|HARKINS, RENEE - Oregon State University|
|STRIK, BERNADINE - Oregon State University|
Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/7/2013
Publication Date: 1/1/2014
Citation: Harkins, R.H., Strik, B.C., Bryla, D.R. 2014. Weed management practices for organic production of trailing blackberry. II. Accumulation and loss of plant biomass and nutrients. HortScience. 49:35-43.
Interpretive Summary: A long-term field study is being conducted to evaluate management practices for organic production of processing blackberries. The objective of the present study was to evaluate the effects of organic fertilizer use under three organic weed management strategies, including no weeding, hand-weeding, and weed mat, on plant growth and leaf and fruit nutrient status. Plants in each treatment were irrigated by drip and fertilized using certified organic liquid fish products. Two popular cultivars, Marion and Black Diamond, were included in the study. Both are predominantly harvested by machine for high-value processed markets and together account for greater than 75% of the 7,200 acres of blackberries produced in Oregon in 2012. Based on the current standards for primocane leaf tissue analysis in caneberries, the organic fertilizers used in the present study were adequate to meet plant demands for P and K in blackberry but were inadequate to meet the need for N in Black Diamond and B in both cultivars. Black Diamond may have a need for more fertilizer than the 50 lb/acre of N applied per year but alternately may have lower leaf tissue nutrient requirements. The results also indicate that more fertilizer may also be needed with limited or no weed control, although additional application may likewise increase weed growth. Low B is easily resolved with a broadcast application of boric acid in the fall or prior to bud break in the spring. In terms of gains in biomass, plant growth was greater in Marion than in Black Diamond during the second year after planting when only primocanes were present but was similar between the cultivars the following year when plants were first cropped. Weed control increased cane and fruit biomass, leaf tissue nutrient concentrations, and nutrient accumulation and loss in both cultivars, but plant nutrient gains and losses exceeded nutrients applied in the organic fertilizer during the first year of fruit production (with weed control) and therefore relied on plant tissue reserves and/or soil nutrients to meet plant demands.
Technical Abstract: A study was conducted to assess the impact of cultivar and weed management on accumulation and loss of plant biomass and nutrients during the first 3 years of establishment when using organic fertilizer in trailing blackberry. Treatments included two cultivars, Marion and Black Diamond, each with either no weed control following the first year or with weeds managed by hand-weeding or the use of weed mat. Each treatment was amended with organically-approved fertilizers at pre-plant and drip fertigated with fish emulsion each spring. Most primocane leaf nutrient concentrations were within the range recommended for blackberry. However, leaf N was low in Black Diamond, especially when grown without weed control, while leaf B was low in all treatments. In many cases, leaf nutrient concentrations were affected by cultivar and weed management in both the primocanes and the floricanes. The concentration of several nutrients also differed between cultivars in the fruit, including Ca, Mg, S, B, and Zn, but only fruit Ca was affected by weed management and only in Marion. In this case, fruit Ca was higher when the cultivar was grown with weed mat than with hand-weeding or no weeding. Total biomass production of primocanes increased from an average of 0.3 t/ha dry weight (DW) during the first year after planting to 2.0 t/ha DW the following year. Plants were first cropped the third year after planting and gained an additional 3.3 t/ha DW. Fruit DW averaged 1.4 t/ha with no weeding, 1.9 t/ha with hand-weeding, and 2.3 t/ha with weed mat. Biomass of floricanes averaged 3.2 t/ha DW and was similar between cultivars and among the weed management treatments. Weeds reduced nutrient accumulation in the primocanes in both cultivars, and accumulation of nutrients was greater in the floricanes than in the previous year’s primocanes. Total nutrients declined from June to August in the floricanes, primarily through fruit removal at harvest and floricane senescence after harvest. Plants generally accumulated the most biomass and nutrients with weed mat and the least with no weed control.