8.5: How Much Do I Apply?

In a previous section, we explained how organic fertilizers are different than commercial, synthetic fertilizers. We often struggle with this next logical step, explaining how much commercial fertilizer to actually apply and how to apply it. The main reason for the struggle is that most home gardeners and many large-scale commercial gardens and small farms can “grow their own” fertilizers so you may not need to apply any fertilizer at all. Larger farms, those over 10 acres, will likely need to apply some fertilizer inputs brought in from off the farm. This is especially true if they are just beginning a transition to organic farming or if the farmland has been run conventionally in continuous corn or soybeans for several years without adequate replacement of nutrients.

The way to figure rates, volume, and amounts for lawns, home gardens, commercial gardens, and farm fields is essentially the same and we will review it in this section. We also cover how organic fertilizer rates and costs stack up against conventional.

Lawn fertilizer application rates are easy to figure out because lawns are a monoculture of mostly bluegrass with a little fescue or related grass species. I do not fertilize my lawn, but again I do not hold lawns in high regard. I think the typical home has too much lawn and too much attention and work is focused on it. Personally, I would rather spend my resources growing food. That said, a lawn was more important to my family when our children were young and we played in the lawn space. Thankfully, in Wisconsin, the nutrient phosphorus is no longer included in a bag of fertilizer you can buy for home lawns because of the environmental water pollution problems it can cause. For more information on the ban on phosphorus on lawns go to the Department of Agriculture webpage that explains the law, which took effect in April 2010. http://datcp.wi.gov/uploads/Environment/pdf/TurfFertHomeownerPub194.pdf

Gardens

When gardening and growing food for home use, gardeners do not need to be very precise and can apply store-bought organic fertilizer without going broke. But commercial gardeners cannot afford to over-apply fertilizer, organic or otherwise. Keeping within a budget for fertility inputs can determine whether or not a CSA or Farmer’s Market garden is profitable. Commercial gardeners adjust fertilizer application rates frequently because each plot or area for individual vegetables has different nutrient needs. The good news is that large-scale gardeners can probably manage to apply nutrients only in the crop row (side-dress) for the biggest benefit without encouraging weeds in between rows as would happen if fertilizer was broadcast. Also, the equipment needed to apply garden fertilizer is small enough do-it-yourself scale to not break the bank. Most fertilizers I will discuss here are granular or dry fertilizers. However, I have used fish emulsions and other liquid fertilizers in the garden. They are relatively easy to apply with just a sprinkler can if you only have a half acre to fertilize. Over a half acre? Consider applying liquid fertilizer through an irrigation system. You will likely need irrigation anyway for that inevitable August dry spell. You may as well plan to fertilize at that time too.

Do not use push lawn spreaders that you can buy for $100 at Home Depot. This type of spreader broadcasts the fertilizer. That is great for a lawn, but not good in a garden since you will be promoting weed growth between rows. Use small spreaders that apply fertilizer only in the row, not broadcasting.

Small Farms

Farms over 5 acres will probably need to use a mechanical aid to apply fertilizer. Your local farmer cooperative has small fertilizer spreaders for rent that are pulled behind a tractor. Many times, if you buy fertilizer through the cooperative the use of the spreader is free as a part of the deal.

Figure \(\PageIndex{1}\): Spreading fertilizer with a tractor

Full Circle Organic Farm explains their fertilization methods:

In our pastures, we often broadcast organic approved composted poultry litter. We spread about 50 pounds per acre in mid-summer to perk up the grasses in their summer slump. We feel like there is a good return on our investment with higher pasture yields through the remainder of the growing season. The nutrient analysis of the fertilizer is 4-3-2. This fertilizer also has 11% calcium added. We buy it in semi-load quantities of 25 tons to spread over 100 acres of pasture. This fertilizer cost is $170/ton delivered (2020 pricing). For the 25 tons we bought that meant a bill of $4,250. That works out to about $42.50 per acre. How much did we pay per pound for the fertilizer? About 8.5 cents per pound of fertilizer.

How Does Our Organic Fertilizer Cost Compare to Conventional Fertilizer Costs?

Since there is 4% nitrogen in the organic fertilizer we bought:

0.04% N x 50lbs/A. = 2 lbs of nitrogen were applied per acre. This cost therefore is $21.25/lb per acre for N.

This is far below the typical rates suggested by universities (50 units N per acre) for grass pastures, but it seems to work for us because we feel N is cycled well and available to our grass pastures without much lost from the system due to volatilization, leaching or runoff. We also use clovers (legumes) to fix nitrogen and feed the grasses. We have about 3.5% organic matter in our pastures compared to our neighbors' fields which run about 1.5% organic matter. As you know from reading a previous paper, this extra two percent organic matter gives us the equivalent of 50 lbs of mineralized nitrogen. We grow our own nitrogen.

Compare this cost with the cost of conventional nitrogen fertilizers. Urea cost about $570/Ton last year (2014). In this scenario, a farmer is paying $570/2000 lbs = about $0.28 cents per pound of fertilizer.

How much nitrogen is that? Urea’s NPK grade is 43% nitrogen. So in a ton (2,000 lbs of urea there is 2,000 x 0.43 = 860 lbs of nitrogen.

A pound of nitrogen from urea costs ($0.28/lb) x (1 lb/0.43 lb) = $0.65/lb of N. Conventional farmers are typically advised to input 50 lbs of synthetic N per acre when they grow pasture or hay. At 0.65 cents per pound, that amounts to about $32.50/A. By the way, because natural gas prices are falling due to fracking technology, N fertilizer costs are also dropping because the energy needed costs less.

You can see why organic farmers have to “grow our own” nitrogen. If we tried applying 50# nitrogen per acre by using organic poultry litter we would have to apply 1250 lbs or a little more than half a ton of poultry litter at a cost of $109/A. Yet our forage yields per acre are equivalent to or higher than conventional farms.

The Cost of Organic Nitrogen Fertilizers is the Biggest Extra Cost in Organic Farming!

The same logic holds true for corn. Our organic corn yields beat the county averages every year. In 2014 our fields yielded about 180 bushels of corn per acre. How is that possible when we only add a few pounds of nitrogen from poultry litter to the corn crop each spring? We take credit for green manure plow down of the previous year’s pasture, we out-winter the dairy cows on the field that will be turned under for corn, thus accumulating manure. We spread composted manure to the field. In all, we likely add close to 100 pounds of nitrogen from organic on-farm sources to our corn field. And almost none of the nitrogen we add to the system is lost like happens in conventional farming. Conventional farms may add 150 lbs N per acre, but they likely lose 1/4 - 1/2 to leaching or volatilization.