Impact of Liquid Fertilizers on Plant Growth, Yield, Fruit Quality, and Fertigation Management in an Organic Processing Blackberry Production System

The impact of organic fertilizer source on the growth, fruit quality and yield of blackberry (Rubus L. subgenus Rubus Watson) cultivars (‘Marion’ and ‘Black Diamond’) grown in machine-harvested, organic production systems for the processed market was evaluated from 2011-2013. The planting was established in spring 2010 using approved practices for organic production and was certified in 2012. Plants were irrigated using a drip line under a porous landscape fabric (weed mat) installed for weed management. Two sources of liquid fertilizer were evaluated: 1) a corn steep liquor and fish waste digestion (2.5–2.5–1.5); and 2) fish solubles and molasses blend (4–0–2). Fertilizers were applied by fertigation through the drip system at rates of 56 kg·ha^–1 N per year in 2011-2012 and 90 kg·ha^–1 N in 2013. The impact of fertigation on drip system performance was evaluated with two maintenance options, “flushing” and “no flushing” of the drip lines. Total yield differed among years, while fruit soluble solid concentration and firmness, and floricane biomass dry weight at pruning were affected by year x cultivar. ‘Black Diamond’ had greater total yield and average fruit weight than ‘Marion’, but produced the most unmarketable fruit. There was no effect of fertilizer source on yield, fruit quality, primocane length, or primocanes/plant in any year, with the exception of fruit weight, which was greater with corn than with fish. ‘Marion’ had a greater floricane biomass when fertilized with fish than with corn. Soil nutrients were within the recommended range, except for B, which was below recommended levels; and only soil nitrate-N was affected by fertilizer source, which was greater with corn than with fish in ‘Black Diamond’, but there was no effect in ‘Marion’. Primocane leaf tissue nutrient concentrations were within recommended levels for all nutrients, except for Ca and B which were below recommended standards in both cultivars. Primocane leaf K and Zn concentrations were greater with fish than with corn. There was no fertilizer source or maintenance effect on emitter flow rate of the drip system in either year. However, flow rates decreased an average of 4.5% in the first year and 19% in the second year. Overall, there were no differences between the fertilizers on plant growth, yield, or fruit quality, and both fertilizers were suitable for planting establishment.