Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu
One principle of managing for improved soil health is that you should always have a crop growing on the soil. This practice will maintain or add organic matter, provide benefits from the action of growing roots, and recycle nutrients.
Where fall cover crops were not planted due to late harvest, spring cover crops can be planted and provide soil health benefits where vegetables and field crops are not scheduled until late May or the month of June.
The most common cover crop options for late March or early April planting include spring oats, mustards and annual ryegrass. Plant oats at 90-120 lbs per acre, mustards at 10-20 lbs per acre, and annual ryegrass at 20-30 lbs per acre.
Field peas are another option for spring planting; however, we are somewhat south of the best zone for spring planting. One type of field pea is the winter pea which is often fall planted in our area but can also be spring planted. It has smaller seed so the seeding rate is 30-60 lbs per acre. Canadian field peas are larger seeded and are also planted as a spring cover crop. Recommended seeding rate is 120-140 lb/a.
Mixtures also can be used. Field peas are well adapted to mixing with spring oats or with annual ryegrass. Reduce seeding rates of each component when using in mixtures.
Many of the mustards have biofumigation potential. When allowed to grow to early flower stage and then incorporated into the soil, they release compounds that act as natural fumigants, reducing soil borne disease organisms. Some biofumigant mustard varieties include Pacific Gold, Idagold, Caliente, and Kodiak.
When used as a biofumigant, mustards should be grown as a crop. You need to add 60-100 lbs of nitrogen per acre to produce the maximum biomass. Nitrogen is also required to produce spring oats and annual ryegrass at similar rates. When planting mixtures with peas, nitrogen rates should be reduced.
An often forgotten spring seeded legume crop that can also be used is red clover. Red clover can be frost seeded into small grains, seeded alone, or mixed with spring oats or annual ryegrass. Seeding rates for pure stands would be 10-16 lbs/a, for mixtures 6-10 lbs/a.