Root growth dynamics and stomatal behaviour of rice (Oryza sativa L.) grown under aerobic and flooded conditions

Aerobic rice culture is a new technology designed to reduce water use, but the vulnerability of rice to aerobic condition has limited its development. The objective of this study was to characterize the root growth and stomatal behaviour of four rice cultivars grown in flooded and aerobic culture for 2 years. In aerobic culture, where the soil water potential at 20-cm depth averaged between −15 and −30 kPa, total root biomass was significantly lower than in flooded culture for the whole growth period, owing to a reduction in root biomass in the surface layer. Dry-matter partitioning to roots decreased, but the ratio of deep root biomass to total root biomass tended to be higher in aerobic culture than in flooded culture. The low root-to-shoot ratio and poor root growth in the surface layer in aerobic culture are attributable to the considerable reduction in adventitious root number. As a result, the varietal difference in total root biomass was due largely to individual root growth in aerobic culture. Stomatal closure was distinct at the vegetative stage in aerobic culture, even when the soil water potential was near field capacity, partly because of the poor rooting vigour. When the soil water potential at 20-cm depth was below −50 kPa, the stomatal behaviour reflected the root growth in the subsurface layer. These results suggest the role of vigorous root growth in soil water uptake and hence, in maintaining transpiration in aerobic rice culture.     

Radiation use efficiency,N accumulation and biomass production of high-yielding rice in aerobic culture

The concept of aerobic culture is to save water resource while maintaining high productivity in irrigated rice ecosystem. This study compared nitrogen (N) accumulation and radiation use efficiency (RUE) in the biomass production of rice crops in aerobic and flooded cultures. The total water input was 800–1300 mm and 1500–3500 mm in aerobic culture and flooded culture, respectively, and four high-yielding rice cultivars were grown with a high rate of N application (180 kg N ha⁻¹) at two sites (Tokyo and Osaka) in Japan in 2007 and 2008. The aboveground biomass and N accumulation at maturity were significantly higher in aerobic culture (17.2–18.5 t ha⁻¹ and 194–233  kg N ha⁻¹, respectively) than in flooded culture (14.7–15.8 t ha⁻¹ and 142–173 kg N ha⁻¹) except in Tokyo in 2007, where the surface soil moisture content frequently declined. The crop maintained higher N uptake in aerobic culture than in flooded culture, because in aerobic culture there was a higher N accumulation rate in the reproductive stage. RUE in aerobic culture was comparable to, or higher than, that in flooded culture (1.27–1.50 g MJ⁻¹ vs. 1.20–1.37 g MJ⁻¹), except in Tokyo in 2007 (1.30 g MJ⁻¹ vs. 1.37 g MJ⁻¹). These results suggest that higher biomass production in aerobic culture was attributable to greater N accumulation, leading to higher N concentration (N%) than in flooded culture. Cultivar differences in response to water regimes were thought to reflect differences in mainly (1) early vigor and RUE under temporary declines in soil moisture in aerobic culture and (2) the ability to maintain high N% in flooded culture.     

Factors that determine grain weight in rice under high-yielding aerobic culture: The importance of husk size

In water-saving rice culture, yield is unstable because spikelet number per unit area and grain weight fluctuate according to water availability. In this study, we investigated the factors that determine grain weight in aerobic culture. We grew four rice varieties in non-puddled, unsaturated (aerobic) soils with a soil water potential at 20-cm depth kept above −60 kPa and in continuously flooded culture in two years. We found a significant variety × water interaction in grain weight in 2009: weights under aerobic culture were 6% and 13% larger than under flooded culture in Sasanishiki and IRAT109, respectively, versus 4% and 10% smaller in Habataki and Takanari. There was no significant variety × water interaction in grain weight in 2010. Sink activity (grain sucrose synthase activity) and source capacity (biomass production and nonstructural carbohydrate content in vegetative tissue) per plant during ripening were higher under aerobic culture than under flooded culture in both years. However, an excessive increase in spikelet number per unit area in Takanari under aerobic culture in 2009 reduced the source capacity per spikelet and single husk size, decreasing grain weight. In 2010, frequent soil drying under aerobic culture during the late reproductive period (around 20 days preceding heading) reduced single husk size, thereby decreasing grain weight. We found that sink activity and source capacity per plant could be both higher under aerobic culture during the ripening period, producing larger grain weight at a soil water potential above-40 kPa at a 20-cm depth relative to those under flooded culture. In contrast, greater drying under aerobic culture during the late reproductive period reduced single husk size, thereby reducing grain weight.     

Chlorophyll meter-based nitrogen management of rice grown under alternate wetting and drying irrigation

Farmers have adopted alternate wetting and drying (AWD) irrigation to cope with water scarcity in rice production. This practice shifts rice land away from being continuously anaerobic to being partly aerobic, thus affecting nutrient availability to the rice plant, and requiring some adjustment in nutrient management. The use of a chlorophyll meter (also known as a SPAD meter) has been proven effective in increasing nitrogen-use efficiency (NUE) in continuously flooded (CF) rice, but its use has not been investigated under AWD irrigation. This study aimed at testing the hypotheses that (i) SPAD-based N management can be applied to AWD in the same way it is used in CF rice, and (ii) combining chlorophyll meter-based nitrogen management and AWD can enhance NUE, save water, and maintain high rice yield. Experiments were conducted in a split-plot design with four replications in the 2004 and 2005 dry seasons (DS) at IRRI. The main plots were three water treatments: CF, AWD that involved irrigation application when the soil dried to soil water potential at 15-cm depth of −20 kPa (AWD₋₂₀) and −80 kPa (AWD₋₈₀) in 2004, and AWD₋₁₀ and AWD₋₅₀ were used in 2005. The subplots were five N management treatments: zero N (N₀), 180 kg N ha⁻¹ in four splits (N₁₈₀), and three SPAD-based N-management treatments in which N was applied when the SPAD reading of the youngest fully extended leaf was less than or equaled 35 (N_SPAD35), 38 (N_SPAD38), and 41 (N_SPAD41). In 2005, N_SPAD32 was tested instead of N_SPAD41. A good correlation between leaf N content per unit leaf area and the SPAD reading was observed for all water treatments, suggesting that the SPAD reading can be used to estimate leaf N of rice grown under AWD in a way similar to that under CF. SPAD readings and leaf color chart (LCC) values also showed a good correlation. There were no water × nitrogen interactive effects on rice yield, water input, water productivity, and N-use efficiency. Rice yield in AWD₋₁₀ was similar to those of CF; yields of other AWD treatments were significantly lower than those of CF. AWD₋₁₀ reduced irrigation water input by 20% and significantly increased water productivity compared with CF. The apparent nitrogen recovery and agronomic N-use efficiency (ANUE) of AWD₋₁₀ and AWD₋₂₀ were similar to those of CF. The ANUE of N_SPAD38 and N_SPAD35 was consistently higher than that of N₁₈₀ in all water treatments. N_SPAD38 consistently gave yield similar to that of N₁₈₀ in all water treatments, while yield of N_SPAD35 about 90% of that of CF. We conclude that a combination of AWD₋₁₀ and SPAD-based N management, using critical value 38, can save irrigation water and N fertilizer while maintaining high yield as in CF conditions with fixed time and rate of nitrogen application of 180 kg ha⁻¹. Treatments AWD₋₂₀ and N_SPAD35 may be accepted by farmers when water and N fertilizer are scarce and costly. The findings also suggested LCC can also be a practical tool for N-fertilizer management of rice grown under AWD, but this needs further field validation.     

【Short Report】Grain Yield and Leaf Area Growth of Direct-Seeded Rice on Flooded and Aerobic Soils in Japan

Abstract

Direct-seeding has been proposed as a water- and labor-saving method to grow irrigated rice. Our objective was to compare the effects of flooded and aerobic conditions on the yield stability of direct-seeded rice. We set up four trials in the field: aerobic, near-saturated and flooded soils with direct seeding, and flooded soil with transplanting. Grain yield of direct-seeded rice was comparable to that of transplanted under flooded conditions. However, the yield of direct-seeded rice under aerobic conditions was up to 21% lower than that under flooded conditions. This poor performance was associated with reduced leaf growth during the vegetative stage. Our results indicate that the yield stability of direct-seeded rice could be lowered by the water-saving irrigation, compared with the conventional flooded culture. In order to save irrigation water, physiological research on direct-seeded rice should target the vulnerability of rice to aerobic soils or to soil moisture fluctuations.     

Growth and Yield of Six Rice Cultivars under Three Water-saving Cultivations

Abstract

We evaluated the genotypic differences in growth, grain yield, and water productivity of six rice (Oryza sativa L.) cultivars from different agricultural ecotypes under four cultivation conditions: continuously flooded paddy (CF), alternate wetting and drying system (AWD) in paddy field, and aerobic rice systems in which irrigation water was applied when soil moisture tension at 15 cm depth reached ?15 kPa (A15) and ?30 kPa (A30). In three of the sixcultivars, we also measured bleeding rate and predawn leaf water potential (LWP) to determine root activity and plant water status. Soil water potential (SWP) in the root zone averaged ?1.3 kPa at 15 cm in AWD, -5.5 and -6.6 kPa at 15 and 35 cm, respectively, in A15, and ?9.1 and ?7.6 kPa at 15 and 35 cm, respectively, in A30. The improved lowland cultivar, Nipponbare gave the highest yield in CF and AWD. The improved upland cultivar, UPLRi-7, and the traditional upland cultivar, Sensho gave the highest yield in A15 and A30, respectively. The yields of traditional upland cultivars,Sensho and Beodien in A30 were not lower than the yields in CF. However, the yields of the improved lowland cultivars, Koshihikari and Nipponbare, were markedly lower in A15 and A30. Total water input was 2145 mm in CF, 1706 mm in AWD, 804 mm in A15, and 627 mm in A30. The water productivity of upland rice cultivars in aerobic plots was 2.2 to 3.6 times higher than that in CF, while those of lowland cultivars in aerobic plots were lower than those in CF. The bleeding rate of Koshihikari was lower in A15 and A30 than in CF and AWD, and its LWP was significantly lower in A15 and A30 than in CF and AWD, but Sensho and Beodien showed no differences among the four cultivation conditions. We conclude that aerobic rice systems are promising technologies for farmers who lack access to enough water to grow flooded lowland rice. However, lowland cultivars showed severe growth and yield reductions under aerobic soil conditions. This might result from poor root systems and poor root function, which limits water absorption and thus decreases LWP. More research on the morphological and physiological traits under aerobic rice systems is needed.     

Yield potential and water use efficiency of aerobic rice (Oryza sativa L.) in Japan

Intensive rice farming in aerobic soil, referred to herein as aerobic rice, can greatly reduce the water input compared to that of flooded rice cultivation. The objective of this study was to compare the potential productivity of aerobic rice and flooded rice using high-yielding varieties at two locations in Japan in two successive years. In aerobic fields, the total amount of water supplied (irrigation plus rainfall) was 800–1300 mm. The soil water potential at 20-cm depth averaged between −15 and −30 kPa each growing season, but frequently reached −60 kPa. The average yield under aerobic conditions was similar to or even higher than that achieved with flooded conditions (7.9 t ha⁻¹ in 2007 and 9.4 t ha⁻¹ in 2008 for aerobic versus 8.2 t ha⁻¹ for flooded). The average water productivity under aerobic conditions was 0.8–1.0 kg grain m⁻³ water, slightly higher than common values in the literature. The super-high-yielding cultivar Takanari achieved yields greater than 10 t ha⁻¹ with no yield penalty under aerobic conditions in 3 out of 4 experiments. The favorable agronomic characteristic of Takanari was its ample sink capacity (grain number × grain weight). In conclusion, high-productivity rice cultivation in aerobic soil is a promising technology for water conservation. With continued breeding, future aerobic rice varieties will possess large numbers of spikelets and sufficient adaptation to aerobic conditions such that they will consistently achieve yields comparable to the potential yield of flooded rice.     

A model explaining genotypic and environmental variation in leaf area development of rice based on biomass growth and leaf N accumulation

Leaf area index (LAI) is one of the major determinants of crop photosynthesis. The objectives of this study were to clarify the relationship between LAI development and crop growth in diverse rice genotypes grown under widely different climate conditions and to develop a model explaining genotypic and environmental variation in LAI dynamics based on environmental and plant factors. Cross-locational experiments were conducted with nine different rice genotypes at eight locations in Asia covering a wide climate range under irrigated conditions with sufficient nitrogen application. The LAI observed at the heading stage ranged from 0.85 to 8.77 among the genotypes grown at the eight locations. A fairly stable allometric relationship was observed between LAI development and above-ground biomass growth during the period from transplanting to 2 weeks before heading over all the genotypes, sites and years (r = 0.91). The allometric relationship was, however, under the influence of leaf nitrogen content per unit leaf area (LNC, g m⁻² leaf) and air temperature. On the basis of these results, we modeled the LAI development as a function of relative crop growth rate (RGR), LNC and air temperature. The rate of LAI decrease associated with leaf senescence was also described as a function of LNC.     

Possible causes of yield failure in tropical aerobic rice

Aerobic rice is a water-saving rice production system for water-short environments with favorable soils and adapted, potentially high-yielding varieties that are direct dry seeded. Soils remain aerobic but supplementary irrigation is applied as necessary. In the dry season of 2004 and 2005, a water by N experiment was set up at the location “Dapdap” in central Central Luzon, Philippines, to explore water and N management strategies in aerobic rice. The experiment was laid out as a split-plot design on a loamy sand soil with three water treatments (irrigation twice per week, once per week, and once in two weeks with modifications) and 5 N levels (0–200 kg ha⁻¹). Average seasonal soil moisture tension ranged from 9.2 to 20 kPa but yield hardly responded to the treatment combinations and ranged from 0 to 2 t ha⁻¹. In addition to trial-specific parameters, root knot nematodes and micronutrients (2005) were monitored. Galling of roots due to nematodes was assessed through a rating scale of 0–5, with 0 = no galling and 5 = >75% of the root system galled. The degree of galling reached a level of 5 at flowering and harvest in 2004, and 3 at tillering and 4 at harvest in 2005. Results of a plant tissue analysis at mid-tillering for Fe, Mn, and Zn showed on average values above critical levels; individual replicates, however, indicated deficiencies for Mn. In addition to actual field observations, we used simulation modeling (ORYZA2000) as a tool to estimate attainable yield under actual water conditions and N inputs to explore how yield failure set in. Simulation results matched observed values for total above-ground biomass and leaf area index quite well when no N was applied. When high rates of N (200 and 165 kg ha⁻¹) were applied, simulated values matched actual field data only until about the panicle initiation stage; afterward, observed values remained below the simulation. We interpreted this as evidence that growth-limiting factors other than water or N affected the crop from this growth stage on. Observations made in the field on root knot nematodes and micronutrients suggested that these two factors, especially root knot nematodes, may have been major constraints to crop development in this experiment.     

Is crop N demand more closely related to dry matter accumulation or leaf area expansion during vegetative growth?

The critical crop nitrogen uptake is defined as the minimum nitrogen uptake necessary to achieve maximum biomass accumulation (W). Across a range of crops, the critical N uptake is related to W by a power function with a coefficient less than unity that suggests crop N uptake is co-regulated by both soil N supply and biomass accumulation. However, crop N demand is also often linearly related to the expansion of the leaf area index (LAI) during the vegetative growth period. This suggests that crop N demand could be also linked with LAI extension. In this paper, we develop theory to combine these two concepts within a common framework. The aim of this paper is to determine whether generic relationships between N uptake, biomass accumulation, and LAI expansion could be identified that would be robust across both species and environment types. To that end, we used the framework to analyze data on a range of species, including C₃ and C₄ ones and mono- and di-cotyledonous crops. All crops were grown in either temperate or tropical and subtropical environments without limitations on N supply. The relationship between N uptake and biomass was more robust, across environment types, than the relationship of LAI with biomass. In general, C₃ species had a higher N uptake per unit biomass than C₄ species, whereas dicotyledonous species tended to have higher LAI per unit biomass than monocotyledonous ones. Species differences in N uptake per unit biomass were partly associated with differences in LAI and N-partitioning. Consequently the critical leaf-N uptake per unit LAI (specific leaf nitrogen, SLN) was relatively constant across species at 1.8–2.0 g m⁻², a value that was close to published data on the critical SLN of new leaves at the top of the canopy. Our results indicate that critical N uptake curves as a function of biomass accumulation may provide a robust platform for simulating N uptake of a species. However, if crop simulation models are to capture the genotypic and environmental control of crop N dynamics in a physiologically functional manner, plant growth has to be considered as the sum of a metabolic (e.g. leaves) and a structural (e.g. stems) compartment, each with its own demand for metabolic and structural N.     

A model for simulating plant N accumulation,growth and yield of diverse rice genotypes grown under different soil and climatic conditions

The objective of this study was to develop a whole-process model for explaining genotypic and environmental variations in the growth and yield of irrigated rice by incorporating a newly developed sub-model for plant nitrogen (N) uptake into a previously reported model for simulating growth and yield based on measured plant N. The N-uptake process model was developed based on two hypotheses: (1) the rate of root system development in the horizontal direction is proportional to the rate of leaf area index (LAI) development, and (2) root N-absorption activity depends on the amount of carbohydrate allocated to roots. The model employed two empirical soil parameters characterizing indigenous N supply and N loss. Calibration of the N-uptake process sub-model and validation of the whole-process model were made using plant N accumulation, and growth and yield data obtained from a cross-locational experiment on nine rice genotypes at seven locations in Asia, respectively. Calibration of the N-uptake process sub-model indicated that a large genotypic difference exists in the proportionality constant between rate of root system development and that of LAI development during early growth stages. The whole-process model simultaneously explained the observed genotypic and environmental variation in the dynamics of plant N accumulation (R² = 0.91 for the entire dataset), above-ground biomass growth (R² = 0.94), LAI development (R² = 0.78) and leaf N content (R² = 0.79), and spikelet number per unit area (R² = 0.78) and rough grain yield (R² = 0.81). The estimated value of the site (field)-specific soil parameter representing the rate of N loss was negatively correlated with cation exchange capacity of the soil and was approximated by a logarithmic function of cation exchange capacity for seven sites (R² = 0.95). Large yearly and locational variations were estimated in the soil parameter for representing the rate of indigenous N supply at 25 °C. With the use of these two soil parameters, the whole-system model explained the observed genotypic and environmental variations in plant N accumulation, growth and yield of rice in Asia.     

A model for explaining genotypic and environmental variation in vegetative biomass growth in rice based on observed LAI and leaf nitrogen content

The objectives of this study are to propose a model for explaining the genotypic and environmental variation in above-ground biomass growth via photosynthesis and respiration processes from transplanting to heading for different rice genotypes grown under a wide range of environments, and to identify the physiological traits associated with genotypic difference in the biomass growth based on model analysis. Cross-locational experiments were conducted with nine different rice genotypes at eight locations in Asia covering a wide climate range under irrigated conditions with sufficient nitrogen application. The crop growth rate observed during the period from transplanting to heading ranged from 3.4 to 19.4 g m⁻² d⁻¹ among the genotypes grown at the eight locations. About one-third of the data sets were utilized for model calibration and the remaining sets were used for model validation. An above-ground biomass growth model was developed by integrating processes of single leaf photosynthesis as a function of stomatal conductance and leaf nitrogen content, growth and maintenance respiration and crop development. To rigorously examine the validity of this process model, measured data were input as external variables for leaf area index (LAI) development and leaf nitrogen content per unit leaf area. The model well explained the observed dynamics in above-ground biomass growth (R² = 0.95*** for validation dataset) of nine rice genotypes grown under a variety of environments in Asia. The model simulation suggested that genotypic difference in the biomass growth was closely related to the difference in the stomatal conductance and leaf nitrogen content, as well as to LAI. This paper proposes the model structure, algorithms and all parameter values contained in the model, and discuss its effectiveness as a component of a more comprehensive model for simulating dynamics of biomass growth, LAI development and nitrogen uptake as a function of genotypic coefficients and environments.     

Alleviating soil sickness caused by aerobic monocropping: Responses of aerobic rice to nutrient supply

Yield decline is a major constraint in the adoption of monocropping of aerobic rice. The causes of the yield decline in the continuous aerobic rice system are still unknown. The objective of this study was to determine if nutrient application can mitigate the yield decline caused by continuous cropping of aerobic rice. Micro-plot experiment was conducted in 2005 dry season (DS) in a field where aerobic rice has been grown continuously for eight seasons from 2001 DS at the International Rice Research Institute (IRRI) farm. Pot experiments were done with the soil from the same field where the micro-plot experiment was conducted and aerobic rice has been grown continuously for 10 seasons. Apo, an upland rice variety, was grown under aerobic conditions with different nutrient inputs in field and pot experiments. The field micro-plot experiment showed that micronutrients had insignificant effect on plant growth under continuous aerobic rice cultivation but the combination of N, P, and K mitigated the yield decline of continuous aerobic rice. A series of pot experiments studying the individual effects of nutrients indicated that N application improved plant growth under continuous aerobic rice cropping, while P, K, and micronutrients had no effect. Increasing the rate of N application from 0.23 to 0.90 g per pot in the continuous aerobic rice soil increased the vegetative growth parameters, chlorophyll meter readings, and aboveground N uptake consistently. Our results suggested that N deficiency due to poor soil N availability or reduced plant N uptake might cause the yield decline of continuous cropping of aerobic rice.     

Application of system dynamics approach for time varying water balance in aerobic paddy fields

Increasing water scarcity has necessitated the development of irrigated rice systems that require less water than the traditional flooded rice. The cultivation of aerobic rice is an effort to save water in response to growing worldwide water scarcity with the pressure to reduce water use and increase water productivity. An accurate estimation of different water balance components at the aerobic rice fields is essential to achieve effective use of limited water supplies. Some field water balance components, such as percolation, capillary rise and evapotranspiration, can not be easily measured; therefore a soil water balance model is required to develop and to test water management strategies. This paper presents results of a study to quantify time varying water balance under a critical soil water tension based irrigation criteria for the cultivation of non-ponded “aerobic rice” fields along the lower parts of the Yellow River. Based on the analysis and integration of existing field information on the hydrologic processes in an aerobic rice field, this paper outlines the general components of the water balance using a conceptual model approach. The time varying water balance is then analyzed using the feedback relations among the hydrologic processes in a commercial dynamic modeling environment, Vensim. The model simulates various water balance components such as actual evapotranspiration, deep percolation, surface runoff, and capillary rise in the aerobic rice field on a daily basis. The model parameters are validated with the observed experimental field data from the Huibei Irrigation Experiment Station, Kaifeng, China. The validated model is used to analyze irrigation application soil water tension trigger under wet, dry and average climate conditions using daily time steps. The scenario analysis show that to conserve scarce water resources during the average climate years the irrigation scheduling criteria can be set as −30 kPa average root zone soil water tension; whereas it can be set at −70 kPa during the dry years, however, the associated yields may reduce. Compared with the flooded lowland rice and other upland crops, with these two alternatives irrigation event triggers, aerobic rice cultivation can lead to significant water savings.     

Yield formation and tillering dynamics of direct-seeded rice in flooded and nonflooded soils in the Huai River Basin of China

Water shortage in the Huai River Basin prompts farmers to adopt water-saving technologies such as direct-seeded nonflooded or aerobic rice. Different cultivation practices impact on tiller growth and development. Improved insight into tiller dynamics is needed to increase yield in these production systems. We conducted field experiments with four direct-seeded rice varieties under flooded and nonflooded conditions in Mengcheng county, Anhui province, in 2005–2006. The soil water content in the nonflooded treatment varied between saturation and field capacity. Yields in nonflooded soil ranged from 3.6 to 4.7 t ha⁻¹, and did not differ significantly from yields in flooded soil that ranged from 3.6 to 5.1 t ha⁻¹. Variety had a significant effect on biomass, yield, panicle number, spikelet number, grain weight, and grain filling percentage. Panicle number was the main factor limiting yield, resulting from a low tiller emergence frequency and a low fraction of productive tillers in both the flooded and the nonflooded soils. On average, the panicle number was 159–232 m⁻², including 34–167 productive tillers per m² for all the varieties under the two water regimes. The contribution of productive tillers to yield varied between 7% and 47%. There were two peaks of tillers that contributed to yield, one at the low (4th or 5th) and one at the high (10th or 11th) phytomer orders. Frequencies of tiller emergence at most phytomer orders were higher in the flooded soil than in the nonflooded soil. There were no significant differences in frequencies of productive tiller emergence and contributions to yield from tillers between the soil water regimes for three of the four tested varieties. To increase yield in direct-seeded nonflooded rice production systems, both the tiller emergence frequency and the fraction of productive tillers should increase through breeding, improved crop management, or a combination.     

氮素供应对春玉米产量及冠层部分指标的影响与相关分析

采用辽宁地区5个地方品种进行低、中、高3个氮素水平的比较试验(N0:不施氮、N1:112 kg/hm~2、N2:225 kg/hm~2),探究氮素对玉米冠层指标的影响及与产量因素的相关性。相关、逐步回归分析表明,随着施氮量升高,品种产量和穗粒数显著提高。不同氮素水平下,冠层指标与产量因素相关性有差异。穗粒数在N0处理下,与吐丝期叶氮比(SLN)和叶片氮浓度呈负相关,相关强度排序为吐丝期SLN吐丝期叶片氮浓度;N1处理下,与乳熟期LAI呈正相关,与吐丝期叶片氮浓度和吐丝期绿叶数呈负相关,相关强度排序为吐丝期叶片氮浓度乳熟期LAI吐丝期绿叶数;N2处理下,穗粒数与冠层指标相关性不显著。百粒重在N0处理下,与吐丝期穗位叶SPAD值呈正相关,与吐丝期LAI和乳熟期穗位叶SPAD值呈负相关,相关强度排序为吐丝期LAI吐丝期SPAD乳熟期SPAD;N1处理下,与乳熟期穗位叶SPAD值呈正相关,与乳熟期LAI呈负相关,相关强度排序为乳熟期LAI乳熟期SPAD值;在N2处理下,与吐丝期比叶面积(SLA)、SLN、乳熟期绿叶数呈负相关,相关强度排序为吐丝期SLN、SLA乳熟期绿叶数。     

Temporal dynamics of light and nitrogen vertical distributions in canopies of sunflower, kenaf and cynara

To enhance eco-physiological and modelling studies, we quantified vertical distributions of light and nitrogen in canopies of three Mediterranean bio-energy crops: sunflower (Helianthus annuus), kenaf (Hibiscus cannabinus) and cynara (Cynara cardunculus). Field crops were grown with and without water stress in 2008 and 2009. Canopy vertical distributions of leaf area index (LAI), photosynthetically active radiation (PAR), specific leaf area (SLA), nitrogen concentration (N_conc) and specific leaf nitrogen (SLN) were assessed over time for each crop × year × water input combination. Light and nitrogen distributions were quantified by the Beer's law (exponential model) and extinction coefficients for light (K_L) and nitrogen (K_N) were calculated. Within a year, K_L did not change significantly over the studied period in all irrigated crops, but differences in K_L were significant between years (sunflower: 0.74 vs. 0.89; kenaf: 0.62 vs. 0.71; cynara: 0.77). K_L estimates were always lower (−48 to −65%) in water-stressed sunflower and kenaf crops because of the reduction in leaf angle. These results should be taken into account, when simulating water-limited biomass production. Vertical SLN distributions were found in canopies when LAI was >1.5 (40 from 51 cases). These distributions were significantly correlated with the cumulative LAI from the top (r² = 0.75-0.81; P < 0.05), providing parameters to upscale photosynthesis from leaf to canopy levels. Vertical SLN distributions followed species-specific patterns over the crop cycle and varied less compared to PAR distributions between years. Lastly, we observed strong associations between SLN and PAR distributions in irrigated sunflower and kenaf canopies (r² > 0.66; P < 0.001). However, observed SLN distributions were less steep than the distributions that would maximize canopy photosynthesis.     

Physiological characterization of introgression lines derived from an indica rice cultivar, IR64, adapted to drought and water-saving irrigation

Water scarcity threatens sustainable rice production in many irrigated areas around the world. To cope with the scarcity, aerobic rice culture has been proposed as a promising water-saving technology. The objective was to elucidate the physiological attributes behind the performance of rice introgression lines in water-saving culture. We evaluated yield potential and physiological adaptation traits to water deficit of BC₃-derived lines with the genetic background of an elite indica cultivar, IR64, in the field and in pot experiments. One line, YTH183, had 26% higher yield than IR64 under non-stress conditions (895 vs. 712 g m⁻² on average). This was attributed to enlarged sink capacity due to large grain size, which contributed to more efficient use of assimilates and hence a higher harvest index. YTH183 also showed better dehydration avoidance under intermittent soil drying, due to the adaptive response of deep rooting to water deficiency. The grain yield of YTH183 exceeded that of IR64 by 92-102% under moderate water deficit caused by limited irrigation in aerobic rice culture (143 vs. 72 g m⁻²). Two introgressed segments on chromosomes 5 and 6 might, at least in part, confer the higher yield potential and greater dehydration avoidance in YTH183 simultaneously. Advanced backcross breeding combined with molecular genetics and physiological characterization of introgressed segments would be effective for developing new rice cultivars with high yield potential and drought adaptation traits.     

Effect of water management on dry seeded and puddled transplanted rice: Part 2: Water balance and water productivity

Labour and water scarcity in north west India are driving researchers and farmers to find alternative management strategies that will increase water productivity and reduce labour requirement while maintaining or increasing land productivity. A field experiment was done in Punjab, India, in 2008 and 2009 to compare water balance components and water productivity of dry seeded rice (DSR) and puddled transplanted rice (PTR). There were four irrigation schedules based on soil water tension (SWT) ranging from saturation (daily irrigation) to alternate wetting drying (AWD) with irrigation thresholds of 20, 40 and 70 kPa at 18–20 cm soil depth. There were large and significant declines in irrigation water input with AWD compared to daily irrigation in both establishment methods. The irrigation water savings were mainly due to reduced deep drainage, seepage and runoff, and to reduced ET in DSR. Within each irrigation treatment, deep drainage was much higher in DSR than in PTR, and more so in the second year (i.e. after 2 years without puddling). The irrigation input to daily irrigated DSR was similar to or higher than to daily irrigated PTR. However, within each AWD treatment, the irrigation input to DSR was less than to PTR, due to reduced seepage and runoff, mainly because all PTR treatments were continuously flooded for 2 weeks after transplanting. There was 30–50% irrigation water saving in DSR-20 kPa compared with PTR-20 kPa due to reduced seepage and runoff, which more than compensated for the increased deep drainage in DSR. Yields of PTR and DSR with daily irrigation and a 20 kPa irrigation threshold were similar each year. Thus irrigation and input water productivities (WP_I and WP_I+R) were highest with the 20 kPa irrigation threshold, and WP_I of DSR-20 kPa was 30–50% higher than of PTR-20 kPa. There was a consistent trend for declining ET with decreasing frequency of irrigation, but there was no effect of establishment method on ET apart from higher ET in DSR than PTR with daily irrigation. Water productivity with respect to ET (WP_ET) was highest with a 20 kPa irrigation threshold, with similar values for DSR and PTR. An irrigation threshold of 20 kPa was the optimum in terms of maximising grain yield, WP_I and WP_I+R for both PTR and DSR. Dry seeded rice with the 20 kPa threshold outperformed PTR-20 kPa in terms of WP_I through maintaining yield while reducing irrigation input by 30–50%.     

Growth and yield potential of Oryza sativa and O. glaberrima upland rice cultivars and their interspecific progenies

A recent breakthrough in generating fertile progeny from Oryza sativa×O. glaberrima crosses gives rice breeders access to a broader range of germplasm. Interspecific crosses might provide new solutions to the low productivity of upland rice systems prone to weed competition. Two field and one pot experiments conducted during 1995 and 1996 served to characterize growth and yield potential of CG14 (O. glaberrima), WAB56-104 (O. sativa) and their progeny. During the 1995 wet season and the 1996 dry and wet seasons, the lines were seeded in a well-drained upland field in Ivory Coast with supplemental sprinkler irrigation. A randomized complete-block design with three replications was used, with cultivar and nitrogen levels as sub-plots. Specific leaf area (SLA), leaf area index (LAI), leaf chlorophyll content (SPAD method) and tiller number were measured at 2-week intervals until flowering. Grain yield and yield components were measured at maturity. In all environments, CG14 produced two to three times the LAI and tiller numbers as WAB56-104. This was associated with a high SLA and low leaf chlorophyll content. Grain yields of CG14 did not respond to N inputs, although the sink potential did. The difference was mainly caused by grain shattering. The progenies had intermediate LAI, SLA and leaf chlorophyll content, but their grain yields, tiller numbers and resistance to lodging and grain shattering were similar to WAB56-104. Across lines, LAI and SLA were significantly correlated. A paddy field experiment confirmed the relationship between LAI and SLA for a wider range of rice cultivars and interspecific progenies. A pot experiment demonstrated that leaf net CO₂ assimilation rates (A_max) followed a common linear function of areal leaf chlorophyll content across cultivars. The main common cause of differential LAI and A_max appeared to have been genotypic patterns of SLA, which might be an important determinant of growth vigor and competitiveness with weeds. The possibility is discussed of combining, in a single line, high SLA during vegetative growth (for weed competitiveness) with low SLA during the reproductive growth phase (for high yield potential), to produce an efficient plant type for low-management conditions.