Spring Cereals Research Articles

Niektóre cechy biologiczne Agrostemma githago L. i Centaurea cyanus L. w różnych siedliskach Wysoczyzny Siedleckiej

The analysis of biological features of Centaurea cyanus and Agrostemma githago as well as their variability and diversity, depending on the occupied habitats, is presented in the paper. For this purpose, 30 specimens were randomly collected from each studied habitat – stubblefields, winter cereals and spring cereals and put to the morphological analysis with respect of the height of plant, number of ramifications of 1st and 2nd categories, length of the ramifications, number of inflorescences, number of seeds at one plant, a thousand-seed weight and aerial dry mass of plant. The values of features were used for statistic calculations. Centaurea cyanus and Agrostemma githago populations collected in Siedlecka Upland habitats revealed internal variability in respect to all analyzed features. Specimens of Centaurea cyanus differed from each other with regard to the above mentioned features, depending on habitat type. Significant differences between populations occurring in winter cereals, depending on the soil conditions as well as between individuals originating from rye cultivations and stubble-fields in identical soil conditions, were demonstrated. Moreover, no significant differences between populations developing in winter and spring cereals on the analogical soil type were found. 
 No significant differences between the majority of the investigated features of Agrostemma githago specimens, developing in rye cultivations and in stubble fields in the same soil conditions were noted. There were also no significant differences in features of the studied species between 2005 and 2006 – no interactions between year of studies and habitat type were observed.

Cultivar and Seeding Rate Effects on the Competitive Ability of Spring Cereals Grown under Organic Production in Northern Canada

Organically managed production systems often experience greater weed pressure than their conventional counterparts, potentially causing yield losses and increased weed seed build‐up. The use of competitive crop cultivars and the cultural practice of increasing seeding rates may moderate such production constraints. Field trials were conducted at two organically managed locations in Alberta, Canada for 2 yr to determine the effect of competition with tame oat (Avena sativa L.), cultivar, and crop seeding rate (300 and 600 seeds m−2) on the competitive ability and agronomic performance of Canadian spring wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.). Cultivars were selected based on their differing heights, tillering capacities, and times to maturity. Simulated weed competition from tame oat reduced grain yield by an average of 27%. Barley cultivars were generally more competitive than wheat cultivars. Height and early maturity were more closely associated with weed suppression and yield maintenance than tillering capacity. The modern semidwarf CDC Go was the highest yielding wheat cultivar, but was a poor weed suppressor. Doubling the seeding rate increased grain yield and weed suppression. This effect was not cultivar specific, which implies that doubling the seeding rate may be a generally effective method of overcoming yield losses and weed seed build‐up associated with increased weed populations under organic production.

Can conversion to organic farming restore the species composition of arable weed communities?

Benefits of organic cropping for biodiversity have usually been demonstrated in relation to modern conventional cropping. In this study, the ability of organic cropping to restore species composition of weed communities was explored by comparing weed communities of present day organic cropping with weed communities at the beginning of the application of modern cropping measures in the 1960s. The data of two weed surveys of spring cereals (conducted in 1961–1964 and 1997–1999) in Finland were utilized for a comparison. Frequency of occurrence and density (plants m −2) of 41 weed species were compared between decades. Partial canonical correspondence analysis (pCCA) was applied to explore the relationship between species composition, management and non-management variables. Eight species had lower and 30 species higher or similar frequency of occurrence in the 1990s’ organically cropped fields than in the fields of the 1960s. However, 18 species had lower and 20 species had higher or similar density in the organically cropped fields than in the fields of the 1960s. Three species were not detected at all in the organically cropped fields. Crop and under-sown grass explained more of the variation in species composition in the 1990s than in the 1960s. The role of drainage and pre-crop was more important in the 1960s than in the 1990s. The most immediate benefit was gained by nitrophilous species that had suffered from herbicide application. The recovery of perennials and non-nitrophilous species will take a longer time. The results suggest that despite some benefits for biodiversity, organic farming at early phase cannot recover weed populations to the same level as before application of intensive cropping measures.

A model simulation analysis of soil nitrate concentrations—Does soil organic matter pool structure or catch crop growth parameters matter most?

Three different soil organic matter (SOM) submodels were tested within the framework of the soil–plant–atmosphere model Daisy. The three submodels were: the original Daisy SOM module (OLD) with relatively non-dynamic humus pools, a recalibrated Daisy SOM module (STD) with the same pool structure as the original, but with a more rapid turnover of the active humus pool, and a newly developed SOM model structure (CNSIM), with inclusion of a soil microbial residuals pool of relatively rapid turnover, and a relatively recalcitrant added organic matter pool, producing a larger and more sustained residual N mineralisation. Furthermore, two different parameterisations of the catch crop submodules, differing in grass growth and N assimilation dynamics, were tested and the relative influence of SOM module or catch crop growth module on the simulated variables assessed. The simulations were carried out with data from a field experiment with four mixed cropping systems and compared to measured results of crop production, N uptake and soil nitrate concentration. The cropping sequence was 3 years of grassland (cut or grazed) followed by 3 years of spring cereals with ryegrass as a catch crop and two levels of fertiliser application. Independently of the SOM module, plant production and nitrogen uptake for cereals were simulated well. The dynamics of the added organic matter (AOM) and SOM of the two Daisy submodules were nearly identical, whereas the CNSIM submodule built much more nitrogen into the AOM pools, especially during the pasture years. During the period with spring barley, the CNSIM module simulated similar amounts of AOM as the other modules. In general, the simulated nitrate concentrations at 100 cm depth were higher than the measured values, but the changed dynamics in the CNSIM simulations resulted in even higher overestimation of the nitrate concentration than the two other modules. The choice of catch crop submodule had a considerable effect on nitrate concentration and therefore the potential for nitrate leaching, possibly overshading more futile differences produced by the different SOM submodules. The simulations show the importance of applying appropriate intercrop submodels when the model is used for simulating rotations with intercropping of grass-clover or undersown catch crops.

Effects of Tillage on the Activity Density and Biological Diversity of Carabid Beetles in Spring and Winter Crops

The effects of tillage regimen (conventional [CT] and no-tillage [NT]) on the activity density and diversity of carabid beetles (Coleoptera: Carabidae) was studied by pitfall trapping within a rain-fed cropping system in northwestern Idaho, 2000-2002. The cropping rotation consisted of a spring cereal (barley, Hordeum vulgare L., in 2000 and 2001; and wheat, Triticum aestivum L., in 2002), spring dry pea (Pisum sativum L.) 2000-2002, and wheat (T. aestivum), spring in 2000 and 2001, and winter in 2002. A total of 14,480 beetles comprised of 30 species was captured, with five numerically dominant species [Poecilus scitulus L., Poecilus lucublandus Say, Microlestes linearis L., Pterostichus melanarius Ill., and Calosoma cancellatum (Eschscholtz)], accounting for 98% of all captures. All species including the dominants responded idiosyncratically to tillage regimen. Adjusting for trapping biases did not significantly change seasonal activity density of Poecilus spp. or Pt. melanarius to tillage. More beetles were captured in CT than in NT crops because of the dominance of P. scitulus in CT, whereas species richness and biological diversity were generally higher in NT crops. Observed patterns suggest that direct effects of tillage affected some species, whereas indirect effects related to habitat characteristics affected others. CT may provide habitat preferable to xerophilic spring breeders. A relationship was found between beetle species size and tillage regimen in pea and to a lesser extent across all spring crops, with large species (>14 mm) conserved more commonly in NT, small species (<7 mm) in CT, and intermediate species (7-14 mm) conserved equally between tillage systems.

Effects of Tillage on the Activity Density and Biological Diversity of Carabid Beetles in Spring and Winter Crops

The effects of tillage regimen (conventional [CT] and no-tillage [NT]) on the activity density and diversity of carabid beetles (Coleoptera: Carabidae) was studied by pitfall trapping within a rain-fed cropping system in northwestern Idaho, 2000–2002. The cropping rotation consisted of a spring cereal (barley, Hordeum vulgare L., in 2000 and 2001; and wheat, Triticum aestivum L., in 2002), spring dry pea (Pisum sativum L.) 2000–2002, and wheat (T. aestivum), spring in 2000 and 2001, and winter in 2002. A total of 14,480 beetles comprised of 30 species was captured, with five numerically dominant species [Poecilus scitulus L., Poecilus lucublandus Say, Microlestes linearis L., Pterostichus melanarius Ill., and Calosoma cancellatum (Eschscholtz)], accounting for 98% of all captures. All species including the dominants responded idiosyncratically to tillage regimen. Adjusting for trapping biases did not significantly change seasonal activity density of Poecilus spp. or Pt. melanarius to tillage. More beetles were captured in CT than in NT crops because of the dominance of P. scitulus in CT, whereas species richness and biological diversity were generally higher in NT crops. Observed patterns suggest that direct effects of tillage affected some species, whereas indirect effects related to habitat characteristics affected others. CT may provide habitat preferable to xerophilic spring breeders. A relationship was found between beetle species size and tillage regimen in pea and to a lesser extent across all spring crops, with large species (>14 mm) conserved more commonly in NT, small species (<7 mm) in CT, and intermediate species (7–14 mm) conserved equally between tillage systems.

Cropping systems alter weed seed banks in Pacific Northwest semi-arid wheat region

Arable land weed seed banks are dynamic and reflect cropping history, current management, and environment. Changes in crop rotation and tillage system can alter weed seed density and species composition. In the semi-arid region of the Pacific Northwest, USA, no-till spring cropping is being studied as an alternative to the traditional winter wheat (Triticum aestivum L.)/dust-mulch fallow (WWF) rotation. Weed seed bank density and species composition were assessed during the first 6 years of an ongoing cropping system study comparing WWF with three no-till rotations; spring wheat (Triticum aestivum L.)/chemical fallow (SWF), continuous spring wheat (CSW), and spring wheat/spring barley (Hordeum vulgare L.) (SWSB). Soil cores were collected at depths of 0–8, 8–15, and 15–23cm in all plots during August each year following crop harvest. Weed seeds were washed from the soil, dried, and germinated in a glasshouse. Weed species most associated with the 0–8cm depth was Bromus tectorum L., the major winter annual grass weed in WWF. Species most associated with 8–15cm depth was Chenopodium leptophyllum (Moq.) Nut. ex S. Wats, a native warm season broadleaf weed that may have long seed bank persistence. An initial high density of B. tectorum was reduced with no-till spring crops and in WWF with intensive management strategies. In comparison an initial low weed seed density of B. tectorum remained low with no-till but increased in WWF with less management. Broadleaf weed species did not become management problems in no-till; however, seed bank weed shifts occurred where winter annual broadleaf species remained following reduction of high densities of B. tectorum. Summer annual broadleaf weed seeds such as C. leptophyllum and Salsola tragus L. were present but not at high densities. Summer annual grass weed seeds were not present and are not typical in this region. In this research, no-till spring cereal based systems did not result in an increase in total seed density at the soil surface. Results from this research show that no-till spring crop rotations are effective at controlling winter annual grass weeds as well as broadleaf weeds normally associated with WWF.

Occurrence of barley yellow dwarf virus and cereal yellow dwarf virus in pasture grasses and spring cereals in Latvia

The relative frequency of three viruses causing barley yellow dwarf disease (BYD) was assessed in spring cereals and pasture grasses at two regions in Latvia in 2000–2002. A total of 2589 leaf samples (367 from spring oats, 743 from spring barley, 1479 from predominant grass species) were collected from 44 fields of spring oats, 84 fields of spring barley, and 26 pastures. We found that isolates of barley yellow dwarf virus-PAV (BYDV-PAV), barley yellow dwarf virus-MAV (BYDV-MAV) and cereal yellow dwarf virus-RPV (CYDV-RPV) were present in these samples of spring cereals and pasture grasses. The most common isolates of barley yellow dwarf virus were BYDV-PAV and BYDV-MAV in both grasses and cereals, but there was a great difference between years and regions. The proportion of BYD symptomatic cereal samples that reacted positively in TAS-ELISA test was 9 to 15%. The overall BYDV/CYDV incidence in pasture grasses ranged from 2 to 19%. The incidence of BYDV/CYDV infection was higher in Festuca elatior than in other grass species. Isolates of CYDV-RPV were rather rare: only found in Lolium perenne and Dactylis glomerata among six grass species tested and more frequently in barley than oats. This paper reports the first quantitative survey of selected BYD-causing viruses in spring cereals and pasture grasses in Latvia and in the Baltic states. We conclude that three selected virus species are prevalent in spring cereals and pasture grasses in Latvia, although with great variation between years. Further studies are needed to obtain knowledge of the most critical factors that determine these fluctuations.

Validation of satellite-derived soil-vegetation indices for prognosis of spring cereals yield reduction under drought conditions – Case study from central-western Poland

The applicability of satellite-derived indices (NDVI) for drought forecasting in reference to spring cereals production in central-western Poland has been analysed. The study was based on field experiment results of spring cereals yield, phenological observations and meteorological data at four agricultural experimental stations from the period 1992–2002. Based on the collected data, the precipitation deficit in relation to water demand in various phenological phases of crop development was calculated. The crop water demand was calculated as ETcrop for 10 day-step using a computer model FAO CROPWAT. The precipitation deficit and cereal grain yield reduction and NDVI in the particular period of crop growth were analysed. The relationship between evapotranspiration (ETcrop) and NDVI for all spring cereals was weak, but much stronger for particular spring cereals. The statistically significant relationships were found between soil moisture in the root zone and soil moisture index (SMI) derived from satellite and meteorological data. Our results suggest that NDVI index was not sufficient for drought forecasting and should be supported by additional data from meteorological stations, such as temperature or the amount of solar radiation.

Breeding Effects on Nitrogen Use Efficiency of Spring Cereals under Northern Conditions

Spring cultivars of barley (Hordeum vulgare L.), oat (Avena sativa L.), and wheat (Triticum aestivum L.) are the most important crops in Finnish agricultural systems. The increasing need to reduce pollution from N fertilizer is concomitantly strengthening the importance of improving the understanding of nitrogen use efficiency (NUE) of these crops. The aim of this work was to study the differences in NUE, defined as the crop's ability to produce yield with one available N unit, among spring cereal cultivars, and to determine the achievements of plant breeding in NUE under northern European growing conditions. Field experiments were conducted in Finland during 2003 and 2004. Samples from matured plants of 17 to 18 cultivars of each of the three cereal species released between 1909 and 2002 were studied. There were no clear differences in NUE among modern spring cultivars. However, there were cultivar differences within species and significant NUE improvements on wheat and particularly for oat across time. There was no clear trend of NUE and year of release of cultivars in two‐row spring barley, probably because breeding for malting barley involves consistent selection for low‐protein cultivars. The study revealed that most breeding effects on NUE were associated with changes in nitrogen uptake efficiency (UPE).

Nutrient discharge from small agricultural catchments in Sweden

Abstract Within the Swedish Monitoring Programme for Agriculture, 27 small agricultural catchments were investigated for between 9 and 14 years (6 years for one catchment), starting in the late 1980s, to determine the impact of agricultural activities on discharge water. The catchments represent major variations in climate, soil types and farming in Sweden and hence long-term average load of total nitrogen (N) and total phosphorus (P) at stream outlets varied widely among the catchments, from 2 to 41 and from 0.1 to 0.9 kg ha −1 yr −1 , respectively. Catchments with large N loads were characterised by several factors favourable for leaching, such as mild winter climate, large precipitation, sandy or organic soils and high animal density in combination with intensive cropping systems with a low percentage of ley. Large P loads were mainly related to factors such as clay and clay loam soils, medium to high precipitation and large proportions of annual crops in the catchments. Flow-normalised time series of monthly loads of nitrate N, phosphate P and particulate P (for 24 catchments) were tested for trends. Significant downward trends were revealed for nitrate N, phosphate P and particulate P for seven, eight and three catchments, respectively, whereas, upward trends were revealed for nitrate N and particulate P for one and two catchments, respectively. Downward nitrate N trends for two catchments were correlated to smaller amounts of applied manure, especially during autumn, and to a decrease in the area of spring cereals and spring rape.

Impact of Management on Weed Species Composition in Organically Cropped Spring Cereals

ABSTRACT Partial Redundancy Analysis (pRDA) was applied to analyse the relationship between weed species composition and agricultural management measures in organically cropped spring cereal fields. Density and dry weight of weed species were assessed in 30 fields situated in the coastal regions of Finland. The pRDA analysis included nine explanatory variables describing management (years since conversion to organic farming, crop rotation, crop, soil pH, fertilization, burial of manure, weed management, application of stubble cultivation and crop dry weight) and two not manipulable variables (location of the field and soil type). The only statistically significant variables appeared to be crop dry weight, years since conversion to organic fanning and cropping of wheat. The abundances of Elymus repens and Cirsium arvense increased as a function of years since conversion to organic fanning. There was no relationship between the ratio of non-nitrophilous to nitrophilous species and the duration of organic farming. The abundances of C. arvense and Sonchus arvensis as well as of most annual species were inversely related to crop dry weight and they were not associated with cropping of wheat. The shade-tolerant species Chenopodium spp., Fallopia convolvulus and Viola arvensis maintained their dry weight in conditions of increasing crop dry weight and cropping of wheat. Galium spp. were associated with cropping of wheat. Weed species associated with years since conversion to organic fanning were only in a few cases identical with species associated with low crop dry weight, which emphasizes the importance of both short- and long-term agricultural management with regard to weed control in organic farming.

Tillage Method and Sowing Rate Relations for Dryland Spring Wheat, Barley, and Oat

Some farmers in the Inland Pacific Northwest (PNW) have reported lower grain yield of spring cereals with no‐till (NT) compared with conservation tillage (CT). A 4‐yr field study was conducted in a 300‐mm annual precipitation zone to determine tillage method and sowing rate effects on seed‐zone water, seed‐zone temperature, plant stand, grain yield, grain yield components, and straw production for three spring‐sown cereal species. Wheat (Triticum aestivum L.), barley (Hordeum vulgare L.), and oat (Avena sativa L.) were sown at 120, 200, and 280 seeds m−2 in a split plot design with NT and CT as main plots and sowing rate × cereal species combinations as subplots. Factors other than tillage method (i.e., drill, sowing date, fertilizer rate, sowing depth) were held constant. There were no differences in plant stand between NT and CT, but grain yield was reduced by 5% in NT in part because of less water in the seed zone compared with CT during early plant development. Disruption of capillary continuity with CT appeared to restrict upward movement of water, resulting in greater retention of water in the seed zone underlying the depth of tillage. Grain yield was not affected by sowing rate for any crop species because increased number of heads per unit area (HPU) and kernels per head (KPH) consistently compensated for reduced plant stand density. With precise seed placement, sowing rate of spring cereals can be reduced by 50% or more from rates commonly used.

Seeding ratios and rates that maximize annual forage production in Black soil zones of central Saskatchewan

Three different seeding densities and four seeding ratios of spring and fall crop components for annual forage production were evaluated for maximizing silage and fall regrowth yield in a 3-yr study at Melfort, Saskatchewan. Binary mixtures of a spring cereal, barley (Hordeum vulgare L.) or oat (Avena sativa L.), and a fall crop, fall rye (Secale cereale L.) or Italian ryegrass (Lolium multiflorum Lam.), were seeded at three total stand seed densities (150, 275 and 400 seeds m-2), which consequently resulted in the following spring:fall seeding crop component ratios: 1:0, 2:1, 1:2 and 0:1. Both spring and fall crops were harvested when the spring cereals were at the soft-dough stage (silage cut) and late in the autumn (fall regrowth cut). Average spring crop component yield was greater for the silage cut (4806 kg ha-1) than for the fall regrowth cut (329 kg ha-1), and total sward yield was greater for the silage cut (5995 kg ha-1) than for the fall regrowth cut (1261 kg ha-1). Productivity of the fall component was 1173 and 929 kg ha-1 for the silage and fall regrowth cuts, respectively. Total crop yield was often maximized with seeding ratios of 60% spring:fall crop component or greater for the different combinations. Fall regrowth cut yields were always maximized by seeding 100% fall crop component. The spring crop component yield, especially for the oat mixtures, contributed very little to fall regrowth yields. Stand seeding rate frequently affected spring component and total crop yield, but not fall crop yield. Silage and annual yield for the spring crop and total sward increased with increase in stand seeding rate. Fall crop yield was not affected by stand seeding rate or its effect was of questionable practical importance. Italian ryegrass produced the most fall regrowth yield. Weed management was identified as a possible area for future research with regard to seeding ratios and rates for annual forage stands. Key words: Monocrop, intercrop, annual forage, seeding rates, seeding ratio

Weed survey of spring cereals in New Brunswick

During 1986 and 1987, a weed survey of 187 New Brunswick cereal fields was conducted. A total of 76 species were identified of which 40 were considered agronomically important. About 50% of the species were perennial. Hemp-nettle (Galeopsis tetrahit), quack grass (Agropyron repens), sheep sorrel (Rumex acetosella), ox-eye daisy (Chrysanthemum leucanthemum), corn spurry (Spergula arvensis), and chickweed (Stellaria média) had the highest relative abundance values. Quack grass and hemp-nettle had the highest densities at 8.0 and 7.1 plants m-2, respectively. The highest weed density (103 plants m-2) was found in oats (Avena sativa) grown after a forage crop. The lowest density (24 plants m-2) was found in wheat (Triticum aestivum) grown after potatoes (Solarium tuberosum). Most of the abundant species were tolerant to MCPA, the most commonly used herbicide. Farmers could make major improvements in cereal weed control by choosing a herbicide that would control species tolerant to MCPA or 2,4-D, and using preplant or postharvest weed control to minimize the impact of perennial weeds.

Simulation of residual effects and nitrate leaching after incorporation of different ley types

The FASSET farm model was used to simulate production in an experiment, where a grass-clover or a grass ley was either cut or grazed with dairy cows receiving low or high N supplements. The six different ley types were ploughed in and followed by 3 years with spring cereals with undersown catch crops. The original model was extended with a new grass and clover model, which included the capability to simulate rhizodeposition and root growth. The new model predicted the observed annual carbon (C) and nitrogen (N) production satisfactorily. The simulated first year residual effects of cut grass or grass-clover ley varied between 0 and 34, while the residual effect of a grazed grass or grass-clover ley varied between 71 and 150 fertilizer equivalents (kg N ha −1). Second and third year residual effects of the grazed leys were ca. 40 and 9 fertilizer equivalents, respectively, while the residual effects of the cut leys were ca. 5 and 3 fertilizer equivalents. The effects of the different treatments on nitrate leaching were simulated quite satisfactorily. However, there was a deviation between the simulated and observed absolute level and timing of nitrate concentrations in suction cups. Scenario analysis showed that this partly could be explained by problems with refractory soil organic matter and gross nitrogen mineralization in soils with high C:N ratios.

Forty‐five years of observed soil moisture in the Ukraine: No summer desiccation (yet)

We present the longest data set of observed soil moisture available in the world, 45 yr of gravimetrically‐observed plant available soil moisture for the top 1 m of soil, observed every 10 days for April–October for 141 stations from fields with either winter or spring cereals from the Ukraine for 1958–2002. We averaged the summer observations over the entire region to account for the observed scale of soil moisture variations, to enhance the portion of the variance that is related to meteorological forcing. The observations show a positive soil moisture trend for the entire period of observation, with the trend leveling off in the last two decades. Although models of global warming predict summer desiccation in a greenhouse‐warmed world, there is no evidence for this in the observations yet, even though the region has been warming for the entire period. While the interannual variations of soil moisture simulated by both the European Centre for Medium‐range Weather Prediction and the National Centers for Environmental Prediction/National Center for Atmospheric Research reanalyses are close to the observations, neither reanalysis simulates the observed upward trend. Climate model simulations for the period show the same general shape as the observations, but differ quite a bit from each other and from the observations. An observed downward trend in insolation may have produced a downward trend in evaporation and may have contributed to the upward soil moisture trend.

Effect of climate change on greenhouse gas emissions from arable crop rotations

The DAISY soil–plant–atmosphere model was used to simulate crop production and soil carbon (C) and nitrogen (N) turnover for three arable crop rotations on a loamy sand in Denmark under varying temperature, rainfall, atmospheric CO2 concentration and N fertilization. The crop rotations varied in proportion of spring sown crops and use of N catch crops (ryegrass). The effects on CO2 emissions were estimated from simulated changes in soil C. The effects on N2O emissions were estimated using the IPCC methodology from simulated amounts of N in crop residues and N leaching. Simulations were carried out using the original and a revised parameterization of the soil C turnover. The use of the revised model parameterization increased the soil C and N turnover in the topsoil under baseline conditions, resulting in an increase in crop N uptake of 11 kg N ha–1 y–1 in a crop rotation with winter cereals and a reduction of 16 kg N ha–1 y–1 in a crop rotation with spring cereals and catch crops. The effect of increased temperature, rainfall and CO2 concentration on N flows was of the same magnitude for both model parameterizations. Higher temperature and rainfall increased N leaching in all crop rotations, whereas effects on N in crop residues depended on use of catch crops. The total greenhouse gas (GHG) emission increased with increasing temperature. The increase in total GHG emission was 66–234 kg CO2-eq ha–1 y–1 for a temperature increase of 4 °C. Higher rainfall increased total GHG emissions most in the winter cereal dominated rotation. An increase in rainfall of 20% increased total GHG emissions by 11–53 kg CO2-eq ha–1 y–1, and a 50% increase in atmospheric CO2 concentration decreased emissions by 180–269 kg CO2-eq ha–1 y–1. The total GHG emissions increased considerably with increasing N fertilizer rate for a crop rotation with winter cereals, but remained unchanged for a crop rotation with spring cereals and catch crops. The simulated increase in GHG emissions with global warming can be effectively mitigated by including more spring cereals and catch crops in the rotation.

Swath grazing potential of spring cereals, field pea and mixtures with other species

There is little information on the relative suitability of cereal species and field pea or their mixtures for winter swath grazing. The objective of this study was to compare the swath grazing potential of small-grain cereal and field pea (Pisum sativa L.) monocultures, their mixtures, and mixtures with other species, by evaluating forage yield in the fall and changes in nutritive value due to weathering from fall until spring. The monocultures and mixtures were seeded in early summer and swathed in late September with conventional farm equipment for 3 yr. Dry matter yield was measured by harvesting a subplot (1.22 × 3.62 m) across each plot prior to swathing. A cross-section sample of swath was taken for quality determination immediately after swathing, in late November and April. In vitro digestible organic matter (IVDOM), protein, and neutral (NDF) and acid detergent fiber (ADF) concentrations were measured for each sampling time. Generally, barley (Hordeum vulgare L.), oat (Avena sativa L.) and field pea monocrops produced similar yields, and mixtures did not out-yield monocrops. Yield of the barley/oat mixture was more stable from year to year than the respective monocrops. Addition of field pea to cereals in mixtures increased crude protein slightly and reduced NDF over cereal monocrops, but field pea mixtures did not improve nutritive value compared with the field pea monocrop. In one year with severe weathering conditions, field pea and field pea mixtures lost nutritive value faster than cereal monocrops initially, but had nutritive value similar to the cereal monocrops by April. Mixtures and monocrops lost nutritive value at a similar rate due to weathering. Added costs of growing mixtures rather than monocrops were not offset by superior yield, nutritive value, or resistance to weathering. Key words: Winter swath grazing, cereal and field pea mixtures, weathering, nutritive value

Weed-species dynamics and management in no-till and reduced-till fallow cropping systems for the semi-arid agricultural region of the Pacific Northwest, USA

Weed management is an important consideration in implementing new cropping systems. In the semi-arid region of the Pacific Northwest, grower interest is increasing in no-till spring cropping systems because of wind erosion from traditional winter wheat Triticum aestivum L./dust-mulch fallow (WWF). However, no-till represents a major shift in production practices and is likely to produce new weed management challenges. A 6-year study was initiated in 1995 to develop no-till spring cropping systems and to examine associated weed management strategies for the region. Large field-size plots were delineated in two adjacent WWF fields designated west and east sites. Rotations in each site were WWF, no-till spring wheat Triticum aestivum L./chemical fallow (SWF), no-till continuous hard-red spring wheat (CSW), and no-till hard-red spring wheat/spring barley Hordeum vulgare L. (SWSB). Weed density and richness were surveyed three times each year and included late-winter, spring in-crop, and prior to crop harvest. Because of previous cropping histories, initial weed density was higher in the east than in the west plots. Weed management for east WWF was more intense than for west WWF and reduced Bromus tectorum L. density without a subsequent increase of other species. In contrast, weed management in west WWF was less intense and B. tectorum increased. No difference in weed density or richness was detected between CSW and SWSB rotations within each field site; therefore, data from these two rotations were combined and analyzed as a single continuous spring cereal (CSC) rotation. After 6 yrs, weed density was lower in east SWF and east CSC rotations at all three assessments. Weed density in the west CSC rotation was low throughout the research except for an occasional increase in volunteer cereal, but problems in chemical-fallow management increased west SWF weed density. Species richness in no-till increased in late-winter assessments after the first year as B. tectorum population declined and dicot species appeared. However, species richness was low at harvest assessments as herbicides controlled dicot weeds better than annual grasses. Weed populations in no-till rotations declined because of late-winter herbicide control of winter-annual weeds, in-crop herbicide control of dicot weeds, and postharvest herbicide applications to control Salsora iberica. The presence of wind-disseminated seed of Lactuca serriola L. and Conyza canadensis L. Cronq. in west SWF suggests these species may be future problems for long-term no-till.