Search

CITATION: Haarhoff, S. J. & Swanepoel, P. A. 2019. Narrow rows and high maize plant population improve water use and grain yield under conservation agriculture. Agronomy Journal, 112 2):921-931, doi:10.1002/agj2.20085.

Anhydrous ammonia (AA) is an important N fertilizer in the United States, and with large farming operations rapid application is needed. This study evaluated the impact of AA application timing and N rates when applied with a high speed low draft (HSLD) or aconventional till knife injection (CTKI) on corn (Zea mays L.) production in no-tillage fields. The study was conducted at sites located in Illinois, Iowa, and Kansas from 2007 to 2009. The experimental design was a split-plot factorial arrangement of application method, timing (fall; spring pre-plant, SP; and sidedress, SD), and five N rates. Fall AA application was least efficient (mean 55 kg N ha–¹ higher optimum N and 2% lower grain yield, GY), with SP and SD equivalent. The HSLD was comparable to the CTKI with most applications, except when high N rates (180 and 225 kg N ha–¹) were applied SP. For these treatments AA injury reduced plant population (PP), early season growth, canopy normalized difference vegetative index (NDVI), and GY. Seedling injury did not occur with any N rate or timing with the CTKI. Shallow AA placement at high speed with the HSLD can provide a viable alternative to traditional deeper knife injection when conditions are suitable for AA application and positioning avoids corn seedling injury. Anhydrous ammonia application with the HSLD, however, should be avoided where high SP AA rates may be placed directly under future corn rows.

Published in Agron. J. 106:1051–1059 (2014) doi:10.2134/agronj13.0435 Copyright © 2014 by the American Society of Agronomy, 5585 Guilford Road, Madison, WI 53711. All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. ABSTRACT The agronomic responses of three contrasting soybean [Glycine max (L.) Merr.] varieties to plant populations were examined in two distinct agro-ecological locations (at Samaru Zaria and Samaru-Kataf), both in the Guinea savanna of northern Nigeria in 2009, 2010, and in 2011 growing seasons. Three soybean varieties: TGx1835-10E, TGx1904-6F, and TGx1448-2E differing in maturity duration (early, medium, and late maturing, respectively), were evaluated at four plant populations (266,700, 333,300, 533,300, and 666,700 plants ha–1) using a split plot arrangement in randomized complete block design with three replications. The plant populations were the main plots, whereas varieties were subplots. The proportion of intercepted photosynthetically active radiation (IPAR) and leaf area index (LAI) increased with increasing plant population at both locations, indicating that high leaf area indices and high degree of canopy closure at higher plant population intercepted more light than the canopy at lower population and subsequently resulted in relatively high grain and fodder yields. At both locations, optimum plant populations ranged from 533,300 to 666,700 plants ha-1 across the years. The northern Guinea savanna location (Samaru Zaria) produced more pods m-2, grain yield, and fodder at higher plant populations than that at the southern Guinea savanna (Samaru-Kataf). Varieties TGx1448-2E and TGx1904-6F intercepted higher proportion of IPAR had higher LAI and produced a greater number of pods m-2, seeds m-2, grain yield, and fodder than TGx1835-10E at both locations in years of good rainfall. These data suggest that soybean yields in the Guinea savanna of northern Nigeria can be increased using higher plant populations than those currently recommended.

The widespread adoption of glyphosate [N-(phosphonylmethyl)-glycine]-resistant soybean [Glycine max (L.) Merr.] and the increased cost of soybean seed have generated interest in determining the minimum plant population needed for maximum yield. The objective of this study was to determine yield and economic return responses to plant population for normal and late planting dates. Cultivars with relative maturities of 2.8 to 4.9 were planted at five seeding rates (43,000 to 560,000 seeds ha -1 ) in May and/or June in 38-cm rows during 2003 to 2005. The effect of plant population on both yield and economic return was explained with a variation of a Mitscherlich equation. Optimum plant population (OPP) and economically optimum plant population (EOPP) were defined as those resulting in 95% of the estimated yield or estimated economic return, respectively, at the maximum plant population. Optimum plant population ranged from 108,000 to 232,000 plants ha -1 for May planting dates and 238,000 to 282,000 plants ha -1 for June planting dates. Economically optimum plant populations were 7 to 33% less than OPPs. Complete canopy cover at R1 produced maximum yield in 8 of 10 comparisons. These results suggest that seeding rates below those that are currently recommended could lower seed costs without reducing yield.

Integrated management strategies are required to minimize ascochyta blight, a fungal disease caused by Ascochyta rabiei (Pass.) Labrousse [teleomorph, Didymella rabiei (Kovachevski) v. Arx] in chickpea (Cicer arietinum L.). This study determined the effect of cultivars varying in plant architecture and plant population density (PPD) on the severity of ascochyta blight Four desi chickpea (with pinnate leaves) and four kabuli chickpea (two with pinnate leaves and two with unifoliate leaves) were grown at 25, 36, 44, 53, and 62 plants m -2 (actual counts 3 wk after initial seedling emergence) at Swift Current from 2002 to 2005 and at Saskatoon in 2004 and 2005. Site-years had a significant effect on ascochyta blight epidemics, with the highest severity at Swift Current in 2005 and lowest at Saskatoon in 2004. Across site-years, ascochyta blight was most severe on 'Evans', followed by 'CDC Xena', and lowest on '222B-11'. Cultivars with pinnate leaves had lower blight severity than those with unifoliate leaves during all growth stages. At the late-pod stage, severity in cultivars with pinnate leaves averaged 15% compared with 48% in unifoliate cultivars. Kabuli cultivars had higher severity than desi cultivars throughout the growing season, and at the late-pod stage, severity was 13% for the desi and 33% for the kabuli. There was a significant interaction between cultivar and PPD for blight severity. Ascochyta blight increased as PPD increased for the majority of the cultivars tested, with a few exceptions. Site-year accounted for the largest portion of the treatment variance in blight severity (69%), followed by cultivar type (25%), and then PPD (6%). Increasing PPD consistently increased seed yield per unit area, despite more disease on plants at higher PPD. Identifying optimum plant populations for groups of cultivars with similar plant architecture should be a component in an integrated strategy to minimize ascochyta blight in chickpea.

The effects of fungicide seed treatments on seeding rate, location, simulated rainfall at emergence, time of planting, and seed quality were analyzed for soybean [Glycine max (L.) Merr.] in this study. Variation in plant emergence allowed estimation of economically optimal seeding rates and partial returns (PR = Gross revenue -Seed cost) across seed treatment options. Study results proved a single seed treatment to be superior across most study conditions. In fact, a comparison of optimally treated to untreated seed revealed that a seemingly insignificant input in terms of cost (

Subsurface drainage is an important water management practice on naturally poorly drained soils, and recommendations for appropriate drain spadngs for particular soils continue to evolve. The objective of this long-term study was to measure corn (Zea mays L.) growth and yield as affected by subsurface drain spacing on a soil that was traditionally not tile drained. Three drain spacings (5, 10, and 20 m) were compared with a nondrained control (40 m) for plant population, grain yield, and moisture content over a 10-yr period on a low-organic-matter silt loam soil. In addition, corn populations, heights at 4 and 8 wk, yield, and moisture were measured with distance from the drain for the 5-, 10-, and 20-m spacings. Significant distance effects occurred more frequently for the 20-m spacing than for the 10- and 5-m spacings, especially for grain yield and moisture. The 10-yr average corn yields were 9.8, 9.7, 9.5, and 9.2 Mg ha -1 for the 5-, 10-, and 20-m plots and the nondrained control plots, respectively. Grain yield was 1.3 to 1.7 Mg ha -1 lower in the nondrained control than in the 5-m spacing in 3 of the 10 yr and was likely due to both planting date delays and wetter soil conditions after planting. The smaller-than-expected yield differences among treatments may reflect the excellent surface drainage in this field as well as optimal planting dates in 7 of the 10 years. The results demonstrate that drainage improvements are a long-term investment and may not provide yield benefit in every year.

Growth of value-added commodities, especially high-protein and tofu soybean [Glycine max (L.) Men.], may offer a profitable option for growers faced with the decline in traditional crops in the south central region of the USA. There is limited information on the production potential and management options necessary for optimal production of value-added soybean crops In this region. The objectives of this study were (i) to determine the production potential of value-added soybean cultivars in the south central region, and (ii) to evaluate various management options for optimal production in this area. Three tofu-type and three high-protein soybean cultivars were compared with commodity-type (check) soybean cultivars under various N and plant density treatments over 4 location/years. Yield and yield component data were collected including seed protein and oil concentrations. Both high protein and tofu-type soybean cultivars had comparable yields and generally greater protein concentrations and larger seed size (tofu-type soybean) than an equivalent check cultivar. The exceptions were cultivars that had, on average, a greater than 10% higher protein concentration than the check cultivar. These higher protein cultivars generally yielded less than other value-added soybean cultivars or the standard check cultivar. The value-added soybean cultivars responded well to management practices currently being used to grow standard commodity cultivars. Neither change in plant population density nor late-season fertilizer applications was necessary to maintain total yield and yield components at a level equivalent to the check cultivar. There is good production potential of value-added soybean cultivars in the south central region, even when grown with current equipment and management practices utilized for commodity soybean crop production.

When irrigation sources are limited, supplemental irrigation at selected growth stages may help avoid crop stress. The objective of this study was to determine the effect of limited, supplemental irrigation at two reproductive growth stages of popcorn (Zea mays L.) grown at different populations. The experiment was conducted from 1995 through 1998 on a Parsons silt loam (fine, mixed, thermic Mollic Albaqualf). The experimental design was a randomized complete block with a split-plot arrangement of treatments. Six irrigation schemes of no irrigation, application of 2.5 or 5 cm at R1 (silk stage) or R3 (milk stage), and 2.5 cm at both R1 and R3 were main plots, and populations of 37 000, 49 000, and 62 000 plants ha -1 were subplots. Popcorn yield was affected by irrigation in only 2 of 4 yr. In the driest growing season (1996), yields were low, but either 2.5 or 5 cm of irrigation applied at R1 increased yields by 60% or more compared with irrigations at R3 or no irrigation. In 1997, 2.5 cm of irrigation at R1 or 2.5 cm at both R1 and R3 resulted in 23 to 27% greater yield than with no irrigation. These responses were partially explained by 12 to 13% greater number of kernels per ear. The optimum plant population was 49000 plants ha -1 ; this treatment maximized yield, kernel weight, and produced one ear per plant. Responses to irrigation were not affected by plant populations for any measured parameters. Popping expansion ratio was unaffected by treatments. Supplemental irrigation at critical reproductive growth stages influences yield but is inadequate to provide consistent yield and quality improvements for popcorn grown in the eastern Great Plains.

Experiments were conducted from 1999 through 2002 in North Carolina to compare interactions of planting pattern, plant population, and irrigation on peanut (Arachis hypogaea L.) pod yield and market grade characteristics. In additional experiments, pod yield and severity of tomato spotted wilt tospovirus associated with the cultivars NC-V 11, NC 12C, VA 98R, and Perry were compared in single row (rows spaced 91 cm apart) and standard twin row (two rows spaced 18 cm apart on 91-cm centers) planting patterns when peanut was dug and vines inverted on two digging dates spaced 10 to 16 d apart. In a third set of experiments, pod yield, market grade characteristics, and severity of tomato spotted wilt tospovirus were compared when the cultivars NC-V 11 and Perry were planted in single row, standard twin row, and narrow twin row (two rows spaced 18 cm apart on 46-cm centers) planting patterns. Peanut pod yield was higher in standard twin row planting patterns than when grown in single row planting patterns in some but not all experiments. Planting peanut in the narrow twin row pattern did not increase peanut pod yield over the standard twin row planting pattern. Less tomato spotted wilt was observed in standard or narrow twin row planting patterns compared with single row planting patterns. Planting peanut in single rows spaced 46 cm apart did not improve yield over peanut planted in single rows spaced 91 cm apart or the standard twin row planting pattern, regardless of irrigation treatment.

Glyphosate [N-(phosphonomethyl)glycine]-resistant soybean [Glycine max (L.) Merr.] cultivars have increased drastically in usage and acceptance. Little information exists to see how glyphosate-resistant soybean cultivars should be managed. The objective of this study was to evaluate different row-spacing and plant population systems using three weed management systems. A field study was conducted from 1997 through 1999 at six locations in Wisconsin. Soybean was planted in 19-, 38-, and 76-cm rows at a recommended (optimum), low, and high plant population for each row-spacing system with three weed management systems [glyphosate-resistant soybean cultivars with glyphosate (GRS/G), glyphosate-resistant soybean cultivars with conventional herbicides (GRS/CN), and conventional soybean cultivars with conventional herbicides (CN/CN)]. In northern Wisconsin, soybean yield in a GRS/G system did not respond to plant population while GRS/CN and CN/CN systems yielded 6% more in high than in low plant population. Additionally, soybean yield responded positively to plant population in 76-cm row CN/CN and GRS/CN systems in northern Wisconsin. In southern Wisconsin, GRS/G and GRS/CN systems yielded 6% less than the CN/CN system. No differences were observed among weed management systems in central and northern Wisconsin. Averaged across weed management systems and plant population, 19- and 38-cm rows yielded 7, 9, and 10% more than 76-cm rows in southern, central, and northern Wisconsin, respectively. No yield differences were observed between optimum and high plant population across Wisconsin, averaging 4% greater yield than the low plant population. The results demonstrated that it might be beneficial to alter management practices when using glyphosate-resistant soybean in some production environments in Wisconsin.

Dryland corn (Zea mays L.) production increased more than 10-fold from 1995 through 2000 in semiarid western Nebraska. Corn population and N fertilizer management recommendations are needed for this area. The objectives of this study were to determine the influence of plant population and N fertility on corn yields in semiarid western Nebraska. In 1999 and 2000, experiments were conducted each year at four sites. Factorial experimental treatments were five plant populations (17 300, 27 200, 37 100, 46 900, and 56 800 plants ha - 1 ) and five N fertilizer rates (0, 34, 67, 101, and 134 kg N ha - 1 ) arranged in a randomized complete block with five blocks. Corn yields ranged from less than 100 kg ha - 1 to more than 5550 kg ha - 1 . Overall, grain yield increased 353 kg ha - 1 with increasing population from 17 300 to 27 200 plants ha - 1 . Population increases above 27 200 plants ha - 1 resulted in inconsistent yield results. Nitrogen fertilization and plant population effects did not interact. Yields were maximized by 202 kg N ha - 1 in the form of soil NO 3 -N and fertilizer N available before crop emergence. Growers are advised to use a plant population of 27 200 plants ha - 1 . Economic optimal fertilizer rate can be estimated using the equation: N t e r t . = (10.6 x P c o r n - P t e r t . )/(0.0526 × P c o r n ) - N s o i l , where P c o r n and P t e r t . are corn and fertilizer price ($ kg - 1 ), respectively, N s o i l is soil test NO 3 -N (kg ha - 1 ) as determined by preplant soil test in a 0- to 120-cm soil sample, and N t e r t . is economic optimal fertilizer rate (kg ha - 1 ).

Dryland corn (Zea mays L.) yield in western Kansas is limited by high temperatures and low rainfall. The number of hectares has increased in recent years due to improved hybrids, acceptance of reduced- and no-till practices, changes in the farm program, and favorable weather conditions. Research was conducted near Garden City, KS from 1996 through 1999 to determine the effects of hybrid maturity, planting date, and plant population on the yield of dryland corn. Five hybrids with maturities of 75 (H1), 92 (H2), 98 (H3), 106 (H4), and 110 d (H5) were planted in mid-April (D1) and early May (D2) of each year (H1 and H2 were not planted in 1996) and thinned to populations of 30 000 (P1), 45 000 (P2), and 60 000 (P3) plants ha -1 in a wheat (Triticum aestivum L.)-corn-fallow rotation. The early May planting date (D2) produced an average of 1.51 Mg ha -1 (31.9%) more grain than did Dl. In the year of the poorest rainfall distribution, D2 resulted in 2.83 Mg ha -1 (96.8%) more grain. Yield usually increased with relative maturity and plant population. The average yield increases were 13.5% from P1 to P2 and 4.3% from P2 to P3. Yield increases with higher populations were greater for earlier hybrids than for later ones. Yield of H5 was 32.6% lower at P3 than P1 in the driest year. Dryland corn should be planted in early May in western Kansas. To minimize yield reductions in dry years, relative maturities should not exceed 106 d, and populations should not exceed P2.

Four safflower (Carthamus tinctorius L.) cultivars were evaluated at five plant populations in experiments over 2 yr at three North Dakota locations. Differences in achene yield due to plant population were not significant. Hybrid AGC-353 produced significantly higher achene yield than the other cultivars. Number of capitula per plant and achenes per capitulum were the yield components most influenced by plant population. Cultivar effects were significant for all yield components. Plant population did not influence achene oil content; however, significant differences among genotypes occurred. Cultivar S-541 and hybrid AGC-353 produced significantly higher and lower achene oil percent, respectively, than the other cultivars. The significantly higher hull content of hybrid AGC-353 compared with the other cultivars caused the low oil content

Previous studies have demonstrated higher corn (Zea mays L.) yield potential for prolific corn hyhrids (more than one ear) compared to nonprolific hybrids (one ear). However, little is known about the relative contribution of the second ear to total yield at various N levels. This study compared yield responses to N rates of 56, 140, and 224 kg N ha −1 of prolific Hybrids A (1202 x Mo17) and B (I117 x B73) with responses of nonprolific Hybrid C (Pioneer 3320) at a uniform low plant population density. All three hybrids gave a positive yield response to N applications. The prolific hybrids increased both in apical ear weight and in subapical ear weight and number in response to N rate. Averaged over N rates, Hybrid A yielded 24% and Hybrid C 14% higher than Hybrid B in 1987 [...]

Pearl millet [Pennisetum glaucum (L.) R. Br.] often is grown in the same areas as sorghum [Sorghum bicolor (L.) Moench]. The crops are similar in use and adaptation, but differ in ways that might affect management requirements. For example, the high tillering capability of millet might result in different responses to plant population and planting date. A study to compare pearl millet and sorghum yield response to rate and date of planting was conducted for 2 yr at St. Johns, on a Naron fine sandy loam (fine-loamy, mixed, thermic Udic Argiustoll), and Manhattan, KS, on a Reading silt loam (fine, mixed, mesic Typic Arguidoll [Argiudoll]) (...)

Initial management strategies, such as established plant stand, significantly affect rice (Oryza sativa L.) crop development, grain yield, and final profits. Critical rice plant population for optimum yield differs greatly among various cultural systems. The objectives of this study were to: (i) characterize effects of increasing plant population on tillering, yield components, yield, and phytomass development in continuously flooded, direct water-seeded rice culture; and (ii) identify which crop development parameters are associated with optimum grain yield in this cultural system (...)

Previous 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, 5O-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(RS) and yield at late plantings is related to increased branch dry matter and branch yield component production. Louisiana Agric. Exp. Stn. manuscript no. 89-09-3350.

(...) The objective was to develop algorithms relating postwinter agronomic characters to potential grain yield. Field trials were conducted 4 yr on Williams loam (fine-loamy, mixed Typic Argiborolls) to measure the effect of four stubble heights (0, 5, 20, and 36 cm) on postwinter plant populations and agronomic characteristics of three cultivars (Roughrider, Mironovskaya, and Centurk). (...)

(...) A 3-yr. soybean field study on Sharkey clay (very fine montmorillonitic, thermic, nonacid, vertic Haplaquept) was planted at post-optimal dates of 20 June and 3 July. Davis (MG VI) and Braxton (MG VII) soybean were planted in 0.5 and 1.0 row spacing (RS) at PPD at 6.4, 13, 26, 38, 51 plants m-under irrigated and nonirrigated conditions (...)

Rate of appearance of fruiting positions in cotton (Gossypium hirsutum L.) is an important component of earliness. The objective of this research was to evaluate the influence of leaf type (size) and population density rate of fruiting position appearance along branches of individual plants. Normal, okra, and superokra leaf cotton plants were grown in rows 51 cm apart in irrigated basins at 11.2 and 18.5 plants/m² in 1973, and 10.0 and 20.0 plants/m² in 1974. Fruiting positions reaching anthesis were tagged daily. Rate of appearance was determined by observing the number of days between successive fruiting branches (sympodial plastochron) and the number of days between first fruiting positions of successive fruiting branches (monopodial plastochron). Plants grown in high population densities generally had larger sympodial and monopodial plastochrons (longer time intervals between appearance of fruiting positions) than plants in the low population. Okra and superokra plants had smaller monopodial plastochron and larger ratios of sympodial to monopodial plastochrons than normal leaf plants. Sympodial plastochron, increased from early to mid-season and then declined. Monopodial plastochrons increased from early season to plateau values at mid-season. The seasonal changes in plasto-chrons did not appear to be related to changes in temperature. This study shows that both leaf type and population density affect rate of fruiting position appearance and earliness in cotton but changes in temperature found in fields may have little effect on plastochrons.

The need for reducing time of crop exposure to pests has given emphasis to cultural changes in row widths and plant densities for upland cotton, Gossypium hirsutum L., and this has challenged available cultivars to avoid losses in yield and fiber quality. Four genotypes, HYC72-234/320 (very early), ‘Auburn M’ (early), MO63-277 BR (medium early), and ‘Stoneville 213’ (medium early to full-season) were drilled and hill-drop seeded in rows 51 cm apart on beds 203 cm wide on Tiptonville silt loam (fine silty-mixed-thermic typic argiudolls). Four planting methods and rates were used to establish the average within-row plant populations of one, five, and nine plants per 31 cm of row. Eleven agronomic characteristics of upland cotton were measured in relation to the four within-row populations. Lint yields, combining genotypes, were significantly reduced by 90–131 kg/ha in stands of nine or more plants compared with stands of one and five plants in 31 cm of row. The percent of barren plants increased and the numbers of open bolls for four rows 1 m long prior to harvest decreased as number of plants per 31 cm of row increased. The lint yields of Auburn M and HYC72-234/320, early and determinate cultivars, were not influenced significantly by the within-row plant densities. Stoneville 213, a full-season indeterminate cultivar, produced significantly lower yields when within-row plant population was highest. Only minor differences were noted in lint fraction, seed size, boll size, and fiber properties due to the various within-row plant densities. Our findings suggest that cultivar fruiting efficiency potential and within-row plant population should be considered when planting dates are delayed or row-widths modified for cotton culture in the northern extremes of the Mississippi Delta.

Plant population density (PPD) exerts a strong influence on maize (Zea mays L.) growth and grain yield. Most PPD studies have usually confounded plant number with spatial arrangement, since row width remained constant and only spacing between plants in row was varied. This study used a systematic design (fan) to observe the effect of 15 PPD (0.8∓15.4 plants m⁻²) on maize reproductive growth in constant spatial arrangement on Lake fine sand (hyperthermic, coated Typic Quartzipsamments) at Gainesville, FL (29°38'N), in 1985 and 1986. All plants produced at least one ear over the 15 PPD range. Ear 2 and Ear 3 were lost at 4.3 and 2.8 plants m 2, respectively The kernel row number per ear (KRNE), kernel number per ear row (KNER), and kernel number per ear (KNE) were influenced by PPD and differed (P Ear 2 > Ear 3). Mean kernel weight (WK) was unaffected by PPD. Yield component vulnerability due to PPD for three-ear plants was: KNE and KNER > ear number per plant (ENP) > KRNE > WK. Kernel, stalk, and total dry matter yield per plant decreased reciprocally with increasing PPD. Kernel yield per land area increased parabolically up to a maximum yield of 1080 g m⁻² at about 10.0 plants m⁻², whereas stalk and total dry matter yield increased asymptotically up to 12.5 plants m⁻². Shelling percentage was constant with inceasing PPD, but harvest index decerased, though not significantly. We conclude that as PPD pressure is gradually removed over a wide PPD range, yield is adjusted in prolific maize hybrids first by KNE and KNER, followed by ENP, KRNE, and WK, which remained relatively stable. Contribution from the Inst. of Food and Agrcultural Sciences, Florida Agric. Exp. Stn. Journal no. 8406.

Poor soybean [Glycine max (L.) Merr.] emergence presents difficult replanting decisions. Most plant population research has involved deficient stands with even distribution rather than the more commonly encountered random gap distribution. The objective was to provide guidelines for making profitable replanting decisions. Field experiments were conducted in 1984 and 1985 to compare growth parameters and seed yield of an adapted cultivar in northern, central, and southern Illinois at 42, 40, and 38 degrees N Lat, respectively. Initial and delayed (21 d) plantings were made in rows 0.76 m apart. Two plant densities (291 550 and 202 350 plants ha-1) and five random stand deficiencies levels (0 to 60%) were established within each planting. The largest effect on seed yield was caused by random stand deficiency follwed by environment and planting date. Stands with randomly imposed 0.31 m gaps totaling 40 and 60% of the plot areas resulted in 10.8 and 21.1% yield reductions, relative to uniform stands in the initial planting, respectively. Replanting delays resulted in a average relative yield loss of 9.0%. Photosynthetic photon flux density measurements were made when the initial planting reached R5 and were expressed as percent light interception (PLI). The PLI at R5 was not related to the 9.0% yield loss due to replanting delay. At the 60% stand reduction level the low plant density mean yield was 6.2% less than the high plant density mean over both plantings. Seed number per plant ranged from 63.9 in replanted full stands to 195.1 in the most deficient initial planted stands. Seed weight effects were minimal and inconsistent. The PLI decreased quadratically with increasing stand reductions from 92.5% in full stands to 80.4% in stands reduced by 60% (over all factors). Relative yield (RY) was regressed on PLI as follows: (i) initial planting: (RY) = 39.65 + 1.4781 PLI (r2 = 0.941, P less than 0.01); and (ii) Delayed replanting: RY = 47.75 + 1.4598 PLI (r2 = 0.944 P less than 0.01). In most environments only stand reductions of over 50% could be justifiably replanted. The results provide guidelines for decisions of whether or not to replant, based on expected yield losses due to irregular initial stand emergence compared with expected losses due to replanting delay.

(...) Light interception was similar at 5 and 3 h before and at solar noon for each PPD measured at ground, ear, and below-tassel levels. Leaf area and light interception were highly concentrated at ear level, but level of light interception shifted upward with increasing PPD. Maxima LAI were 1.7, 2.6, and 4.0 at tasseling for the 1.7, 2.6, and 6.3 plants m −2 , respectively (...)