Subsequent Wheat Yield Research Articles

Alternative cereal crop rotations in a no‐tillage dryland under Mediterranean conditions

AbstractCereal crops are frequently rotated with broadleaf crops to achieve the benefits associated with crop diversification. However, broadleaf crops often fail in Mediterranean drylands due to their lower adaptation to drought. Alternative cereal crops such as triticale (×Triticosecale Wittmack) and oat (Avena sativa L.) can help diversify drylands in the Ebro valley, dominated by barley (Hordeum vulgare L.) and wheat (Triticum aestivum L.) cultivation. A 6‐year field experiment was conducted with five crop sequences under no‐tillage: triticale–wheat–barley (TWB), oat–wheat–barley (OWB), fallow–wheat–barley, monocrop wheat, and monocrop barley. Wheat and barley grain yield, N use efficiency, and water use efficiency responses were evaluated, and economic analyses of the whole sequences were performed. Oat increased subsequent wheat yields by 15% and barley yields by 12% (p < 0.001) compared to monocropping. Similar water and N availability at sowing suggest additional synergies in an OWB rotation (possibly pest reduction), contributing to the yield increase of both crops. However, this rotation was less profitable than a TWB rotation (p = 0.002) due to the limited adaptation of oat to Mediterranean settings. Long fallowing lacked consistent benefits in water and N availability for subsequent crops. This practice protects farmers from economic losses in low‐yielding seasons, but there is an associated opportunity cost in favorable years. The introduction of alternative cereal crops has demonstrated benefits for wheat and barley production, although greater understanding of the synergistic mechanisms involved is essential to ascertain whether resource efficiency is maintained beyond the studied timeframe.

Legume-based rotation enhances subsequent wheat yield and maintains soil carbon storage

Legume-based rotation enhances subsequent wheat yield and maintains soil carbon storage

Peanut-based Rotation Stabilized Diazotrophic Communities and Increased Subsequent Wheat Yield.

The introduction of legumes into rotations can improve nitrogen use efficiency and crop yield; however, its microbial mechanism involved remains unclear. This study aimed to explore the temporal impact of peanut introduction on microorganisms related to nitrogen metabolism in rotation systems. In this study, the dynamics of diazotrophic communities in two crop seasons and wheat yields of two rotation systems: winter wheat - summer maize (WM) and spring peanut → winter wheat - summer maize (PWM) in the North China Plain were investigated. Our results showed that peanut introduction increased wheat yield and biomass by 11.6% (p < 0.05) and 8.9%, respectively. Lower Chao1 and Shannon indexes of the diazotrophic communities were detected in soils that sampling in June compared with those sampling in September, although no difference was found between WM and PWM. Principal co-ordinates analysis (PCoA) showed that rotation system significantly changed the diazotrophic community structures (PERMANOVA; p < 0.05). Compared with WM, the genera of Azotobacter, Skermanella, Azohydromonas, Rhodomicrobium, Azospirillum, Unclassified_f_Opitutaceae, and Unclassified_f_Rhodospirillaceae were significantly enriched (p < 0.05) in PWM. Furthermore, rotation system and sampling time significantly influenced soil properties, which significantly correlated with the top 15 genera in relative abundance. Partial least squares path modeling (PLS-PM) analysis further showed that the diazotrophic community diversity (alpha- and beta-diversity) and soil properties (pH, SOC and TN) significantly affected wheat yield. In conclusion, legume inclusion has the potential to stabilize diazotrophic community structure at the temporal scales and increase subsequent crop yield.

Intensifying dryland wheat systems by integrating guar increased production and profitability

Guar [Cyamopsis tetragonoloba (L.) Taub.], is a summer legume with heat- and drought-tolerance properties that is produced in the U.S. Southern Great Plains, but is often restricted to a catch crop or substitute crop following cotton failures. This is despite the large domestic market for guar gum and the opportunity to diversify regional cropping systems with guar, potentially adding ecosystem benefits like biological N fixation (BNF). To address this, a systems research study was conducted near Chillicothe, TX from 2018 to 2021 to evaluate the integration of guar into no-till dryland winter wheat (Triticum aestivum L.) systems. Treatments included integrated wheat-guar systems differing in cropping intensity, 1.33 crops yr−1 (WG1.3) and 2 crops yr−1 (WG2), plus guar (G1) and wheat (W1) monocrop systems with 1.0 crop yr−1. Results showed that crop rotation sequence influenced seasonal guar yields, with negative yield impacts when guar immediately followed wheat. Consequently, the average seasonal guar yield was greatest in G1 and WG1.3 (1.01 and 0.96 Mg ha−1, respectively), followed by WG2 (0.64 Mg ha−1). Seasonal wheat yield averaged 2.31 Mg ha−1 across years, with no differences among systems. Across years, cumulative system yield was greatest for WG2, followed by W1 and WG1.3, then G1. Similarly, average annual net income followed the trend of G1 < W1 < WG1.3 < WG2, with values ranging from US$ 62.7–213.0 ha−1 year−1. Although overall production and net income were somewhat greater for WG2 than WG1.3, seasonal risks of crop failure and economic loss were lower for the WG1.3 system under the regional climate. There was no direct evidence of guar BNF benefits on subsequent wheat yield and quality, though inclusion of guar enhanced soil NO3-N at varying levels among systems, particularly following wet growing seasons and in less intensive systems.

Soybean Crops Penalize Subsequent Wheat Yield During Drought in the North China Plain.

Contemporary wisdom suggests that inclusion of legumes into crop rotations benefit subsequent cereal crop yields. To investigate whether this maxim was generically scalable, we contrast summer soybean–winter wheat (SW) with summer maize–winter wheat (MW) rotation systems in an extensive field campaign in the North China Plain (NCP). We identify heretofore unseen interactions between crop rotation, synthetic N fertilizer application, and stored soil water. In the year with typical rainfall, inclusion of soybean within rotation had no effect on wheat ear number and yield, while N fertilization penalized wheat yields by 6–8%, mainly due to lower dry matter accumulation after anthesis. In contrast, in dry years prior crops of soybean reduced the rate and number of effective ears in wheat by 5–27 and 14–17%, respectively, leading to 7–23% reduction in wheat yield. Although N fertilization increased the stem number before anthesis in dry years, there was no corresponding increase in ear number and yield of wheat in such years, indicating compensating reduction in yield components. We also showed that N fertilization increased wheat yield in MW rather than SW as the former better facilitated higher dry matter accumulation after flowering in dry years. Taken together, our results suggest that soybean inclusion reduced soil available water for subsequent wheat growth, causing yield penalty of subsequent wheat under drought conditions. We call for more research into factors influencing crop soil water, including initial state, crop water requirement, and seasonal climate forecasts, when considering legumes into rotation systems. Graphical Response of wheat population and yield to soybean inclusion under limited-irrigation.

Replacing fallow with warm‐season annual crops in dryland wheat systems

AbstractRotating wheat (Triticum spp.) with fallow is a popular practice in the North American Great Plains, in spite of environmental degradation and economic inefficiencies. Two‐year crop sequences were established in four fields in central Montana to determine if grain yield could be maintained when wheat followed warm‐season annual crops compared with fallow in shallow (soil depth ≤650 mm) dryland soils. More than 15 warm‐season species along with three crop mixtures were managed as cover, forage, and grain or seed crops in the 1st year. Differences were not detected in volumetric soil water content (VWC) following fallow and warm‐season crops (P &gt; .8). Wheat yield following fallow averaged 2.1 Mg ha–1 and was comparable following warm‐season broadleaf crops and grass‐broadleaf crop mixtures (2.0 Mg ha–1, P &gt; .50), while trending downward slightly following grasses (1.9 Mg ha–1, P = .08). Previous crop management (cover, forage, and grain or seed crop) did not affect subsequent wheat yield (P = .98), but did affect wheat grain protein (P &lt; .01). Wheat grain protein concentration was higher following fallow (124 g kg–1) than warm‐season grass and broadleaf crops, as well as mixtures (116 g kg–1), but was below the 132 g kg–1 threshold indicating N deficiency, regardless of previous‐year treatment. These results indicate that grain yield of wheat can be maintained following warm‐season annual crops compared with fallow in central Montana and similar semi‐arid environments with shallow soils, though soil N supplementation is needed to optimize grain yield and quality.

Nitrogen-15 labelling and tracing techniques reveal cover crops transfer more fertilizer N to the soil reserve than to the subsequent crop

Estimating the capacity of cover crops (CC) to capture soil nitrogen (N) and to transfer captured N to subsequent crop remains a challenge because CC biomass production, N content and decomposition rate vary depending on environmental conditions and management practices. The objectives of this study were (1) to compare biomass production and N accumulation by a mixture of red and white clovers intercropped with barley, and oat, field pea and oilseed radish grown as catch crops after barley harvest, (2) to determine the capacity of different CCs to catch and transfer fertilizer N (mineral or pig slurry) to subsequent wheat and the soil reserve, and (3) to determine the influence of CC type on yield of spring wheat in the next year. A 2-y crop rotation (barley – wheat) was repeated twice on a sandy loam using 15N-labelled fertilizers applied at the time of CC establishment. Fertilization increased above-ground biomass yield in oat and oilseed radish, but had little effect on legume CCs. The legume CCs accumulated more total N in their biomass (63–127 kg N ha−1) than non-legume CCs (47–68 kg N ha−1). However, oat and oilseed radish were more efficient at capturing the applied fertilizer 15N (33–51 %) than legume CCs (2–36 %). Intercropped clovers resulted in the largest increases in subsequent wheat yields (23–92 %), followed by oilseed radish and field pea. At the end of the 2-y rotation (wheat harvest), the recovery of fertilizer 15N by subsequent wheat was < 10 %, whereas 26–60 % were still present in the 0−30 cm soil layer. We conclude that non-legume CCs have a good capacity to capture applied fertilizer N, whereas legume CCs (especially clovers) had a limited capacity. Nevertheless, clovers CC resulted in the greatest wheat yields in the following year, likely due to efficent transfer of symbiotically fixed N and improved soil quality, whereas fertilizer N captured by non-legume CCs was mainly routed to the soil N reserve, with potential to supply N to subsequent crops through a legacy effect.

Interseeding Camelina and Rye in Soybean with Varying Maturity Provides Soil Cover without Affecting Soybean Yield

Low adoption to utilize cover crops interseeded into soybean (Glycine max (L.) Merr.), in the northern Plains in the USA, is due to a short growing season and a few adapted winter-hardy species. The objective was to evaluate the impact of interseeded winter camelina (Camelina sativa (L.) Crantz) and winter rye (Secale cereale L.) using different soybean relative maturities on soybean yield, canopy coverage, spring cover crop biomass, and subsequent wheat (Triticum aestivum L.) yield. Cover crops interseeded into early-maturing (0.4–0.8) soybean cultivars had more fall coverage compared with the 0.9 maturity cultivar, but the spring biomass was similar for all maturities. The soybean yield of the 0.9 cultivar was significantly higher, 2365 kg ha−1 compared with 2037 kg ha−1 for the 0.4 cultivar. Rye outperformed winter camelina and had higher fall canopy cover (15 vs. 7%), spring canopy cover (16% vs. 4%), and higher spring biomass (313 vs. 100 kg ha−1 dry matter). Spring wheat, after rye, yielded 90% of the check. It is not recommended to plant spring wheat following winter rye, but there was no negative yield effect from winter camelina. Interseeding cover crops into soybean in the northern Plains is possible but needs further research to optimize interseeding systems.

Pea and Barley Forage as Fallow Replacement for Dryland Wheat Production

Core Ideas Forage yields from pea, especially winter pea, were competitive with hay barley yields.Crude protein yield from pea forage was 40 to 110% greater than barley.Crop harvest at the bloom stage used the least soil water and nitrogen.Wheat yield following pea averaged 82 to 88% of that on chemical fallow. There is a growing interest in the use of annual forages in rotation with wheat (Triticum aestivum L.). The objectives of this study were to: (i) compare forage yield and quality of spring and winter pea (Pisum sativum L.), barley (Hordeum vulgare L.), and a pea–barley mixture harvested at flowering (early), pod (late), or grown to maturity; and (ii) compare the cropping‐sequence effects of these cropping treatments for three N fertilizer rates, subsequent wheat yield, and grain quality relative to chemical fallow. This study was conducted at Amsterdam, MT, from 2003 to 2006. Pea forage yield at the pod stage was 1.2 Mg ha−1 (30%) and 3.7 Mg ha−1 (60%) greater than at the flower stage for spring and winter pea, respectively. At the same harvest times, spring barley forage averaged 1.8 Mg ha−1 (32%) greater either as a sole species or when mixed with spring pea. Forage quality of pea forage was high regardless of harvest timing. Protein yield for spring and winter pea forage averaged 0.28 (60%) and 0.38 Mg ha−1 (81%) greater than the barley forage treatments across harvest times and years. Significant differences in stored soil water (19 mm) and soil nitrate N (10 kg N ha−1) were found between flowering and pod forage harvest timing in pea, but these differences only nominally affected subsequent wheat yield or quality. Wheat following pea averaged approximately 85% of the yield on chemical fallow. Among the cropping treatments, the greatest wheat yield and protein occurred following winter pea harvested at the flower stage.

Canola versus wheat rotation effects on subsequent wheat yield

Winter canola (Brassica napus L.) (WC) is considered the most promising oilseed crop for diversifying wheat (Triticum aestivum L.)-based cropping systems in the Inland Pacific Northwest, USA (PNW). Canola serves as a break or non-host crop for many important soilborne pathogens of wheat and helps farmers control weeds. Most studies in the literature report that canola has a positive effective on subsequent wheat yield. We conducted a 6-yr field experiment near Davenport, WA to measure the effects of WC versus winter wheat (WW) on the subsequent production of spring wheat (SW). Averaged over the years, there were no differences between WC and WW in soil water use or overwinter water recharge into the soil following these crops. Subsequent SW had excellent plant stands, was weed free, was adequately fertilized, and had no foliar or root diseases. Root lesion nematode populations were miniscule and insignificant. Average SW seed yield following WC was 3292 kg/ha versus 3897 kg/ha following WW; a 17% reduction (p < 0.0001). Visual differences in SW plant height and spike density between treatments were also apparent. Spring wheat grain yield differences could not be attributed to the variables measured. This study provides novel information for ongoing efforts to promote and expand canola production and the influence of brassica crops on the subsequent performance of wheat.

Hemp Yields and Its Rotation Effects on Wheat under Rainfed Mediterranean Conditions

Core Ideas Rainfed Mediterranean environments might be suitable for double‐purpose hemp production. Hemp is a good predecessor for wheat under rainfed Mediterranean conditions. The beneficial effects of hemp on the subsequent wheat yield appear to last for 2 yr. Monocropping hemp over 2 yr, does not reduce its grain and biomass yields. Hemp (Cannabis sativa L.) has a low impact on the environment requiring few added resources, and has multiple downstream applications. There is little information on hemp biomass, seed yields, and response to NPK fertilization under humid rainfed Mediterranean conditions. Moreover, the effects of hemp on subsequent wheat (Triticum aestivum L.) crops have not been determined. To address these issues, we performed a field study for 6 yr in Catalonia (northeastern Spain). Hemp treatments included: hemp monoculture, unfertilized hemp succeeding wheat, and NPK‐fertilized hemp succeeding wheat. In turn, wheat treatments included: wheat monoculture, first‐, second‐, and third‐year wheat succeeding unfertilized hemp, and first‐, second‐, and third‐year wheat succeeding NPK‐fertilized hemp. The hemp biomass yields (5340–10,090 kg ha−1) were similar to or lower than those achieved in other European regions whereas the hemp seed yields were relatively high (604–1434 kg ha−1). Both the biomass yield and seed yield greatly increased with NPK fertilization. The rotation effects of hemp on the subsequent wheat crops increased the wheat yield by 1368 and 155 kg ha−1 in the first and second years, respectively, but in the third year the yield was similar to the wheat monoculture. The beneficial effects of hemp on wheat therefore appear to last for 2 yr. We conclude that dual‐purpose hemp (harvested for fiber and seed) is an excellent predecessor for wheat, improving the sustainability of cereal‐based cropping systems under humid rainfed Mediterranean conditions.

Rotating alfalfa with dry bean as an alternative to corn-soybean rotations in organic systems in the Upper Midwest

AbstractDry bean (Phaseolus vulgaris) can be grown as a local food source and as an alternative to soybean (Glycine max) to diversify organic crop rotations. To understand the benefits of diversification of organic cropping systems, the effects of preceding alfalfa (Medicago sativa) and corn (Zea mays) crops on yields of five dry bean types and one soybean type, and the effect of bean type on following spring wheat (Triticum aestivum) yields, were tested at four Minnesota locations. Dry bean and soybean yields following alfalfa were 25% greater than yields following corn at two of four locations, though bean yields following corn were greater at one location. A preceding alfalfa crop benefited bean yields at locations where hog manure or no manure was applied to corn, whereas bean yields following corn fertilized with cow manure were similar to or greater than bean yields following alfalfa. Among dry bean types, black bean yielded similarly to soybean at three of four locations, but dark red kidney bean consistently yielded 25–65% lower than soybean. Navy, pinto and heirloom dry bean types yielded similarly to soybean at two of four locations. Across locations, weed biomass was 3–15 times greater in dry bean than in soybean and dry bean yield response to weed competition varied among bean types. However, dry bean, regardless of the preceding crop, demonstrated the potential to produce yields comparable with soybean in organic systems and the substitution of dry bean for soybean did not affect subsequent wheat yields. More studies are needed to identify nitrogen fertility dynamics in organic systems as they relate to dry bean yield.

Effect of Mineral and Bio-Nitrogen Fertilization on Maize (Zea mays L.), some Soil Properties and Subsequent Wheat (Triticum aestivum, L.) Yield

Effect of Mineral and Bio-Nitrogen Fertilization on Maize (Zea mays L.), some Soil Properties and Subsequent Wheat (Triticum aestivum, L.) Yield

Cover crops can affect subsequent wheat yield in the Central Great Plains

This research documented water use, grain yield, and water use efficiency of wheat following a 10‐species cover crop mixture and single‐species plantings (planted no‐till into proso millet residue) compared with winter wheat following a no‐till fallow period. The study was conducted under varying water availability conditions in western Nebraska and northeastern Colorado. Earn 0.5 CEUs in Soil &amp; Water Management by reading this article and taking the quiz at www.certifiedcropadviser.org/certifications/self‐study/775.

Cover Crop Effect on Subsequent Wheat Yield in the Central Great Plains

Crop production systems in the water‐limited environment of the semiarid central Great Plains may not have potential to profitably use cover crops because of lowered subsequent wheat (Triticum asestivum L.) yields following the cover crop. Mixtures have reportedly shown less yield‐reducing effects on subsequent crops than single‐species plantings. This study was conducted to determine winter wheat yields following both mixtures and single‐species plantings of spring‐planted cover crops. The study was conducted at Akron, CO, and Sidney, NE, during the 2012–2013 and 2013–2014 wheat growing seasons under both rainfed and irrigated conditions. Precipitation storage efficiency before wheat planting, wheat water use, biomass, and yield were measured and water use efficiency and harvest index were calculated for wheat following four single‐species cover crops (flax [Linum usitatissimum L.], oat [Avena sativa L.], pea [Pisum sativum ssp. arvense L. Poir], rapeseed [Brassica napus L.]), a 10‐species mixture, and a fallow treatment with proso millet (Panicum miliaceum L.) residue. There was an average 10% reduction in wheat yield following a cover crop compared with following fallow, regardless of whether the cover crop was grown in a mixture or in a single‐species planting. Yield reductions were greater under drier conditions. The slope of the wheat water use–yield relationship was not significantly different for wheat following the mixture (11.80 kg ha−1 mm−1) than for wheat following single‐species plantings (12.32–13.57 kg ha−1 mm−1). The greater expense associated with a cover crop mixture compared with a single species is not justified.

Productivity and carbon footprint of perennial grass–forage legume intercropping strategies with high or low nitrogen fertilizer input

A three-season field experiment was established and repeated twice with spring barley used as cover crop for different perennial grass-legume intercrops followed by a full year pasture cropping and winter wheat after sward incorporation. Two fertilization regimes were applied with plots fertilized with either a high or a low rate of mineral nitrogen (N) fertilizer. Life cycle assessment (LCA) was used to evaluate the carbon footprint (global warming potential) of the grassland management including measured nitrous oxide (N2O) emissions after sward incorporation.Without applying any mineral N fertilizer, the forage legume pure stand, especially red clover, was able to produce about 15tabovegrounddrymatterha−1year−1 saving around 325kgmineralNfertilizerha−1 compared to the cocksfoot and tall fescue grass treatments. The pure stand ryegrass yielded around 3t DM more than red clover in the high fertilizer treatment. Nitrous oxide emissions were highest in the treatments containing legumes. The LCA showed that the low input N systems had markedly lower carbon footprint values than crops from the high N input system with the pure stand legumes without N fertilization having the lowest carbon footprint. Thus, a reduction in N fertilizer application rates in the low input systems offsets increased N2O emissions after forage legume treatments compared to grass plots due to the N fertilizer production-related emissions. When including the subsequent wheat yield in the total aboveground production across the three-season rotation, the pure stand red clover without N application and pure stand ryegrass treatments with the highest N input equalled. The present study illustrate how leguminous biological nitrogen fixation (BNF) represents an important low impact renewable N source without reducing crop yields and thereby farmers earnings.

Water Use Efficiency and Rain Water Productivity of Wheat under Various Tillage-Glyphosate Interactive Systems

Abstract Rainfed wheat is generally grown in rotation with summer fallow in medium to high rainfall zone of Pothwar plateau of Pakistan. The present study was, therefore, conducted to investigate the impact of shallow and deep tillage practices, with and without herbicide (glyphosate) application, on moisture conservation and subsequent wheat yields. The study also aimed to examine the feasibility of substituting intensive shallow tillage with single application of glyphosate. The experiment was laid out in randomized complete block design with three replicates and net plot size of 14 m x 10 m, during 2007 and 2008 at two locations i.e high and medium rainfall. Wheat cultivar “GA-2002” was planted as a test crop. The data showed the superiority of conservation tillage in terms of conservation of moisture and increasing grain yields. Results also elaborated that tillage cannot be completely eliminated for profitable fallow management. However, deep ploughing with moldboard followed by single application of glyphosate proved potential option for substituting shallow tillage carried out during summer (kharif). The additional benefits under this tillage system included saving in fuel, labour and lower depreciation and maintenance costs for tillage machinery in addition to unquantifiable environmental benefits.

Wheat biomass and yield increased when populations of the root-lesion nematode (Pratylenchus thornei) were reduced through sequential rotation of partially resistant winter and summer crops

The root-lesion nematode, Pratylenchus thornei, can reduce wheat yields by &gt;50%. Although this nematode has a broad host range, crop rotation can be an effective tool for its management if the host status of crops and cultivars is known. The summer crops grown in the northern grain region of Australia are poorly characterised for their resistance to P. thornei and their role in crop sequencing to improve wheat yields. In a 4-year field experiment, we prepared plots with high or low populations of P. thornei by growing susceptible wheat or partially resistant canaryseed (Phalaris canariensis); after an 11-month, weed-free fallow, several cultivars of eight summer crops were grown. Following another 15-month, weed-free fallow, P. thornei-intolerant wheat cv. Strzelecki was grown. Populations of P. thornei were determined to 150 cm soil depth throughout the experiment. When two partially resistant crops were grown in succession, e.g. canaryseed followed by panicum (Setaria italica), P. thornei populations were &lt;739/kg soil and subsequent wheat yields were 3245 kg/ha. In contrast, after two susceptible crops, e.g. wheat followed by soybean, P. thornei populations were 10 850/kg soil and subsequent wheat yields were just 1383 kg/ha. Regression analysis showed a linear, negative response of wheat biomass and grain yield with increasing P. thornei populations and a predicted loss of 77% for biomass and 62% for grain yield. The best predictor of wheat yield loss was P. thornei populations at 0–90 cm soil depth. Crop rotation can be used to reduce P. thornei populations and increase wheat yield, with greatest gains being made following two partially resistant crops grown sequentially.

Integrating sheep grazing into wheat–fallow systems: Crop yield and soil properties

The two predominant systems for weed management in summer fallow are tillage with a field cultivator or multiple applications of broad spectrum herbicides with zero tillage. Both systems are based on substantial use of off farm resources. Our objective was to determine if strategic grazing of sheep may allow grain growers to more sustainably manage crop residues, volunteer crop, and other weeds during fallow periods. We conducted a study near Bozeman, Montana, USA, comparing three fallow weed management systems in two crop rotations from 2005 to 2008. Fallow weed management systems were conventional tillage, chemical-fallow (herbicide application), and sheep grazing. The crop rotations were summer fallow–spring wheat and summer fallow–winter wheat. In late fall, chemical-fallow treatment had greater residue cover and soil water content than did tilled- or grazed-fallow. At 0–15-cm depth, soil had lower bulk density in chemical- and tilled-fallow than in grazed fallow. Similarly, soil NO3-N, Ca, SO4-S concentrations and EC were lower following grazed-fallow than tilled-fallow, but Na concentration was higher following grazed-fallow than tilled- or chemical-fallow. Following spring and winter wheat, soil properties were not influenced by treatments. Grain yield was greater in winter wheat than in spring wheat but the trend reversed in protein concentration. Although soil properties varied among treatments, fallow management system had little influence on yield or quality of spring and winter wheat. Sheep grazing during fallow periods had limited impact on subsequent wheat yield and quality, and is a suitable practice for weed and residue management in wheat–fallow systems.

Effect of sweetclover cultivars and management practices on following weed infestations and wheat yield

There is a renewed interest, especially among organic growers, in using either white sweetclover (Melilotus alba Desr.) or yellow sweetclover [M. officinalis (L.) Lam.] as cover crops. Sweetclover cultivars and tillage practices have changed since these crops were widely used as cover crops in the first half of the 20th century. Experiments were initiated in 1999, 2000, and 2002 to compare the effect of high- and low-coumarin cultivars and crop termination methods on weed suppression, available soil N, moisture conservation and following crop yield. Weed suppression was usually more effective when sweetclover residues were left on the surface than when removed as hay. Sweetclover termination at 70% bloom was often more effective in suppressing weeds than termination at the bud stage. In the summer and fall after termination, surface residues of Yukon, a high-coumarin and drought-tolerant cultivar, reduced lamb’s-quarters (Chenopodium album L.) density by &gt; 80% compared with the no sweetclover check and essentially eliminated flixweed [Descurainia Sophia (L). Webb]. In the following spring, Yukon reduced kochia [Kochia scoparia (L.) Schrad.] density by &gt; 80% and wild oat (Avena fatua L.) biomass by &gt; 30% compared with the no sweetclover check. There was no difference in available N for a following crop between treatments with surface residue and cultivated fallow. Available soil moisture was about 10 mm less after the highest yielding sweetclover cultivars than after cultivated fallow, but subsequent wheat yield was not reduced. Maximum wheat yields were obtained after Yukon and Arctic sweetclover were grown as cover crops. It may be possible for organic growers to manage weeds with sweetclover in a reduced tillage system that leaves most of the plant residues on the soil surface. Key words: Cover crop, weed suppression, allelopathy, nitrogen, soil moisture