Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/26/2010
Publication Date: 11/15/2010
Citation: Banuelos, G.S., Hanson, B. 2010. Use of Se-enriched mustard and canola seed meals as potential bioherbicides and green fertilizers in strawberry production. HortScience. 45:1-6. Interpretive Summary: Uniquely, seed harvested from Brassica plants used for the phytomanagement of Se in the San Joaquin Valley (SJV) contain the trace element Se. Hence, meals produced from these seeds may be potentially useful as a green fertilizer for biofortifying food crops with nutrients, including essential Se. We tested both canola and mustard seed meals (after oil extraction) as potential bio-herbicide and green fertilizers in strawberry production under controlled and field conditions. Treatments consisted of firstly amending potted soils with various rates of Se-enriched canola or yellow mustard seed meal produced from plants grown in a Se phytomanagement/biofuel project in the Westside of the SJV. Seeds were cold-processed for their oil on Red Rock Ranch, Five Points, CA. The Se-enriched seed meals (containing ˜ 2.2 mg Se/ kg dry matter (DM) and other nutrients were applied as a dry granulated meal at rates equivalent to 0, 2, and 6 tons/ acre directly to soil. For the field study, similar Se-enriched seed meal amendment treatments were used as the growth chamber experiments. Within each field microplot, a single row of ten different weed species, including barnyardgrass, annual bluegrass, common chickweed, large crabgrass, horseweed, little mallow, redroot pigweed, common purslane, Italian ryegrass and yellow nutsedge was seeded. In the environmental chamber study, no yield benefits from seed meal amendments were observed. In fact, the highest rates of either mustard or canola seed meal lowered berry yields compared to yields from control treatments. In the potted plants, berry Se concentration was two- to ten-fold higher when soil was amended with either Se-enriched canola or mustard seed meals, irrespective of rate of meal application. In the field study, strawberry fruit yield increased with all seed meal treatments compared to the control treatment, except at the high rate of mustard and canola meal application. Mustard meal appeared to be slightly more effective than canola meal for weed control. While weed and nutrient management solely with Se-enriched Brassica seed meal is unlikely to reach acceptable standards in conventionally strawberry production, amending soils with seed meals may have commercial viability in organic agriculture as a part of an integrated pest management and fertility plan. When considered in an agricultural system context, the coupling of phytomanagement of Se-contaminated soils, biofuel production, organic fertilizer and pest management, and Se-biofortification of a food crop may provide central California growers a unique production and marketing opportunity and is worthy of additional research.
Technical Abstract: New plant-based products can be produced from seed harvested from Brassica species used for phytomanaging selenium (Se) in the westside of central California. We tested Se-enriched seed meals produced from canola (Brassica napus) and mustard (Sinapis alba) plants as potential bio-herbicides and as green fertilizers in strawberry production under both controlled and field conditions for two seasons, respectively. Treatments consisted of adding each meal (containing 2.2 mg Se kg/DM), respectively, to the soil (Hanford sandy loam) at rates equivalent to 0, 2, and 6 tons/ acre seven days prior to planting in controlled and field conditions. In the controlled green fertilizer study, the highest rates of either meal lowered berry yields by a high of 30% compared to no application (control) conducted in growing pots. Among the nutrient accumulation, berry Se, calcium (Ca), manganese (Mn) and zinc (Zn) significantly increased with most Brassica meal treatments and most significantly with the mustard meal. Fruit Se concentrations were as high as 221 and 396 ug/kg DM from the addition of high canola and mustard meals, respectively. In bio-herbicide and green fertilizer field studies, planting beds (35-m long 0.9-m wide 20 cm high) were created in the same Hanford sandy loam soil used in the growth chamber experiments. Each bed contained nine microplots (3 x 0.9 m in size). The mustard treatments (described above) were applied the same day as planting of different weed seeds, which included; barnyardgrass (Echinochloa crus-galli), annual bluegrass (Poa annua), common chickweed (Stellaria media), large crabgrass (Digitaria sanguinalis), horseweed (Conyza canadensis), little mallow (Malva parviflora), redroot pigweed (Amarathus retroflexus), common purslane (Portulaca oleracea), Italian ryegrass (Lolium multiflorum), and yellow nutsedge (Cyperus esculentus). Weed emergence data were collected and total above ground biomass for each species was collected 8-10 weeks after seeding. The greatest reductions in resident weed biomass occurred, with both mustard meal and high canola meal treatments. The mustard treatments, irrespective of rate, lowered the emergence of summer-germinating and resident winter annual weeds slightly more than canola meal treatments compared to control plots. In field strawberry production, fruit yields significantly increased with all Brassica treatments, except a 42% fruit yield reduction was observed at high rate of mustard seed application. Although lower than the Se concentrations measured in the growth chamber study, fruit Se concentrations were as high as 47 and 66 ug/kg DM from the addition of canola and mustard meals, respectively. In addition, some significant increases in fruit Ca, P and Mn concentrations were observed for all Brassica meal treatments. Amending soils with only Brassica seed meals will likely be insufficient for attaining complete weed control and for providing adequate nutrition under field conditions. Its use may have more practical viability in organic agriculture as both a potential bio-herbicide and as a green fertilizer source, as well as in greenhouse production where the meals efficacy is greater within a confined root zone. Moreover, more research is recommended for examining the addition of Se-enriched meal to crop production as a means to enrich food products with Se.