Seed balls, also known as earth balls or nendo dango (Japanese: 粘土団子 ) , consist of a variety of different seeds rolled within a ball of clay, preferably volcanic pyroclastic red clay. Various additives may be included, such as humus or compost. These are placed around the seeds, at the center of the ball, to provide microbial inoculants. Cotton-fibres or liquefied paper are sometimes mixed into the clay in order to strengthen it, or liquefied paper mash coated on the outside to further protect the clay ball during sowing by throwing, or in particularly harsh habitats.
The technique for creating seed balls was rediscovered by Japanese natural farming pioneer Masanobu Fukuoka. The technique was also used, for instance, in ancient Egypt to repair farms after the annual spring flooding of the Nile. In modern times, during the period of the Second World War, this Japanese government plant scientist working in a government lab, Fukuoka, who lived on the mountainous island of Shikoku, wanted to find a technique that would increase food production without taking away from the land already allocated for traditional rice production which thrived in the volcanic rich soils of Japan.
To make a seed ball, generally about five measures of red clay by volume are combined with one measure of seeds. The balls are formed between 10mm and 80mm (about ½" to 3") in diameter. After the seed balls have been formed, they must dry for 24-48 hours before use.