Monocropped Soybean Research Articles

Soybean Canopy Development as Affected by Population Density and Intercropping with Corn: Fractal Analysis in Comparison with Other Quantitative Approaches

ABSTRACTTo better understand how crops intercept light, the complexity of plant structure needs to be characterized. Fractal analysis provides a novel approach for quantifying the geometric structure of individual plants. The objectives of this study were to determine (i) an appropriate methodology for estimating fractal dimension (FD) two‐dimensionally for complex three‐dimensional structures of plants such as soybean [Glycine max (L.) Merr.]; (ii) whether the temporal pattern of FD for soybean structure is altered by population density or intercropping with corn (Zea mays L.); and (iii) how the FD for soybean structure compares with other quantitative measures of shoot development. Soybean plants were randomly sampled in monocropped soybean and intercropped corn‐soybean plots grown at the same site in three successive years. Sampled plants were cut at the stem base, and leaf blades were immediately detached. Leafless plant structure was photographed from the side which allowed maximum appearance of branches and petioles. The FD was estimated two‐dimensionally from the scanned and processed images. Fractal dimension of soybean leafless structure increased with time for all treatments, coincident with the increasing complexity of structure as shoots developed. The rate of linear increase of FD with time varied among treatments. Leaf area per plant, plant height, and number of leaves per plant increased with time for all treatments, indicating a positive correlation with FD. In contrast, light penetration decreased during canopy development, and was negatively correlated with FD. Whereas leaf area evaluates the surface available for light interception, FD characterizes its geometric distribution in space.

Sorghum Intercropping Effects on Yield, Morphology, and Quality of Forage Soybean

Shading patterns when two forage species are intercropped may be different than in a monocrop environment. Our objectives were to quantify yield and forage quality response of forage soybean [Glycine max (L.) Merr.] intercropped with forage sorghum [Sorghum bicolor (L.) Moench] and compare to the measurements of monocrop soybean. Soybean plants were harvested from the middle portion of individual rows in plots containing only soybean and from plots having alternating soybean and sorghum rows spaced 76 cm apart. Morphological and forage quality measurements were determined on leaf and stem fractions. Morphological measurements included main stem length, node number, leaf area ratio (LAR), specific leaf weight (SLW), and stem diameter. Forage quality constituents included in vitro dry matter disappearance (IVDMD), neutral detergent fiber (NDF), hemicellulose, and cellulose, and crude protein (CP) concentrations. Intercropped soybean had 6 more plants m−1 of row, less advanced morphological development, and 2.3 Mg ha−1 less dry matter than monocrop soybean. Leaf IVDMD, NDF, hemicellulose, and cellulose did not differ between intercrop and monocrop soybean. However, stem IVDMD was 33 g kg−1 greater for intercropped than monocrop soybean, reflecting the 36 g kg−1 decrease in NDF concentration. Intercropped soybean was lodged both years more than monocrop soybean, which may have been due to the significant decrease in stem NDF. Leaf CP concentration was 25 g kg−1 greater for monocrop soybean than intercropped soybean; however, stems from intercropped soybean had 12 g kg−1 greater CP than monocrop soybean stems. Soybean exhibited a high degree of morphological plasticity, presumably in response to increased competition for solar radiation. Although forage quality of intercrop soybean was greater than monocrop soybean, intercropping forage‐type soybean with another tall‐growing forage does not appear to be practical because of the decrease in dry matter accumulation.

Economic assessment of irrigated and nonirrigated soybean cropping rotations on a clay soil

Experiments were conducted in Keiser, Arkansas on a Sharkey silty clay soil for three years to examine soybean, wheat, and grain sorghum rotations. Treatments also included selected variation of conventional versus no till and alternative wheat residue management. Both irrigated and nonirrigated strategies were investigated. Agronomic results show that irrigated soybean yields average about 1,344 kg ha‐1 (20 bu A‐1) higher than comparably treated nonirrigated soybean treatments. Economic analysis using enterprise budgets reveals three top rotations regardless of irrigation: continuous monocropped soybean, wheat fallow followed by monocropped soybean, and wheat‐soybean double‐cropped with burned wheat stubble. Statistical analysis demonstrates the profitability of irrigation and the dependence of the most economical crop rotation upon weather conditions.

Comportamento de Sternechus subsignatus (Boheman) em dez espécies vegetais de verão para rotação de culturas ou cultura armadilha no plantio direto

O desenvolvimento de Sternechus subsignatus (Boheman) (Coleoptera: Curculionidae) foi avaliado em dez espécies vegetais sob condições naturais num solo manejado há três anos no sistema de plantio direto corn soja cultivada no verão. Foram observados o número de plantas atacadas, a oviposição, o núrnero e peso de larvas, o número de larvas hibernantes no solo e o número de adultos emergidos. O inseto se reproduziu e desenvolveu ern feijão (Phaseolus vulgaris L) guandu anão (Cajanus cajan L), lab-lab (Dolichos lablab L.) e soja (Glycine max L.) e ao contrário, em crotalária júncea (Crotalaria júncea L). girassol (Helianthus annuus L.), milheto (Pennisetum americanum Leek), milho (Zea mays L), mucuna preta (Stizolobium aterrimum Piper et Tracy) e sorgo (Sorghum bicolor L.) não completou o ciclo de vida. Os resultados indicaram que a cultura do feijão, guandu anão, lab-lab e soja aumentaram a população do inseto. Entretanto, ocorreu redução na população do inseto corn as culturas da crotalária júncea, girassol, milheto, milho, mucuna preta e sorgo. As quatro primeiras espécies são hospedeiras preferenciais, podendo ser usadas como culturas armadilhas e as demais, não são hospedeiras, pois propiciam a diminuição da população do inseto, sendo ideais para uso em sistemas derotação de culturas no verão, em áreas infestadas, para substituir o monocultivo da soja em plantio direto.

Off-Site Runoff Losses of Metolachlor and Metribuzin Applied to Differing Soybean (Glycine max) Production Systems

Three soybean production systems coupled with conventional tillage (CT) or no-tillage (NT) were evaluated for metolachlor and metribuzin loss in water from runoff. Metolachlor and metribuzin concentrations were similar in runoff from CT or NT soybean following winter wheat, with stubble burned, and CT or NT monocrop soybean. However, metolachlor and metribuzin concentrations were higher in runoff water from the CT doublecrop soybean planted into winter wheat stubble than NT. In all 3 yr of the study, the majority of total losses occurred in the first three runoff events. Total loss of metolachlor in runoff from the doublecrop system with winter wheat stubble present was 0.6% in 1991 to 1.1% in 1990 from CT, and 0.2% in 1990 to 0.6% in 1991 from the NT. Similar results were observed from the CT and NT doublecrop with burned winter wheat stubble and the monocrop systems. Metribuzin loss patterns were similar to metolachlor, but the fraction lost was slightly higher. Multi-variate regression was used to describe and predict herbicide losses, and R2values ranged from 0.66 to 0.98 for both metolachlor and metribuzin.

Parasitism and Disease Incidence in the Green Cloverworm (Lepidoptera: Noctuidae) in Strip-Intercropped Soybean Agroecosystems

We examined the effects of strip-intercropping soybean, Glycine max , and sorghum, Sorghum bicolor , on rates of insect parasitism and fungal disease incidence in larvae of the green cloverworm, Plathypena scabra (F.), a widespread and occasionally serious pest of soybeans, during an endemic year. A completely randomized design with two cropping systems (monocropped soybean and soybean intercropped with sorghum), two sorghum heights (dwarf sorghum ≈1 m in height; tall sorghum ≈2 m in height), and two row patterns (2 rows of sorghum alternating with 10 rows of soybean; 6 rows of sorghum alternating with 6 rows of soybean) was used. Abundance (number per row-meter) of P. scabra larvae, rates of larval parasitism and incidence of the entomopathogenic fungus, Nomuraea rileyi (Farlow) Sampson did not differ significantly among treatments or their interaction. Soybean yield (grams dry weight of beans per row-meter) did not differ significantly among treatments but sorghum grain yield and biomass (grams dry weight per row-meter) were significantly lower in dwarf sorghum planted in wide rows because of competing weed populations. Results suggest that neither the accrual of P. scabra larvae in soybean nor the impact of the parasitoid-pathogen complex on P. scabra mortality is affected by structural or taxonomic agroecosystem diversification at the scale studied. n

Net Returns from Eight Irrigated Cropping Systems on Clay Soil

Considerable research has been conducted on the agronomic relationships of cropping systems adapted to the clay soils of the lower Mississippi River floodplain (30°-37° North latitude); however, only a few studies included the determination and evaluation of net returns. An 8-yr study (1984-1991) was conducted on a Tunica clay (clayey over loamy, montmorillonitic, nonacid, thermic Vertic Haplaquept) to determine net returns above specified costs from eight nonirrigated cropping systems. The cropping systems included 1) monocrop corn (Zea mays L.) ; 2) monocrop soybean [Glycine max (L.) Merr.] ; 3) monocrop grain sorghum [Sorghum bicolor (L.) Moench.] ; 4) biennial rotation of corn and soybean ; 5) biennial rotation of grain sorghum and soybean ; 6) continuous wheat (Triticum aestivum L.)-soybean doublecrop ; 7) biennial rotation of corn and wheat-sobyean doublecrop ; and 8) biennial rotation of grain sorghum and wheat-soybean doublecrop. Cropping systems that included grain sorghum as a component produced the highest average net returns. Average net returns per acre from grain sorghum-soybean ($76), grain sorghum and wheat-soybean doublecrop ($64), and monocrop grain sorghum ($60) systems were significantly higher than from the monocrop soybean ($25), monocrop corn ($-9), and corn and wheat-soybean doublecrop ($16) systems. Average net returns per acre from the wheat-soybean doublecrop ($48) and the corn-soybean ($42) systems were similar and in the intermediate range. Data indicate that monocrop corn and soybean systems and the corn-wheat-soybean system are not profitable when grown in nonirrigated environments on clay soils in the lower Mississippi River alluvial plain.

Significance of soil N on dry matter production and N balance in soybean/sorghum mixed cropping system

Abstract The importance of the soil nitrogen (N) level in dry matter production and N economy of soybean/sorghum mixed cropping system was studied using the 15N-dilution method. The N levels of the granite regosol used in the experiment varied due to previous management. The soil with a high nitrogen content (HSN) had been treated with animal waste materials and urea and cultivated with maize in the previous year, while the soil with a low N content (LSN) was not treated. Values of total nitrogen extractable with 2 mol L1 KC1 were 4.2 × 10-4 kg kg-1 for the HSN condition and 1.3 × 10-4 kg kg-1 for the LSN condition. Soybean and sorghum were planted as monocrops or in mixed cropping. The spacing was 18 cm × 18 cm for both cropping systems. Total dry weight was significantly larger under HSN than LSN conditions for both cropping systems. The dry weight in the soybean/sorghum mixed cropping system under HSN conditions was larger than that of the respective monocrops. However the total dry weight in the soybean/sorghum mixed cropping system under LSN conditions was smaller than that of the soybean monocrop. Biological nitrogen fixation (BNF) accounted for more than 90% of the N accumulated by soybean. The BNF of component soybean was higher than that of the monocrop. Furthermore, the BNF of soybean under LSN conditions was higher than that under HSN conditions, for both cropping systems. Soil N was the major source of N for both mono- and mixed cropped sorghum. Although the soybean BNF activity under LSN conditions was higher than that under HSN conditions, N transfer to component sorghum under LSN conditions was lower compared to that under HSN conditions. Nitrogen transferred accounted for about 7% of the total amount of N accumulated by component sorghum under HSN conditions. It is suggested that the N transfer may be due to the greater extent of root intermingling of component soybean and sorghum. Consequently, it is suggested that a certain amount of N is essential for a high dry matter production and N economy in the mixed cropping system.

Impact of rainfall and tillage systems on off‐site herbicide movement

Abstract Ground cover associated with conservation‐ and no‐till cropping systems can alter runoff and herbicide loss from the soil surface. This study was conducted in 1987 and 1988 to evaluate runoff losses of soil‐applied alachlor and imazaquin in five different soybean cropping systems. Cropping systems used were: 1) conventionally tilled monocrop soybean planted in May; 2) conventionally tilled monocrop soybean planted in June; 3) conventionally tilled doublecrop soybean with incorporated wheat stubble; 4) no‐till doublecrop soybean with burned wheat stubble; and 5) no‐till doublecrop soybean planted into standing wheat stubble. Runoff was lower in 1988 due to a lack of precipitation and dry soil conditions. Herbicide loss in both years was greatest in doublecrop soybean with incorporated wheat stubble, which corresponded to higher runoff. Lower herbicide loss in June‐planted monocrop soybean was attributed to a rougher seedbed that retarded runoff. May‐planted monocrop soybean also lost very little h...

Cropping System and Consolidation Effects on Rill Erosion in the Georgia Piedmont

AbstractConsolidation and changes in surface horizon properties induced by no‐tillage may reduce soil loss to levels beyond those attributable to surface residue alone. To evaluate effects of consolidation and surface horizon modification induced by long‐term no‐tillage on rill erodibility (Kr) and critical hydraulic shear (τc), simulated rainfall and inflow were applied to plots managed under conventionally tilled monocropped soybean [Glycine max (L.) Merr.], conventionally tilled monocropped grain sorghum [Sorghum bicolor (L.) Moench], and no till double cropped crimson clover (Trifolium incarnatum L.) and grain sorghum at three sites with differing surface horizon clay contents. All surface residue was removed prior to rainfall simulation, and conventionally tilled cropping systems were evaluated in both consolidated and freshly tilled conditions. Increases in organic C from 9.3 to 12.9 g kg−1 and water‐stable aggregates from 50 to 76% induced by no‐tillage resulted in a 60 to 70% decrease in Kr for the no‐till system, compared with conventionally tilled systems. No differences in Kr were observed for the two conventionally tilled systems. No differences in τc were observed among the tillage systems. Consolidation within the conventionally tilled treatments reduced Kr by ≈60% from that observed for freshly tilled soil. The reduction was attributed to greater resistance to detachment by flow associated with soil strength increases due to consolidation. Differences in Kr and τc among the sites were small and were not readily explained by any of the soil properties evaluated. These results indicate that consolidation and modification of surface soil properties under no‐till cropping systems are important factors that contribute to reduced rill soil loss observed under no‐tillage.

Cropping Systems for Clay Soil: Crop Rotation and Irrigation Effects on Soybean and Wheat Doublecropping

(...) Field experiments were conducted from 1984 to 1989 to evaluate alternate cropping systems for a Tunica clay soil (clayey over loamy, montmorillonitic, nonacid, thermic Vertic Haplaquept) in the lower Mississippi River Valley. Specific objectives were to (i) determine the seed yield response of monocrop soybean and doublecrop soybean and wheat grown in rotation in irrigated and nonirrigated environments, and (ii) determine the increase in gross income for soybean due to irrigation. Seed yields of monocrop soybean averaged over the 6-yr test period exeeded yield from doublecrop soybean in the irrigated (41.3 vs. 32.5 bu/acre) and nonirrigated (18.0 vs. 9.2 bu/acre) environments, respectively. (...)

Cropping System Effects on Interrill Soil Loss in the Georgia Piedmont

Differential soil development and erosion in the southern Piedmont have resulted in surface horizons with variable thickness. Tillage has degraded these surface horizons and has mixed varying proportions of clayey B horizon into the plow layer, leaving soil surfaces with differing properties within the same or similar soil series. To test the effectiveness of three cropping systems in reducing interrill soil loss from these landscapes, simulated rainfall was applied to three sites of Typic Kanhapludults with differing surface horizon thickness and clay content. Each site contained plots that had been managed under conventional-tilled monocrop soybean (Glycine max [L.] Merr.), conventional-tilled monocrop grain sorghum (Sorghum bicolor [L.] Moench), and no-till double-cropped crimson clover (Trifolium incarnatum L.) and grain sorghum for 5 yr. Before tillage of the sites (consolidated state) and with residue from the previous years crop left on the surface, interrill soil loss from the no-till grain sorghum was only 12% of that from conventionally tilled soybean. Soil loss from conventionally tilled grain sorghum was 63% less than from conventionally tilled soybean. When residue was removed from the consolidated surface, soil loss from all treatments increased, and no difference in soil loss was found between the two conventionally tilled cropping systems. The no-till treatment, however, had 70% less soil loss than the conventionally tilled systems. The reduction in soil loss under no-till with residue removed from the surface was attributed to a mean increase in organic C from 10 to 23 g kg−1 and a mean increase of water-stable aggregates from 51 to 87% in the 0- to 0.015-m layer that were induced by no-tillage. After tillage of the conventional-tilled plots, interrill soil loss increased by about 45%, compared with the consolidated soils. This increase in soil loss is attributed to increased detachability of the soil after tillage. With residue removed, the three sites had similar amounts of runoff and soil loss. These results indicate that modification of surface soil properties by no-till cropping systems is an important factor influencing runoff and interrill-soil-loss reductions observed with no-tillage.

Weed Control in Soybean under Different Cropping and Tillage Systems

Studies were established in 1987 and 1988 near Brooksville and Poplarville, MS, to evaluate six weed-control systems in monocrop soybean [Glycine max (L.) Merr.] and doublecrop wheat (Triticum aestivum L.) ― soybean planted both with and without prior tillage. (...)

Relay Intercropping Soybeans into Wheat in Kansas

Research was conducted to evaluate relay intercropping of soybeans [Glycine max (L.) Merr.] into winter wheat (Triticum aestivum L.) in areas of Kansas where length of growing season and inadequate rainfall limit the productivity of doublecropped soybeans. Objectives of the study were to: (i) examine the response of soybean and wheat cultivars to solid and skip-row planting patterns, and (ii) compare soybean and wheat performance when planted in monocropped and intercropped systems across a range of environments. Winter wheat cultivars Agripro ‘Mustang’ and Pioneer ‘2157’ were planted in 10-in. rows in a solid and one-out-of-three skip-row pattern at six environments in northern and western Kansas in 1985 and 1986. All but one environment was irrigated. Soybean cultivars ‘Sparks’, ‘Sherman’, and Asgrow ‘A3127’ were planted alone or intercropped into wheat at the late boot stage. Wheat yields in skip-row patterns were 13% lower than those in monocrop solid patterns, whereas intercropping soybeans into solid-seeded wheat reduced wheat yields 4%. Intercropped soybeans yielded 72% of monocropped soybeans. Soybean yields in the two intercropped planting patterns were similar, but there was a tendency for yields in the skip-row pattern to be greater than those in the solid planting pattern. No genotype X planting pattern interactions were observed for either crop. Relay intercropping did not appear to be a viable production option in far western kansas, where soybeans were less able to compete effectively with wheat. In eastern Kansas under dryland or irrigated conditions, or under irrigated conditions in the central part of the state, relay intercropping has the potential to increase gross returns over those of doublecropping or monocrop wheat production. Intercrop gross returns were only marginally higher than those for monocrop soybean production.

Multiple Cropping Systems in Small Grains in Northeast Nebraska

Relay intercropping soybean [Glycine max (L.) Merr.] into small grain has been suggested as a way to move multiple cropping further north, or as an alternative to conventional doublecropping in the lower Midwest. Our objective was to compare conventional monocrop soybean, grain sorghum [Sorghum bicolor (L.) Moench], and forage sorghum with relay intercropping and doublecropping in oat (Avena sativa L.) or winter wheat (Triticum aestivum L.). Field experiments were conducted from 1982 through 1986 in northeast Nebraska at 42.2° latitude, 97° longitude, further north and west than the usual multiple cropping regions. Skip-row spacings every fourth drill row were left in the small grain where relay intercrops were later planted in 28- or 30-in. spacings. All doublecropping followed removal of oat or winter wheat for forage, while with relay intercropping, cereals were harvested for grain. Weed control in a relay intercropping system also was investigated. Averaged over the eight location-years, small grain yields with relay intercropping were reduced 34% compared to solid-seeded monoculture yield because of wheel traffic damage and the skip-row spacing effect. Average soybean yield with relay intercropping and doublecropping was 28% of conventional monoculture yield and relay intercropping was never superior to sequential doublecropping. Similar results were found with grain sorghum as relay intercropping and doublecrop yields averaged 15% of conventional grain sorghum. Relay intercrop and doublecrop forage sorghum yielded 37% and 54% of monoculture forage sorghum. Relay intercropping may make it possible at more northern latitudes to harvest cereal crops for grain rather than for forage as is usually done in a double-crop system, which would be advantageous for cash grain producers. Satisfactory weed control was achieved in the relay intercrop system by applying herbicide on the green wheat or oats plus row banding herbicide at crop planting. Economic analyses indicated that monocrop systems generally provided greater returns than relay intercrop or doublecrop systems. Returns in the doublecrop system were more favorable than with relay intercropping, particularly with the wheat-forage sorghum crops. Relay intercropping requires that many cultural practices be meshed for successful results.

Long‐Term Wheat, Soybean, and Grain Sorghum Double‐Cropping under Rainfed Conditions

AbstractInadequate amounts and distribution of rainfall are most often the major limiting factors to crop production in the southern Great Plains. This is especially true for summer crops, whether grown in mono‐ or double‐cropping situations. This study was conducted at the Oklahoma Vegetable Research Station, Bixby, OK from 1976 to 1987 on a Wynona silt loam soil (Cumulic Haplaquolls) with 0 to 1% slope. The objective was to determine the effects of long‐term double‐cropping on the potential for sustaining grain yields of wheat [Triticum aestivum (L.) em. Thell], soybean [Glycine max (L.) Merr.], and grain sorghum (Sorghum bicolor L. Moench) produced on the same land under rainfed conditions. Over a 12‐yr period monocropped wheat averaged 3050 compared with 2510 and 2450 kg ha−1 when double‐cropped with soybean and grain sorghum, respectively. Conventionally tilled monocropped soybean and grain sorghum and no‐till double‐cropping of both soybean and grain sorghum after wheat produced grain 11 out of 12 yr. Monocropped soybean averaged 2470 compared with 1930 kg ha−1 for no‐till double‐cropped soybean. Monocropped grain sorghum averaged 5130 compared with 4200 kg ha−1 for double‐cropped grain sorghum. During the years of near 30‐yr average rainfall amounts and distribution (5 out of 11), yields of double‐cropped soybean and grain sorghum were competitive with those of monocropped soybean and grain sorghum. These results indicate that yields of double‐cropped wheat, soybean, and grain sorghum can be sustained over long periods of time. In eastern Oklahoma double‐cropping on a deep medium textured soil produced more total grain that resulted in more efficient use of climatic, land, labor, and equipment resources when compared with monocropping.

Effect of intercropping and organic soil amendments on native VA mycorrhizal fungi in an oxisol

Abstract The effect of monocropping and intercropping of soybean and maize together with rice straw, maize straw, and pongamia leaf soil amendments on native vesicular‐arbuscular (VA) mycorrhizal fungi was studied. Intercropping stimulated proliferation of VA mycorrhizal fungi compared to monocropping with maize or soybean. In the soil cultivated with soybean there were more mycorrhizal propagules as compared to maize. Addition of organic amendments to soil increased the proliferation of VA mycorrhizal fungi. Of the three organic amendments studied, addition of pongamia leaf showed the highest increase of native mycorrhizal presence, followed by maize straw. Addition of rice straw to soil had the least stimulatory effect. Increase in the number of VA mycorrhizal propagules in soil was correlated with improved plant P uptake.

Short‐Term Crop Rotation Systems for Soybean Production

AbstractContinuous monocrop soybean [Glycine max (L.) Merr.] production has been common in Louisiana for 20 yr. This field study was undertaken to determine if, and how, short‐term crop rotations could increase soybean yield on a Providence silt loam (fine‐silty, mixed, thermic Typic Fragiudalfs) in southeast Louisiana. Eight 2‐yr rotations were evaluated in a field following 15 yr of continuous soybean production. Rotations investigated were: continuous soybean; soybean rotated with grain sorghum (Sorghum bicolor L.); soybean rotated with fallow; soybean doublecropped with winter wheat (Triticum aestivum L.); soybean alternated with winter wheat underseeded with alfalfa (Medicago sativa L.); and three additional rotations, identical to the first three listed with the addition of a winter ryegrass (Lolium multiflorum L.) cover crop. Two soybean cultivars, Centennial and Davis, with different plant parasitic nematode susceptibility, were evaluated in each rotation. Over four complete rotation cycles, Centennial consistently out‐yielded Davis. Soybean grown after either grain sorghum or fallow consistently out‐yielded soybean grown following soybean. This difference existed during favorable and unfavorable growing seasons and was greater for Davis than for Centennial. Insect populations were not high at the study site and did not have a major impact on crop yields. Soybean cyst nematode (Heterodera glycines Inchinohe) populations were higher under Davis than Centennial soybean, increased each year, and were greater with continuous soybean than with rotation. Control of cyst nematode populations appeared to be the main reason for the beneficial rotation effect observed in this study.

Seedbed Tillage and Irrigation Effects on Yield of Mono‐ and Doublecrop Soybean and Wheat on a Silt Loam

AbstractDoublecropping soybean [Glycine max (L.) Merr.] and wheat (Triticum aestivum L.) is an accepted cropping system in the Midsouth. Soybean is either planted after wheat with subsoiling or disking and harrowing, or both, to prepare a seedbed, or is seeded directly into the wheat stubble. The objective of this study was to determine the yield response of ‘Forrest’ soybean (Maturity Group V) when planted in a conventional monocrop system and in conventional and no‐till doublecrop systems following wheat. The three cropping systems were evaluated in both an irrigated and nonirrigated environment on a Dundee silt loam (fine‐silty, mixed, thermic Aerie Ochraqualf), making a total of six treatments. The six treatments were arranged in a randomized complete‐block design with four replicates, and remained in the same location for the duration of the 3‐yr study. Soybean was planted at a rate of 44 kg ha−1 in rows 1 m apart, whereas wheat was drill‐seeded at a rate of 101 kg ha−1 in rows 0.18 m apart. Average wheat yields for the four doublecrop treatments were not significantly different within or across years. The 3‐yr average was 3475 kg ha−1. Irrigated monocrop soybean produced the highest average yield of 3165 kg ha−1, whereas nonirrigated monocrop soybean and the irrigated doublecrop soybean with either no seedbed tillage or conventional seedbed tillage averaged 2491,2596, and 2740 kg ha−1, respectively, and were statistically similar. Yields from the nonirrigated doublecrop soybean with no‐till and conventional seedbed tillage were the lowest and averaged 1940 and 1909 kg ha−1, respectively. Soybean yields from all treatments in both the irrigated and nonirrigated environments decreased in a nearly linear fashion from 1984 to 1986. This was largely due to a decline in the number of seed produced, and was apparently caused by higher maximumminimum temperatures during the R1 to R5 growth periods as the experiment progressed in time.

Soybean‐Wheat Doublecropping: Implications from Straw Management and Supplemental Nitrogen'1

AbstractDoublecropped soybean [Glycine max (L.) Merr.] following winter wheat (Triticum aestivum L.) is usually planted past the optimum date for monocropped beans. To make good yield, early growth of doublecropped soybean is very important. The purpose of this experiment was to determine wheat straw leachate, wheat straw management, and supplemental N effects on soybean germination, growth, and yield. Leachate concentrations of 0, 20, and 100 g L−1 (straw to deionized water) were used for germination and radicle growth studies. Leachate concentrations of 0, 2, and 20 g L−1 were used in sand culture and the Ap horizon of Okolona silty clay (fine, montorillonitic, thermic Typic Chromudert) to study germination and early growth of soybean. A 3‐yr experiment on Okolona silty clay, consisting of six management practices and two N levels (0 and 28 kg ha−1), was used to study soybean growth and yield in the field. Management practices consisted of monocropped soybean planted near the optimum date and at the doublecropped date and doublecropped soybean planted where wheat straw was either burned, physically removed, soil‐incorporated, or left standing. Germination was not significantly affected by leachate but was reduced by late planting in the field. The 100 g L−1 leachate inhibited radicle growth, while 20 g initially inhibited but then stimulated radicle growth. The 20 g L−1 leachate inhibited early growth in the laboratory but only in the silty clay, while the 2 g L−1 leachate stimulated growth, especially in the sand. Wheat straw inhibited growth and yield in the field. Supplemental N was most effective in overcoming depressed growth and yield where straw was left on the soil surface. Early monocropped soybean produced the largest average yield, but doublecropped soybean where straw was burned produced the greatest economic returns.