4163:
Killed Cover Crop Residue Impacts On Onion Growth and Management in Semi-Arid New Mexico
Alternative cultural practices in vegetable farming are one way in which the arid southwest is adjusting to its limited water resources and urban expansion. During the summer months in the U.S., New Mexico is a major supplier of fresh market onion (Allium cepa), producing nearly 80% of the crop, and accounting for approximately $47.5 million in sales in 2008. The use of killed cover crops as a pre-plant practice may be one way to moderate water use, improve stand establishment, and increase yields of direct seeded, spring-sown onions. The presence of cover crops can also decrease feeding of onion thrips (Thrips tabaci) and their associated damage including the spread of pathogens, particularly the economically important Iris yellow spot virus (IYSV). In this study, four annual cover crop species were evaluated for their impact on soil moisture content of spring-sown onion in the field. Field research was conducted at the New Mexico State University Leyendecker Plant Science Research Center. Cover species included oats (Avena sativa ‘Monida’), ryegrass (Lolium multiflorum ‘Gulf’), winter rye (Secale cereale) and winter wheat (Triticum aestivum ‘Promontory’ ). Cover crops were established in the fall, over wintered, then killed with the application of glyphosate, and plant biomass was left undisturbed. An in-furrow application of wheat straw was used as a fifth cover treatment in addition to a bare soil control. Plots were established in a randomized complete block design (RCBD) with four replications and irrigation was accomplished by flooding furrows. Spring onion cultivar ‘Caballero’ was direct seeded in March 2009, and irrigation scheduling was established using soil moisture equipment utilizing Frequency Domain Reflectrometry (Diviner 2000). IYSV disease severity was measured using a scale of 1-9 to evaluate disease pressure in each treatment. Soil moisture content data indicates that the cover treatments provided a buffer from water loss in the top 40 cm of the soil in this water intensive crop while also decreasing IYSV disease pressure. However, the presence of the cover crop residues presented some cultural challenges including an allelopathic effect in the ryegrass treatments. Consequently, photosynthesis rates and yields were depressed in these treatments. A killed cover crop can provide both the benefit of a cover for input reduction, and also contributes to a diverse rotation schedule, but must be managed with the primary crop with care.