Showing papers on "Sowing published in 2012"

Breeding for the future: what are the potential impacts of future frost and heat events on sowing and flowering time requirements for Australian bread wheat (Triticum aestivium) varieties?

Abstract: Extreme climate, especially temperature, can severely reduce wheat yield. As global warming has already begun to increase mean temperature and the occurrence of extreme temperatures, it has become urgent to accelerate the 5-20 year process of breeding for new wheat varieties, to adapt to future climate. We analyzed the patterns of frost and heat events across the Australian wheatbelt based on 50 years of historical records (1960-2009) for 2864 weather stations. Flowering dates of three contrasting-maturity wheat varieties were simulated for a wide range of sowing dates in 22 locations for 'current' climate (1960-2009) and eight future scenarios (high and low CO2 emission, dry and wet precipitation scenarios, in 2030 and 2050). The results highlighted the substantial spatial variability of frost and heat events across the Australian wheatbelt in current and future climates. As both 'last frost' and 'first heat' events would occur earlier in the season, the 'target' sowing and flowering windows (defined as risk less than 10% for frost ( 35 °C) around flowering) would be shifted earlier by up to 2 and 1 month(s), respectively, in 2050. A short-season variety would require a shift in target sowing window 2-fold greater than long- and medium-season varieties by 2050 (8 vs. 4 days on average across locations and scenarios, respectively), but would suffer a lesser decrease in the length of the vegetative period (4 vs. 7 days). Overall, warmer winters would shorten the wheat season by up to 6 weeks, especially during preflowering. This faster crop cycle is associated with a reduced time for resource acquisition, and potential yield loss. As far as favourable rain and modern equipment would allow, early sowing and longer season varieties (i.e. in current climate) would be the best strategies to adapt to future climates.

Increased yield potential of wheat-maize cropping system in the North China Plain by climate change adaptation

Abstract: In the North China Plain, the grain yield of irrigated wheat-maize cropping system has been steadily increasing in the past decades under a significant warming climate. This paper combined regional and field data with modeling to analyze the changes in the climate in the last 40 years, and to investigate the influence of changes in crop varieties and management options to crop yield. In particular, we examined the impact of a planned adaptation strategy to climate change -“Double-Delay” technology, i.e., delay both the sowing time of wheat and the harvesting time of maize, on both wheat and maize yield. The results show that improved crop varieties and management options not only compensated some negative impact of reduced crop growth period on crop yield due to the increase in temperature, they have contributed significantly to crop yield increase. The increase in temperature before over-wintering stage enabled late sowing of winter wheat and late harvesting of maize, leading to overall 4–6% increase in total grain yield of the wheat-maize system. Increased use of farming machines and minimum tillage technology also shortened the time for field preparation from harvest time of summer maize to sowing time of winter wheat, which facilitated the later harvest of summer maize.

Detection of two major grain yield QTL in bread wheat (Triticum aestivum L.) under heat, drought and high yield potential environments.

Abstract: A large proportion of the worlds’ wheat growing regions suffers water and/or heat stress at some stage during the crop growth cycle. With few exceptions, there has been no utilisation of managed environments to screen mapping populations under repeatable abiotic stress conditions, such as the facilities developed by the International Wheat and Maize Improvement Centre (CIMMYT). Through careful management of irrigation and sowing date over three consecutive seasons, repeatable heat, drought and high yield potential conditions were imposed on the RAC875/Kukri doubled haploid population to identify genetic loci for grain yield, yield components and key morpho-physiological traits under these conditions. Two of the detected quantitative trait loci (QTL) were located on chromosome 3B and had a large effect on canopy temperature and grain yield, accounting for up to 22 % of the variance for these traits. The locus on chromosome arm 3BL was detected under all three treatments but had its largest effect under the heat stress conditions, with the RAC875 allele increasing grain yield by 131 kg ha−1 (or phenotypically, 7 % of treatment average). Only two of the eight yield QTL detected in the current study (including linkage groups 3A, 3D, 4D 5B and 7A) were previously detected in the RAC875/Kukri doubled haploid population; and there were also different yield components driving grain yield. A number of discussion points are raised to understand differences between the Mexican and southern Australian production environments and explain the lack of correlation between the datasets. The two key QTL detected on chromosome 3B in the present study are candidates for further genetic dissection and development of molecular markers.

Climate-driven simulation of global crop sowing dates

Abstract: Aim To simulate the sowing dates of 11 major annual crops at the global scale at high spatial resolution, based on climatic conditions and crop-specific temperature requirements. Location Global. Methods Sowing dates under rainfed conditions are simulated deterministically based on a set of rules depending on crop-and climate-specific characteristics. We assume that farmers base their timing of sowing on experiences with past precipitation and temperature conditions, with the intra-annual variability being especially important. The start of the growing period is assumed to be dependent either on the onset of the wet season or on the exceeding of a crop-specific temperature threshold for emergence. To validate our methodology, a global data set of observed monthly growing periods (MIRCA2000) is used. Results We show simulated sowing dates for 11 major field crops world-wide and give rules for determining their sowing dates in a specific climatic region. For all simulated crops, except for rapeseed and cassava, in at least 50% of the grid cells and on at least 60% of the cultivated area, the difference between simulated and observed sowing dates is less than 1 month. Deviations of more than 5 months occur in regions characterized by multiple-cropping systems, in tropical regions which, despite seasonality, have favourable conditions throughout the year, and in countries with large climatic gradients. Main conclusions Sowing dates under rainfed conditions for various annual crops can be satisfactorily estimated from climatic conditions for large parts of the earth. Our methodology is globally applicable, and therefore suitable for simulating sowing dates as input for crop growth models applied at the global scale and taking climate change into account.

Changes in time of sowing, flowering and maturity of cereals in Europe under climate change

Abstract: The phenological development of cereal crops from emergence through flowering to maturity is largely controlled by temperature, but also affected by day length and potential physiological stresses. Responses may vary between species and varieties. Climate change will affect the timing of cereal crop development, but exact changes will also depend on changes in varieties as affected by plant breeding and variety choices. This study aimed to assess changes in timing of major phenological stages of cereal crops in Northern and Central Europe under climate change. Records on dates of sowing, flowering, and maturity of wheat, oats and maize were collected from field experiments conducted during the period 1985–2009. Data for spring wheat and spring oats covered latitudes from 46 to 64°N, winter wheat from 46 to 61°N, and maize from 47 to 58°N. The number of observations (site–year–variety combinations) varied with phenological phase, but exceeded 2190, 227, 2076 and 1506 for winter wheat, spring wheat, spring ...

Endophyte-assisted promotion of biomass production and metal-uptake of energy crop sweet sorghum by plant-growth-promoting endophyte Bacillus sp. SLS18

Abstract: The effects of Bacillus sp SLS18, a plant-growth-promoting endophyte, on the biomass production and Mn/Cd uptake of sweet sorghum (Sorghum bicolor L), Phytolacca acinosa Roxb, and Solanum nigrum L were investigated SLS18 displayed multiple heavy metals and antibiotics resistances The strain also exhibited the capacity of producing indole-3-acetic acid, siderophores, and 1-aminocyclopropane-1-carboxylic acid deaminase In pot experiments, SLS18 could not only infect plants effectively but also significantly increase the biomass of the three tested plants in the presence of Mn/Cd The promoting effect order of SLS18 on the biomass of the tested plants was sweet sorghum > P acinosa > S nigrum L In the presence of Mn (2,000 mg kg−1) and Cd (50 mg kg−1) in vermiculite, the total Mn/Cd uptakes in the aerial parts of sweet sorghum, P acinosa, and S nigrum L were increased by 652%/400%, 552%/311%, and 186%/256%, respectively, compared to the uninoculated controls This demonstrates that the symbiont of SLS18 and sweet sorghum has the potential of improving sweet sorghum biomass production and its total metal uptake on heavy metal-polluted marginal land It offers the potential that heavy metal-polluted marginal land could be utilized in planting sweet sorghum as biofuel feedstock for ethanol production, which not only gives a promising phytoremediation strategy but also eases the competition for limited fertile farmland between energy crops and food crops

Seed Production: Principles and Practices

Abstract: Part 1: Principles of Seed Production: Flowering ans seed set. Seed formation and development. Fundamentals of seed production. Planting. Harvesting. Conditioning. Drying and storage. Seed quality and performance. Evolution of the seed industry. Seed certification. Seed marketing. Seed legislation and law enforcement. Part II: Seed Production of Specific Crops. Cereal seeds. Corn. Sorghum. Small grains. Rice. Millets. Buckwheat. Peanut. Sunflower. Rapeseed/canola. Forage legume seeds. Alfalfa. True clovers (cool-season). Miscellaneous forage legumes. Warm-season forage legumes. Cool-season grasses. Major forage grasses. Warm-season grass seeds. Praire grasses. Savannah grasses. Grain legumes. Field and garden beans. Vegetable seeds. Onion. Tomato. Cabbage. Lettuce. Cucumber. Carrot. Sugarbeet. Flower seed production. Flower seeds. Wild flowers and native species. True seeds. Hickory. Pines. Index.

Nine years of vegetation development in a postmining site: effects of spontaneous and assisted site recovery

Abstract: Summary1. Highly disturbed areas such as surface-mined land provide a great challenge for ecologicalrestoration. The goal is to identify appropriate restoration approaches in a continuum betweentechnical reclamation and spontaneous succession. In particular, on slopes endangered by erosion,appropriate methods are needed that quickly establish vegetation cover but also take into accountthenaturalpotentialsofthesite.2. IntheminedareaRosbach(Saxony-Anhalt,Germany),weevaluatedtheeffectsofspontaneoussuccessionandassistedsiterecovery(speciesintroductionthroughhaytransferandsowing)duringa 9-year experiment. We asked how rates and pathways of vegetation development differ betweentreatmentsandwhetherspeciescompositionconvergesovertimeowingtospeciesexchange.3. The application of green hay as well as the sowing of regional seed mixtures clearly acceleratedvegetation development and led to the rapid establishment of species-rich grasslands. Hay transferwas mostsuccessful owingtothe highamount of transferabletargetspecies.Moreover,bothtreat-mentsfacilitatedtheestablishmentofcryptogamsandprovidedeffectiveerosioncontrol.Also,haytransfer and sowing clearly affected the pathway of succession. Calamagrostis epigejos migratedfrom nearby source populations and became increasingly dominant at sites with spontaneous suc-cession. In contrast, the species-rich grasslands established after hay transfer and sowing werehighlyresistanttoinvasionofCalamagrostisandotherruderals.4. Speciesexchangebetween treatmentsled toincreasingsimilarityinvegetation composition overtime. Nine yearsafter implementation of theexperiment, wedid not findany significantdifferencesbetween treatments in terms of total vegetation cover, species richness and the number of targetspecies. However, the dominance ratio between target and nontarget species differed significantly.Species introduction through hay transfer and sowing led to a permanently higher abundance ofgrassland species and a lower coverage of ruderals compared with spontaneously developed sites.Hence, our results highlight the importance of initial floristic composition and the order of speciesarrivalsforlong-termvegetationdevelopment.5. Synthesis and applications. Hay transfer and sowing of regional seed mixtures are appropriaterestoration tools to achieve rapid revegetation when no potential seed sources of target species areavailable nearby or there are undesirable species that need to be suppressed. Our results show thatintroducedgrasslandspeciesareabletogrowunderpostminingsiteconditionsandcanmigrateintoadjacent spontaneously developing sites. A combination of spontaneous and assisted site recoverycanpromotethedevelopmentofspecies-richgrasslandsinpostmininglandscapes.Key-words: biodiversity, Calamagrostis epigejos, ecological restoration, erosion control,grasslands, hay transfer, mulch seeding, species introduction, successionIntroduction

Exploring warm-season cover crops as carbon sources for anaerobic soil disinfestation (ASD)

Abstract: Anaerobic soil disinfestation (ASD) has been shown to be an effective strategy for controlling soilborne plant pathogens and plant-parasitic nematodes in vegetable and other specialty crop production systems. Anaerobic soil disinfestation is based upon supplying labile carbon (C) to stimulate microbially-driven anaerobic soil conditions in moist soils covered with polyethylene mulch. To test the effectiveness of warm-season cover crops as C sources for ASD, a greenhouse study was conducted using a sandy field soil in which several warm-season legumes and grasses were grown and incorporated and compared to molasses-amended and no C source controls. Greenhouse pots were irrigated to fill soil porosity and covered with a transparent polyethylene mulch to initiate a 3-week ASD treatment prior to planting tomatoes. Soilborne plant pathogen inoculum packets, yellow nutsedge (Cyperus esculentus L.) tubers, and Southern root-knot nematode (Meloidogyne incognita (Kofoid & White) Chitwood; M.i.) eggs and juveniles were introduced at cover crop incorporation. In nearly all cases, ASD treatment utilizing cover crops as a C source resulted in soil anaerobicity values that were equal to the molasses-amended fallow control and greater than the no C source fallow control. In trial 1, Fusarium oxysporum Schlechtend.:Fr. (F.o.) survival was reduced by more than 97% in all C source treatments compared to the no C source control but there was no effect of C source in Trial 2. Carbon source treatments were inconsistent in their effects on survival of Sclerotium rolfsii Sacc. (S.r). In general, the number of M.i. extracted from tomato root tissue and root gall ratings were low in all treatments with cover crop C source, molasses C source, or composted poultry litter. Germination of yellow nutsedge tubers was highest in the no C source control (76%), lowest in the molasses control (31%), and intermediate from cover crop treatments (49% to 61%). Warm-season cover crops have potential to serve as a C source for ASD in vegetable and other crop production systems, but more work is needed to improve consistency and further elucidate mechanisms of control of soilborne plant pathogens and weeds during ASD treatment utilizing cover crops.

Pre-treatment of seeds with static magnetic field ameliorates soil water stress in seedlings of maize (Zea mays L.).

Abstract: The effect of magnetic field (MF) treatments of maize (Zea mays L.) var. Ganga Safed 2 seeds on the growth, leaf water status, photosynthesis and antioxidant enzyme system under soil water stress was investigated under greenhouse conditions. The seeds were exposed to static MFs of 100 and 200 mT for 2 and 1 h, respectively. The treated seeds were sown in sand beds for seven days and transplanted in pots that were maintained at -0.03, -0.2 and -0.4 MPa soil water potentials under greenhouse conditions. MF exposure of seeds significantly enhanced all growth parameters, compared to the control seedlings. The significant increase in root parameters in seedlings from magnetically-exposed seeds resulted in maintenance of better leaf water status in terms of increase in leaf water potential, turgor potential and relative water content. Photosynthesis, stomatal conductance and chlorophyll content increased in plants from treated seeds, compared to control under irrigated and mild stress condition. Leaves from plants of magnetically-treated seeds showed decreased levels of hydrogen peroxide and antioxidant defense system enzymes (peroxidases, catalase and superoxide dismutase) under moisture stress conditions, when compared with untreated controls. Mild stress of -0.2 MPa induced a stimulating effect on functional root parameters, especially in 200 mT treated seedlings which can be exploited profitably for rain fed conditions. Our results suggested that MF treatment (100 mT for 2 h and 200 for 1 h) of maize seeds enhanced the seedling growth, leaf water status, photosynthesis rate and lowered the antioxidant defense system of seedlings under soil water stress. Thus, pre sowing static magnetic field treatment of seeds can be effectively used for improving growth under water stress.

Crop yield and weed growth under conservation agriculture in semi-arid Zimbabwe

Abstract: Constraints to effective weed management may be the main reason for the small area under minimum tillage (MT) in smallholder farming in southern Africa. The effect of maize residue mulching and intensity of hand hoe weeding on the growth of weeds, cowpea (Vigna unguiculata cv. IT 86D-719) and sorghum (Sorghum bicolor cv. Macia) was investigated in the fifth and sixth years of a conservation agriculture (CA) field experiment at Matopos Research Station (28°30.92′E, 20°23.32′S). The experiment was a split-plot randomized complete block design with three replications. Tillage was the main plot factor (conventional tillage – mouldboard plough compared against MT systems – ripper tine and planting basins) and maize residue mulch rate (0, 4 and 8 t ha−1) the sub-plot factor. Hoe weeding was done either four times (high weeding intensity) or twice (low weeding intensity) during the cropping season. Planting and weeding were done at the same time in all treatments. There was markedly greater early season weed growth in MT systems relative to mouldboard plough (MBP) in both crop species. In sorghum, MT (planting basins: 40.3 kg ha−1; ripper tine: 34.8 kg ha−1) systems had higher cumulative weed biomass measured after planting than MBP (29.9 kg ha−1) system. Maize mulching was generally associated with increased mid- to late-season weed growth in the two crops probably due to improved soil moisture conservation during periods of low precipitation. Weed suppression by the maize mulch was observed only in sorghum and limited to early in the cropping season with no effect observed for the remainder of the sorghum rotation phase. The high weeding intensity treatment had lower weed growth in both crops and better sorghum yield than low weeding intensity. The MT systems had poor crop establishment which translated into low yields. Cowpea grain yield obtained from MT systems was less than 300 kg ha−1 compared to 413 kg ha−1 in MBP. The poor sorghum establishment in MT systems translated into low grain yield as sorghum grain yield was lowest in planting basins (2602 kg ha−1) and highest in MBP with 4159 kg ha−1. Results suggest that CA systems require early and frequent hoe weeding even after four years to reduce weed infestations and improve crop growth. This higher demand on a smallholder household's limited labor supply throughout the cropping season will be a key determinant of the spread and adoption of CA in southern Africa.

Inoculation with Azospirillum, associated with nitrogen fertilization in maize

Abstract: The biological nitrogen fixation is an alternative to supply the nitrogen needed for maize. The objective of this study was to evaluate the development and yield of maize in response to inoculation with Azospirillum associated with nitrogen fertilization. We conducted two field experiments in the summer harvest, the first in the 2000/2001 crop year in the region of Marechal Cândido Rondon, under conventional tillage, and second in the 2002/2003 agricultural year in the region of Cascavel, under no tillage. The experimental design in both experiments was a randomized complete block, with four replications, 2x2x2 factorial, with two levels of nitrogen at sowing (zero and 20 kg ha-1), two levels of inoculum (zero and 200 g ha-1) and two levels of nitrogen in topdressing (zero and 100 kg ha-1). There was evaluated the height of ear insertion, total plant height, leaf N content, shoot dry biomass and grain yield. The height of ear insertion and total plant height were not influenced by the factors under study. Nitrogen fertilization at sowing increased the leaf N content, causing the opposite effect when combined with inoculation. Inoculation with Azospirillum in the absence of nitrogen, provide productivity increases of 15.4% and 7.4% for 2000/2001 and 2002/2003 crops, respectively. The inoculation provided productivity similar to that obtained with 100 kg ha-1 in topdressing in crop 2000/2001, while in association with the topdressing, reduced productivity and shoot dry biomass in crop 2002/2003.

Effect of Intercropping and Crop Arrangement on Yield and Productivity of Late Season Maize/soybean Mixtures in the Humid Environment of South Southern Nigeria

Abstract: Field experiments were carried out between September and December in 2007 and 2008 at Akamkpa (150 15'' N; 80 22'' E), Nigeria. The objective was to investigate yield and productivity of maize and soybean as sole crops and as additive mixtures (100:100) in response to five levels of nitrogen (0, 25, 50, 75 and 100 kg/ha) and five crop arrangements (sole maize at 53,333 plants/ha, sole soybean at 266,666 plants/ha and maize: soybean intercrop arrangements of 1:1, 2:2 and 1:2). The trial was a split-plot design in a randomized complete block with nitrogen in main plot and crop arrangement in sub-plot, with three replications. Intercropping had no significant effect on grain yield of maize in 2007. In 2008, maize grain yield grain yield reduction in mixture was 6 percent compared to sole cropping. Soybean seed yield reduction in mixture was 32 and 43 percents in 2007 and 2008, respectively. Crop arrangement significantly influenced yield components and yield in both maize and soybean. Planting maize and soybean in 1:1, 2:2 or 1:2 arrangement had no significant effect on maize in 2007 but depressed grain yield of maize by 38, 35 and 14 percents in 2008. Spatial arrangement of maize and soybean in 1:1, 2:2, and 1:2 depressed soybean yield by 51, 44 and 45 percents in 2007 and by 86, 64 and 73 percents in 2008. Intercropping reduced the relative maize grain yield by only 1 percent in 2007 and from 4 to 9 percents in 2008. Soybean relative yields were from 31 to 34 percent lower than sole crop yield in 2007 and 39 to 46 percent lower in 2008. The relative yield totals for both 2007 and 2008 were well above unity, an indication that the system was highly productive. This implies that intercrops were 64, 66 and 63 percents in 2007 and 43, 57 and 65 percents in 2008, more productive than the sole crops at 2:2, 1:2 and 1:1 arrangements, respectively. Late season maize and soybean may be planted in 2:2 or 1:2 arrangements to take advantage of optimum soybean seed yield and 65-100 percents of the maize grain yield in the humid South Southern Nigeria.

Organic no-tillage system effects on soybean, corn and irrigated tomato production and economic performance in Iowa, USA

Abstract: Novel technologies to reduce tillage in organic systems include a no-tillage roller/crimper for terminating cover crops prior to commercial crop planting. The objective of this experiment was to compare: (1) weed management and yield effects of organic tilled and no-tillage systems for corn (Zea mays L.), soybean [Glycine max (L.) Merr.] and irrigated tomato (Lycopersicon esculentum Mill.), using a roller/crimper and two cover crop combinations [hairy vetch/rye (Vicia villosa Roth/Secale cereale L.) and winter wheat/Austrian winter pea (Triticum vulgare L./Pisum sativum L. ssp. arvense (L.) Poir.)]; and (2) the economic performance of each system. Weed management ranged from fair to excellent in the organic no-tillage system for soybean and tomato crops, with the rye/hairy vetch mulch generally providing the most weed suppression. Corn suffered from low rainfall, competition from weeds and hairy vetch re-growth and, potentially, low soil nitrogen (N) from lack of supplemental fertilization and N immobilization during cover crop decomposition. No-tillage corn yields averaged 5618 and 634 kg ha−1 in 2006 and 2007, respectively, which was 42–92% lower than tilled corn. No-tillage soybeans in 2007 averaged 2793 kg ha−1 compared to 3170 kg ha−1 for tilled soybeans, although no-tillage yields were 48% of tilled yields in the dry year of 2006. Irrigated tomato yields averaged 40 t ha−1 in 2006 and 63 t ha−1 in 2007, with no statistical differences among tillage treatments. Economic analysis for the three crops revealed additional cover crop seed and management costs in the no-tillage system. Average organic corn returns to management were US$55,515 in the tilled system. Overall, the organic no-tillage soybean and irrigated tomato system demonstrated some promise for reducing tillage in organic systems, but until economic benefits from soil carbon enhancement can be included for no-tillage systems, soil improvements probably cannot offset the economic losses in no-tillage systems. Irrigation could improve the performance of the no-tillage system in dry years, especially if grain crops are rotated with a high-value irrigated tomato crop.

Responses of Maize Hybrids to Twin-Row Spatial Arrangement at Multiple Plant Densities

Abstract: Published in Agron. J. 104:1747–1756 (2012) doi:10.2134/agronj2012.0231 Copyright © 2012 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. T continuous increase in maize grain yield in the world’s primary growing areas during the last decades was mainly driven by the development of crowding stress tolerant hybrids that allowed for dramatic increases in plant population and, therefore, in production per unit area (Russell, 1984; Tollenaar and Wu, 1999; Duvick, 2005). Maize grain yields in the United States have also increased due to earlier planting dates (Kucharik, 2008) and more extensive use of irrigation (Cassman, 1999). Sustaining maize grain yield increases into the future requires continued reconsideration of current agronomic practices. Decreasing row spacing at equal plant density promotes more equidistant plant spacing, theoretically reducing plant-toplant competition, while improving plant resource capture and utilization (Duncan, 1984; Andrade et al., 2002; Barbieri et al., 2008) and decreasing weed competition through earlier canopy closure (Bullock et al., 1988). Nonetheless, sharply contrasting conclusions have been reported regarding grain yield response to narrow rows (Nielsen, 1988; Porter et al., 1997; Barbieri et al., 2000; Farnham, 2001; Ma et al., 2003; Andrade et al., 2002; Shapiro and Wortmann, 2006; Yilmaz et al., 2008), and the grain yield benefi t from the implementation of this practice may not warrant the additional machinery investment required. Th e spatial confi guration known as twin rows (Karlen and Camp, 1985) is not a new concept. Twin-row planting systems have proven to be advantageous to soybean [Glycine max (L.) Merr.] yields vs. the single-wide-row alternative of 76-cm spacing (Janovicek et al., 2006) and have gained renewed interest for U.S. maize production in the past decade. Th eoretically, twinrow maize planting systems appears to be an opportunity to derive the benefi ts of narrow rows without need of major changes in harvest, nutrient, or pest application equipment. While the distance between consecutive maize plants within a row at around 85,000 pl ha–1 is around 15 cm for 76-cm planting row widths, in a precisely distributed twin-row arrangement with a 20-cm distance between paired rows, plants ought to be approximately 25 cm from their closest neighbors. Twin-row research has been performed across the United States with varying success, but recent studies showed no consistent grain yield benefi t from twin-row over single-row confi gurations at the same plant densities in the states of Alabama, Iowa, Missouri, or Nebraska (Elmore and Abendroth, 2007; Nelson and Smoot, 2009; Balkcom et al., 2011; Novacek, 2011). In conditions without major nutrient or water limitations, maize grain yield depends most on radiation interception and radiation-driven photosynthetic conversion effi ciencies around ABSTRACT Twin-row planting systems in maize (Zea mays L.) have been proposed as an alternative spatial arrangement that should theoretically decrease plant-to-plant competition, alleviate crop crowding stress and improve yields. Uncertainty remains, however, as to whether twin rows are a feasible option to increase plant densities and improve grain yields. Th ree hybrids (DKC62-54, DKC61-19, and DKC57-66) were grown from 2009 to 2011 to evaluate the individual and interacting eff ects of plant density (PD1 = 69,000; PD2 = 81,000; PD3 = 93,000; and PD4 = 105,000 plants [pl] ha–1) and spatial confi guration (conventional single 76-cm row width vs. 20-cm twin rows spaced 76-cm between paired-rows) on dark prairie soil in WestCentral Indiana. Th e primary research objectives were to determine (i) whether the twin-row spatial arrangement permits higher optimum plant densities, (ii) whether hybrids vary in their response to a twin-row arrangement, and (iii) diverse morphophysiological trait responses to density and spatial treatments. Twin rows never yielded signifi cantly more than single rows at any plant density or hybrid combination in any year of this study. Furthermore, there was no evidence that grain yield-optimizing plant densities were any higher with twin vs. single rows in any hybrid. Twin rows slightly increased leaf area index (LAI) at silk emergence stage in 2010 (mean LAI = 4.8) and 2011 (mean LAI = 4.0), but not in 2009 (mean LAI = 4.4). Despite higher plant spacing variation, radiation interception was initially favored by earlier canopy closure with twin-row planting, but the relative radiation-interception advantage declined as plant density increased and at a later vegetative stage.

Models and tests of optimal density and maximal yield for crop plants

Abstract: We introduce a theoretical framework that predicts the optimum planting density and maximal yield for an annual crop plant. Two critical parameters determine the trajectory of plant growth and the optimal density, , where canopies of growing plants just come into contact, and competition: (i) maximal size at maturity, , which differs among varieties due to artificial selection for different usable products; and (ii) intrinsic growth rate, g, which may vary with variety and environmental conditions. The model predicts (i) when planting density is less than , all plants of a crop mature at the same maximal size, , and biomass yield per area increases linearly with density; and (ii) when planting density is greater than , size at maturity and yield decrease with −4/3 and −1/3 powers of density, respectively. Field data from China show that most annual crops, regardless of variety and life form, exhibit similar scaling relations, with maximal size at maturity, , accounting for most of the variation in optimal density, maximal yield, and energy use per area. Crops provide elegantly simple empirical model systems to study basic processes that determine the performance of plants in agricultural and less managed ecosystems.