Winter, 1990 (v2n2)
Improving Soil Quality in Annual Crops = Better Production
A group of 40 row and field crop farmers met with extension specialists
at the Kearney Agricultural Center in Parlier November 28 to discuss
current information on ecologically sound soil management for
annual cropping systems. The theme was Enhancing Soil Quality
for Successful Production.
Soil quality characteristics addressed at the workshop included:
structure, tilth, soil-water relationships, weed management, and
soil fertility. Highlights of the meeting follow.
Organic Matter
Tillage and crop residue management were highlighted in presentations
by Lloyd Elliott, director of the USDA Cotton Research
Station, Shafter and Jim Rumsey, assistant professor of
agricultural engineering at UC Davis. Elliott emphasized the importance
of increasing organic matter content and enhancing the activity
of beneficial microorganisms that break down organic matter. He
said they are the keys to improving water infiltration and nutrient
cycling. High levels of soil organic matter have also been shown
to improve the crop's ability to resist various pest problems,
Elliot said. Two major factors may limit row and field crop production
under higher organic matter levels: 1) the lack of environmentally
sound weed control methods; and 2) the need for better equipment
and implements that allow for planting into crop residues and
a rougher seed bed.
Low-Till
Minimum tillage is a specific practice that has been show to enhance
soil organic matter levels and soil tilth. Rumsey defined it as
the minimum soil manipulation necessary for crop production or
for meeting tillage requirements under the existing soil conditions.
Some of the primary reasons farmers make use of minimum tillage
include: 1) reducing runoff and soil erosion; 2) conserving soil
moisture; and 3) saving money through reduction of energy and/or
labor inputs in tillage. Rumsey said research on field corn and
processing tomatoes at the UC Davis Student Experimental Farm
is developing useful information for row crop farmers. The number
of field operations were reduced from eight to two in field corn,
and from eight to three in processing tomatoes. Some of the preliminary
conclusions drawn from two years of data are shown in the following
table. More information is required in order to assess the effects
of minimum tillage on insects, diseases, and soil fertility, Rumsey
said.
| Consideration | Tillage | Tillage |
| crop yield | best | close |
| crop quality | same | same |
| weed control | best | problem |
| stand establishment | best | problem |
| soil compaction | least | variable |
| water infiltration | OK | best |
| soil moisture | OK | best |
| labor | most | least |
| operating costs | most | least |
| capital requirement | most | less |
Water-Soil Balance
Research has shown that irrigation practices must be adapted to
the changing soil conditions as growers work to modify soil structure
and improve infiltration rates. Blaine Hanson, a UC Davis
extension irrigation specialist, presented some of the key principles
in improving irrigation efficiency in annual cropping systems.
Irrigation efficiency is defined as the beneficial use of water
divided by the applied water. A high irrigation efficiency means
that losses of water are minimal. The resulting benefits of high
irrigation efficiencies include: 1) reduced water costs; 2) reduced
pumping costs; 3) better retention of mobile plant nutrients within
the root zone; and 4) protection of ground water supplies due
to less deep percolation of chemicals through soil profile.
In practical terms, the key to high irrigation efficiencies is
uniformity of water application, Hanson said. Uniformity
refers to the evenness with which water is applied throughout
a field. The uniformity of surface irrigation systems can be improved
by: 1) reducing the length of the irrigation run; 2) adjusting
the furrow inflow rate; 3) creating a smoother furrow surface
for water to move along; and 4) implementing a surge flow program
whereby the flow of water at a particular furrow is intermittent
instead of continuous. Knowing application and infiltration rates
for a particular field are essential for obtaining highest efficiencies.
The best technology available to growers for determining appropriate
application rates is to manually probe the soil to monitor what
is happening in the soil profile, Hanson said.
The uniformity of sprinkler irrigation systems can be improved
by: 1) maintaining uniform pressure throughout the sprinkler system;
2) repairing all leaks; 3) maintaining a uniform nozzle size;
and 4) avoiding irrigation on windy days.
Subsurface Drip Irrigation
Larry Schwankl, a UC Davis extension irrigation specialist,
discussed subsurface drip irrigation in row crop production. A
summary of advantages and disadvantages follows.
Advantages. 1) Uniform water application when properly
designed and maintained. 2) Reduced labor requirements compared
to conventional surface irrigation system. 3) Increased efficiency
of water and chemical use due to direct delivery to crop root
zone. 4) Maintenance of a dry soil surface allows for access to
field at all times and reduced weed growth. 5) Irrigation
effectiveness is not influenced by poor surface infiltration characteristics.
6) Documented yield increases for some crops and locations.
Disadvantages. 1) Installation and removal of buried drip
systems can be both difficult and expensive (reported costs as
high as $400/acre.) 2) Depending on water quality, proper maintenance
and operation of a subsurface drip system may require sophisticated
filtration systems plus chlorine and/or acid treatments to prevent
clogging of drip lines. 3) Difficult to detect and repair leaks
and clogging. 4) Subsurface drip systems require qualified and
extensive management. 5) Potential problems with germination
and stand establishment for some crops. 6) Initially high capital
costs ($1,000/acre or more depending on manufacturer) may prohibit
use in some crops.
An economic assessment should also take into account the life
of the lateral drip lines, usually about five to seven years.
Most California growers, however, feel they would need to get
back into the field within three to five years for deep ripping,
Schwankl noted.
Weed Control
Weeds are one potentially limiting factor for growers making use
of minimum tillage and other low-input practices to enhance soil
quality. Tom Lanini, a UC Davis extension weed ecologist,
presented several low-input and non-chemical options for vegetable
crop growers. Lanini stressed the importance of balancing a number
of weed control practices rather than relying on one single control
method. General approaches should include cultivation, biological
control, mulches of various kinds, and capitalizing on the crop's
ability to compete, he said.
Living mulches block light, compete directly with weeds and may
be allelopathic (suppress weeds with release of toxic substances)
depending on the particular species used. Lanini summarized recently
published work on subclover and other living mulches (see California
Agriculture, November/December 1989).
Cultivation is probably the most widely used method of weed control,
Lanini noted. It is possible to enhance the effectiveness of cultivation
by scheduling cultivations according to the crop's ability to
compete with problem weeds. Lanini said studies conducted over
the past three years showed that field bindweed could be effectively
controlled in processing tomatoes with two cultivations conducted
at approximately three and six weeks from planting. A general
rule of thumb for controlling annual weeds in vegetable crops
is to insure two to ten weeks of weed-free conditions after crop
emergence to obtain profitable yields, he said. The specific length
of time depends on the rate of crop growth and the time of year.
Lanini described the lengths of time for weed-free conditions
required by several other vegetable crops. Times are shown below:
| Crop | Required weed-free period |
| cucumber | 2 - 4 weeks |
| bell pepper | 8-10 |
| lettuce | 4 - 6 |
| cauliflower | 4 - 6 |
Soil Fertility
As growers look at alternative soil management strategies, some
of the key questions they ask center on soil fertility: How can
farmers maintain adequate levels of soil fertility? Are organic
sources of nutrients sufficient to meet the nutrient needs of
their specific crops? Are cover crops or green manures really
feasible for individual farmers' production systems? Can an individual
farmer maintain adequate fertility levels in his/her soil and
not contaminate groundwater?
These were some of the questions addressed by three speakers at
the workshop. Stuart Pettygrove, UC Davis extension soils
specialist, presented important principles for using manure and
compost. The cumulative effects of manure applications on soil
properties include: 1) improved permeability; 2) resistance to
compaction; 3) increased water holding capacity; and 4) decreased
surface crusting. It is difficult to assign a dollar value to
these particular benefits, Pettygrove said. Nutrient values are
easier to assign, but there are a number of considerations that
complicate the actual management of nutrients, particularly nitrogen.
Pettygrove said the four compounding factors are: 1) the water
content of the manure; 2) the actual nitrogen content of the material;
3) the nitrogen availability; and 4) the method of application.
All these will ultimately influence the nitrogen contribution
made by the manure, he said. Though the decay series (nitrogen
release rates over time) is an important concept for manure management,
it should not be regarded as an accurate management tool, Pettygrove
said. The biological process of organic matter breakdown makes
nitrogen rates too variable and unpredictable, he said. Tighter
nutrient management can be achieved through the use of compost
containing more stable nitrogen compounds available to the crop
over time, he added.
Cover Crops
Growers heard Rick Miller, a UC Davis postgraduate agronomy
researcher, discuss the use of cover crops in annual production
systems. He talked about four years use of cover crops at the
UC Davis Student Experimental Farm where he has been growing them
in conjunction with field corn and processing tomatoes. Cover
crop selection and management in annual cropping systems is described
extensively by Miller in Covercrops for California Agriculture,
published by the UC Division of Agriculture and Natural Resources
(publication 21471, see Cover Crops, p.2 to order.)
UC Davis extension soils specialist Roland Meyer said sufficient
levels of nitrogen can be supplied to crops while maintaining
groundwater quality. Accomplishing this requires an approach to
fertility management that combines: 1) knowing the amount of nitrogen
removed in the harvested portion of the crop being grown; 2) an
assessment of the nitrogen supply capabilities of an individual
farmer's soil; and 3) appropriate applications of fertilizer nitrogen
where needed along with sound irrigation management practices.
Gabe Bethlenfalvay, a soil ecologist with the USDA-Agricultural
Research Service in Albany, presented soil quality issues at a
more technical level. Research by Bethlenfalvay and others shows
the importance of beneficial soil fungi (mycorrhizae) in enhancing
soil structure and improving nutrient and water transfer from
the soil solution to the growing crop. Though the significance
of mycorrhizae is well-known, there is still much to be done to
improve them and their management in an agricultural setting,
Bethlenfalvay said.
Allan Fulton, Kings County farm advisor, reminded the audience
that information discussed at the workshop can be used to help
solve specific San Joaquin Valley soil problems including clay
pans, hard pans, saline soils, wind erosion, nutritional problems,
water infiltration, perched (high) water tables, pathogens, and
nematodes. Fulton said the challenge to San Joaquin Valley farmers
and researchers is determining how to integrate different soil
management practices, and understanding the ramifications of any
changes to other aspects of a cropping system.
Index for Sustainable Agriculture Winter, 1990