Wheat-fallow Cropping System Research Articles

Straw Residual Retention on Wheat Photosynthetic Characteristics, Utilization of Water and Nitrogen, and Reactive Nitrogen Losses

Straw residual retention is an emerging and promoted practice in rain-fed northwest China, but its effect on wheat photosynthetic characteristics, the utilization of water and nitrogen, and reactive nitrogen losses is poorly understood. A two-year consecutive field experiment was conducted to investigate the impacts of residual incorporation into soil and nitrogen application on wheat nitrogen and water utilization, yield and nitrogen losses during 2018–2020. The split-plot design of two tillage systems [conventional tillage (CT), and straw residue incorporated into soil (SR)] and three nitrogen rates [0 kg ha−1 (N0), 144 kg ha−1 (N144), 180 kg ha−1 (N180)] was implemented. Our results demonstrated that compared to CT, SR significantly influenced several key metrics. Compared with CT, SR increased the wheat photosynthetic rate (Pn), transpiration rate (Tr), leaf area index (LAI), leaf total chlorophyll (Chl-total), glutamine synthetase (GS) and nitrate reductase (NR) by an average of 5.38%, 12.75%, 8.21%, 5.79%, 16.21% and 20.08%, respectively (p < 0.05). In addition, SR increased the wheat grain yield and nitrogen uptake accumulation (NUA), evapotranspiration (ET), precipitation storage efficiency (PSE), and mineral nitrogen residual after harvest (except for SR-N180 in 2019–2020), but decreased the apparent nitrogen recovery when compared with CT. However, there was an insignificant difference in the ammonia (NH3) volatilization and nitrous oxide (N2O) emissions of SR and CT. With an increase in the N-fertilization rate, the Pn and Tr, NH3 volatilization, N2O emission, mineral nitrogen residual (except for SR-N180 in 2019–2020), LAI, Chl-total (except for SR-N180 and CT-N180 in 2018–2019), GS, NR, grain yield, WUE, and NUA increased significantly; however, the ET, PSE, apparent nitrogen recovery (ANR), and nitrogen harvest index (NHI) decreased significantly. Furthermore, the differences between N144 and N180 in terms of the photosynthetic characteristics of wheat, the utilization of water and nitrogen, and yield were not significant. Overall, straw retention with N144 could be recommended as a resource-saving and environment-friendly management practice in a rain-fed winter wheat–fallow cropping system in northwest China.

Enzyme activities distinguish long-term fertilizer effects under different soil storage methods

Long-term nitrogen fertilization imparts significant effects on the soil environment and soil microbial communities relevant to nutrient cycling. Understanding the complex interactions between soil biology, management practices, and the soil environment is an important step toward improving soil health. The Crop Residue study of the Long-Term Plots at Pendleton, Oregon USA demonstrate declines in soil quality with acidification and reduced soil carbon under a wheat-fallow cropping system. Soil enzyme activity (β-glucosidase, β-glucosaminidase, acid and alkaline phosphatase, arylsulfatase, and arylamidase) and ammonia oxidation was measured in plots managed with three different fertilizer treatments (no fertilization, urea-ammonium nitrate, and manure) at two stages of crop growth. The fertilizer treatments had a strong impact on total carbon and nitrogen and produced a broad range of soil pH from 4.8 (urea-ammonium nitrate) to 5.7 (no fertilizer) and 6.7 (manure). Overall, potential nutrient cycling activity (hydrolytic enzymes and ammonia oxidation) was enhanced in manure-fertilized soils except for acid phosphatase which was greater in the low pH soil. Treatment trends in the proportional geometric mean (an index of soil nutrient cycling capacity) were generally consistent over a 32-year transect excluding acid phosphatase. All activities were highly correlated to total carbon, nitrogen, and sulfur. Except for β-glucosaminidase, all enzymes were also highly correlated to pH. The only enzyme to vary by crop phase was β-glucosidase which was greater at boot than tillering. Soils remaining after the analyses were oven-dried at 40 °C and stored in a non-climate-controlled warehouse for archiving. After 2-years of storage, the oven-dried soils were re-assessed for hydrolytic enzyme activity to determine whether the ability to distinguish treatment differences is retained in archived soils. The oven-dried archived samples showed similar contrasts as the soils analyzed moist between manure and the other fertilizer treatments, although the level of activity was significantly reduced. Overall, long-term fertilization with manure slowed the decline in soil acidity and enhanced soil function relevant to nutrient cycling and organic matter dynamics in the wheat-fallow cropping system.

Soil surface management of legume cover has the potential to mitigate nitrous oxide emissions from the fallow season during wheat production

Soil surface management, i.e., mulch by film, straw or cover crop, is very important to water availability in soil on drylands worldwide, especially during the fallow season, when there is a high concentration of soil nitrate nitrogen (N) to produce nitrous oxide (N2O). To determine whether soil surface management affects N2O emissions during the fallow season, we conducted an experiment to compare N2O emissions from a wheat field that received different surface soil management strategies: control (CK), straw mulch and incorporation (SR), planting legume green manure and incorporation (GM), SR plus GM (SR + GM), and plastic film mulch (FM). The results showed that the average hourly N2O emissions during the fallow season were in the order SR (7.4 μg N m−2 h−1), GM (10.7 μg N m−2 h−1), SR + GM (11.7 μg N m−2 h−1), FM (15.5 μg N m−2 h−1), and CK (16.4 μg N m−2 h−1). Correspondingly, reduced total N2O emissions were observed in the SR, GM and SR + GM treatments, with an average reduction of 39.0% (from 302 to 184 g N ha−1) while increased N2O emissions were from the GM and SR + GM treatments in the wheat growing season. Additionally, N2O emissions were related to soil nitrate N content, microbial biomass and moisture. Overall, considering N2O emissions, C and N inputs by plant residues and grain yield, the management of GM has the potential to reduce greenhouse gas emissions and improve soil C sequestration and soil fertility. These results emphasized the importance of legume green manure to wheat-fallow cropping systems.

Effect of Cover Crop on Farm Profitability and Risk in the Southern High Plains

Cover cropping has been promoted for improving soil health and environmental quality in the southern High Plains (SHP) region of the United States. The SHP is one of the more productive areas of the country and covers a large landmass, including parts of Oklahoma, New Mexico, and Texas. This region faces challenges in sustainable crop production due to declining water levels in the Ogallala Aquifer, the primary source of water for irrigated crop production. This study examines the impact of integrating cover crops in the winter wheat (Triticum aestivum L)-based rotations on farm profitability and risk in the SHP. The study combines experimental yield data with other secondary information, including market prices, to conduct simulation analysis and evaluate the risk involved in introducing cover crops in a wheat-fallow cropping system. The results show that, due to the additional monetary costs involved, none of the cover crop options is economically viable. However, when secondary benefits (erosion control and green nitrogen) or government subsidies are included in the analysis, one of the cover crop options (peas) dominates the fallow alternative. Moreover, when the secondary benefits and a government subsidy are combined, two cover crop alternatives (peas and oats) emerge as more profitable options than leaving land fallow. These results highlight the importance of agricultural research and extension programs that are making a concerted effort to develop more productive farming techniques and increase public awareness about the long-term benefits of adopting soil health management systems such as cover cropping in the SHP region.

Growth, phenology and yield modeling for wheat-fallow cropping system in Gujarat

CropSyst is a daily time step crop growth simulation model that can be used to study the effect of cropping systems management on crop productivity and environment. A total five years experimental field observations (2009-10 to 2013-14) comprising four sowing dates, viz. November 1, 15, 30 and Dec 15 for wheat-fallow crop rotations were used to simulate the growth, phenology and yield for wheat cultivar GW 322 at Anand (Gujarat). Among the five years observations, initial two years observations (2009-10 and 2010-11) were used for model parameterization and remaining year’s observations (2011-12 to 2013-14) were used for model performance evaluation. The results indicated that the model was able to predict the wheat phenology precisely in terms of mean bias error (MBE) and root mean square error (RMSE) which was less than 6 days for all the phenological stages except maturity date on Dec 15 sowing. Nov 15 sowing has resulted in maximum grain and biological yield and found to be optimum date for sowing followed by Nov 30 for this region while Dec 15 resulted in highest yield reduction. It was also observed that CropSystmodel was efficient in simulation of yield and biomass of wheat crop during various years of observations. The model has efficiently predicted grain and biological yield with ±10% of model error for wheat crop. However, it failed to predict the leaf area index (LAI) precisely. It may also be concluded that the model error were less for early and normal sown crops but increased with the delay in sowing.

Rush skeletonweed management in Pacific Northwest winter wheat–fallow cropping systems

Winter wheat production in the inland Pacific Northwest depends on effective weed control strategies to maintain consistent and economically sustaining yields. Control of rush skeletonweed in the winter wheat–fallow cropping system is a new challenge for wheat producers in this region. Earn 1 CEU in Integrated Pest Management by reading this article and taking the quiz at www.certifiedcropadviser.org/education/classroom/classes/679.

Producing High‐Residue, No‐Till Fallow in the Low‐Rainfall Zone of the Pacific Northwest

Core Ideas Use of a stripper header to leave tall stubble for high‐residue no‐till. Winter triticale outperforms winter wheat in low rainfall dryland production. Tall crop residue reduces wind speeds at the soil surface. The low‐rainfall wheat production zone of eastern Washington is subject to wind erosion because of fine‐textured soils, low soil organic matter content, and tillage‐based winter wheat–summer fallow practices. Annual no‐till spring cropping systems to replace the low‐residue, erosive summer‐fallow period have not been economical. We conducted a 4‐year study at Ralston, WA to evaluate winter triticale (× Triticosecale) and non‐semi‐dwarf winter wheat (Triticum aestivum) biomass production, yield, nutrient use efficiency, and seed‐zone soil moisture during no‐till fallow and establishment of fall‐seeded canola. Treatments included winter triticale and winter wheat, both harvested with either a stripper header or conventional cutter‐bar header. Winter triticale produced more grain per pound of N fertilizer and per inch of soil water available than winter wheat, and overall yield was 30–80% greater than that of winter wheat. Full‐height cereals produced 20–90% more biomass than semi‐dwarf winter wheat. Stripper‐header triticale stubble maintained with no‐till chemical fallow (NTCF) reduced average wind speed at the soil surface to less than one‐half of the average wind speed recorded over reduced‐tillage winter wheat fallow. Soil moisture in the 0‐ to 3‐inch seed zone was greater and more uniform in stripper‐header no‐till fallow than in reduced‐tillage fallow. Maintenance of soil moisture by stripper‐header standing stubble was conducive to timely planting and establishment of fall‐seeded canola and led to greater crop establishment in no‐till fallow. Growing a high‐biomass cereal crop such as winter triticale or standard‐height winter wheat and harvesting with a stripper header produces a high‐residue, no‐till fallow that is a viable alternative to the traditional winter wheat–fallow cropping system.

A regional life cycle assessment and economic analysis of camelina biodiesel production in the Pacific Northwestern US

The primary goal of this study was to model the soil emissions during camelina and wheat production in a three-year cycle in the Pacific North West region of the United States considering spatial variations in agro-climatic factors. The second goal of this study was to evaluate the effect of regional agro-climatic variations on the life cycle impact of biofuel production from camelina. DNDC (Denitrification-Decomposition) model was used to estimate the soil emissions in different regions, and openLCA software was used to quantify the environmental impacts of camelina biodiesel production in the State of Oregon. The suitable lands for the cropping system were lands with winter wheat-fallow cropping system and rainfall of 20–40 cm. The model was run for 60 years to reach to the soil organic carbon (SOC) equilibrium point. The results from the cycle with the SOC equilibrium were used to conduct life cycle assessment (LCA). Energy allocation method was selected to allocate LCA results based on the energy content of products and co-products. The results showed that the global warming potential of camelina biodiesel produced under two scenarios was significantly different (P-value < 0.01) such that no-tillage practice had lower GHG emissions compared to conventional tillage system. Uncertainty analysis was carried out using Monte Carlo method, and the results showed that there could be up to 23% variation in soil emissions due to variation in air temperature and SOC. The break-even cost for a three-year crop rotation (winter wheat-fallow-camelina) was estimated to be 1715 $/ha/3y; therefore, locations with income equal or more than the break-even cost and low environmental impacts are suitable for the winter wheat-fallow-camelina rotation system.

Biosolids and conservation tillage: Impacts on soil fungal communities in dryland wheat-fallow cropping systems

Organic amendments and conservation tillage are important management tools for reducing soil erosion and improving soil health in agricultural systems, yet the impacts of these practices on soil microbial communities is poorly understood. We evaluated the effects of biosolid amendments and conservation tillage on soil fungal communities in a dryland wheat (Triticum aestivum L.) –summer fallow cropping system in the inland Pacific Northwest, USA (PNW). Biosolids or synthetic fertilizer was used in combination with conventional (disk) or conservation (undercutter) tillage. Fungal communities were characterized from soil and biosolid aggregates after the second application of biosolids in 2015 and before and after the second application of biosolids in 2016 using high-throughput amplicon sequencing. Biosolid amendments substantially altered fungal community composition, but not diversity, relative to synthetic fertilizer. In contrast, although many more fungal taxa were influenced by conservation tillage when synthetic fertilizer was applied, conservation tillage had relatively little effect on soil fungal communities receiving biosolids, suggesting that the form of N supplied (mineral or organic) may mediate the effects of increasing surface crop residue on fungal communities. Biosolid-mediated shifts in fungal communities were correlated with differences in soil characteristics, especially C, N, and P, and were persistent for at least three years after the initial biosolid application. A small number of taxa, including Fusarium, Ulocladium, Gymnoascus, Mortierella, and Neurospora, were highly enriched by biosolids in soil and dominated fungal communities of biosolid aggregates. Results show biosolids can have strong and lasting impacts on soil fungal communities, likely due to their effects on soil nutrients, and select for a small number of fungi capable of utilizing biosolids as a food source.

Factors Influencing Farmer Willingness to Fallow Winter Wheat and Ecological Compensation Standards in a Groundwater Funnel Area in Hengshui, Hebei Province, China

Land use/land cover change will have a certain impact on the regional ecological environment. This study uses the questionnaire survey method, an opportunity cost method and a logistic model to evaluate the suitability of an ecological compensation standard for a winter- wheat-fallow cropping system in a groundwater funnel area in Hebei. The main factors affecting farmers’ willingness to fallow fields provide a theoretical basis for scientifically and rationally developing a rotation policy in the groundwater funnel area. The results indicate the following: (1) nearly 87% of the surveyed farmers would accept a winter-wheat-fallow policy, whereas 13% would not; (2) farmer educational level, the total number of participants in the agricultural labor force, dependency rate, farmers’ attitudes toward a winter wheat-fallow policy in the groundwater funnel area and the farmer level of trust in government policy have significant positive effects farmer intention to fallow, whereas the number of days of participation in farming, the cultivated land quality and the per capita area of cultivated land have a significant negative effect on farmers’ fallowing intentions; (3) considering only the impact of winter wheat on groundwater, the proposed compensation standard for farmers who accept the policy is 0.00095 $/hm2; (4) some policy implications are put forward to improve the effectiveness of the winter wheat fallowing policy in the groundwater funnel.

Spatial Patterns and Cross-Correlations of Temporal Changes in Soil Carbonates and Surface Elevation in a Winter Wheat-Fallow Cropping System

Soil erosion and deposition impact the sustainability of agricultural lands within the semiarid Great Plains in the United States. Temporal differences between high-resolution digital elevation maps provide physical estimates of spatial erosion or deposition, and the depth to a calcic horizon is a chemical indicator. We hypothesized that soil surface layer CaCO3 concentration is inversely correlated with the change in surface elevation (Δz). We studied a 109-ha field in northeastern Colorado under winter wheat (Triticum aestivum L.)–fallow rotation in alternating strips perpendicular to the prevailing wind. Soil samples (top 30 cm) collected from 185 landscape positions in 2001 and 2012 were analyzed for CaCO3 using a modified pressure-calcimeter method. The change in CaCO3 (ΔC) was significantly correlated with large-scale erosional and depositional areas (west and east blocks, respectively) and with soil units, whereas Δz was correlated with management strips and blocks. The west block had an average ΔC of 3.2 g kg−1 with 2.0 cm of erosion, whereas the east block decreased by 4.4 g kg−1 with 4.2 cm of deposition. Summit positions had the highest CaCO3, and toeslope positions had the lowest. We found inverse relationships between Δz and ΔC in summit and toeslope positions at both erosional (Δz < −5 cm) and depositional (Δz > 5 cm) areas, but Δz was not correlated significantly with ΔC overall. High values of CaCO3 (>100 g kg−1) decreased with time. A high-resolution map of Δz showed complex spatial patterns across scales, which inferred water and wind erosion and deposition affected by terrain and management.

Long‐term‐fertilization effects on soil organic carbon, physical properties, and wheat yield of a loess soil

AbstractThe large dryland area of the Loess Plateau (China) is subject of developing strategies for a sustainable crop production, e.g., by modifications of nutrient management affecting soil quality and crop productivity. A 19 y long‐term experiment was employed to evaluate the effects of fertilization regimes on soil organic C (SOC) dynamics, soil physical properties, and wheat yield. The SOC content in the top 20 cm soil layer remained unchanged over time under the unfertilized plot (CK), whereas it significantly increased under both inorganic N, P, and K fertilizers (NPK) and combined manure (M) with NPK (MNPK) treatments. After 18 y, the SOC in the MNPK and NPK treatments remained significantly higher than in the control in the top 20 cm and top 10 cm soil layers, respectively. The MNPK‐treated soil retained significant more water than CK at tension ranges from 0 to 0.25 kPa and from 8 to 33 kPa for the 0–5 cm layer. The MNPK‐treated soil also retained markedly more water than the NPK‐treated and CK soils at tensions from 0 to 0.75 kPa and more water than CK from 100 to 300 kPa for the 10–15 cm layer. There were no significant differences of saturated hydraulic conductivity between three treatments both at 0–5 and 10–15 cm depths. In contrast, the unsaturated hydraulic conductivity in the MNPK plot was lower than in the CK plot at depths of 0–5 cm and 10–15 cm. On average, wheat yields were similar under MNPK and NPK treatments and significantly higher than under the CK treatment. Thus, considering soil‐quality conservation and sustainable crop productivity, reasonably combined application of NPK and organic manure is a better nutrient‐management option in this rainfed wheat–fallow cropping system.

Conserving and Optimizing Limited Water for Crop Production

Proper soil and crop management systems are critical for sustainable production in semi-arid environments, and there are principles that apply to both dryland (non-irrigated) and limited-irrigation systems. In the non-irrigated environment, crop residue from no-till systems permits more diverse crop rotations with less frequent fallow, which leads to increased precipitation-use efficiency. Soil improvements from no-till systems include decreased soil erosion, increased soil organic matter, improved soil structure, and increased infiltration rate. These soil improvements create a positive feedback loop by making more water available to the crop, increasing yields, and returning more crop residues to the soil. In the Great Plains of the United States, we have found that annualized grain production from no-till systems with less frequent fallow can be increased by 75% with an increase in economic return from 13% to 36% compared with the traditional wheat-fallow cropping system. There is also a need to increase water productivity for irrigated crop production because of competition for water by municipal and industrial users, drought, and declining groundwater supplies. The adoption of cropping systems that use less water and insure economic sustainability must be developed. We have found that limited-irrigation practices that time irrigations with critical growth stages can reduce water use of corn by 50% while reducing yields by only 30%. Alfalfa was found to have great potential for limited irrigation because of its natural drought tolerance and perennial growth habit. Many of the principles of water-conservation practices identified in the United States are adaptable to India's conditions. Soil and crop management systems that use less water and that are sustainable and economically viable in India's limited water environment must be developed.

Modeling Nitrogen Management Effects on Winter Wheat Production Using RZWQM and CERES‐Wheat

Agricultural system models can provide an alternative, less time‐consuming and inexpensive means of determining the optimum crop N requirement under varied soil and climatic conditions. In this context, we parameterized the Root Zone Water Quality Model (RZWQM) for winter wheat (Triticum aestivum L.) production and then evaluated it along with the CERES‐Wheat model to assess their potential as N management tools at Akron, Co. Both models were evaluated with data from five N treatments (0, 28, 56, 84, and 112 kg N ha−1) and three crop seasons (1987–1988, 1988–1989, and 1989–1990). Data from 1987–1988 zero‐N treatment were used for model calibration, and the rest of the data were used for model validation. Genetic coefficients for winter wheat (cv. TAM 107) were developed for the CERES‐Wheat model. The crop parameters required for the generic crop model of RZWQM were parameterized using information from the literature or by calibration. Both models were calibrated first for soil moisture and then for biomass and grain yield. Grain yield predictions had a root mean square error (RMSE) of 500 and 363 kg ha−1, respectively, for CERES‐Wheat and RZWQM. Aboveground biomass was predicted with RMSEs of 1247 and 1441 kg ha−1, respectively. Long‐term simulations of both RZWQM and CERES for winter wheat growth using historical weather data (1912–2001) showed that 56 kg ha−1 N applied as broadcast incorporated is a viable N management option in eastern Colorado, taking into account the grain yield, crop N uptake, N leaching into groundwater, and residual soil N at harvest. Model simulations also showed that the wheat–fallow cropping system is less water use efficient than a continuous wheat system under rainfed agriculture in eastern Colorado.

PHOSPHORUS PARTITIONING AND PHOSPHATASE ACTIVITY IN SEMI-ARID REGION SOILS UNDER INCREASING CROP GROWTH INTENSITY 1

Reduction in the use of fallow in traditional wheat-fallow cropping systems, along with other management changes such as reduced tillage, raise questions about nutrient management, particularly phosphorus (P) management, in such soils. Phosphorus is focused on because of its low soil mobility and its common application in wheat cropping systems. Consequently, we initiated a study with the following objectives: (i) Measure changes in soil available P status during the fallow year under two different cropping intensities; (ii) Determine differences in P status with soil depth and topographic position; (iii) Relate changes in P fractions (organic, inorganic) to P availability; and (iv) Relate P availability (as measured by Bray and Kurtz [B&K] extraction) to soil phosphatase activity. We sampled soils by depth, topographic position, and season during the fallow year in farmers’ fields used for wheat-fallow (w-f) or wheat-proso millet-fallow (w-m-f) cropping systems located near Sidney, Nebraska. Soils were analyzed for B&K-P, total P (TP), inorganic P (IP), organic P (OP), organic matter (OM), and phosphatase activity. Soils under w-m-f were up to 5 mg P kg−1 soil higher in B&K-P than those under w-f, but differences were not significant. Soils at footslope positions were significantly higher in OP, IP, TP, OM, and phosphatase activity, probably because of a combination of deposition of eroded soil and higher average soil moisture content. Differences in P-related properties across seasons were inconsistent. B&K-P was strongly correlated to phosphatase activity, OM, IP, and TP (all P < 0.0001). The general absence of differences in any measured quantity between cropping systems suggests that cropping intensity can be increased in semiarid climates such as the study site, at least over the short-term, without concerns of inducing P deficiencies. Phosphatase activity, although related to P availability, does not offer greater benefits in predicting soil P supply than established soil tests.

Soil Quality Assessment after Weed‐Control Tillage in a No‐Till Wheat–Fallow Cropping System

Adoption of reduced‐tillage fallow systems in the western USA is limited by winter annual grass weeds such as downy brome (Bromus tectorum L.). Moldboard plowing is an effective means of controlling downy brome in winter wheat (Tritcum aestivum L.)–fallow systems. The purpose of this study was to assess the influence of plowing and secondary tillage operations, for the purpose of weed control, on soil quality attributes of a silt loam soil that had been cropped in a sub‐till or no‐till (NT) winter wheat–fallow system for more than 20 yr. Compared with undisturbed NT, downy brome populations in plowed NT decreased 97 and 41% in the first and third crops following tillage, respectively. Wheat yields in plowed NT treatments were 30 and 9% greater in the first and third crops following tillage, respectively, compared with undisturbed NT. Soil quality indicators assessed were organic C (OC), total N, inorganic N, pH, electrical conductivity, bulk density, water infiltration rate, and pore‐size distribution. Five years after tillage, soil OC decline in the 0‐ to 7.5‐cm depth was 20% in plowed compared with undisturbed NT; however, OC increased 15% in the 7.5‐ to 15‐cm depth and was not different in the 0‐ to 30‐cm depth. Total soil N followed similar trends. Soil inorganic N in plowed NT decreased 37%, and soil pH increased 9%, compared with undisturbed NT, at the 0‐ to 7.5‐cm depth. Occasional tillage with the moldboard plow in a reduced‐ or no‐tillage management system will help control winter annual grass weeds, while retaining many of the soil quality benefits of conservation‐tillage management.

Comparison of Three Alternative Oilseed Crops for the Central Great Plains

Diversification of the traditional dryland cropping system in the central Great Plains (winter wheat [Triticum aestivum L.]-fallow) could lead to a more sustainable production system. Selection of suitable crops to rotate with winter wheat requires knowledge of productivity under a widely varying precipitation regime. The objectives of this study were to determine water use/yield relationships and likely average production levels for spring canola (Brassica napus L.), crambe (Crambe abyssinicia Hochst), and sunflower (Helianthus annuus L.), and to determine differences in oil concentration and soil water extraction patterns among these three crops. Canola, crambe, and sunflower were grown under a line-source, gradient irrigation (GI) system to determine seed yield and oil concentration under a range of water use. Sunflower was also grown in several dryland rotations following a variety of crops, which resulted in a range of starting soil water conditions. Soil water extraction was monitored with a neutron probe and time-domain reflectometry. All three crops exhibited linear responses of yield to water use. Sunflower was less responsive than canola and crambe, which had nearly identical water use/yield functions. Oil concentrations showed a trend for increasing oil content with increasing water use. Sunflower extracted water from lower soil depths than canola and crambe, which were similar in soil water extraction. Median yield levels predicted from long-term precipitation records at Akron, CO, were 1130, 1180, and 1520 Iblacre for canola, crambe, and sunflower, respectively. All three crops are agronomically feasible oilseed crops for dryland rotations with winter wheat in the central Great Plains.

Sunflower Response to Nitrogen and Phosphorus in Wheat-Fallow Cropping Systems

Sunflower (helianthus annuus L) is often grown as an alternative crop in wheat (Triticum awstivum L.)-fallow areas of the northern High Plains. Optimum management of fertilizers is important to maximize profit potential and avoid environmental concerns. The objectives of this research were to determine the environmental and soil conditions where seed yield, oil content, and chlorophyll responses to added N and P fertilizers should be expected for sunflower grown in the northern High Plains. Sunflower was grown over 40 site-years in the Nebraska Panhandle during 1993 and 1994 on producers' fields. Fertilizer treatments were four rates of N (0, 35, 70, and 105 lb N/acre) with or without 69 lb P 2 O 5 /acre. All fertilizers were broadcast and incorporated shortly after planting. Sunflower was grown in a wheat-sunflower-fallow cropping system. Fertilizer effect was evaluated for three sunflower seed yield goals: high (>1000 lb/acre), medium (500-1000 lb/acre), and low (<500 lb/acre). Application of P did not influence sunflower seed yield and oil content. Regardless of the initial soil nitrate level or yield goals, application of N beyond 35 lb/acre did not influence seed yield in 80% of the site-years. However, the percentage seed oil content was reduced significantly by increasing levels of N for most site-years. The relationship between the N levels and oil content had an r 2 value of 0.96 for the high, 0.93 for the medium, and 0.94 for the low yield goals. Residual nitrate level did not significantly influence either the seed yield or the seed oil content. Chlorophyll meter readings increased with application of N fertilizers at six site-years; however, at these sites N did not significantly affect seed yield. The results indicate that fertilizer N and P application in the region is not producing economic returns. The yields were highly variable and not significantly affected by the growing season, total precipitation, or soil moisture content at time of planting. The lack of response to N or P fertilizers regardless of the soil N and P level, indicate that other growth factors such as precipitation and temperature at critical growth stages and types of sunflower cultivars are the possible sunflower yield-controlling factors for the region.

Sediment yield and seasonal soil erodibility for semiarid cropland in western Canada

Despite its importance to the degradation of the land resource, few estimates of soil loss or soil erodibility for water erosion from cropland have been made for the semiarid Brown soil zone of western Canada. To estimate these, we calibrated the event-based Modified Universal Soil Loss Equation with measured sediment yield for three 5-ha fields near Swift Current, Saskatchewan. The calibration used predetermined C, LS, P, and warm-season K factors with all erositivities and the K factors for other seasons optimized. Using this calibrated equation with 31 yr of measured runoff data, mean annual sediment yield for a conventional-tillage spring wheat-fallow cropping system on an undulating landscape (0 to 5% slopes) was estimated to be 0.8 Mg ha−1 yr−1. Estimated erosion from fallow land from 16 March to 15 April constituted 86% of the mean annual sediment yield. Erosion occurring during rainfall-runoff were relatively unimportant, accounting for about 4% of the estimated total sediment yield. An exceptionally severe rainstorm was predicted to have caused erosion of many Mg ha−1but the frequency of such events on a given field is too low to greatly affect mean annual erosion. Apparent field-scale soil erodibility was least in the winter (November to 15 March) when the soil would typically be frozen to the surface and was greatest in April when the soil would typically be partially frozen. Apparent erodibility in the summer and in late March was intermediate between those values. Key words: Erosion, runoff, snow, Universal Soil Loss Equation

Fallow Method Affects Downy Brome Population in Winter Wheat

Downy brome (Bromus tectorum L.) is a prevalent weed infesting winter wheat (Triticum aestivum L.) in the Great Plains. Long-term field research was initiated in 1980 on a Williams loam soil (fine-loamy, mixed Typic Argiborolls) near Sidney, MT, to determine the effect of stubble mulch (SM), minimum-till (MT), and no-till (NT) fallow methods on downy brome proliferation in winter wheat-fallow cropping systems. In 1981, downy brome was not observed in the plot area. By 1989, downy brome comprised 32% of the winter wheat community phytomass in the SM method, but was not detected in winter wheat of the MT or NT methods. Winter wheat grain yield in 1989 was 23 and 29% less in the SM method infested with downy brome than in the MT or NT methods, respectively. Pronamide eliminated downy brome during the fallow period in the MT and NT methods, and thus reduced downy brome population in the following winter wheat crop.