I held back from posting on this thread, hoping that someone else could give you feedback on the specific book you asked about. And it happened!
I grew a small amount of wheat in 2008/2009 between the sidewalk and the street. I planted the kernels every 4" or so, but could've planted every 2" or so and had even more wheat to harvest. I got my information from Jon Jeavons' How to Grow More Vegetables...
(which is one of the two or three books I recommend most often, depending on the question[s] being asked).
Despite the title, Jeavons doesn't restrict himself to vegetables; the title is a holdover from his original book, published 30 or so years ago. He's now in the 7th edition, each one thoroughly revised based on recent research on spacing of plants, human nutritional needs, compost building, etc. He discusses "calorie crops"--staples of nutrition like potatoes, wheat, and other backbones of many vegetarian diets around the world. He helps new gardeners with soil of whatever condition/quality not to get overwhelmed in the first couple of years and to move towards as much self-reliability as possible, given their own circumstances. Those who have a quarter-acre or more will find his information thrilling (I believe):
In his discussion on soil sustainability, Jeavons asserts (with lots of evidence) that it is possible for the bulk of the vegetable/plant calories for one person's diet for one year to be grown on 4,000 square feet. One acre = 43,650 square feet, so a quarter-acre lot contains 10,912 sq ft, give or take. If the layout is favorable to gardening, this means that HALF of the plant calories for TWO people could be grown on that 4,000-sq-ft area per year. The details are in his book. Note, however,
that these numbers do *not* apply to new gardeners; they are a goal to strive for after the skills of feeding the soil, maintaining the "living mulch" beds, growing "compost crops" and "calorie crops" and others have been mastered.
Jeavons' book is available for circulation in my local public library. Maybe you can leaf through it at your local library and see whether its information speaks to you and your situation. It certainly isn't attainable for me, but it has helped me make the most of my 96 sq. ft. and alter my planting plans to my specific micro-growing conditions so that I harvest healthy, vibrant crops for as much of the year as I can, rather than fighting and swearing about non-productive eggplant, zucchini, and peppers.
He also broadened my understanding of what was compostable, and has directly reduced what goes into the trash container at my house. Long-term victories, every one!
Sunset Zone 17, USDA Zone 9