Re: Why does an acre of corn yield more total protein than an acre of soy?

First, are you sure an acre of corn DOES produce more protein per acre than
soybean and how big the difference is? Confirm it using the two websites in the
references which give yields and protein contents. The third reference (Smith
1995) notes that soybean contains about 3.8 pounds of nitrogen per bushel (page
392), and corn contains 0.77 pounds of nitrogen per bushel (p. 39). Thus, the
corn yield in bushels per acre would have to be about 5 times more than the
soybean yield for it to produce more protein. The nitrogen content is directly
proportional to protein content.

If it is true that corn produces more protein per acre, there could be a number
of factors involved. You might be on the right track for one factor, nitrogen
fixation requires a large amount of energy, which comes from soybean
photosynthesis. That assumes you are relying on the soybean to provide most of
its own nitrogen. Do soybean growers use nitrogen fertilizer or do they rely on
the soybean to fix nitrogen? If you fertilize the soybeans with all the nitrogen
they require, does the yield increase? You can find info on soybean production
using google.com and searching for soybean production.

Other possibilities:
1. Hybrid vigor in corn given almost all corn grown commercially is hybrid corn.
2. Corn has been a crop longer so perhaps it has been bred longer for higher
yields or higher protein content.
3. The different types of photosynthesis between the two crops.
4. Is corn harvest index higher than that of soybean?

References


North American corn and soybean yield


USDA National Nutrient Database for Standard Reference

Smith, C.W. 1995. Crop Production: Evolution, History and Technology. New York:
Wiley.