- Agronomic, Economic,
and Environmental Comparison of Pest Management in Conventional
and Alternative Tomato and Corn Systems in Northern California.
- Changes In Soil
Chemical Properties Resulting From Organic And Low-Input
- Dynamics Of Soil
Microbial Biomass And Activity In Conventional And Organic
- Ground Beetle Abundance
and Community Composition in Conventional and Organic Tomato
Systems of California's Central Valley.
- Determinants of
Soil Microbial Communities: Effects of A agricultural Management,
Season, and Soil Type on Phospholipid Fatty Acid Profiles.
- New Frontiers in Nematode
- Bacterial-Feeding Nematodes
in Conventional and Organic Farming Systems.
- Transition from Conventional
to Low-Input Agriculture Changes Soil Fertility and Biology.
- Interrelationships between
microbial dynamics and carbon flow in agroecosystems.
- Respiration Rates of Microbivorous
- Dynamics of Nematode Communities
in Tomatoes Grown in Conventional and Organic Farming Systems,
and Their Impact on Soil Fertility.
- Thermal constraints to
population growth of bacterial-feeding nematodes.
- The Effect of Nitrogen
Source and Crop Rotation on the Growth and Yield of Processing
- Population Energetics of
Bacterial-Feeding Nematodes: Stage-Specific Development
and Fecundity Rates.
- Alternative Systems Aim
to Reduce Inputs, Maintain Profits.
- Researchers Find Short-Term
Insect Problems, Long-Term Weed Problems.
- Conventional, Low-Input,
and Organic Farming Systems Compared.
- An Interdisciplinary, Experiment
Station-Based Participatory Comparison of Alternative Crop
Management Systems for California's Sacramento Valley.
M. S. Clark, H. Ferris, K. Klonsky, W.T. Lanini, A.H.C. vanBruggen, and F.G. Zalom. 1998. Agronomic, Economic, and Environmental Comparison of Pest Management in Conventional and Alternative Tomato and Corn Systems in Northern California. Agriculture, Ecosystems, and Environment 68:51-71
The effectiveness, economic efficiency, and environmental
impact of pest management practices was compared in
conventional, low-input, and organic processing tomato
and field corn systems in northern California. Pests,
including arthropods, weeds, pathogens, and nematodes,
were monitored over an eight-year period. Although both
crops responded agronomically to the production-system
treatments, arthropods, pathogens, and nematodes were
found to play a relatively small role in influencing
yields. In contrast, weed abundance was negatively correlated
with tomato and corn yields and appeared to partially
account for lower yields in the alternative systems
compared to the conventional systems. Lower pesticide
use in the organic and low-input systems resulted in
considerably less potential environmental impact but
the economic feasibility of reducing pesticide use differed
dramatically between the two crops. The performances
of the organic and low-input systems indicate that pesticide
use could be reduced by 50% or more in corn with little
or no yield reduction. Furthermore, the substitution
of mechanical cultivation for herbicide applications
in corn could reduce pest management costs. By contrast,
pesticide reductions in tomato would be economically
costly due to the dependence on hand hoeing as a substitution
for herbicides. Based on the performance of the low-input
and organic tomato systems, a 50% pesticide reduction
would increase average pest management costs by 50%.
M.S. Clark, W.R. Horwath,
C. Shennan, and K.M. Scow. 1998. Changes In Soil Chemical
Properties Resulting From Organic And Low-Input Farming Practices.
Agronomy Journal (in press)
Soil chemical properties were studied during the transition
from conventional to organic and low-input farming practices
over an 8-yr period at the Sustainable Agriculture Farming
Systems Project in California's Sacramento Valley to
document changes in soil fertility status and nutrient
storage. Four farming systems which differed in crop
rotation and the use of external inputs were established
on land that had been previously managed conventionally.
Fertility in the organic system depended upon animal
manure applications and winter cover crops while the
two conventional systems received synthetic fertilizer
inputs. The low-input system was managed using cover
crops and animal manure during the first 3 yr and with
cover crops and synthetic fertilizer for the remaining
5 yr. Soil chemical properties were compared 4 and 8
yr after establishment. Most of the observed changes
in soil chemical properties were consistent with predictions
based upon nutrient budgets. Inputs of C, P, K, Ca,
and Mg were higher in the organic and low-input systems
as a result of manure applications and cover crop incorporations.
After 4 yr of production, soils in the organic and low-input
systems had higher soil organic C, soluble P, exchangeable
K, and pH. Discontinuation of manure applications in
the low-input system in year 4 resulted in declining
levels of organic C, soluble P, and exchangeable K in
low-input farming system. Differences in crop rotation
also had a significant effect on organic C levels due
to the presence or absence of corn in the cropping sequence.
Differences in total N appeared to be related partially
to inputs, however, differences in the efficiency of
the farming systems to store excess N inputs were also
suggested. The low-input system appeared to be most
efficient in storing excess N, while the conventional
systems were least efficient. Electrical conductivity
(EC), soluble Ca, and soluble Mg levels were tightly
linked but not consistently different among treatments.
Relatively stable EC levels in the organic system indicated
that the use of animals manures has not resulted in
increased salinity. Overall, the findings of this study
indicate that organic and low-input farming in the Sacramento
Valley result in small but important increases in soil
organic C and larger pools of stored nutrients which
are critical for long-term fertility maintenance.
N. Gunapala And K.
M. Scow. 1998. Dynamics Of Soil Microbial Biomass And Activity
In Conventional And Organic Farming Systems. Soil Biology
and Biochemistry (in press)
Dynamics of microbial communities during two growing
seasons were compared in soils under tomatoes managed
by conventional (2-and 4 -y rotations), low imput, or
organic practices. Fumigation extractable carbon (FEC)
and nitrogen (FEN), potentially mineralizable N, arginine
ammonification and substrate induced respiration (SIR)
were significantly higher in organic and low input than
conventional systems on most sample dates. Microbial
variables were significantly negatively correlated with
amount of soil mineral N in the conventional 4 y system
, whereas they were positively correlated with mineral
N in the organic system. The C-to-N rations of material
released after fumigation extraction were significantly
higher in the conventional than organic soils. In all
farming systems, soil moisture was positively correlated
with FEC or FEN, but negatively correlated with the
C-to-N ratio of the microbial biomass and SIR. Soil
temperature was negatively correlated with FEC and FEN,
but positively correlated with the C-to-N ratio of microbial
M. Sean Clark. 1998.
Ground Beetle Abundance and Community Composition in Conventional
and Organic Tomato Systems of California's Central Valley.
Applied Soil Ecology (in Press)
Ground beetle abundance and community characteristics
were compared in tomato systems under conventional and
organic management. Beetles were sampled with pitfall
traps over a 10-mo period during 1997 in plots that
had been under consistent management at the University
of California at Davis since 1988. Abundance and species
richness were greater in the organic system compared
to the conventional system. Six of the 17 species collected
were found only in organically-managed plots. However,
no differences in species diversity or evenness according
to the Shannon and Simpson indices were found. These
results were found to be consistent with those of most
other studies on ground beetle communities in conventional
and organic annual cropping systems.
D.A. Bossio, K.M. Scow,
N. Gunapala, K.J. Graham. 1997. Determinants of Soil Microbial
Communities: Effects of A agricultural Management, Season,
and Soil Type on Phospholipid Fatty Acid Profiles. Microbial
Phospholipid fatty acid (PLFA) profiles were measured
in soils from organic, low-impute, and conventional
farming systems that are pert of the long term Sustainable
Agriculture Farming Systems (SAFS) project. The farming
systems differ in whether their source of fertilizer
is mineral or organic, and in whether a winter cover
crop is grown. Sustained increases in microbial biomass
resulting from high organic matter inputs have been
observed in the organic and low-input systems. PLFA
profiles were compared to ascertain whether previously
observed changes in biomass were accompanied by a change
in the composition of microbial community. In addition,
the relative importance of environmental variables on
PLFA profiles was determined. Reduce analysis ordination
showed that PLFA profiles from organic and conventional
systems were significantly different from April to July.
On ordination plots, PLFA profiles from the low-impute
system fell between organic and conventional systems
on most sample dates. A group of fatty acids ( i14:0,
a15:0, 16:1w7c, 16:1w5c, 14:0, and 18:2w6c) was enriched
in the organic plots throughout the sampling period,
and another group (10ME16:0,20H 16:1and ME17:0 ) was
consistently lower in relative abundance in the organic
system. In addition, another group (15:0,a17:0, i16:0,
17:0 and 10Me18:0) was enriched over the short term
in the organic plots after compost incorporation. The
relative importance of various environmental variables
in governing the composition of microbial communities
could be ranked in the order: soil type > time > specific
farming operation (e.g., cover crop incorporation or
sidedressing with mineral fertilizer) > management system
> spatial variation in the field. Measures of the microbial
community and soil properties (including microbial biomass
carbon and nitrogen, substrate induced respiration,
basal respiration, potentially mineralizable nitrogen,
soil nitrate and ammonium, and soil moisture) were seldom
associated with the variation in the PLFA profiles.
J. Cavero, R.E. Plant,
C. Shennan. 1996. The Effect Of Nitrogen Source And Crop Rotation
On The Growth And Yield Of Processing Tomatoes.
Vegetable crops such as processing tomatoes (Lycopersicon
esculentum MILL) are usually complex in terms of nitrogen
(N) dynamics because of the large amounts absorbed by
the crop, the short growing season and the use of irrigation.
Complexity increases when N is supplied from an organic
source. A crop simulation model could be very useful
to improve N management in this crop. Processing tomatoes
were grown on raised beds and furrow irrigated in 1994
and 1995 in the Sacramento Valley of California. Fertilizer
N and/or purple vetch (Vicia sativa L. ) as green manure
and composed turkey manure were used as sources of N.
The Erosion productivity Impact Calculator (EPIC) model
was calibrated with 1994 data and validated with 1995
data. Plant growth was accurately simulated in the conventional
systems that used fertilizer N and in the low input
system that used fertilizer N plus vetch. The model
accurately simulated above-ground biomass in a system
that used vetch and no synthetic fertilizer N, but it
over-predicted Leaf Area Index (LAI). Nitrogen deficiency
was observed in the plants in this system. The model
simulated nitrogen deficiency mainly as a reduction
in biomass production but in the real world the reduction
of leaf area was the first effect of nitrogen deficiency
in the vegetative phase. Yields were accurately predicted
except when diseases e.
H. 1992. New frontiers in nematode ecology. Journal
Future areas of emphasis for research and scholarship
in nematode ecology are indicated by pressing agricultural
and environmental issues, by new directions in applied
and by current technological advances. Studies in nematode
ecology must extend beyond observation, counting, and
simple statistical analysis. Experimentation and the
testing of hypotheses are needed for understanding the
biological mechanisms of ecological systems. Opportunities
for fruitful experimentation in nematode ecology are
emerging at the ecosystem, community, population, and
individual levels. Nematode ecologists will best promote
their field of study by closely monitoring and participating
in the advances, initiatives, developments, and directions
in the larger field of ecology.
Key words: Approach, biodiversity, concept,
level of organization, population regulation, scale,
theory, trophic roles, variability.
Department of Nematology
25:374-382(Abstr.)., University of California, Davis,
H., R. C. Venette, S. A. Lau, K. M. Scow, and N. Gunapala.
1994. Bacterial-feeding nematodes in conventional and organic
farming systems. Journal of Nematology
We investigated temporal relationships among bacterial-feeding
nematodes, (BFN), fertility, and microbial biomass in
soils managed under conventional and organic farming
systems. There were more BFN in the conventional than
the organic plots in the early spring, but numbers were
greater in the organic plots following incorporation
of a winter cover crop. Numbers of BFN in the organic
plots were positively correlated with measures of microbial
abundance and activity, including microbial biomass
carbon, microbial biomass nitrogen, and substrate-induced
respiration. These correlations were not significant
in the conventional plots. The BFN community was less
diverse in the organic than in the conventional plots
due to temporal predominance of individual species,
which was related to temperature-niche characteristics
of the species. Temporal predominance influences the
contribution of BFN species to nitrogen mineralization
during key periods of plant growth.
Department of Nematology
26:544. (Abstr.)., University of California, Davis,
H. and S. Lau. 1992. Respiration rates of microbivorous
nematodes. Journal of Nematology
Temperature-dependent respiration rates were determined
from CO2 evolution of populations on pH-buffered gel
in sealed chambers. Chambers were maintained at constant
temperature and flushed with CO2-free air before respiration
measurements. The air above the gel surface in each
chamber was circulated through an infrared gas analyzer
before and after 30 min. respiration periods to measure
change in gas concentration. Respiration of associated
bacteria was adjusted using CO2 evolution from nematode-free
bacteria control flasks. Total nematode biomass in each
chamber was estimated from length and width measurements
of a representative sample. CO2 evolution rates were
standardized for age structure of the test population.
Rates ranged from approximately 0.005 mg CO2 per mg
nematode per hour at 15 C to 0.024 at 26 C for Cruznema
tripartitum and 0.028 at 30 C for Acrobeloides bodenheimeri.
These two species, differing in thermal maxima for respiration
rates, were obtained from the same field soil. Respiration
rates for a laboratory population of Caenorhabditis
elegans were comparable, with a maximum at 25 C. Because
respiratory rates per unit biomass are similar, participation
of these nematodes in energy flow in an ecosystem is
a function of size of individuals, and of individual
and population growth rates.
Department of Nematology
24:589. (Abstr.)., University of California, Davis,
H., R.C. Venette, and S.S. Lau. 1996. Dynamics of nematode
communities in tomatoes grown in conventional and organic
farming systems, and their impact on soil fertility. Applied
Soil Ecology 3: 161-175 (Abstr.).
Nematode communities were monitored intensively through
a tomato (Lycoperscion esculentum L.) growing
season in plots managed by conventional and organic
farming practices. The temporal dynamics of individual
species of bacterial feeding nematodes differed and
suggested differing importance of species in their contribution
to N-mineralization in the organically managed soil.
Species with r-selected , colonizer characteristics
were most responsive to incorporation of organic matter
and the subsequent increase of microbial biomass. Bacterial
feeding nematode populations were lowest early in the
growing season when tomato plants exhibited symptoms
of nitrogen deficiency. We hypothesize that increasing
abundance, biomass, and activity of these nematodes
in the spring by organic matter incorporation at the
end of the previous crop would reduce the observed nitrogen
stress. Fungal feeding nematodes were more abundant
in the conventional than the organic plots during the
periods of organic matter decomposition, possibly related
to the higher carbon:nitrogen ratios of the crop residues
incorporated into the conventional soils than of the
manures and leguminous cover crops incorporated into
the organic soils. Predaceous and omnivore nematode
populations were low in both farming systems, and plant-parasitic
nematode species reflected the crop sequences in rotations
used in each system.
Key Words : Bacterial-feeding Nematodes;
Soil Fertility; Nematode Community dynamics; Nematode
abundance and biomass.
H., M. Eyre, R.C. Venette, and S. S. Lau. 1996. Population
energetics of bacterial-feeding nematodes: stage-specific
development and fecundity rates. Soil Biology and Biochemistry
28 (3): 271-280, (Abstr.).
By grazing on bacteria, bacterial feeding nematodes
participate in decomposition food webs and N mineralization
to an extent determined by metabolic and behavioral
attributes and by life history. We determined the stage-specific
development and fecundity rates for eight species on
a physiological time scale to allow time and temperature-varying
predictions of population progressions. Development
from egg to adult of four species in the Rhabditidae
(Bursilla labiata, Caenorhabditis elegans, Cruznema
tripartitum and Rhabditis cucumeris) was
faster than that for three species in the Cephalobidae
(Acrobeloides bodenheimeri, A. buetschlii and
Cephalobus persegnis) on a Julian time (calendar)
basis at 20 degrees C. Development in the Rhabditidae
was generally faster on a physiological (degree-day)
time scale as well, but those times are not directly
comparable as the basal threshold for degree-day (DD)
accumulation differed among species. The fecundity period
for females of the seven species varied between 55 and
75% of the total duration of the life course, during
which they produced between 125 eggs (B. labiata)
and 567 eggs (C. tripartitum). Simulated population
growth under favorable temperature conditions, using
parameter values determined in these studies, indicated
rapid population growth in the large-bodied , highly-fecund
rhabiditid species (R. cucumeris and C. tripartitum).
Population growth was intermediate in the small-bodied
, less-fecund rhabiditids with short egg production
periods ( B. labiata), slower in the cephalobids
(A. bodenheimeri and A. buetschlii )
and slowest in C. persegnis. R. cucumeris spent
a greater portion of its development time in the egg
stage than did any of the other species.
K. and P. Livingston. 1994. Alternative systems aim to reduce
inputs, maintain profits. California Agriculture. 48(5):
H. Ferris, 1996. Thermal constraints to population growth
of bacterial-feeding nematodes. Soil Biol. Biochem.
29 (1): 63-74.
Bacterial feeding nematodes are important participants
in decomposition pathways and nutrient cycles in soils.
The contribution of each species to component processes
depends upon the physiology of individuals and the dynamics
of populations. Having determined the effects of temperature
on metabolic rates of several species of bacterial-feeding
nematodes, we now present the effects of temperature
on population growth rates and relate those to observed
Cavero J., R.E. Plant,
C. Shennan, and D. Friedman. 1997. The Effect of Nitrogen
Source and Crop Rotation On the Growth and Yield of Processing
Tomatoes Nutrient Cycling in Agroecosystems. 47:
Four Crop Rotation Strategies were studied in 1994 and
1995 in relation to growth and yield of irrigated processing
tomatoes (Lycopersicum esculentum Mill.) The
four treatments were three four-year rotation systems
[conventional( conv-4), low input and organic] and a
two-year rotation system [conventional (conv-2)]. The
4-year rotation was tomato-safflower-corn-wheat (or
oats+vetch)/beans, and the 2-year rotation was tomato-wheat.
Purple vetch (Vicia Sativa L.) was grown as a
green manure cover crop preceeding tomatoes in the low
input and organic systems. Nitrogen was supplied as
a fertilizer in the conventional systems, as vetch green
manure plus fertilizer in the low input system, and
as vetch green manure plus turkey manure in the organic
system. Tomato cv. Brigade was direct-seeded in the
conventional systems and transplanted to the field in
the low input and organic systems. In both years the
winter cover crop was composed of a mixture of vetch
and volunteer oats with N contents of 2.2% in 1994 and
2.7% (low input) or 1.8% (organic) in 1995. In 1994
yields were higher in conventionally grown tomatoes
because a virus in the nursery infected the transplants
used in the low input and organic systems. In 1995 tomatoes
grown with the conv-4 systems had similar yields, which
were higher than those of tomatoes grown with the conv-2
and organic systems...
Scow, K.M., O. Somasco,
N. Gunapala, S. Lau, R. Venette,
Ferris, R. Miller, and C. Shennan. 1994. Transition from
conventional to low-input agriculture changes soil fertility
and biology. California Agriculture 48(5):20-26.
Growers converting from conventional to low-input and organic
farming systems must rely on organic sources for adequate
soil fertility. At the Sustainable Agriculture Farming
Systems (SAFS) project at UC Davis, we measured soil
fertility and biological parameters in four farming
systems. By the end of the first 4 years, pH and percent
nitrogen were consistently higher in organic and low-input
than conventional plots for all crops. Levels of organic
matter, phosphorous and potassium were significantly
higher in the organic than conventional 2-year plots.
Microbial biomass levels were consistently higher in
organic and low-input systems, while plant parasitic
nematode numbers were consistently lower. Nitrogen deficiency
appeared to be a problem in organic tomatoes during
the transition period. More research is needed into
the dynamics of soil nutrient availability in low-input
systems. For instance, we may need to develop new methods
of assessing soil fertility in organically fertilized
Scow, K.M., 1996. Interrelationships
Between Micorbial Dynamics and Carbon Flow in Agroecosystems.
In: Jackson, L.E. (ed.) Ecology in Agriculture Ch. 11:367-403.
Temple S.R., O.A. Somasco,
M. Kirk and D. Friedman. 1994. Conventional, low-input, and
organic farming systems compared. California Agriculture.
Cover-crop nitrogen supply and weed management were
the most important challenges facing low-input and organic
farming systems when compared to conventional systems
in the first 4 years of the Sustainable Agriculture
Farming Systems project at UC Davis. Cover-crop timing
and management, using appropriate equipment, were important
for the success of transitional systems. The participation
of local farmers ensured that optimal agricultural practices
were used to manage all farming systems. Researchers
regularly consulted grower-cooperators to determine
"best farmer practices" of conventional, low-input and
organic farming systems.
Temple, S.R., D.B. Friedman,
H. Ferris, K. Scow, and K.
Klonsky. 1994. An interdisciplinary, experiment station-based
participatory comparison of alternative crop management systems
for California's Sacramento Valley. American Journal of
Alternative Agriculture 9 (1 & 2): 64-71.
In 1989 a group of researchers, farmers and farm advisors
initiated an interdisciplinary study of the transition
from conventional to low-input and organic management
of a 4-year, five-crop rotation. Crop yields initially
varied among systems, but now appear to be approaching
each other after a transition period that included the
development of practices and equipment most appropriate
for each system. Farming practices and crop production
costs are carefully documented to compare the various
systems' economic performance and biological risks.
Supplying adequate N and managing weeds were challenges
for the low-input and organic systems during the first
rotation cycle, and experiments are being conducted
on an 8-acre companion block to find solutions to these
and other problems. Leading conventional and organic
growers provide a much-needed farmer perspective on
cropping practices and economic interpretations, because
we try to provide "best farmer" management of each system.
Research groups within the project are focusing on soil
microbiology, economics, pest management, agronomy and
cover crop management.