Cover Crop Establishment Research Articles

Minimizing Interspecific Competition in Soybean by Optimizing Cover Crop Self‐Seeding

Developing self‐seeding cover crop systems that minimize interspecific competition with soybean [Glycine max (L.) Merr.] are possible if cover crop growth is restricted to optimize cover crop seed production and dispersal. The objectives of this research were to quantify cover crop seed production, viability, and self‐seeding when growing concurrently with soybean. Winter wheat (Triticum aestivum L.), triticale (X Triticosecale Wittmack), and rye (Secale cereale L.) were seeded at two target rates (99 and 198 seeds m−2). Three seed dispersal methods (natural seed rain, simulated combine, and mechanical preharvest) were also tested to disperse mature cover crop seed. Wheat combined with mechanical seed dispersal before soybean harvest exhibited the greatest consistency in self‐seeding (171 and 123 plants m−2 in 2007 and 2008) regardless of establishment seeding rate. Additionally, wheat averaged 51 and 32% green groundcover in the fall of 2007 and 2008. Wheat seed viability (>82%) exceeded rye and triticale at soybean harvest, approximately 60 to 80 d after seed maturity. Cover crop species or establishment seeding rate did not affect soybean seed yield either year. Averaged across seeding rate and seed dispersal treatments, wheat self‐seeding systems exhibit the greatest potential for adoption, although soybean yield was 27% lower in 1 of 2 yr compared with a no cover crop control.

Comparative study of soil properties under various cultivation regimes of different crops

Establishment of cover crops is an effective way to reverse the soil fertility decline, which can be caused by a range of inappropriate traditional agriculture practices, particularly tillage and inorganic fertiliser application. In this study, soil properties were assessed under various cultivation regimes of different crops, including legumes, grass, and nursery natural rubber (NR) trees (Hevea brasiliensis Muell. Arg.), in southern Vietnam. The crops studied had all been growing for 7 years commencing in 1999, on light-textured Acrisols. Soils under the cultivation regime of creeping legumes including Calopogonium caeruleum, Pueraria phaseoloides, and Stylosanthes gracilis had significantly higher carbon (C) and nitrogen (N) concentrations and porosity than soils under the other management types studied. Soils under Brachiaria ruziziensis and P. phaseoloides had the highest aggregate stability. Cultivation regimes with tillage, field traffic, and inorganic fertilisers applied to nursery NR trees increased phosphorus (P) availability, but this was accompanied by increased soil compaction and reductions in most of the other soil properties analysed. Relative to the nursery NR cultivation, creeping-legume cultivation increased soil C concentration (by 95%), soil pHH2O (by 19%), macro-aggregates (by 29%), and porosity (by 8%). From principal component analysis, three soil properties—soil organic carbon (SOC), porosity, and P availability—were selected as key indicators suitable for the evaluation of the effects of cultivation on soils. Establishment of C. caeruleum and B. ruziziensis was most effective in improving soil C content, and soil porosity was significantly higher under C. caeruleum and P. phaseoloides. These findings suggest that each cover crop had its own dominant agro-characteristics and that selection of a cover crop to either improve soil fertility or reduce compaction should be considered by farmers in this region.

Labile Organic Matter, Aggregates, and Stratification Ratios in a Semiarid Vineyard with Cover Crops

Under semiarid Mediterranean climatic conditions, scarce attention has been given to the utilization of permanent cover crops (PCCs) in vineyard agroecosystems to increase soil organic C (SOC) and to improve the soil quality. We evaluated the feasibility of two permanent cover crops (resident vegetation, RV, and ‘Aurora gold’ blue fescue [Festuca longifolia Thuill.] vegetation, FV) to increase SOC and to improve the soil quality with respect to conventional tillage in a semiarid vineyard. We studied the influence of these management practices on the labile organic matter fractions (particulate organic C [POC], potentially mineralizable N [PMN], and water‐soluble C [WSC]), on the water aggregate stability (WAS) and on the stratification ratios (SRs) of these soil attributes. The field experiment was conducted on a fine‐loamy, mixed, thermic Typic Haploxerept soil in a vineyard located in the La Rioja region (northeast Spain). Soil samples were collected from four soil layers (at depths of 0–2.5, 2.5–5, 5–15, and 15–25 cm) during June 2008, 4 yr after cover crop establishment. The SOC content, POC, WSC, PMN, and WAS were measured. At a depth of 0 to 2.5 cm, the cover crops increased SOC, POC, WSC, PMN, and WAS. The C sequestration rates for RV and FV were 1.34 ± 0.31 and 1.52 ± 0.70 Mg ha−1 yr−1, respectively. Regression analyses indicated positive strong correlations among all parameters monitored. The SRs of the SOC, POC, and PMN were >2 in all depth ratios calculated and therefore were efficient indicators of the soil quality improvement caused by the PCCs. In a semiarid Mediterranean vineyard, a PCC has proven to be an effective strategy to enhance the SOC and to improve the soil quality in the short term.

Weed suppression in organic pepper ( Capsicum annuum L.) with winter cover crops

Weed control is a major constraint for organic production around the world. Field studies were conducted in pepper ( Capsicum annuum L.) from 2004 to 2006 at the Black Sea Agricultural Research Institute experimental field in Turkey to determine the weed suppressive effects of winter cover crops. Treatments consisted of ryegrass ( Lolium multiflorum L.), oat ( Avena sativa L.), rye ( Secale cereale L.), wheat ( Triticum aestivum L.), gelemen clover ( Trifolium meneghinianum Clem.), Egyptian clover ( Trifolium alexsandrinum L.), common vetch ( Vicia sativa L.), hairy vetch ( Vicia villosa Roth.) and a bare fallow with no cover crop. Weed density and total weed dry biomass were assessed at 14, 28, and 56 days after incorporation to quantify effects of cover crops during a subsequent pepper crop. Cover crop establishment was similar in both growing seasons and individual species produced in the range of 1800–3500 kg/ha biomass. Ryegrass produced the greatest biomass compared with other species. Weed dry biomass production just before cover crop incorporation varied with year and cover crop species. Hairy vetch, ryegrass, oat and common vetch were the most competitive cover crops based on total weed dry biomass. Hairy vetch was the most promising cover crop and reduced weed density by 73% and 70% at 28 and 56 DAI, respectively. Pepper yields were higher following all cover crops except Egyptian clover. The highest yield was obtained from hairy vetch plots in both years. This research indicates that cover crops such as hairy vetch, ryegrass, oat and common vetch could be used in integrated weed management programs to reduce weed infestation in organic pepper.

Seed Priming of Winter Annual Cover Crops Improves Germination and Emergence

Enhancing soil‐protecting living cover over the winter is an important challenge in temperate row crop production. This note reports on novel findings for cover crop seed priming, a process of controlled hydration and drying. The effects of seed priming over durations of 0, 2, 4, 8, 12, 24, and 36 h were evaluated for four species that varied in seed size and germination characteristics: cereal rye (Secale cereale L.), perennial ryegrass (Lolium perenne L.), hairy vetch (Vicia villosa Roth), and oriental mustard (Brassica juncea L.). A logistic function modeled response was used to quantify onset of germination, time to 50% germination (t50), maximum germination rate, final germination percentage (K), seedling emergence, and establishment in laboratory germination paper and soil core assays. Rye seed germinated rapidly regardless of priming treatment. Under the optimum environmental conditions of a laboratory germination assay, the smallest seeded cover crop, perennial ryegrass, was the only species to show a final germination response that was higher in primed (86%) than untreated seed (78%). However, seed germination rates of three species were influenced by priming: 50% germination was reached 8, 6, and 9 h earlier in hairy vetch, mustard, and perennial ryegrass, respectively. Compacted soil assays showed that priming (24 h) improved seedling emergence by 36% and 57% for hairy vetch and perennial ryegrass, respectively, compared with untreated seed. These results were consistent across experiment runs. Seed priming shows promise as a new technology for improving cover crop establishment in compacted soil.

Establishment and Growth of Self‐Seeded Winter Cereal Cover Crops in a Soybean–Corn Rotation

Perpetuating cereal cover crops through self‐seeding may increase adoption by reducing risk and cost. Winter rye (Secale cereale L.), wheat (Triticum aestivum L.), and triticale (× Triticosecale Wittmack) were used to develop self‐seeding cover crop systems in a soybean [Glycine max (L.) Merr.]–corn (Zea mays L.) rotation. Cereals were planted and managed chemically and mechanically in varying configurations. The objectives were to (i) quantify temporal establishment patterns after one cycle of self‐seeding, (ii) quantify shoot biomass, N uptake, and seed production growing concurrently with corn, and (iii) quantify cover crop establishment after two cycles of self‐seeding. Final plant densities for most species by treatment combinations were fully established within 1 wk after soybean (Cycle 1) harvest. Fall green ground cover after soybean was consistently higher with wheat and ranged from 16 to 61%. Straw biomass the following July ranged from 50.4 to 79.1 g m−2 in wheat, 20.1 to 39.3 g m−2 in triticale, and 0.0 to 52.7 g m−2 in rye. Combined spring and maturity maximum N uptake was 20.7, 21.2, and 35.0 kg ha−1 for triticale, wheat, and rye. Cycle two cover crop seed production was greatest in wheat and ranged from 559 to 1280 seeds m−2. Wheat also consistently had greater self‐seeding plant establishment after two cycles than rye and triticale, which ranged from 5 to 21% of the original plant densities and 19 to 64% of the cycle one plant densities. Future research on self‐seeding cereal cover crops should focus on efficient technologies for seed dispersal.

Establishment and Growth of Self-Seeded Winter Cereal Cover Crops in a Soybean–Corn Rotation

Perpetuating cereal cover crops through self-seeding may increase adoption by reducing risk and cost. Winter rye (Secale cereale L.), wheat (Triticum aestivum L.), and triticale (× Triticosecale Wittmack) were used to develop self-seeding cover crop systems in a soybean [Glycine max (L.) Merr.]–corn (Zea mays L.) rotation. Cereals were planted and managed chemically and mechanically in varying configurations. The objectives were to (i) quantify temporal establishment patterns after one cycle of self-seeding, (ii) quantify shoot biomass, N uptake, and seed production growing concurrently with corn, and (iii) quantify cover crop establishment after two cycles of self-seeding. Final plant densities for most species by treatment combinations were fully established within 1 wk after soybean (Cycle 1) harvest. Fall green ground cover after soybean was consistently higher with wheat and ranged from 16 to 61%. Straw biomass the following July ranged from 50.4 to 79.1 g m−2 in wheat, 20.1 to 39.3 g m−2 in triticale, and 0.0 to 52.7 g m−2 in rye. Combined spring and maturity maximum N uptake was 20.7, 21.2, and 35.0 kg ha−1 for triticale, wheat, and rye. Cycle two cover crop seed production was greatest in wheat and ranged from 559 to 1280 seeds m−2. Wheat also consistently had greater self-seeding plant establishment after two cycles than rye and triticale, which ranged from 5 to 21% of the original plant densities and 19 to 64% of the cycle one plant densities. Future research on self-seeding cereal cover crops should focus on efficient technologies for seed dispersal.

Potential for a Rye Cover Crop to Reduce Nitrate Loss in Southwestern Minnesota

Cover cropping practices are being researched to reduce artificial subsurface drainage NO3–N losses from agricultural lands in the Upper Mississippi watershed. This study was designed to investigate the influences of fall planting date and climate on cereal rye (Secale cereale L.) biomass and N uptake in the spring, and to assess subsurface drainage NO3–N loss reductions. A soil–plant–atmosphere simulation model, RyeGro, was developed and used to predict rye cover crop establishment and growth, soil water balance, N cycling, and drainage NO3–N losses from mid‐September through May in southwestern Minnesota. An imbedded stochastic weather generator provided model climate inputs. Inclusion of a rye cover crop sown on 15 September reduced N losses by 11.1 kg N ha−1 or 45% for a corn (Zea mays L.)–soybean [Glycine max (L.) Merr.] crop rotation. Fall sowing dates of 1, 15, and 30 October resulted in reductions of 7.8, 5.8, and 4.6 kg N ha−1, respectively, by the end of May. Desiccation of the rye on 1 May resulted in reductions of 4.5, 2.2, 1.2, and 0.7 kg N ha−1, for the 15 September and 1, 15, and 30 October sowing dates, respectively. Cover cropping practice provides promising opportunities for reductions in N losses for cropping rotations wherein the primary crops are harvested before mid‐September and planted after mid‐May. We predict that a winter rye crop can reduce drainage NO3–N losses on average 7.4 kg N ha−1 for southwestern Minnesota if planted on 15 September and desiccated on 15 May.

(156) Improved Cover Crop Establishment and Growth Is Related to Planting Date in Organic Concord Grape Production

Concord grape (Vitis labrusca L.) accounts for a majority of juice grapes produced in Washington State. Because synthetic nutrients are not permissible in USDA organically-certified production systems, legume cover crops are used to supply nitrogen (N) to the crop. In order to supply a sufficient amount of N, the cover crop must successfully establish and produce large quantities of biomass. This study evaluates how the planting date influences emergence and biomass production of hairy vetch (Vicia villosa subsp. villosa L.) and yellow sweet clover [Melilotus officinalis (L.) Lam.] when used as legume green manures. The research was conducted on a commercial vineyard and a research vineyard from 2003–05. Treatments for the study consisted of yellow sweet clover and hairy vetch planted in both the spring and fall. Plots receiving soluble N sources were planted with wheat (Triticum aestivum L.) or rye (Secale cereale L.). Because of the large relative seed sizes of rye, wheat, and hairy vetch compared to yellow sweet clover, these treatments established faster with good stands in 2004. In 2005, clover plots had high emergence and biomass production because of water management modifications. Biomass data from the commercial vineyard in May 2005 indicates that fall-planted vetch produced more biomass than spring-planted vetch. Fall-planted hairy vetch and yellow sweet clover in the research vineyard showed higher biomass production than spring- and fall-planted hairy vetch and yellow sweet clover. When hairy vetch and yellow sweet clover are planted in the fall, they generally have better seedling emergence and biomass production due to the heightened aggressiveness exhibited by competing weed species during late spring and summer.

Manure Slurry-Enriched Micro-Site Seeding of Biosuppressive Covers

There is increasing interest among growers in novel establishment systems for cover crops that can rehabilitate and protect soil. Cropping intensification has led to yield declines, compacted and poor quality soil, and increased pest problems. Cover crops in the Brassica (mustard) family offer benefits in soil conservation, improvement in soil quality, reduction in nitrate leaching, and suppression of certain pests and soil borne fungal diseases. Establishment of cover crops by conventional methods following harvest presents a significant challenge as soil is generally dry, compacted, uneven, and far from an ideal environment for seed germination. An alternative method, manure slurry-enriched micro-site seeding, incorporates aeration tillage, manure application, and seeding in a single operation. The objective of this work was to evaluate manure slurry-enriched micro-site seeding of cover crops by assessing stand establishment and biomass yield of oilseed radish and oriental mustard. The species were chosen for contrasting seed size, thus allowing evaluation of how small versus medium seeded brassica respond to aeration tillage, manure application, and seeding done in a single efficient 'manure slurry-enriched micro-site seeding' operation. Results of field trials in 2004 and 2005 were consistent with the new manure slurry seeding process as an efficient and effective cover crop establishment method. Compared to direct-drilling, manure slurry seeded plant stands (plants m-2) were significantly less (a = 0.10) in five of seven comparisons but biomass yields (kg ha-1) were similar because individual plant biomass was up to six times greater with manure slurry seeding. Biomass (aboveground and total) of manure slurry seeded plants was significantly greater in two of seven comparisons and there were no instances when the conventionally seeded crops yielded significantly more than the manure slurry seeded crops. Seed size did not affect the success of the manure slurry seeding method.

Using cover crops to establish white and black spruce on abandoned agricultural lands

Vegetation control is a critical factor in reforestation. On abandoned agricultural lands, an alternative to herbicide application is the use of cover crops to compete with the weeds and to improve survival and growth rates of transplanted species. A factorial experiment was carried out on four sites to test this hypothesis. The experiment included three factors. The first factor consisted of lime versus no lime application. The second factor included four cover crop combinations and a control. Cover crop combinations were winter barley (Hordeum vulgare) underseeded with either birdsfoot trefoil (Lotus corniculatus), Kentucky bluegrass (Poa pratensis), ladino clover (Trifolium repens), or a mixture of Kentucky bluegrass and ladino clover. The third factor consisted in planting either white (Piceaglauca) or black (Picea mariana) spruce seedlings. Winter barley did not establish as rapidly and vigorously as expected. Nevertheless, the cereal reduced weed populations in the establishment year. For broadleaf weeds, this reduction was not large enough to allow a carryover during subsequent years. In contrast, subsequent increase of the grassy weed populations was slowed down in the presence of cover crops. The establishment of the other cover crops was poor and highly variable from site to site. It is not clear whether this relative failure was due to growing conditions, poor establishment of the cereal cover crop, or to other factors. Liming and cover crops had little effect on spruce growth but black spruce seedlings grew taller than white spruce seedlings at two out of four sites, and basal diameter of white spruce reached larger values than did black spruce. For white spruce, this might constitute an advantage in old fields where seedlings are prone to lodging under weed pressure. Finally, it was noted that seedling survival was exceptionally high in all treatments.

A microcosm approach to assessing the effects of earthworm inoculation and oat cover cropping on CO 2 fluxes and biological properties in an amended semiarid soil

We designed a microcosm experiment to assess the influence of inoculation with Eisenia foetida earthworms and the establishment of an Avena sativa cover crop on biological (enzyme activities and labile carbon fractions) soil quality indicators in a soil treated with a composted organic residue, and to determine the contribution of these treatments to carbon dioxide emissions from the soil to the atmosphere of the microcosm. The microcosms were incubated for 53 days under 28 °C/18 °C day/night temperatures. The addition of earthworms and the planting of A. sativa increased dehydrogenase activity of compost amended soil by about 44% after 23 days of incubation. The metabolic potential, calculated as the ratio dehydrogenase activity/water soluble C, was higher in the compost amended soil planted with A. sativa. The highest total amount of CO 2–C evolved occurred in the soil treated with composted residue and earthworms (about 40% of the total amount of CO 2 evolved came from earthworm activity). The planting of A. sativa increased the decomposition rate constant of organic matter in the amended soil but decreased the potentially mineralizable C pool. In conclusion, the establishment of an A. sativa cover crop and the addition of E. foetida to a degraded agricultural soil treated with composted residue were effective treatments for improving the biological and biochemical quality and the metabolic potential of the soil.

Cover cropping to reduce nitrate loss through subsurface drainage in the northern U.S. corn belt.

Despite the use of best management practices for nitrogen (N) application rate and timing, significant losses of nitrate nitrogen (NO3(-)-N) in drainage discharge continue to occur from row crop cropping systems. Our objective was to determine whether a autumn-seeded winter rye (Secale cereale L.) cover crop following corn (Zea mays L.) would reduce NO3(-)-N losses through subsurface tile drainage in a corn-soybean [Glycine mar (L.) Merr.] cropping system in the northern Corn Belt (USA) in a moderately well-drained soil. Both phases of the corn-soybean rotation, with and without the winter rye cover crop following corn, were established in 1998 in a Normania clay loam (fine-loamy, mixed, mesic Aquic Haplustoll) soil at Lamberton, MN. Cover cropping did not affect subsequent soybean yield, but reduced drainage discharge, flow-weighted mean nitrate concentration (FWMNC), and NO3(-)-N loss relative to winter fallow, although the magnitude of the effect varied considerably with annual precipitation. Three-year average drainage discharge was lower with a winter rye cover crop than without (p = 0.06). Over three years, subsurface tile-drainage discharge was reduced 11% and NO3(-)-N loss was reduced 13% for a corn-soybean cropping system with a rye cover crop following corn than with no rye cover crop. We estimate that establishment of a winter rye cover crop after corn will be successful in one of four years in southwestern Minnesota. Cover cropping with rye has the potential to be an effective management tool for reducing NO3(-)-N loss from subsurface drainage discharge despite challenges to establishment and spring growth in the north-central USA.

The Use of Winter Annual Legume Cover Crops in a Wheat-Grain Sorghum Rotation in South Central Kansas

ABSTRACT Winter annual legumes in humid regions of the country can have a positive effect on subsequent corn (Zea mays) and grain sorghum (Sorghum bicolor) crops, mainly through N contribution of the legume and, in some cases, soil improvement. However, water use by the cover crop in drier regions has the potential to reduce yields in subsequent crops. This study was initiated in central and south-central Kansas to look at both the agronomic and economic implications of adding a winter annual legume cover crop to a winter wheat (Triticum aestivum)-grain sorghum rotation. Experiments included researcher-managed on-station trials and cooperative (i.e., farmer-managed) trials with farmers using hairy vetch (Vicia villosa) and Austrian winter pea (Pisum arvense). Results showed that in good rainfall years, establishment of cover crop was adequate, and no significant difference occurred between sorghum yields following cover crops versus following wheat with fertilization. On-station trials showed a significant nitrogen (N) contribution from hairy vetch and benefits to sorghum. During years with low rainfall, cover crop establishment was poor, N contribution from the cover crop was low, and grain sorghum yields were reduced because of water use by the cover crop. Variable costs were similar between cover crop and fertilized treatments, but gross returns and, consequently, net returns were lower in the cover crop plots because of this yield reduction. For cover crops to be attractive options for farmers in this part of Kansas: they must be used also for livestock feed and/or for early spring grazing; other cultivars or management systems that use less water must be developed; experiments must be conducted to ascertain benefits of cover crops during the second rotation cycle; and the price of N fertilizer must increase to the point that use of alternative sources is economical. Also, the use of cover crops by farmers in regions of variable rainfall should not be “recipe driven” but “response driven”, using cover crops in years where rainfall is adequate, and not planting or destroying stands during dry years to conserve water for the cash crop.

Evaluating the use of two contrasting legume species as relay intercrop in upland rice cropping systems

In the savanna zone of West Africa with a prolonged dry season, the successful growth of legumes as short-season fallow necessitates relay establishment of cover crops into the preceding food crop. Inappropriate choice of legume species and establishment dates may result in severe interspecific competition for light, water and nutrients and a subsequent yield loss in the main crop. In the current study, the highly competitive Cajanus cajan L. and the weakly competitive Stylosanthes hamata Taub. were relay-seeded into two upland rice cultivars with different competitive ability (WAB56-50, WAB450-24-3-2-P18-HB syn. V4 ) at different sowing dates, ranging from 0 to 84 days after rice sowing (DARS). Using a logistic function was adequate to describe rice grain yield, final rice biomass and legume biomass at 1 week after rice harvest as a function of legume sowing date. Rice biomass and grain yield were significantly ( P<0.001) reduced when legumes were established between 0 and 28 DARS. Beyond 56 DARS no competition effects on rice were observed. At these late sowing dates only relatively low amounts of legume biomass were obtained, due to a combined effect of a more severe competition by the rice crop and a shorter growing period. The derived yield loss–legume biomass relationship showed that C. cajan was the most appropriate legume species of the two under study, to suit a relay intercropping system with upland rice, as it produced reasonable amounts of biomass at low levels of rice grain yield loss. This conclusion was confirmed by results on the after-effect of the legumes, where only the improved fallow by C. cajan gave a significant increase in the yield of the subsequent rice crop. Optimum sowing time of C. cajan was between 30 and 35 DARS. The effect of selecting a specific legume was found to surpass that of choosing either one of the two rice cultivars, for which contrasting results were obtained in 2 years of experimentation.

Legume Cover Crops with Winter Cereals in Southern Manitoba

The opportunity to include late‐season cover crops in northern cropping systems has been enhanced with the adoption of winter cereal production; however, cover crop feasibility has not been evaluated in these regions. Field experiments were conducted at two sites in Manitoba in 1998 and 1999 to (i) assess establishment and dry matter (DM) production of legume cover crops that were relay‐cropped [alfalfa (Medicago sativa L.) and red clover (Trifolium pratense L.)] or double‐cropped [chickling vetch (Lathyrus sativus L.) and black lentil (Lens culinaris Medik. subsp. culinaris)] with winter cereals [winter wheat (Triticum aestivum L.) and fall rye (Secale cereale L.)], (ii) assess the effect of relay cover crops on cereal grain yield, and (iii) characterize the effects of a red clover cover crop on the microclimate after winter wheat harvest. Establishment and midseason DM of the relay crops were not affected consistently by cereal crop type. Legume DM at freeze‐up was similar in winter wheat and fall rye systems and ranged from 190 to 1800 kg ha−1, with moisture availability being the critical factor. Across all site‐years, final DM for red clover, alfalfa, chickling vetch, and lentil averaged 1157, 690, 746, and 634 kg ha−1. Relay crops did not affect main‐crop grain yield but did significantly reduce main‐crop DM production in some cases. The red clover cover crop created a moderating effect on late summer and fall surface (5‐cm height) air temperatures and decreased soil moisture availability. Including relay and double crops in winter cereal‐based cropping systems appears feasible in southern Manitoba.

USING WINTER COVER CROPS TO IMPROVE SOIL AND WATER QUALITY

This article reviews literature about the impacts of cover crops in cropping systems that affect soil and water quality and presents limited new information to help fill knowledge gaps. Cover crops grow during periods when the soil might otherwise be fallow. While actively growing, cover crops increase solar energy harvest and carbon flux into the soil, providing food for soil macro and microrganisms, while simultaneously increasing evapotranspiration from the soil. Cover crops reduce sediment production from cropland by intercepting the kinetic energy of rainfall and by reducing the amount and velocity of runoff. Cover crops increase soil quality by improving biological, chemical and physical properties including: organic carbon content, cation exchange capacity, aggregate stability, and water infiltrability. Legume cover crops contribute a nitrogen (N) to subsequent crops. Other cover crops, especially grasses and brassicas, are better at scavenging residual N before it can leach. Because growth of these scavenging cover crops is usually N limited, growing grass/legume mixtures often increases total carbon inputs without sacrificing N scavenging efficiency. Cover crops are best adapted to warm areas with abundant precipitation. Water use by cover crops can adversely impact yields of subsequent dryland crops in semiarid areas. Similarly, cooler soil temperatures under cover crop residues can retard early growth of subsequent crops grown near the cold end of their range of adaptation. Development of systems that reduce the costs of cover crop establishment and overcome subsequent crop establishment problems will increase cover crop utilization and improve soil and water quality.

Evaluation of Potential Cover Crops for Inland Pacific Northwest Vineyards

Numerous cover crops for orchards and vineyards have been evaluated, but many selections do not necessarily perform well in the cold, arid environment of the inland Northwest. A cover crop between vine rows can mitigate wind erosion and subsequent damage to young vines. However, low rainfall, gusty winds, and sandy soils that cause significant wind erosion problems can exacerbate cover crop establishment, and cold winters can limit cover crop survival. During 1998, 175 plant accessions were screened for performance as vineyard cover crops at Prosser, Washington. Assessed attributes included percent emergence, percent vegetative cover, stand duration, and plant height. Based on that assessment, seven domestic selections and four foreign Medicago species (medics) were identified for additional evaluation in a research trial in 1999. Additionally, seven accessions and two mixes of species that met the growth criteria and had commercial availability were evaluated in a commercial, drip-irrigated vineyard near Prosser in 1999. Vine water potential and soil moisture were determined in addition to the identical growth criteria from the 1998 study. Cover crop treatments did not lead to detectable water stress in the vines (midday y = -0.84 to -1.30 MPa). However, dry soil between vine rows due to precision drip irrigation inhibited germination and establishment of legumes; therefore, grasses had better emergence rates. Of the mixed species, a grass mix (Canada) composed of crested wheatgrass (Agropyron cristatum L.), pubescent wheatgrass (Elytrigia intermedia L.), and perennial rye (Lolium perenne L.; 40:40:20), depleted soil water the least and showed the least effect on vine water potential. Early season weeds were suppressed by most cover crop species; however, season-long suppression of weed growth was observed only for the Canada mix and crested wheatgrass cv. Fairway.

Residual tillage and bush‐fallow effects on soil properties and maize intercropped with legumes on a tropical Alfisol

Abstract. After six years of bush‐fallow, residual effects on soil productivity of tillage practices prior to the fallow were investigated on an Alfisol in south western Nigeria. In 1996 fallow was followed by maize intercropped with cover crops of Pueraria phaseoloides, Mucuna pruriens or cowpea (Vigna unguiculata) and no intercrop. Parameters measured included soil properties, ground cover, crop growth and yield, rainfall erosivity, runoff and soil loss.In spite of six‐years of bush‐fallow and establishment of cover crops, soil erosion was significantly greater on plots that had been conventionally cultivated previously using disc ploughs, harrows and mechanical rotovators (1.78 t ha−1season−1) compared to previously no‐till plots (1.34 t ha−1season−1). Crop growth and yields were least and soil loss greatest (2.83 t ha−1season−1) on the previous bare plot.Maize grain yield was highest using Pueraria phaseoloides as an intercrop (2.15 t ha−1) followed by a cowpea intercrop (1.92 t ha−1), maize without intercrop (1.87 t ha−1) and Mucuna pruriens intercrop (1.71 t ha−1). The maize grain yields reflected levels of competition from the cover crops. Cowpea–maize intercrop may be most suitable for farmers because maize yields were satisfactory and cowpea grain serves as additional subsistence. Cowpea yields were 390 kg ha−1. Soil erosion was also moderate using cowpea as an intercrop (1.71 t ha−1season−1). However, Pueraria phaseoloides gave the best erosion control with a soil loss of 1.34 t ha−1season−1.

Comparison of two spring seeding methods to establish forage cover crops in relay with winter cereals

The establishment of cover crops, in relay, to minimise soil erosion, improve soil physical condition and provide a main-season crop in rotation with potatoes ( Solanum tuberosum L.) is a recommended agronomic practice in Atlantic Canada. This is usually achieved by seeding winter rye ( Secale cereale L.) or winter wheat ( Triticum aestivum L.) immediately after potato harvest for ground cover followed, the next spring, by inter-seeding an annual or biennial forage crop by drilling. Spring drill seeding can, however, be delayed or prevented by wet ground conditions, thus, making broadcast seeding a considered alternative. This study examined, therefore, the comparative merits of spring broadcast seeding and drill seeding of two adapted forages, Italian ryegrass ( Lolium multiflorum Lam.) and red clover ( Trifolium pratense L.), into a standing crop of fall-seeded winter rye or winter wheat. Crop performance was evaluated, using meter-square quadrats, as ground coverage and grain yield (of cereals). Soil compaction, evaluated as shear strength in the 0–15 cm layer (avoiding wheel tracks) of a fine sandy loam (Orthic Podzol), was greater after drill seeding than after broadcast seeding by a factor of 7.2% and was attributed to the greater ground-contact mass of the drill seeder. The forage crops provided 5.5% more ground coverage with drill seeding than with broadcast seeding. However, seeding method had no effect on the cereal host crops' ground coverage or grain yield. Ryegrass coverage was 123% of red clover coverage and winter rye coverage was 176% of winter wheat coverage. Forage coverage, in this study, suffered no setback because of the greater soil compaction associated with drill seeding. However, soils are subject to greater compaction under wetter conditions, thus, broadcast seeding is expected to be a better option, the wetter the spring.