Cover cropping in California’s
Central Valley has been reserved for permanent crops rather than annual
row crops, such as tomatoes. However, over the past couple of years,
a few growers on the west side of Fresno County have been experimenting
with cover crops as a way to increase organic materials in their soils,
reduce tillage and boost yields.
Jeff Mitchell, an extension specialist with the Department of Plant
Sciences at the University of California, Davis, says that growers
who use cover crops as surface mulches in conservation tillage systems
can reduce tillage by as much as 60 percent. Cover crops are more
commonly associated with vineyards, almonds and orchards, Mitchell
says. However, new strategies and different equipment are being developed
to adapt cover crops to tomato fields. Jesse Sanchez, farm manager
for R.A. Sano Farms in Firebaugh, says that this year he planted a
cover crop on about 1,000 acres of tomatoes. He planted the cover
crop last year in September on 60-inch beds and let it grow for 60
days before killing it with Roundup. Later on in March, during planting
season, he tilled the ground in 12-inch wide strips in the center
of the beds, putting herbicides on at the same time. Shortly after
that, he transplanted the tomato plants directly into the mulch.
“We plant right in the center of the bed, and then we try not
to put anymore tractors in the field until harvest time,” he
explains.
On average, Sanchez says he’s been getting an extra two to
10 tons per acre in his cover-cropped fields. Fruit size and quality
coming out of such fields also seems to be better.
“You see higher solids in the tomatoes. Some have brix levels
as high as 6.2 to 6.4,” Sanchez says. “Once cannery is
paying us more for that (the higher brix), and we’re trying
to get other canneries to do the same.”
The cost of planting the cover crop in the fall is relatively negligible
since workers need to pre-irrigate the fields during the same time
the cover crop is planted anyway, Sanchez points out.
“We use the same water to irrigate the cover crop that we would
be using to pre-irrigate the fields anyway,” he explains.
Sano Farms use to rotate tomatoes with cotton, but this became increasingly
difficult to do, Sanchez says. The soil was getting harder to till,
and whenever heavy rains fell during the fall and they were forced
to work the ground wet, it would contribute to additional soil compaction
problems.
Alan Sano of Sano Farms concurs that the use of cover crops mellows
the soil.
“We used to triticale and barley, and the triticale did a lot
better,” he says. The reason is triticale has a deeper and more
widespread root system; hence, it helps put more organic material
into the soil and helps loosen it up.
In past years, Sano says he experienced problems with his soil getting
so compacted and hard that it would crack and force water across the
beds and into other rows. This was especially true during wet years
when the workers planted cotton and needed to work the fields when
they were still wet.
“The soil would get so tight, we’d have to do three to
four hour sets,” Sano recalls. Six- to eight-hour sets would
cause root rot and kill the plants. Water, not absorbed quickly enough
would drown the plants.
Using cotton as a rotation crop in between tomatoes also did not
seem to be helping very much, Sanchez adds. The cotton doesn’t
have as many roots as crops, such as triticale, which help enrich
the soil. Next year instead of using cotton as a rotation, he plans
to use cover crops on more than 3,000 acres of tomatoes.
Aside from enriching the soil, one of the goals with using cover
crops in conservation tillage systems is to reduce tillage by about
half, Mitchell says. But fewer passes through the field can create
other challenges, such as difficulties controlling weeds.
“Weeds are still a problem in cover crop surface mulch production
systems, Mitchell admits. “Right now for better control, we
cultivate early and then as late in the season as we possibly can.”
In his experiments with tilled and no till cover crops in organic
tomato fields in Meridian, Calif., Mitchell found that the percent
weed cover in the cover crop mulches was 1.6 to 12.5 times higher
in the surface mulches (no till) systems versus the incorporated cover
crop systems the first year; the second year it averaged 2.4 to 7.4
times higher.
“This indicates the inability of even quite high residue surface
cover crop mulches to provide satisfactory weed control for conservation
tillage production,” Mitchell says.
To counter the problem with weeds, Sanchez converted several hundred
acres of tomatoes to drip irrigation. This, he explains eliminated
the need to put any tractors in the field between transplanting and
harvest.
“With the drip, we noticed more nightshade control, and dodder
wasn’t as much of a problem,” Sanchez observes.
But even without the drip system, Sanchez says he found himself using
fewer herbicide applications to control weeds in the cover-cropped
fields.
“We were probably spending $30 less per acre on herbicides,”
he says.
Considering the overall savings in herbicides, less tillage and higher
tomato yields, cover cropping is likely to become a permanent part
of the farm’s program, Sanchez believes.
Cover crops in tomato fields have other far reaching implications
for growers, Mitchell adds. As growers face the future, many will
be dealing with added government regulations limiting their tillage
practices.
“By reducing the number of operations in the fields, we were
able to reduce total dust emissions by 67 percent,” Mitchell
says.
Although cover cropping and conservation tillage in row crops in
not yet widely adapted in California, growers in other parts of the
world, including Brazil, are taking a much closer look at the practices.
There’s a lot going on in Brazil, Mitchell points out. Processed
tomato growers, in particular, are cutting back on their tillage practices
considerably. And while the cost of reducing tillage practices may
be only a small part of a grower’s budget, there are other benefits
in addition to the cost savings.
