High Plant Population Density Research Articles

Effects of plant density and mulching on the performance of late-season tomato (Lycopersicon esculentum) in southern Nigeria

The growth and yield of late-season tomato was studied at Akure, Nigeria, from 1995 to 1998. In each year, treatments were 0 (bare ground) or 12 kg/ha grass mulch applied to tomatoes at densities of 1·9, 2·8, 3·7 and 5·6 plants/m2 in a factorial combination. Increase in plant density and mulching reduced soil temperature at 5 cm depth while only the latter enhanced soil moisture at 10 cm depth throughout tomato growth. The improved soil hydrothermal regime resulted in earlier onset of flowering, 50% flowering date and date of first harvest respectively and shorter fruit harvest duration in tomato grown on either bare ground or at increased plant density.Although increased plant density reduced shoot dry weight per plant at final harvest, both root length per plant and root dry weight per plant were enhanced. Fruit yield/ha increased as plant density increased although yield of the individual plants and their components were significantly reduced. Because of compensation at higher plant population densities, it is economical to grow late-season tomato at 5·6 plants/m2. Mulching enhanced growth and yield of tomato compared to bare ground and the result emphasizes the need for early and rapid growth of late-season tomato before the onset of terminal drought.

Yield Improvement in Temperate Maize is Attributable to Greater Stress Tolerance

ABSTRACTA retrospective analysis of the physiological basis of genetic yield improvement may provide an understanding of yield potential and may indicate avenues for future yield improvement. Rate of yield improvement of maize (Zea mays L.) hybrids in Ontario, Canada has been ≈1.5% yr−1 during the last five decades. Comparison of short‐season hybrids representing yield improvement from the late 1950s to the late 1980s showed that genetic yield improvement was 2.5% per year and that most of the genetic yield improvement could be attributed to increased stress tolerance. Differences in stress tolerance between older and more recent hybrids have been shown for high plant population density, weed interference, low night temperatures during the grain‐filling period, low soil moisture, low soil N, and a number of herbicides. Yield improvement is the result of more efficient capture and use of resources, and the improved efficiency in resource capture and use of newer hybrids is frequently only evident under stress. Improved resource capture has resulted from increased interception of seasonal incident radiation and greater uptake of nutrients and water. The improved resource capture is associated with increased leaf longevity, a more active root system, and a higher ratio of assimilate supply by the leaf canopy (source) and assimilate demand by the grain (sink) during the grain‐filling period. Improvements of resource use under optimum conditions have been small, as leaf photosynthesis, leaf‐angle distribution of the canopy, grain chemical composition, and the proportion of dry matter allocated to the grain at maturity (i.e., harvest index) have remained virtually constant. Genetic improvement of maize has been accompanied by a decrease in plant‐to‐plant variability. Results of our studies indicate that increased stress tolerance is associated with lower plant‐to‐plant variability and that increased plant‐to‐plant variability results in lower stress tolerance.

Effects of Population Density and Planting Pattern on the Yield and Yield Components of Leafy Reduced‐Stature Maize in a Short‐Season Area

AbstractMaize hybrids that yield well, mature earlier with low grain moisture contents, tolerate higher population densities and take advantage of narrow row spacings better than the currently available hybrids would be more suitable for production in short‐season areas. Leafy reduced‐stature maize hybrids, which have only recently been developed, have traits which address these criteria. The objective of this study was to evaluate the effects of different population densities (65 000 and 130000 plants ha−1) and planting patterns (single rows 76 cm apart and paired rows with 20 cm between rows within a pair of 56 cm between rows of adjacent pairs) on the yield and yield components of two leafy reduced‐stature (LRS1 and LRS2), one non‐leafy reduced‐stature (NLRS), and two conventional corn hybrids (Pioneer 3979, < 2500 CHU; and Pioneer 3902, 2600‐2700 CHU) at two locations. All hybrids had higher kernel numbers per row and single plant grain yields at the lower population densities when in paired rows. However, as plant density increased, these variables decreased more in the conventional hybrids than the LRS and NLRS hybrids, which demonstrates the greater tolerance of the latter to the stresses associated with higher plant densities. Grain yield was higher for the two LRS hybrids and the NLRS hybrid at 130000 plants ha−1 than 65 000 plants ha−1 Grain yield of conventional hybrids was reduced at the higher population density. The LRS hybrids matured before both conventional hybrids and out yielded Pioneer 3979 at the higher plant population density in both row spacings at both sites. Harvest index was not affected by population density and this value was not different among the NLRS and conventional hybrids. However, the harvest index of the LRS hybrids was greater than the others. LRS and NLRS hybrids had lower moisture contents and earlier maturities than conventional hybrids. Rapid growth of the first ear and higher harvest index values might are indications that LRS hybrids are more tolerant of higher population densities than the conventional hybrids.

Twenty Cycles of Biparental Mass Selection for Prolificacy in the Open‐Pollinated Maize Population Golden Glow

Selection for increased ears per plant may be an effective method for increasing grain yield in maize (Zea mays L.). Since 1970, biparental mass selection for prolificacy has been carried out in the open‐pollinated maize population Golden Glow. The objectives of this study were to (i) evaluate the direct and correlated responses to 20 cycles of mass selection for prolificacy in Golden Glow, and (ii) relate changes prolificacy to the population's performance at different plant population densities. Yield trials were conducted in 1993 at Madison and Arlington, WI, and in 1994 at Madison, Arlington, and Hancock, WI. In each location and year, the trials were grown at four plant population densities: 28 889 plants ha−1; 44 444 plants ha−1; 57 778 plants ha−1; and 73 333 plants ha−1. Ears per plant increased by 3.3% per cycle, from an average of 0.98 ears plant−1 for C0 to 1.63 ears plant−1 for C20. Grain yield per plant and grain yield per hectare both increased by 1% per cycle, from 126.5 g plant−1 and 5.91 Mg ha−1 for C0 to 151.9 g plant−1 and 7.16 Mg ha−1 for C20. Days to midpollen, days to midsilk, silk delay, and grain moisture decreased across cycles of selection. Root lodging decreased while stalk lodging did not change. Number of ears per plant was significantly and positively correlated with both grain yield per plant (r = 0.71) and grain yield per hectare (r = 0.76). The later, more prolific cycles yielded more than the initial population at high plant population density. The principal benefit of prolificacy for Golden Glow is that it may contribute to the population's ability to produce grain under competitive stress.

Plant Spatial Arrangement Affects Growth, Yield, and Pod Distribution of Cayenne Peppers

The effect of planting population density (as a function of in-row plant spacing and number of rows per bed) on the growth, yield, and pod distribution of cayenne pepper (Capsicum annuum var. annuum L. cv. Carolina Cayenne) was investigated in a 2-year study. In 1988, 15 -, 30-, 45-, and 60-cm in-row spacings in a single row were evaluated, and in 198915 -,30-, and 60-cm in-row spacings in single and double rows were evaluated. Plant population densities at these respective spacings ranged from≈ 11,100 to 44,400 and 11,100 to 88,900 plants/ha. In 1988, pepper plants grown at the highest density (15-cm in-row spacing, 44,400 plant/ha) produced less fruit per plant but more fruit per hectare than those grown in lower densities. In 1989, yields with either a 15-cm in-row spacing in a single row or a 30-cm in-row spacing in double rows (both with 44,400 plants/ha) were higher than in the others. In general, less fruit were located in the lower part of the plant canopy when planted in higher plant population densities.

Soybean nodulation and grain yield as influenced by N-fertilizer rate, plant population density and cultivar in southern Quebec

Optimum soybean (Glycine max (L) Merr.) production requires information on the interaction between cultivars, population densities and fertilizer nutrients as related to climate and region. Consequently, field experiments were conducted to determine the effects of N-fertilizer rate, plant population and cultivar on soybean nodulation and grain yield on two soils in southern Quebec. N-fertilizer application consistently depressed soybean nodulation, but it improved soybean growth where initial soil inorganic-N levels were low. High plant population densities had little effect on individual plant nodulation, but they increased fresh nodule mass per unit area. Grain yields were increased with high plant population densities. The two cultivars tested, Apache and Maple Arrow, generally produced similar grain yields on the Ste. Rosalie soil, where yields were low due to moisture stress or low initial inorganic-N levels. On the more productive Ormstown soil, Apache produced higher grain yields than Maple Arrow.Key words: Glycine max (L.) Merr., N fertilization, plant population, nodulation, grain yield

Effects of hybrids, population densities, fertilization and irrigation on grain corn (Zea mays L.) in Quebec

The increase in area for corn production in eastern Canada has stimulated the search for improvements in corn management practices to obtain higher yields. The purpose of this study was to investigate the effects of maize (Zea mays L.) hybrids, plant population density, rates of fertilization and irrigation on grain yield. A field experiment was conducted on a Chicot sandy clay loam soil in Quebec from 1984 to 1986. Corn attained grain yields of 10.9–15.2 Mg ha−1. These yields were attained only when all management inputs were at optimum levels. No single hybrid was superior over the 3-yr-period. High plant population densities, if not accompanied by other inputs, decreased yields. In moist, cooler years, effects of management factors were reduced, and only high plant population densities seemed to increase production. High rates of fertilization increased yields only when other management levels were high.Key words: Population density, irrigation, fertilization, hybrid, Zea mays, grain

Smut Incidence and Yield Losses of Corn Cultivars under Different Plant Population Densities

AbstractSix corn cultivars were grown, under field conditions, at two population densities of 14285 and 22875 plants/ acre. All were subjected to an artificial infection at 6‐leaf growth stage to determine their reactions to smut disease and yield losses. Changes in plant chemical composition, including K and N contents of ear‐leaf, were performed at silking stage. The results showed that corn cultivars imposed wide variations to smut reaction. Susceptibility to smut disease was less prevalent on D.H 204 and 3‐way cross 310 and more abundant on D.H 215, Iskandria 11 and El‐Kabera 1. The corn cultivar Giza 2 appeared an intermediate reaction. Smut incidence at high population density was markedly depressed by 6.6 % below the comparable level at low population rate. Differences in yield losses between low and high plant population densities were actually limited for smut resistant cultivars, while the opposite was true for the more susceptible ones. On average, the yield losses at the low population density varied from 2.5 % for D.H 204 to 14.4 % for Iskandria 11. The calculated losses of the respective cultivars declined to 2.3 and 9.2 % at the thicker stand. The overall effect of increasing smut infection on yield losses, as revealed from the regression coefficients of the response curves, was clearly pronounced at the higher plant population, whereas the yield was substantially improved by 9.7 %. Varietal response to smut performance was explained on the basis of vigor growth and K/N ratio of ear‐leaf.

Plant Population Density and Row Spacing Effects on Soybean at Post‐Optimal Planting Dates

AbstractInformation on cultural practices for determinate soybean, Glycine max (L.) Merr., at post‐optimal planting dates is needed in the southern USA where planting is often delayed by weather or doublecropping. The objective of this study was to examine the effects of plant population density (PPD) on determinate soybean at two postoptimal planting dates in relation to interrow spacing, plant architecture, and yield components. 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 m row spacing (RS) at PPD at 6.4,13, 26, 38, 51 plants m−2 under irrigated and nonirrigated conditions. Yields were higher at the 0.5 m RS than at the 1.0 m RS, and were higher at the June date than at the July date. Highest yields at the June date (2.99 and 1.97 Mg ha−1) were with PPD of 38 and 13 plants m−2 at the 0.5 and 1.0 m RS, respectively. Yields were highest at the July date (2.45 and 1.53 Mg ha−1) with PPD of 51 and 26 plants m−2 at the 0.5 and 1.0 m RS, respectively. Increase in PPD up to 38 plants m−2 increased main stem length and decreased all other plant components. Decrease in main stem yield was proportionately smaller than the increase in PPD resulting in a net yield gain from higher PPD. Decrease in branch stem yield was proportionately greater than the increase in PPD resulting in a net yield loss from PPD increase. For determinate soybean planted at a 0.5 m RS an increase in PPD above that needed at optimal dates was necessary to obtain highest yields at post‐optimal planting dates. Soybean planted at the 1.0 m RS had much lower yield and was much less responsive to increase in PPD.

Determinate‐ and Indeterminate‐Type Soybean Cultivar Responses to Pattern, Density, and Planting Date

Soybean [Glycine max (L.) Merr.] seed yield is influenced by planting date, pattern, and density of seeding, but cultivars differing in growth habit may vary in response to cultural treatments. Narrow‐row compared to conventional wide‐row plantings have consistently produced higher seed yields in the northern USA, where early maturity groups (MG) and indeterminate (INDT) types are commonly used. Positive responses to narrow rows have been less consistent in the southern USA, where late MG and determinate (DT) cultivars are common. Therefore, we hypothesize that this disparity in seed yield response to narrow‐row culture between the two areas is due to inherent differences in DT‐ and INDT‐type canopies resulting from their growth habits. This study, conducted in Gainesville, FL (29 ° 38′N) in 1984 and 1985, employed ‘Duocrop’ (INDT) and ‘Kirby’ (DT), May and July planting dates, 0.91‐, 0.61‐, and 0.30‐m interrow spacings, and 0.18‐ and 0.08‐m intrarow spacings in a Randomized Complete Block (RCB) design. Node and pod numbers, leaf area index (LAI), crop growth rate (CGR), total biomass, and seed yields were significantly increased (per unit land area) with increasing plant population density (PPD) up to a certain PPD, depending on spatial arrangement. The greatest seed yield of both INDT and DT types was from the May planting, narrow‐row culture (0.30 m), and high PPD, but response to PPD was confounded with squareness (ratio of intra‐ to interrow distance among plants) of planting pattern. High PPD (18 to 42 plants m−2 and high squareness values gave higher seed yields than combinations of lower PPDs and lower squareness values. We conclude that seed yield of both DT and INDT soybean in subtropical latitudes is optimized by May seeding, high PPD (40 plants m−2), and use of square planting patterns as approximated by narrow‐row culture.

Effect of nitrogen supply on the comparative productivity of maize and sorghum in a semi-arid tropical environment I. Leaf growth and leaf nitrogen

A study was conducted under fully-irrigated conditions in tropical Australia to examine the influence of variable nitrogen supply on leaf initiation, expansion and senescence and on leaf nitrogen in maize and sorghum. Leaf area development in sorghum was more responsive to N than in maize. Maximum leaf area indices of 7.4 and 3.8 recorded for sorghum and maize, respectively, were associated with sorghum having a longer period of vegetative development and a higher plant population density than maize. The main effect was on leaf expansion, with differences in leaf initiation being relatively small. The concept of a minimum specific leaf nitrogen ( SLN) defined as the minimum amount of leaf N per unit leaf area required for leaf expansion, is proposed. The data indicate that if N uptake and allocation to leaves is sufficient to maintain SLN above 1.0 g m −2 then leaf expansion proceeds at its potential rate. There was little leaf senescence in either species during the vegetative period, but during grain-filling leaf senescence was more pronounced in sorghum and at low rates of applied N. Throughout the life cycle, SLN was higher rates of applied N and was higher in maize than in sorghum. During grain-filling, the decline in SLN was more pronounced in maize than in sorghum, and was greater at lower rates of applied N.

PHOTOMORPHOGENIC REGULATION OF REPRODUCTIVE DEVELOPMENT IN GROUNDNUT AND THE SIGNIFICANCE OF NYCTINASTIC LEAF MOVEMENTS

SummaryMany leguminous species are grown under relatively high plant population densities > 250000 plants ha−1. It is argued that these plants can tolerate high population densities because their nyctinastic leaf movements allow their aerial parts to receive directly the last light of the day, which increases the Pfr level in the plants before the onset of darkness, causing them to develop like unshaded plants. Measurements of irradiance above and below the canopy of a densely planted crop of groundnut (Arachis hypogaea fastigiata Waldron) showed that, during daytime, when the leaf laminae were horizontally orientated, only 10% of the incident light reached the ground, while after sunset, with the leaves in the vertical position, 70 to 90 % of the incident light could penetrate to the ground. Natural light, available to the plants after this time, was capable of inducing the straightening of hypocotyl hooks of dark‐germinated seedlings, a typical red light requiring photomorphogenic reaction. Laboratory experiments showed that groundnut plants, receiving daily 5 min red light immediately after the end of the photoperiod, developed significantly more branches and more reproductive organs than plants receiving 10 min far red light. The greater adaptability of two leguminous plants, bush bean (Phaseolus vulgaris L.) and groundnut, to high population density was demonstrated by comparing their performance with that of maize (Zea mays L.), okra (Abelmoschus esculentus Moench), safflower (Carthamus tinctorius L.) and sesame (Sesamum indicum L.) under a high and a low population density. Although crowding caused the plants of all six species to grow taller, with fewer branches and fewer reproductive organs, the harvest index of the two leguminous species remained unaffected by the population density, while that of the remaining four species was significantly reduced by the higher population density.

Investigations into the use of plant growth regulators in oil-seed sunflower (Helianthus annuusL.) husbandry

SUMMARYThe effects of some plant growth regulators on the growth and development of two cultivars of oil-seed sunflower (cvs Flambeau and Luciole) were examined in 1977 and 1978. Sunflower is a marginal crop for the United Kingdom, being late maturing and susceptible to infection by grey mould (Botrytis cinerea) during the seed-filling period.An experiment in 1977 indicated that suitable growth regulators might improve sunflower husbandry principally by shortening the stem, allowing late applications of fungicide and insuring against lodging. A mixture of mepiquat chloride and ethephon (BAS 098 OOW) was the most effective stem shortener. Daminozide gave variable effects on yield depending on the rate and time of treatment. The number of seeds per m2 was the major determinant of yield; 1000-seed weights and oil contents were similar for all treatments. The proportion of linoleic acid in the oil was very high in all experiments.In 1978 a second experiment involving daminozide and two sunflower cultivars revealed seasonal and varietal differences in response. The timing of growth regulator application seemed critical to affect seed yield. The third experiment, in 1978, investigated the results of applying BAS 098 OOW to four plant population densities varying from 40000 plants/ha to 160000 plants/ha. High plant population density advanced maturation by 2 weeks, but in these plots the crop lodged in the absence of growth regulator treatment.

Nodulation and nitrogen accumulation in field beans (Vicia Faba L.)

SUMMARYThe effects of plant population density, defoliation and removal of pods and apical buds on dry matter, nodulation and nitrogen accumulation in field bean (Viciafaba L.) were investigated in the field in 1973 and 1974.In 1973 seed yield, dry matter and nitrogen accumulation were similar at 50 and 150 plants/m2 while in 1974 40 plants/m2 was significantly different from 80, 120 and 160 plants/m2 which were similar in these attributes. At similar densities, these crops generally had similar leaf areas and nodule weights/m2 during the early pod-filling period while at earlier growth stages leaf area and nodule development were greater at the higher plant population densities. Leaf area and nodule weight per plant were positively correlated as were absolute growth rate per plant and nitrogen assimilation rate per unit weight of nodule.Substantial leaf removal reduced weight but not the nitrogen assimilation rate of nodules determined from plant nitrogen content. Leaf removal did not significantly reduce dry matter but reduced nitrogen yield by reducing seed yield provided that the removed leaves were accounted for.Pod removal reduced dry-matter and nitrogen yield as well as nitrogen assimilation rate of nodules. Pod removal, however, substantially increased number and weight of nodules. Most of these late-formed nodules were located on the older parts of the lateral roots. Removal of the shoot apex had minor effects on nitrogen yield but reduced nodulation towards the completion of pod-filling.

The response of onions to solar heating, agricultural practices and pink-root disease

Solar heating (solarisation) of the soil, by means of mulching with transparent polyethylene sheets in the hot season, is used for disease control. The effect of soil solarisation, under different agricultural practices, on incidence of pink-root disease caused by Pyrenochaeta terrestris, and on onion yield and quality was investigated. Onions were seeded in beds of non-infested, either non-solarised or solarised, soil and transplanted into growth containers filled with soil either non-infested or infested with the pink-root pathogen. Growth of plants pre-grown in solarised beds was improved as compared to plants originated from non-infested beds. Plants grown in the infested soil suffered considerably, as expressed in leaf number and length, root quantity and bulbing-process. In a field experiment, early sowing resulted in a higher disease incidence than later sowing. Soil solarisation controlled the disease, improved seedling survival and increased yield in most cases. Delay in harvest to 100% falling tops increased yields and reduced percentage of undersized bulbs. At high plant-population density (170 plants m −2), percentage of small bulbs was higher and rates of double bulbs were lower than at low plant density (90 plants m −2). Soil solarisation resulted in effective disease control and higher yields and facilitated accurate planning of plant population in the field, extension of the growing-season and higher yields of better quality.

Effect of plant population and time of harvest on yield and quality of maize (Zea maysL.) grown for silage

Abstract Maize (hybrid PX61O) was sown at 85000 (Treatment 1), 181000 (Treatment 2), and 362 000 (Treatment 3) seeds per hectare in large plots (1.0 ha in 1975-76; 0.5 ha in 1976-77). In 1976-77 (Year 2) deaths of maize plants were greatest during the first 110 days growth and amounted to 10, 11, and 24% of established seedlings for Treatments 1, 2, and 3, respectively. Total dry weight per plant, the proportions of leaves, stem, grain, cob, and tassel, and the concentrations ofN, P, K, Na, Ca, and Mg, were assessed at intervals until the ‘hard dent’ growth stage (30-35% total plant DM), about 160 days from sowing. High plant population densities had little effect on mineral concentration, but reduced total dry weight per plant and reduced the weight of individual shoot components, especially leaves, stems, and grain. For Treatments 1, 2, and 3 respectively in Year 2, grain represented 38, 28, and 21 % of plant dry weight at 144 days from planting and 49, 43, and 33% of plant dry weight at 167 days from planting. At the ‘hard-dent’ growth stage in 1975-76 (Year 1), sampling estimates of DM yield per hectare of 21.3, 27.4, and 36.1 t.ha-1 for Treatments 1, 2, and 3, respectively, were 12, 38, and 68% greater than yields measured by harvesting whole plots. In Year 2, yield estimates of 22.0, 25.0, and 24.4 t.ha-1 of DM for these treatments were 8, 14, and 4%, respectively, above yields measured by total harvest. The optimum plant population for maize silage, the growth and development of maize grown at different plant populations, the quality of the crop at ensiling, and problems encountered in accurately sampling large plots of maize for estimation ofDM yield per hectare are discussed.

Sorghum-pigeonpea intercropping and the effects of plant population density

SummaryThe use of growth resources is examined in an intercropping combination of early sorghum (82 days) and later-maturing pigeonpea (173 days) in a row arrangement of 2 sorghum: 1 pigeonpea.Prior to sorghum harvest, light interception by the intercrop combination was almost as high as sole sorghum. After sorghum harvest, light interception by the remaining pigeonpea was very poor and it is suggested that pigeonpea yield could be increased with higher plant population density and better plant distribution. Soil water measurements indicated that this would increase the amount of water being transpired through the crop but would not increase the total evapotranspiration demand. Higher nutrient concentrations in the intercrop pigeonpea compared with sole pigeonpea during this post-sorghum period suggested that yield of intercrop pigeonpea was not limited by nutrient stress, though the total uptake of nutrients by both crops was much greater from intercropping than sole cropping.

Path Coefficient Analysis of Sugarbeet Purity Components1

An analysis of the association of 10 chemical and agronomic characters with purity in three sugarbeet (Beta vuigaris L.) genotypes was used to develop models to identify the components having the greatest effect on purity.Potassium, betaine, and Na followed by NO3‐N, amino N, and sucrose were the most important variables in the 12 best models developed to explain purity. R2 values (percentage of ascribed variation in purity) for these 12 best models ranged from 89.5 to 94.7%. Soluble nonsucrose constitutents increased in quantity from high plant population density to low density, but this linear change did not greatly affect models constructed to account for juice purity either at regular or low N fertility.