Optimum Planting Date Research Articles

Conventional vs. No‐Till Corn Following Alfalfa/Grass: Timing of Vegetation Kill

AbstractProducers who plant no‐till corn (Zea mays L.) following hay or pasture are concerned about herbicide application timing and efficacy to kill perennial vegetation, plant residue effects on corn growth, and optimal corn planting date. A field study was conducted near Arlington, WI, from 1985 to 1988 to evaluate the influences of (i) conventional (CT) vs. no‐till (NT), (ii) fall vs. spring kill of perennial vegetation, (iii) late‐April vs. mid‐May planting, and (iv) three hybrid maturities on corn following legume/grass sod. Parameters measured include residue cover, soil temperature, and soil moisture after planting; corn emergence percentage; days to emergence; days to silk; grain moisture; and grain yield. Tillage by time of vegetation kill interactions were important for corn development and grain yield. Few differences were observed between fall and spring plowing in CT. For NT, however, chemically killing perennials in the spring compared to in the fall resulted in greater residue cover after planting (6–90% vs. 40%), and cooler and drier soil in the seed zone after planting. Emergence was delayed 1.5 to 4.0 d with spring‐kill NT and subsequent development was delayed throughout the growing season. Spring‐kill NT resulted in lower grain yields (−10 to −50%) compared to fall‐kill NT in 3 of 4 yr. For NT, when perennial vegetation was killed in the fall and corn was planted early, plant growth and grain yields were comparable to those for CT. Fall‐kill NT produced consistent growth and yield responses during the study years, whereas spring‐kill NT results were more variable, with poorest results in the drought of 1988.

Black Polyethylene Mulch Doubled Yield of Fresh-market Field Tomatoes

Field experiments were conducted to a) maximize total yield of fresh-market field tomato (Lycopersicon esculentum Mill.) cultivars using black polyethylene mulch (BPM), and b) increase fruit size and yield during the last 5 weeks of the production period by reducing the number of synthate sinks per plant through eliminating all flowers that appeared during this period. Unmulched treatments under trickle irrigation and multiple applications of soluble fertilizer yielded an average of 43 t·ha-1 for `Sunny' and `Pik-Rite' over the two planting dates. With BPM, total yield increased by 95% to 84 t·ha-1. Although total yield increases due to BPM over the control were highly significant in both cultivars and over the two planting dates, yield increases were higher for the early than for the optimum planting date. BPM also significantly increased early production of `Pik-Rite' but not `Sunny', and the increase in early production was more pronounced for the optimum than the early planting date. Sink reduction during the last 5 weeks of the growing season had no effect on yield or fruit weight during that period.

Planting dates and seeding rates for soft white winter wheat in eastern Ontario

A study was made to determine optimum fall planting dates and rates of seeding of soft white winter wheat (Triticum aestivum L.) in three counties in eastern Ontario. This area is considered marginal for winter survival of the crop, although yield potential is high. Plots were sown at Douglas (lat. 45°33′), Ottawa (lat. 45°23′) and Kemptville (lat. 45°00′). Four planting dates were used at Douglas and Ottawa (dates 1 to 4) and five dates at Kemptville. These were: date 1, 27 August; date 2, 10 September; date 3, 24 September; date 4, 8 October; and date 5, 22 October. Split-plot designs were used, with dates as main plots and with rates and cultivars randomized as subplots. Harvest years were between 1983 and 1987. Winter survival was generally reduced below 60% in later plantings, but survival remained high from the date 4 planting in two years at Ottawa. Grain yields were increased by early plantings. Maximum yields at Douglas were obtained from dates 1 and 2; at Ottawa and Kemptville, from dates 1 to 3. A significant advantage of date 2 planting was recorded at Kemptville. Kernel weight and test weight were reduced by late planting dates. Grain yields and winter survival were highly correlated at seven of nine location-years. At Ottawa, there was a significant yield increase from the 160 kg ha−1 seeding rate, compared with 130 kg ha−1, the currently recommended rate. Yield increases from higher seeding rates were greater at later planting dates. Cultivar effects on grain yields were frequently significant, but were less so on winter survival. The cultivar Houser produced the highest yield in five of nine location-years.Key words: Winter survival, wheat (winter), sowing date, sowing rate

Explanations for Greater Light Interception in Narrow‐ vs. Wide‐Row

Increased light interception (LI) is considered the main factor responsible for greater seed yield in narrow‐ compared with wide‐row soybean [Glycine max (L.) Merr.] culture. The objectives of this study were to determine the roles of leaf area index (LAI) and light interception efficiency (LIE) in creating greater LI in narrow‐row culture. Light interception efficiency is defined as LI/LAI. Field studies were conducted during 1987 and 1988 at optimal (May) and late (July) planting dates, with cultivars Forrest (Maturity Group V) and Centennial (Maturity Group VI), and at 100‐cm (wide) rows/normal density, 50‐cm (narrow) rows/normal density, and 50‐cm rows/high density. Plots were sampled at the V7, Rl, R3, R5, R6.5, and R6.8 developmental stages. The experiment was conducted at Baton Rouge, LA, on a Mhoon silty clay (fine‐silty, mixed, nonacid, thermic Typic fluvaquent) soil. Greater LI in narrow rows was more pronounced at late compared with optimal plantings and in Forrest, the short‐season cultivar, compared with Centennial, the full‐season cultivar. Results indicated that LAI was the dominant factor responsible for greater LI in narrow rows. Light interception efficiency played an important role in narrow‐row increased LI only when LAI was low and little mutual shading occurred. Selection criteria for cultivar‐genotype performance in narrow‐row culture at late plantings should be based on rapid leaf expansion rates (LER) and high LAI accumulation during vegetative and early reproductive development. Attainment of LAI of 3.5 to 4.0 by R1 should optimize yield. Due to a significant planting date × cultivar × developmental stage interaction for LAI, selection should be done at late rather than optimal planting dates.

Knowledge-based systems in agriculture

Using simulation models to time optimum planting dates making tactical pest control decisions using regression embedded within an expert system establishing knowledge-based irrigation schedules diagnosing plant stress with model-based reasoning systems integrating expert systems for farm-level decision support.

Branch Dry Weight in Relation to Yield Increases in Narrow‐Row Soybean

AbstractPrevious studies indicated total dry matter at R5 (TDM,R5) played a more important role in narrow‐row yield increases at late compared to optimal planting dates in soybean [Glycine max (L.) Merr.]. The objective of this study was to test the hypothesis that greater TDM(R5) in narrow vs. wide rows at late plantings stimulates yield by increasing vegetative branch dry matter (BDM,R8), branch yield components, and branch reproductive dry matter (BRDM). Field studies were conducted during 1987 and 1988 at optimal (May) and late (July) planting dates, with two commercial soybean cultivars (Forrest, Maturity Group V and Centennial, Maturity Group VI), and 100‐cm (wide) rows/normal plant population, 50‐cm (narrow) rows/normal plant population, and 50‐cm rows/high plant population. The test was conducted at Baton Rouge, LA on a Mhoon silty clay (fine‐silty, mixed, nonacid, thermic, Typic, Fluvaquents) soil. Narrow compared to wide row spacing resulted in greater BDM(R8) at both planting dates. However, increased BDM(R8) was correlated with whole plot yield (r2 = 0.92***, significant at P = 0.001) only at the late planting. Narrow‐row‐increased BDM(R8) was responsible for greater yield at this planting date because it was associated with increasing branch yield components which are reduced by late planting: branch number, total branch length, branch node number, and branch pod and seed production. In conclusion, data supported the hypothesis that the close association between narrow‐row‐increased TDM(R5) and yield at late plantings is related to increased branch dry matter and branch yield component production.

Planting Dates Related to Tuberous Root Yield, Vine Length, and Quality Attributes of Yam Bean

Abstract Plant growth and tuberous root development in yam beans (Pachyrrhizus erosus L. Urb) were investigated using a series of 2-week plantings from April to December. Decreasing daylength at time of planting initiated tuberous root development, whereas increasing daylength inhibited tuberous root development and promoted vine and leaf growth. Once tuberous root formation and flowering began, stem and leaf growth ceased. At the time of planting, the critical daylength for tuberous root formation and flowering was 11 to 12 hr. The optimum planting date in Hawaii for maximum tuber yield of 24 t·ha–1 for yam beans was found to be September to October. Tuberous root development was sigmoidal, with dry matter percentage declining from 17.5% to 9%. There was little change in tuberous root acidity or total sugars during growth. Titratable acidity was about 20 meq·g–1 fresh weight if not induced to form tuberous roots, and ≈15 meq·g–1 fresh weight in plants forming tuberous roots. Total sugar was in the range of 30 to 50 mg·g–1 fresh weight during tuberous root growth of induced plants. Total phenols in the tuberous root declined during development, whereas roots from plants uninduced to form tuberous roots had an increased level of total phenols.

Optimum sorghum planting dates in western Sudan by simulated water budgets

The Soil-Plant-Air-Water (SPAW) model previously developed and tested was used to simulate soil water budgets and crop water-stress for sorghum in the dryland region of western Sudan. Limited climatic data were combined with general observations of sorghum growth and soils to provide daily water budgets at one site for 11 years. Probability distribution of computed water budget components and water-stress index resulting from simulation of nine possible planting dates for each year were used to determine the optimum planting period for minimal crop water-stress. The water budget analysis showed a distinct optimum planting period of June 20 to July 10 with planting in early July as the most likely for best production. These results agreed well with general experience. The technique will be similarly useful for other locations, for research designs of soil water management, yield forecasting, and planning and management of agricultural resources.

Effects of bulb source, sowing date and nitrogen nutrition on the seed yield of the white dehydration onion (Allium cepaL.) in the Sudan

SummaryExperiments over three seasons at Hudeiba Research Station, Northern Region, Sudan evaluated the effects of bulb source, sowing date and nitrogen nutrition on seed yield of the white dehydration onion cv. Nasi. The bulb sources used were whole bulbs and summer multiplied bulbs (splits obtained by the vegetative propagation of bulbs that produced seeds in the preceding winter). Whole bulbs consistently gave higher seed yields than summer multiplied bulbs. The optimum planting dates were mid-October to mid-November. Nitrogen fertilization appreciably increased onion seed yield in two years out of three.

Growth and Development of the Florunner Peanut Cultivar as Influenced by Population, Planting Date and Water Availability1

Abstract The influence of planting date, plant population, and row pattern on peanut (Arachis hypogaea L.) growth and development was studied at two locations in Georgia. Twin rows were found to give faster canopy closure at high populations (212,000 plants ha-1) but not at low populations (26,500 plants ha-1). No yield differences due to row pattern were found. Increasing population increased competition for light which increased plant height and the percent of total dry matter partitioned to the stem. Population effect on yield was dependent on planting date and environmental conditions. When an optimum planting date (28 April 1983) was combined with adequate moisture (65 cm of water during season), increasing population from 30,000 to 240,000 plants ha-1 increased yield from 5290 to 6840 kg ha-1. A combination of an optimum planting date and moisture-limiting conditions (33 cm) resulted in a positive yield response of 20% as population was increased from 26,000 to 208,000 plants ha-1. Combining a late planting date (3 June 1983) with either adequate moisture (66 cm) or moisture-limiting conditions (35 cm) resulted in no yield response due to population. Late planting dates significantly reduced grade.

Planting Date Affects Survival and Height Growth of Hybrid Poplar

In this study I investigated the effects of planting date for soaked versus unsoaked cuttings of two hybrid poplar clones under irrigated versus unirrigated and weedy versus weed-free conditions. Cuttings were planted each year for 4 years. Survival at the end of the first growing season was generally greater than 90% for all planting dates. At the end of the second growing season survival for trees planted before July 16 was again generally more than 90%. However, cuttings planted from July 30 through August 27 showed a major decline in survival and survival of fall planted cuttings ranged from 6 to 90%. Mortality of late summer- or fall-planted cuttings occurred prior to the beginning of the second growing season and was attributed to frost heaving. The tallest trees were not those planted at the earliest possible dates (April in Rhinelander). Instead, the tallest trees at the end of the first and second growing seasons were those planted in early- and mid-May. This optimum planting period was the same regardless of clone, soaking, irrigation, or weed treatment. Actual optimum planting date would change with location and local climatic conditions. Some climatic indices may prove more universal in predicting when to plant. Although tentative, it appears that for best growth, unrooted hybrid poplar cuttings should be planted in soil warmer than 10 °C. Trees do not grow as well if planted immediately after soil frost leaves the ground. Key words: Energy plantations, plantation establishment, woody biomass, intensive culture, Populus.

Planting Date Effects on Seedling Development of Perennial Warm‐Season Forage Grasses. II. Seedling Growth1

AbstractPerennial warm‐season forage grasses can improve animal performance in summer when cool‐season grasses become dormant and low in forage quality. Rapid establishment of acceptable stands is a factor limiting their use. Field experiments were conducted to determine optimum planting dates of perennial warm‐season forage grasses, determine effects of planting date on seedling growth and partitioning of dry matter between roots and shoots, and compare strategies of seedling growth among perennial warm‐season grasses and an annual weed. Seeds of big bluestem (BB) (Andropogon gerardiiVitman), Caucasian bluestem (CB) [Bothriochloa caucasica(Trin.) C. E. Hubb.], indiangrass (IG) [Sorghastrum nutans(L.) Nash], switchgrass (SG) (Panicum virgatumL.), and an annual species, crabgrass (CG) [Digitaria sanguinalis(L.) Scop.] were planted at approximately 2‐week intervals from early April to late June in 1982 and 1983. A split‐plot design was used with five replications. Soil was a Mexico silt loam (fine, montmorillonitic, mesic Udollic Ochraqualf). Weeds were removed by hand shortly after their emergence in 1982, while weed emergence was prevented by methyl bromide (bromomethane) treatment in 1983. All species within a given planting data were harvested when BB reached the fifth collared‐leaf stage. Crabgrass developed more leaves, had greater leaf area, and accumulated more dry matter than did perennials showing that it would exhibit strong competition to perennials during establishment. Among perennials, SG and IG developed more leaf area and accumulated more dry matter than did CB and BB. However, CB developed more leaves and tillers than did other perennials, but leaves were small. Both SG and CB had higher leaf area ratios and lower root/shoot ratios than did IG and BB. Big bluestem required fewer days to reach the fifth collared‐leaf stage on later plantings than on early plantings, but in 1982 total dry matter accumulation at the fifth leaf stage was similar among planting dates. In 1983, however, dry matter accumulation and leaf area of BB were highest when seeds were planted on 6 and 16 May. In both years the root/shoot ratio of BB was highest for early plantings and decreased as planting was delayed. Other species showed similar trends. Dry matter production averaged over planting dates for CB, IG, and SG, respectively, was 1.2, 2.5, and 2.1 times greater than BB in 1982, and 1.6, 2.6, and 3.4 times greater than BB in 1983. Perennial warm‐season forage grasses are adapted for planting between late April and mid‐May, a period when low temperatures occur to partially chill seeds and adequate soil moisture is available to allow development of the permanent root system prior to drought conditions.

Planting Date Effects on Seedling Development of Perennial Warm‐Season Forage Grasses. I. Field Emergence1

AbstractSlow establishment of perennial warm‐season forage grasses is a problem in their utilization to improve animal production in summer when cool‐season grasses are less productive. A field experiment was conducted to determine temperature effects on field emergence, estimate base temperature required for emergence in the field, and provide insight toward optimum planting dates for warm‐season perennial forage grasses. Big bluestem (BB) (Andropogon gerardiiVitman), Causasian bluestem (CB) [Bothriochloa caucasica(Trin.) C. E. Hubb.], indiangrass (IG) [Sorghartrum nutans(L.) Nash], switchgrass (SG) (Panicum virgatumL.), and an annual species, crabgrass (CG) [Digitaria sanguinalis(L.) Scop.] were compared in a split‐plot field experiment with five replications. Unchilled seeds of each species were planted at approximately 2‐week intervals in a Mexico silt loam soil (fine, montmorillonitic, mesic Udollic Ochraqualf) near Columbia, MO from early April to late June in 1982 and 1983. Emerging seedlings were recorded frequently. The logistic function was used to fit the emergence data. No emergence data were obtained for CG since natural emergence also occurred. Maximum emergence percentage was obtained following planting on 30 Apr. and 2 June 1982, and 6 and 16 May 1983. Indiangrass had the highest emergence percentages of pure live seed with 38 and 51% in 1982 and 1983, respectively, followed by SG, BB, and CB. Survival percentage of emerged seedlings averaged about 90%, but was reduced to near 70% on late plantings when soil dried out rapidly. Entries with high emergence percentages also had their highest emergence rates (ER) at Et50(time to reach 50% of final emergence). Corrected ER index and ER50(reciprocal of Et50) were closely correlated (r= 0.99, P<0.01). Both are good indices for evaluating speed of emergence. However, ER50is based on actual measurements and has more agronomic significance and biological meaning. Base temperatures required for emergence in 1982 were estimated as 9.4, 9.9, 10.8, and 11.4 °C for IG, BB, SG, and CB, respectively. For 1983 temperatures were 10.0, 10.8, 10.4, and 9.5 °C, respectively. The data suggest optimum planting dates for these species between late April and mid‐May to maximize emergence percentage and reduce risks of high temperature and soil moisture stress.

Corn Emergence as Influenced by Soil Temperature, Matric Potential, and Aggregate Size Distribution

The effects of soil physical parameters on corn (Zea mays L.) emergence were determined in a growth chamber experiment. The treatments included three different soils, four soil temperature regimes (5–15, 10–20, 15–25, and 20–30°C), four soil matric potentials (−10, −33, −100, and −500 kPa), and seven aggregate size distributions (geometric mean diameter = 0.5, 1.0, 1.9, 3.6, 5.6, 6.8, and 11.1 mm). Corn was planted at 50 mm depth in soil aggregate mixtures contained in aluminum cylinders 152 mm in height by 76 mm inside diameter. Cylinders were placed in a growth chamber with a 10°C diurnal fluctuation and time to corn emergence was determined. Based on the growth chamber study, guidelines are developed that define best seedbed conditions for corn emergence. Time to corn emergence was influenced by the independent variables in the following order: soil temperature » soil matric potential > soil aggregate size distribution. Emergence time was related to soil temperature by a power function. Corn emergence was most rapid at the warmest soil temperature (20–30°C) when soil moisture was at or above field capacity and when aggregate size distribution corresponded to a geometric mean diameter between 1.0 and 6.8 mm. Time to corn emergence was less than 21 d for all soils and matric potentials when mean soil temperature was at least 15°C. The negative effect of low soil temperatures on corn emergence was partially compensated by high soil matric potential. A corn emergence model was developed from the relationship between percent emergence and growing degree days at the seed zone depth. Relationships between percent emergence and seed zone growing degree days were approximately the same for three soils and varied with the soil matric potential. The corn emergence model indicated a requirement of 59, 62, 67, and 76 seed zone growing degree days for 75% corn emergence at soil matric potentials of −10, −33, −100 and −500 kPa, respectively. The model was tested using corn emergence data from a field study consisting of eight combinations of three tillage and three surface residue treatments. Field data on corn emergence corresponded well with the growth chamber results obtained with constant diurnal soil temperature cycles. Heat units needed for 75% corn emergence under various tillage and residue conditions at field moisture content (matric potential = 0 to − 10 kPa) corresponded to 52 seed zone growing degree days. This corn emergence model should be useful in predicting optimum planting dates based on measured or predicted historical seed zone temperatures.

Yield Components Associated with Soybean Yield Reductions at Nonoptimal Planting Dates1

AbstractExpansion of the optimal planting dates for soybean [Glycine max (L.) Merr.) would allow for more flexibility in management to fit into weather and cropping patterns. A field study was conducted to determine yield components associated with soybean seed yield reductions at nonoptimal planting dates in the southeastern USA. This information provides insight into how seed yield reductions occur at nonoptimal planting dates. Optimal planting period in the area is between early May and early June. Cultivars Forrest, Tracy‐M, Centennial, Davis, Ransom, Bragg, and experimental genotype D77‐12480 were planted at early April (nonoptimal), mid‐May (optimal), and mid‐June (nonoptimal) planting dates in 1981 and 1982 at Baton Rouge, LA (30° N Lat) on an Olivier silt loam (fine‐silty, mixed, thermic Aquic Fragiudalf) soil. At maturity, plant samples were separated into main and branch stem components. Main and branch stem length, branch number, node number, fertile node number, pod number, pods per fertile node, seed per pod, seed size, and seed yield were determined. In all genotypes, seed yield reduction at the mid‐June planting date was related to a decline in branch seed yield associated with a reduction in number of branches and branch nodes. The decreased number of fertile branch nodes resulted in fewer branch pods and seed. Davis and D77‐12480 showed no seed yield reduction at the early April planting date. Reduced seed yield of the other genotypes at the early April planting date was related to a reduction in branch nodes and proportion of the branch nodes that were fertile. The decreased number of fertile branch nodes resulted in fewer branch pods and seed. In conclusion, seed yield reduction at nonoptimal planting dates was associated with reductions in branch rather than main stem yield components.

Grain and Forage Yields of Irrigated Second‐Crop Corn Seeded on Five Planting Dates1

AbstractCorn (Zea mays L.) is a widely‐grown summer crop in the United States. Where the growing season is of sufficient length, a second crop can be accommodated. This study identifies the optimum planting date and best of seven experimental hybrids for second crop grain and forage yields. The experimental hybrids with subtropical germplasm and/or heat tolerance were evaluated for five planting dates on a Typic Paleudult in seven to eight replications for 2 years. Previous studies considered fewer hybrids over a narrow range of planting dates. Among our plantings ranging from 1 June to 1 August, the 1 June planting achieved the maximum forage yield of 42.0 Mg ha−1 while a mid‐June planting gave an optimum grain yield of 4.40 Mg ha−1 when averaged over both years. The heat‐tolerant hybrids, C6862 and C7867, produced about two‐thirds the yields of other hybrids during 1981 with below normal growing conditions but in 1980 were fully competitive with the five hybrids having tropical germplasm when excessive heat, moisture much below normal, and insect pressure prevailed during the summer growing season. Significant interactions between hybrids and planting dates occurred for grain yields in 1980 and for grain and forage yields in 1981. The best average grain and forage yields of 4.43 and 38.5 Mg ha−1, respectively, were produced by X5802. Forage yields were much more consistent than grain yields when viewed over years or hybrids. To maximize the probability of success, summer plantings of corn should be made as early as possible, and an option to harvest as forage should always be maintained to prevent losses when adverse weather conditions suppress grain yields.

Premature Flowering in Soybean Yield Reductions at Nonoptimal Planting Dates as Influenced by Temperature and Photoperiod1

AbstractThe optimum time for soybean [Glycine max (L.) Merr.] planting in the southeastern USA is from early May to early June. Planting at other times has consistently resulted in seed yield losses which have been blamed on premature flowering induced by short photoperiods. Objectives in this study were to characterize the photoperiod response of soybean cultivars commonly grown in the southeastern USA, determine if daylength differences between optimal and nonoptimal planting dates in the southeastern USA are great enough to cause premature flowering, determine the interaction of photoperiod and temperature factors on the length of the vegetative stage, and evaluate the ability of delayed flowering genotypes to avoid yield losses at nonoptimal planting dates. The studies were conducted in both growth chambers (to provide daylengths of 12 to 16 h and temperatures of 21 to 30°C) and in the field (Aquic Fragiudalf soil). Group V cultivars had smaller increases in vegetative period as daylength increased and had a longer daylength beyond which flowering did not occur compared to Group VI, VII, and VIII cultivars. The critical daylength using constant photoperiod durations for achieving an adequate vegetative period was determined to be between 14 and 14½ h in ‘Forrest’, ‘Centennial’, and ‘Tracy‐M’, while ‘Bedford’, ‘Davis’, ‘Ransom’, ‘Bragg’, and ‘Braxton’ had a critical photoperiod between 13½ and 14 h. Based on these studies, daylength encountered by soybeans planted early (e.g., early April) is short enough to cause premature flowering. Daylength encountered by some cultivars planted late (e.g., mid‐June) is not short enough to cause premature flowering. However, daylength is short enough to cause premature flowering in most cultivars at a July planting date. Field data supported these predictions. Evaluation of delayed flowering genotypes in photoperiod and field studies showed promise for avoidance of yield losses caused by short‐day induced premature flowering. Temperature photoperiod interaction studies showed that warm temperature (27°C) compared to cold temperature (21°C) decreased the time to first flowering and had its greatest effect under short rather than long days. This effect was greater in Group VI and VII cultivars compared to Group V cultivars.

Planting Date and Cultivar Effect on Winter Rape Production1

AbstractThe optimum planting date of six cultivars of winter rape (Brassica napusL.) was determined at Moscow, Idaho on a Palouse silt loam (fine‐silty, mixed, mesic pachic, Ultic Haploxeroll). The cultivars were seeded in early August, mid‐August, late August, and mid‐September of 1978, 1979, and 1980. Data were taken on winter survival, seed yield, oil content, nodes to fist flower, reproductive nodes, and plant height. Optimum planting dates for winter rape were early to mid‐August. Both winter survival and seed yield declined when the cultivars were established in mid‐September. A significant cultivar ✕ planting date interaction for both seed yield and winter survival occurred only in the 1978–1979 trial in which plants were exposed to a minimum temperature of −30°C. Seed yield at the late planting date of this trial was closely associated to winter survival (r = 0.93**; df = 14). Oil content, nodes to first flower, reproductive nodes and plant height were not highly sensitive to planting date. The utilization of cultivars with high levels of cold tolerance could probably improve performance of late seeded rape fields. Average seed yields of 3376, 3866, and 4682 kg ha−1were observed in the 1978 to 1979,1979 to 1980, and 1980 to 1981 trials, respectively. Average oil content of individual cultivars ranged from 406 to 490 g kg−1. Based on the results of this study it appears that cultivars of winter rape recently introduced from northern Europe have excellent potential as oilseed crops in the Pacific Northwest.

Selected Determinate Soybean Cultivar Yield Responses to Row Spacings and Planting Dates1

AbstractPrevious studies to determine row spacing (RS)‐planting date (PD) effects on yield of determinate soybeans [Glycine max (L.) Merr.] in the southern USA have been conducted north of 33° Lat, and have produced conflicting results. Current data on the effects of these planting variables are not available for a large portion of the Gulf Coast area that now supports a large and rapidly expanding soybean industry. The objectives OP this experiment were to study: 1) the effects of selected RS and PD on yield of selected cultivars of determinate soybeans; 2) the interaction of RS with PD; and 3) the interaction of cultivars with RS and PD.Five cultivars, ‘Forrest,’ ‘Davis,’ ‘Lee 74,’ ‘Centennial,’ and ‘Bragg’ were planted in RS of 25, 50, and 100‐cm on 6 PD between 15 April and 1 July in 1976, 1977, 1978, and 1979. The field plots were located on a Mhoon silty clay soil (Typic Fluvaquent). Averaged over years, the five cultivars evaluated produced significantly higher yields when grown in 25 and 50‐cm RS compared with the 100‐cm RS. The interaction between cultivar and RS was significant due to variability among cultivars in the yield increase when RS was reduced; 3 q/ha with Davis and Bragg, 4 q/ha with Lee 74, and 6 q/ha with Forrest and Centennial. The size of yield increases resulting from reduced row spacing was relatively consistent across PD. Because lower yields were recorded at all three RS at nonoptimum PD the yield increases, when expressed as a percentage of the yields obtained in 100‐cm rows, were larger at the nonoptimum dates, however. Optimum PD was not affected by RS but differed among cultivars. Forrest and Lee 74 had highest yields when planted on 15 May while the other three cultivars had similar yields at PD from 1 May to 1 June. Results indicated that significantly higher yields are possible with current determinate cultivars when both RS and PD are selected for individual cultivars.

Development of a Model for Use in Maize Replant Decisions1

AbstractReduced stands after planting may force maize (Zea mays L.) producers to consider the feasibility of replanting. The objective of this research was to develop guidelines for replanting decisions based on planting date, hybrid maturity class, population density, and plant distribution. Maize was planted at central and northern Illinois locations in 3 successive years. In each experiment adapted and early season hybrids were planted at three dates ranging from late April through early June. Plots were thinned to final densities of 30,890; 41,180; 51,480; and 61,780 plants/ha. The three lower densities were distributed uniformly within the row, with small gaps ranging from 0.42 to 0.85 m long, and with large gaps 1.5 m long.Adapted hybrids tended to yield more than early season hybrids when planted before 20 May, but the overall effects of hybrid maturity class were minor. Regression analysis indicated that the optimum planting date was near 6 May, and planting either 2 weeks before or after 6 May reduced yields by less than 5%. However, a rapid decrease in yield due to planting date occurred when planting was delayed past 20 May. Averaged across environments, the interaction of planting date with density and plant distribution was not significant. Before mid May the major factors to consider in replant situations are density and plant distribution within the row. After mid May, calendar date increases in importance. A model for uniformly spaced plants is presented that predicts yield on the basis of planting date and population density. Compared to uniform spacing within the row, small gaps reduced yield by an average of 1.9% while large gaps reduced yield by 5.4%.