Effect of the insect growth regulator novaluron on diamondback moth, Plutella xylostella L. (Lepidoptera: Plutellidae), and its indigenous parasitoids

Research to evaluate effective and selective insecticides through periodic screening is needed to strengthen diamondback moth (DBM) (Plutella xylostella L.) management. The efficacy of the insect growth regulator novaluron on DBM and effects on the parasitoids Diadegma sp. (Hym.: Ichneumonidae), Apanteles sp. (Hym.: Braconidae) and Oomyzus sokolowskii Kurdjumov (Hym.: Eulophidae) were evaluated. Novaluron was compared with the microbial insecticide Bacillus thuringiensis (Bt) var. aizawai, the pyrethroid insecticide λ- cyhalothrin and the organophosphate insecticide profenofos. Two replicated experiments were conducted on head cabbage, Brassica oleracea var. capitata, planted in March and May 2007 at Wonji in the Central Rift Valley of Ethiopia. Infestation by DBM was less with novaluron and Bt compared with other treatments for both planting dates. Infestation with λ-cyhalothrin and profenofos was comparable with the untreated control. Yields were greatest with novaluron and were 80 and 32.5% (12.4 and 7.4 t ha⁻¹) greater than the untreated treatment for the first and second plantings, respectively. Diadegma sp. accounted for 91% of the parasitoid complex observed. Parasitism of DBM by Diadegma sp. ranged between 10 and 43% among treatments. Parasitism was less with λ-cyhalothrin and profenofos compared with other treatments. Owing to its efficacy against DBM and relative safety to its parasitoid, Diadegma sp., novaluron can be used in integrated DBM management for low elevation brassica production in the Central Rift Valley of Ethiopia.     

Influence of rate of development of water deficit on the expression of maximum osmotic adjustment and desiccation tolerance in three grain sorghum lines

An experiment was conducted to quantify the effect of rate of development of water deficit (R_ψ) on the expression of maximum osmotic adjustment (OA) and desiccation tolerance (DT) in three grain sorghum lines, TAM422, Tx2813 and QL27. DT was determined as the lethal relative water content (RWC^L) and lethal leaf water potential (ψ^L) of leaves, i.e. the value of these traits just prior to tissue death. Five rates of development of water deficit were generated by using different soil volumes in which the decrease in leaf water potential ranged from 0.093 MPa day⁻¹ to 0.153 MPa day⁻¹. The expression of maximum OA increased markedly with a reduced R_ψ, for all three lines. In contrast, DT decreased only slightly with a reduced R_ψ. The three lines differed for expression of maximum OA and DT. Both TAM422 and Tx2813 had higher maximum OA, higher RWC^L and lower ψ^L than QL27. There was a significant line-by-R_ψ interaction for the expression of OA and DT. The interaction was much smaller than the effect of lines for the expression of maximum OA. Therefore, the absolute level of OA for the three sorghum lines and the magnitude of the difference between them changed with the R_ψ without affecting their ranking. As with maximum OA, the interaction for RWC^L was smaller than the line effect. The RWC^L of TAM422 and QL27 was stable across rates of development of water deficit. The results indicated that low R_ψ increased the expression of OA and decreased ψ^L but had little effect on RWC^L. While line-by-soil-volume interactions were observed, these were largely explained by the increase in magnitude of the variation for the traits as R_ψ decreased and were not the result of changes in rank of the lines among soil volumes. Therefore, the current screening strategy is considered to be appropriate for examining genetic variation for OA and DT in grain sorghum. Opportunities exist for using smaller pots and soil volumes where large numbers of genotypes are examined.     

Evaluation of chemical disinfestants in reducing Verticillium dahliae conidia in irrigation water

Irrigation water disinfestation is an unexplored option for reducing Verticillium dahliae inoculum in water and consequently for more efficiently managing Verticillium wilts in Andalusia. We assessed Suppressive Efficacy (SE; water was infested and subsequently treated) and Preventive Efficacy (PE; previously treated water was subsequently inoculated) of OX-VIRIN^®, OX-AGUA AL 25^® and Deccoklor^® in reducing water infestations by V. dahliae conidia. Five concentrations of each disinfestant, the lowest three being recommended by the manufacturer, were tested in vitro against six V. dahliae isolates. Validation assays were carried out in experiments under natural environmental conditions in spring. The four highest concentrations of OX-VIRIN^® (0.8–51.2 mL L⁻¹), the three highest of OX-AGUA AL 25^® (46.4–417.5 μL L⁻¹) and the two highest of Deccoklor^® (0.375 and 3.75 mL L⁻¹), showed an in vitro-efficacy (SE and PE) of 96.2, 80.0 and 100.0% after 30, 5 to 30 and 15 days respectively. Therefore, recommended concentrations for OX-VIRIN^® and OX-AGUA AL 25^® showed a greater in vitro-effectiveness than those recommended for Deccoklor^®. Assays in natural environmental conditions proved that OX-VIRIN^® at the recommended concentration of 3.2-mL L⁻¹, applied every 28 days to water, was the most effective treatment (SE and PE), with a 100% reduction of the average relative viability after 56 days. Other chemical treatments showing high in vitro-efficacy, such as OX-VIRIN^® at 0.8 mL L⁻¹ and OX-AGUA AL 25^® at 46.4 μL L⁻¹ showed an SE of 99.9% after 14 and 28 days when applied every 28 and 14 days, respectively. However, PE of OX-AGUA AL 25^® at 46.4 μL L⁻¹ was only 59 and 38% after 28 and 14 days respectively, depending on the experiment.     

Comparison of selection indices to identify productive dry bean lines under diverse environmental conditions

This research was designed to quantify the effect of seasonal rainfall on production of dry bean (Phaseolus vulgaris L.) in the Rift Valley of East Africa, where insufficient soil moisture often limits productivity, and compare methods to identify productive lines. Twenty dry bean lines were evaluated for seed yield in a randomized complete-block design under soil moisture stress and nonstress environments during 1988, 1989 and 1992. Soil moisture stress levels were imposed by altering sowing dates (early vs. late) after the onset of the rainy season. Mean seed yield increased 8 kg ha⁻¹ for each mm of seasonal rainfall that occurred during the growing season. Lines differed in response to soil moisture stress, and their response varied with environments. Six selection indices, including arithmetic mean (AM), geometric mean (GM), drought response index (DRI), susceptibility index (S), response to drought (RD), and percent reduction (PR), were calculated for each line to determine correlations between indices and yields in stress (Y_s) and nonstress (Y_ns) environments. AM and GM were the only indices positively correlated with both Y_s and Y_ns. AM had the largest correlation with Y_ns (r=0.90) whereas GM had the largest correlation with Y_s (r=0.93). DRI, PR and S were correlated with Y_s (r=0.86, −0.82 and −0.83, respectively) but not with Y_ns. Conversely, the index RD was correlated with Y_ns (r=0.73) but not Y_s. The indices PR and S evaluated change in line performance across environments rather than line performance in either environment. GM and AM appear to be the most useful selection indices for identifying high yielding lines for both nonstress (early sown) and stress (late sown) conditions in the Rift Valley, while DRI has potential for use as a selection criteria only for stress environments.     

Radiation utilization efficiency,latent heat flux,and crop growth simulation in irrigated rice during post-flood period in east coast of India

To study the radiation utilization efficiency, latent heat flux, and simulate growth of rice during post-flood period in eastern coast of India, on-farm trial was conducted with three water regimes in main plots (W ₁ = continuous flooding of 5 cm, W ₂ = irrigation after 2 days of water disappearance, and W ₃ = irrigation after 5 days of water disappearance) and five nitrogen levels in subplots (N ₁ = 0 kg N ha^?1, N ₂ = 60 kg N ha^?1, N ₃ = 90 kg N ha^?1, N ₄ = 120 kg N ha^?1, and N ₅ = 150 kg N ha^?1) on a rice cultivar, ‘Lalat’. Average maximum radiation utilization efficiency (RUE) in terms of above ground dry biomass of 2.09 (±0.05), 2.10 (±0.02), and 1.9 (±0.08) g MJ^?1 were computed under W ₁, W ₂, and W ₃, respectively. Nitrogen increased the RUE significantly, mean RUE values were computed as 1.60 (±0.07), 1.78 (±0.02), 2.060 (±0.08), 2.30 (±0.07), and 2.34 (±0.08) g MJ^?1 when the crop was grown with 0, 60, 90, 120, and 150 kg ha^?1 nitrogen, respectively. Midday average latent heat flux (on clear days) varied from 7.4 to 14.9 and 8 to 13.6 MJ m^?2 day^?1 under W ₂ and W ₃ treatments, respectively, at different growth stages of the crop in different seasons. The DSSAT 4.5 model was used to simulate phenology, growth, and yield which predicted fairly well under higher dose of nitrogen (90 kg and above), but the model performance was found to be poor under low-nitrogen dose.     

Phenotyping of Urochloa humidicola grass hybrids for agronomic and environmental performance in the Piedmont region of the Orinoquian savannas of Colombia

In the low fertility acid soils of the Orinoquian savannas of Colombia, Urochloa humidicola cv. Tully or Humidicola is one of the most widely planted tropical forage grasses for improving livestock productivity. Low nutritional quality of this grass limits sustainable livestock production in this region. In this study, we conducted a phenotypic evaluation under field and greenhouse conditions of one of the first hybrid populations of U. humidicola generated from the forage breeding program of CIAT. Our objective was to identify a set of new hybrids of U. humidicola that combine improved productivity and nutritional quality plus the biological nitrification inhibition (BNI) trait/ability to reduce nitrogen (N) losses via leaching and nitrous oxide (N₂O) emissions. To this end, we tested 118 hybrids (planted in pots) in the greenhouse for over 6 months and measured potential nitrification rates (NR) using soil microcosm incubation. NR values observed ranged from 0.27 to 5.75 mg N-NO₃⁻ kg soil⁻¹ day⁻¹. Later, 12 hybrids with different levels of NR were selected and field-tested in the Orinoquia region over a 4 years period (2013–2017) for dry matter production, nutrition quality (crude protein, in vitro digestibility and fibres content) and NR in each year. In the rainy season of 2018, two hybrids with superior agronomic performance and contrasting field level NR (Uh08/1149 and 0450) were subjected to analysis of soil-borne N₂O emissions after fertilization during 13 days. The NR values recorded were not directly correlated with the forage quality parameters evaluated, however, the two grasses with the lowest NR values were among those with the highest biomass production, crude protein content, and N uptake. The grass hybrid Uh08/1149 and the germplasm accession CIAT 16888 were found as materials with superior forage value, with production of 14.1 and 14.6 tons dry matter ha⁻¹ year⁻¹ (up to 8% higher than the cv. Tully), crude protein of 11.5 and 9.1% per cut (up to 20% higher than the cv. Tully), and N uptake of 31.6 and 25.7 kg N ha⁻¹ cut⁻¹ (up to 30% higher than the cv. Tully). Additionally, these two grasses are likely to exhibit high-BNI ability, with potential to improve N use efficiency in managed pastures.     

Effect of the type of fertilizer and source of irrigation water on N use in a maize crop

An experiment in a maize crop evaluated the influence of several types of commercial nitrogenous fertilizers with different action mechanisms — urea (soluble), Floranid-32 (low water solubility) and Multicote 4 (coated fertilizer) — on maize grain and biomass yields, as well as on plant N use. The fertilizers were applied as a top-dressing of 294 kg N ha⁻¹. All treatments additionally received 64 kg N ha⁻¹ as 8.0 (N):6.5 (P):12.5 (K) compound prior to seedbed preparation. The influence of NO⁻₃ content in the irrigation water was also assessed, using water with either 2.5 or 35 mg l⁻¹ of NO⁻₃. Irrigation plus rainfall totalled 513 mm (1.20 potential ET). Nitrogen lost during the cultivation period was calculated from the N balance of the topsoil.Results obtained under these experimental conditions showed that the type of fertilizer did not alter maize grain and biomass yields. Yields for maize irrigated with the higher NO⁻₃ water were systematically greater than those obtained with irrigation water of low NO⁻₃ content.Nitrogen lost from the topsoil during the cultivation period varied between 240 and 280 kg N ha⁻¹ for all treatments, and was well correlated with NO⁻₃-N leached into the aquifer during the same period.     

Effects of soil water content and nitrogen supply on the productivity of Miscanthus × giganteus Greef et Deu. in a Mediterranean environment

Miscanthus × giganteus is one of the most promising biomass crops for non-food utilisation. Taking into account its area of origin (Far East), its temperature and rainfall requirements are not well satisfied in Mediterranean climate. For this purpose, a research was carried out with the aim of studying the adaptation of the species to the Mediterranean environment, and at analysing its ecophysiological and productive response to different soil water and nitrogen conditions. A split plot experimental design with three levels of irrigation (I₁, I₂ and I₃ at 25%, 50% and 100% of maximum evapotranspiration (ETm), respectively) and three levels of nitrogen fertilisation (0 kg ha⁻¹: N₀, 60 kg ha⁻¹: N₁ and 120 kg ha⁻¹: N₂ of nitrogen) were studied. The crop showed a high yield potential under well-watered conditions (up to 27 t ha⁻¹ of dry matter). M. × giganteus, in Mediterranean environment showed a high yield potential even in very limited water availability conditions (more than 14 t ha⁻¹ with a 25% ETm restoration). A responsiveness to nitrogen supply, with great yield increases when water was not limiting, was exhibited. Water use efficiency (WUE) achieved the highest values in limited soil water availability (between 4.51 and 4.83 g l⁻¹), whilst in non-limiting water conditions it decreased down to 2.56 and 3.49 g l⁻¹ (in the second and third year of experiment, respectively). Nitrogen use efficiency (NUE) decreased with the increase of water distributed (from 190.5 g g⁻¹ of I₀ to 173.2 g g⁻¹ of I₂); in relation to N fertilisation it did not change between the N fertilised treatments (N₁ and N₂), being much higher in the unfertilised control (177.1 g g⁻¹). Radiation use efficiency (NUE) progressively declined with the reduction of the N fertiliser level (1.05, 0.96 and 0.86 g d.m. MJ⁻¹, in 1994, and 0.92, 0.91 and 0.69 g d.m. MJ⁻¹, in 1995, for N₂, N₁ and N₀, respectively).     

Relations between summer crops and ground cover legumes in a subtropical environment 3. Soil water use under sorghum and sunflower

Vigna trilobata (L.) Verdc. and Medicago scutellata L. are short herbaceous legumes that help to reduce soil erosion when grown in association with row crops in the sub-humid/semi-arid subtropics. Soil water use and root distribution beneath sorghum (Sorghum bicolor (L.) Moench) and sunflower (Helianthus annuus L.) with and without V. trilobata were measured on a vertisol in South East Queensland. Sorghum was sown in October and January at densities of 10 and 5 plants m⁻² and sunflower at densities of 5 and 2.5 plants m⁻². V. trilobata seed was broadcast at 150 seeds m⁻². Pure stands of V. trilobata and M. scutellata were also sown.Soil profiles were uniformly wet to at least 2 m depth at each sowing date and remained so for the first 40 days of each growth cycle. Thereafter profiles dried rapidly over the next 40 days, providing opportunities for assessing soil water use. Subsequent rain restored and sustained profile water content until crop maturity.Undersown V. trilobata hastened soil drying, resulting in the extraction of 21 mm more water by maturity of the October sown crops. In pure stands, V. trilobata extracted water at the same rate as sunflower from the top 1.0 m of the soil profile, but not from the deeper layers. However, pure stands of M. scutellata extracted much less soil water than V. trilobata, with negligible extraction from below 0.8 m. Sunflower extracted 48 mm more water than sorghum in the January sowing because it had more roots and extracted more water from below 1.4 m.The capacity of V. trilobata to grow deep roots allows it to compete strongly for soil water and decrease yield of the main crop. Thus, a shallow-rooting plant would be preferred as a ground cover.     

Management of herbicide-resistant Phalaris minor in wheat by sequential or tank-mix applications of pre- and post-emergence herbicides in north-western Indo-Gangetic Plains

Development of cross resistance or multiple cross resistance in Phalaris minor in wheat will continue to increase, as the weed develops mechanisms of resistance against new herbicides. This weed is a major threat to wheat productivity in north-western India, and as such needs to be addressed with integrated weed management approaches, including crop and herbicide rotations, herbicide combinations along with cultural and mechanical methods. Three field experiments were conducted during 2008–09 to 2012–13 along with large plot adaptive trials during 2012–13 with the objective to evaluate the efficacy of sequential applications of pendimethalin applied pre-emergent followed by clodinafop, sulfosulfuron, or pinoxaden applied post-emergent and tank-mix applications of metribuzin with these post-emergence herbicides for the management of herbicide-resistant P. minor in wheat. Clodinafop 60 g ha⁻¹ or sulfosulfuron 25 g ha⁻¹ at 35 days after sowing (DAS) and pendimethalin 1000 g ha⁻¹ as pre-emergence did not provide consistently effective control of P. minor in wheat. An increase in the dose of clodinafop from 60 to 75 g ha⁻¹ and of sulfosulfuron from 25 to 30 g ha⁻¹ also did not improve their efficacy to a satisfactory level. However, pinoxaden 50 g ha⁻¹ provided effective control (97–100%) of P. minor but not of broadleaf weeds. The tank-mix application of metribuzin with clodinafop 60 g ha⁻¹ or sulfosulfuron 25 g ha⁻¹ at 35 DAS and the sequential application of pendimethalin 1000 g ha⁻¹ or trifluralin 1000 g ha⁻¹ just after sowing followed by clodinafop 60 g ha⁻¹ or sulfosulfuron 25 g ha⁻¹ at 35 DAS provided 90–100% control of P. minor along with broadleaf weeds in wheat, thus resulting in improved grain yields (4.72–5.75 t ha⁻¹) when compared to clodinafop 60 g ha⁻¹ (3.85–5.60 t ha⁻¹) or sulfosulfuron 25 g ha⁻¹ alone (3.95–5.10 t ha⁻¹). The efficacy of mesosulfuron + iodosulfuron (a commercial mixture) 14.4 g ha⁻¹ against P. minor was not consistent across the experiments and over the years. The ready-mix combination of fenoxaprop + metribuzin (100 + 175 g ha⁻¹) at 35 DAS provided effective control of weeds but its varietal sensitivity needs to be determined before its use in field conditions. The tank-mix or sequential application of herbicides would be a better option than their applications alone to manage the serious problem of herbicide-resistant P. minor in wheat.     

Effect of neemarin on life table indices of Plutella xylostella (L.)

The effects of neemarin at 5, 10, 15 and 20 mg l⁻¹ on the life table indices of Plutella xylostella (L.) were studied on cauliflower in the laboratory. Survivorship was increased with increasing concentrations. A total of 69% eggs hatched at 20 mg l⁻¹ compared 85% in the control. Mortality (d_x) of 1st instars was higher than the other instars in both exposed and unexposed individuals. Life expectancy (e_x) was high in the untreated control and reduced at 20 mg l⁻¹. Development times of immatures were prolonged to 32 days at 20 mg l⁻¹ as compared to 18.6 days in the untreated control. Neemarin significantly reduced the emergence of adults. Potential fecundity (P_f) was 34 females/female/generation at 20 mg l⁻¹ and 92 in the control. The net reproductive rate (R₀) was significantly reduced with the increase in concentration. The intrinsic rate of increase (r_m) and finite rate of increase (λ) were significantly decreased at 20 mg l⁻¹ as compared to other concentrations tested and in the control. Mean generation time (T_c) and corrected generation time (τ) were prolonged at 20 mg l⁻¹ and significantly differed to those of the untreated control. Doubling time (DT) was significantly extended to 28.4 days at 20 mg l⁻¹ as compared to 6.1 days in the control.     

Radiation interception and the accumulation of biomass and nitrogen by soybean and three tropical annual forage legumes

Field experiments were conducted at Gatton and Dalby in southeastern Queensland to determine parameters associated with radiation interception and biomass and nitrogen (N) accumulation for the ley legume species, phasey bean (Macroptilum lathyroides (L.) Urban) and vigna, (Vigna trilobata (L.) Verdc.). Sesbania (Sesbania cannabina Retz.), a native legume species, and soybean (Glycine max (L.) Merrill)) were included in the study for comparison. The most important differences between species related to differences in radiation interception, radiation-use efficiency (RUE), N-accumulation efficiency and the partitioning of N to plant parts. During early growth, soybean intercepted more radiation than the other species, primarily because of its greater leaf area index (LAI). Sesbania had the highest RUE (1.08 g MJ⁻¹) followed by phasey bean (0.94 g MJ⁻¹), soybean (0.89 g MJ⁻¹) and vigna (0.77 g MJ⁻¹). The efficiency of N-accumulation was greater in soybean (0.028 g N g⁻¹) and phasey bean (0.030 g N g⁻¹) than in vigna (0.022 g N g⁻¹) and sesbania (0.021 g N g⁻¹). In all species, the proportion of N allocated to leaves declined throughout the experimental period, being more rapid in soybean than in sesbania and phasey bean. Despite this decline in total N partitioned to the leaves, both soybean and phasey bean maintained a relatively stable specific leaf nitrogen (SPLN) throughout the experimental periods although sesbania and vigna displayed rapid decreases in SPLN. The large variation between species in RUE and N-accumulation efficiency indicates that the development of ley legume cultivars with a combination of traits for more efficient legume production, water use and soil N-accumulation in the water-limited environments of the grain belt of eastern Australia may be possible. The sensitivity of forage production, water use and soil N-accumulation to variation in RUE and N-accumulation efficiency needs to be quantified using modeling techniques prior to embarking on screening programs to select appropriate germplasm for evaluation studies.     

Demographic changes in Helicoverpa armigera after exposure to neemazal (1% EC azadirachtin)

We estimated the effect of 5, 10, 15 and 20 mg l⁻¹ of neemazal (1% EC azadirachtin) on life table parameters of Helicoverpa armigera (Hübner) developing on chickpea (Cicer arietinum L.). The effects were assessed on the survivals emerged from 6th instar larvae that had ingested neemazal-treated chickpea pods. Survivorship (I) and expectancy of life (e_x) were highest with the commencement of age (egg) and decreased gradually with the advancement of age with all the concentrations of neemazal including unexposed cohort. All the eggs hatched in the unexposed group while highest numbers of unhatched eggs (10%) were recorded with 20 mg l⁻¹. Mortality of 1st instars was higher at 20 and 15 mg l⁻¹ than that of other concentration tested. Potential fecundity (pf) was reduced in concentration dependent manner and was lowest with 20 mg l⁻¹ (418 eggs/female/generation) and highest in control (898 eggs/female/generation). Net reproductive rate (R₀) was significantly reduced with the increase in concentration of neemazal. The intrinsic (r_m) and finite rate of increase (λ) were significantly decreased at 20 mg l⁻¹ than that of unexposed population. The mean generation time (T_c) was prolonged at 20 mg l⁻¹ and significantly differed with non-treated individuals. Development of immature stages was prolonged to 38 days with 20 mg l⁻¹ while reduced to 32 days with 15 mg l⁻¹ of neemazal as compared to 37 days in untreated individuals. Doubling time (DT) was significantly extended to 5.02 days with 20 mg l⁻¹ as compared to 3.84 days in the non exposed ones.     

Using dazomet to reduce broomrape seed banks in soils with low moisture content

Dazomet (Basamid^®) is a dry powder formulation that releases the toxic gas methyl isothiocyanate for the control of soil borne pests and weed seeds when applied to moist soils. We evaluated its efficacy for destroying Phelipanche mutelii (branched broomrape) seed banks. Dazomet is typically used where effectiveness can be improved with the addition of water but we examined its performance in soils with low moisture content in container experiments and field trials. In containers, less than 10% of P. mutelii seed remained viable 30 days after dazomet applications of 112.8–338.4 kg ha⁻¹ at soil moisture content from 0.05 to 0.15 g g⁻¹. Seeds buried at a depth of 5 cm needed to be in contact with the product for longer than one week before viability was affected. An initial field trial did not detect a decline in seed viability 7 days after dazomet application. Viability assessments in a second field trial were made 30 days after dazomet application with an airseeder at a rate of 338.4 kg ha⁻¹. Less than 10% of P. mutelii seeds at a depth of 5 cm survived and dazomet was as effective as two other soil fumigants, methyl bromide and a methyl iodide/chloropicrin mixture. The release of methyl isothiocyanate is reduced in soils in containers with low soil moisture content but occurs over a long time period. Methyl isothiocyanate dissipated more rapidly in soils in containers with higher soil moisture content and at lower dazomet application rates. A higher application rate is required in the field to ensure the dazomet powder is evenly distributed through the soil profile and there is adequate methyl isothiocyanate resident in the top soil layer to achieve seed kill. This has consequences for plant back times in fumigated land following dazomet application.     

Soil fertility management in irrigated rice systems in the Sahel and Savanna regions of West Africa: Part II. Profitability and risk analysis

In irrigated rice production in West Africa, nitrogen (N) and phosphorus (P) fertilizers make up about 20% of total production costs. This research seeks to evaluate whether those fertilizers are profitable under current use by farmers and to identify the factors that may improve fertilizer efficiency and profitability. A combination of farmer surveys and on-farm trials were used to determine actual fertilizer use, costs, and net revenues from fertilizer in key irrigated systems in Mali (Office du Niger), Burkina Faso (Kou Valley), and Senegal (Thiagar and Guédé). A second paper provides an agronomic analysis of soil fertility management at these sites. Net returns to fertilizer use were estimated and value/cost ratios (VCRs) calculated. A value/cost ratio of 1.5–2.0 was considered desirable for farmer adoption under West African conditions. Average VCRs for fertilizers ranged from 1.6 in the Kou Valley in Burkina Faso, to 3.6 in the Office du Niger, Mali. In researcher-managed on-farm trials in Thiagar, Senegal, fertilizers had VCRs of 1.5–3.1. Large N doses of 180 kg N ha⁻¹ still had VCRs of 2.5. Farmers in the region used less than recommended doses of N, with the exception of farmers in the Office du Niger, Mali. With an average application of 89 kg N ha⁻¹, farmers in Thiagar, Senegal were able to gain 54 000 FCFA ha⁻¹ (US$ 110) of net revenues from the fertilizers with fertilizer N recovery rates averaging 34%. Improving that recovery rate by 50% could increase net revenues by 50%. In field trials in Thiagar, increasing N application to 180 kg ha⁻¹ resulted in net returns of near 200 000 FCFA ha⁻¹ for an investment of 118 000 FCFA ha⁻¹. Risk of negative net returns was found in Thiagar and in Kou Valley, and was related to weed infestation and water scarcity, respectively. Farmers in the dry season in Kou Valley had a 33% probability of net losses with fertilizer application because of unreliable water supply. In contrast, no farmers had negative returns in the Office du Niger inspite of high N application rates. Farmers can improve profitability and economic efficiency in irrigated rice production in two ways. First, they can modify crop management practices (date of seeding, date and mode of fertilizer application, etc.) in order to improve the recovery rate of applied N, thus relaxing the nitrogen fertilizer constraint. Second, for farmers able to purchase additional fertilizer, there are gains to be made by increasing applied nitrogen at least to recommended levels in most areas. Credit allocations that restrict fertilizer purchases are counterproductive given the profitability of fertilizers. Negative returns were found only in areas with high risks of water scarcity or weed infestation. Researchers and development agents need to develop more site-specific fertilizer recommendations that correspond to weather, cultivars, prices of inputs and outputs, and fertilizer products.     

Tolerance of Amaranthus palmeri populations from California to postemergence herbicides at various growth stages

In recent years, poor control of Amarathus palmeri S. Wats. plants with glyphosate in many agricultural and non-crop has been observed in the San Joaquin Valley (SJV), California, USA. Studies were conducted to assess if these were glyphosate-resistant (GR) populations. Populations from 23 different locations of the SJV were exposed to glyphosate application of 840 g ae ha⁻¹ at the 5 to 8 leaf stage of the plant and compared against a known GR and glyphosate-susceptible (GS) population from New Mexico, USA. None of the plants from the SJV survived the glyphosate application suggesting that they were GS. Plant mortality following application of glyphosate (840 g ae ha⁻¹), glufosinate (490 g ai ha⁻¹), paraquat dichloride (660 g ai ha⁻¹), saflufenacil (50 g ai ha⁻¹), rimsulfuron (70 g ai ha⁻¹⁾, and a tank-mix of glyphosate (840 g ae ha⁻¹) + saflufenacil (50 g ai ha⁻¹) applied at the 4 to 6, 8 to 10, and 12 to 16 leaf stages of A. palmeri was determined on potted plants grown outdoors. Complete control was obtained with all the treatments applied at the 4 to 6 leaf stage but control was reduced to less than 70% and 20% with glyphosate and glufosinate, respectively at the later stages. The other treatments provided 100% control at all growth stages. Combinations of saflufenacil + glyphosate, saflufenacil + glufosinate, saflufenacil + dicamba, rimsulfuron + glyphosate, tembotrione + glyphosate, flumioxazin + pyroxasulfone + glyphosate, flumioxazin + pyroxasulfone + glyphosate, dicamba + paraquat dichloride, and glyphosate + glufosinate were also tested on 8 to 10 leaf stage A. palmeri plants and all the combinations provided 100% control.     

Influence of mineral nitrogen on nitrogen fixation by lupin (Lupinus angustifolius) as assessed by 15N isotope dilution methods

The effect of soil mineral N (NO₃+NH₄) on the proportion (P) of N₂ fixed by lupin (Lupinus angustifolius cv. Illyarrie) grown on red-earth over two seasons was measured in field crops by ¹⁵N isotope dilution, using either the natural abundance of ¹⁵N or enrichment of soil N with K¹⁵NO₃. The reference plants used were wheat or linseed. Differences in concentrations of soil mineral N were induced by pretreatment with either cereal straw (3, 6 or 15 t ha⁻¹) or ammonium nitrate (60, 90, 100, 120, or 150 kg N ha⁻¹).The two ¹⁵N method produced similar estimates of P in untreated soil, but for some treatments there were substantial discrepancies between the natural abundance and the enrichment methods. In addition, although the effect of fertilizer N was evident regardless of the reference plant, linseed gave higher estimates of P than did wheat. The possible reasons for these differences are discussed.From values determined after enrichment of soil N with ¹⁵N and with wheat as a reference, P declined by up to 0.23 units with additions of ammonium nitrate up to 150 kg N ha⁻¹. In the N fertilizer treatments, mineral N substituted for fixed N₂ since the total N of lupin was unaffected by the level of soil mineral N. Pretreatment with N fertilizer (90 or 150 kg N ha⁻¹) diminished the potential benefit to soil N from N₂ fixation by lupin, producing an average net loss of 33 kg N ha⁻¹. At sowing, cereal straw had reduced soil mineral N. However, although this soil treatment did not significantly reduced total lupin N, no significant increase in N₂ fixation was detected.     

Evaluation of potential biocides for control of the earthworm Eukerria saltensis (Oligochaeta: Ocnerodrilidae), a pest of rice in southern Australia

The earthworm Eukerria saltensis can cause severe crop establishment problems in aerially sown rice grown on heavy clay soils in southern Australia. Damage occurs indirectly through destabilization of the topsoil, increased water turbidity, and mobilization of soil nutrients into the water column which leads to increased algal growth. We investigated the possibilities for chemical control of E. saltensis using laboratory bioassays and a series of field trials involving either the use of enclosures in flooded crops or soil incorporation of pesticides into rice fields during fallow periods or shortly before flooding. The four most toxic compounds in 7 day soil/water laboratory bioassays were carbofuran, acetamiprid, bendiocarb and lambda-cyhalothrin which provided corrected mortalities of 86–100% at 2 mg a.i. L⁻¹. Other compounds that showed some level of efficacy (corrected mortality >20% at one or more rates) were imidacloprid, esfenvalerate, thiacloprid, niclosamide and alpha-cypermethrin. Twenty-six of the 38 pesticides evaluated failed to produce mean corrected mortalities >6% at application rates of up to 2 mg a.i. L⁻¹. Eight trials were conducted in flooded rice crops using small stainless steel enclosures and carbofuran, thiodicarb, niclosamide and bendiocarb at rates of 1 and 2 kg a.i. ha⁻¹. Trials were assessed 8–14 days after chemical application. None of these treatments produced a statistically significant decrease in Eukerria biomass, although consistent downward trends in response to higher treatment rates were evident in 2 trials (one with carbofuran and one with bendiocarb). Three trials with liquid pesticides watered into fallow rice fields were conducted with carbofuran (0.5, 1.0 and 5.0 kg a.i. ha⁻¹) and thiodicarb (0.94 and 1.87 kg a.i. ha⁻¹) however only the 5.0 kg a.i. ha⁻¹ carbofuran treatment provided significant (P < 0.05) levels of control. Preflood soil applications of liquid carbofuran, thiodicarb and niclosamide (2 kg a.i. ha⁻¹), granular carbofuran and granular ethoprophos (0.5–2 kg a.i. ha⁻¹) also did not provide statistically significant levels of control, although the 2 kg a.i. ha⁻¹ liquid and granular carbofuran treatments did provide moderate levels of suppression (49–84%). Although further field trials with compounds such as acetamiprid and lambda-cyhalothrin may prove valuable, our results suggest chemical control of E. saltensis may be difficult to achieve with environmentally acceptable pesticides applied at economically viable rates. Cultural approaches such as appropriate crop rotations and landforming to ensure uniformly shallow water should continue to form the basis of Eukerria management programs.     

Parthenium hysterophorus L. control in response to pyraflufen-ethyl application

Pyraflufen-ethyl is a phenylpyrazole herbicide for control of annual and perennial broadleaf weeds. Greenhouse and field studies were conducted to determine pyraflufen-ethyl efficacy for control of Parthenium hysterophorus at the rosette and flowering stages, respectively. Both growth stages were treated with pyraflufen-ethyl at six rates ranging from 0.46 to 14.60 g a.i. ha⁻¹. Aboveground dry weight of rosette P. hysterophorus was reduced 90% by pyraflufen-ethyl at 2.33–2.65 g a.i. ha⁻¹ 14 days after treatment (DAT). At the label use rate of 0.91–3.64 g a.i. ha⁻¹ for control of broadleaf weeds, pyraflufen-ethyl was estimated to provide 13–58% and 5–32% control of flowering P. hysterophorus 60 and 87 cm in height, respectively at 21 DAT. These results show that pyraflufen-ethyl can control rosette P. hysterophorus within the label use rate for broadleaf weeds. However, rates higher than the label use rate are required for control of flowering P. hysterophorus, showing that pyraflufen-ethyl must be applied at the early stages of P. hysterophorus growth for effective control.     

Effect of N rate,timing and splitting and N type on bread-making quality in hard red spring wheat under rainfed Mediterranean conditions

Three different experiments were designed to study the effects of N fertilizer rate, timing and splitting, and the response to combined application of N and S fertilizer on the bread-making quality of hard red spring wheat (Triticum aestivum L.) over a 3-year period in Vertisols under rainfed Mediterranean conditions. The following parameters were analyzed: grain yield, test weight, grain protein content, gluten index and alveograph parameters (W: alveogram index; P: dough tenacity; L: dough extensibility; P/L: tenacity–extensibility ratio). The N rate experiment included rates of 0, 100, 150 and 200 kg N ha⁻¹ applied on four different sites. The experiment was designed as a randomized complete block with four blocks. For the experiment on N timing and splitting, a single rate of 150 kg N ha⁻¹ was used, different fractions being applied at sowing, tillering and stem elongation, at a single site; again, experimental design was a randomized complete block with four blocks. Finally, for the experiment on the response to combined application of N and S fertilizer, a single fertilizer dose of 150 kg N ha⁻¹ was applied in two forms (urea+ammonium nitrate and urea+ammonium nitrosulfate) with one leaf application at ear emergence (zero, 25 kg S ha⁻¹, 25 kg N ha⁻¹, $\text{25}\text{kg}\text{S}\text{ha}{}^{\mathrm{-1}}\text{+25}$ kg N ha⁻¹ and 50 kg N ha⁻¹), also at a single site, using a split-plot design with four replications. Year-on-year variation in rainfall led to marked variations in wheat yield, grain protein content and bread-making quality indices. A close correlation was observed between rainfall over the September–May period and both grain yield and grain protein content (optimum values for both being recorded in the rainfall range 500–550 mm) as well as the alveogram index. A negative correlation was observed between mean maximum temperatures in May and both test weight and alveogram index (W). N fertilizer rate had a more consistent effect on bread-making quality than on grain yield. The highest values for grain yield were recorded at an N rate of 100 kg ha⁻¹, while maximum grain protein content values were recorded at 150 kg ha⁻¹. Application of half or one-third of total fertilizer N at stem elongation improved grain yield and grain protein content with respect to applications at sowing alone or at both sowing and tillering. Increased N rates led to a considerable increase in W values and to a reduction in the P/L ratio, thus improving dough balance, with a negative effect on the gluten index. Leaf application of N at ear emergence only affected grain protein content and the W index. Soil or leaf application of S had no effect on protein quality indices. The response of grain yield and grain protein content to fertilizer N differed from that reported for temperate climates.