Recently, several blogs from Frog Hollow Farm have dealt with cover crops. Planting cover crops is a cultural practice than can address soil quality and environmental issues concerning water. Cover crops are not grown for harvest. They provide multiple benefits, some of which are listed below:
Fix atmospheric nitrogen that later becomes available for soil microbes and fruit trees
Behind the big shed, new prune trees are replacing older trees that have been cut down. This is the area where worms were put into planting holes in December. This area has also been seeded with Phacelia tanacetifolia (common name phacelia), a native California nectar producing plant that attracts beneficial native bees. Phacelia is also an important cover crop because it efficiently traps nitrates (most common mineral form of soil nitrogen) that may remain in the soil at the end of the growing season. This cover crop can reduce leaching/loss of the nitrate-nitrogen with winter rains and/or loss as atmospheric nitrogen. Phacelia will accomplish two important functions in the orchard: attract native bees and trap nitrogen in the soil.
Another plant that will hopefully accomplish two functions in the orchard is sour clover (Melilotus indicus). Melilotus is not a native California plant but it produces coumarin (in its roots). Coumarin is a blood thinner and anecdotal evidence suggests that gophers avoid the roots of this plant. Gophers are a very big problem at Frog Hollow Farm because they kill a lot of trees by eating the roots. This week we planted Melilotus in a test area to see if it can grow in the orchard. If everything works out, we will plant some Melilotus in the re-plant area and hope that the gopher anecdote is true. Melilotus is also used as a cover crop because it is a nitrogen-fixer, in contrast to phacelia which is a nitrogen scavenger. Melilotus and other members of the bean family associate with a type of soil borne bacteria (rhizobia) that can convert atmospheric nitrogen into nitrogen that can be used by microbes and plants.
In the replant area, we hope to grow two cover crops that will attract beneficial native bees and repel gophers. These crops will combine the nitrogen scavenging of phacelia with the nitrogen fixing of the sour clover. When these crops decompose (green manure; low to moderate C:N ratios), they will quickly cycle nitrogen back to the soil.