Here are recommendations for the amount of food a family of five needs for a year. Both of the following recommendations are from the early 1930's. However, I don't see why they can't be applied today.
The first is from Flight from the City by Ralph Borsodi for the Dayton Homestead program.
Bread, cerals, baked goods - 750 pounds
Vegetables and fruits - 3,000 pounds
Butter, lard and other fats - 250 pounds
Meat and poultry - 500 pounds
Eggs - 200 dozen
Milk - 300 gallons
Borsodi had specific ideas in mind for producing this food although he was quite flexible such as having a cow rather than goats if land were available. He planned on 25 cockerels or capons, 2 buck goat kids and 2 pigs for meat. There would be 25 laying hens for eggs. There would be 3-4 hives for honey.
He felt that 500 quarts of fruits and vegetables would have to be canned or dehydrated.
In Dayton (Ohio), he believed this amount of food and feed for the animals would require 3-5 acres.
The next recommendation was from the Department of Home Economics of the U.S. Department of Agriculture. I'm guessing at the weights of bushels and pecks below.
Flour, cerals - 400 pounds
Potatoes and sweet potatoes - 400 pounds
Dried beans - 1 peck (about 15 pounds)
Tomatoes and citrus fruit - 10 bushels (about 700 pounds
Leafy, green and yellow vegetables - 585 pounds
Dried fruit - 75 pounds
Other vegetables and fruit - 1,400 pounds
Butter, other fats - 165 pounds
Sugar - 200 pounds
Lean meat and poultry - 620 pounds
Eggs - 145 dozen
Milk - 400 gallons
They had no suggestions as to how to produce this much food.
So, what kinds of yields might you expect in order to produce this food? I've taken late 1970's average vegetable production figures for the U.S. and converted them to pounds per 100 square feet. I used this time period since it certainly doesn't take into account some of the technical advances that are available today and it is highly unlikely that any person is going to have technology greater then this in a collapse.
It also takes into account the fact that many people will be doing "serious" vegetable growing for the first time. They not only won't know what they are doing from a cultural point of view but they are likely to have the wrong vegetable varieties for their area.
Now, someone is going to look at the following figures and argue that they currently get higher yields or that bio-intensive, permaculture, mulch culture or one of the many other growing methods produce ten times as much. My response is, yes, they look low to me too. But that's they way it is and I don't think people will get higher yields in the long term.
There are a number of reasons this will be the case. First, nutrients such as phosphorous are going to be in short supply (There is only a 25 year supply that can be commercially mined before it is exhausted.). Nitrogen also presents a problem. Yes, you can use legume cover crops. The trouble is that you then have to grow and harvest the seed for them. Second, climatological and geographic location have a tremendous influence on crop yields. Lastly, the ability to irrigate will have an immense impact on yields. In fact, water for irrigation will probably be the limiting factor rather then nutrients.
Droughts come and go in the Midwest and east coast and need to be considered. However, in the west, one simply has to irrigate since there is little, if any, precipitation during the growing season.
Although actual irrigation needs vary throughout the growing season, let's say you are irrigating 1 acre of crops and that you apply 1 inch of water per week (During peak heat periods the amount of water is often far higher.). So, how much will you need to apply per month? An acre-foot is 325,851 gallons and an inch of water per week roughly equals a third of an acre-foot. Therefore, you will be applying almost 100,000 gallons per month or over 3,000 gallons per day.
Now let's carry it a step further. Assume you have a well that can pump 10 gallons per minute (a good residential well). How many hours does your pump have to run each day for irrigation? Five hours - for 1 acre. Realistically, five hours per day of pumping isn't going to happen, muchless 15 hours. And, unless you are willing to invest lots and lots of money, PV panels aren't going to work either.
If you live in California, you can get the evapotranspiration for your area. Click on the data tab at the top. Free registration is required. You don't have to be a grower to register.
Given these constraints, this is why I suggested that some from of hydroponics was probably the only sustainable way to grow food.
Here are the yields in pounds per 100 square feet. They were taken from the 1980 edition of Knott's Handbook for vegetable Growers.
Bean, processing - 9
Bean, lima, processing - 7
Beets, processing - 60
Broccoli - 20
Brussels sprouts - 29
Cabbage, processing - 92
Carrot, topped - 64
Cauliflower - 23
Celery - 115
Corn, processing - 23
Corn, feed - 15
Cucumbers - 24
Eggplant - 46
Lettuce - 53
Melon, Persian - 28
Melon, Honeydew - 41
Muskmelon - 32
Okra - 23
Onion - 71
Pea, processing, shelled - 6
Pepper, Bell - 25
Potato - 58
Pumpkin - 92
Spinach, fresh - 16
Squash, summer - 69
Squash, winter - 92
Sweet potato - 27
Tomato, fresh - 39
Tomato, processing - 101
Turrnip - 69
Watermelon - 27
Wheat - 10
For comparison, here are the yields of crops grown hydroponically in a greenhouse. One of the charts in the book, Hydroponic Food Production by Resh didn't say how many crops were grown during the year. I've put an * by crops where the yield is per crop for susre.
Bush beans - 21*
Beets - 55
Broccoli - 60*
Cabbage - 41*
Cucumbers - 64*
Lettuce - 48
Oats - 6
Peas - 414
Radish - 41*
Rice - 12
Potatoes - 322
Soya - 36
Tomatoes - 207*
Wheat - 9
I want to close by returning to Borsodi's 500 quarts (100 per person) to be canned each season. Here are some canning yields to help you determine how much you need to grow. The data is from the Farm Journal's Freezing and Canning Cookbook .
Apples - bushel - 16-20
Berries - 32 quarts - 24
Peaches - bushel - 18-24
Pears - 46 pound box - 16-22
Plums - 28 pound lug - 12-15
Tomatoes (chunk) - bushel - 20
Tomatoes (juice) - bushel - 12-16
Beans, lima, in pod - bushel - 6-8
Beans, snap, green, wax - bushel - 15-20
Beets, without tops - bushel - 17-20
Carrots - bushel - 17-20
Corn, whole kernel - bushel - 8-9
Okra - 1 1/2 pounds - 1
Peas, in pod - bushel - 6-10
Pumpkin/winter squash - 1 1/2-3 pounds - 1
Summer squash - 2-4 pounds - 1
And, don't forget the grain or hay you have to raise for the animals. For example, a laying hen that is confined eats about a bushel of grain a year.
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