Semiarid Canadian Prairies Research Articles

Long-term effect of cropping system and nitrogen and phosphorus fertilizer on production and nitrogen economy of grain crops in a Brown Chernozem

Assessment of the long-term impact of fertilizers and other management factors on crop production and environmental sustainability of cropping systems in the semi-arid Canadian prairies is needed. This paper discusses the long-term influence of N and P fertilizers on crop production, N uptake and water use of hard red spring wheat (Triticum aestivum L.), and the effect of the preceding crop type [flax (Linum usitatissimum L.) and fall rye (Secale cereale L.)] on wheat grown on a medium-textured, Orthic Brown Chernozem at Swift Current, Saskatchewan. We analysed 36 yr of results (1967–2002) from eight crop rotation-fertility treatments: viz., fallow-wheat receiving N and P (F-W, N + P), three F-W-W treatments fertilized with (i) N + P, (ii) P only, and (iii) N only; two other 3-yr mixed rotations with N + P (i) F-flax-W (F-Flx-W) and (ii) F-fall rye-W (F-Rye-W); and two continuous wheat rotations (Cont W), one receiving N + P and the other only P. Growing season weather conditions during the 36-yr period were near the long-term mean, but the first 22 yr were generally drier than normal while the last 14 yr (1989–2002) had average to above-average growing conditions. This was partly responsible for grain and N yield being greater in the latter period than in the first 22 yr. The 36-yr average response of wheat grown on fallow to P fertilizer was 339 kg ha-1, while the response to N fertilizer over this period was only 123 kg ha-1. The 36-yr average response of wheat grown on stubble to N was 344 kg ha-1 for F-W-(W) and 393 kg ha-1 for Cont W. Neither flax nor fall rye influenced the yield response of the following wheat crops. Annualized grain production for F-W (N + P), F-W-W (+ N) and F-W-W (+ P) rotations were similar (1130 kg ha-1 yr-1); this was about 15% lower than for F-W-W (N + P), 40% lower than for Cont W (N + P), and 5% lower than for Cont W (+ P). Annualized aboveground N yield for Cont W (N + P) was 57% higher than for Cont W (+ P). Regressions were developed relating straw to grain yields for wheat, flax and fall rye. The amount of NO3-N left in the soil was directly related to amount of N applied and inversely to N removed in the crop. Thus, F-(W)-W (+ N) left about 28% more NO3-N in the rooting zone than F-(W)-W (N + P), while F-W-(W) (N + P) left 20% more than F-W-(W) (+ P), and Cont W (N + P) left 39% more than Cont W (+ P). F-Rye-W (N + P) left much less NO3-N in the soil than any other fallow-containing system and similar amounts to Cont W (N + P). Key words: Yields, grain protein, N and P fertilizer, straw/grain regressions, water use, soil nitrate

The Economics of Sustainable Agriculture Alternatives on the Semiarid Canadian Prairies: The Case for Legumes and Organic Amendments

ABSTRACT The economic performance of rotations with reduced summerfallow frequency, legume crop alternatives, and manure applications was evaluated using data from a rotation experiment established in 1992 on Brown Chernozemic soil at Bow Island, Alberta (Alberta Crop Diversification Center South). Net returns and variability were calculated for each of the six rotations under test and for different fertilizer treatments, including manure (a total of 20 rotation and fertilizer treatment combinations). A farm-level economic risk model was formulated to simulate optimal rotation selection under uncertainty and risk aversion. The six rotations included continuous wheat (W), fallow-wheat (FW), fallow-wheat-wheat (FWW), flax-wheat-fallow (FxWF), legume-Allan wheat (LW), and grass (G). The wheat and flax phases of the fertilized rotations were fertilized with 0, 20 or 40 kg N ha−1 (0, 17.9 or 35.7 1bs N ac−1) and with 0 or 8.6 kg P ha−1 (7.7 lbs P ac−1). The W and FW rotations also had a manure treatment. Of the traditional cropping systems, the FWW and FW rotations (with applications of 40 kg ha−1 N: 8.6 kg ha−1P (35.7 1bs ac−1N: 7.7 1bs ac−1 P)and 20 kg ha−1N: 8.6kg ha−1P(17.81bs ac−1 N: 7.7 1bs ac −1 P), respectively), exhibited the highest returns and the FW(20,8.6) rotation experienced less variability. The simulation revealed that increases in net returns could be attained through the introduction of a LW rotation because of its ability to fix N and thus reduce the input costs. Risk averse producers would be expected to plant a combination of LW(0,0) and FW(40,8.6). W and FW rotations with manure treatments were not as profitable as those with chemical fertilizer treatments.

Effect of Moisture and Temperature on Disease of Green Foxtail Caused by Drechslera gigantea and Pyricularia setariae.

Leaf wetness duration, temperature, intermittent leaf wetness, and delayed leaf wetness were investigated for their influence on disease of green foxtail caused by Drechslera gigantea and Pyricularia setariae to determine the potential of these two fungi as bioherbicide agents in the Canadian prairies. For both fungi, disease severity increased with increasing leaf wetness duration at 15, 20, 25, 30, and 32°C. At 10°C, conidia of both fungi showed minimal germination, regardless of leaf wetness duration; however, an increase in conidial germination, appressoria formation, and disease occurred at 15°C. Conidia of both species showed 80% or greater germination at all temperatures above 15°C, whereas the optimum temperatures for appressoria formation by D. gigantea and P. setariae were 23 and 25°C, respectively. Maximum disease occurred after 48 h of leaf wetness at 32°C for D. gigantea and at 25°C for P. setariae. Disease caused by both fungi decreased when 4 h of continuous leaf wetness was followed by a 20-h dry period, and after an 8-h delay in leaf wetness following inoculation. Both fungi required immediate and prolonged periods of leaf wetness at temperatures of 15°C and above to cause severe disease on green foxtail. The moisture requirements of these fungi may limit their effectiveness as bioherbicide agents in the semi-arid Canadian prairies.

Cropping frequency effects on yield of grain, straw, plant N, N balance and annual production of spring wheat in the semiarid prairie

Producers in the semiarid Canadian prairies practice frequent summerfallow to conserve water and reduce the risk of crop failure, but this practice promotes soil degradation. In contrast, annual cropping enhances soil quality but results in greater economic risk. We need to know what is the most suitable cropping frequency for this region. In 1985, based on results of the first 18 yr of a long-term crop rotation experiment being conducted on a medium-textured, Orthic Brown Chernozem at Swift Current, Saskatchewan, we modified the experiment to allow comparison of four cropping frequencies over the period 1985–2002. These were fallow-spring wheat (Triticum aestivum L.) (F-W), F-W-W, F-W-W-W-W-W, and continuous wheat (Cont W). All systems received recommended rates of N and P fertilizer. Growing season precipitation during the 1985–2002 period was 10% above average so that grain yields were also above average for this region. We assessed yields of grain, straw and N in aboveground plant parts, N concentration in grain and straw, harvest index, nitrogen harvest index and water use efficiency, and the average annual production (on a rotation basis) of grain, straw and aboveground N yield, and related these characteristics to water deficit. Water deficit was the main factor responsible for annual variations in the characteristics assessed. Of these characteristics, cropping frequency influenced only the average annual productivity factors; it rarely influenced the characteristics when they were assessed on a rotation-phase basis. Assuming cropping frequency (x) for the 2-yr, 3-yr, 6-yr and Cont W rotations is 50%, 67%, 83%, and 100%, respectively, then average annual yields (y) in kg ha-1 yr-1 were related to frequency as follows: (1) for grain yield y = 768 + 10.7 x, r2 = 0.99; (2) for straw yield y = 1159 + 18.9 x, r2 = 0.99; and (3) for aboveground plant N yield y = 23.7 + 0.36 x, r2 = 0.99. The regression between annual grain production and cropping frequency at Swift Current for 1985 to 2002 had a much higher slope than the relationship for the same experiment in the much drier 1967 to 1984 period. Further, the equations for Swift Current in 1985–2002 were similar to the relationships obtained for systems in the subhumid Black Chernozems, indicating such relationships are greatly influenced by weather conditions. These relationships may be useful for conducting economic analyses and for modeling N balance. We conducted an apparent N balance analysis which indicated that all four rotations have lost N from the system in inverse proportion to the frequency of cropping. However, changes in total N in the 0- to 0.3-m depth of soil suggest that they have not lost N and that Cont W gained N over the course of the study. We are not able to explain this apparent anomaly and recommend further research on this question. Key words: Fallow frequency, grain yield, N concentration, N yield, water deficit, water use efficiency, N balance

Long-term assessment of management of an annual legume green manure crop for fallow replacement in the Brown soil zone

In the Brown soil zone of western Canada summerfallowing (F) is traditionally used to reduce the water deficit associated with cereal production, but frequent use of this practice results in soil degradation and reduces the N-supplying capacity of soils. Some scientists suggest that an annual legume green manure crop (LGM) could be used as a partial-fallow replacement to protect the soil against erosion and increase its N fertility, particularly when combined with a snow-trapping technique to replenish soil water used by the legume. We assessed this possibility by comparing yields, N economy, water use efficiency, and economic returns for hard red spring wheat (W) (Triticum aestivum L.) grown in rotation with Indianhead black lentil (Lens culinaris Medikus) green manure (i.e., LGM-W-W) vs. that obtained in a traditional F-W-W system. Further, we assessed whether a change in manage ment of the LGM crop (i.e., moving to earlier seeding and earlier turn-down) was advantageous to the overall performance of this practice. The study was conducted over 12 yr (1988–99) on a medium-textured Orthic Brown Chernozem at Swift Current, Saskatchewan. Wheat stubble was left tall to trap snow, tillage was kept to a minimum, and the wheat was fertilized based on NO3 soil tests. When we examined results after 6 yr, we concluded that by waiting until full bloom to turn down the legume (usually late July or early August) so as to maximize N2 fixation, soil water was being depleted to the detriment of yields of the following wheat crop. The change in management of the LGM crop since 1993 resulted in wheat yields following LGM equaling those after fallow (due to improved water use efficiency), a gradual and significant increase over time in grain protein and in N yield of aboveground plant biomass of wheat in the LGM-W-W compared to the F-W-W system, plus a gradual decrease in fertilizer N requirements of wheat in the LGM system accompanying an improvement in the N supplying power of the soil. These savings in N fertilizer, together with savings in tillage and herbicide costs for weed control on partial-fallow vs. conventional-fallow areas, and higher revenues from the enhanced grain protein, more than offset the added costs for seed and management of the LGM crop. Thus, our results imply that, if producers seed the LGM in April and turn it down in early July, an annual LGM-cereal rotation is a viable option in the semiarid Canadian prairies; however, one negative consequence of adopting this management strategy is the possibility of enhancing NO3 leaching. Key words: Nitrogen yields, grain protein, green fallow, summerfallow substitute, economic returns, NO3 leaching

Cropping frequency, wheat classes and flexible rotations: Effects on production, nitrogen economy, and water use in a Brown Chernozem

Producers in the semiarid Canadian prairies rely on frequent summerfallowing (F) to conserve water, control weed infestations, and maximize soil mineral N reserves, but this practice often results in soil degradation. A crop rotation experiment was initiated in 1987 on a medium-textured, Orthic Brown Chernozem at Swift Current, Saskatchewan, to determine the most ideal cropping frequency for wheat in this region and whether a fixed rotation such as fallow-wheat (Triticum aestivum L.) - wheat (F-W-W) or F-W-W-W would be more effective than flexible rotations in which fallowing is decided each spring based on criteria such as available soil water (if water), or the need to control perennial weed infestations (if weeds). The study also compared the production of traditional Canada Western Red Spring (CWRS) wheat class with the newer higher-yielding (Hy), Canada Prairie Spring (CPS) wheat class. We analyzed results of six rotations over the first 12 yr of the study. The rotations included F-W-W, F-W-W-W, F-Hy-Hy, Continuous wheat (Cont W), Cont W (if weeds), and Cont W (if water). Reduced tillage management was used and stubble was cut tall to enhance snowtrap. Fertilizer N was applied based on soil tests and fertilizer P was applied based on the general recommendations for the region. Over the 1988–1999 period, weather conditions were generally favourable and yields were above average for this region. Canada Prairie Spring wheat outyielded CWRS by 32% when grown on fallow and by 17% when grown on stubble; however, straw yields of the two wheat classes were similar on fallow and CPS was 11% less than CWRS on stubble. Harvest index (HI) averaged 44% for CPS and 37% for CWRS wheat. Water use efficiency for CWRS wheat grown on fallow averaged 7.2 kg ha-1 mm-1 and for CPS 9.4; when grown on stubble the respective values were 6.3 and 7.5 kg ha-1 mm-1. Grain N concentration for CWRS was slightly higher for wheat grown on fallow (25.7 g kg-1) than on stubble (24.5 g kg-1), but was similar for CPS wheat on grown on fallow and stubble (21.9 g kg-1). Straw N concentration averaged 3.8 g kg-1 for CWRS and 4.4 g kg-1 for CPS. Nitrogen yield for grain from CPS was 9% greater than from CWRS when grown on fallow, but there was no effect of wheat class when grown on stubble. Nitrogen yield of CPS straw was 15% greater than for CWRS when grown on fallow, but on stubble N yield was generally not affected by wheat class. Nitrogen harvest index (NHI) averaged about 80% for both wheat classes, whether grown on fallow or stubble. On a rotation basis, grain produced with F-W-W was 1502 kg ha-1 yr-1. The F-W-W-W and Cont W (if weeds) rotations produced 9% more grain than F-W-W, while Cont W (if water) produced 24% more, F-Hy-Hy produced 26% more, and Cont W produced 30% more than F-W-W. Nitrogen production in the grain, straw and aboveground plant material was lowest in F-W-W, highest in Cont W, and intermediate for other rotations. Although the economic and soil quality assessments have yet to be completed, a preliminary conclusion based on crop production characteristics alone suggests that a flexible cropping system in which available soil water in spring is used as the determining criterion is superior to a fixed F-W-W or F-W-W-W rotation. Key words: Yield, N concentration, N yield, water deficit, wheat classes, regressions

Optimum plant population density for chickpea and dry pea in a semiarid environment

Chickpea (Cicer arietinum L.), an annual grain legume, is being broadly included in cereal-based cropping systems throughout the semiarid Canadian prairies, but information on optimum plant population density (PPD) has not been developed for this region. This study, which was conducted from 1998 to 2000 in southwestern Saskatchewan, determined the effect of PPD on field emergence, seed yield and quality, and harvestability of kabuli and desi chickpea compared with dry pea (Pisum sativum L.). Seed yields of all legumes increased with increasing PPD when the crops were grown on conventional summerfallow. The PPD that produced the highest seed yields ranged from 40 to 45 plants m-2 for kabuli chickpea, from 45 to 50 plants m-2 for desi chickpea, and from 75 to 80 plants m-2 for dry pea. When the legumes were grown on wheat stubble, the PPD that gained optimum seed yield ranged from 35 to 40 plants m-2 for kabuli chickpea, from 40 to 45 plants m-2 for desi chickpea, and from 65 to 70 plants m-2 for dry pea. The proportion of large-sized (>9-mm diameter) seed in the harvested seed was >70% when the kabuli chickpea was grown on summerfallow regardless of PPD, whereas the large-seed proportion decreased with increasing PPD when the crop was grown on wheat stubble. Increases in PPD advanced plant maturity by 1.5 to 3.0 d and increased the height of the lowest pods from the soil surface by 1.4 to 2.0 cm (or 5 to 10%), with desi chickpea receiving the greatest benefits from increased PPD. The percentage of plants established from viable seeds per unit area decreased substantially as PPD increased, with kabuli chickpea emergence decreasing from 90% at PPD = 20 plants m-2 to 72% at PPD = 50 plants m-2, from 81 to 69% for desi type, and from 83 to 59% for dry pea . The reason for the low field emergence with increased PPD is unknown, but methods which lead to improved field emergence represent a great opportunity to increase seed yield and reduce production costs for both chickpea and dry pea in this semiarid region. Key words: seed size, Cicer arietinum, Pisum sativum, seeding rate, summerfallow

Yield and water use efficiency of pulses seeded directly into standing stubble in the semiarid Canadian Prairie

In semiarid climates, appropriate management of the previous crop stubble in combination with seeding method is important to improve growing conditions for the subsequent crop. To determine the effects of standing stubble of various heights on the microclimate and on the growth and yield of pulse crops, we seeded desi chickpea (Cicer arietinum L. “Cheston”), field pea (Pisum sativum L. “Grande”), and lentil (Lens culinaris L. “Laird”) directly into cultivated, short (15 to 18 cm), and tall (25 to 36 cm) spring wheat (Triticum aestivum L.) stubble. Standing stubble changed the microclimate near the soil surface by reducing soil temperatures, solar radiation, wind speed, and potential evapotranspiration throughout the life cycle of these crops. Microclimate effects were much more pronounced for tall versus short stubble. The three pulses responded similarly to increasing stubble height. Vine length increased as stubble height increased, but the plants did not stand more erect. However, there was a tendency for plant height to increase as stubble height increased. Tall and short stubble increased the overall average grain yield by 13 and 4% compared to cultivated stubble. Crop water use was not affected by stubble height so the increased grain production was due to increased water use efficiency. Tall and short stubble increased the overall average water use efficiency by 16 and 8% compared to cultivated stubble. Key words: Stubble height, pulse, microclimate, evapotranspiration, yield

In Search of a Sustainable Cropping System for the Semiarid Canadian Prairies

ABSTRACT Producers in the semiarid Canadian prairies have begun to extend and diversify their cropping systems. These newer cropping systems are often considered to be more sustainable. We examine the agronomic, environmental, and economic effects of reducing summerfallow use and including grain lentil (Lens culinaris Medikus) in rotation with spring wheat (Triticum aestivum L.). Data from a long-term crop rotation experiment conducted on a medium texture soil at Swift Current, Saskatchewan were analyzed. Four cropping systems were evaluated over the 1979 to 1997 period; namely, fallow-wheat (F-W), fallow-wheat-wheat (F-W-W), continuous wheat (W), and wheat-lentil (W-L). Nitrate leaching below the 120 cm rooting depth of wheat was lower under continuously cropped systems than under fallow-based rotations, and was lowest overall for W-L. Wheat, whether grown on fallow or stubble, used almost all of the available water in the 0–120 cm depth soil profile, but lentil extracted about 1.5 cm less water than wheat. On average, wheat yield was unaffected by inclusion of lentil in the rotation; however, grain protein content was higher in 11 of 18 years. The incidence of leaf spotting diseases in wheat was lowest for wheat grown after lentil and highest for wheat grown on fallow. Soil quality (soil organic carbon, mineralizable N and C, light fraction organic C, and water stable aggregates) increased with cropping intensity in the order of W-L ≥ W > F-W-W > F-W. Although inputs of non-renewable energy and CO2 emissions were higher for the continuous compared to fallow-based rotations, including lentil in the rotation lowered the energy requirements for N fertilizer and provided an overall 19% reduction in CO2 emissions. The economics favored the W-L system whenever lentil price was above $350 t−1. The level of financial risk was lowest for F-W and F-W-W, intermediate for W-L, and highest for W. Our findings confirm the recent changes in land use practices being adopted by producers, and clearly show that extending and diversifying crop rotations by reducing fallow and including pulse crops in the rotation will improve the overall sustainability of agricultural production in this semiarid region.

Monitoring the hydrology of Canadian prairie wetlands to detect the effects of climate change and land use changes.

There are millions of small isolated wetlands in the semi-arid Canadian prairies. These sloughs' are refuges for wildlife in an area that is otherwise intensively used for agriculture. They are particularly important as waterfowl habitat, with more than half of all North American ducks nesting in prairie sloughs. The water levels and ecology of the wetlands are sensitive to atmospheric change and to changes of agricultural practices in the surrounding fields. Monitoring of the hydrological conditions of the wetlands across the region is vital for detecting long-term trends and for studying the processes that control the water balance of the wetlands. Such monitoring therefore requires extensive regional-scale data complemented by intensive measurements at a few locations. At present, wetlands are being enumerated across the region once each year and year-round monitoring is being carried out at a few locations. The regional-scale data can be statistically related to regional climate data, but such analyses cast little light on the hydrological processes and have limited predictive value when climate and land use are changing. The intensive monitoring network has provided important insights but it now needs to be expanded and revised to meet new questions concerning the effects of climate change and land use.

Tillage Effects on Carbon Fluxes in Continuous Wheat and Fallow–Wheat Rotations

The traditional cropping system in semiarid regions of the Canadian prairies involves frequent summer fallowing with several tillage operations to control weeds during the fallow period. Recently, there has been a trend toward reduced tillage and more intensive cropping, but the impact of this shift in management on sequestration of atmospheric CO2 remains uncertain. In 1995 and 1996, we measured fluxes of CO2 in a tillage experiment that had been initiated in 1982 on a silt loam (Typic Haploboroll) in southwestern Saskatchewan. The experiment comprised two spring wheat (Triticum aestivum L.) rotations (continuous wheat [Cont. W] and fallow–wheat [F–W]), each with conventional tillage (CT) and no‐till (NT) treatments. In Cont. W, CO2 fluxes tended to be lower under NT than under CT (mean annual flux was ≈20 to 25% less for NT than CT). In F–W, tillage effects on mean annual CO2 flux were significant (P < 0.05) in the wheat phase only (NT ≈ 10% less than CT). Tillage had negligible effect on C inputs in crop residues. Lower CO2 fluxes under NT than under CT were attributed to slower decomposition of crop residues placed on the surface of NT soil than when they were incorporated. With good growing conditions (and thus large inputs of residues) between 1989 and 1996, there was an accumulation of partially decomposed residues on the surface of NT soil. Carbon in surface residues represented about one‐half of the C gained by NT soil. In Cont. W, surface residue C (in 1996) amounted to 3.6 t ha−1 under NT vs 1.4 t ha−1 under CT. Residue C amounts were smaller in the F–W system: 1.7 t ha−1 (NT) and 0.7 t ha−1 (CT). Based on our results, producers on medium‐textured soils in the semiarid Canadian prairies who switch from the traditional wheat production system (conventionally tilled fallow–wheat) to continuous no‐till cropping could, potentially, sequester 5 to 6 t C ha−1 in soil organic matter and surface residues in 13 to 14 yr.

Phenotypic diversity in four woody species on the Canadian prairies

Genetic diversity is a prerequisite for plant adaptation and maintenance of a sustainable ecosystem. Not much information is available on the genetic diversity of woody species on the semi-arid Canadian prairies. We used RAPD fragments to assess the diversity of four woody species of the Elaeagnaceae family, sea buckthorn (Hippophae rhamnoides L.), Russian olive (Elaeagnus angustifolia L.), buffaloberry (Shepherdia argentea Nutt.) and silverberry (Elaeagnus commutata Bernh. Ex Rydb.) collected from several locations in southwestern Saskatchewan. The RAPD fragments were used to generate molecular data for this experiment. Of the total scorable RAPD fragments, 86, 80, 55.2, and 36.5% were polymorphic in sea buckthorn, buffaloberry, silverberry and Russian olive, respectively. Estimates of phenotypic diversity by AMOVA and Shanon's information index revealed that buffaloberry and sea buckthorn had relatively high phenotypic diversity and Russian olive had low phenotypic diversity. Key words: Sea buckthorn, silverberry, buffaloberry, Russian olive, RAPD, phenotypic diversity, Hippophae, Elaeagnus, Shepherdia

Herbicide Transport on Wind‐Eroded Sediment

AbstractAlthough wind erosion is a pervasive soil degradation problem on the semiarid Canadian prairies, few studies have been conducted on wind‐eroded sediment as an environmental pathway for herbicide transport. An experiment was conducted on a clay loam soil at Lethbridge, AB, in 1993 to 1994, to examine wind‐eroded sediment as a transport mechanism for two soil‐incorporated [trifluralin (2,6‐dinitro‐N,N‐dipropyl‐4‐trifluoromethylaniline) and triallate (S‐2,3,3‐trichloroallyl diisopropylthiocarbamate)] and four surface‐applied herbicides [diclofop {(±)‐2‐[4‐(2,4‐dichlorophenoxy)phenoxy]propanoic acid), bromoxynil (3,5‐dibromo‐4‐hydroxybenzonitrile), mecoprop {(±)‐2‐(4‐chloro‐2‐methylphenoxy)propanoic acid}, and 2,4‐D (2,4‐dichlorophenoxyacetic acid)]. The concentrations of diclofop and bromoxynil in sediments decreased with increasing capture height, with the 100‐cm height having significantly lower concentrations (diclofop, 627 µg kg−1; bromoxynil, 70 µg kg−1) than the 10‐cm height (diclofop, 1132 µg kg−1; bromoxynil, 231 µg kg−1). This implies that these herbicides were primarily associated with larger soil particles captured closer to the soil surface. For the soil‐incorporated herbicides, concentrations were significantly higher in the surface soil (0–2.5 cm) than in the wind‐eroded sediment, whereas concentrations of surface‐applied herbicides were generally higher in wind‐eroded sediment than in surface soil. Overall wind erosion losses (expressed as a percent of amount applied) of the two soil‐incorporated herbicides (1.5%) were about three times lower than those of the four surface‐applied herbicides (average loss, 4.5%). The results demonstrate the potential hazard of environmental transport of herbicides on wind‐eroded sediment and its associated implications for off‐site air and water quality.

Distribution and forms of P under cultivator- and zero-tillage for continuous- and fallow-wheat cropping systems in the semi-arid Canadian prairies

Conservation tillage may affect the dynamics of nutrient transformations in the soil. We assessed the effect of fallow-wheat, and continuous wheat under zero-tillage and cultivator-tillage management on phosphorus concentration in the grain (GPC), phosphorus uptake in the grain, NaHCO 3 extractable-P (Olsen-P) and on forms and distribution of P in the surface 10 cm of the soil for a 12-year tillage field experiment established on an Orthic Brown Chernozemic soil (Aridic Haploboroll) in southwestern Saskatchewan, Canada. Grain yield was the main factor affecting GPC, with the lower-yielding continuous-wheat system having the highest GPC, most likely resulting from luxury uptake of P. Phosphorus taken in the grain, however, was directly proportional to grain yield. Olsen-P in the soil was highly variable from year to year, and was not affected by tillage or rotation. From 1982 to 1989, when P removed in the grain was less than P applied as fertilizer, Olsen-P in spring samples increased, on average, by 0.9 mg kg −1 year −1 in the fallow-wheat and by 1.4 mg kg −1 year −1 in the continuous-wheat cropping systems. From 1990 to 1994, when grain yields increased due to more favourable moisture conditions, crop removal of P exceeded P fertilization, and Olsen-P concentration remained relatively stable. Converting the original cultivator tilled fallow-wheat system to zero-tilled continuous wheat produced a significant increase in total soil P as a result of increased accumulation of labile and moderately labile forms of P in the surface 6 cm of the soil, especially in organic forms. When either zero-tillage or continuous-wheat were adopted by themselves, there were no changes in the amounts of P in the different pools. The proportion of organic P in the labile and moderately labile pools in the surface 6 cm of soil, however, increased significantly with respect to the cultivator tilled fallow-wheat control. This reflected increased levels of crop residues returned to the soil in the continuous-wheat cropping system and reduced rates of residue decomposition in the zero-tillage system. The increase in labile forms of P near the surface in zero-tilled soils may have substantial impact on soil sampling for prediction of P fertilizer requirements, and on surface water quality in reduced tillage systems.

Effects of tillage method and fallow frequency on leaf spotting diseases of spring wheat in the semiarid Canadian prairies

Leaf spotting diseases of wheat ( Triticum spp.) are widespread in western Canada. Because these diseases are residue-borne, they are expected to be affected by changes in the quality and quantity of crop residues. A field study was conducted to determine the effects of summerfallow and tillage practices on leaf spotting diseases of spring wheat ( T. aestivum L.) in the semiarid area of the western Canadian prairies. Leaf spot severity was greater in wheat grown after fallow than in continuous wheat when these systems were managed using either cultivator- or zero-tillage methods. Disease severity in wheat after fallow was similar in all three tillage methods: cultivator-, reduced-, and zero-tillage. Pyrenophora tritici-repentis (Died.) Drechs. (tan spot) was the pathogen most commonly isolated from lesioned leaf tissue. Crop residues collected in the spring of 1995 and 1996 from cultivator- and zero-tillage treatments were examined for the presence and density of fungal infective structures. The density of mature and immature structures, especially of P. tritici-repentis, was greater in residues from two years previous than in those from the previous growing season. Most of the residues in the continuous wheat system were from the previous crop. The apparent lower amount of initial inoculum available in a continuous wheat system than in wheat grown after fallow would explain the higher leaf spotting severity in the latter system. In addition, lower levels of infective structures on residues were found in wheat after fallow in zero- rather than in cultivator-tillage. However, similar disease levels in cultivator- and zero-tillage treatments suggest that the more favourable microclimate for disease development in a zero-tillage system might have compensated for the lower amounts of residue-borne inoculum.

Vadose Zone Flow and Transport in Cracked Heavy Textured Soil

Investigated were physical processes governing vadose zone water flow and solute transport in a heavy-textured crack-prone soil of the semiarid Canadian Prairies. Soil moisture, soil temperature, and relevant meteorological observations were recorded over a period of about two years. Environmental chloride and tritium concentrations in the soil water were determined. Analysis of the data indicates that during snow melt, water and solutes are flushed down rapidly via cracks and fissures in the root zone. The soil at these depths is still frozen during snow melt. In late spring after the entire soil profile thaws, water and solutes move downward by a diffusion dominant advective-diffusive flow mechanism. The chloride and tritium profiles obtained within the vadose zone support this argument. This conceptual model of the flow and transport processes is supported by calculations of advective and diffusive soil water flux from chloride profiles. Simulation of the tritium profile using a simple analytical model also gives very good agreement with measured data.

Management practices for black lentil green manure for the semi-arid Canadian prairies

Previous research with lentil (Lens culinaris Medic.) green manure in the semiarid prairies of western Canada has indicated that water use by the green manure crop often reduces grain yield of the succeeding cereal crop compared to those obtained after conventional summerfallow. In this study, we evaluated several green manure management practices that have potential to trap snow and enhance overwinter soil water recharge. These practices included: using herbicides to halt the growth of the green manure crop thus eliminating the need for soil incorporation, planting mustard (Sinapis alba L.) strips after incorporation, and leaving standing strips of non-incorporated lentil. Our results showed that none of the green manure management strategies increased wheat (Triticum aestivum L.) yield or grain protein concentration compared to wheat grown on conventional summerfallow. Leaving strips of standing lentil during bud stage incorporation provided barriers for wind erosion protection, while not decreasing wheat yield or protein content. Glyphosate or 2,4-D amine applied at bud stage of the lentil, and without soil incorporation, reduced available soil N. However, 2,4-D did not halt plant growth and water use quickly enough to avoid reducing yield of the succeeding wheat crop, while glyphosate generally halted water use more rapidly. The inability of the green manure management strategies to increase wheat yields over that obtained from conventional summerfallow was because the soil rooting zone is typically filled to capacity with water by this latter practice under the prevailing soil and climatic conditions. If green manuring is practised, early incorporation with lentil leave strips is the most promising management system. However, even with improved water management practices, green manuring did not demonstrate a consistent advantage over summerfallow, which may be required to offset the added economic costs required to enact this practice. Key words: Lens culinaris, legumes, summerfallow, soil nitrogen, soil water, wheat

Tillage and summerfallow effects on leaf spot diseases of wheat in the semiarid Canadian Prairies

Tillage and summerfallow effects on leaf spot diseases of wheat in the semiarid Canadian Prairies

Soil quality attributes as influenced by annual legumes used as green manure

Tilled fallow-wheat ( Triticum aestivum L.) (F-W) is the most commonly used cropping system in the semiarid Canadian prairie. However, because F-W degrades soil, a partial fallow annual legume green manure (GM)-wheat system has been proposed as a viable alternative. We conducted a 6 yr study to assess the influence of four GM-W systems, compared to F-W and continuous wheat (Cont. W), on some soil quality attributes, in a medium-textured, Aridic Haploboroll at Swift Current, Saskatchewan, Canada. The four GM legumes used were black lentil ( Lens culinaris Medikus), Tangier flatpea ( Lathyrus tingitanus L.), chickling vetch ( Lathyrus sativus L.) and feedpea ( Pisum sativum L.). Analysis of soil taken from the 0–10 cm depth after growing wheat in the sixth year, showed that most of the soil biochemical and physical attributes assessed were significantly improved (compared to F-W) by increasing cropping intensity, and by using the GM systems. A sensitivity analysis (ratio of other treatment values to value for F-W) showed that Cont. W and the GM-W systems increased most of the soil quality attributes tested. Among the GM systems the lentil-W generally increased sensitivity the most, while feedpea-W usually increased it the least. The labile attributes were more sensitive indicators of changes in soil quality than total organic C or N. The sensitivity of the attributes decreased in the sequence: Initial potential rate of N mineralization>C mineralization>wet aggregate stability>light fraction of soil organic matter>total organic C or N. Although the amount of crop residue returned to the soil is known to have an important influence on soil quality, we were not able to demonstrate this in this short-term study.

Restoration of Productivity to a Desurfaced Soil with Livestock Manure, Crop Residue, and Fertilizer Amendments

AbstractMany agricultural fields on the semiarid Canadian prairies have areas of inherently low productivity associated with loss of soil quality due to erosion. This study compared the efficacy of various amendments in restoring productivity to a desurfaced fine‐loamy, mixed Typic Haploboroll (Lethbridge series) in southern Alberta. In spring 1992, 14 amendment treatments (including livestock manures, crop residues, combinations of straw and chemical fertilizer, and fertilizer alone) were applied to a site where the Ap horizon (≈ 15‐cm depth) had been mechanically removed to simulate erosion. The manures and crop materials were incorporated into the degraded surface on an equivalent dry‐weight basis at 20 Mg ha−1. The plots were seeded to spring wheat (Triticum aestivum L.) in 1992, 1993, and 1994. The overall best amendments were hog manure, poultry manure, and alfalfa hay. In all years, yields from desurfaced plots amended with hog or poultry manure were not significantly different from plots with no topsoil removal. Nitrate‐N concentration in the 0‐ to 60‐cm soil depth explained 71% of the variation in restorative ability of the amendments, while extractable P concentrations in the 0‐ to 15‐cm depth explained 16% of this variation. Results demonstrate that livestock manures and crop residues can restore productivity to eroded soils by substituting for lost topsoil. Application of high rates of manure to severely eroded soils offers a means of utilizing the large amounts of manure generated by southern Alberta feedlot operations.