From bluestem@webserf.net Tue Oct 12 14:52:20 1999 Date: Tue, 12 Oct 1999 14:50:00 +0100 From: Bluestem Associates To: "sanet-mg@ces.ncsu.edu" Subject: Re: fertigation-grade rock phosphate? On Mon, 11 Oct 1999 22:43:55 -0600 (MDT), Nathan/Rachna Boone wrote: > Can anyone help me compare the following two methods of applying >rock phosphate: > >1) Using micronized rock phosphate fed into irrigation lines at 25-100 lbs >per acre. ($30 for 25 lbs) > >vs. > >2) Field broadcasting of one ton/acre of granulated rock phosphate ($140/ton) > > >A local farmer has asked me what makes more sense, and I'm not sure how to >compare them. Any ideas??? Golly, I just can't get away from this, can I ? Actually I don't think a lot of either method. Micronized rock phsophate is still *suspended* in water, not dissolved, and it seems ready made for plugging something somewhere. Irritation systems (excuse me, irrigation systems) are enough trouble without giving them another excuse to act up. $30-120/ acre is an outrageous cost for 5 - 20 lbs of *total* phosphate, of which only 10-20% will be available the first year. Field broadcasting is a better option, but still not a good one. If it's Idaho phosphate the granulation is usually pretty good, but if it's from Florida what they call "granules" are really small clumps that didn't fully break up when they dried and ground the old slime-pond residues. Your biggest challenge in New Mexico --- or most anywhere west of about 98-W longitude --- is that the soils are usually alkaline. The stable form of phosphate in those soils is calcium phosphate, which is the same stuff you'd be adding and expecting to have released. Doesn't work very well. Phosphate rock needs an acid environment (preferably below pH 6.3) to break down. Your best bet out there is to mix phosphate with manure, compost it, and apply the compost to the land. The organic acids in the manure will release much of the phosphate, and the phosphate will stabilise much of the manure nitrogen against loss during the composting process. What's going on chemically is that much of the nitrogen in manure is in the form of ammonium carbonate (unstable). That reacts with the calcium phosphate to form calcium carbonate (limestone) and mono-ammonium phosphate (stable). This is the same MAP sold as 12-50-0 at the local fertilizer plant, but if you 'make' it this way it's allowed for organic production, while the stuff in a bag will get you busted. Go figure. You can add about 50 lb of phosphate rock per cubic yard of manure, and if moderately composted and applied at about 5 tons/acre it will add about 200 lb/ac of phosphate to the system, including phosphate from the manure. Most of it will be reasonably available, so your client should get a crop growing quickly to transfer the phosphate to the living fraction of the system. Otherwise it will eventually react with the soil and revert to calcium phosphate, which gets you back where you started. 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