Soil-Building with Cover Crops in California Almond Orchards

Lonnie Hendricks
UCCE Merced Cnty, 2145 W Wardrobe Ave, Merced, CA 95340-6496

A cover crop trial with ten cover crop mixes was planted in fall 1992 in Atwater at the Arnold almond orchard. Each plot is two middles wide and replicated twice. Comparisons are also being made in 5 orchards with established cover crops.

The following cover crops are being compared: Blando brome, Zorro fescue, Cahaba white vetch, subclover mix, rose clover, non-tillage clover, bur medic, annual clover mix, resident vegetation, Beneficial Blend, and Insectary Mix.

Samples show the two highest OM levels are in the Beneficial Blend and the Insectary Mix. The established resident vegetation has the highest OM level in the Arnold orchard. The top OM levels are in the established vetch covers in the R. Eck and G. Anderson orchards and in the resident vegetation in the R. Anderson orchard. The two year vetch/clover cover in the C. Lashbrook orchard and the new resident cover in the T. Takar orchard have intermediate OM levels.

Ladybird beetles were abundant in the established vetch/clover cover crops at the G. Anderson, R. Eck and C. Lashbrook orchards during April and May. Ladybird beetle levels were moderate in the resident vegetation in the T. Takhar and R. Anderson Orchards. In the Arnold test planting there were high ladybird beetle numbers in the Beneficial Blend, Insectary Mix, vetch and clovers. Numbers were low in the resident vegetation, Blando brome, Zorro fescue, and in the bur medic which made poor growth this first year.

The levels of beneficial, parasitic wasps were measured in each of the cover crops. These levels are highly variable, but appear to be lower in the resident vegetation at the Arnold's and in the Takhar orchard.

Earthworm activity has been measured as a way of estimating soil and health and viability. Most of the earthworms were found in the established covers in both the G. and R. Anderson orchards and in the Eck orchard. Moderate numbers were found in the Lashbrook orchard which has only had vetch cover crop for 2 years. No worms were found in the Takhar orchard or in the newly established covers at the Arnold farms. The Arnold orchard was "seeded" with earthworms in April 1994 to start a population.

During the 1993 growing season no insecticides were applied to the five innovative orchards, except for the T. Takhar orchard. In the Takhar orchard a dormant spray of diazinon plus oil and copper, and a hullsplit spray of Lorsban was used.

Table 1. PTB caused more damage to the crop than NOW in 1993.
Rejects Due to Worms
Orchard/Culture	1988 TOTAL	1989 TOTAL	1990 TOTAL	1991 TOTAL	1992 TOTAL	1993 TOTAL
GA:VETCH/NO SPRAY	2.8	1.1	0.4	0.2	1.8	2.1
RA:NATIVE/NO SPRAY	2.7^a	1.8^a	2.9	0.6	1.6	2.7
TT:NATIVE/DORM+HSPLT		9.5^b	6.5^b	0.4	4.3	2.2^b
PC:VETCH/Bt+Goniozus				3.9	3.9	2.2
RE:VETCH/NO SPRAY						4.1
^a: RA dormant spray 1988 and 1989 only. ^b: TT annual dormant spray plus hullsplit

Return to the index for the
Cover Crop Research and Education Summaries