From bluestem@webserf.net Sun Oct 10 18:13:43 1999 Date: Sun, 10 Oct 1999 21:09:22 +0100 From: Bluestem Associates To: "sanet-mg@ces.ncsu.edu" Subject: Seaweed and Fish for minerals (Rateaver) Bargyla --- I can't agree with you on your two major points. First, few of the people I inspect actually use seaweed or fish. This sample is biased owing to its location in the cash-crop heartland. I know that the hort folks use more. Second, fish and seaweed just don't get the job done when it comes to minerals, even in a horticultural operation. The quantities are simply insufficient. When I was in commercial-scale organic production, I used both fish and seaweed in the *greenhouse.* We also used seaweed to great effect as a pre-transplant soak, but that is hormonal and not mineral in mode of action. The only time I would use fish in the field was when I had some left over that I wanted to get rid of. More on fish below. I also threw liquid seaweed into my foliar sprays if I had some left over, mostly because I grew up 3 km from the Atlantic and I like the way seaweed smells. Properly timed applications of seaweed are helpful in a number of horticultural field situations --- concentrating tuber set in potatoes, for example --- but again, this is hormonal, not mineral. The hormones in seaweed may even help tall fescue and other pasture crops absorb soil nutrients more effectively, as well as reduce some of the problems associated with grazing endophyte-infected fescue (Vivien Allen's work at Texas Tech). As a *source* of minerals, however, liquid seaweed is virtually useless agronomically at economically viable application rates. As just one example, assume a seaweed extract contains 0.1% zinc ---this is generous. Assume 2 gal/ac application rate (20 L/ha) --- this is four times normal application rates. This application rate will bring to the system about 0.3 ounces of zinc per acre, or less than 0.01 ppm against normal background levels of 2 ppm, and I'm nudging the calculations in favour of the seaweed by just about an order of magnitude, without getting into the whole topic of the inefficiency of foliar absorption. As a source of zinc and/or anything else, seaweed just isn't worth what it costs. If seaweed applications will pay their way (they often do) it is on their role as a source of carefully timed exogenous hormones and growth regulators. Fish solubles, on the other hand, are purchased and applied as a source of nitrogen. Except in highly specialised situations (like a greenhouse) applications of fish emulsion make no agronomic or economic sense. Typical fish solubles contain about 5% nitrogen and weighs 9.7 lbs/gallon. Let's call it ten. Two gallons of fish provides one pound of nitrogen. Depending on source and volume, fish solubles cost $4 to $8 per gallon at the farm. That is $8 to $16 per pound of nitrogen, folks! Typical farm application rates are 2 to 10 gallons per acre, providing 1 to 5 pounds of nitrogen. One decent thunderstorm will give you 3 to 5 lb/ac nitrogen and doesn't cost $24 to $80 per acre. While we're looking at organic nitrogen prices, here are some comparisons. Fish solubles @ $6/gal = $12.00/lb N Purchased compost @ $20/yard = $4.00/lb N Fish meal @ $450/ton = $2.25/lb N Alfalfa meal @ $130/ton = $2.10/lb N Blood meal @ $450/ton = $2.10/lb N Feather meal @ $500/ton = $1.80/lb N Dry chicken manure @ $130/ton = $1.65/lb N Soybean meal @ $200/ton = $1.45/lb N On-farm compost @ $2/yard = $0.40/lb N Alfalfa plowdown @ $35/ac = $0.35/lb N Sweetclover plowdown @ $25/ac = $0.20/lb N Conventional nitrogen costs between $0.15 and $0.30 per pound, depending on source. If there's any logic to using fish solubles as a source of nitrogen in most organic production systems, it has so far escaped me. Bart PS --- As an aside, if anyone wants to know the details of fish meal and fish solubles production/manufacture, contact me off list. I have inspected five different menhaden plants and can probably tell you more about the process than you ever wanted to know. To Unsubscribe: Email majordomo@ces.ncsu.edu with the command "unsubscribe sanet-mg". If you receive the digest format, use the command "unsubscribe sanet-mg-digest". To Subscribe to Digest: Email majordomo@ces.ncsu.edu with the command "subscribe sanet-mg-digest". All messages to sanet-mg are archived at: http://www.sare.org/san/htdocs/hypermail