Selecting & Using Cover CropsUnit 1.6 | Part 1 – 273b) In fall, time planting to take advantage of soil warmth and ensure strong germination;
cool soils will reduce germination and favor winter weeds
c) Select cover crops with allelopathic properties (e.g., mustards, cereal rye) that will
reduce weed pressure
d) Drill cover crop seed into ground where a flush of weeds (due to irrigation or early rain)
has been lightly tilled at the time of weed emergence; plant cover crop seed to residual
moisture.
e) Till field where weeds are emerging using a quick pass with a rotary hoe or tine weeder
as cover crop seed emerges (blind cultivation); depends on timing of weed and cover
crop emergence
- Cover crop incorporation
a) Timing of cover crop incorporation linked to current and predicted weather, and degree
of moisture in the field. Test soil moisture often to determine correct timing.
b) Test moisture using “feel” method (see Appendix 1, Judging Soil Moisture by Feel, in Unit
1.5, Irrigation–Principles and Practices). Moisture level is correct when medium to heavy
soils form a ball that can be easily broken apart. If soil “ribbons” when squeezed it is too
wet to work.
c) Once correct soil moisture is reached, flail mow cover crop if volume is high and if cover
crop is high in C and lignin
d) Mix cover crop residue with soil to facilitate breakdown and bed formation. A
mechanical spader is ideal for cover crop incorporation, but expensive.
e) Heavy offset wheel disc is most commonly used for incorporation. Adequate
incorporation may require several passes; chiseling after several passes will facilitate the
disc’s ability to turn soil and will break up compaction cause by the disc.
D. Special Cases
- Orchards and vineyards
a) Annual or perennial cover crops can be used in orchards and vineyards. Perennial
cover crops provide the benefit of year-round cover, but they also need management
(particularly mowing) to control weeds and pests, provide wildlife habitat, and prepare
for harvest.
b) In California, native cover crops (e.g., perennial bunch grasses) may provide cover
without increasing water demand
- Garden scale
a) Cover crops can be used effectively on a garden or small orchard scale. Fall- and winter-
grown cover crops can either be chopped and incorporated to break down prior to bed
formation and planting, or skimmed and used as a compost ingredient.
b) Note that it’s important to incorporate compost where cover crops are harvested in
order to replenish organic matter and nutrients
E. How to Roughly Estimate N Contribution from a Cover Crop
Most growers do not regularly estimate the total N contribution from cover crops, relying
instead on general estimates from sources such as Extension or USDA field stations. However,
knowing where the values come from and how you could obtain them yourself can give you
an overall deeper understanding of N management in cover crops. Doing an estimate can also
help you understand how different cover crops or different parts of your farm are performing
in terms of N contributions. See the demonstration, How to Estimate the N Contribution from a
Cover Crop (page 275) for details.
Lecture 2: Cover Crop Selection, Planting & Care