Why Fertilize Your Vegetables?
There is a simple reason why we fertilize our vegetable gardens. Tomatoes, squash or peppers use up available nutrients in a matter of a few years and each successive crop will get smaller and smaller.
This personal experience is backed up by research from the University of Nebraska’s Knorr Holden research plot, continuously planted with corn since 1910. The crop yield steadily decreased every year until 1942, the year after the first annual application of 12 tons of cow manure. Yield increased every year after that in a linear fashion for over a decade. Overall soil health greatly increased, including available water holding capacity, availability of soil enzymes, trace minerals and available carbon in the soil.
So, what does this tell us? Mother Nature knows best. It is estimated that 30 to 60 million buffalo manure factories roamed the Great Plains before we began to plow them. Even so, 40 years of corn production depleted that huge deposit. We need to apply dust bowl lessons to our own gardening practices. Rich compost produces bumper crops.
Why my sudden interest in cow poop? This year, we (that really means my wife) grew the largest San Marzano tomatoes I have ever seen. A plum tomato originating in Italy, they grew four-and-a-half inches long in no-dig raised beds that were not nearly as productive last year. Inquiring minds want to know why. While this is not definitive research like the Nebraska plot, all the things we did this year were research driven. We grew a cover crop, composted it in place and left the roots in the ground. We always add compost when we plant, but this year we also added cow manure. That was the recipe for success!
So, why not just throw on miracle plant fertilizer from the corporate chemistry set? I admit I am basically lazy. I am also frugal (read cheap) and want great tasting vegetables for little work. This can be an oxymoron.
Commercial fertilizers cost more than “cardboard tomatoes,” so neither one interests me. Chemical fertilizers are sold according to their nitrogen, potassium and phosphorus content (N-P-K). A balanced fertilizer has equal numbers, like 5-5-5. But mined and synthesized chemicals are all that are in the bag. The trace minerals I mentioned in the manure are missing. For information’s sake, cow manure is 3-2-1. It costs $3 per 2 cubic foot bag. Chicken manure has more of all the normally measured elements (5-4-2), but the product I looked at had been reduced to 3-2-2 with added compost, at twice the price. Cow manure is a bargain containing sulfur, magnesium, calcium and other micronutrients.
Organic fertilizers use the same system of nutrient classification. But the word “organic” doubles the price! And, if I use fish emulsion, my dog will literally eat the dirt. By following the Nebraska research formula of 12 tons per acre, I calculated an application of .61 pounds per square foot; 1 cubic foot of manure is 25 pounds. Along with our compost, we applied a little over half a 2 cubic foot bag per 4×12 raised bed. So, the next time someone tells you something isn’t worth “blank,” tell them about my tomatoes or U. Nebraska’s corn!
Jim Bliss is a University of California Cooperative Extension Master Gardener of Tuolumne County.
