Soybean Stands Research Articles

Simulation of moderate levels of slug injury to soybean

Slugs became a significant problem in soybean, Glycine max (L.) Merrill, in the eastern USA cornbelt as growers adopted conservation tillage production practices. Little information is known about the consequences from slug injury on soybean growth and yield. This study examined the effects of moderate levels of simulated slug injury, i.e., stand loss and defoliation to the unifoliate and 1st trifoliate leaflets, to the crop. Soybean stands were established at levels at and above those requiring replanting, and defoliation was done by removing 50% of the unifoliate and 1st trifoliate leaflets. Plant growth measurements were taken during the summer and yields recorded. The greatest impact on yield was from reduced plant stands, with 50% defoliation of the unifoliate leaflet having a much lesser impact. There was little effect from injury to the 1st trifoliate. Results suggest that growers should be most concerned when slug injury causes reduced stands and from defoliation to the unifoliate leaflet. Early planting that allows for maximum growth of the plant before slugs become active in later spring would lower the potential for economic losses.

An analytical model for estimating canopy transpiration and carbon assimilation fluxes based on canopy light-use efficiency

We develop a simple, analytical model for canopy resistance to canopy–atmosphere gas exchange that is well suited for incorporation into regional-scale land-surface parameterizations. This model exploits the conservative nature of canopy light-use efficiency (LUE) in carbon assimilation that is observed within broad categories of plant species. The model paradigm assumes that under standard environmental conditions, a canopy will operate at the field-measured LUE, but will deviate from this standard efficiency as conditions change. Effective LUE estimates generated by the model respond to variations in atmospheric humidity, CO 2 concentration, the composition of solar irradiation (direct versus diffuse beam fractions), and soil moisture content. This modeling approach differs from scaled-leaf parameterizations in that a single estimate of nominal canopy LUE replaces both a detailed mechanistic description of leaf-level photosynthetic processes and the scaling of these processes from the leaf to canopy level. This results in a model that can be evaluated analytically, and is thus computationally efficient and requires few species-specific parameters. Both qualities lend themselves well to regional-and global-scale modeling efforts. For purposes of testing, this canopy resistance submodel has been embedded in the Atmosphere–Land Exchange (ALEX) surface energy balance model. The integrated model generates transpiration and carbon assimilation fluxes that compare well with estimates from iterative mechanistic photosynthetic models, and with flux measurements made in stands of corn, soybean, prairie grasses, desert shrubs, rangeland, and black spruce. Comparisons between modeled and measured evapotranspiration (LE) and carbon assimilation ( A c) fluxes yield mean-absolute-percent-differences of 24% (LE) and 33% ( A c) for hourly daytime fluxes, and 12% (LE) and 18% ( A c) for daily-integrated fluxes. These comparisons demonstrate robustness over a variety of vegetative and climatic regimes, suggesting that this simple analytical model of canopy resistance will be useful in regional-scale flux evaluations.

A Markov chain model of canopy reflectance

Markov properties of stand geometry are incorporated into an analytical multispectral canopy reflectance model. The correlation of leaf positions in adjacent layers significantly influences the gap probability in a stand and, consequently, the canopy reflectance (CR) and its angular distribution. The sensitivity analysis demonstrated that the effect is greatest on the angular distribution of multiply scattered radiation. Validation of the new CR model that considers the Markov stand geometry demonstrated an improved agreement between model calculations and measured directional reflectance distribution of near infrared (NIR) reflectance for barley and soybean stands. As a consequence, inversion of the new model in the NIR spectral region and in two spectral bands simultaneously allowed significantly better estimation of the leaf area index of a stand than the Nilson-Kuusk model which assumes a Poisson stand geometry.

242 WATER, NUTRIENT, AND ACID REQUIREMENTS FOR CROPS GROWN HYDROPONICALLY IN A CELSS

Requirements for water, nutrient replenishment and acid (for pH control) were monitored for stands of wheat, soybean, potato, and lettuce grown in a recirculating hydroponic culture using a modified 1/2 Hoagland solution with NO3-N. Water use at full canopy cover for all crops ranged from 4 to 5 L m-2 day-1. When averaged over the entire crop cycle, nutrient stock solution (∼0.9 S m-1) use varied from 0.2 L m-2 day-1 (lettuce: to 0.75 L m-2 day-1 (wheat), while acid use varied from 6 mmol m-2 day-1 (lettuce and soybeans) to over 40 mmol m-2 day-1 (wheat). Water-per unit biomass was highest for soybean and lettuce (0.3 to 0.4 L g DW), and least for wheat and potato (0.15 L g DW). Nutrient replenishment per unit biomass was highest for lettuce, 34 mL g-1 DW, with other crops ranging from 21-26 mL g-1 DW. Acid requirements were highest for wheat, 1.2 mmol g-1 DW, and lowest for potato, 0.7 mmol g-1 DW. On a PAR basis, acid needs were highest for wheat, 0.6 mmol mol-1 photons, with all other crops near 0.4 mmol mol-1. Acid data suggest that wheat nutrient uptake favors anions more strongly than the other species, or that more nitrate loss (e.g., denitrification) may occur during wheat growth.

ETHYLENE EVOLUTION BY CROP STANDS GROWN IN A CLOSED, CONTROLLED ENVIRONMENT

Ethylene concentrations were monitored using gas chromatography (GC/PID) throughout growth and development of wheat, soybean, and lettuce stands grown hydroponically inside a large, closed growth chamber (20 m2 area, 113 m3 vol.). For wheat (cv. Yecora Rojo), ethylene concentration increased from < 10 ppb to about 120 ppb at about 28 days after planting (pre-anthesis) and then declined sharply over the next 4 weeks to a plateau of about 10 ppb during canopy maturation and senescence. A similar pattern of evolution was measured for soybean stands (cv. McCall), with peak concentrations of 40 to 70 ppb occurring near 50 days after planting. Unlike wheat, a slight increase in ethylene was noted in the latter stages of soybean stand senescence. For lettuce stands (cv. Waldmann's Green), ethylene increased slowly to 10 to 15 ppb by 24 days after planting, and then rose sharply to 40 ppb by 28 days, when plants were harvested. Data will be used to define ranges for phytotoxicity studies and to project atmospheric contaminant control needs for tightly closed plant growth systems.

Soybean Production as Affected by Tillage in a Corn and Soybean Management System: II. Seed Treatment Response

While fungicide seed treatment is needed for crops such as corn (Zea mays L.) and cotton (Gossypium hirsutum L.), its importance is not as well defined in soybean [Glycine max (L.) Merr.]. This study evaluated the effectiveness of seed treatment on eight soybean cultivars grown in a corn-soybean rotation with five tillage systems. Nontreated soybean seed was compared with seed treated with either captan (N-[(trichloromethyl)thio]-4-cyclohexene-1,2-dicarboximide) or metalaxyl (N-(2,6-dimethylphenyl)-N-(methoxyacetyl)alanine methyl ester) in no-till (NT), ridge-till (RT), fall moldboard plow (MP), fall chisel plow (CP), and fall Paraplow (PP) tillage systems at Morris, Lamberton, and Waseca, MN. Tillage did not affect response to seed treatment at any location. Seed treatment affected soybean performance at Waseca only in 1986 where captan and metalaxyl seed treatments significantly enhanced soybean stands and increased soybean yield of ‘Elgin’ and ‘1677’. At Lamberton, both seed treatments improved stand and yield of Elgin in 1986. Poor germinability and seedling vigor of the Elgin seedlot likely resulted in its large response to seed treatment. The cultivar 1677 appeared to be very susceptible to seedling diseases and thus responded to seed treatment in 1986 at Waseca when soil was relatively wet for 6 wk after planting. Based on the results obtained in these studies, seed treatment generally is not necessary to obtain adequate stands and high yields in soybean. Response to seed treatment was related to seed quality and cultivar susceptibility to seedling disease rather than to tillage practices.

Soybean Growth Responses and Intraspecific Competition from Simulated Seedcorn Maggot Injury

AbstractThe consequences of early‐season insect injury on subsequent plant development often are obscure. Further, such injury may produce intraspecific competition between injured and uninjured plants. We examined these issues by studying the impact of simulated seedcorn maggot (SCM) [Delia platura (Meigen) (Diptera: Anthomyiidae)], injury to soybean [Glycine max (L.) Merr.], in field studies from 1983 to 1986 in Iowa. Simulated SCM injury includes plant density (simulating stand reductions) and normal to Y‐plant ratios (simulating various proportions of plumule injury). The Y‐plants are plants that have had the plumule destroyed and subsequently develop two main stems. Our objectives were to describe how simulated SCM injury affected: (i) development of soybean stands, individual normal plants, and individual Y‐plants, and (ii) intraspecific competition between normal and Y‐plants. Higher crop growth rates (CGRs) and leaf area indices (LAIs) were associated with higher plant densities. Generally, plumule‐injured plants were more affected by plant density than uninjured plants. Examinations of competition between uninjured and plumule‐injured plants indicated that uninjured plants were competitively superior to plumule‐injured plants. Competitive interactions were influenced by plant density, Phenological delay associated with plumule injury contributed to height differences between uninjured and injured plants, which led to substantial differences in leaf area, number of nodes, and other developmental parameters between injured and uninjured plants. Consequently, unequal competitive ability between uninjured and injured plants was identified as a major consequence of plumule injury.

Cocklebur and Velvetleaf Interference with Soybean Grown at Different Densities and Planting Patterns

AbstractTwo common problems in soybean [Glycine max (L.) Merr.] fields are weeds and incomplete crop plant stands, and these problems may interact in their influence on soybean yield. A study was conducted in 1986 and 1987 to examine whether weed interference was influenced by soybean plant stand and planting pattern. In full stands (26 plants/m row) of soybean, common cocklebur (Xanthium strumarium L.) and velvetleaf (Abutilon theophrasti Medic.) spaced 1.5 m apart in the row decreased soybean yields 29 and 34%, respectively, in 1986 and 19 and 15%, respectively, in 1987. Decreasing the soybean stand 20, 40, and 60% without weeds resulted in yield losses of 8, 18, and 34% (across both years) in evenly spaced soybean plants, while similar stand losses caused by removal of sections of row resulted in yield losses of 14, 28, and 35%, across both years, respectively. When common cocklebur and velvetleaf were present, percentage yield decreases due to stand losses were similar to those in the weedfree treatment; there was no interaction between weed treatment and stand loss treatments. Light interception by the canopy, measured only in 1987, was higher in weedy plots than in weedfree plots, with the additional interception presumably due to the weeds. Common cocklebur produced more dry weight than did velvetleaf, but the two weeds had similar effects on soybean yield. These results indicate that, while weed competition and stand loss can both cause substantial yield losses in soybean, the effect of these factors is additive when both occur in the same field, and weed growth is not greatly enhanced by decreased competition resulting from loss of soybean stand.

Yield Compensation for Stand Deficiencies by Determinate and Indeterminate Growth‐Habit Soybean

AbstractSoybean [Glycine max (L.) Merr.] stands that emerge poorly are often replanted without taking into consideration the yield compensating ability of the plant in the field. This study was done to determine if compensation for yield in deficient soybean stands is influenced by the growth habit (determinate versus indeterminate). Gaps imposed at or before stage V2 were used to generate stand deficiencies. Compensation for yield in stands having gaps of fixed sizes was measured in the indeterminate cultivar Cumberland and the determinate cultivars Gnome, Sprite, and Pixie in 1981 and 1982. Three seeding dates were used in trials conducted on a Flanagan silt loam (Aquic Argiudoll) at Urbana, IL, and on a Cisne silt loam (Mollic Albaqualf) at Brownstown, IL. Compensation in yield for missing plants was found in both the rows with gaps and in adjacent full rows. Grain yields in gapped rows, having stand reductions equal to 63%, averaged 1614 kg/ha, or 55% of the control plot yield of 2923 kg/ha. Yields in adjacent full rows increased as much as 19% in response to the 63% stand reduction in gapped rows. In 1983, the determinate cultivar Sprite and the indeterminate, Asgrow A3127, were compared under farm field conditions where random gaps of various size were imposed as treatments. A single timely seeding was used. High levels of yield compensation for missing plants were again measured. Grain yields resulting from 60% stand reductions were only 25% less than those of full stands. Analysis of variance was used to evaluate gap x cultivar responses. The lack of a cultivar × gap interaction found in the analysis of variance suggested compensation for irregular or gap‐filled stands was not influenced by the growth habit of the soybean.

Effects of Soybean Stand Reduction and Phytophthora Root Rot on Yield

Effects of Soybean Stand Reduction and Phytophthora Root Rot on Yield

Influence of Soil Compaction on Soybean Stand, Yield, and Phytophthora Root Rot Incidence1

AbstractSoil physical factors can influence plant growth and disease incidence. The objective of the present research was to determine if soybean [Glycine max(L.) Merr.] stand establishment and Phytophthoraroot rot incidence were influenced by soil compaction under Illinois growing conditions. Field experiments were conducted for 2 years (1983 and 1984) on a Drummer silty clay loam soil (fine‐silty, mixed mesic Typic Haplaguoll). Plots were compacted once in the spring of each year after the first disking by driving a tractor over the plots. Soil bulk density was increased significantly in both years by tractor compaction. In both years, initial stands and final stands for ‘Corsoy’, (susceptible to Phytophthora megaspermaDrechs. f.sp. glycineaKuan and Erwin) were reduced in the compacted plots. In 1983 there was no effect of soil compaction on initial and final stands for ‘Corsoy 79’ soybeans (resistant to races 1,2,3,6,7,8, and 9 of P. megaspermaf.sp. glycinea) but in 1984 final stands were lower with Corsoy 79 on compacted plots. The number of plants killed by the fungus was significantly increased by soil compaction for Corsoy in both 1983 and 1984. In 1983 there was no difference in seed yield of Corsoy 79 in compacted and noncompacted field plots. In both years the yield of Corsoy was significantly lower in the compacted plots. There was also a significant difference in yield between Corsoy and Corsoy 79 in both years in the compacted plots.

Distribution of Screwworms (Diptera: Calliphoridae) Relative to Land Use and Topography in the Humid Tropics of Southern Mexico

The distribution of adult screwworms ( Cochliomyia hominivorax [Coquillet]) relative to land use and topography was studied on the humid Pacific coastal plain of southern Chiapas, Mexico. Native screwworms were always more abundant when windoriented traps, baited with the attractant swormlure-4, were upwind and within 150 m of warm-blooded animals. Densities of flies were greatest in ecotones that included pastures and any tall vegetation. Flies also were abundant near houses with domestic animals. Flies were least common in low-profile stands (<0.75 m high) of young banana, young soybean, and pastures without animals. These data indicate that habitat preferences exist, that they are easily identifiable by land use, and that trapping efficiency can be improved by placing traps near and upwind of warm-blooded animals. The habitat preferences of sterile screwworms (strain M-83), released from a central ground release station, were similar to those of native flies within the study area; sterile and native males showed similar distributions to females. The data indicate that the dispersal of sterile flies within 2.1 km of the release point was adequate, and that current flight lane patterns for aerially releasing sterile screwworms appear adequate in southern Mexico.

Adult Seedcorn Maggots in Soybeans Relay Intercropped into Winter Wheat

Adult seedcorn maggot, Delia platura Meigen, populations were determined in 1980 and 1981 in relay intercropped soybeans, in soybeans for which a wheat cover crop had been disked into the soil, and in soybeans planted without wheat. Influence of planting date on seedcorn maggot populations also was evaluated for early-, mid-, and late-May plantings. Seedcorn maggot populations were not increased in relay intercropped soybeans in either year, but were 8.5 times greater in wheat disked areas compared with soybeans planted without wheat. Fewer seedcorn maggots were collected in late May compared with early and mid-May in both years. Reductions in soybean stands, caused by seedcorn maggot, occurred only in 1981.

Soybean Stand Establishment and Yield as Affected by Herbicides and Cultural Practices1

AbstractWhen reduced soybean (Glycine max (L.) Merr.) stands occur, herbicides are often blamed for the problem. The object of this research was to determine if metribuzin [4‐amino‐6‐tert‐butyl‐3‐(methylthio)‐as‐triazin‐5 (4H)‐one] and/or vernolate (S‐propyl dipropylthiocarbamate) herbicides interact with other cultural variables to reduce stands and grain yield. Cultural variables researched in the field included soybean seed vigor, cultivar, planting depth, planting date, and surface versus incorporated herbicide application. In field experiments on a Typic Haploquoll soil herbicides were applied at slightly higher than recommended rates, and soybeans were seeded in 75‐cm row widths at a density of 350,000 seed/ha.In all experiments visual symptoms of herbicide leaf damage occurred, but herbicide treatments had minor effects on stand establishment and grain yield. In contrast, several other variables significantly reduced stands and grain yields. Differences in seedbed condition created by different planting dates altered stand establishment. Seed lots low in seed vigor (as measured by cold test germination) resulted in reduced stands and in some situations reduced grain yields when compared with high vigor seed sources. Compared with a 1.9 cm planting depth, a 3.8 cm planting depth reduced stands in crusted seedbeds. In contrast, the shallow depth caused stand problems in a dry seedbed. Of the cultural variables affecting stand establishment and grain yield, none exhibited a significant interaction with herbicide treatment. In a greenhouse study, extremely high vernolate rates were more detrimental to emergence of low vigor than high vigor seed. Our data suggests that even when visual symptoms of herbicide injury occur, cultural variables such as seedbed conditions, seed quality, and minor differences in planting depth are often the major variables causing stand problems.

Studies on Utilization of Solar Radiation by Crop Stands

If we want to know the strictly meaning utilization efficiency of solar energy by crop plants, it is necessary to make clear absorption rates of photosynthetically active radiation (PhAR), because they can never convert any radiation except PhAR to the energy for their growth. Also for researching the development of solar energy utilization by crop stands, it would be useful to compare the various types of crop stands in conversional efficiencies of solar radiation. For this purpose, rice (var. Tyotama) and soybean (var. Tamanishiki) plant populations were used to study. In order to obtain the absorption rates of short wave radiation and PhAR in the stands, following items of radiant energy were measured; incident energy to the top of canopy, albdo of canopy and transmissive energy into the ground surface. On the other hand, to estimate photosynthetically fixed energy by the stands, total dry matter produced and its combustion energy were measured on successive growing period.Results are summarized as follows:1. Rate of energy absorption increased with leaf area index (LAI). The absorp tion rate of soybean stand was higher than rice at low LAI, but the maximum absorption rate at high LAI was not different in both stands. These values were 73% for short wave radiation and 88% for PhAR (fig. 4).2. Combustion energy per unit dry weight of whole plant was little changed throughout growing season. Combustion energy of soybean was higher than that of rice. These averaged values were 3676 and 4165 cal/g for rice and soybean plants respectively (table 4).3. Utilizational efficiencies of radiation (Eueff), which were obtained from dividing the fixed energy into stand by incident solar energy onto canopy, were low at early growing stage. There was no difference in Eueff between rice and soybean stands. But later, Eueff increased and reached maximum, then decreased gradually. The maximum value of Eueff of the PhAR were estimated to be 4.5-5% for rice stand and 3-3.5% for soybean (fig. 6).4. Conversional efficiencies (Eoeff), which were obtained from dividing the fixed energy in stand by solar energy absorbed into the canopy, were almost constant at early stage but decreased progressively at later for both crop stands. Eoeff of rice stand were always higher than those of soybean. The mean value of Eoeff of PhAR in early sage is 5-6% for rice stand and 3-4% for soybean (fig. 7).

Field Comparison of Twelve Dinitroaniline Herbicides

The effects of twelve substituted dinitroaniline herbicides on soybeans [Glycine max(L.) Merr., ‘Corsoy’], velvetleaf (Abutilon theophrastiMedic.), and giant foxtail (Setaria faberiHerrm.) were evaluated under field conditions in 1971 and 1972; and the relative persistence of herbicide residues in soil was determined by field bioassay. Of the herbicides tested, dinitramine (N4,N4-diethyl-α,α,α-trifluoro-3,5-dinitrotoluene-2,4-diamine), trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine), and benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2, 6-dinitro-p-toluidine) reduced soybean stands in 1971. Only dinitramine reduced soybean stands in 1972 when applied in low rates, but all of the herbicides except CGA-10832 (N,N-propyl-N-cyclopropylmethyl-4-trifluoromethyl-2,6-dinitroaniline) and chlornidine [N,N(2-chloroethyl)-2,6-dinitro-4-methylaniline] reduced soybean stands at high rates. Overall, oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide), dinitramine, and BAS-3921 H[N-propyl-N-(2-chloroethyl)-2,6-dinitro-4-trifluoromethylaniline] provided the best velvetleaf control; while trifluralin, benefin, CGA-10832, and BAS-3921 H produced the most satisfactory giant foxtail control. In 1972, residues of seven of the herbicides caused injury to oats planted over the plot area 355 days after the original herbicide application. The greatest oat injury was caused by trifluralin and oryzalin. Oats were not injured, however, from dinitramine residues when planted only 75 days after the herbicide application.

Effects of Repeated Applications of Herbicides on Soybeans

Repeated postemergence treatments of 3-[p-(p-chlorophenoxy)phenyl]-1,1-dimethylurea (chloroxuron), 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea (linuron), or 2-sec-butyl-4,6-dinitrophenol (dinoseb) can be applied to soybeans (Glycine max (L.) Merr.) without severe injury to the foliage throughout the growing season. However, multiple treatments of 2,4-bis(isopropylamino)-6-(methylthio)-s-triazine (prometryne) resulted in more foliar injury early in the season than from similar treatments of chloroxuron, linuron, or dinoseb. Chlorotic veination appeared in the upper leaves of soybeans treated with prometryne late in the season, and injury was greater from multiple applications than from a single application. Chloroxuron and dinoseb resulted in stem injury which increased with repeated applications. Seed yields were lower from plots treated with repeated applications of prometryne compared with untreated plots or plots treated with a single application. Multiple applications of chloroxuron, linuron, or dinoseb did not affect seed yields. Soybean stands were significantly lower in 1 year from three or four applications of linuron and four applications of prometryne compared with fewer applications of each herbicide. Seed quality was best in dinoseb-treated plots and poorest in prometryne-treated plots regardless of the number of applications.

Influence of “Pop‐up” Fertilizers on Soybean Stands and Yield1

AbstractBoth liquid and granular fertilizers containing nitrogen, phosphorus, and potassium were applied directly in the seed zone of soybeans (Glycine max (L.) Merrill) at planting. An application of 35.5 liters/ha (3.8 gallons/acre) of a liquid 5.0‐8.8‐4.2 (N‐P‐K) “popup” fertilizer reduced stands by 57.8% and yields by 20.3%. Plant stands were reduced when only 11.2 kg/ha (10 lb/acre) of a granular 10‐15‐5 (N‐P‐K) “popup” fertilizer was applied in the seed zone at planting.

Combinations of Herbicides and other Pesticides on Soybeans

The growth of soybean (Glycine max (L.) Merr.) seedlings was retarded when treated with either methyl 3-amino-2,5-dichlorobenzoate (amiben methyl ester) or α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) when compared with soybeans treated with either 3-[-p-(p-chlorophenoxy)phenyl]-1,1-dimethylurea (chloroxuron) or 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea linuron. Seedling growth of soybeans also was retarded when treated with amiben methyl ester alone or applied in combination with O,O-diethyl S[2-(ethylthio)ethyl] phosphorodithioate (disulfoton). Insecticides did not influence growth of soybeans. Linuron applied in combination with O,O-diethyl S-[(ethyl-thio)methyl] phosphorodithioate (phorate). or methyl-N-[(methylcarbamoyl)oxy] thioacetimidate (methomyl) and amiben ester applied in combination with phorate produced significantly lower seedling vigor during only 1 year than when each pesticide was applied alone. Soybean stands were significantly lower only in 1 year when linuron was applied in combination with methomyl. None of the pesticides applied alone or in combination caused significant differences in date of maturity, lodging, seed yield, seed size, or seed quality during either year.

Tillage and Residue Management Practices for Soybean Production in a Soybean‐Small Grain Rotation1

abstractManagement of oat straw residues and tillage practices for soybean production in an oat‐soybean rotation were studied. The effects of tillage practices on soybean yields were not significant. Burning the oat straw before planting soybeans had no significant effect on yields. Fertilization of soybeans after growing the oats did not increase bean yields. Tillage and residue management had no marked influence on soil temperatures and available moisture. Soybean stands were somewhat larger if the oat straw was burned or moved from the seed zone. Properties of the lister‐plant‐tilled and disk‐harrow‐tilled soils were more favorable for soybean growth than those of the turnplow‐tilled soils, although this was not reflected in soybean yields.