Mario Viveros

UCCE Farm Advisor, Kern County

Deciduous Tree Fruits and Nuts

September 30, 2002

The 2002 almond crop has been harvested and it is one that will be in our mind for many years. There is no question, this year's crop was a big one. There were many orchards that produced more than 3,000 meat pounds per acre and there were a few that went more than 4,000 meat pounds per acre. The down side of this yield was the small kernels. I saw some Padres that looked like beans.

Growers have been asking: Can we expect 2002 yields in 2003? It is difficult to answer that question since there are many components that determine yields. Weather during bloom plays a critical role in pollination and fruit set. We don't know the type of weather for the 2003 bloom season. Furthermore, we are weather takers and have no control over it. This doesn't mean we shouldn't prepare our orchard for next year's crop. There are things a grower can do in the fall to improve orchard performance in the future.

Orchard cover crops are not new in almonds. In fact, they have been promoted by U.C. Cooperative Extension advisors for more than 40 years. However, at the present time, there are very few orchards in the Southern San Joaquin Valley with a cover crop. I believe growers should consider a cover crop for their orchards. Cover crops do increase water penetration and decrease the dusty conditions during harvest.

The best time to plant a cover crop is during the fall. Planting at this time will insure a good start before winter weather starts. If you plan to prune your orchard, plant in every other middle between the tree rows so as to leave a middle for the accumulation of the brush (prunings). In the next year, plant the middle where the brush was this year. On this basis, you will be alternating middles with prunings and cover crop.

The best cover crop to increase the rate of water penetration is barley at 70 to 80 lbs. per acre. Other covers that have done well in Kern County are blando brome, oats and zorro fescue. All have improved water penetration. The barley and oats should be mowed high (6 to 8 inches) by the middle of April. Then, the subsequent mowings should be low enough to destroy the crown. The blando brome and zorro fescue should be allowed to go to seed. These grasses can re-seed themselves every year.

A cover crop will need an additional 30 - 40 pounds of nitrogen in the spring to compensate for the nitrogen tie-up by the bacteria that are decomposing the residue. The cover crop will also require extra water. It is estimated that 12 to 18 inches of water are needed for a healthy cover crop.
The biggest benefit of cover cropping will be improved soil conditions and better water penetration. These benefits are cumulative, usually realized after a few years rather than following just one season. In addition, cover crops do firm up the orchard floor which leads to less dusty conditions at harvest. This can be important in the future, if people continue to complain about the dust during almond harvest.

There are disadvantages with cover crops. Heavy residue is produced when plants are allowed to mature before mowing. This can interfere with harvest efficiency. In the case of barley, it should be mowed before crown formation. The crown can make the sweeping operation impossible.
Cover crops tend to encourage gopher populations, especially in young orchards. They can also increase ant populations and in time allow undesirable weeds to develop.

One of the biggest disadvantages of cover crops is frost in the spring. The ground of a cover crop can be 1 - 2 degrees F cooler than bare ground. The danger of frost is less in the Southern San Joaquin Valley than in the Central and Northern San Joaquin. However, in Kern County, we have had frost in almonds in the last week of April. For this reason, in the spring, it's important to maintain soil moisture in the top 18 inches. In the event of frost, the soil moisture will provide enough heat to prevent frost damage.