Effect of Soil Compaction on Dry Matter Production and Water Use of Rice (Oryza sativa L.) under Water Deficit Stress during the Reproductive Stage

Abstract

The effect of a long term of soil compaction on dry matter production (DMP) and water use in rice cultivated under limited water supply during the reproductive stage is unknown. Our objectives were to determine which of the transpiration (Tr) or water use efficiency (WUE) is dominant in determining DMP under compacted and desiccated soil conditions. When irrigation in the period around the reproductive stage was terminated in artificially compacted and non-compacted fields, the rate of suppression of DMP by soil compaction was similar in the three rice cultivars, but DMP was higher in drought resistant cultivars having deep root density at the heading stage. Six cultivars were grown in pots of 1.0 m in depth containing the soils of three levels of soil bulk density (SBD). Water supply was restricted by keeping the water table in the pot deep without irrigation during the reproductive stage. DMP and Tr in all cultivars decreased with increasing SBD, and a close relationship was seen between DMP and Tr. WUE was thus a fairly stable factor for all cultivars examined. Tr was positively correlated with root length density and was relatively maintained at a high SBD in drought-resistant cultivars having a higher root length density. We concluded that water shortage under compacted soil conditions during reproductive stage suppressed the DMP, and DMP suppression accompanied a reduction of Tr due to poor root development rather than the reduction of WUE. In the drought-resistant cultivars reduction of DMP was relatively small due to their highly developed root systems that allowed high water absorption from the deep layers in the compacted soil.     

Genotypic Variation in Biomass Production at the Early Vegetative Stage among Rice Cultivars Subjected to Deficient Soil Moisture Regimes and Its Association with Water Uptake Capacity

References

Genetic improvement in water uptake ability and/or water use efficiency (WUE) of rice cultivars is one option to enhance productivity under water-limited conditions. We examined the genotypic variation in biomass production among 70 rice cultivars (69 cultivars of NIAS global rice core collection and Azucena) under different soil moisture conditions, and to identify whether water uptake ability or WUE is responsible for the variation, if any. Two-week-old seedlings were transplanted into pots and grown for three weeks in an environmentally-regulated growth chamber under three soil moisture regimes: flooded (?0.02 MPa soil water potential) and two unflooded (?0.10 and ?0.52 MPa) conditions. Substantial genotypic variations in total dry weight (TDW) were observed under all three regimes. Among all the cultivars tested, TDW was significantly correlated with water uptake ability, but not with WUE. However, several cultivars exhibited comparably higher WUE while showing superior biomass production under the ?0.52 MPa regime. The amount of water uptake was significantly correlated with root dry weight among cultivars regardless of moisture regimes, while substantial genotypic difference in the amount of water uptake per unit root dry weight was observed. These results indicate that a marked genotypic difference exists in biomass production at the early vegetative growth under water-deficient conditions, and that this difference appears to be ascribed primarily to greater water uptake capacity, and additionally to higher WUE in drought-tolerant cultivars.     

Root plasticity under fluctuating soil moisture stress exhibited by backcross inbred line of a rice variety,Nipponbare carrying introgressed segments from KDML105 and detection of the associated QTLs

In rainfed lowland rice ecosystem, rice plants are often exposed to alternating recurrences of waterlogging and drought due to erratic rainfall. Such soil moisture fluctuation (SMF) which is completely different from simple or progressive drought could be stressful for plant growth, thereby causing reduction in yield. Root plasticity is one of the key traits that play important roles for plant adaptation under such conditions. This study aimed to evaluate root plasticity expression and its functional roles in dry matter production and yield under SMF using Nipponbare, KDML 105 and three backcross inbred lines (BILs) and to identify QTL(s) associated with root traits in response to SMF at two growth stages using Nipponbare/KDML105 F₂ plants. A BIL, G3-3 showed higher shoot dry matter production and yield than Nipponbare due to its greater ability to maintain stomatal conductance concomitant with greater root system development caused by promoted production of nodal and lateral roots under SMF. QTLs were identified for total nodal root length, total lateral root length, total root length, number of nodal roots, and branching index under SMF at vegetative and reproductive stages. The QTLs detected at vegetative and reproductive stages were different. We discuss here that relationship between root system of G3-3 and the detected QTLs. Therefore, G3-3 and the identified QTLs could be useful genetic materials in breeding program for improving the adaptation of rice plants in target rainfed lowland areas.     

Genotypic Variations in Response of Lateral Root Development to Fluctuating Soil Moisture in Rice

Abstract

Developmental plasticity in lateral roots may be one of the key traits for the growth of rice plants under soil moisture fluctuations. We aimed to examine responses in seminal root system development to changing soil moisture for diverse rice cultivars. Special attention was paid to the two different types of lateral roots ; the generally long, thick L type capable of branching into higher orders, and the non-branching S type. Plants were grown in half-split polyvinyl chloride tubes fixed with transparent acrylic plate for root observation under glasshouse conditions. When plants were grown first under drought conditions, then rewatered, the seminal root system development in terms of dry weight and total length was promoted as compared with plants grown under continuously well-watered conditions in IR AT 109 and Dular, drought tolerant cultivars. Promoted production of L type lateral roots mainly contributed to the development of the longer seminal root system. Plants exposed to soil submergence before they were grown under drought conditions did not show such promoted responses in these two cultivars. However, in KDML 105, a drought tolerant cultivar, the production of especially L type laterals was substantially promoted under drought and rewatered conditions. Honenwase was characterized by the shallow root system and great reduction in root system length when soil moisture becomes limited. These facts show that genotypic variations exist in the plastic response of rice seminal root system and that the L type lateral root plays a key role in manifestation of this plasticity.     

Comparison of Root System Development in Two Rice Cultivars During Stress Recovery from Drought and the Plant Traits for Drought Resistance

Summary

A greenhouse experiment was conducted to compare root system development of two upland rice cultivars, IRAT 13 and Senshou, during recovery from drought stress and to identify the plant traits that confer drought resistance. From 62 days after sowing (62 DAS), drought stress was given for 6 d followed by rewatering for 14 d. Root length density (RLD) and root diameter (thickness) were measured at the end of the stress and rewatering periods. Control plants were well-watered throughout the study. Gultivar IRAT 13 had thicker roots and higher relative RLD (ratio of RLD in drought-stressed plants to that in control plants) than under drought stress, and significantly higher root growth recovery after rewatering cultivar Senshou. Related plant traits such as evapotranspiration (ET), leaf and stem dry weights and weight of senescent leaves (dead leaves) in IRAT 13 were significantly more favorable for drought resistance compared to Senshou.     

Root Development,Water Uptake,and Shoot Dry Matter Production under Water Deficit Conditions in Two CSSLs of Rice: Functional Roles of Root Plasticity

Abstract

Root traits that can contribute to drought resistance have not been clearly indentified. We examined the role of root system development in enhancing water uptake and contribution to dry matter production by using the root box-pinboard method, with which quantitative assessment of root system development and the water uptake of root are possible. Chromosome segment substitution lines CSSL45 and CSSL50, and the recurrent parent Nipponbare were grown under continuously waterlogged conditions (control), and various intensities of water deficit in root boxes. There was no significant difference among the genotypes in shoot growth and root development, while CSSL45 and CSSL50 showed greater shoot dry weight than Nipponbare under water deficit conditions. This was due to their abilities to promote root system development as compared with Nipponbare, which facilitated greater water extraction than Nipponbare, especially under the mild water deficit condition of 20–25% w/w soil moisture contents. Furthermore, the increased root length density did not exceed the estimated critical value for water uptake, which indicates that plastic root system development was functionally effective and efficient for the enhancement of water uptake under mild water deficit conditions.     

播后镇压和冬前灌溉对土壤条件和冬小麦生育特性的影响

为揭示冬灌和镇压的作用,以冬小麦品种石新828和石麦12号为材料,研究了冬灌和镇压措施对麦田土壤水热条件和冬小麦生育特性的影响。结果表明,与不冬灌相比,冬灌条件下,冬季和春季土壤含水量提高,土壤温度较稳定。与不镇压相比,镇压处理的冬前和起身期土壤含水量及冬前夜间土壤温度提高。冬灌处理冬小麦在越冬后各时期的总茎数、LAI、干物质积累量有所降低,开花期叶片光合速率显著下降,灌浆后期叶片SPAD值下降也较快,每穗总小穗数、结实小穗数、穗粒数和产量均减少。镇压使小麦开花前干物质积累量减少,但对成熟期干物质积累量影响不显著,因为开花后光合速率提高,叶片SPAD值下降较缓慢,开花后干物质积累较多。镇压处理成熟期的单位面积穗数降低,但由于穗粒数和千粒重提高,镇压与不镇压的产量差异不显著。从本研究结果看,冬灌是一项防冻保苗的有效措施,与播后镇压配合可减缓冬季低温和温度剧烈变化对小麦的不利影响。     

Roles of Root Aerenchyma Development and Its Associated QTL in Dry Matter Production under Transient Moisture Stress in Rice

Abstract

Enhanced aerenchyma development in rice under transient drought-to-waterlogged (TD-W) stress promotes root system development by promoting lateral root production. This study analyzed the quantitative trait loci (QTLs) associated with the plasticity in aerenchyma development under TD-W stress. A mapping population of 60 F₂ genotypes of chromosome segment substituted lines (CSSL) derived from CSSL47 and Nipponbare crosses were grown in rootboxes and evaluated for shoot and root growth, and aerenchyma development (expressed as root porosity). The TD-W stress was imposed starting with water saturated soil condition at sowing and then to progressive drought from 0 to 21 days after sowing (DAS) prior to exposure to sudden waterlogging for another 17 days (21 to 38 DAS). We performed simple and composite interval mapping to identify QTLs for aerenchyma development. QTL associated with aerenchyma development was mapped on the short-arm of chromosome 12 and designated as qAER-12. The effect of qAER-12 on the plasticity in aerenchyma development under TD-W was significantly associated with the increase in lateral root elongation and branching. This resulted in greater root system development as expressed in total root length and consequently contributed to higher dry matter production. This qAER-12 is probably the first reported QTL associated with aerenchyma development in rice under TD-W and is a useful trait for the improvement of the adaptive capability under fluctuating soil moisture conditions.     

Performance of a High-Yielding Modern Rice Cultivar Takanari and Several Old and New Cultivars Grown with and without Chemical Fertilizer in a Submerged Paddy Field

Abstract

A high nitrogen-uptake capacity and effective use of absorbed nitrogen for dry matter and grain production are required to improve the production cost and environmental pollution. We characterized grain yield, dry matter production and nitrogen accumulation in six rice cultivars: Sekitori (released in 1848) and Aikoku (1882), referred to as SA cultivars hereafter; Koshihikari (1956); Nipponbare (1963) and Asanohikari (1987), referred to as NA cultivars hereafter; and Takanari (in 1990) as a high-yielding modern cultivar. The plants were grown with and without chemical fertilizer in a submerged paddy field. When plants were supplied with manure and chemical fertilizer, Takanari consistently produced the heaviest grain and dry matter, followed by the NA cultivars, and the SA cultivars the lightest. Dry matter production before heading was greater in Takanari and the NA cultivars due to the longer duration of vegetative growth. Dry matter production after heading was greatest in Takanari, with a larger crop growth rate (CGR), and smallest in the SA cultivars with a shorter ripening time. Greater dry matter production during ripening was accompanied by the greater accumulation of nitrogen by Takanari and NA cultivars. These plants developed a larger amount of roots. The smaller light extinction coefficient of the canopy was also attributed to the higher CGR in Takanari. When plants were grown without chemical fertilizer, Takanari also produced heavier grain and dry matter, followed by the NA cultivars. The heavier grain in these cultivars resulted from the greater dry matter production before heading, which was due to the longer period of vegetative growth. The greater dry matter production and nitrogen accumulation by Takanari and NA cultivars were evident when plants were grown with chemical fertilizer. Koshihikari was characterized by a higher CGR and greater nitrogen accumulation during ripening in the absence of chemical fertilizer which should be noted in efforts to decrease rates of nitrogen application.     

Characterization of the morphological and physiological traits of rice cultivars with adaptation to unflooded condition during early vegetative growth

This study aimed to characterize the physiological and morphological traits that are associated with adaptation to unflooded soil conditions in rice. Four indica rice cultivars (Puluik Arang, Badari Dhan, Shwe Nang Gyi, and Ratul), which were previously identified as highly or less adaptable to unflooded soil conditions, were grown under flooded and unflooded (soil water potential; －0.10 MPa) soil conditions. Water uptake was measured every day for three weeks, and then the leaf water potential, the stomatal conductance, the dry matter weight, shoot and root morphological traits were measured. Puluik Arang and Badari Dhan exhibited greater leaf area expansion and higher maintenance of root development under the unflooded condition than that by other cultivars. The leaf water potential and stomatal conductance of fully expanded highest leaf in Puluik Arang and Badari Dhan were not affected by unflooded soil regime. Leaf area and root morphological traits were significantly correlated with water uptake regardless of soil moisture regimes. These results suggested that Puluik Arang and Badari Dhan exhibited great water uptake capacity through physiological and morphological adaptation of shoot and root traits to unflooded condition, resulting in great biomass productivity under the condition.     

Effects of Soil Moisture Conditions before Heading on Growth of Wheat Plants under Drought Conditions in the Ripening Stage: Insufficient Soil Moisture Conditions before Heading Render Wheat Plants More Resistant to Drought during Ripening

Abstract

Plants growing on soil with insufficient moisture need deep and dense roots to avoid water stress. In crop plants, the production of dry matter during ripening of grains is critically important for grain yield. We postulated that shoot growth would be suppressed but root growth would continue under an insufficient soil moisture condition before heading, while shoot growth would be more vigorous than root growth under a sufficient soil moisture condition. We anticipated that the plants growing under an insufficient soil moisture condition before heading would produce more dry matter and grain under an insufficient soil moisture condition during ripening. In order to examine our hypotheses and to determine the fundamental conditions for improving grain yield and efficient use of irrigated water under limited irrigation, we grew wheat plants (Triticum aestivum L., cv. Ayahikari) in pots (30 cm in diameter, 150 cm in height) with insufficient soil moisture (PD-D pots) or sufficient soil moisture (PW-D pots) for six weeks before heading followed by full irrigation, and then insufficient soil moisture condition during ripening. The growth of shoots was suppressed significantly but that of roots was not before heading in PD-D plants, with a higher resultant ratio of root to shoot than in PW-D plants. The former retained a high leaf water potential and, therefore, were able to produce more dry matter and grain during soil moisture depletion during ripening as compared with the latter plants. We also obtained similar results with field-grown plants.     

Matching the Expression of Root Plasticity with Soil Moisture Availability Maximizes Production of Rice Plants Grown in an Experimental Sloping Bed having Soil Moisture Gradients

Abstract

Soil moisture distributions in rainfed lowland rice environments are largely determined by the position in the toposequence. In this study, we developed an experimental sloping bed that can simulate the soil hydrological conditions in sloping rainfed lowland rice environments to examine if the expression of promoted root system development in relation to soil moisture availability along the soil profile may maximize water uptake and dry matter production under drought. The gradient of available water along both the surface soil layer and the vertical soil profile was successfully created by manipulating ground water levels in the experimental sloping bed indicating the practical effectiveness of this experimental system. Then, two contrasting genotypes, IRAT109 (upland rice adapted japonica) and KDML105 (lowland adapted indica) were grown for plasticity evaluation. Dry matter production was maintained even at a higher position in the toposequence in IRAT109, but decreased in KDML105. Such maintenance of dry matter production in IRAT109 was attributed to its greater ability to increase root length density in a deeper soil layer, where more soil moisture is available. In contrast, KDML105 maintained root length density in the upper soil layer, and could not utilize the soil moisture available in the deeper soil layer. These results imply that the genotype that expressed root plasticity with root system developing in the soil portion where more soil moisture was available showed greater dry matter production than the genotype that showed root plasticity in the soil layer where soil moisture was less available.     

麦后水、旱直播稻秸秆还田效果对比试验

通过麦后水、旱直播稻秸秆还田与不还田试验对比,探索麦后水、旱直播稻秸秆还田与不还田之间生长差异及对产量的影响。结果表明,水直播与水直播秸秆还田在出苗与齐苗效果上优于旱直播和旱直播还田,其中,水直播最为优越;在发苗方面,水、旱直播稻在播后的前20d秧苗长势优于水、旱秸秆还田的处理,其中水直播又优于旱直播。从操作简便角度讲,旱直播比水直播省事,便于生产上操作。从水稻生长稳健、稳产角度讲,生产上应选用水直播还田操作方式。     

Yield and growth characteristics of erect panicle type rice (Oryza sativa L.) cultivar,Shennong265 under various crop management practices in Western Japan

Erect panicle rice cultivars utilize solar energy effectively and have improved ecological growing conditions. Among such cultivars, Shennong265 has been grown successfully throughout Northern China. Nevertheless, no studies have yet examined the relationships between crop dry matter productivity, weather conditions, and nitrogen uptake of the erect panicle type rice cultivar in Japan. The objective of our study was to evaluate the productivity of erect panicle rice Shennong265 in Western Japan under varied conditions. Three rice cultivars, Shennong265, Nipponbare, and Takanari were grown in the field under different fertilizer and plant density conditions in Western Japan; using this information, we compared yield and growth characteristics of Shennong265 with those of Nipponbare and Takanari. Although Shennong265 had radiation use efficiency similar to that of the high yielding cultivar (Takanari) and much higher leaf nitrogen content than Takanari and Nipponbare, the average grain yield of Shennong265 grown under normal fertilizer and plant density conditions was approximately 6.9 t ha^?1 as against 6.2 t ha^?1 for Nipponbare and 9.6 t ha^?1 for Takanari. These results suggest that, while Shennong265 has a high yield potential, the environmental conditions including climate, fertilizer, and planting period provided in this study were not suitable for achieving its maximum yield. The reduced performance of Shennong265 may be caused by insufficient fertilizer after heading and by shorter growth periods, as well as by the climate of Western Japan. Additional fertilizer application during the heading stage and earlier transplanting may be needed to obtain higher Shennong265 yields in Western Japan.     

Study of water stress effects in different growth stages on yield and yield components of different rice (Oryza sativa L.) cultivars

A field experiment was conducted during 2001-2003 to evaluate the effect of water stress on the yield and yield components of four rice cultivars commonly grown in Mazandaran province, Iran. In northern Iran irrigated lowland rice usually experiences water deficit during the growing season include of land preparation time, planting, tillering stage, flowering and grain filing period. Recently drought affected 20 of 28 provinces in Iran; with the southeastern, central and eastern parts of the country being most severely affected. The local and improved cultivars used were Tarom, Khazar, Fajr and Nemat. The different water stress conditions were water stress during vegetative, flowering and grain filling stages and well watered was the control. Water stress at vegetative stage significantly reduced plant height of all cultivars. Water stress at flowering stage had a greater grain yield reduction than water stress at other times. The reduction of grain yield largely resulted from the reduction in fertile panicle and filled grain percentage. Water deficit during vegetative, flowering and grain filling stages reduced mean grain yield by 21, 50 and 21% on average in comparison to control respectively. The yield advantage of two semidwarf varieties, Fajr and Nemat, were not maintained under drought stress. Total biomass, harvest index, plant height, filled grain, unfilled grain and 1000 grain weight were reduced under water stress in all cultivars. Water stress at vegetative stage effectively reduced total biomass due to decrease of photosynthesis rate and dry matter accumulation.     

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.     

Toposequential Variation in Soil Fertility and Rice Productivity of Rainfed Lowland Paddy Fields in Mini-Watershed (Nong)in Northeast Thailand

Abstract

Mini-watersheds called Nongin Thai are geographical components of rainfed lowland rice culture in Northeast Thailand, and constitute distinct units in understanding environmental constraints for low and unstable rainfed rice production there. The toposequential variation of soil fertility and its relation to rice productivity within mini-watersheds, was examined by phytometry of sampled soils and field measurements of rice growth and yield. The phytometry experiment with irrigated potted rice using soils sampled from various rice fields within each mini-watershed, revealed that soil fertility as evaluated by rice dry matter production showed a 5 times difference among the fields at most. The difference in the soil fertility was ascribed primarily to that in nitrogen (N) supply capacity, which itself had a strong correlation with soil organic carbon (SOC) content. Accordingly, the biomass production of pot-grown rice was proportional to SOC. content, which suggested the usefulness of SOC as an index for soil fertility evaluation. The effect of clay on the soil fertility was much less than that of SOC. The actual rice yield in each field also showed quite large field-to-field variation, most of which was explained by the SOC content, rice growth duration and fertilizer application rate even though water availability also affected the yield. The yield positively correlated with growth duration and hence with earlier transplanting. Both SOC and clay contents of fields showed steep gradients with ascending field elevation within mini-watersheds, resulting in a marked toposequential distribution of rice yield. The toposequential distributions of SOC and clay contents imply that rice culture after deforestation accelerated soil erosion from upper to lower fields. The large toposequential gradient in soil fertility requires different resource and crop management for each toposequential position, in order to improve rice productivity of the mini-watershed as a whole.     

灌水对不同小麦品种耗水特性和土壤硝态氮运移的影响

为了解灌水对不同小麦品种耗水特性和土壤硝态氮运移的影响,在大田条件下,以济麦20和泰山22为材料,设置4种水分处理[W0处理（全生育期不灌水）、W1处理（灌底墒水＋拔节水）、W2处理（灌底墒水＋拔节水＋开花水）、W3（灌底墒水＋拔节水＋开花水＋灌浆水）],每次灌水量60mm,分析了不同灌水处理下小麦0～200cm土层土壤含水量、土壤水消耗量、土壤硝态氮运移及籽粒产量的差异。结果表明,（1）依据土壤含水量受灌水影响的程度和变异系数,将0～200cm土壤分为3个层次：活跃层（0～60cm）、次活跃层（60～140cm）和相对稳定层（140～200cm）。（2）两品种W1处理的冬前、开花和成熟期0～60cm土层土壤硝态氮含量低于W0处理;冬前期60～140cm土层高于W0处理,140～200cm土层与W0处理无显著差异;开花期60～140cm和140～200cm土层高于W0处理;成熟期0～60cm土层高于W2、W3处理,60～140cm和140～200cm土层低于W3处理。拔节期济麦20W1处理60～140cm和140～200cm土层土壤硝态氮含量高于W0处理,泰山22的低于W0处理。（3）济麦20各处理0～200cm土层土壤水消耗量均高于泰山22。济麦20W1处理0～60cm和60～140cm土层土壤水消耗量高于W2处理,籽粒产量、水分利用效率高于W2、W3处理;泰山22W2处理0～60cm土层的土壤水消耗量与W1处理无显著差异,60～140cm和140～200cm土层的土壤水消耗量低于W1处理,水分利用效率与W1处理无显著差异,但高于W3处理,籽粒产量高于W1、W3处理。济麦20和泰山22分别以底墒水、拔节水各灌60mm和底墒水、拔节水、开花水各灌60mm为节水、高产、氮素淋溶量低的最佳灌水模式。     

Drought-induced root plasticity of two upland NERICA varieties under conditions with contrasting soil depth characteristics

To identify differences in root plasticity patterns of two upland New Rice for Africa (NERICA) varieties, NERICA 1 and 4, in response to drought under conditions with contrasting soil profile characteristics, soil moisture gradients were imposed using a sloping bed system with depths ranging 30–65 cm and a line-source sprinkler system with a uniformly shallow soil layer of 20 cm depth. Varietal differences in shoot and root growths were identified only under moderate drought conditions, 11–18% v/v soil moisture content. Further, under moderate drought soil conditions where roots could penetrate into the deep soil layer, deep root development was greater in NERICA 4 than in NERICA 1, which contributed to maintaining dry matter production. However, under soil conditions with underground impediment to deep root development, higher shoot dry weight was noted for NERICA 1 than for NERICA 4 at 11–18% v/v soil moisture content, which was attributed to increased lateral root development in the shallow soil layer in NERICA 1. Enhanced lateral root development in the 0–20-cm soil layer was identified in NERICA 1 even under soil conditions without an impediment to deep root development; however, this did not contribute to maintaining dry matter production in upland rice. Thus, we show different root developmental traits associated with drought avoidance in the two NERICA varieties, and that desirable root traits for upland rice cultivation vary depending on the target soil environment, such as the distribution of soil moisture and root penetration resistance.     

Comparison of empirical models for predicting yield loss of irrigated rice (Oryza sativa) mixed with Echinochloa spp.

Crop yield losses due to weeds can be described by empirical models. The objective of this study was to compare empirical models to predict interference by a mixed population of Echinochloa colona and E. crusgalli. in irrigated rice. Three experiments, one under field conditions and two under greenhouse conditions, were set up during the growing season of 2005/2006. The treatments tested in the field were 6 rice cultivars: BRS Atalanta, IRGA 421, IRGA 416, IRGA 417, Avaxi; and BRS Fronteira and 10 Echinochloa spp. densities, naturally present in the soil seedbank under field conditions. The variables soil cover, shoot dry weight of the Echinochloa spp. and their relative mass were evaluated in relation to the rice cultivars. The greenhouse experiments were carried out both in monoculture and replacement series to evaluate shoot dry mass and leaf area production, both for the crop and the weed species. The data obtained for the variables were analysed using linear and non-linear regression models. The fitting of the data to the empirical models varied as a function of the rice cultivars and variables tested. Among the models describing crop yield loss as a function of the evaluated variables, the single-parameter empirical model presented a better prediction than the two-parameter model. For the two-parameter models, yield loss estimation was obtained by the evaluated variable. In general, shoot dry mass of the weed was a better predictor of irrigated rice yield loss than soil cover.