Conservation Tillage Management Research Articles

Effect of fallow frequency, flexible rotations, legume green manure, and wheat class on the economics of wheat production in the Brown soil zone

Producers in the semiarid Brown soil zone of Saskatchewan have historically produced spring wheat (Triticum aestivum L.) in fallow-based rotations because these cropping systems are profitable and risk efficient; however, their use has also been most damaging to soil quality. New wheat types and management methods have been developed that may offer wheat producers opportunities to enhance economic returns, while improving environmental sustainability. This study compares the economic merits of reducing fallow (F) frequency, using an annual legume green manure (LGM) crop as a summer fallow replacement, adopting a flex-cropping approach based on available soil water reserves (if water) or the need to control problem weeds (if weeds), and the production of Canada Western Red Spring (CWRS) wheat (W) versus the higher yielding Canada Prairie Spring (CPS) wheat class (HY). The results are based on 15 yr of data from seven crop rotations included in an ongoing experiment being conducted on an Orthic Brown Chernozem at the Semiarid Prairie Agricultural Research Centre at Swift Current, Saskatchewan. The crop rotations included F-W-W, LGM-W-W, F-HY-HY, F-W-W-W, continuous W (Cont W), Cont W (if water), and Cont W (if weeds). Cropping systems were managed using conservation tillage practices. They were fertilized with recommended rates of N and P based on soil tests, and crop residue was maintained as tall as possible (usually > 30 cm) to enhance snow trapping. The 1988–2002 study period was characterized by above normal growing season precipitation; thus, grain yields were also above average for this region. Results showed that producers will earn the highest net return with Cont W ($41 ha-1), despite this rotation having the highest production costs. Net returns ranked second highest for F-W-W-W, F-HYHY, and the flex-crop rotations (about $15 ha-1 less than Cont W), and ranked lowest for F-W-W and LGM-W-W (about $25 ha-1 less). However, since 1993, when the LGM was managed more effectively than in the first 6 yr, LGM-W-W was more profitable than F-W-W. On average, it was more profitable to produce CPS compared with CWRS wheat when the CPS/CWRS price ratio was greater than 0.8. Producers who are highly averse to risk would still choose cropping systems that included some summer fallow, while those with lower risk aversion would choose Cont W, but with all-risk crop insurance. In the absence of an all-risk crop insurance program, producers would typically choose Cont W (if water), F-W-W-W, or F-W-W. We concluded that area producers, who practice conservation tillage management and use tall stubble for snowtrapping, can enhance farm income by moving to more intensive cropping systems, and while doing so, they will foster improved environmental sustainability. Key words: Crop rotations, wheat, summer fallow, legume green manure, flex-cropping, production costs, net returns, income variability

Soil CO 2 flux from a norfolk loamy sand after 25 years of conventional and conservation tillage

Tillage affects the ability of coarse-textured soils of the southeastern USA to sequester C. Our objectives were to compare tillage methods for soil CO 2 flux, and determine if chemical or physical properties after 25 years of conventional or conservation tillage correlated with flux rates. Data were collected for several weeks during June and July in 2003, October and November in 2003, and April to July in 2004 from a tillage study established in 1978 on a Norfolk loamy sand (fine-loamy, kaolinitic, thermic Typic Kandiudults). Conventional tillage consisted of disking to a depth of approximately 15 cm followed by smoothing with an S-tined harrow equipped with rolling baskets. Conservation tillage consisted of direct seeding into surface residues. Flux rates in conservation tillage averaged 0.84 g CO 2 m −2 h −1 in Summer 2003, 0.36 g CO 2 m −2 h −1 in Fall 2003, 0.46 g CO 2 m −2 h −1 in Spring 2004, and 0.86 g CO 2 m −2 h −1 in Summer 2004. Flux rates from conventional tillage were greater for most measurement times. Conversely, water content of the surface soil layer (6.5 cm) was almost always higher with conservation tillage. Soil CO 2 flux was highly correlated with soil water content only in conventional tillage. In conservation tillage, no significant correlations occurred between soil CO 2 flux and soil N, C, C:N ratio, pH, bulk density, sand fraction, or clay fraction of the surface 7.5 cm. In conventional tillage, sand fraction was positively correlated, while bulk density and clay fraction were negatively correlated with soil CO 2 flux rate, but only when the soil was moist. Long-term conservation tillage management resulted in more uniform within- and across-season soil CO 2 flux rates that were less affected by precipitation events.

Ammonia volatilization from surface-applied poultry litter under conservation tillage management practices.

Land application of poultry litter can provide essential plant nutrients for crop production, but ammonia (NH(3)) volatilization from the litter can be detrimental to the environment. A multiseason study was conducted to quantify NH(3) volatilization rates from surface-applied poultry litter under no-till and paraplowed conservation tillage managements. Litter was applied to supply 90 to 140 kg N ha(-1). Evaluation of NH(3) volatilization was determined using gas concentrations and the flux-gradient gas transport technique using the momentum balance transport coefficient. Ammonia fluxes ranged from 3.3 to 24% of the total N applied during the winter and summer, respectively. Ammonia volatilization was rapid immediately after litter application and stopped within 7 to 8 d. Precipitation of 17 mm essentially halted volatilization, probably by transporting litter N into the soil matrix. Application of poultry to conservation-tilled cropland immediately before rainfall events would reduce N losses to the atmosphere but could also increase NO(3) leaching and runoff to streams and rivers.

Tillage system effects upon productivity of a dryland winter wheat–chickpea rotation in the northwest region of Iran

Dryland winter wheat ( Triticum aestivum L.) is a major crop in the northwest region of Iran that is generally grown in rotation with 14-month fallow or chickpea ( Cicer arietinum L.). Information is limited on the success of more intensive dryland cropping systems with conservation tillage management. An experiment was conducted to determine the effect of five tillage systems on crop yield in a winter wheat–chickpea rotation during a 3-year period on a clay loam (Vertic Calcixerepts) in East Azerbaijan, Iran. The tillage systems consisted of moldboard plowing+disking as conventional tillage; chisel plowing+disking as reduced tillage; sweep plowing as minimum tillage; no tillage without and with previous crop residue. The highest wheat yield in three years was obtained with minimum tillage, whereas the yield of chickpea was greatest under no tillage with or without residue. Winter wheat or spring chickpea yield under no tillage with and without residues was not significantly different. Reduced-tillage wheat and chickpea yields were 14 and 27% higher than with conventional tillage, respectively. Average wheat grain yield with no and minimum tillage was significantly greater (27–31%) than under conventional tillage. No-tillage chickpea yield was significantly greater (24–57%) than under reduced, minimum or conventional tillage. The traditional system of moldboard plowing after wheat and chickpea could be replaced by conservation tillage systems that increase yield and will likely improve soil properties in the long term.

Effects of tillage method and crop rotation on non-renewable energy use efficiency for a thin Black Chernozem in the Canadian Prairies

Producers in the Canadian Prairies have begun to extend and diversify their cereal-based rotations by including oilseed and pulse crops, and by managing these newer cropping systems with minimum- and zero-tillage practices. This study examined the implications of these land use changes on non-renewable energy requirements (both direct and indirect), energy output, and energy use efficiency for monoculture cereal, cereal–oilseed, and cereal–oilseed–pulse rotations, each managed using conventional (CT), minimum (MT), and zero (ZT) tillage practices on a thin Black Chernozem in Saskatchewan, Canada. The crop rotations included: spring wheat ( Triticum aestivum L.)–spring wheat–winter wheat–fallow (Ws–Ws–Ww–F), spring wheat–spring wheat–flax ( Linum usitatissimum L.)–winter wheat (Ws–Ws–Fx–Ww), and spring wheat–flax–winter wheat–field pea ( Pisum sativum L.) (Ws–Fx–Ww–P). The findings, based on 12 years of data, showed that non-renewable energy use for the complete cropping systems was largely unaffected by tillage method, but that it differed significantly with crop rotations. Energy requirements were lowest for Ws–Ws–Ww–F (average 6389 MJ ha −1), intermediate for Ws–Fx–Ww–P (11% more), and highest for the Ws–Ws–Fx–Ww (28% more). The substitution of pea for spring wheat in the Ws–Fx–Ww–P versus Ws–Ws–Fx–Ww rotation reduced total energy use by 13%, reflecting the minimal requirement for N fertilizer by pulses due to their ability to biologically fix N, and from the lower fertilizer N rate that was applied to spring wheat grown after the legume. The use of MT and ZT practices provided significant energy savings (compared to CT) in on-farm use of fuel and in machine operation and manufacture for some cropping system components (e.g., summerfallow preparation, spring wheat grown on pea stubble, and for pea grown on cereal stubble), but these savings were often offset by higher energy requirements for herbicides and for N fertilizer with conservation tillage management. Gross energy output averaged 32 315 MJ ha −1 for Ws–Ws–Ww–F, 41 287 MJ ha −1 (or 28% more) for Ws–Ws–Fx–Ww, and 42 961 (or 33% more) for Ws–Fx–Ww–P. Tillage method had little overall influence on energy output for the monoculture cereal and cereal–oilseed–pulse rotations, but it was generally lower with CT than with MT or ZT management for the cereal–oilseed rotation. Energy use efficiency, measured as grain produced per unit of energy input and as the ratio of energy output to energy input, was highest for the cereal–oilseed–pulse rotation (373 and 6.1 kg GJ −1, respectively) and lower, but generally similar, for the cereal–oilseed and monoculture cereal rotations (298 and 5.1 kg GJ −1, respectively). The use of conservation tillage management enhanced overall energy use efficiency for the two mixed rotations, but not for the monoculture cereal rotation. We concluded that adopting diversified crop rotations, together with minimum and zero tillage management practices, will enhance non-renewable energy use efficiency of annual grain production in this sub-humid region.

Mineralogy of eroded sediments derived from highly weathered Ultisols of central Alabama

Coarse-textured surface horizons are common in highly weathered southeastern US coastal plain soils. These soils have historically been managed under conventional tillage practices, but conservation tillage management practices are increasing. Although clay (<2 μm) contents are low in these surface horizons (typically <100 g kg −1), the reactive nature of this fraction tends to play a dominant role in colloidal facilitated pollutant transport. Studies have suggested that enrichment of certain minerals occurs in transported sediments, thus, we evaluated sediment size and the mineralogical partitioning of clay minerals of soil versus runoff sediment under simulated rainfall. In addition, because water dispersible clay (WDC) has been shown to be correlated with soil erodibility, we evaluated WDC differences as a function of tillage practices. Plots were established at a site in the upper coastal plain of central Alabama, where soils classified as coarse-loamy, siliceous, subactive, thermic Plinthic Paleudults and Typic Hapludults (FAO-Acrisols). Surface tillage treatments were established in 1988, and included conventional tillage (CT) versus no surface tillage (NT) treatments, with crop residue remaining or removed, and with or without paratilling (non-inversion subsoiling). Within these plots, simulated rainfall (target intensity=50 mm h −1 for 2 h) was applied to replicated 1 m×1 m areas, and runoff and sediment were collected. Mineralogical analyses of soils and sediment were conducted using thermogravimetric analysis (TGA) and X-ray diffraction (XRD) techniques. WDC quantities were highly correlated with percent soil organic carbon (SOC) ( r 2=0.76), which was a function of tillage treatment. Although no differences in the mineralogy of the <2 μm sediment were observed between tillage treatments, runoff sediments (<2 μm) were enriched in quartz (qtz) and relatively depleted with kaolinite compared to in situ soils. These findings will facilitate development of mechanistic models that predict sediment attached losses of nutrients and pesticides.

Tillage effects on microbial biomass and nutrient distribution in soils under rain-fed corn production in central-western Mexico

Quantifying how tillage systems affect soil microbial biomass and nutrient cycling by manipulating crop residue placement is important for understanding how production systems can be managed to sustain long-term soil productivity. Our objective was to characterize soil microbial biomass, potential N mineralization and nutrient distribution in soils (Vertisols, Andisols, and Alfisols) under rain-fed corn ( Zea mays L.) production from four mid-term (6 years) tillage experiments located in central-western, Mexico. Treatments were three tillage systems: conventional tillage (CT), minimum tillage (MT) and no tillage (NT). Soil was collected at four locations (Casas Blancas, Morelia, Apatzingán and Tepatitlán) before corn planting, at depths of 0–50, 50–100 and 100–150 mm. Conservation tillage treatments (MT and NT) significantly increased crop residue accumulation on the soil surface. Soil organic C, microbial biomass C and N, potential N mineralization, total N, and extractable P were highest in the surface layer of NT and decreased with depth. Soil organic C, microbial biomass C and N, total N and extractable P of plowed soil were generally more evenly distributed throughout the 0–150 mm depth. Potential N mineralization was closely associated with organic C and microbial biomass. Higher levels of soil organic C, microbial biomass C and N, potential N mineralization, total N, and extractable P were directly related to surface accumulation of crop residues promoted by conservation tillage management. Quality and productivity of soils could be maintained or improved with the use of conservation tillage.

Minimum and Delayed Conservation Tillage for Wheat–Fallow Farming

Maintaining crop residue, clods, and roughness on the soil surface during summer fallow is critical for wind erosion control in the low‐precipitation (&lt;300 mm annual) dryland wheat (Triticum aestivum L.) production region of the inland Pacific Northwest, USA. Conventional farming practices are intensive, involving eight or more tillage operations during the fallow cycle. My objective was to evaluate fallow conservation tillage management systems for soil water storage, residue retention, surface and subsurface soil cloddiness, surface roughness, wheat stand establishment, and grain yield during 6 yr at Lind, WA. The soil is a Shano silt loam (coarse‐silty, mixed, superactive, mesic Xeric Haplocambids). Treatments were (i) conventional (tillage), (ii) minimum (herbicides and tillage), and (iii) delayed minimum (herbicides and delayed tillage). Averaged over years, precipitation storage efficiency in the soil was 51, 54, and 57% over winter, and 24, 26, and 26% at the end of the fallow cycle, for conventional tillage (CT), minimum tillage (MT), and delayed minimum tillage (DMT), respectively. Surface residue and surface clod mass were consistently reduced by 45% or more in CT compared with MT and DMT. There were no differences among treatments in seed‐zone water content at time of sowing in September nor in grain yield in any year or when averaged across years. Results show that the long‐term practice of minimum and delayed minimum tillage during fallow significantly increased surface residue and clod retention for erosion control with no adverse agronomic affects compared with conventional tillage.

Residue removal and tillage interaction effects on soil properties under rain-fed corn production in Central Mexico

Determining the effects of residue removal and tillage systems on surface crop residue accumulation, organic carbon sequestration and nutrient cycling is essential for sustainable land management. This study evaluated the effects of 6 years of conventional and conservation tillage with different amounts of crop residues left on the soil surface on selected soil properties of a Vertisol and an Andisol used for rain-fed corn ( Zea mays L.) production in Central Mexico (Apatzingán and Casas Blancas, Mich.). The results showed that conservation tillage, i.e. no tillage (NT) with 100, 66 and 33% of crop residues left on the field, and minimum tillage (MT), significantly increased surface crop residue accumulation on the soil surface. In the 0–50 mm surface layer, organic C, microbial biomass C and N, inorganic and total N, and extractable P were approximately twice higher with NT/100%, NT/66%, NT/33%, and MT than with conventional tillage (CT) and NT/0% treatments. Higher levels of soil organic C, microbial biomass C and N, inorganic and total N, and extractable P were directly related to surface accumulation of crop residues promoted by conservation tillage management. Removal of surface crop residues can seriously reduce production sustainability in climates where stressful conditions occur. In general, the mid-term (6 years) sustainability of Vertisol and Andisol for rain-fed corn production seemed to be enhanced by conservation tillage management. To obtain the benefits of conservation tillage in the sub-humid tropical region of Apatzingán (Vertisols), where organic matter is rapidly oxidized, it is necessary to leave at least 60% of the crop residue on the soil surface, while in the sub-humid temperate region of Casas Blancas (Andisol), where organic matter is oxidized slower, leaving 30% of crop residue is sufficient.

Energy performance of conservation tillage management for spring wheat production in the Brown soil zone

There is growing interest in the potential for improving nonrenewable energy use efficiency of traditional agricultural production activities in the Canadian prairies. This study, which was conducted on three soil textures in the Brown soil zone of southwestern Saskatchewan, examined the energy performance of conventional tillage (CT), minimum tillage (MT), and no-tillage (NT) management practices for spring wheat grown in fallow-wheat (F–W) and continuous wheat (Cont W) rotations over a 12-yr period (1982–1993). Metabolizable energy output increased with cropping intensity on a silt loam at Swift Current and on a clay at Stewart Valley (average of 16 751 MJ ha–1 for F–W and 24 110 MJ ha−1 for Cont W), but not on a sandy loam at Cantuar (average 14 828 MJ ha−1) where soil water-holding capacity was limited. Further, because grain yield was rarely significantly influenced by tillage method, the latter had little influence on the overall output of metabolizable energy. Total input of nonrenewable energy per unit of rotation also increased with cropping intensity (average 2585 MJ ha−1 for F–W and 5274 MJ ha−1 for Cont W). This was primarily because of the higher rates of N fertilizer that were required with stubble cropping. We found little or no net energy savings with NT management; the F–W (MT) system tended to have the lowest overall nonrenewable energy requirement at all test sites. Although the use of conservation tillage practices provided significant energy savings in fuel and machinery, particularly for F–W systems, these were largely offset by increases in the energy input for herbicides, and higher rates of N fertilizer that were required for NT managed areas. Consequently, net energy produced (energy output minus energy input) had similar patterns as metabolizable energy output. In contrast, when efficiency was expressed as ratios of energy output to energy input, or quantity of wheat produced per unit of energy input, the values were higher for F–W (average 6.2 and 456 kg GJ−1, respectively) than for Cont W systems (average 3.8 and 278 kg GJ−1, respectively). These measures of energy efficiency also tended to be higher for CT and MT than for NT management on the medium- and fine-textured soils, but on the coarse-textured soil, tillage had no influence on the energy efficiency of the cropping systems. We concluded that the potential for achieving energy savings by adopting conservation tillage management for monoculture wheat rotations is low in this semiarid region. This was because of the lack of consistent yield advantages with MT and NT, and due to the few tillage operations that are traditionally used to control weeds on summerfllow areas and to prepare the seedbed with CT management. Key words: Wheat, minimum tillage, no-tillage, nonrenewable energy, energy output/input, energy efficiency

Long-term tillage and nitrogen fertilization effects on soil properties of an Alfisol under dryland corn/cotton production

Greater knowledge of the long-term effects of tillage and N fertilization on soil chemical and physical properties is needed in order to assess the contributions of these practices to sustainable land management, especially in warm, subhumid climates where organic matter is quickly oxidized. Soil properties were evaluated after 16 years of corn ( Zea mays L.)/cotton ( Gossypium hirsutum L.) production under conventional-bedding (CT), moldboard (MB), chisel (CH), minimum tillage (MT), and no-tillage (NT) with low (45 N kg ha −1) and high (90 N kg ha −1) N fertilization on an Orelia sandy clay loam (fine-loamy, mixed, hyperthermic Typic Ochraqualf) soil in south Texas (USA). Tillage systems significantly affected soil bulk density in the 0- to 200-mm soil depth. No-tillage bulk densities ranged from 5 to 19% higher than for the other tillage treatments while those from MB ranged from 7 to 21% lower. Conservation tillage treatments (NT and MT) resulted in a 30 to 135% increase in surface crop residues compared with other tillage treatments, while plots with the high N rate exhibited 8% more residue than with low N fertilization. In the 0- to 50-mm surface layer, organic C, total N, and extractable P were approximately 64, 78, and 110% higher with NT than with the average of the other tillage treatments. Higher N fertilization increased organic C, total N, and extractable P by 9, 7, and 19%, respectively, in the 200-mm depth. No-tillage decreased cation exchange capacity (CEC) and soil pH as compared with MB, CH, and CT in the 0- to 50-mm soil layer. Residual NO 3 −-N to a depth of 1200 mm under NT and MT was consistently less than with the other tillage treatments. Higher levels of soil organic C, total N, and extractable P and lower concentrations of NO 3 − were directly related to surface accumulation of crop residues promoted by conservation tillage management. The long-term sustainability for crop production on this soil appeared to be enhanced with reduced tillage management.

Long-term tillage effects on atrazine and fluometuron sorption in Coastal Plain soils

Conservation tillage (CnT) management practices are known to increase levels of soil organic matter (SOM) in southeastern Coastal Plain soils. Plant residues in CnT systems accumulate at the surface and, with time, will form a layer enriched in SOM. The authors hypothesize that herbicide sorption will be highest in this SOM-enriched zone of CnT systems when compared to sorption at a similar depth in conventional tillage (CT) systems. The objective was to characterize the impact of two different tillage systems, CnT and CT, on sorption of atrazine [6-chloro- N-ethyl- N′-(1-methylethyl)-1,3,5-triazine-2,4-diamine] and fluometuron [ N,N-dimethyl- N′-3-(trifluoromethyl)phenyl urea] in plots of Norfolk loamy sand (fine-loamy, siliceous thermic Typic Kandiudult). The plots have been under CnT and CT management for 18 yrs. Bulk (0–15 cm) and five equal incremental soil samples to a 15 cm depth were collected from 10 CnT and 10 CT plots, and the atrazine (ATR) and fluometuron (FLMT) sorption coefficients ( K d) were measured using batch equilibration. Significantly higher herbicide K d values occurred in the CnT 0–3 cm samples, indicating that the highest amount of herbicide sorption occurred in the top few cm of soil. This corresponded to the stratified soil organic carbon (SOC) contents in topsoil of the CnT plots. In addition, analyses of covariance using SOC as the covariant to test for tillage effects indicated complex interactions among SOC, tillage, and depth. Those results confirm that tillage and soil depth will affect SOC contents of a Norfolk loamy sand, which correspondly will influence the magnitude of ATR and FLMT sorption.

Economics of reduced tillage fallow-crop systems in the Dark Brown soil zone of Alberta

The use of conservation tillage management in fallow cropping systems reduces soil erosion and improves soil quality. The economic benefits of these alternate tillage methods are less certain. This study examined the economic returns from reduced tillage methods on fallow using yield and input data from two experiments at the Agriculture and Agri-Food Canada Research Centre at Lethbridge, Alberta. One experiment was long-term study initiated in 1955 with eight treatments, the second was a 5-yr study with 15 treatments. Results from the 5-yr study indicated no difference in net returns between conventional and reduced tillage fallow systems. In contras, the long-term study net returns were highest for tilled systems and lowest for herbicide-only systems. The long-term study had a build-up of weeds that are difficult to control with herbicides alone. The resulting lower average yield and higher herbicide costs of the herbicide-only treatments in the long-term study accounted for most of the contrasting results between the two experiments. An economic evaluation of tillage practices requires the entire system to be evaluated, not just the tillage component. Key words: Economics, tillage, reduced tillage, conservation practices, weed control

Corn‐Weed Interactions with Long‐Term Conservation Tillage Management

AbstractThe use of monoculture production systems such as continuous corn (Zea mays L.) in conservation‐tillage systems has created a requirement for information concerning crop and weed responses to annual herbicide inputs. The objective of this 5‐yr investigation (1981–1985) was to evaluate weed problems and delineate weed and crop interactions in continuous conservation‐tillage corn as affected by annual herbicide applications. Preemergence treatments contained selected combinations of triazines or a triazine plus alachlor [2‐chloro‐N‐(2,6‐diethylphenyl)‐N‐(methoxymethyl)acetamide]. Preemergence or preplant incorporated herbicide mixtures were applied at common usage rates and compared for their effects on weed cover, weed species stability, and grain production. All plots were essentially weed‐free the first year. Weed cover in most treatments increased significantly by the second year with fall panicum (Panicum dichotomiflorum Michx.) dominating the flora in Years 2 and 3, and smooth pigweed (Amaranthus hybridus L.) dominating in Years 4 and 5. Smooth pigweed reached densities of 85% in several treatments. Fall panicum was the dominant weed in pre‐plant incorporated treatments that contained atrazine [6‐chloro‐N‐ethyl‐N'‐(l‐methylethyl)‐1,3,5‐triazine‐2,4‐diamine] plus a carbamothioate herbicide. Grain yields were negatively correlated with fall panicum densities in the second year in all herbicide treatments. Smooth pigweed densities were negatively correlated with grain yields in the fifth year in all preemergence treatments. Smooth pigweed densities were lower in triazine plus alachlor treatments than in double triazine treatments for the last 2 yr of the study.

Economics of tillage systems for spring wheat production in southwestern Saskatchewan (Canada)

The economic performance of continuous wheat ( Triticum aestivum L.) and fallow-wheat rotations grown under conventional, minimum- and zero-tillage management practices on silt loam, sandy loam and heavy clay in southwestern Saskatchewan was determined during the relatively dry period of 1982–1988. The costs and returns for each rotation-tillage system were evaluated annually based on 1989–1990 price and cost conditions, and for various other plausible scenarios. Gross returns on silt loam were higher for continuous wheat (average 228 $ ha −1) than for fallow-wheat systems (average 155 $ ha −1). On the sandy loam, gross returns were similar for all cropping systems (average 112 $ ha −1); on the heavy clay, they were higher for fallow-wheat than for continuous wheat (139 versus 119 $ ha −1). Conservation tillage management increased gross returns over that obtained with conventional tillage only in years when growing season temperatures were high and precipitation was poorly distributed, or when the 21-month summerfallow period was droughty. On silt loam, gross returns were significantly lower with conservation tillage in as many as 3 of 7 years. On silt loam, net returns were highest for conventionally tilled continuous wheat when wheat prices were> 175 $ t −1; at lower wheat prices, conventionally tilled fallow-wheat was the most profitable. On the other soils, minimum- and zero-tillage fallow-wheat provided the highest net returns at all wheat prices tested, with minimum tillage being slightly better at low wheat prices, but at these sites conventionally tilled fallow-wheat was not studied. The cost of production was highest for continuous wheat and for zero-tillage management. For fallow-wheat systems, conservation tillage required lower expenditures than conventional tillage for fuel, labor, machine repair and machine overheads; costs for minimum tillage averaged 9 $ ha −1 and for zero tillage 15 $ ha −1 lower on the silt loam. These savings were more than offset by increased herbicide costs which averaged 26 and 64 $ ha −1 higher for minimum-tillage and zero-tillage systems, respectively. We concluded that producers in southwestern Saskatchean who are motivated primarily by short-term profit will find little incentive to adopt conservation tillage systems for spring wheat production, unless they are situated on soils that have already incurred severe soil loss or the soils are highly prone to further erosion losses.

Psychological disorders in rheumatoid arthritis: a growing consensus?

Previous reviews of psychological factors in arthritis have emphasised the methodological weaknesses of many studies, especially those attempting to measure personality after years of disabling disease. To make sense of the published reports three factors need to be considered separately: previous personality, social stresses, and current mental state. Each can now be measured reliably and independently of symptoms which might be directly attributable to the arthritis. There is a growing consensus that the normal range of personality is represented among patients with early arthritis, that the prevalence of depression is similar to that of patients with other medical conditions, and that social stress is more closely related to depression than activity and the disabling effect of arthritis. Longitudinal studies are now required to examine which social stresses can be attributed to the disabling effect of arthritis. Depression and social stress often manifest themselves to the rheumatologist as excessive complaints of pain and frequent clinic attendances so appropriate psychosocial treatments may reduce this behaviour.

Environmental Effects on Nitrogen Dynamics in Soybean under Conservation and Clean Tillage Systems

AbstractSoybean [Glycine max (L.) Merr.) obtains required N from the soil via root uptake of mineralized organic matter and fertilizer, and from the air by symbiotic gaseous N2 fixation and ammonia (NH3) absorption. The purpose of this study was to evaluate environmental and tillage effects on dynamic N transport under conservation (NT) and clean tillage (CT) management systems. Soil, plant, and microclimate measurements were made concurrently with estimates of gaseous N2 (using 15N2 techniques) and NH3 uptake from the atmosphere. Soybean growth and N uptake characteristics were similar in both tillage systems, except during a 14‐d drought period, which caused water stress in the CT system, but not the NT system. Nitrogen fixation decreased in the CT system to less than half that of the NT system fixation rate, resulting in a seasonal reduction of 29% in the CT system. Net NH3 transport varied from net absorption by the canopy during periods of adequate soil water to net evolution by the CT system during the drought‐stress period. Integration of the net NH3 flux density curves indicated that approximately 3% of the NT system and less than 1% of the CT system plant N was derived from the atmosphere. Also during the drought‐stress period, there was a net loss of plant N to the soil in the CT system indicated by soil and plant mass balance. Insect infestation was much greater in the NT system, reflecting insects' preference for a higher N crop, resulting in a significant N removal from the system. This study showed that soybean in these systems decreased soil N by about the amount of harvested N yield.

Effect of Applied and Residual P on Double‐Cropped Wheat and Soybean under Conservation Tillage Management1

AbstractIn the Piedmont area of Southeastern USA, the economic advantages of double‐cropped wheat (Triticum aestivumL. Thell) and soybean (Glycine maxL. Merr.) have recently resulted in increased acreage of both crops. In many cases, the rotation is wheat and soybean under conservation tillage management. Many soils in this region of the USA are low in P, and it may be advantageous to raise these soils to the high soil test range before initiating conservation tillage practices. The purposes of this study were to determine if it is necessary to raise low P soils to the high soil test range prior to initiating conservation tillage systems and to determine how long a single high rate of P will maintain yields equal to those obtained with annual or biannual applications. Wheat and soybean were double‐cropped under conservation tillage management on a Cecil sandy loam soil (clayey, kaolinitic Typic Hapludult) from 1978 to 1981. The P treatments were applied as a one‐time application in the fall of 1977. Broadcast rates of P were 0,64, 128,256, and 384 kg ha−1. Two annual P applications of 64 kg P ha−1were also included for comparison of residual soil P and annually applied P. One‐time applications of 128 or more kg P ha−1provided sufficient soil P to maintain soybean yields significantly higher than the zero P application rate 4 years after application. The 128 kg P ha−1treatment also produced consistently good wheat yields for 3 years after application, but the 256 and 384 kg P treatments reduced wheat yields in 1978 due to increased lodging and glume blotch ((Septoria nodorum). The data indicate that a single application of 128 kg P ha−1can maintain wheat and soybean yields for at least 3 years in a double‐cropping conservation tillage system without significantly reducing micronutrient uptake. Phosphorus fertilization increased soil P levels and plant tissue P. Applied P increased extractable soil Zn, but decreased the concentration of Zn, Cu, and Mn in the soybean plant tissue.

Moisture Conservation Potential with Conservation Tillage Treatments in the Thick Loess Area of Western Iowa1

AbstractMoisture is usually in short supply for production of corn (Zea mays L.) on thick loess derived soils in western Iowa. Practices that conserve moisture should increase crop yields but quantitative data is very scarse. The objectives were to develop a yield response curve for moisture applicable in western Iowa and evaluate the potential effect of conservation tillage systems on corn yields. Computerized modeling techniques were used to develop the yield response curve and to evaluate conservation practices.Moisture stress indices, which were highly correlated with measured corn yields, were used to evaluate the effectiveness of modeled tillage treatments in terms of corn yield. The model budgeted daily soil moisture use based on initial soil moisture measurements, actual weather data, and simulated hydrologic processes. The appropriate hydrologic processes were modified to approximate the tillage system under study. The hydrologic processes assumed most altered by conservation tillage management were surface runoff and surface evaporation in the spring fallow period.The modeled tillage practices were evaluated at three assumed spring soil moisture levels in combination with actual long term weather records. When spring soil moisture levels were at 100% of the plant‐available water capacity (PAWC), tillage practices had little effect on estimated corn yields. At the medium and low spring soil moisture levels, modeled conservation tillage was effective in increasing yield estimates over those obtained with conventional tillage.