Popcorn (Zea mays L. var. everta) yield and yield components as influenced by the timing of broadcast flaming

Farmers are interested in producing popcorn under organic production systems and propane flaming could be a significant component of an integrated weed management program. The objective of this study was to collect baseline information on popcorn tolerance to broadcast flaming as influenced by propane dose and crop growth stage at the time of flaming. Field experiments were conducted at the Haskell Agricultural Laboratory of the University of Nebraska, Concord, NE in 2008 and 2009 using five propane doses (0, 13, 24, 44 and 85 kg ha⁻¹) applied at the 2-leaf, 5-leaf and 7-leaf growth stages. Propane was applied using a custom-built research flamer driven at a constant speed of 6.4 km h⁻¹. Crop response to propane dose was described by log-logistic models on the basis of visual estimates of crop injury, yield components (plants m⁻², ears plant⁻¹, kernels cob⁻¹ and 100-kernel weight) and grain yield. Popcorn response to flaming was influenced by the crop growth stage and propane dose. Based on various parameters evaluated, popcorn flamed at the 5-leaf showed the highest tolerance while the 2-leaf was the most susceptible stage. The maximum yield reductions were 45%, 9% and 16% for the 2-leaf, 5-leaf and 7-leaf stages, respectively. In addition, propane doses that resulted in a 5% yield loss were 23 kg ha⁻¹ for the 2-leaf and 7-leaf and 30 kg ha⁻¹ for the 5-leaf stage. Flaming has a potential to be used effectively in organic popcorn production if properly used.     

Timing and propane dose of broadcast flaming to control weed population influenced yield of sweet maize (Zea mays L. var. rugosa)

Farmers are interested to produce sweet maize under organic production systems and propane flaming could be a potential alternative tool for weed control in organic sweet maize production. Therefore, the objective of this study was to investigate the response of sweet maize to broadcast flaming as influenced by propane dose and crop growth stage. Field experiments were conducted at the Haskell Agricultural Laboratory of the University of Nebraska, Concord, NE in 2008 and 2009 using five propane doses applied at three different growth stages of V2 (2-leaf), V5 (5-leaf) and V7 (7-leaf). The propane doses were 0, 13, 24, 44 and 85 kg ha⁻¹. The response of sweet maize to propane flaming was evaluated in terms of visual crop injury, effects on plant height, yield components (plants m⁻², tillers plant⁻¹, number of ears plant⁻¹, cob length and number of seeds cob⁻¹) and fresh marketable yield. The response of different growth stages of sweet maize to propane doses was described by log-logistic models. Based on most parameters tested, V7 was the most tolerant while V2 was the least tolerant stage for broadcast flaming. The maximum yield reductions with the highest propane dose of 85 kg ha⁻¹ were 22%, 12% and 6% for V2, V5 and V7 stages, respectively. Furthermore, a 5% yield reduction was evident with 23, 25 and 36 kg ha⁻¹ of propane for V2, V5 and V7 growth stages, respectively, suggesting that plants flamed at V7 stage can tolerate higher dose of propane for the same yield reduction compared to the other growth stages. We believe that flaming has a potential to be used effectively in organic sweet maize production if properly used.     

Weed control and crop tolerance to propane flaming as influenced by the time of day

Time of day has been observed to affect flaming efficacy. The basis for the differential plant response is not well understood; however, daily variation in leaf relative water content (RWC) is thought to contribute to the response. Leaf RWC is the ratio of the amount of water in the leaf tissue compared to when fully turgid. To determine the influence of leaf RWC in plant response to propane flaming, greenhouse experiments were conducted during April and repeated in September of 2009. Two crops [4-leaf maize (Zea mays) and second trifoliate soybean (Glycine max)] and two weed species [5-leaf velvetleaf (Abutilon theophrasti) and 6-leaf green foxtail (Setaria viridis)] were flamed with four propane doses of 0, 29, 43 and 87 kg ha⁻¹ at 0, 4, 8 and 12 h after sunrise-HAS. Leaf RWC was measured before treatment application. Flaming treatment was conducted utilizing a hand flamer with one VT 2-23 C vapor phase burner positioned 20 cm above soil surface and angled horizontally at 30°. The propane pressure was 120 kPa and the application speeds were 1.6, 3.2 and 4.8 km h⁻¹. The plant responses evaluated were plant injury and fresh weight at 7 days after treatment (DAT). All plant species were more susceptible to flaming during the afternoon when they had lower leaf RWC at 8 HAS; however, the response of these plants did not differ with the plants flamed at 12 HAS. Green foxtail flamed at 87 kg ha⁻¹ at 0, 8 and 12 HAS had injury of 62, 76 and 82%, respectively. The same response was observed in velvetleaf which had 80% injury when flamed with 87 kg ha⁻¹ at 0 HAS and 93% injury when flamed at 12 HAS with the same propane dose at 7 DAT. Similar trends occurred for maize and soybean suggesting that leaf RWC could be one of the factors affecting plant response to flaming. Practical implication is that flaming operation should be conducted in the afternoon in order to improve efficacy of weed control and reduce propane consumption rate.     

Growth stage impacts tolerance of winter wheat (Triticum aestivum L.) to broadcast flaming

Organic wheat producers are interested in testing propane flaming as part of an integrated weed management program for organic wheat production. Therefore, the objective of this study was to collect baseline information on winter wheat tolerance to broadcast flaming as influenced by its growth stage at the time of flaming and dose of propane. Field experiments were conducted at the Haskell Agricultural Laboratory of the University of Nebraska, Concord, Nebraska in 2007–2008 and 2008–2009 utilizing six doses of propane applied at four growth stages including: four leaves-4L, three tillers-3 T, shoot elongation-SE and boot stage-BS. The propane doses were 0, 12, 31, 50, 68 and 87 kg ha⁻¹ and were applied using a custom built flamer driven at a constant speed of around 6 km h⁻¹. Crop response to propane doses was described by log-logistic models based on visual estimates of crop injury, various yield components (spikes m⁻², kernels spike⁻¹ and 1000-kernel weight) and grain yield. Overall response to flaming was influenced by the growth stage of wheat and propane dose. In general, wheat at 3 T was the most tolerant and at BS was the most susceptible stage to broadcast flaming. Flaming negatively affected all yield components of wheat. Reduction of grain yield increased with increase in propane dose at each growth stage. The maximum yield losses of about 21%, 32%, 63% and 74% were obtained with the highest propane dose of 87 kg ha⁻¹ applied at 3 T, SE, 4L and BS growth stages, respectively. Due to unacceptable yield loss, the use of broadcast flaming in winter wheat at the tested growth stages is not recommended.     

The effects of cover cropping on yield and weed control of potato in a transitional system

Cover cropping can have various beneficial effects to the cropping system such us the increase of soil nutrient content and weed suppression. In this respect, the species used for covering is of great importance. This paper reports results on the yield and weed control effects in potato crops preceded by different cover crops over a 2-year period (2003 and 2004) in Central Italy (Viterbo). Results were obtained in the frame of a more complex study set up in 2002 where in a 3-year chick-pea/potato/tomato rotation, each crop was preceded by 7 different soil managements: 5 cover crops (rapeseed, Italian ryegrass, hairy vetch, snail medick and subclover) + 1 unfertilised weedy fallow (cover crop absent) + 1 control (weedy fallow fertilised with mineral N at a rate of 170 kg ha⁻¹ for potato). Two different weed control regimes in potato were also applied [weed-free crop (1 inter-row hoeing + 1 hilling up + manual weeding on the row); mechanical control (1 inter-row hoeing + 1 hilling up)]. Cover crops were sown in September and cut and ploughed just before potato planting in March. The potato crops following the cover crops were only fertilised with green manure. Averaged over years, all the cover crops produced more above-ground dry biomass than the weedy fallow (4.79 t ha⁻¹ on average vs 2.36 t ha⁻¹). Hairy vetch and subclover accumulated the highest N in the incorporated biomass (169 and 147 kg ha⁻¹), followed by snail medick (108), rapeseed (99), ryegrass (88) and weedy fallow (47). Rapeseed and ryegrass were the most efficient weed suppressors and had the least proportion of weed biomass (<1%) of the total produced by the cover, while they also reduced weed emergence in the following potato crops (8.8 plants m⁻²vs 25.5 plants m⁻² with all other cover crops). Following subclover and hairy vetch the potato crop yield was similar to that obtained by mineral N-P-K fertilisation (48.5 t ha⁻¹ of fresh marketable tubers). Mechanical weed control compared to weed free crop always reduced potato yield and the reduction, averaged over years, was greater in N-P-K mineral fertilised control (−23.6%) and smaller in ryegrass (−7.9%).     

Tolerance of selected weed species to broadcast flaming at different growth stages

Organic producers rank weeds as the most important pests that limit their crop production. In order to optimize the use of propane flaming as a weed control tool, the objective of this study was to test tolerance of selected weed species to broadcast flaming performed at different growth stages. Six annual species, including one grass [barnyardgrass (Echinochloa crus-galli)] and five broadleaves [field bindweed (Convolvulus arvensis), kochia (Kochia scoparia), ivyleaf morning glory (Ipomoea hederacea), velvetleaf (Abutilon theophrasti) and Venice mallow (Hibiscus trionum)] were flamed at three growth stages with six doses of propane. The propane doses applied were 0, 12, 31, 50, 68 and 87 kg/ha. Flaming treatments were applied utilizing a custom built flamer mounted on a four-wheeler moving at a constant speed of 6.4 km/h. Species response to propane were described by log-logistic models based on visual injury ratings and dry matter (DM) for each weed species. Overall response to flaming varied among species, growth stage and propane dose. Broadleaf weeds were more susceptible to flaming than the grass regardless of the growth stage. A dose of 76 kg/ha of propane was needed to obtain 90% DM reduction for 7-leaf (L) barnyardgrass compared to much lower doses of 40, 49, 55, 56 and 51 kg/ha propane for 8-L bindweed, 6-L kochia, 10-L morning glory, 7-L velvetleaf and 5-L Venice mallow, respectively. Moreover, the tolerance of both grassy and broadleaf weed species to broadcast flaming increased with increase in plant size. A 90% DM reduction in velvetleaf was obtained with 42, 56 and 102 kg/ha of propane for 5-L, 7-L and 16-L stages, respectively. The tested broadleaf weed species were effectively controlled (90% DM reduction) with propane dose of 30–60 kg/ha when flamed at early growth stages (3-L to 14-L), while the same dose of propane provided only 80% DM reduction in barnyardgrass when flamed at vegetative stages (4-L to 7-L). It was not possible to obtain 90% DM reduction in barnyardgrass when flamed at flowering stage with the propane doses tested in this experiment.     

Expanding the Context of Weed Management

Abstract

Concerns about current weed control practices have increased the consideration of new weed management strategies. In recent times, weed control practices for major crops have been influenced greatly by the availability of selective herbicides. Herbicides are critical tools, but weed science must integrate more components to create weed management systems. Changes in weed management can be attained within the framework of existing cropping systems. However, for the longer term, new methods and approaches to weed management are needed. Weed scientists need to play a central role in the development of new cropping systems to make weed management an integral component of the system. This volume contains a series of review articles and original research that presents innovative approaches to weeds and weed management. It is our hope that these papers will stimulate discussion on a broader view of weeds and weed management.     

Association between climate indices,aridity index,and rainfed crop yield in northeast of Iran

Agricultural drought occurs when there is a deficit in soil water supply to crops. Severe drought limits crop water availability and reduces yield. Rainfed crop production is very vulnerable to drought conditions and farmers in northeast of Iran who heavily depend on their rainfed cereals production usually suffer from drought occurrence. Based on history, any severe drought resulted in severe financial problems and forced the affected farmers to move to cities in search of alternative jobs. Any possibility to enable the farmers to mitigate or adapt to drought is highly required. In this study, the relationship between aridity index (AI) and detrended crop yield (1985–2005) of selected crops (wheat and barley) and the influence of three climate indices (AO, NAO and NINO-3.4) were assessed for Khorasan province in northeast of Iran. All associations were assessed at annual, seasonal (wet and dry seasons) and monthly scale considering both concurrent and lag correlations (1-year and 2-year lag). Our results indicated a significant correlation (P < 0.05) between the AI and crops yield mostly in central Khorasan province. Our study also showed that correlation coefficient between AI and barley yield was stronger than AI and wheat yield across all study locations. Seasonal (wet) AI showed significant correlation with crops yield. These results demonstrated that, in some areas of Khorasan, drought is one of the key causes of interannual yield variability. We also observed a significant association between NAO and NINO-3.4 with AI. Precipitation is one of the components of AI, so AI response to NAO and NINO-3.4 can be related to the observed association between this index and precipitation. It seems that these indices could be useful tools to monitor drought patterns and subsequent yield variability in some regions of Khorasan province.     

Cover Crops as Affecting Soil Chemical and Physical Properties and Development of Upland Rice and Soybean Cultivated in Rotation

Cover crops can provide changes in soil chemical and physical properties, which could allow a sustainable development of soybean and upland rice rotation in Brazilian Cerrado. The objective of this study was to determine the effects of cover crops(cultivated in the offseason) in the soybean-upland rice rotation(cultivated in the summer season) on the soil chemical and physical properties, yield components and grain yield of the cash crops. The experimental design was a randomized block design in factorial scheme 4 × 2 with six replications. Treatments were composed by four cover crops: fallow, millet(Pennisetum glaucum) + Crotalaria ochroleuca, millet + pigeon pea(Cajanus cajans), and millet + pigeon pea + Urochola ruziziensis in the offseason with one or two cycles of cover crops, with rice(Oryza sativa)or soybean(Glycine max) in the summer season. Cover crops alone provided no changes in soil chemical properties. However, the rotation cover crops/cash crops/cover crops/cash crops reduced p H, Al and H + Al and increased Ca, Mg, K and Fe contents in the soil. The cover crops millet + pigeon pea and millet + pigeon pea + U. ruziziensis improved soil physical properties in relation to fallow,especially in the 0–0.10 m soil layer. In spite of the improvement of the soil physical properties after two years of rotation with cover crops and cash crops, the soil physical quality was still below the recommended level, showing values of macroporosity, S index and soil aeration capacity lower than 0.10 m3/m3, 0.035 and 0.34, respectively. Upland rice production was higher under mixtures of cover crops than under fallow, mainly because of soil physical changes done by these mixtures of cover crops.Soybean grain yield was similar under all cover crops tested, but was higher after the rotation cover crops/upland rice/cover crops than after only one cycle of cover crops.     

Weed control and sweet maize (Zea mays L.) yield as affected by pyroxasulfone dose

Pyroxasulfone is a new herbicide being considered for registration in sweet maize in Canada; however, there is still little information on the doses required to provide 90% control of annual grass and broadleaved weeds found in southwestern Ontario. The objective of this study was to determine pyroxasulfone doses that would provide at least 90% control of several economically important weeds, without impacting final sweet maize yield by more than 5% in comparison to a weed-free control. Six field trials were conducted over a two-year period (2007 and 2008) at three Ontario locations to evaluate the effectiveness of pyroxasulfone at doses ranging from 31.25 to 1000 g a.i. ha⁻¹. The doses required to reduce weed biomass by at least 90% (I₉₀) varied by weed species. Doses of 93, 499, and 111 g a.i. ha⁻¹ were required to reduce the biomass by 90% of redroot pigweed, common lambsquarters and green foxtail, respectively. There was greater than 95% control of velvetleaf, large crabgrass and barnyardgrass with 31.25 g a.i. ha⁻¹, the lowest dose tested. Sweet maize yield could not be consistently maintained within 5% of the weed-free control. There are several factors that may have contributed to the reduced yield, including soil texture effects, competition as a result of poor common lambsquarters control, and hybrid sensitivity. These results show that biologically effective weed control with pyroxasulfone may be achieved at lower than proposed doses for several weed species; it remains unclear if this is economically sustainable due to the potential impacts on yield.     

Relationships between numbers of main stems and yield components of potato (Solanum tuberosum L. cv. Erntestolz) as influenced by different daylengths

Summary The relationshops between numbers of main stems and some measures of growth and yield, as well as total tuber yield, were examined for potatoes grown under different daylengths. Leaf area, tuber number and tuber yield per plant increased significantly with increasing daylength and number of main stems. Numbers of main stems and leaf area were correlated positively with tuber number and tuber yield and negatively with average tuber weight. The correlations were stronger with stem number than with leaf area and were differently affected by daylength. Standard regression coefficients indicated that stem number has strong positive and negative relationships with tuber number and average tuber weight, respectively. Since tuber number was a better determinant of yeild than average tuber weight, the final relationship between the numbers of main stems and tuber yield remained positive for all daylengths. Determinants that will best explain variation in tuber total yield, tuber number, and average tuber weight are suggested.     

Growth and yield of bell pepper as influenced by growing environment,mulch, and planting date

Bell pepper (Capsicum annuum L. var. grossum Sendt.) production is often constrained by prevailing sub-optimal temperature conditions. The treatments that enhance earliness and extend availability period may substantially increase value of the crop. This two-year study (2010–11 and 2011–12) was conducted to investigate the comparative effect of two growing environments (open field vs. polyhouse), three planting dates (15 October, 30 October, and 15 November), and four mulch treatments (black polythene, clear polythene, paddy straw, and no-mulch) on growth and yield of bell pepper. The highest fruit number, fruit weight, early yield, marketable yield, and total yield were obtained when the crop was planted in the polyhouse on 30 October under black polythene mulch. Thus, the use of polyhouse and black plastic mulch, when combined with appropriate planting date, improves early and total yields of bell pepper in areas where the production is constrained by sub-optimal temperature conditions.     

Tuber yield and tuber quality of several potato cultivars as affected by seasonal high temperatures and by water deficit in a semi-arid environment

Summary The effects of high temperatures and water deficit on potatoes were investigated under field conditions. Nine cultivars and one un-named seedling were grown in the spring and in the summer under high temperatures. In both seasons the cultivars were grown under 3 water regimes: adequate water supply, moderate water deficit, and severe water deficit that were achieved by a modification of the single line source sprinkler irrigation system. Severe drought reduced tuber yields in both seasons. Moderate tolerance to a moderate water deficit in the spring season was exhibited by Draga, Désirée, and Monalisa. Late and intermediate cultivars produced high tuber yields in the spring season, and early cultivars had relatively smaller yield losses in the summer. The extent of tuber disorders, sprouting, rotting and malformation, varied considerably. High temperatures enhanced sprouting, rotting and malformation and drought may enhance sprouting and malformation. This investigation was supported by a grant from the Ministry of Foreign Affairs, Technical Assistance Department, Netherlands.     

Cuphea growth, yield, and oil characteristics as influenced by climate and soil environments across the upper Midwest USA

Cuphea is a potential new oilseed crop rich in medium-chain fatty acids (C8:0 to C14:0) that may serve as a renewable, biodegradable source of oil for lubricants, motor oil, and aircraft fuel. Impacts of climate and soil environment on cuphea growth and development are not well understood. The objective of this study was to evaluate the influence of climate and soil on growth, seed yield, and seed oil characteristics of two semi-domesticated cuphea genotypes [PSR23 and HC-10 (Cuphea viscosissima Jacq. × C. lanceolata W.T. Aiton)] and three wild species [Cuphea wrightii, Cuphea lutea, and C. viscosissima (VS-6-CPR-1)] that show potential for domestication. The study was conducted in 2007 and 2008 at field sites in North Dakota (ND), Minnesota (MN), Iowa (IA), and Illinois (IL). Cuphea PSR23 and HC-10 were direct seeded in the field, while the three wild species were transplanted. The two plantings were treated as separate experiments. Plant growth, seed yield and oil content for the two direct-seeded lines tended to be distinctly greater in MN and ND than IL and IA, which was related more to growth temperature than soil environment. The three wild species generally performed similarly across the four different environments. C. wrightii had the greatest oil content, ranging from 320 to 360 g kg⁻¹, which was comprised of 59-64% lauric acid. For each genotype, the content of its most prominent saturated medium-chain fatty acid (e.g., C10:0 or C12:0) increased with decreasing latitude of field site. Seed yields for C. wrightii and C. lutea were as high as 1116 kg ha⁻¹. Combined with relatively high seed oil contents (280-350 g kg⁻¹) these species may be good candidates for domestication. Results indicate that PSR23 and HC-10 are more regionally adapted than the wild species studied, which tended to exhibit a greater range of adaptability to climate and soil conditions.     

Reduced dairy grassland yields in Central Norway after a single springtime grazing event by pink‐footed geese

Populations of migratory geese overwintering in Europe have risen rapidly during recent decades, leading to increased pressure on available forage resources and more grazing on agricultural lands. Farmers throughout Europe have complained of yield losses due to goose grazing. In spring, the Svalbard‐breeding population of pink‐footed goose (Anser brachyrhynchus) migrates through specific staging sites in Norway, where the geese graze on dairy grasslands and other types of agricultural lands in the early growing season. Despite this, little is known of the impacts of goose grazing on hay biomass and quality in Norway. An experiment using exclosures to prevent goose grazing, and plots that were open for grazing, was established in Central Norway to test the effects of variable grazing intensity on dairy grassland yields. A single spring‐grazing event had severe negative impact at the site with the highest grazing intensity, leading to a 25% reduction in forage yield (milk feed units per hectare) as compared to ungrazed areas. The impacts on the sites with lower grazing intensity were more subtle. The overall reduction (across all sites) of biomass yield was 26%. Forage quality, in terms of milk feed units per kg, was not much affected. Grazing increased the proportion and diversity of weeds, as evidenced by a 49% increase of the Shannon biodiversity index, and there was a 1·3% decrease in the proportion of herbage biomass of sown species. Hence, we have confirmed farmer reports on yield losses, gaining an increased understanding of the overall farmer costs associated with goose grazing in this northern latitude region.     

Simulation of water use and production of potatoes as affected by soil compaction

Summary The SWACRO simulation model was used to calculate water balances and associated potatotuber productions in a loamy sand soil with different types of compaction. Results for a noncompacted soil were compared with those for soils with a strong ploughpan and those with compacted surface soil. Input data consisted of: (1) measured hydraulic conductivity and moisture retention data for major soil horizons, (2) measured rooting depths and water-table levels, (3) calculated potential transpiration according to the modified Penman equation and (4) measured precipitation. Root extraction of water was simulated by two approaches, comparing the Feddes and Hoogland et al. extraction terms. The former procedure yielded best results in this study. The SWACRO model yielded good predictions of the soil water regime and tuber productions for the three treatments in the dry year 1976. A sensitivity analysis indicated that variations of water-use efficiencies did not significantly affect thedifferences in crop productions observed. Formerly: Soil Survey Institute, P.O. Box 98, 6700 AA Wageningen, the Netherlands.     

Biomass production and nitrogen accumulation and remobilisation by Miscanthus × giganteus as influenced by nitrogen stocks in belowground organs

The nitrogen (N) requirement of dedicated crops for bioenergy production is a particularly significant issue, since N fertilisers are energy-intensive to make and have environmental impacts on the local level (NO₃ leaching) and global level (N₂O gas emissions). Nitrogen nutrition of Miscanthus × giganteus aboveground organs is assumed to be dependent on N stocks in belowground organs, but the precise quantities involved are unknown. A kinetic study was carried out on the effect of harvest date (early harvest in October or late harvest in February) and nitrogen fertilisation (0 or 120 kg N ha⁻¹) on aboveground and belowground biomass production and N accumulation in established crops. Apparent N fluxes within the crop and their variability were also studied.Aboveground biomass varied between 24 and 28 t DM ha⁻¹ in early harvest treatments, and between 19 and 21 t DM ha⁻¹ in late harvest treatments. Nitrogen fertilisation had no effect on crop yield in late harvest treatments, but enhanced crop yield in early harvest treatments due to lower belowground biomass nitrogen content. Spring remobilisation, i.e. nitrogen flux from belowground to aboveground biomass, varied between 36 and 175 kg N ha⁻¹, due to the variability of initial belowground nitrogen stocks in the different treatments. Autumn remobilisation, i.e. nitrogen flux from aboveground to belowground organs, varied between 107 and 145 kg N ha⁻¹ in late harvest treatments, and between 39 and 93 kg N ha⁻¹ in early harvest treatments. Autumn remobilisation for a given harvest date was linked to aboveground nitrogen accumulation in the different treatments. Nitrogen accumulation in aboveground biomass was shown to be dependent firstly on initial belowground biomass nitrogen stocks and secondly on nitrogen uptake by the whole crop.The study demonstrated the key role of belowground nitrogen stocks on aboveground biomass nitrogen requirements. Early harvest depletes belowground nitrogen stocks and thus increases the need for nitrogen fertiliser.     

Sulphur nutrition of sunflower (Helianthus annuus) as affected by nitrogen supply: Effects on vegetative growth,the development of yield components,and seed yield and quality

The effects of sulphur and nitrogen nutrition on the growth and yield components of a hybrid confectionery sunflower (cv. Kernel) were investigated in a glasshouse experiment using controlled S and N supplies that ranged from deficient to more than adequate, and in which the S supplies of some plants were changed at defined stages of growth. S deficiency delayed floret initiation and anthesis but not seed maturity; N deficiency delayed all developmental phases including seed maturity. S and N deficiencies reduced plant height and leaf area. N deficiency caused a reduction in leaf number, but S deficiency did not. Both S and N deficiencies reduced yield by reducing the number of seeds per plant and by decreasing single seed weight. Oil concentration in seeds was the same for all levels of S supplied, but it was reduced by increased N supply. Changing the S supply at the end of floret initiation and at anthesis indicated that floret number and therefore seed number per plant were mainly established by the S suplly before the end of floret initiation. Single seed weight responded positively to increased S supply after floret initiation but only if the N supply was adequate; there was no response to increased S supply after anthesis.Concentrations of S and N in plant organs increased with increasing S and Nsupplies, but seeds were much less responsive than vegetative organs. Plants grown on high N but low S had the highest concentrations of N in their tissues, but the highest S concentrations did not occur in high S low N plants. Cysteine and methionine decreased by 30% in seeds of S-deficient but N-sufficient plants, whereas arginine increased by 34% compared with nutrient-adequate plants.We suggest that an adequate supply of S to young sunflower plants is required, particularly up to floret initiation, to obtain large floret numbers and maximum leaf area. An adequate supply of S is also required between the end of floret initiation and anthesis to prevent floret abortion and allow development of large seeds. Sulphur stress in sunflower during seed filling results in kernels with low levels of essential S-containing amino acids.     

Investigation of Thrips tabaci Lind. as a cotton pest and the development of strategies for its control in Punjab

Thrips tabaci Lind. migrates from the lower to the upper portion of the cotton plant as the season progresses and plants increase in size. The population level of thrips on seedlings should be determined by visual observations of leaf damage instead of scouting. The crop should be sprayed before the damage level is such that seedling leaflets have a cup-like appearance. Combined attack by thrips (14.6 per leaf) and jassid (4.6 per leaf) caused a 37.6% loss in the yield of seed cotton. Granule application at the seedling stage and foliar sprays at later stages is suggested as a control strategy. Thrips and jassids appear to be mutually exclusive but the exact mechanism is not known.     

Improving sink regulation,and searching for promising traits associated with hybrids,as a key avenue to increase yield potential of the rice crop in the tropics

Yield advantage of hybrid rice in the tropics has been reported recently as the result of higher biomass accumulation and better biomass partitioning over the whole crop growth. Considering that increasing biomass accumulation is the main target for higher yield potential in sub-tropical and temperate conditions, it is relevant to investigate in a wide range of growing conditions in the tropics if improved biomass partitioning plays a significant and consistent role in higher yield of hybrids. The growth pattern of two high-yielding and popular hybrid (H1) and inbred (I1) of the same maturity group was compared under six contrasted growing conditions to evaluate traits related to sink regulation. Grain yield of H1 was consistently higher than that of I1 by 16–32% with respect to the situation. Higher partitioning coefficients of the hybrid to key organs were confirmed over the whole crop growth for this set of environments whereas crop growth rates of hybrid were not consistently higher than that of inbreds. Sink strength index, as a way to express sink regulation at maturity more efficiently than harvest index, was higher with hybrids in five out of six environments. In search for promising traits related to sink regulation, higher specific leaf area of hybrids at very early stage was associated with higher leaf area, and earlier cessation of tiller production with hybrids coincided with higher partitioning of biomass to early culm growth: yet, maximum tiller number ranged from 548 to 962 tiller m⁻² with H1 and from 629 to 1427 tiller m⁻² with I1 while culm dry weight at 55 days after sowing ranged from 65 to 81 g m⁻² with H1 and from 46 to 53 g m⁻² with I1. This analysis strongly reinforced the pertinence of improving sink regulation for increasing yield potential in the tropics.