & Soil Sciences

Chip Simmons – Extension Fresh Produce Food Safety, Dept. of Horticulture

Matthew Vann – Extension Leader, Dept. of Crop & Soil Sciences

Soil Fertility Assessment

(based on Agronomic Services- 2024 Hurricane Helene Soil Management)

Hurricane Helene caused great devastation throughout much of western NC. This situation calls for a vigilant approach to soil and crop management that includes assessment on a field-by-field basis.

Remove any visible debris from the field. Storm water is powerful and can push and float all kinds of debris into fields, including large objects such as cars. Debris may be buried and not noticed until future tillage operations. Growers should keep records of expenses incurred as related to restoration including debris removal. Documentation with pictures is encouraged. If there is reason to believe insurance claims can be made with any loss, contact your agent.

For areas where erosion has occurred, significant topsoil is lost. If so, phosphorus, potassium, and significant micronutrients such as manganese, zinc and copper, may have been removed. The remaining soil may have a low pH and nutrient content. If not being replaced by fill, soil sampling existing soil is strongly encouraged. Any fill for reconstruction purposes (grading, filling gullies) should be tested for general soil fertility prior to use. There are no state regulations on topsoil quality in NC, so it is buyer beware.

Sediment or soil eroding from other locations may be deposited over native soil in fields. This can potentially impact fertility. Since this deposition is often topsoil from other locations to floodplain areas, it may have high nutritive value. If predominantly sand has been deposited, it may have relatively low nutrient levels. Deposits may be seen visually over existing soil, but the depth of deposition cannot be accurately assessed. Use of a soil probe can be helpful. Probe down to see where the soil layer transitions into native soil and measure the depth of deposition. Use the following considerations in assessment and management.

• Maps can be drawn of depositions across a field as evaluated. Zones can possibly be created from this effort and may be helpful for future management decisions.
• 0 – 2 inches of deposition. Consider this to minimally impact drainage and fertility. It may be best to mix the overlying sediment with native soil with normal tillage using a disc or shallow tillage implement.
• 2 – 4 inches of deposition. Considerable deposition has occurred and may impact field management and crop production. If 3 or 4 inches of soil overlies the field, consider soil sampling this depth for soil fertility, especially for pH, phosphorus, and potassium levels. While sampling, take a sample from the next 3- or 4-inch depth for comparison purposes.
• More than 4 inches of deposition. Great deposition has occurred. Soil sample the deposited layer for soil fertility and evaluate.
• Movement of soil such as grading and other soil management such as tillage in such situations should be carefully evaluated on a site-by-site basis. Note textural / soil type differences when evaluating. Layers that are very different in texture could potentially cause drainage issues. If fieldwork is planned, wait until the soil is dry enough to reduce compaction.
• Soil stabilization is one of the first steps for the recovery of impacted areas. If possible, consider planting a cover crop with rapid growth and an extensive root system. It will help stabilize the soil, reduce erosion and stimulate soil biological activity.

In flooding situations, there are often concerns over pollutants in soils. Given the widespread origin of floodwaters, it is difficult to assess contamination of soils since various unknown chemicals can be associated with these events. If there are known chemicals of concern at a given location, use of a commercial environmental lab that offers analysis for contaminants is an option but can be expensive. Soil fertility labs do not offer this service. To initially evaluate crop growth impacts, plants such as wheat and soybeans can be grown in soil collected from fields of concern in a greenhouse setting to bioassay for materials toxic to plant growth.

Soil Contamination

To ensure food and feed safety, growers should wait 60 days after the flood waters have receded to plant any crop for human consumption or a crop that will be processed for animal feed, such as wheat for grain. To reduce this 60 day waiting period, deposited sediments can be tested for bacterial contamination. To do this, growers can submit a soil sample to a private lab that can test for generic E. coli, Salmonella, and shiga toxin-producing E. coli (STECs; specifically E. coli 0157:H7). Generic E. coli should be analyzed using a quantitative method and Salmonella and STECs can be analyzed using a presence/absence method. If the sample results show high generic E.coli (>1000 cfu) or presence of Salmonella or an STEC, tillage is recommended to encourage further breakdown and planting should be delayed until the full 60 days have passed. Animals should be excluded from previously flooded pastures for 60 days following a flood event. Vegetation should be removed and allowed to regrow for a minimum of two weeks prior to grazing. If you allow animals to graze previously flooded pastures or cover crops planted prior to 60 days after the event, be on the lookout for illness, stop grazing if animals start getting sick, and call a vet immediately. Find more recommendations on flood-damaged pastures and feed

Sediments should also be tested for heavy metal contamination. This analysis is not offered by NCDA&CS. So, you will also need to submit samples to a private lab for analysis. Sediments should be tested for lead, arsenic, cadmium and mercury at a minimum (listed as primary metals of concern in Table 1). Other heavy metals of concern could be copper, cobalt, nickel, antimony, selenium, vanadium, and zinc (listed as secondary metals of concern in Table 1). For agronomic purposes, a general fertility analysis will include zinc and copper and indicate whether there is a risk of zinc or copper toxicity. A list of certified laboratories can be found on the NC Department of Environmental Quality’s website. Note that not all of these labs will be able to perform every analysis. Consult the laboratory’s website and call prior to submitting a sample. If soil analysis results indicate sediments have levels above those listed in Table 1, consult someone with NC Extension to discuss further options.

Table 1. Screening levels for heavy metals in deposited sediments. Concentrations higher than the levels listed would necessitate further discussion about desired future use, crop selection, and remediation options.

Forage Establishment and Management Considerations

Helene’s pass left many damaged pastures, animal handling facilities, and infrastructure. Bottomlands received soil (and mud) at most likely record accumulation rates. As efforts continue to shift from rescue to recovery, the need for hay and fencing supplies to feed and manage livestock are becoming more apparent.

For information on planting rates, depth, best dates and possible dates for planting, as well as general recommendations by crop or time of the year, see the NC Extension Forage Planting Guide or the searchable online tool.

Early October, 2024, was a generally considered good time (specially temperature-wise) to plant cool-season annual forages in the Mountains. However, back then in early October and most likely still today as of late October, regular or normal activities to prepare a seedbed continue to be limited and must be accomplished considering the risks associated with unstable and uneven landscapes. If using a no-till drill is not possible, land and livestock managers should consider broadcasting as the planting method for rye, wheat, ryegrass, and/or clovers, especially in areas currently with bare soil that accumulated as a result of Helene’s pass, as a strategy to cover and hold the soil in place during winter, and to potentially provide some forage for grazing.

Planting during the November-February timeframe with the expectation of good crop germination, emergence, and growth, will be challenging in the Mountains mainly due to low temperatures, but also due to other challenges associated with unstable areas where it will be risky to run planting equipment. Cool-season forages show fastest and uniform germination when soil temperatures are approximately 50°F. From the end of October towards early November and onwards, soil temperatures are more frequently recorded at ≤50°F, hence erratic and slower germination rates of planted crops are likely to occur. Land and livestock managers can continuously check weather variables by accessing the State Climate Office ECONet weather station network. After germination, adequate weather conditions are needed for emergence and development of the planted forages; unfortunately, as time passes by, weather conditions are not the most conducive to support plant growth and development until spring. Frost-seeding rye (and other small grains), ryegrass or clover seed will be the best option to establish forages in mid-to late-winter and to try to get a head-start in spring 2025.

In the absence of forage available for grazing, or limited forage available in the field, livestock managers will most likely rely on conserved forages (i.e., hay or haylage) to support livestock needs during the winter. To donate or request hay and livestock assistance, sign up in the NCDA Livestock Assistance Form and check Livestock Donation Supply Sites. Also, please check with your local County Extension Office. Livestock can also be fed concentrates as a supplement but not as the sole source of feed. Ruminant livestock needs fiber in the diet (usually provided by the forages) to maintain good digestive health.

Cover Crop Establishment

Grasses and small grains will be the best option if there is an attempt to plant cool-season cover this fall due to their lower germination temperatures. Consider winter hardiness and winter kill temperature when selecting a species if overwintering is a priority.

No-till drill would be the most reliable method for planting but may not be an option for most farmers. If broadcasting, light incorporation after planting can improve results. Seed left on the soil surface is subject to morning dews and can expand then rupture if allowed to dry out during the day. Lack of precipitation remains a concern for thorough establishment. Ideally, the cover crop would be planted before a rain event for proper germination.

Seeding rates included in the NC Extension Forage Planting Guide should be recommended. Even if the goal is not forage, the current weather and field conditions warrant higher seeding rates to enhance the likelihood of success.

Due to weather and field conditions, successfully establishing fall-planted cover crops is not guaranteed. Farmers need to understand this risk if selecting this option. They also must be aware that allowing any successfully established cover to mature past the heading stage can introduce the risk of reseeding and volunteer establishment, which may not be desired.

While several clovers have minimum germination temperatures in the low 40s, it may be more effective to frost-seed them in late winter. This could be an option for several small grains as well. If you cannot plant immediately, waiting until late winter to early spring for frost-seeding may be best.

Listed online resources:

Planting Guide for Forages in North Carolina 

NCDA&CS Livestock Assistance Form

Livestock Donation Supply Sites

ECONet weather station network

Additional resources:
Cover Crop Species Selection Tool

Soil Testing: Agronomic Division Soil Testing – NCDA&CS

Regional Agronomists: Agronomic Division Field Services– NCDA&CS

N.C. Cooperative Extension Service

NC Soil and Water Conservation – NCDA&CS (For guidance on installation and remediation of conservation practices)

NC State -Agricultural Risk Management Brief: “In the Aftermath of a Hurricane Helene: What do Farmers with Crop Insurance need to do?”

FDA Guidance: Crops Harvested from Flooded Fields Intended for Animal Food: Questions and Answers

FDA Guidance: Guidance for Industry: Evaluating the Safety of Flood-affected Food Crops for Human Consumption

Produce Safety Alliance Guidance: Food Safety for Flooded Farms

Leafy Green Marketing Agreement Guidance: Flooding