Just a quick bit of background. We were new to dairying 5 years ago but have been interested in natural farming forever. We started out doing everything "by the book" as relayed to us by farm advisors and fertiliser company reps. Suspicions arose early (eg no lime was recommended) and we started educating ourselves. Our current system borrows from lots of sources. We shop around for supplies rather than "work with" any fert company rep. Details below.
We operate two systems - one feeds the soil and the other feeds the plants. Each year we take multiple samples of soil from around the farm, and also take clipping samples of the plants. These all get sent off to the lab for analysis.
We use the soil tests to design bulk loads containing dry mixes of the major elements. These mixes are ground-spread by a contractor once a year. The dry mixes are based on the Albrect/Kinsey method which aims to get a pre-determined balance of the major cations (K, Ca, Mg, Na) adhering to soil particles. We are aiming for 68% Ca, 12% Mg, 5% K and 2% Na. We also dry spread P at this time if required (in slow-release form, not super-phosphate) and elemental sulphur. I built a little spreadsheet to do the calculations, which depend on the total cation exchange capacity (CEC) of the soil. Last year it was too expensive to spread enough of this to achieve the Albrecht ratios in one hit, so we applied roughly half. I'm about to re-do the calculations for this year and place the orders.
The cost of this dry spread last year was about 1/2 of what we had been spending on the advice of fertco reps. We look on this programme as a slow and steady building of soil fertility.
The herbage tests are used to design foliar sprays that we apply in the early morning to feed the plants directly. We use two different types of foliar spray. The first aims to supply enough of every element to bring the herbage test result up to the optimal level. Here are our targets - they are based on what cows love to eat and we are basically assuming that plants need the same stuff (leap of faith there, but hey, science is experimental isn't it?):
I made a little spreadsheet (happy to share) that accepts the herbage test results and then calculates how much of each thing to add to the brew, bearing in mind that the products aren't full strength (our source of iron, for example, is only 13% Fe) and how much grass is in the paddock (kgDM/ha). We make 1000 litres of these foliar sprays at a time (enough for 4ha) in this wonderful example of kiwi innovation.
Its called a tow'n'fert and is made by the nice people at Metalform in Dannevirke. The cool thing is that the whole mix stays in suspension courtesy of a grunty trash pump, so we can apply stuff that doesn't disolve in water provided the particles aren't too big.
The other cool thing is that a liquid spray is really the only practical way of applying trace elements. For example, a typical mix might require 750 litres of water, 150kg of fine limeflour, 40kg of P, ..., 5kg of Fe, 20g of copper sulfate, 800ml of Boron and 2 teaspoons of Molybdenum. You are just not going to get that mixed properly if its in a 10 tonne truckload of dry spread fertiliser.
The third cool thing is that these very complex mixes turn out to be pretty cheap, like around $20/hectare.
Oh and by the way, the herbage tests have virtually never called for nitrogen so a lot of the 3T of urea we bought last season is still sitting in the shed. We are aiming to grow clover and other legumes, which are suppressed by urea, but will pull large amounts of N from the air and supply it to other plants.
We are a bit nervous about this trace element brew (ie scared of overdosing on trace elements), so we only do it once between each herbage test. In the meantime, we just load it with a basic mix of fine limeflour and a proprietary seaweed + fish silage brew. Our aim is to get right around the farm with the liquids about 4 times per season.
That's it. Pretty simple really and we love not having to deal with the product pushers from the fertiliser companies. Taking personal ownership of the issues is the way to eliminate those guys.
The jury is definitely still out, but so far this appears to be a cheaper system and to grow more plant food. The almost total absence of urea is just a happy coincidence.