Estimation of the N fertiliser requirement of cotton grown after legume crops

In a series of legume-based cropping systems experiments, the economic optimum N fertiliser rate for cotton ranged from 0 to 186 kg N ha⁻¹ depending on the cropping system and soil N fertility. The economic optimum N fertiliser rate was closely correlated with pre-sowing soil nitrate-N (0–30 cm) and petiole nitrate-N (at early flowering). Pre-sowing soil nitrate-N and petiole nitrate-N were also strongly correlated with cotton N uptake at late boll-filling and lint yield of unfertilised cotton.These analyses allow for the estimation of the N fertiliser requirement, providing revised calibrations that more precisely estimate the N-fertiliser requirement of irrigated cotton crops where legume cropping has substantially improved soil N fertility. Such management tools are essential to avoid the problems associated with over- or under-fertilizing cotton crops.The importance of optimising N fertiliser application was demonstrated by examining the effects of crop N nutrition on cotton maturity and fibre quality. Crop maturity (rate of boll opening) was delayed by 1 day for each 83, 16 or 24 kg fertiliser N applied per hectare in the three experiments. Increasing N fertiliser rates generally increased fibre length, and tended to increase fibre strength, whereas micronaire tended to decline.     

Foliar sprays of concentrated urea at maturity of pigeonpea to induce defoliation and increase its residual benefit to wheat

The pigeonpea (Cajanus cajan (L.) Millsp.) crop retains appreciable amounts of green foliage even after reaching physiological maturity, which if allowed to defoliate, could augment the residual benefit of pigeonpea to the following wheat (Triticum aestivum L.) in a pigeonpea–wheat rotation. The effect of addition of leaves present on mature pigeonpea crop to the soil was examined on the following wheat during the 1999/2000 growing season at Patancheru (17°4′N, 78°2′E) and during the 2001–2003 growing seasons at Modipuram (29°4′N, 77°8′E). At Patancheru, an extra-short-duration pigeonpea cultivar ICPL 88039 was defoliated manually and using foliar sprays of 10% urea (30 kg/ha) and compared with a millet (Pennisetum glaucum (L.) R.Br.) crop, naturally senesced leaf residue and no-leaf residue controls. At Modipuram, the effect of 10% urea spray treatment on mature ICPL 88039 was compared with the unsprayed control. At both locations, the rainy season crops were followed by a wheat cultivar UP 2338 at four nitrogen levels applied in a split plot design, which at Patancheru were 0, 30, 90 and 120 kg N ha⁻¹ and at Modipuram 0, 60, 120 and 180 kg N ha⁻¹. At Patancheru, urea spray added 0.5 t ha⁻¹ of extra leaf litter to the soil within a week without significantly affecting pigeonpea yield. This treatment, however, increased mean wheat yield by 29% from 2.4 t ha⁻¹ in the no-leaf residue pigeonpea or pearl millet plots to 3.1 t ha⁻¹. At Modipuram, the foliar sprays of urea added more leaf litter to the soil than at Patancheru. Here, increase in subsequent wheat yield due to additional pigeonpea leaf litter was 7–8% and net profit 21% more than in the unsprayed control. The addition of pigeonpea leaf litter to the soil resulted in a saving of 40–60 kg N for the following wheat crops in both the environments. The results demonstrated that pigeonpea leaf litter could play an important role in the fertilizer N economy in wheat. The urea spray at maturity of the standing pigeonpea crop significantly improved this contribution in increasing wheat yield, the effect of which was additional to the amount of urea used for inducing defoliation. The practice, if adopted by farmers, may enhance sustainability of wheat production system in an environmentally friendly way, as it could reduce the amount of fertilizer N application to soil and enhance wheat yield.     

The effect of late-season urea spraying on grain yield and quality of winter wheat cultivars under low and high basal nitrogen fertilization

The late-season foliar application of urea may increase yield and grain quality of wheat (Triticum aestivum L.). Limited information is available regarding the effect of late urea spraying on the performance of wheat cultivars under various basal N fertilization rates. Field experiments were conducted during 2000 through 2002 to evaluate the responses of six winter wheat cultivars to foliar urea (30 kg N ha⁻¹) treatment around flowering at low (67 kg N ha⁻¹) and high (194 kg N ha⁻¹) basal N fertilization rates. Following urea spraying at low N rate, all cultivars increased grain yields to a similar extent (by an average of 7.8% or 509 kg ha⁻¹) primarily due to an increase in the 1000-kernel weight. No yield response to the late-season urea treatment occurred at high basal N rate where grain yields averaged 24.9% (1680 kg ha⁻¹) higher than those at low N rate. In contrast, late foliar urea application similarly improved grain quality at both low and high N rates by an average of 5 g kg⁻¹ (4.5%) for protein content, 3.2 cm³ (11.9%) for Zeleny sedimentation, and 20 g kg⁻¹ (8.6%) for wet gluten. These quality increments were consistent in all growing seasons regardless of significant variations in grain yields and protein concentrations across years. However, most cultivars failed to achieve breadmaking standards at low N rate as quality increments associated with the urea treatment were relatively small when compared to those achieved by high basal N rate. Late urea spraying had no effect on the falling number, whereas some cultivars showed small, but significant reduction in the gluten index at both N rates. Cultivars improved the hectolitre weight with the late-season urea treatment only at low N rate. Significant cultivar × urea interactions existed for most quality traits, which were due to the cultivar differences in the magnitude of responses. Thus, late-season urea spraying consistently produced larger yields at low basal N rate, and resulted in cultivar-dependent increases in protein content, Zeleny sedimentation, and wet gluten at both low and high N rates.     

Effect of Milling and Parboiling Processes on Arsenic Species Distribution in Rice Grains

This study identified the role of milling and parboiling on arsenic (As) content and its species in large numbers of rice samples. Total As contents were 108 ± 33 μg/kg in polished rice grains (PR), 159 ± 46 μg/kg in unpolished rice grains (UR), 145 ± 42 μg/kg in parboiled polished rice grains (PPR) and 145 ± 44 μg/kg in parboiled unpolished rice grains (PUR). The percentages of inorganic As (iAs) were 66% ± 8% in PR and from 72% to 77% in other grain categories. The polishing process reduced the As content in the rice grains, removing outer part of the UR with high amount of As, whereas the parboiling technique transferred the semimetal content within the grain. Total As and iAs contents were not significantly different in UR, PPR and PUR, homogenizing its distribution inside the grains. The results allowed to understand how different operations affect As fate and its chemical forms in grains.     

Residual effect of poultry litter applied to cotton in conservation tillage systems on succeeding rye and corn

The burgeoning poultry industry in the southeastern US is presenting a major environmental problem of safe disposal of poultry litter (PL). In a comprehensive study, we explored ways of PL use in conservation tillage-based cotton (Gossypium hirsutum L.) production systems on a Decatur silt loam soil in north Alabama, from 1996 to 1999. The study reported here-in presents the residual effects of PL applied to cotton in mulch-till (MT) and no-till (NT) conservation tillage systems in 1997 and 1998 cropping seasons on N uptake, growth, and yield of rye (Secale cereale, L.) cover crop and rotational corn (Zea mays L.) in 1999. Rye was grown without additional N, whereas corn was grown at three inorganic N levels (0, 100, and 200 kg N ha⁻¹). Poultry litter was applied to cotton in 1997 and 1998 at 0, 100, and 200 kg N ha⁻¹. Residual N from PL applied to cotton in 1997 and 1998 produced up to 2.0 and 17.3 Mg ha⁻¹, respectively, of rye cover crop and corn biomass (includes 7.1 Mg ha⁻¹ of corn grain yield) without additional fertilizer. Therefore, in addition to supplying crop residues which reduce soil erosion, increase soil organic matter, and conserve soil moisture, the rye cover crop was able to scavenge residual N left by the cotton crop, which would otherwise, be at risk of being leached and pollute groundwater resources. Poultry litter applied to cotton also increased corn grain quality as shown by up to 100% increase in grain N content compared to the 0N treatment. Using PL with a slower rate of N release compared to inorganic fertilizer to meet some of the N requirements of corn, will not only reduce N fertilizer costs for corn, but will also reduce the risk of nitrate N leaching into groundwater. The maximum amount of crop residues added to the cotton based cropping system by residual N from PL and inorganic N was 21.3 Mg ha⁻¹. This will lead to an increase in soil organic carbon and soil structure in the long term and a reduction in soil erosion, thereby further improving soil productivity, while at the same time, protecting the environment from nitrate pollution and soil degradation. Our study demonstrates that cotton under conservation tillage system in combination with rye cover crop and rotational corn cropping could use large quantities of PL thereby avoiding serious potential environmental hazards.     

Duration of the grain-filling period in maize is not affected by photoperiod and incident PPFD during the vegetative phase

Total number of initiated leaves and duration from sowing to silking increases when photoperiod is increased during the photoperiod-sensitive phase in maize (Zea mays L.). Little is known, however, about possible other effects of photoperiod and incident photosynthetic photon flux density (PPFD) on rate of development and duration of life cycle. A study was undertaken to quantify effects of photoperiod and incident PPFD from sowing to the 15-leaf stage on rate of leaf appearance and duration of the grain-filling period. The short-season maize hybrid Pioneer 3902 was grown in growth cabinets from sowing to the 15-leaf stage with either (i) a 10 h photoperiod at high PPFD (650 μmol m⁻² s⁻¹), (ii) a 20 h photoperiod consisting of 10 h of high PPFD followed by 10 h of low PPFD (5–50 μmol m⁻² s⁻¹), or (iii) a 20 h photoperiod of high PPFD. From the 15-leaf stage to maturity the plants were placed under a 16 h photoperiod in a growth room. Increasing photoperiod from 10 to 20 h increased final number of initiated leaves and delayed silking but did not affect rate of leaf appearance. Doubling incident PPFD to a value similar to that under Ontario field conditions during the summer resulted in a 16% increase in rate of leaf appearance and in a significant increase in total number of initiated leaves. Differences in final number of initiated leaves and in rate of leaf appearance from sowing to the 15-leaf stage among treatments resulted in a 4-day difference in silking date between the 10 h photoperiod treatment and the two 20 h photoperiod treatments. Duration of the grain-filling period did not differ among the three treatments.     

Breeding for perennial growth and fertility in an Oryza sativa/O. longistaminata population

The development of perennial cultivars (CVs) of upland rice would give farmers a new tool to reduce soil erosion from hilly fields, thereby mitigating a problem of regional concern in Southeast Asia. Oryza longistaminata is an undomesticated, perennial, rhizomatous relative of domesticated Asian rice (Oryza sativa). Using five sets of 4 × 2 factorial mating designs, we crossed rhizomatous interspecific genotypes (IGs) from an intermated O. sativa/O. longistaminata population with male-fertile IG selections from the intermated population, and with O. sativa CVs. Parents and progeny were planted in an upland field at IRRI using a randomized complete block design and evaluated for rhizome expression, survival after 1 year, vigor of the survivors, and yield. For the IG parents, rhizome expression was variable and penetrance of most genotypes was incomplete, but genotypes that demonstrated the potential for moderate rhizome expression had high penetrance (89% average). The CV parents yielded 11.0 g/plant on average but none produced rhizomes or survived 1 year. The IG parents averaged yields of 3.1 g/plant, 57% rhizomatous and 36% survival. The IG/IG progeny averaged yields of 4.2 g/plant, 32% rhizomatous and 37% survival. The IG/CV progeny averaged yields of 6.0 g/plant, 18% rhizomatous and 16% survival. Nine IG/IG progeny and six IG/CV progeny were rhizomatous, perennial, and yielded at least 5 g/plant, and five of these yielded more than 10 g/plant. For the IG parents and IG/IG progeny, rhizome presence and expression were positively associated with survival and vigor of the survivors. General combining ability effects were significant for percent survival and yield but not percent rhizomatous. Specific combining ability effects were significant for percent rhizomatous, percent survival and yield. By selecting female parents for long rhizomes and male parents for fertility, considerable gains in rhizome expression, survival and yield were made. The development of perennial upland rice CVs should be feasible via introgression of genes from O. longistaminata.     

Fertility in an interspecific rice population and its effect on selection for rhizome length

Fertility barriers, which are common in many wide crosses, can hinder efforts to introgress genes. In this study, we examined an intermated Oryza sativa/Oryza longistaminata population and assessed how fertility barriers affected selection for long rhizomes, a polygenic trait. Rhizomes are typical of O. longistaminata but not found in O. sativa. In the intermate population, we observed that pollen-fertility and self-fertility were generally low but exceptional individuals of high fertility were found in nearly all generations. About 1/5th of the genotypic variation for self-fertility was accounted for by pollen-fertility, based on a significant linear regression. Intermating improved self-fertility more than backcrossing for one generation. Heritability estimates via parent-offspring regression were 17 ± 7% for pollen-fertility and 39 ± 9% for self-fertility. The data indicated that many genes contributed to the fertility barriers. Individuals with relatively high fertility or long rhizomes (>8 cm) were observed infrequently in the intermated population, and there was no evidence of association between low fertility and presence of long rhizomes. By evaluating a large population, we were able to obtain a few rare recombinants that had both self-fertility greater than 10% and long rhizomes.     

Impact of guar and xanthan gums on proofing and calorimetric parameters of frozen bread dough

The influence of guar and xanthan gum and their combined use on dough proofing rate and its calorimetric properties was investigated. Fusion enthalpy, which is related to the amount of frozen water, was influenced by frozen dough formulation and storage time; specifically gum addition reduced the fusion enthalpy in comparison to control formulation, 76.9 J/g for formulation with both gums and 81.2 J/g for control, at 28th day. Other calorimetric parameters, such as T_g and freezable water amount, were also influenced by frozen storage time. For all formulations, proofing rate of dough after freezing, frozen storage time and thawing, decreased in comparison to non-frozen dough, indicating that the freezing process itself was more detrimental to the proofing rate than storage time. For all formulations, the mean value of proofing rate was 2.97 ± 0.24 cm³ min⁻¹ per 100 g of non-frozen dough and 2.22 ± 0.12 cm³ min⁻¹ per 100 g of frozen dough. Also the proofing rate of non-frozen dough with xanthan gum decreased significantly in relation to dough without gums and dough with only guar gum. Optical microscopy analyses showed that the gas cell production after frozen storage period was reduced, which is in agreement with the proofing rate results.     

Antifungal activity in vitro of Flourensia spp. extracts on Alternaria sp., Rhizoctonia solani,and Fusarium oxysporum

There are 32 species of Flourensia genus with 9 native to Mexico. These species contain compounds with potential use for pest control. In this paper, we report the antifungal activities of ethanol extracts from three endemic species in Coahuila state: Flourensia microphylla, Flourensia cernua, and Flourensia retinophylla. Also, preliminary information on the chemical composition of the extracts is included. Antifungal activity was tested against three pathogens attacking commercial crops: Alternaria sp., Rhizoctonia solani, and Fusarium oxysporum. The extracts concentration varied from 10 to 1500 μl l⁻¹. The ANOVA showed highly significant differences (P ≤ 0.01) with the extracts, the doses, and on the interaction extract × dose. Inhibition effect was observed from 10 μl l⁻¹ in all three species. Total inhibition was found only with F. cernua and F. retinophylla at 1000 μl l⁻¹ for R. solani, the three species inhibited the three pathogens at 1500 μl l⁻¹. Infrared analysis showed similar absorption signals for the extracts of the three species although in different concentration. This suggests that similar compounds may be present. The control of these pathogens by natural compounds is interesting both for environmental and economic reasons. The use of semiarid lands plants may improve the socioeconomic level of the people within the region.     

Adaptation and yield of pigeonpea in different environments in Tanzania

Pigeonpea is grown in wide range of cropping systems and environments, both in East Africa and internationally. An important feature of adaptation to these diverse systems and environments is the timing of flowering and maturity. Most traditional cultivars grown in Tanzania are medium to late flowering types (>150 days), although extra-early flowering cultivars are now available. The aim of the present investigation was to measure biomass (BY) and seed (SY) yield of a set of phenologically diverse cultivars to determine their adaptation to contrasting environments in Tanzania. Ten cultivars, from extra-early (60 days) to late (>180 days) flowering, were planted at six locations varying in mean temperature, photoperiod and rainfall. Days to flowering (DTF) and maturity, and above-ground BY and SY at maturity, were measured. A stress index (ETr:ETm ratio, 100 = no stress) was computed for each site. Rainfall and the stress index at the different sites varied from 322 to 1297 mm and 57 to 89, respectively. Among cultivars, DTF varied from 55 to 320 days, the stress index from 3 to 98, BY from 700 to 25,000 kg ha⁻¹, and SY from 0 to 4000 kg ha⁻¹. The highest yielding environment was at Selian, where mean temperatures were favourable (19 °C) and no stress occurred. At all sites there was an optimum DTF, which for SY varied from <100 to 150 days. The best adapted cultivars were ICP 7035, ICPL 90094, Kat 50 and QP37, which were all medium flowering (c. 150 day) types. Extra-early cultivars such as ICPL 86005 also showed considerable potential, especially in short-season environments.     

Ultrahigh CO2 levels enhances cuphea growth and morphogenesis

Applications of ultrahigh CO₂ treatments accelerated cuphea (Cuphea viscosissima × C. lanceolata ‘PSR23’) growth and development and aided in seedling establishment. The growth (fresh weight) and morphogenesis (number of leaves and roots and seedling length) were determined in cuphea seedlings exposed to 350, 1500, 3000, 10,000, or 30,000 μmol mol⁻¹ CO₂ for 30 days under greenhouse conditions. Greater CO₂ levels, especially the ultrahigh levels (i.e. ≥3000 μmol mol⁻¹ CO₂) resulted in significantly higher (P ≤ 0.05) fresh weights, leaf numbers, root numbers, and seedling lengths compared to seedlings grown under ambient air (350 μmol mol⁻¹ CO₂). For example, cuphea ‘PSR23’ Morris heavy seedlings showed the greatest seedling fresh weight, leaf number, root number, and seedling length when supplemented with 10,000 μmol mol⁻¹ CO₂ increasing 607%, 184%, 784%, and 175%, respectively, when compared to seedlings grown without CO₂ enrichment.     

The influence of rainfed and limited irrigation conditions and early vs. late plantings on kenaf as a potential industrial crop in the southern High Plains,USA

Kenaf (Hibiscus cannabinus L.) is a nonwoody fiber source with many uses. To evaluate the dry matter yield potential of kenaf at two locations in the southern High Plains of the USA and the effects of late planting/late emergence as a possible replacement for hail damaged cotton, four varieties were grown in 2004 and 2005 at New Mexico State University's Agricultural Science Centers at Clovis, under limited irrigation, and Tucumcari, under rainfed conditions. Each study was a randomized complete block design having four replicates. A year × location interaction existed (P < 0.0469) for kenaf yield largely due to precipitation amount and distribution. Either late planting or late emergence due to low soil moisture at planting significantly reduced yields (3.62 vs. 0.63 Mg ha^?1 for mid-May planting and emergence and early July emergence or planting, respectively, P < 0.0001). Consequently, kenaf would not be suitable for recovering input costs when planted after failure of cotton. The very late maturing variety Gregg had consistently lower numeric yields than Dowling, Everglades 41, and Tainung 2 in all comparisons, with the strongest trend within the emergence date comparison (P < 0.0912). Kenaf varieties should be selected for any location that finish blooming approximately three to four weeks prior to the average first autumn freeze to allow for maximum growth.     

Impact of redox agents on the physico-chemistry of wheat gluten proteins during hydrothermal treatment

The impact of the oxidants potassium bromate and potassium iodate and the reducing agent dithiothreitol (DTT) on the rheological behaviour of 20% (w/v) gluten-in-water suspensions during thermal treatment was monitored with the rapid visco analyser (RVA). The suspensions were subjected to a linear temperature increase from 40 to 95 °C in 14 min, a holding step of 40 min at 95 °C, a cooling step (7 min) with a linear temperature decrease to 50 °C, and a final holding step at 50 °C (13 min). Potassium iodate (1.18 and 1.77 μmol/g protein) and potassium bromate (1.52 and 15.2 μmol/g protein) decreased RVA viscosities in the holding step and increased sodium dodecyl sulphate (SDS) protein extractabilities suggesting a greater heat resistance and decreased gliadin–glutenin cross-linking. In contrast, in the presence of DTT (1.65 and 3.30 μmol/g protein) RVA viscosity increased at lower temperatures and lowered SDS extractabilities. It is postulated that low concentrations of reducing agent facilitate gliadin–glutenin cross-linking during heating while oxidants hinder gluten polymerization due to decreased levels of free sulphydryl groups and less flexibility of the glutenin chains.     

Methyl jasmonate,alone or in combination with genistein,and Bradyrhizobium japonicum increases soybean (Glycine max L.) plant dry matter production and grain yield under short season conditions

Jasmonic acid (JA) is a plant hormone produced via the octadecanoid pathway from its precursor, linolenic acid. Jasmonates are involved in plant wound responses and defense against insects and fungal elicitors. They can also act as signal molecules in the Bradyrhizobium-soybean symbiosis. Pre-incubation of Bradyrhizobium japonicum inocula with gensitein (Ge), an effective inducer of nodulation genes in this species enhances soybean nodulation, nitrogen fixation and yield under low spring soil temperature field conditions. Since jasmonates are also able to induce nodulation genes and cause the production of lipo-chitooligosaccharides (LCOs) by B. japonicum, we conducted two field experiments, in southwestern Quebec, Canada, to determine whether pre-incubation of B. japonicum with methyl jasmonate (MeJA) alone or in combination with genistein (Ge), prior to inoculation, increased soybean plant dry matter production and grain yield. Experiments at each site used a two factor randomized complete block design (RCBD) with four replicates. Two B. japonicum strains (USDA3 and 532C) and four inducer molecule treatments [control, Ge (20 μM), MeJA (50 μM), and Ge + MeJA (20 μM + 50 μM)] were used in the study. The bacterial cultures were induced for 24 h with the inducer molecules and then applied into the furrows at the time of planting. Both Ge and MeJA, alone or in combination, increased plant growth, dry matter accumulation, and grain yield. This study showed that MeJA, alone or in combination with Ge, can be used to promote soybean plant growth and grain yield under short season field conditions.     

Effect of supplementation of blue green alga (Spirulina) on outcome of pregnancy in rats

To study the supplementary effect of Spirulina, pregnant rats were fed 5 different kinds of diets (casein, Spirulina, wheat gluten, Spirulina + wheat gluten, Spirulina-without additional vitamins and minerals), each providing 22% protein during the period of pregnancy. The outcome of pregnancy was assessed from litter and dams' weight and litter size. Maternal weight gain was found to be maximum with Spirulina + wheat gluten and least with the wheat gluten diet. Rats receiving Spirulina containing diets produced significantly (p<0.05) higher litter size than those receiving casein and wheat gluten. In spite of having higher litter size, Spirulina containing diet groups produced pups with birth weights comparable to those of casein. Spirulina appears to be a good dietary supplement during pregnancy.     

Some characteristics of reduced leaf photosynthesis at midday in maize growing in the field

Maize was grown in the high-radiation arid summer environment of Davis, California, and its leaf photosynthetic rate was measured over diurnal courses on cloudless days with the leaf held perpendicular to the sunlight. On days of high atmospheric vapor pressure deficit (VPD), leaf photosynthesis reached a maximum in the late morning and then decreased gradually as the day progressed, though the soil was well irrigated. When CO₂ concentration in the measurement chamber was raised to about 1000 μmol mol⁻¹, photosynthesis was enhanced, but more in the afternoon than in the morning. As a result, rates measured at high CO₂ in the morning and afternoon were essentially the same. There was also no difference in the curves of photosynthetic rate (A) versus intercellular CO₂ concentration (C_i) for the morning and afternoon. Hence, photosynthetic capacity was similar for the two periods and there was no evidence of photoinhibition by the high photosynthetic photon flux density at noon. Further, C_i and photosynthetic rates A measured over a range of photon flux density were lower in the afternoon than in the morning. These results indicate that A at noon and early afternoon was more limited than in the morning by epidermal conductance (mostly stomatal). On a day of low VPD, however, midday depression in A and epidermal conductance were not evident for the well-irrigated plants. Without irrigation and with leaves at a lower midday water potential, midday reduction in conductance and A was much more marked, beginning late in the morning. Epidermal conductance of maize grown in the field in Davis is are not sensitive to VPD. Therefore, the midday reduction in conductance and A was more likely the result of low leaf water potential caused by high transpiration rates.     

Determination of Some Metals Which are Important for Food Quality Control in Bread

This study is the small part of the big project related to the metallic contamination in foodstuff. The work presented here allowed determination the level of iron, copper, zinc, lead and cadmium in bread samples obtained from 20 bakeries in Ankara and Samsun, Turkey. The atomic absorption spectrophotometry method was used to determine these metals. The mean values of iron, copper, zinc, lead, and cadmium levels were found as 19·2±8·1 mg/kg-dry weight (dw), 2·1±1·0 μg/kg-dw, 10·0±3·0 μg/kg-dw, 86·8±176·0 μg/kg-dw, and 12·2±6·1 μg/kg-dw, respectively. No significant differences were found in copper and lead levels of samples obtained from bakeries in general, and in copper and cadmium levels of the samples from different provinces (P>0·05), while they were considered significant in iron, zinc, and cadmium levels of samples in general, and in iron, zinc and lead levels of samples from different provinces (P<0·05).     

Source–sink relations and kernel weight differences in maize temperate hybrids

Maize (Zea mays L.) kernel weight (KW) response to changes in assimilate availability per kernel during grain filling suggests that plants establish an early kernel sink potential that place them to grow close to a saturating assimilate availability condition during late grain-filling, meaning source limitations are common only early in kernel development. As maize reproductive efficiency in kernel set is not constant across different plant growth rates (PGR) around flowering, we used PGR per kernel during this period as an indicator of source availability per kernel. We tested whether PGR per kernel during flowering or during the effective grain-filling period were correlated to genotypic and environmental differences in final KW. Plant growth rate during both periods, KW, kernel growth rate during the effective grain-filling period, total duration of grain filling and kernel number per plant were measured in 12 commercial genotypes differing in KW sown at two sites under full irrigation. As expected from the curvilinear response relating kernel number per plant and PGR around flowering, increased PGRs resulted in higher PGR per kernel around this period (r² = 0.86; p < 0.001). Differences in final KW due to genotypes or environments were significantly explained by the PGR per kernel around flowering (r² = 0.40; p < 0.001), and not by the PGR per kernel during the effective grain-filling period. Genotypes differed in kernel growth rate (p < 0.001) and grain-filling duration (p < 0.001). The former was well explained by PGR per kernel around flowering (r² = 0.66; p < 0.001), but showed no relationship with the PGR per kernel during the effective grain-filling period. Grain-filling duration was partially explained (r² = 0.27; p < 0.01) by the ratio between PGR per kernel during the effective grain-filling period and kernel growth rate, but differences in duration were negligible compared to those observed in the ratio (∼41% versus ∼130%, respectively). Together, these results support the importance of source availability per kernel during early grain filling on the determination of maize potential sink capacity and final KW. Early resource availability per kernel was accurately estimated as PGR per kernel around the period of kernel number determination, which helped explain genotypic and environmental differences in maize final KW as well as in kernel growth rate.