Panicle Density Research Articles

Influence of Lime and Gypsum on Growth and Yield of Upland Rice and Changes in Soil Chemical Properties

Upland rice is an important crop in the cropping systems of South America, including Brazil. Two greenhouse experiments were conducted to determine influence of lime and gypsum on yield and yield components of upland rice and changes in the chemical properties of an Oxisol. The lime rates used were 0, 0.71, 1.42, 2.14, 2.85, and 4.28 g kg−1 soil. The gypsum rates were 0, 0.28, 0.57, 1.14, 1.71, and 2.28 g kg−1. Lime as well as gypsum significantly increased plant height, straw and grain yield, and panicle density in a quadratic fashion. Adequate lime and gypsum rates for maximum grain yield were 1.11 g kg−1 and 1.13 g kg−1, respectively. Plant height, straw yield, and panicle density were positively related to grain yield. Lime as well as gypsum application significantly changed extractable calcium (Ca), magnesium (Mg), hydrogen (H)+aluminum (Al), base saturation, and effective cation exchange capacity. In addition, liming also significantly increased pH, extractable phosphorus (P) and potassium (K), calcium saturation, magnesium saturation, and potassium saturation. Optimum acidity indices for the grain yield of upland rice were pH 6.0, Ca 1.7 cmolc kg−1, base saturation 60%, and calcium saturation 47%. In addition, upland rice can tolerate 42% of acidity saturation.

Comparison of Conventional and Polymer Coated Urea as Nitrogen Sources for Lowland Rice Production

Nitrogen (N) is one of the most yield limiting nutrients in lowland rice production. Improving N use efficiency is essential to reduce cost of crop production and environmental pollution. A greenhouse experiment was conducted with the objective to compare conventional and polymer coated urea for lowland rice production. Grain yield, straw yield, panicle density, maximum root length, and root dry weight were significantly increased in a quadratic fashion with the increase of N rate from 0 to 400 mg kg−1 soil. Nitrogen source X N rate interactions for most of these traits were not significant, indicating that lowland rice responded similarly to change in N rates of two N sources. Based on regression equations, maximum grain yield was obtained with the application of 258 mg N kg−1 soil and maximum straw yield was obtained with the addition of 309 mg N kg−1 soil. Nitrogen use efficiency (grain yield per unit of N applied) was maximum for polymer coated urea compared to conventional urea. Root length and root dry weight improved at an adequate N rate, indicating importance of N fertilization in the absorption of water and nutrients and consequently yield. Polymer coated urea had higher soil exchangeable calcium (Ca) and magnesium (Mg), Ca saturation, Mg saturation, base saturation, and effective cation exchange capacity compared to conventional urea. There was a highly significant decrease in soil exchangeable potassium (K) with increasing N rates at harvest of rice plants.

Comparative Efficiency of Phosphorus Sources for Upland Rice Production

Rice (Oryza sativa L.) is a staple food for more than 50% of the world’s population, and phosphorus (P) is one of the most yield-limiting nutrients for rice production in tropical acidic soils worldwide. A greenhouse experiment was conducted to evaluate efficiency of six P sources for upland rice production. The P sources used were simple superphosphate (SSP), polymer-coated SSP (PSSP), triple superphosphate (TSP), polymer-coated TSP (PTSP), monoammonium phosphate (MAP), and polymer-coated MAP (PMAP). There were four P rates [50, 100 200, and 400 mg phosphorus (P) kg−1] applied with four sources plus one control treatment [0 mg phosphorus (P) kg−1]. Plant height, straw yield, grain yield, panicle density, root dry weight, maximum root length, and 1000-grain weight were significantly increased with increasing P rates in the range of 0 to 400 mg P kg−1. However, P-use efficiency (mg grain produced per mg P applied) was decreased with increasing P rate. Based on regression equation, overall maximum plant height was obtained with the application of 235 mg P kg−1, maximum straw yield with the application of 265 mg P kg−1, and maximum grain yield at 227 mg P kg−1. Based on maximum grain yield, the P source were classified as PMAP > SSP = MAP > PSSP > TSP > PTSP in the upland rice production efficiency. Overall, maximum panicle density was obtained with the addition of 231 mg P kg−1 and maximum 1000-weight was obtained with the addition of 226 mg P kg−1. Similarly, overall root dry weight and maximum root length were achieved with the application of 261 and 298 mg P kg−1 of soil. Most of the growth and yield components had a significant positive association with grain yield. Optimum soil acidity indices such as pH; exchangeable calcium (Ca), magnesium (Mg), and potassium (K); Ca, Mg, and K saturation; base saturation; and acidity saturation were established for maximum upland rice grain yield.

Requirement of Micronutrients by Lowland Rice

Lowland or flooded rice is mainly responsible for about 76% of total rice production at global level, yet information on micronutrient requirements for this crop is limited. Six greenhouse experiments were conducted at the National Rice and Bean Research Center of EMBRAPA, Santo Antônio de Goiás, Brazil, to determine requirements of zinc (Zn), copper (Cu), boron (B), molybdenum (Mo), manganese (Mn), and iron (Fe) for lowland rice grown on a Brazilian Inceptisol. The levels of micronutrients used were Zn (0, 10 20, 40, and 80 mg kg−1), Cu (0, 5, 10, 20, and 40 mg kg−1), B (0, 5, 10, 20, and 40 mg kg−1), Mo (0, 2, 4, 8, and 16 mg kg−1), Mn (0, 50, 100, 300, and 600 mg kg−1), and Fe (0, 250, 500, 1000, and 2000 mg kg−1). Grain yield was significantly increased in a quadratic fashion with the addition of Zn, Cu, B, Mo, Mn, and Fe. The adequate rates of micronutrients for maximum grain yield were Zn 33 mg kg−1, Cu 25 mg kg−1, B 26 mg kg−1, Mo 10 mg kg−1, Mn 250 mg kg−1, and Fe 1269 mg kg−1. In addition to grain yield, plant height, straw yield, panicle density, and root growth of lowland rice were also improved with the addition of most of these micronutrients. Improvement in root growth has special significance in improving nutrient-use efficiency under nutrient-stress conditions. Micronutrient-use efficiency (grain yield per unit nutrient applied) was in the order of Cu > Zn > Mn > Fe > Mo > B.

Sparse‐Flowering Orchardgrass Represents an Improvement in Forage Quality During Reproductive Growth

ABSTRACTOrchardgrass (Dactylis glomerata L.) is a major component of many pastures in temperate North America. Early and profuse flowering in pastures is problematic, because livestock refuse to consume flowering stems, prompting many graziers to simply avoid using this species. The objective of this research was to determine the impact of reduced flowering on the quality of harvested forage under two harvest managements of orchardgrass. Six cultivars, three normal cultivars and three sparse‐flowering cultivars (mean panicle density of 141 vs. 61 panicles m⁻2, respectively), were evaluated in field experiments at 21 locations in North America under a 3‐cut harvest management. These cultivars were also evaluated at seven locations under a 5‐cut harvest management. Sparse‐flowering cultivars averaged 9% greater crude protein (CP), 3% lower neutral detergent fiber (NDF), 2% greater NDF digestibility, and 2% greater in vitro dry matter digestibility (IVDMD) than normal cultivars. For the two digestibility measures, differential panicle density between the cultivar groups explained a significant portion of variability, indicating that the increase in forage quality was proportional to the decrease in panicle density below a threshold of about 50 panicles m⁻2. Lastly, differences in regrowth forage quality between cultivar groups were smaller, less consistent, and of lesser statistical significance than for first harvest. While selection for sparse flowering in orchardgrass resulted in significant cause‐and‐effect increases in first‐harvest forage quality, these effects were too small to offset the reduced forage yield associated with the sparse‐flowering trait.

GENETIC VARIABILITY AND SELECTION CRITERIA IN RICE

Genetic parameters, correlation and path analysis for 12 yield and quality traits were studied during rabi, 2009 - 10 in 21 genotypes of rice. High estimates of GCV were recorded for plant height, number of filled grains/panicle and grain yield/plant. Heritability in broad sense was high for all the characters exc ept spikelet fertility. High heritability coupled with high genetic advance as per cent mean were recorded for number of productive tillers/plant, panicle density, number of filled grains/panicle, 1000 - grain weight, grain yield/plant and kernel length. Gra in yield/plant exhibited highly significant and positive correlation with days to 50 % flowering, plant height, productive tillers/plant, panicle length, panicle density and filled grains/panicle. Path coefficient studies indicated maximum direct positive effect of plant height, productive tillers, filled grains/panicle and kernel length and kernel breadth on grain yield/plant.

Sparse‐Flowering Orchardgrass is Stable Across Temperate North America

ABSTRACTOrchardgrass (Dactylis glomerata L.) is a major component of many pastures in temperate North America. Early and profuse flowering in pastures is problematic due to livestock refusal to consume flowering stems. The objective of this research was to determine the stability and agronomic impact of recently developed sparse‐flowering orchardgrass populations across temperate North America. Six cultivars, three sparse flowering and three normal flowering, were grown at 21 locations in temperate North America and evaluated for panicle density, heading date, and forage yield. Sparse‐flowering cultivars had 57% fewer panicles than normal‐flowering cultivars, but this effect was highly dependent on mean winter temperature, with normal‐flowering cultivars showing twice as much temperature sensitivity compared to sparse‐flowering cultivars. Forage yield of sparse‐flowering cultivars was reduced by approximately 24 to 32% for first harvest and 2 to 9% for regrowth harvests compared to normal‐flowering cultivars and this reduction in forage yield was independent of mean winter temperature. The forage yield reduction associated with sparse flowering is most likely due to a combination of physiological load (loss of stems) and opportunity cost (lack of selection pressure for yield), suggesting an opportunity to improve forage yield potential of this sparse‐flowering germplasm pool.

Genetic Variation for Grain Yield and Related Traits in Temperate Red Rice (Oryza sativa L.) Ecotypes

The present study was carried out in Kashmir (India) to assess the genetic variability for grain yield and component traits among 14 red rice ecotypes from temperate region (locally known as Zag for its coloured kernels) and correlation and path coefficients were also studied for fifteen agro-morphological characters. Genotypic and phenotypic coefficients of variation were high for grain yield, secondary branches per panicle and panicle weight; moderate for grain number per panicle, grain length:breadth (L:B) ratio and panicle density. High heritability accompanied by high to moderate genetic advance for panicle density, days to 50% flowering, plant height, grain number indicated the predominance of additive gene action for the expression of these characters. Grain yield was found to be positively and significantly correlated with number of tiller per plant, panicle density m-2 and number of grain per panicle at both genotypic and phenotypic levels indicating the importance of these characters for yield improvement in this material. The results of genotypic path analysis revealed that panicle density had the highest positive direct effect followed by plant height and days to flower. The overall results indicated that selection favouring higher panicle density, test weight and panicle weight and medium plant height with a reasonable balance for moderate grain number would help to achieve higher grain yield in this population of red rice ecotypes.

Growth and yield of rice (Oryza sativa L.) under resource conservation technologies in the irrigated drylands of Central Asia

Increasing water shortage and low water productivity in the irrigated drylands of Central Asia are compelling farmers to adopt resource conservation technologies, such as dry seeded, non-flooded rice. Alternate wet and dry (AWD) water management combined with alternative establishment methods, e.g., zero tillage planting in bed and flat layouts, and residue retention, may substantially reduce rice irrigation water requirement. Field experiments were conducted in a rice–wheat cropping system to evaluate these technologies and to identify the underlying processes responsible for possible reductions in rice yield. Zero till dry seeded rice (DSR) on the flat (DSRF) and on raised beds (DSRB), combined with three levels of wheat and rice straw residue retention – none (R0), 50% (R50) and 100% (R100) were therefore evaluated during the 2008 and 2009 growing seasons, using AWD water management. These treatments were compared with water seeded rice (WSR) grown with conventional tillage (dry tillage) on the flat under continuous flood irrigation (WSRF-R0-FI) or alternate wet and dry irrigation (WSRF-R0-AWD). The use of AWD reduced irrigation amount to only 30% of the amount of water applied to continuously flooded rice. However, yield of residue removed AWD treatments was lower than yield of the continuously flooded treatment by 27% in 2008 and by 40% in 2009. The significant reduction in rice yield in all treatments with AWD was caused by reduced growth rate, resulting in lower biomass, leaf area, panicle density, number of florets panicle−1 and floret fertility, with significant differences in the second year. In 2008, this appeared to be due to water deficit stress in the AWD treatments. In 2009, the reduction in growth and yield with AWD was greater, and more so as the level of residue retention increased. Residue retention reduced rice yield by 59% in 2009 with R100 compared to the R0. By far the biggest cause was a reduction in floret fertility. The reduction in fertility with AWD in 2009 appeared to be due to cold damage, whereas the continuously flooded rice appeared to have been protected from cold damage by the floodwater. The weather during the period from panicle initiation (PI) to flowering in 2009 was very cold, with 20 days with minimum temperature less than 15°C. About 1 in 10 years experience such low temperatures in this region. Therefore, the development of varieties with greater cold and water deficit stress tolerance is needed if non-flooded rice culture and surface residue retention are to be adopted in this region.

A CRITICAL ASSESSMENT OF THE IMPORTANCE OF SEEDLING AGE IN THE SYSTEM OF RICE INTENSIFICATION (SRI) IN EASTERN INDIA

SUMMARYA survey of the system of rice intensification (SRI)-related literature indicates that different authors have drawn conflicting inferences about rice yield performances under the SRI, chiefly because the SRI methodology has been variously advocated, interpreted and implemented in the field using different rice varieties, seedling ages at transplantation, cultivation seasons and nutrient management regimes. In particular, the SRI method of single-seedling transplantation (SST) has potential economic advantage due to reduced seed costs, but it is not clear whether SST is an effective management strategy across a range of seedling ages, and whether there is any specific seedling age that is optimal for yield improvement of a given rice variety. This is an important consideration in rain-fed ecosystems where variable rainfall patterns and lack of controlled irrigation make it difficult to reliably transplant at a specific seedling age as recommended for the SRI. We conducted a five year-long experiment on a rain-fed organic farm using a short-duration upland and a medium-duration lowland landrace, following the SRI methodology. Rice seedlings of different ages (6, 10, 14, 18 and 28 days after establishment) were transplanted at 25 cm × 25 cm spacing in three replicated plots. The performance for each landrace was examined with respect to productive tillers, panicle density, total grain counts per hill and grain yield per unit area. Performances of seedlings of different ages were compared with that of control plots that employed all SRI practices with the exception that 28-day-old seedlings were transplanted with three seedlings per hill. The results indicate that (1) the SRI can improve mean panicle density if seedling age ≤ 18 days, but that responses differ between varieties; (2) the number of productive tillers per hill is significantly less in SST than that of multiple seedling transplants (MST) of 28-day-old seedlings of both upland and lowland varieties; (3) the total grain numbers per hill of the lowland variety is significantly greater for 14-day-old SST than 28-day-old MST; (4) the grain yield per unit area from young SRI transplants is significantly greater than that from 28-day-old MST for the lowland variety, although the magnitude of the improvement was small; (5) for the upland variety, grain yields declined with the oldest seedlings, but planting multiple seedlings per hill made the yield of the oldest transplants on par with that of younger seedlings planted singly. Our findings suggest that transplanting younger seedlings under the SRI management may not necessarily enhance grain yields.

Effects of farmers’ cultural practices on the weedy rice infestation and rice production

An on-farm trial was conducted at the Muda Agricultural Development Authority rice fields, Kedah, Peninsular Malaysia from November, 2003 to July, 2006 to study the impacts of farmers’ cultural practices on the weedy rice infestation and rice production. Five sample farmers (A, B, C, D and E) from five different sampling sites were selected on the basis of severity of weedy rice infestation on their fields in earlier seasons. Field observations and monitoring were carried out for collecting data and recording the agronomic practices done by the farmers from land preparation to harvesting of the crops. The number of weedy rice panicles per unit area was recorded from 50 sampling spots per plot using 1 × 1 m quadrat. Rice plants and the weedy rice within the quadrats were harvested. Data on grain yields and yield components were recorded. The collected data were analyzed statistically and mean differences in weed infestation were adjudged using standard error of means. Results revealed that the farmers used different rice varieties and applied different agronomic practices, which resulted in variable intensities of weedy rice infestations and production of variable rice grain yields. The farmers A and B, who followed transplanting and water seeding for crop establishment, applied pre-planting herbicides (2 to 3 times) during land preparation and used regular surveillance and monitoring (20 to 25 times) of their plots, had less weedy rice infestation (32.22 panicles/m2) and higher rice yields (6.70 to 8.88 t/ha). The farmers C, D and E, used wet direct seeding for crop establishment, applied no or less time of pre-planting herbicides (1 time) and had less field surveillance (10 to 15 times/season), had consequently a higher weedy rice panicle density (154.94 panicles/m2) and less rice yields (3.57 to 6.27 t/ha). Key words: Farmers’ cultural practice, weedy rice infestation, wet direct seeding, water seeding, transplanting.

Structural equation modeling in the plant sciences: An example using yield components in oat

Lamb, E. G., Shirtliffe, S. J. and May, W. E. 2011. Structural equation modeling in the plant sciences: An example using yield components in oat. Can. J. Plant Sci. 91: 603–619. Structural equation modeling (SEM) is a powerful statistical approach for the analysis of complex intercorrelated data with a wide range of potential applications in the plant sciences. In this paper we introduce plant scientists to the principles and practice of SEM using as an example an agronomic field trial. We briefly review the history of SEM and path analysis and introduce the statistical concepts underlying SEM. We demonstrate the use of observed and latent variable structural equation models using a multi-site multi-year field trial examining the effects of seed size and seeding density on the plant density and yield of oat in Saskatchewan. Using SEM allowed for insights that a standard univariate analysis would not have revealed. We show that seeding density has strong effects on plant and panicle density, but has very limited effects on final yield. Plant density has a consistent non-linear effect on panicle density across location that was not affected by precipitation. In contrast, the implicit effect of precipitation on seed number appears to be the main driver for final yield. Incorporating precipitation data into the model demonstrates how mechanistic models can be developed by including in the path diagram variables that would normally treated as random factors in a mixed model analysis. Finally, we provide a guideline to assist plant scientists in determining whether SEM is an appropriate method to be used for the analysis of their data.

Structural equation modeling in the plant sciences: An example using yield components in oat

Lamb, E. G., Shirtliffe, S. J. and May, W. E. 2011. Structural equation modeling in the plant sciences: An example using yield components in oat. Can. J. Plant Sci. 91: 603-619. Structural equation modeling (SEM) is a powerful statistical approach for the analysis of complex intercorrelated data with a wide range of potential applications in the plant sciences. In this paper we introduce plant scientists to the principles and practice of SEM using as an example an agronomic field trial. We briefly review the history of SEM and path analysis and introduce the statistical concepts underlying SEM. We demonstrate the use of observed and latent variable structural equation models using a multi-site multi-year field trial examining the effects of seed size and seeding density on the plant density and yield of oat in Saskatchewan. Using SEM allowed for insights that a standard univariate analysis would not have revealed. We show that seeding density has strong effects on plant and panicle density, but has very l...

Effect of water management on dry seeded and puddled transplanted rice. Part 1: Crop performance

An alarming rate of ground water depletion and increasing labour scarcity are major threats to future rice production in north west India. Management strategies that reduce the irrigation amount and labour requirement while maintaining or increasing yield are urgently needed. Dry seeded rice (DSR) has been proposed as one means of achieving these objectives, but little is known about optimal water management for DSR. Therefore a field study was conducted on a clay loam soil in Punjab, India, during 2008 and 2009, to investigate the effects of irrigation management on the performance of puddled transplanted rice (PTR) and dry seeded rice. Irrigation scheduling treatments were based on soil water tension (SWT) ranging from ponding/saturation (daily irrigation) to alternate wetting and drying (AWD) with irrigation thresholds of 20, 40 and 70 kPa at 18–20 cm soil depth. Rainfall was above average and well distributed in 2008 (822 mm), and average and less well distributed in 2009 (663 mm). With daily irrigation, crop duration of PTR and DSR was the same. Shifting from daily irrigation to AWD delayed crop maturity by 8–17 d, and DSR was more affected than PTR, and more so in the drier year. Crop performance in terms of tiller density, leaf area index and growth rate was better in DSR than PTR with daily and 20 kPa irrigation scheduling. However, crop performance was poorer in DSR than PTR at higher (40 and 70 kPa) irrigation thresholds, more so in the drier year when DSR showed signs of severe iron deficiency which was not overcome with iron sprays. Yield components were similar in both establishment methods when irrigation was scheduled daily or at 20 kPa, but panicle density and the number of filled grains per panicle were significantly lower at 40 and 70 kPa in DSR than PTR. Each year, yield of DSR and PTR were similar when irrigation was scheduled daily or at 20 kPa. Yields of both PTR and DSR declined under higher water deficit stress (40 and 70 kPa irrigation thresholds), but more so in DSR, and more so in the drier year. There was a very large and significant decline in irrigation water input with irrigation at 20 kPa compared to daily irrigation in both establishment methods, but only a very small decline in irrigation amount when the threshold was increased from 20 to 40 and 70 kPa. Irrigation water use in DSR-AWD treatments was significantly lower than in respective PTR treatments (e.g. by 33–53% when irrigation was scheduled at 20 kPa). The results suggest the feasibility of reducing irrigation amount while maintaining yield by replacing PTR with DSR with AWD, provided that soil tension is kept lower than 20 kPa at 20 cm depth, but that this threshold needs to be tested over a wider range of seasonal and site conditions and varieties.

Control of Molinia caerulea by cutting management on sub-alpine grassland

There has been a considerable expansion of Molinia caerulea after the cessation of cutting management of Nardus stricta sub-alpine grasslands in the Giant Mts. (Krkonoše/Karkonosze/Riesengebirge, the Czech Republic) in the last 50 years. The aim of this study was to investigate whether the reestablishment of traditional management (one cut per year in late July) could reverse Molinia encroachment and help to restore the original Nardus grassland. The cover of Molinia significantly decreased from 79% to 7%, the height of the canopy from 45 to 14 cm, biomass production from 313 to 54 g m −2 and panicle density from 129 to 18/m 2 after 6 years of cutting management. During the course of the experiment, no seedlings of Nardus were recorded in mown plots, although Nardus was common in the neighborhood. After Molinia retreat bare ground was partly colonized by Avenella flexuosa and partly remained free of vegetation. No significant effect of cutting management on species richness per 1 m 2 was recorded. Cutting significantly decreased K availability in the soil, although the amount of K removed was only 8 g/m 2 over 6 years. The N:P, N:K and K:P ratios in the plant biomass were not significantly affected by mowing compared to the unmanaged control, indicating P and K limitation but not N limitation in both treatments. Reestablishment of traditional management (one cut per year in late July) reversed Molinia encroachment but did not increase species richness or restore the original Nardus grassland over 6 years.

Tillage, Seeding, and Nitrogen Rate Effects on Rice Density, Yield, and Yield Components of Two Rice Cultivars

Research was conducted for 2 yr on a Crowley silt loam soil (fine, smectitic, thermic Typic Albaqualfs) near Crowley, LA to evaluate the main effects of tillage, seeding and N rate and potential interactions on rice (Oryza sativa L.) density, yield, and yield components. Two tillage systems (conventional and fall‐stale seedbed), four seeding rates (162, 323, 484, and 646 seed m−2) and four N rates (101, 134, 168, and 202 kg ha−1) were evaluated. ‘Jupiter’ and ‘Cheniere’ a medium and long grain cultivar, respectively, were evaluated in separate experiments. Conventional tillage reduced rice plant density as compared with fall‐stale seedbed tillage due to crusting following flush irrigation during seedling emergence. A tillage by N rate interaction was not observed, suggesting optimal N rates are similar for rice grown using a conventional or fall‐stale seedbed. Rough rice grain yield was optimized at 202 and 168 kg N ha−1 for Jupiter and Cheniere, respectively. Grain yields were optimized for Jupiter at 323 seed m−2, while Cheniere required a seeding rate of more than 323 seed m−2 Panicle density was found to be the single most influential yield component on rice yield and was able to explain 49 and 51% of the variation in yield for Jupiter and Cheniere, respectively. Filled grain panicle−1 was inversely related to panicle density highlighting the ability of rice to tiller as a yield compensatory measure when less than optimum rice densities exist. However, total yield compensation may not be feasible at low seeding rates.

Nitrogen use for high productivity and sustainability in cashew

Interest in cashew production in Australia has been stimulated by domestic and export market opportunities and suitability of large areas of tropical Australia. Economic models indicate that cashew production is profitable at 2.8 t ha −1 nut-in-shell (NIS). Balanced plant nutrition is essential to achieve economic yields in Australia, with nitrogen (N) of particular importance because of its capacity to modify growth, affect nut yield and cause environmental degradation through soil acidification and off-site contamination. The study on a commercial cashew plantation at Dimbulah, Australia, investigated the effect of N rate and timing on cashew growth, nut production, N leaching and soil chemical properties over five growth cycles (1995–1999). Nitrogen was applied during the main periods of vegetative (December–April) and reproductive (June–October) growth. Commercial NIS yields (up to 4.4 t ha −1 from individual trees) that exceeded the economic threshold of 2.8 t ha −1 were achieved. The yield response was mainly determined by canopy size as mean nut weight, panicle density and nuts per panicle were largely unaffected by N treatments. Nitrogen application confined to the main period of vegetative growth (December–April) produced a seasonal growth pattern that corresponded most consistently with highest NIS yield. This N timing also reduced late season flowering and undesirable post-November nut drop. Higher yields were not produced at N rates greater than 17 g m −2 of canopy surface area (equating to 210 kg N ha −1 for mature size trees). High yields were attained when N concentrations in Mveg leaves in May–June were about 2%, but this assessment occurs at a time when it is not feasible to correct N deficiency. The Mflor leaf of the preceding November, used in conjunction with the Mveg leaf, was proposed as a diagnostic tool to guide N rate decisions. Leaching of nitrate-N and acidification of the soil profile was recorded to 0.9 m. This is an environmental and sustainability hazard, and demonstrates that improved methods of N management are required.

Interactions Between Weedy Rice and Cultivated Rice in Italy

Field studies were carried out in 1997 and 1998 in northwest Italy with the aim of determining the effects of weedy rice competition on rice growth dynamics and yield. ‘Arborio’ (medium-high tall size, high early vigour) and ‘Thaibonnet’ (semi-dwarf size, low early vigour) rice cultivars were grown in competition with weedy rice at four densities (0, 10, 20, and 40 plants m-2). For both cultivars the plant height, the aboveground biomass and the number of tillers were determined at different intervals. With some exceptions, all the measured rice growth parameters were not remarkably affected by weedy rice interference. Weedy rice plants grown in competition with ‘Arborio’ were generally taller and produced more biomass. Weedy rice competition resulted in up to 50% (in ‘Thaibonnet’) and 48% (in ‘Arborio’) yield losses. The yield losses observed in both varieties were primarily related to the reduction of yield components, and of panicle density and number of filled grains per panicle, in particular.

Nitrogen Application in Irrigated Rice Grown in Mediterranean Conditions: Effects on Grain Yield, Dry Matter Production, Nitrogen Uptake, and Nitrogen Use Efficiency

ABSTRACT Field experiments were conducted in the major rice growing area of Chile to evaluate the effects of nitrogen (N) fertilization and site on grain yield and some yield components, dry matter production, N uptake, and N use efficiency in rice cultivar ‘Diamante’. Two sites (indicated as sites 1 and 2) and six N rates (0, 50, 100, 150, 200, and 300 kg N ha−1) were compared. Nitrogen fertilization increased yield, panicle density, spikelet sterility, dry matter production, and N uptake at maturity. 90% of maximum yield was obtained with 200 kg N ha−1 in site 1 (12,810 kg ha−1) and with 100 kg N ha−1 in site 2 (8,000 kg ha−1). These differences were explained by lower panicle density, and the resulting lower dry matter production and N uptake in site 2. Nitrogen use efficiency for biomass and grain production, and grain yield per unit of grain N decreased with N fertilization. While, agronomic N use efficiency and N harvest index were not affected. All N use efficiency indices were significantly higher in site 1, except grain yield per unit of grain N. The observed variation in N use efficiency indices between sites would reflect site-specific differences in temperature and solar radiation, which in turn, determined yield potentials of each site. On the basis of these results, cultivar ‘Diamante’ would correspond to a high-N use efficiency genotype for grain yield.

Management of wild oat (Avena fatua L.) in tame oat (Avena sativa L.) with early seeding dates and high seeding rates

Traditionally, farmers have delayed seeding to manage wild oat (Avena fatua L.) in tame oat (Avena sativa L.) crops, but this practice can adversely affect grain yield and quality. The objectives of this study were: (1) to evaluate the effectiveness of using high seeding rates with early-seeded oat to maintain grain yield and quality, and (2) to determine an optimum seeding rate to manage wild oat and maximize grain yield and quality. The factors of interest were wild oat density (low and high density), seeding date (early May, mid May, early June and mid June), and tame oat seeding rate (150, 250, 350 and 450 viable seeds m-2). The study was conducted at Indian Head and Saskatoon, SK, in 2002, 2003 and 2004, at Winnipeg, MB, in 2002, and at Morden, MB, in 2003 and 2004. Wild oat biomass, wild oat panicle density and wild oat seed in the harvested sample decreased as seeding rate increased, while tame oat biomass and grain yield increased. Wild oat density ranged between 0 and 100 plants m-2 with averages of 10 plants m-2 in the low density treatment and 27 plants m-2 in the high density treatment. At low seeding rates, grain yield decreased with increasing wild oat density. The difference in grain yield between the two wild oat densities decreased as the seeding rate increased. There was a curvilinear decrease in grain yield as seeding was delayed. A seeding date × seeding rate interaction was noted for test weight, plump seed, thin seed and groat yield. Seed quality improved as seeding rate increased for only the mid-June seeding date. Even though the mid-June test weight increased as the seeding rate increased it was always lower than the early May test weight at any seeding rate. The results from this study established that in the presence of wild oats, early seeding of tame oat is possible providing high seeding rates, 350 plants m-2 are used.Key words: Wild oat competition, wild oat density, wild oat biomass, grain yield, grain quality