I have a 10x15' raised bed in a community garden. Every spring I add compost and fertilizer, and then both in lesser quantities throughout the season. Never letting the plot sit dormant for a season has finally caught up with me (and that's really not an option because there are rules about not planting your garden). Last June the soil became completely spent, turning to grey dust. I dumped compost, peat moss and grossly exceeded the amount of fertilizer you're supposed to use per square foot. That got me through the summer and fall without incident. So for this coming season, which for me starts early May in Philadelphia, what can I do to avoid this problem from reoccurring? I was thinking of buying cow manure -- how much should I buy, and after I mix it in, how many days until I can plant? Any other suggestions? Thanks.
It is difficult to diagnose from a distance. Is your soil clay or sand? If it did not look like rich black dirt, your compost applications might be too little. I put in two inches most years. If you put in too little compost, you may have some micronutrient deficiency, a condition that will not be helped by synthetic fertilizer, but will be helped by large amounts of compost. I try to prevent that by also giving some wood ash to the garden. In Philly, you will probably have acid soil as well, so you might try a couple of pounds on your plot.
And if you grossly overdid the fertilization you might have an excess of one or more macronutrients, specially if the soil is clay and retains them. That, in turn, might chemically prevent the absorption of other nutrients.
If you don't want to test the soil, two inches of manure will alleviate whatever you may have. Even if it is a chemical imbalance, it will buffer it some. It certainly has enough nutrients to get you through a season without other fertilization. Many vegetables can be planted through manure after a single good rainfall. Most greens, squashes and melons, garlic, tomatoes and potatoes, will happily grow in manure that was laid a month before. Just lay it on top, clear a little space when you plant, to avoid direct contact with the young plant, and let the worms pull it in for you.
Top with the manure and also enough gypsum almost to hide the manure. This will help break up the clay. Then, top with enough bone meal almost to hide the gypsum. The bone meal supplies phosphorus, which must be present in the root zone ahead of time because it does not dissolve and leach through the soil.
Water the gypsum to rinse it into the soil. Then, after the soil is almost dry (moist but not wet enough to form a sticky clod), rototill to a depth of at least a foot into the native soil (i.e., with 6 inches of manure, till down 18 inches -- 6 + 12). In a community garden near my house, several gardeners will get together to rent a rototiller for a day, sharing it for all their parcels.
The manure is more for organic matter than for nutrients. If you don't over-feed, a 6-inch layer tilled into the soil should be good for 2-3 years. You won't have to do any serious tilling until the manure has to be replaced. Excess nitrogen speeds the decomposition of the manure. Over-feeding means it might have to be replaced yearly.
Also, over-feeding with nitrogen promotes leaf growth at the expense of roots, flowers, and fruits. This is okay for lettuce, spinach, cabbage, basil, and other leaf vegetables. But excess nitrogen inhibits the production of carrots, raddishes, and other root vegetables; tomatoes, peppers, beans, peas, and other fruit vegetables; and artichokes, cauliflower, and other edible flowers.
The gypsum, however, leaches away and needs to be replaced each growing season. The bone meal does not leach at all; a generous application before tilling will be good for as long as 5 years. (You can substitute super-phosphate for the bone meal, but use only half as much. It might last 10 years in the soil before the plants have exhausted the supply of phosphorus.)
If the clay is not impossible, you might omit the gypsum but not the bone meal. Both gypsum and bone meal supply calcium, which is required for root growth.
My clay is adobe, so sticky you spend more time getting it off the spade than digging. They ruined a good source of bricks when they built this tract. I use a 50-pound sack of gypsum in my standard residential (R1) lot in less than a year. It allows me to grow plants that cannot tolerate heavy, soggy soil.
The manure has substantial amounts of nutrients. It is 2-1-2 by dry weight. The OP needs something like half a ton. That is 10 lbs of nitrogen right there. And of course there is plenty of calcium. Imagine drying and burning all that manure. The leftover ash (several pounds) is 50% calcium.
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