Biofumigation is a sustainable method of soil management in cash crop rotations that can increase soil organic matter (SOM), moderate soil pH, suppress weeds and soilborne pathogens through glucosinolates (GSL), and increase water infiltration. This 2-year (2011–13) field study evaluated four different Brassica crops for their biofumigant potential in a chile pepper rotation system in southern New Mexico. The four cultivars included: three mustards (Brassica juncea ‘Caliente 61’, ‘Caliente 199’, and ‘Pacific Gold’) and one broccoli (Brassica oleracea var. botrytis ‘Arcadia’). As a result of concerns that these mustards could be hosts for nematodes, a greenhouse study was conducted in the second year to evaluate the biofumigant crops for their southern root-knot nematode (Meloidogyne incognita, RKN) host suitability and their seedling establishment in the presence of RKN. In Year 1 (2011), conditions were ideal, which resulted in high mustard biomass production and, consequently, significantly higher SOM and lower pH than the bare soil control plots. However, there were no chile pepper yield differences among treatments. Conditions were much less favorable in Year 2 and the resultant poor biomass production did not cause an increase in SOM as seen in Year 1. In the RKN greenhouse study, broccoli was the least susceptible biofumigant crop. After one nematode generation (683 cumulative heat units), RKN populations were less than half of the original inoculum level on the broccoli. However, RKN populations increased in the presence of ‘Caliente 61’, ‘Caliente 199’, and ‘Pacific Gold’. Overall, broccoli produced lower biomass and lower GSL concentrations than the mustard treatments but may be a valuable crop for growers with nematode issues because RKN populations decreased in its presence. Based on high biomass production and high GSL concentration, ‘Caliente 199’ showed the most potential as a biofumigant crop for southern New Mexico.
Rachel E. Rudolph, Carl Sams, Robert Steiner, Stephen H. Thomas, Stephanie Walker, and Mark E. Uchanski
Rachel E. Rudolph, Thomas W. Walters, Lisa W. DeVetter, and Inga A. Zasada
One of the primary production challenges red raspberry (Rubus idaeus) growers in the Pacific northwestern United States confront is root lesion nematode [RLN (Pratylenchus penetrans)]. In this perennial production system, red raspberry serves as a sustained host for RLN. When a red raspberry planting is slated for removal in the fall, a new red raspberry planting quickly follows in the same field the following spring. The primary crop that occurs in rotation with red raspberry is a winter wheat cover crop to provide soil coverage and protection during the winter. The objectives of this research were to determine if winter wheat (Triticum aestivum) provides a green bridge for RLN in continuous red raspberry production systems and to determine if modified winter cover cropping practices can be used to reduce population densities of RLN before replanting red raspberry. Four trials were established in fields being replanted to red raspberry and the following modified winter cover cropping practices were considered: cover crop planting date (at fumigation or 2 weeks after fumigation), termination date (cover crop kill with herbicide 2 or 6 weeks before incorporation compared with the industry standard of incorporation immediately before planting), and the additional application of methomyl. ‘Rosalyn’ and ‘Bobtail’ winter wheat planted as cover crops in these trials were demonstrated to be maintenance hosts for RLN (ranging from 10 to 947 RLN/g winter wheat root across trials) allowing them to be a green bridge for RLN to infect the following red raspberry crop. Altering winter wheat cover crop planting date, termination date with herbicide, or methomyl application did not affect RLN population densities in the subsequent red raspberry crop. Although planting an RLN maintenance host may be of concern to growers, the advantages of reduced soil erosion and nitrate leaching associated with cover cropping outweigh the perceived risk to the subsequent red raspberry crop.
Rachel E. Rudolph, Lisa W. DeVetter, Chris Benedict, and Inga A. Zasada
A survey was conducted in Washington State in 2015 and 2016 to gauge grower perceptions, understanding, and current practices regarding soil quality. Soil quality has been defined as the ability of the soil to sustain plants, animals, and humans over time. Many current practices of modern agriculture can be detrimental to soil quality, including soil tillage and soil fumigation, both of which are commonly used for the Washington red raspberry (Rubus idaeus) production system. The area between red raspberry beds, known as the alleyway, is frequently tilled and kept bare, without groundcover, to manage weeds. Growers commonly fumigate the soil before planting red raspberry to manage soilborne pathogens and plant-parasitic nematodes. The majority of red raspberry growers surveyed consider soil quality quite often in relation to the management of their fields. The majority of growers during both years considered cover crops to have a positive impact on soil quality. However, growers also perceived soil fumigation to have a positive impact on soil quality. The majority of growers responded that they were willing to adopt alleyway cover crops for a variety of reasons, including improving red raspberry production, physical soil quality, and beneficial soil microorganism populations. This survey demonstrated that there is interest in soil quality among growers; however, there is a difference in perceptions between growers and researchers regarding how management practices impact soil quality.
Rachel E. Rudolph, Lisa W. DeVetter, Inga A. Zasada, and Cedar Hesse
Cover crops can lessen soil erosion and compaction, improve water infiltration, enhance nutrient availability, suppress weeds, and assist with pest management. However, cover crops are not commonly used in alleyways of established red raspberry (Rubus idaeus) fields in the Pacific Northwest of the United States. Rather, the space between red raspberry beds is repeatedly cultivated and the soil is kept bare, which has detrimental effects on soil quality. Adoption of alleyway cover crops is limited because red raspberry growers are concerned about resource competition between a cover crop and red raspberry crop. A 2-year study was conducted in an established ‘Meeker’ red raspberry field in northwest Washington to evaluate the effects of eight annually seeded alleyway cover crops (cultivars of wheat, cereal rye, triticale, oat, and ryegrass), one perennial ryegrass alleyway cover crop, mowed weed vegetation, and the industry standard of cultivated bare soil (Till) on the physical, chemical, and biological properties of soil quality in alleyways and raised beds. This included evaluating soil bulk density (D b), compaction, organic matter, pH, cation exchange capacity (CEC), macro- and micronutrients, and bacterial and fungal community structure; red raspberry yield and fruit quality were also evaluated. Although there were statistically significant differences among treatments across sampling dates for CEC, there were no consistent trends. Alleyways planted with the perennial ryegrass mix had the lowest mean D b 6 and 24 months after seeding. Tilled alleyways had the lowest D b 12 and 18 months into the study. Red raspberry grown adjacent to Till did not result in a significantly higher estimated yield or fruit total soluble solids than raspberry grown adjacent to cover crops in either year of the experiment. Differences in microbial community structure were observed among seasons rather than treatments. These results do not demonstrate significant effects of alleyway cover crops on red raspberry productivity when applied to established fields. The potential benefits of alleyway cover cropping on soil quality may outweigh any concerns regarding resource competition. Changes in soil quality are often difficult to quantify and require long-term study.