Red raspberry is a high-value, economically important crop in northwestern Washington State. In 2017, 9600 acres of red raspberry were harvested in Washington, with a value of more than $52 million (U.S. Department of Agriculture, 2018). The majority of red raspberry grown in Washington is for processing, not fresh market. Red raspberry is a high-maintenance perennial crop. Growers rely heavily on years of experience and specific management practices to produce high-yielding and high-quality crops. Many of those practices are common in modern agriculture, but they can be detrimental to soil quality.
Soil quality, or soil health, has been defined as the “continued capacity of the soil to function” as a living ecosystem that sustains plants, animals, and humans (Karlen et al., 1997; U.S. Department of Agriculture, 2017). For the purposes of this survey, we used the term “soil quality,” but we recognize that the term “soil health” is often used or preferred. Physical, chemical, and biological soil properties are taken into account when considering soil quality. Red raspberry growers must manage all three properties of the soil to ensure a productive crop.
It is common for Washington growers to maintain the same red raspberry planting for 4 years or more. Because suitable land for red raspberry is limited in the region, growers frequently replant red raspberry after removing the previous red raspberry planting. After the last harvest of a red raspberry planting (late summer to early fall), growers remove the posts and trellising wire, mow the old canes, incorporate the old planting material into the soil, and deep-rip to disrupt hard pans. Many growers will then prepare the site for fumigation, fumigate, and/or plant a cover crop during the fall. Others may wait until spring to fumigate. In both cases, the soil is tilled in the spring, beds are shaped, red raspberry is planted, and new posts and trellising wire are put in place. Soil tillage and fumigation are two management practices that are central to the production of red raspberry in Washington State.
Tillage is heavily relied on in the red raspberry production system before planting and after a planting has been established. From the time a planting is removed in the fall until replanting in the spring, at least three tillage events can occur, such as deep ripping, cultivation before fumigation, disking to incorporate the winter cover crop, and bed formation. When a planting is established, red raspberry growers frequently practice alleyway (the area between the red raspberry beds where machinery passes; ≈6 ft wide) tillage to manage weeds. Although tillage can be useful for achieving the production goals outlined here, repeated tillage can also cause soil compaction and contribute to the loss of the physical structure of the soil (Magdoff and Van Es, 2009). Tillage can increase soil erosion, particularly of soil organic matter, which resides on or near the surface, which leads to the loss of soil quality and productivity (Bauer and Black, 1994; Pierce and Lal, 1994). An estimated loss of 30% to 50% of soil carbon has also been attributed to intensive tillage of agricultural soils (Schlesinger, 1986). Additionally, the repeated use of heavy machinery may lead to increased soil compaction, which can affect crop performance and yield (Raper, 2005; Voorhees et al., 1979). For red raspberry, at least 10 to 12 harvest events occur over the course of 4 weeks, which are all conducted using harvest equipment.
One countermeasure to repeated and frequent tillage after establishing a red raspberry planting would be seeding an alleyway groundcover or cover crop. A cover crop is a living groundcover that can be planted with, before, or after the main cash crop. An alleyway cover crop could be planted adjacent to the red raspberry crop and mowed periodically rather than tilled or incorporated into the soil. In conversations with many red raspberry growers, they cited concerns that an alleyway cover crop could be detrimental to crop productivity by competing for water and nutrients, similar to weeds. Growers are also concerned that an alleyway cover crop could increase population densities of root lesion nematode [RLN (Pratylenchus penetrans)], a ubiquitous plant-parasitic nematode in the region. This nematode has a wide host range, including red raspberry and many common cover crop species, and it is thought to be a major contributor to red raspberry crop decline (McElroy, 1977; Pinkerton et al., 2009; Zasada et al., 2015). By feeding on roots, RLN can cause plants to weaken, produce less fruit, and eventually die. In a recent field study in which nine different cover crops grown in the alleyways between red raspberry beds were evaluated, no differences in fruit yield or RLN population densities were observed compared with bare tilled soil (Rudolph et al., 2017). Alleyway cover cropping has the potential to reduce soil erosion during wet winters and dry summers and lessen soil compaction and bulk density.
The primary method that red raspberry growers use to manage RLN and other soilborne pathogens, including root rot (Phytophthora rubi), is soil fumigation before establishing a new planting (Walters et al., 2017). Soil fumigation is the application of pesticides directly to the soil in the form of a gas or liquid. Commonly used soil fumigants in the red raspberry production system include 1,3-dichloropropene (a nematicide), chloropicrin (a fungicide), and metam sodium (a broad-spectrum nematicide and fungicide). Fumigation can help delay the infection of plants by soilborne diseases for a few years, but it does not eliminate the organisms that cause disease (Walters et al., 2017). Soil fumigation requires further soil disruption, and it can negatively affect the beneficial soil microbial population. Because soil fumigants are broad-spectrum, they also have nontarget effects on nonpathogenic microorganisms that may be important to maintaining biological soil health (Collins et al., 2006; Gamliel et al., 2000).
Another important component in the red raspberry production system is weed management. As previously mentioned, tillage is used to achieve weed management; however, herbicides are also used. Red raspberry growers traditionally manage in-row weeds through a combination of pre-emergent and postemergent herbicides (Galinato and DeVetter, 2016). Simazine is one of the most widely used preplant herbicides. Because of the sprawling growth habit of first-year primocanes, weed management following planting and during the year of establishment is usually performed by manual laborers to avoid chemical injury from herbicide contact. After establishment, in-row weeds are often managed through contact herbicides. Concern regarding contact herbicides and establishing raspberry are minimal because growers typically remove the first few flushes of primocane growth through the practice of primocane burning (Barney et al., 2007).
Although tillage, fumigation, and herbicide practices by red raspberry growers are relatively well-known by researchers, they are largely observational and not well-documented. By working with growers over the past decade and discussing their field management plans, certain methods have been observed as common practice among conventional red raspberry growers. However, it has been unknown whether red raspberry growers perceive soil quality as important. The objectives of this survey were to document grower practices that have the potential to impact soil quality, growers’ reasons for these practices, and growers’ perceptions of how these practices affect the soil environment and soil quality.
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