Fall Gardening and Fertilizer Cost Calculations

More On Fall Crop Selection

Yesterday we transplanted our 30-day old starts of fall brassicas:

 Bak Choy, Baby Choy—a dwarf cultivar from the Burpee seed rack at Lowe’s

 Broccoli, Thompson—a variety developed specifically for fall culture, from Southern Exposure

Brussels Sprouts, Catskill—an old standby from the Burpee seed rack

 Cabbage, Early Flat Dutch—starts from a gardening friend

Cabbage, Savoy Perfection—also from Southern Exposure, recommended for fall growing

Chinese Cabbage, Michihili—the standard “napa” type, from Mayo Garden Seeds

We had previously transplanted cauliflower ‘Frosty’ from the same July 21 sowing, and those plants are now almost a foot tall. All of our brassicas receive a dusting of Dipel weekly. Today, I fed each transplant about two tablespoons of cottonseed meal, working it into the soil at the base of the plant.

We also started five Romaine lettuce cultivars:

·         Anuenue—developed for Hawaiian heat, our seeds came from Southern Exposure

·         Freckles—from the Burpee seed rack

·         Forellenschluss—also from Burpee

·         Jericho—originally from Israel, another one from Southern Exposure

·         Generic-- a green variety that grows well here, purchased from Mayo Garden Seeds

We expect these plants to be ready to go into the ground in three weeks. Romaine lettuces are more heat tolerant, and so will perform well despite the unusually warm early autumn days we are likely to experience.

A Note on Amy’s Sugar Gem

We purchased the seeds of this “patio” size tomato from Southern Exposure on the basis of their glowing catalog entry. We have not been disappointed. Besides abundant fruit production despite the unseasonably hot, humid summer, the plants have remained free of common problems. The fruits resist cracking, even with the boom-and-bust rainfall distribution we had this year. The flavor is superb, they keep a week or so after picking. If you are inclined to canning, Amy’s Sugar Gem is a cinch to peel after 30 seconds in a boiling water bath. Cut a tiny slit in the blossom end with a serrated knife, plop them in rapidly boiling water for no more than half a minute, and transfer to a sink full of cold water with a slotted spoon. After another half minute, the peels can be slipped off easily with your fingers, and the fruit will remain whole and undamaged.

Determining Fertilizer Costs

I covered this topic in The New American Homestead. Here is how to compare the cost of different brands and types of fertilizers. Nitrogen, phosphorus and potassium percentages by weight are printed on every fertilizer package. Phosphorus and potassium are abundant and cheap, but nitrogen, in a form that plants can use, is not. Natural sources include volcanoes and lightning, but by far the majority of natural nitrogen comes from the activities of beneficial bacteria. Organic nitrogen sources consist of the tissues of plants or animals that have been concentrated in some way to render them effective as fertilizer. Cottonseed meal is one example. It contains about 6% nitrogen, and is a good source for the home vegetable gardener. A three pound bag costs $8.72, including tax, at my local garden center. Since six percent of the contents of the bag is nitrogen, the weight of the nitrogen is 0.18 pounds. (.06 X 3) Dividing the cost by the weight of nitrogen yields a value of $48.45 per pound of nitrogen.

We can use this same method to calculate the relative cost of any nitrogen source. Earthworm castings were on offer at another store I frequent. The best price was $43.69, including tax, for a 30-pound bag. The label says it is 1% nitrogen, so the bag contains 0.3 pounds of nitrogen, at a cost of $145.63 per pound!

Bear in mind that in both cases, nitrogen fixed by soil bacteria was taken up by plants that were in turn processed (either by worms or a cotton gin) into a usable material. This material then had to be packaged and transported, all at additional cost. The less concentrated the nitrogen source, the more transportation costs add up. At one percent nitrogen, you have to ship 99 pounds of inert material for every pound of nitrogen. Understanding this, you can begin to understand the costs.

Now let’s calculate the cost for artificially-fixed nitrogen. This is what is added to chemical fertilizer mix. A 40-pound bag of 10% nitrogen fertilizer at Lowe’s is $18 with tax. If you do the math, you will find the cost per pound of nitrogen is $4.50. Unfortunately, the external costs of producing this nitrogen by artificial means are not taken into account. The energy required to produce ammonia or other forms of nitrogen that can be utilized by crops is produced at the cost of large amounts of carbon dioxide and other kinds of pollution, because natural gas is both the feedstock and the energy source for the process.

According to a publication from Iowa State University:

“ Due to the consumption of natural gas as an energy source and as feedstock in ammonia produc­tion, the price of N fertilizer is typically related to supply and price of natural gas. A modern ammonia production plant requires net energy consumption of approximately 29.7 million BTUs per ton of N (Kongshaug and Jenssen). Upgrading ammonia to other N fertilizers requires even more energy: 35.9 million and 31.4 million BTUs per ton for urea and urea/ammonium nitrate manufacture, respectively. “

This is equivalent to burning a gallon of diesel fuel for every 10 pounds of fixed nitrogen thus obtained, in terms of the energy needed. But how much diesel fuel was needed to move the earthworm castings from their source to Knoxville? Ten pounds of nitrogen would be half a ton of bagged worm poo. Calculations far more complex than the ones above would be needed to accurately compare the overall environmental cost of various forms of fertilizer. How much energy was expended, for example, to grow the cotton that ended up in my cottonseed meal? Were pesticides involved? No labeling requirement, to my knowledge, exists for soil amendments.

Conscientious gardeners everywhere might benefit from having this knowledge, but it is not easy to obtain.