Adding fertility to the farm comes in many forms: cover cropping, composting, and spreading of a variety of powders, pellets and potions.  To me, cover cropping and composting help address the greater fertility needs and long-term productivity of the soil. Spreading of certain minerals, such as lime, contribute to this same broad approach as well, and the combination of these practices forms the basis of a healthy soil where crops can thrive. In addition, there are the amendments that I add to specifically boost the following crop, including high nitrogen byproducts like blood meal and feather meal, and mined minerals like sulfate of potash. These are typically relatively concentrated (for organic) materials, chosen for specific known deficiencies.  

I use soil testing to assess my need for soil amendments, looking first at creating a generally healthy soil for vegetable production and then adjusting slightly for crops that can use a little extra nitrogen, and leaving out nitrogen for legumes, which will fix their own. Most of my amending is done with final bed preparation using a drop spreader. I’ve moved away from broadcast spreading over the years, although it has its own advantages. I don’t use much top dressing, side dressing, or fertigation, but I see those all as refinements that can benefit crops, particularly in difficult-to-adjust, poor soils.
   
Broadcasting
Spreading amendments isn’t really much different than spreading seed and many times the same tools can be used for both operations. The simplest broadcasting tool is simply the hand, and at a very small scale this works well, but it takes a bit of skill and practice to get the application even and consistent. For slightly larger settings a shoulder bag type spreader will work, although they have very limited capacity. Push type broadcasters will hold a bit more in their hopper (earthway.com has examples of both of these types of spreaders).  These options might be suited to operations up to a couple of acres. There are several tractor-mounted versions of broadcast spreaders, the ubiquitous cone spreaders which are PTO powered being the most common. There are also larger trailer boxes that hold tons of materials, which can be either PTO or ground drive.  All of these options basically have a metering mechanism that dribbles material onto a rotating plate with beaters that throw the material twenty feet or more. The advantage to broadcasting is that the tools tend to be much less expensive, and they can spread large areas quickly. The problem is that they are strongly affected by any wind, which tends to blow materials airborne and sometimes the material doesn’t even make it onto the field. Especially in small areas, it’s hard to control the spreading around edges and corners and coverage is very hard to get completely even. There is always some waste of material around the edges of the field with broadcasting, which in another light could also be considered environmental contamination on a small scale.

Drop spreading
Instead of dropping material onto a spinning plate, drop spreaders drop it directly onto the ground. This virtually eliminates wind effects, and allows very precise application from edge to edge and into tight corners, but it also means that you have to drive over every bit of ground, and the hopper capacity tends to be smaller, requiring more frequent loading for larger areas. Drop spreaders are made in sizes from 2‘ up to 24‘ or more and they are typically a bit more expensive than broadcast spreaders. The large metering mechanism adds to their cost, as well as needing some sort of agitator across the entire width of the drop box to keep material flowing evenly.  Drop spreaders are almost always ground driven, but they can be pushed or pulled by hand or tractor, or mounted on a 3 point.

Sidedressers
There are many variations on fertilizer boxes that meter out material down a tube, or several tubes, where it can be directed into a band, or buried with a shank.  These can be mounted on tool bars or on the tractor itself.  They typically have smaller boxes, with less capacity, as they are designed more for supplemental feeding than large scale spreading.  The metering mechanisms are driven either by ground, PTO, or by 12 volt electric motors which can be hooked to the battery of the tractor and switched on an off from the cab of the tractor.

Comparing options
All of these options have their places and applications around the farm. The one I find the most useful on a diverse vegetable operation is the drop spreader. While it’s a bit slower and more expensive, I can spread regardless of wind conditions, even right next to an existing crop that’s ready for harvest. It also spreads evenly from edge to edge.  Most models have enough clearance to topdress an existing crop of garlic in the spring, or you can get high clearance models – like the Gandy Nursery Special (gandy.net) or the Schaper Bros. model carried by Market Farm Implement (marketfarm.com). The high-clearance models can be modified to funnel amendments to individual lines, very similar to a side dresser.

For common minerals such as lime, in a big field application in most areas you can hire a service to come out and spread for you – usually they’ll use a broadcast spreader of one sort or another.  ometimes the farm supplier that sells the lime will also rent out a spreader so that you don’t have to own one.

One issue with spreaders of all sorts, especially cheap lawn types, is the maximum rate they will put out. Organic amendments are not as concentrated as synthetic formulations which translates into higher rates being necessary, many times by more than a factor of two to four times the rate of synthetics. Depending on the texture of the material, bridging and uneven flow can be a problem as well. Calibrations will change between materials due to differences in particle size and texture. I’ve found that mixing different materials together often helps improve flow, partly just by increasing the rate and the hole opening. 

I’ve put quite a bit of cover crop seed through drop spreaders. This works well for smaller sized seed, but anything over vetch sized seed usually won’t fit through the holes, or gets torn up by the agitator. Broadcast spreaders are probably one of the most common cover crop seeding tools. Because seeds are heavier than most amendments, they aren’t quite as affected by the wind, and the larger hole opening in a broadcast spreader allows seeds of all sizes to pass through easily. Conceivably you could use a side dresser to seed single rows, although the metering mechanism isn’t as well suited at this scale of equipment.  With all of the spreaders, you still need to cover and press in seed after spreading it, which requires a following operation.

For sidedressers, these can also be used as a kind of drop spreader by mounting a plate at an angle that the tubes drop onto.  As the material slides down the plate and onto the ground it spreads out. There’s a great example of a Matermac 12 volt side dresser being used more like a drop spreader at wannafarm.com.

Typically when you’re actually sidedressing you want to lay down the material under the surface so that it doesn’t blow away. This is accomplished with a shank, much like the opening shoe of a seeder. Sidedressers can also be mounted on cultivating tools, letting the cultivation equipment work the dropped amendment into the soil. I used a very old ground drive sidedresser for a few years. The original shanks for burying the amendment were long gone which meant I was just leaving bands of material on the surface. I would simply follow sidedressing with a cultivation to help work the material into the surface of the soil.  If you’re sidedressing with drip irrigation you want to make sure you’re applying the material in a zone that will get moisture, as most nutrients are transported to roots through water. 

One final word of advice with spreaders is to keep them dry.  Many amendments, when combined with moisture will both create hard cakes that clog everything and are very difficult to clean out. In addition they are frequently very corrosive, which is why critical parts on quality spreaders are made from stainless steel or even plastic.

Josh Volk writes regularly about tools and equipment for Growing for Market. He farms near the edge of Portland, Oregon, and helps farmers around the country improve their systems. Visit www.slowhandfarm.com.

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