Guayule production on the southern high plains

Guayule has long been known as a potential source of natural rubber. Native guayule populations are scattered throughout 300,000 km² of rangeland in the Chihuahuan Desert of Texas and Mexico. The only native indigenous U.S. stands occur in the Trans Pecos region of southwest Texas, and represent the most northern extension of the plant's habitat. Maximum air temperatures of over 38 °C are frequent and minimum temperatures of −23 °C have been recorded. Guayule has been successfully cultivated across the arid and semi-arid Southwestern U.S., but new production areas need to be identified in order to meet the expected world-wide shortage of natural rubber by 2020. The objective of our study was to determine if guayule production could be successful farther north on the Southern High Plains near Halfway, TX. Guayule seedlings were transplanted May 18, 2006 at the Texas AgriLife Research Station at Halfway. Seed used included four released lines, AZ-1, AZ-2, AZ-3, and AZ-4; a released USDA cultivar (11591); and three unreleased breeding lines, N9-3, N6-5, and N13-1. Guayule cold damage was estimated in June of 2007 and 2008 using the following index: (1) no damage, (2) slight - injury of terminals to 6 cm, (3) moderate - 2/3 of plant volume injured, (4) severe - all aerial portions killed but resprouting, and (5) complete - beyond recovery with no regrowth. Plant harvests were conducted in April 2008 and March 2009. Following the 2006/2007 winter the cold damage index ranged from 1.2 in 11591 to 3.8 in AZ-1. The minimum air temperature was −15 °C. There was minimal cold damage during the 2007/2008 and 2008/2009 winters. Biomass of the 24 month-old shrubs harvested in 2008 varied from 9639 kg/ha in 11591 to 13,393 kg/ha in AZ-4. Shrub biomass in 2009 ranged from 26,721 kg/ha in 11591 to 32,951 kg/ha in N6-5. Rubber yield in 2008 was 222 and 639 kg/ha in AZ-3 and N6-5, respectively. Line AZ-3 yielded 717 kg/ha of rubber in 2009 while line AZ-4 yielded 2006 kg/ha. The critical factor in winter survival appeared to be the temperature regime that existed in the late fall and early winter: a gradual and progressive onset of low temperatures that allowed the shrubs to be dormant when freezing temperatures occurred. Lines 11591 and N6-5 had the least cold damage and hold promise for establishment and rubber production on the Southern High Plains of Texas. Certain production criteria make this area an ideal guayule production site: the long-term annual rainfall averages 460 mm, irrigation water salinity is less than 1 E.C. and is pumped from only 90 m, and center pivot sprinklers are available for establishing guayule by direct-seeding.     

Comparative analysis of physiological characteristics and yield components in sugarcane cultivars

Sugarcane in an important crop due to the economic value of its products. Physiological characteristics and yield components of sugarcane were studied in three field-grown sugarcane cultivars B 63118, POJ 2878 and Ja 60-5. Three growth stages were identified: formative phase (until 140 DAP), grand growth (140–300 DAP) and maturity (after 300 DAP). Results indicated that cultivars showed contrasting yield mainly after 300 DAP. At ripening, the most productive cultivar (Ja 60-5) achieved higher leaf area, an optimum leaf area index for light interception, a high and stable net assimilation rate and an elevated leaf area and biomass duration. In addition, this cultivar showed the higher density and lower area of leaf sieve elements as compared with other, which could influence the high translocation rate (1.85 cm min⁻¹) at 8 MAP. The higher efficiency of this process in Ja 60-5 might also be supported by a higher (15–25%) apparent free space of stem parenchyma as compared with POJ 2878 and B 63118. Our results suggest that Ja 60-5 reduced carbon partitioned to foliar respiration which led to a higher partitioning of sucrose to stems evidenced by a higher Pol%.     

Impact of intercropping of medicinal and aromatic plants with organic farming approach on resource use efficiency in arecanut (Areca catechu L.) plantation in India

The present investigation was conducted at Vittal, Karnataka, India during 2004-2007 to study the feasibility of intercropping of medicinal and aromatic plants (MAPs) in arecanut plantation. The results revealed that MAPs can be successfully grown as intercrops in arecanut plantation with increased productivity and net income per unit area. Kernel equivalent yield of MAPs varied between 272 kg ha⁻¹ in case of Piper longum to 1218 kg ha⁻¹ in Cymbopogon flexuosus. Pooled data indicated that Asparagus racemosus produced fresh root yield of 10,666 kg ha⁻¹ of arecanut plantation and contributed to maximum kernel equivalent yield of 1524 kg ha⁻¹ among all medicinal and aromatic plants. Intercropping of MAPs in arecanut was found economical. The net return per rupee investment was highest in C. flexuosus (4.25) followed by Bacopa monnieri (3.64), Ocimum basilicum (3.46) and Artemisia pallens (3.12). The total system productivity of arecanut + MAPs intercropping system varied from 2990 to 4144 kg ha⁻¹. Arecanut + O. basilicum intercropping system registered significantly higher production efficiency 8.2 kg ha⁻¹ day⁻¹ than other systems. Intercropping of MAPs had more positive effect on soil pH in arecanut based cropping system. The soil pH was 5.6 in 2004 and it was 0.3-0.9 units higher in 2007. Soil organic carbon (SOC) content varied significantly due to intercropping of MAPs at the end of experiment. The SOC content increased in Aloe vera, A. pallens, P. longum and B. monnieri, while it depleted in grasses and rhizomatic MAPs. Based on demand and marketing opportunities for MAPs, farmers are advised to grow aromatic plants in large areas on a community basis to meet huge industrial demand and variety of medicinal crops in small areas to meet the requirement of traditional systems of medicine.     

Heritability of,and genotypic correlations between,aflatoxin traits and physiological traits for drought tolerance under end of season drought in peanut (Arachis hypogaea L.)

More rapid progress in breeding peanut for reduced aflatoxin contamination should be achievable with a better understanding of the inheritance of, aflatoxin trait and physiological traits that are associated with reduced contamination. The objectives of this study were to estimate the heritability of aflatoxin traits and genotypic (r_G) and phenotypic (r_P) correlations between drought resistance traits and aflatoxin traits in peanut. One hundred-forty peanut lines in the F_4:6 and F_4:7 generations were generated from four crosses, and tested under well-watered and terminal drought conditions. Field experiments were conducted under the dry seasons 2006/2007 and 2007/2008. Data were recorded for biomass (BIO), pod yield (PY), drought tolerance traits [harvest index (HI), drought tolerance index (DTI) of BIO and PY, specific leaf area (SLA), and SPAD chlorophyll meter reading (SCMR)], and aflatoxin traits [seed infection and aflatoxin contamination]. Heritabilities of A. flavus infection and aflatoxin contamination in this study were low to moderate. The heritabilities for seed infection and aflatoxin contamination ranged from 0.48 to 0.58 and 0.24 to 0.68, respectively. Significant correlations between aflatoxin traits and DTI (PY), DTI (BIO), HI, biomass and pod yield under terminal drought conditions were found (r_P = −0.25** to 0.32**, r_G = −0.57** to 0.53**). Strong correlations between SLA and SCMR with A. flavus infection and aflatoxin contamination were also found. Positive correlations between SLA at 80, 90, and 100 DAP and aflatoxin traits were significant (r_P = 0.13** to 0.46**, r_G = 0.26** to 0.81**). SCMR was negatively correlated with aflatoxin traits (r_P = −0.10** to −0.40**, r_G = −0.11** to −0.66**). These results indicated that physiological-based selection approaches using SLA and SCMR might be effective for improving aflatoxin resistance in peanut.     

Forage soybean yield and quality response to water use

Forages could be used to diversify reduced and no-till dryland cropping systems from the traditional wheat (Triticum aestivum L.)-fallow system in the semiarid central Great Plains. Forages present an attractive alternative to grain and seed crops because of greater water use efficiency and less susceptibility to potentially devastating yield reductions due to severe water stress during critical growth stages. However, farmers need a simple tool to evaluate forage productivity under widely varying precipitation conditions. The objectives of this study were to (1) quantify the relationship between crop water use and dry matter (DM) yield for soybean (Glycine max L. Merrill), (2) evaluate changes in forage quality that occur as harvest date is delayed, and (3) determine the range and distribution of expected DM yields in the central Great Plains based on historical precipitation records. Forage soybean was grown under a line-source gradient irrigation system to impose a range of water availability conditions at Akron, CO. Dry matter production was linearly correlated with water use resulting in a production function slope of 21.2 kg ha⁻¹ mm⁻¹. The slope was much lower than previously reported for forage production functions for triticale (X Triticosecale Wittmack) and millet (Setaria italic L. Beauv.), and only slightly lower than slopes previously reported for corn (Zea mays L.) and pea (Pisum sativa L.) forage. Forage quality was relatively stable during the last four weeks of growth, with small declines in crude protein (CP) concentration. Values of CP concentration and relative feed value indicated that forage soybean was of sufficient quality to be used for dairy feed. A standard seed variety of maturity group VII was found to be similar (in both productivity and quality) to a variety designated as a forage type. The probability of obtaining a break-even yield of at least 4256 kg ha⁻¹ was 90% as determined from long-term precipitation records used with the production function. The average estimated DM yield was 5890 kg ha⁻¹ and ranged from 2437 to 9432 kg ha⁻¹. Regional estimates of mean forage soybean DM yield ranged from 4770 kg ha⁻¹ at Fort Morgan, CO to 6911 kg ha⁻¹ at Colby, KS. Forage soybean should be considered a viable alternative crop for dryland cropping systems in the central Great Plains.     

Growing maize in clumps as a strategy for marginal climatic conditions

Under dryland conditions of the Texas High Plains, maize (Zea mays) production is limited by sparse and erratic precipitation that results in severe water stress particularly during grain formation. When plant populations are reduced to 2.0–3.0 plants m⁻² to conserve soil water for use during grain filling, tillers often form during the vegetative growth and negate the expected economic benefit. We hypothesized that growing maize in clumps spaced 1.0 m apart would reduce tiller formation, increase mutual shading among the plants, and conserve soil water for grain filling that would result in higher grain yield. Studies were conducted during 2006 and 2007 at Bushland, TX. with two planting geometries (clump vs. equidistant), two irrigation methods (low-energy precision applicator, LEPA, and low-elevation spray applicator, LESA) at three irrigation levels (dryland, 75 mm and 125 mm in 2006; and dryland, 50 mm and 100 mm in 2007). For dryland plots in 2007, clump plants had only 0.17 tillers (0.66 tillers m⁻²) compared with 1.56 tillers per plant (6.08 tillers m⁻²) for equidistant spacing. Tillers accounted for 10% of the stover for the equidistant plants, but less than 3% of the grain. Clump planting produced significantly greater grain yields (321 g m⁻² vs. 225 g m⁻² and 454 g m⁻² vs. 292 g m⁻² during 2006 and 2007, respectively) and Harvest Indexes (0.54 vs. 0.49 and 0.52 vs. 0.39 during 2006 and 2007, respectively) compared with equidistant plants in dryland conditions. Water use efficiency (WUE) measurements in 2007 indicated that clumps had a lower evapotranspiration (ET) threshold for initiating grain production, but the production function slopes were 2.5 kg m⁻³ for equidistant treatments compared to 2.0 kg m⁻³ for clump treatments. There was no yield difference for method of irrigation on water use efficiency. Our results suggest that growing maize in clumps compared with equidistant spacing reduced the number of tillers, early vegetative growth, and Leaf Area Index (LAI) so that more soil water was available during the grain filling stage. This may be a useful strategy for growing maize with low plant populations in dryland areas where severe water stress is common.     

Large scale cultivation of Cynara cardunculus L. for biomass production—A case study

Large scale cultivation of the cardoon Cynara cardunculus L. for biomass production was installed using common agricultural practices and machinery in a total of 77.4 ha in southern Portugal in a region characterized by very hot and dry summers. This species is a perennial with an annual growth cycle. Installation by sowing was successful in spite of the extreme drought that occurred during this first cycle (221 mm), and the plants developed well during the second cycle (with 556 mm rainfall) with a mean density of 27 thousand plants per ha. Aerial photographs showed that 45.8 ha of the field had over 50% of ground cover by cardoon plants. The observed differences in soil occupation could be explained by rock outcrops, soil heterogeneity and land topography. The field biomass yield was estimated at 7.5 t ha⁻¹ and the plants at harvest had on average 2.1 m height and 2.2 cm stalk diameter, with 5.3 capitula per plant. Stalks represented 59.1% of total dry biomass. The capitula contain small oil seeds with an average of 126 seeds per capitulum and weighing 32 g per 1000 seeds. The mean seed yield was 603 kg ha⁻¹. The results of this experiment confirm that Cynara crops are suitable for biomass production in Mediterranean regions and that large scale operation can be applied including whole plant harvest or field fractionation for seed recovery. Careful attention to cultural practices was deemed important for field homogeneity and production. The observed plant variation, namely in oil seed production, suggests potential improvements through breeding.     

Reducing labour and input costs in soybean production by smallholder farmers in south-western Kenya

We conducted experiments in 2006 and 2007 in south-western Kenya to reduce labour and input cost of soybean production through different planting systems (point-placement was compared to planting in trenches and broadcasting), weeding frequencies (once or twice), and the use of local inputs (at 20 kg P ha⁻¹). Di-ammonium phosphate (DAP) was compared to manure, ashes, combinations of those, 1/2 Tithonia 1/2 DAP (TD) and no input. 1/3rd of the labour was saved when placing seeds in trenches as compared to individual holes without losing significant grain yield. Broadcasting requires 1/9th of the planting time while losing only 15% grain. 5% grain was lost by weeding once instead of twice, while saving 36% of the time. The time saved at planting can be more productively invested in collecting inputs. Plots without input yielded 537 kg ha⁻¹ grain and 642 kg ha⁻¹ biomass in 2006. Inputs increased both grain and biomass yields significantly with 27–51%, without significant difference between local and mineral inputs (with exception of TD). Using local input is thus a reasonable decision for farmers. Farmers concluded that the experiments had led to options for different types of farmers, with different access to resources, to increase their soybean production.     

Pre and postemergence herbicides for weed control in castor crop

Weed management is among the main factors limiting cultivation of castor (Ricinus communis) in extensive fields, particularly when labor is scarce or expensive. This experiment evaluated the efficiency of weed management programs using preemergence (clomazone, pendimethalin, and trifluralin) and a postemergence herbicide (chlorimuron-ethyl) applied at 20 days after emergence in castor plants cv. BRS Energia under rainfed conditions in Apodi, Brazil. No phytotoxicity was observed on the castor plants, and the postemergence herbicide significantly increased castor seed yield to 1466 kg ha⁻¹ complementing the weed control of preemergence herbicides treatments in which seed yield was 1207 kg ha⁻¹. Seed yield on weedy and weed-free treatments was 760 and 1971 kg ha⁻¹, respectively. Weeds were kept under a satisfactory control up to 40 days after emergence. This program resulted in reasonable weed control because the preemergence herbicides controled monocotyledon weeds, while the postemergence herbicide controlled broad leafed species being selective to castor plants.     

Influence of planting date on growth, artemisinin yield, seed and oil yield of Artemisia annua L. under temperate climatic conditions

Artemisia annua L. is an annual aromatic antibacterial herb, with effective antimalarial properties due to the presence of artemisinin. The intention of the present study was to establish plant survival, growth attributes, yield attributes and artemisinin yield of A. annua cv CIM - Arogya with different transplanting months in two cropping seasons (March 2005-February 2006 and March 2006-February 2007) under temperate climatic conditions of Himalaya, India. Artemisinin yield in the dried leaves was found maximum amongst the plants that were transplanted in March (24.39 kg ha⁻¹) and minimum in those transplanted in November (3.39 kg ha⁻¹).     

Modeling nutrient and water productivity of sorghum in smallholder farming systems in a semi-arid region of Ghana

The CERES-sorghum module of the Decision Support System for Agro-Technological Transfer (DSSAT) model was calibrated for sorghum (Sorghum bicolor (L.) Moench) using data from sorghum grown with adequate water and nitrogen and evaluated with data from several N rates trials in Navrongo, Ghana with an overall modified internal efficiency of 0.63. The use of mineral N fertilizer was found to be profitable with economically optimal rates of 40 and 80 kg N ha⁻¹ for more intensively managed homestead fields and less intensively managed bush fields respectively. Agronomic N use efficiency varied from 21 to 37 kg grain kg⁻¹ N for the homestead fields and from 15 to 49 kg grain kg⁻¹ N in the bush fields. Simulated grain yield for homestead fields at 40 kg N ha⁻¹ application was equal to yield for bush fields at 80 kg N ha⁻¹. Water use efficiency generally increased with increased mineral N rate and was greater for the homestead fields compared with the bush fields. Grain yield per unit of cumulative evapo-transpiration (simulated) was consistently higher compared with yield per unit of cumulative precipitation for the season, probably because of runoff and deep percolation. In the simulation experiment, grain yield variability was less with mineral N application and under higher soil fertility (organic matter) condition. Application of mineral N reduced variability in yield from a CV of 37 to 11% in the bush farm and from 17 to 7% in the homestead fields. The use of mineral fertilizer and encouraging practices that retain organic matter to the soil provide a more sustainable system for ensuring crop production and hence food security.     

Soybean yield trends from 1972 to 2003 in mid-western USA

The increases in crop yield that played an important role in maintaining adequate food supplies in the past may not continue in the future. Soybean (Glycine max L. Merrill) county yield trends (1972–2003) were examined for evidence of plateaus using data (National Agricultural Statistics Service) for 162 counties (215 data sets) in six production systems [Iowa, Nebraska (irrigated and non-irrigated), Kentucky and Arkansas (irrigated and non-irrigated)] representing a range in yield potential. Average yield (1999–2003) was highest in irrigated production in Nebraska (3403 kg ha⁻¹) and lowest in non-irrigated areas in Arkansas (1482 kg ha⁻¹). Average yield in the highest yielding county in each system was 31–88% higher than the lowest. Linear regression of yield versus time was significant (P = 0.05) in 169 data sets and a linear-plateau model reached convergence (with the intersection point in the mid-1990s) in 35 of these data sets, but it was significantly (P = 0.10) better in only three data sets (<2% of the total). Absolute (kg ha⁻¹ year⁻¹) growth rates were associated with productivity, but relative rates were not with the mean relative rates ranging from 1.0 to 1.3% over the six systems. There was, however, a two- to threefold range in relative rate among counties within systems in Nebraska, Iowa, Kentucky and Arkansas (irrigated). Yield did not change (linear regression not significant, P = 0.05) between 1972 and 2003 in 41 counties in non-irrigated areas of Arkansas and Nebraska and in six Kentucky counties of which four had high levels of double-cropping soybean after wheat (Triticum aestivum L.). I found no convincing evidence that soybean yields are reaching plateaus but the technology responsible for this yield growth was apparently completely ineffective in low-yield, high-stress environments.     

Improving crop yield and N uptake with long-term straw retention in two contrasting soil types

Retention and/or reincorporation of plant residues increases soil organic nitrogen (N) levels over the long-term is associated with increased crop yields. There is still uncertainty, however, about the interaction between crop residue (straw) retention and N fertilizer rates and sources. The objective of the study was to assess the influence of straw management (straw removed [S_Rem] and straw retained [S_Ret]), N fertilizer rate (0, 25, 50 and 75 kg N ha⁻¹) and N source (urea and polymer-coated urea [called ESN]) under conventional tillage on seed yield, straw yield, total N uptake in seed + straw and N balance sheet. Field experiments with barley monoculture (1983-1996), and wheat/barley-canola-triticale-pea rotation (1997-2009) were conducted on two contrasting soil types (Gray Luvisol [Typic Haplocryalf] loam soil at Breton; Black Chernozem [Albic Argicryoll] silty clay loam at Ellerslie) in north-central Alberta, Canada. On the average, S_Ret produced greater seed yield (by 205-220 kg ha⁻¹), straw yield (by 154-160 kg ha⁻¹) and total N uptake in seed + straw (by 5.2 kg N ha⁻¹) than S_Rem in almost all cases in both periods at Ellerslie, and only in the 1997-2009 period at Breton (by 102 kg seed ha⁻¹, 196 kg straw ha⁻¹ and by 3.7 kg N ha⁻¹) for both N sources. There was generally a considerable increase in seed yield, straw yield and total N uptake in seed + straw from applied N up to 75 kg N ha⁻¹ rate for both N sources at both sites and more so at Breton, but the response to applied N decreased with increasing N rate. The ESN was superior to urea in increasing seed yield (by 109 kg ha⁻¹), straw yield (by 80 kg ha⁻¹) and total N uptake in seed + straw (by 2.4 kg N ha⁻¹) in the 1983-1996 period at Breton (mainly at the 25 and 50 kg N ha⁻¹ rates). But, urea produced greater straw yield (by 95 kg ha⁻¹) and total N uptake in seed + straw (by 3.3 kg N ha⁻¹) than ESN in the 1983-1996 period at Ellerslie. The N balance sheets over the 1983-2009 study duration indicated large amounts of applied N unaccounted for (ranged from 740 to 1518 kg N ha⁻¹ at Breton and from 696 to 1334 kg N ha⁻¹ at Ellerslie), suggesting a great potential for N loss from the soil-plant system through denitrification and/or nitrate leaching, and from the soil mineral N pool by N immobilization. In conclusion, the findings suggest that long-term retention of crop residue may gradually improve soil productivity. The effectiveness of N source varied with soil type.     

Lucerne management in an organic farming system under dry site conditions

Biological nitrogen fixation (BNF) as a result of the legumes–rhizobia symbioses is the main source of nitrogen in organic farming systems. Lucerne (Medicago sativa L.), used as green manure or as forage legume, is important on arable farms under dry site conditions. In a field experiment on organically managed agricultural fields, we examined the impacts of the utilisation system (harvested = forage production versus mulched = green manure) and the crop composition (pure lucerne crops versus lucerne–grass mixtures) on yield, biological nitrogen fixation (BNF), soil inorganic N content, N balance and water consumption of autumn-cultivated lucerne crops. The study was conducted at the University of Natural Resources and Applied Life Sciences, Vienna, in eastern Austria—a region characterized by pannonian site conditions (9.8 °C mean annual temperature, 545 mm average total precipitation) and stockless farming systems. Our results indicate that the utilisation system and the crop composition had no marked influence on above- and below-ground dry matter (DM) and N yield, soil inorganic N contents, BNF, or water use efficiency of lucerne. The level of symbiotically fixed N₂ in harvested lucerne was 89–125 kg N ha⁻¹ (27–33% Ndfa = nitrogen derived from atmosphere) in the first year and 161–175 kg N ha⁻¹ (47–49% Ndfa) in the second year of the study. The high soil inorganic N supply in the first year increased the N uptake from soil by lucerne and led to a reduced BNF. Under the dry and unfavourable conditions in both study years, the nitrogen release from the legume mulch was retarded and BNF in mulched lucerne was not reduced. Assuming low gaseous N losses by mulching (15–30 kg N ha⁻¹), the green manure system reached a positive N balance (+137 to +186 kg N ha⁻¹) for the subsequent crops because abundant residues remained on the field.     

Comparative growth of spring-planted canola, brown mustard and camelina

With increased emphasis for diesel substitution, production of brown mustard (Brassica juncea), canola (Brassica napus) and camelina (Camelina sativa) used as biodiesels may increase in the High Plains. Since these are new crops to this region, understanding their growth is critical for their acceptance. The objective was to elucidate the growth pattern of these crops when spring-planted in western Nebraska. Field trials were conducted in 2005, 2006 and 2007 with early May planting. Plots were seeded 2 cm deep at 200 plants m⁻². Four plants were destructively sampled at about 28, 40, 53, 61, and 82 days after planting (DAP). Canopy growth was field measured. Canopy heights peaked by 61 DAP at 95, 85 and 70 cm for brown mustard, canola and camelina, respectively. Stem length increased to 82 DAP at the rates of 1.24, 1.22 and 0.85 cm/d for brown mustard, canola and camelina, respectively. Root weight accumulated linearly from 28 to 61 DAP. The Brassica grew roots faster and achieved higher weights than camelina. From 28 to 40 DAP, vine fresh weight accumulated rapidly for these crops, leveled and then gradually declined as leaves desiccated. Vine dry weight increased to 61 DAP and then plateaued. The maximum vine dry weights, reached at 61 DAP, were 4.3, 4.5 and 3.0 g/plant for brown mustard, canola and camelina, respectively. By 61 DAP, pods were present and accumulated dry matter while leaves senesced. Pod fresh weight reached its peak at 61 DAP while its dry weight increased linearly to 82 DAP at rates of 0.36, 0.24 and 0.096 g/d for brown mustard, canola and camelina, respectively. Harvest in 2006 showed no significant (p < 0.05) difference between crops with a mean yield of about 1500 kg ha⁻¹. Fatty acid composition was dramatically different between the crops as previously reported. The growth patterns of these crops indicated that all three would be suitable for production in the northern High Plains.     

Effect of trifluralin,pronamide, haloxyfop-p methyl,propaquizafop, and isoxaben on weed control and oilseed rape yield in Iran

In order to investigate the effect of trifluralin, pronamide, haloxyfop-p methyl, propaquizafop and isoxaben on weed control and oilseed rape yield, a two year field experiment was conducted at Darab, Iran, during 2004–2005 and 2005–2006 growing seasons. Herbicides reduced weed biomass compared with the weedy check. In 2004–2005, at 16 WAP (weeks after planting), application of trifluralin plus propaquizafop plus isoxaben at 1200 + 200 + 250 g a.i./ha and trifluralin plus haloxyfop-p methyl plus isoxaben at 1200 + 100 + 500 g a.i./ha provided best control (80%) of wild mustard (Sinapis arvensis L.), compared to other treatments. At 8 and 16 WAP, wild mustard control decreased to 47 and 42%, respectively, when trifluralin was applied alone at 1400 g a.i./ha. In 2005–2006 at 16 WAP, maximum reduction in wild mustard biomass (82%) was achieved with trifluralin plus propaquizafop plus isoxaben at 1200 + 200 + 250 g a.i./ha. In both years, all herbicide treatments controlled fumitory (Fumaria officinalis L.) 64–96%. In 2004–2005, at 16 WAP, wild oat (Avena fatua L.) biomass reduction by trifluralin plus propaquizafop plus isoxaben at 1200 + 200 + 250 g a.i./ha was 95%. In 2005–2006, at 8 and 16 WAP, minimum biomass reduction of wild oat (37–53%) was observed with trifluralin at 1200 and 1400 g a.i./ha. In both years, at 8 and 16 WAP, the most effective herbicide treatments were trifluralin plus propaquizafop plus isoxaben and trifluralin plus haloxyfop-p methyl plus isoxaben regardless of the dose applied and provided maximum reduction in total weed biomass (77–89%) compared to other treatments. Results of both years showed that all herbicide treatments increased oilseed rape grain yield as compared with the weedy check but percentage of oil was not affected by various herbicide treatments. Maximum grain yield was obtained with trifluralin plus haloxyfop-p methyl plus isoxaben at 1200 + 100 + 500 g a.i./ha.     

Changes in agronomic traits of sunflower hybrids over 20 years of breeding in central Argentina

This paper applies linear mixed model and pattern analyses to 122 on-farm trials of commercial and near-commercial sunflower (Helianthus annuus L.) hybrids grown over 15 years in 32 locations of central Argentina to determine the contributions of change in characteristics of germplasm pools to increases in oil yield. The ‘Relative Peak Performance’ (best linear unbiased predictors, BLUPs) of 49 hybrids released for the conventional market between 1983 and 2005 showed genetic gains of 11.9 kg ha⁻¹ year⁻¹, 0.19% year⁻¹ and 16.1 kg ha⁻¹ year⁻¹ for oil yield, grain-oil concentration and grain yield, respectively. Oil yield improvement was consistent across three market segments and a biplot of genotype-by-attribute BLUPs summarised 20 years of breeding to demonstrate how the merging of two germplasm pools of differing maturity, achene type and grain-oil concentration resulted in step-wise improvements in grain yield and grain-oil concentration and a move toward an intermediate maturity. The analysis of general combining ability within a breeding program shows that the female and male germplasm pools were improved in different ways over time. On the female side, much of this improvement was to encompass different combinations of the determining traits of oil yield, while on the male side the improvement was more linear in terms of exploitation of genotypic variance for oil yield per se.     

Impact of organic manure and chemical fertilizers on artemisinin content and yield in Artemisia annua L

Artemisinin isolated from the aerial parts of Artemisia annua L. is a promising and potent antimalarial drug. It posses remarkable activity against both chloroquinine resistant as well as chloroquinine sensitive strains of Plasmodium falciparum. It is also useful in the treatment of cerebral malaria. The relatively low content of artemisinin in A. annua and unavailability of cost effective and viable synthetic protocol however, are major obstacles to the commercial production of the drug. The enhanced production of artemisinin is hence, highly desirable, which can be achieved by adequate and judicious supply of plant nutrients. The present experiment was therefore, designed to study the effect of organic manure (15 tonnes ha⁻¹) and chemical fertilizers (N₄₀₊₄₀, P₄₀, K₄₀, S₁₅₊₁₅ kg ha⁻¹; nitrogen, phosphorus, potassium and sulphur) on the accumulation of artemisinin and biomass in various plant parts through the developmental stages of A. annua L. Artemisinin yield (kg ha⁻¹) was also determined through the developmental stages of A. annua L. Artemisinin content and artemisinin yield of dried leaves were increased significantly at pre-flowering stage in the plants treated with NPKS (27.3% and 53.6%) and NPK (18.2% and 33.5%), respectively, when compared with control. Maximum dry yield of leaf ranging from 2596 to 3141 kg ha⁻¹ was observed at pre-flowering stage with various treatments.     

Progress over 20 years of sunflower breeding in central Argentina

This paper applies linear mixed model analysis to 122 on-farm trials of commercial and near-commercial sunflower (Helianthus annuus L.) hybrids grown over 15 years in 32 locations of central Argentina to quantify increases in oil yield and to determine the contributions of change in both biotic stress resistance and yielding ability in favourable environments. The best linear unbiased predictors (BLUPs) from this analysis can be regarded as measures of ‘relative peak performance’ of hybrids in environments for which they were selected, and are a better measure of their adaptation compared to small trial sets of ‘historical’ hybrids. The BLUPs of 49 commercial hybrids released between 1983 and 2005 showed a genetic gain for oil yield of 11.9 kg ha⁻¹ yr⁻¹. Special purpose hybrids that were converted for single traits or that were developed for low-technology markets lagged by 5–15 years in terms of genetic gain. Genetic gains came about due to both an increase in the number of hybrids with resistance to the major biotic stress (Verticillium dahliae Klebahn) and a genetic gain in oil yield of 14.4 kg ha⁻¹ yr⁻¹ within these hybrids. Based on the data and the estimated time lag between commercial release and peak use, the improvement in oil and grain yield of conventional hybrids in central Argentina will be sustained until at least 2010, with evidence that the new germplasm pools still have substantial genetic variance to be exploited.     

Pest-damage relationships for Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) on vegetative soybean

The response of vegetative soybean (Glycine max) to Helicoverpa armigera feeding was studied in irrigated field cages over three years in eastern Australia to determine the relationship between larval density and yield loss, and to develop economic injury levels. Rather than using artificial defoliation techniques, plants were infested with either eggs or larvae of H. armigera, and larvae allowed to feed until death or pupation. Larvae were counted and sized regularly and infestation intensity was calculated in Helicoverpa injury equivalent (HIE) units, where 1 HIE was the consumption of one larva from the start of the infestation period to pupation. In the two experiments where yield loss occurred, the upper threshold for zero yield loss was 7.51 ± 0.21 HIEs and 6.43 ± 1.08 HIEs respectively. In the third experiment, infestation intensity was lower and no loss of seed yield was detected up to 7.0 HIEs. The rate of yield loss/HIE beyond the zero yield loss threshold varied between Experiments 1 and 2 (−9.44 ± 0.80 g and −23.17 ± 3.18 g, respectively). H. armigera infestation also affected plant height and various yield components (including pod and seed numbers and seeds/pod) but did not affect seed size in any experiment. Leaf area loss of plants averaged 841 and 1025 cm²/larva in the two experiments compared to 214 and 302 cm²/larva for cohort larvae feeding on detached leaves at the same time, making clear that artificial defoliation techniques are unsuitable for determining H. armigera economic injury levels on vegetative soybean. Analysis of canopy leaf area and pod profiles indicated that leaf and pod loss occurred from the top of the plant downwards. However, there was an increase in pod numbers closer to the ground at higher pest densities as the plant attempted to compensate for damage. Defoliation at the damage threshold was 18.6 and 28.0% in Experiments 1 and 2, indicating that yield loss from H. armigera feeding occurred at much lower levels of defoliation than previously indicated by artificial defoliation studies. Based on these results, the economic injury level for H. armigera on vegetative soybean is approximately 7.3 HIEs/row-metre in 91 cm rows or 8.0 HIEs/m².