There are several different choices for Plant By-Products to feed your lawn: 

Alfalfa Meal - This is readily available in pellet for at most farm stores as an inexpensive animal feed. It contains about 3% nitrogen and works well as a soil amendment because it is a grass product. 

Corn Gluten - Corn gluten can be spread on lawns as a weed suppressant. When applied to a lawn, it inhibits germination of seeds. It is also quite high in nitrogen, containing almost 10%. NOTE: Do not apply to yards when you are overseeding. The new seeds will not come up. 

Cottonseed Meal - Rich in nitrogen, containing 7%, this is a popular fertilizer in the South where cotton is grown. However, since most cotton in the US is heavily sprayed with pesticides, this is not a popular fertilizer amongst the organic community. 

Soybean Meal - On the more expensive side, Soybean Meal is found in many natural fertilizers due to its high nitrogen content of 7%. 

Seaweed Products - In multiple studies, Seaweed Products have been found to contain all 16 elements necessary for plant growth. Dried, it contains about 1% nitrogen and phosphorous and 5% potassium. It is also found to contain a particular hormone that is responsible for cell division and enlargement called cytokinin. Organic lawn specialists have reported increased germination and seedling vigor in yards treated with Seaweed Products. 

Wood Ash - Readily available to anyone who burns wood at their home, Wood Ash is used to raise soil pH. It contains 2% phosphorus, 6% potassium, and about 20% calcium. Note: Do not use from unknown sources or if your soil pH levels are adequate or high.