Soil health is always a good investment

As nursery growers, we ask a lot of our soils. They work for us 365 days a year and never take a break. Since crop growth and plant health are literally rooted in the soil, we need to consider what qualities make a soil ideal for plant growth and how we can help our soil reach its full potential. For nursery crops, the ideal soil will be loose and friable to support strong root growth yet should be well-structured to hold together when digging out root balls. It will also have high levels of biological activity and nutrient holding capacity while resisting pathogens and limiting weed growth. This may seem like a tall order, but focusing on practices that support soil health can have additive effects that can lead to real cost-saving benefits in the field.

“Soil health, also referred to as soil quality, is defined as the continued capacity of soil to function as a vital living ecosystem that sustains plants, animals & humans,” according to the USDA Natural Resource Conservation Service (NRCS).

We can think of soil health like a bank account. It requires some smart initial investments, but the benefits will pay dividends over the long term if we stay the course. The sooner you can start investing in soil health, the better off your plants will be. Improving soil health is a process that will require attention each year to build upon the initial investments, but employing a few simple, cost-effective strategies can go a long way toward enhancing this key resource.

While soil science is a vast and complex topic, improving soil health can be distilled down to two key strategies: 1. Minimizing soil disturbance. 2. Adding and maintaining high levels of organic matter.

Minimizing soil disturbance

Soil disturbance in a field nursery occurs through general field operations. Strategies to minimize soil losses and soil compaction are the first step to protect the valuable soil that is currently in your field. Soil losses from erosion can be caused by wind or water. Bare soil is more susceptible to erosion than soil that is covered with plants or mulch, and sloped land is also more vulnerable. On sloped lands, contour plantings can help to minimize erosion, especially in combination with field edge buffer strips. Vegetative buffers can slow runoff and trap sediment, which can significantly reduce soil losses. Planting turfgrass or other cover crops between rows will further help to conserve soil in production areas, while reducing the number of times that heavy equipment has to make passes on the field can help to reduce soil compaction. The impacts of soil compaction are also worse when the soil is wet, so putting equipment on the field when it is wet should be avoided entirely. If soil compaction becomes a problem, restricting root growth or water movement through the soil, corrective measures can be taken, including using a subsoiler to break up the compaction layer, combined with cover crops or other organic matter additions to help repair the damage. However, frequent tillage will deplete organic matter, disturb soil organisms, and reduce porosity, leading back to a cycle of compaction issues. Minimizing tillage and using equipment such as a spader instead of a roto-tiller when tillage is required can help to reduce these impacts.

Soil Organic Matter (SOM)

Perhaps the most essential component of soil health is soil organic matter (SOM), which refers to the living, and previously living, carbon-based components of the soil. This includes living organisms (i.e. plant roots, bacteria, and fungi), fresh residues (i.e. fresh leaves or grass clippings), and other components in various stages of decomposition. Adequate SOM enhances biological activity, improves soil structure, increases water holding capacity, sequesters carbon, and improves cation exchange capacity (CEC). Cation exchange capacity refers to the ability of SOM or other soil particles to hold onto cations (such as Ca²⁺, Mg²⁺, and K⁺) in a way that makes them available to plants and reduces the potential for leaching of these nutrients.

In field nurseries, soil removal when harvesting is somewhat unavoidable, but it can be mitigated by adding organic matter to build new soil. Compost can be added to the whole field or just to planting rows if material and transportation costs are an issue. Incorporating compost in a new field or between cropping cycles is a useful practice to compensate for soil lost from harvest and to restore organic matter to the fields. After the field has been planted, a row mulcher is a very useful piece of equipment that can be pulled behind a tractor down the aisles and side discharge compost or other organic mulches onto the planted rows. Compost should be tested for nutrients and pH before it is applied so that the supplemental fertility can be appropriately integrated into current fertilizer programs. Though organic mulches may require upfront costs, they can provide multiple cost-saving benefits throughout the season, including slow-release nutrition, reduced erosion, reduced weed growth, conserving soil moisture, and moderating soil temperature fluctuations.

Cover cropping for SOM

Cover crops offer another strategy to build SOM and stimulate microbial activity by deliberately growing plants to feed the soil. There are many different options of cover crops that are applicable for nurseries, with each one having specific qualities for soil health and management considerations. Cover crops can be used between cropping cycles and/or during crop production, either between rows or within a planted row. Developing a comprehensive cover cropping strategy based on your soil health goals and your unique farming system can be achieved with an understanding of what each cover crop has to offer.

Sorghum sudangrass (Sorghum bicolor x S. bicolor var. sudanese) is a common annual summer cover crop for field nurseries and is one of the best options for increasing organic matter and restoring depleted soils. Sorghum sudangrass can grow 5 to 12 feet tall and can add up to 5,000 lbs. of dry mass per acre, with a strong root system that can help to break up soil compaction. This cover crop is a great option for preparing fields for their next cropping cycle. It is best established in the spring, when soils have warmed, and allowed to grow through the whole season. Mowing during the season, when stalks are 3 to 4 feet tall encourages root growth and tillering. The plants can be disked in the fall or will winter-kill in northern climates. Sorghum sudangrass is also an option for planting in aisles, especially if it is managed by mowing throughout the season.

Cereal rye (Secale cereale), often referred to as winter rye, can be planted later in the season and survives the winter to help stabilize the soil and absorb excess nutrients that may still be in the field from the previous cropping system. Cereal rye will resume its growth in the spring, at which point it can be incorporated to add organic matter and release the nutrients that it had accumulated.

Forage radish (Raphanus sativus) is a cover crop that is often used to help break up soil compaction as it forms a thick root that grow 12 to 20 inches deep. Like rye, forage radish is also very good at taking up excess nitrogen, however, radish will not survive the winter, so it is best planted in the summer and allowed to grow through the season. The radish roots will decompose the following spring and release the nutrients that had accumulated.

Clovers (Trifolium spp.), including red clover, white clover, and crimson clover are legumes, meaning that they can fix nitrogen from the atmosphere. This N becomes a part of the plant and is eventually released into the soil as the clover breaks down. Clovers can be planted between cropping cycles or between rows of actively growing crops. White clover is the lowest growing and tolerates mowing and traffic well, making it the best option for living cover in the aisles.

Reaping the benefits

While it can be challenging to quantify the direct benefits of improving soil health, there are examples that we can use as a starting point. A 5-year study conducted at the Morton Arboretum found that additions of compost and wood chip mulch led to improvements in soil quality and increased growth of red maple (Acer rubrum) and river birch (Betula nigra) on depleted soils. After five years, trees mulched with wood chips had 170% greater biomass compared to untreated trees. Wood chip treatments also reduced soil bulk density by 10%, increased soil moisture by 26%, increased SOM by 25%, increased microbial respiration by 33%, and increased K by 24%. Compost additions improved tree biomass by 82% and resulted in 13% increased soil moisture, 57% increased SOM, 33% increased microbial respiration, 68% increased N, 1,544% increased P, and 64% increased K. They concluded that SOM increases were the single most important soil indicator for tree growth.

To see whether you are experiencing improvement on your own operation, consider keeping records that document field inputs such as woodchips or compost as well as cover crops grown in specific areas each year. Over time, you can compare outcomes such as year-to-year nursery crop yields from improved areas, or perhaps document cost-savings such as reduced time weeding or watering areas where you’ve invested in soil improvement.

Along with improving overall productivity, focusing on soil health is a worthwhile investment that can build resilience into nursery systems when extreme weather events occur. Increased levels of organic matter can enhance the water holding capacity of the soil, providing plants with enough water during periods of drought and reducing irrigation requirements. Additionally, increased porosity and infiltration associated with soil organic matter can help to reduce erosion, runoff, and flooding when excessive rainfall events occur.

The improvements realized by increasing SOM are dependent on many factors and will vary from farm to farm. The creative strategies by which SOM is managed will also take on many forms that are specific to each operation. However, the long-term impacts on soil quality, plant health, and farm system resilience cannot be overstated. Keeping good records, documenting the improvements in your soil and any associated changes in plant growth or water, fertilizer, or chemical use, will provide site-specific evidence that your investment in soil health is starting to pay off.

William Errickson is an agriculture agent and assistant professor at Rutgers Cooperative Extension of Monmouth County, located at the New Jersey Agricultural Experiment Station.