The interaction between the roots of cassava (Manihot esculenta Crantz) and soil physical properties has previously been analyzed. This interaction results in differences in production of plant material and in the physicochemical features of the roots, suggesting that changes in soil physical conditions may be related to changes in root anatomy. This work described the anatomical development of the tuberous cassava roots (cv. IAC 576-70) under different tillage systems. Roots grown under three different tillage systems (minimum, conventional and no tillage) were examined at 15, 30, 60, 90, 120, 150 and 180 days after planting (DAP). The tillage systems did not appear to influence root anatomy during root development; at 15 and 30 DAP roots had early secondary growth; at 60 DAP the process of tuber formation had started; at 90 DAP the secondary xylem had completely differentiated to allow storage of starch; at 120, 150 and 180 DAP roots exhibited a similar anatomical structure to that observed at 90 DAP. From these results we conclude that the anatomical structure of cassava tuberous roots is established by 90 DAP and the sequence of establishment and development of tissues that make up the tuberous roots is not influenced by tillage systems during the first 180 DAP.
The differences in osmotic stress tolerance and morphological characteristics of the root system of stress-tolerant and stress-sensitive rice cultivars were clarified by examining genetic variation. Fifty-four Rice Diversity Research Set cultivars, and Azucena, IRAT109, Dular (drought-tolerant), IR64 (drought-sensitive), and IR28 (salt-sensitive) were used. Rice seedlings were cultivated for 14 days by water culture (control). Polyethylene glycol 6000 was dissolved in the culture medium as osmotic stress treatment on day 7 to adjust the water potential to –0.42 MPa (stress treatment). The stress treatment to control ratio (S/C ratio) was calculated to evaluate the degree of stress tolerance. The dry-weight S/C ratio in the shoot showed a significant varietal difference from 0.874 to 0.376 and that in the root from 0.931 to 0.342, and root, respectively, and these values were significantly correlated. Five osmotic stress-tolerant and 5 stress-sensitive cultivars were selected, and their root-system morphology was investigated in detail. The number of the L-type lateral roots, which were longer and thicker, increased 1.5 – 3.6 times that of the control with osmotic stress treatment in the tolerant cultivar group. It slightly decreased 0.8 – 0.9 times that of the control with osmotic stress in the sensitive cultivar group. The number of crown roots and S-type lateral roots, which were finer and shorter, decreased with stress in both cultivar groups; however, this decrease was significantly lower in the tolerant cultivar group. Thus it is suggested that the maintenance of root-system development, especially L-type lateral roots under osmotic stress, involves genetic variation in the genes responsible for the dry matter production.
Rice yield and quality decrease under high temperature conditions during the grain-filling period particularly in early-ripening cultivars that are directly subjected to midsummer heat. As the grain growth rate increases under high temperature conditions, the grain requires greater amounts of assimilates for the shortened grain-filling period and occasionally experiences a lack of assimilates. The stay-green trait that can maintain assimilation during the active grain-filling period is expected to mitigate the negative impact on grains due to the lack of assimilates. Our objectives were to evaluate the stay-green trait of rice maintaining assimilation rates under high temperature conditions during the active grain-filling period using the leaf incubation method. When whole leaves or leaf segments were floated on water at 20 – 40ºC under dark conditions, a leaf color reading (SPAD) showed steady genotypic differences at 25 – 35ºC. When flag leaf segments of early-ripening cultivars from the Japanese Rice Collection (JRC) were incubated at 35ºC under dark conditions, the SPAD values of incubated leaves well reflected those in the top three-leaves in standing plants during the active grain-filling period (r = 0.774, p < 0.005). Under ambient and elevated temperature conditions (+3 – 4ºC), the SPAD values and photosynthetic rates of genotypes that ranked higher for the trait by the leaf-incubation test, tended to be higher during the active grain-filling period. The results suggest that the leaf incubation method is suitable for the first-step selection of the stay-green trait of rice associated with the maintenance of assimilation rates under high temperature conditions during the grain-filling period.
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.
Identifying the mechanisms regulating starch remobilization after heading in rice leaf sheaths is essential to understand the capability of the source for grain filling. In the present study, the changes in starch content and expression levels of α-amylase genes in the third leaf sheaths of Takanari, a high-yielding indica cultivar, were compared with those of Nipponbare, a standard japonica cultivar, during the post-heading stage to examine the starch remobilization characteristics in the leaf sheath of a high-yielding cultivar. Starch content in Takanari tended to decrease at a faster rate than in Nipponbare starting 3 days after heading. The decrease in starch content during 12 days after heading was greater in Takanari than in Nipponbare. Of eight genes predicted to encode α-amylase in the rice genome, RAmy2A and RAmy3C were primarily expressed in the leaf sheaths after heading. Moreover, RAmy2A mRNA level peaked at 9 days after heading in both cultivars. Particularly in Takanari, the RAmy2A mRNA levels rapidly increased from 3 to 9 days after heading. In addition, α-amylase activity was significantly higher in Takanari than in Nipponbare at 9 days after heading. Our results suggest that the rapid degradation of starch in the leaf sheaths of Takanari at the post-heading stage may be attributed, at least in part, to the enhancement of α-amylase activity caused by an increase in RAmy2A transcription level.
The agronomic and physiological effects of waterlogging in winter wheat were examined at four growth stages in the 2011/2012 and 2012/2013 seasons. In both seasons, the greatest yield penalties occurred by waterlogging at the tillering stage (10%–15% decrease), followed by the jointing stage; however, waterlogging at the grain filling stage had less effect on the yield. The lower grain yield caused by waterlogging at the tillering stage was primarily reflected in reductions in spike and grain numbers per m2. Waterlogging at the jointing and booting stages reduced grain weight through reduced dry matter translocation. In addition, waterlogging at the tillering stage significantly reduced chlorophyll content and thus photosynthetic capacity, resulting in a lower Fv/Fm ratio, apparent electron transport rate (ETR), effective quantum yield of photosystem II (ΦPSII) and photochemical quenching (qP). However, waterlogging at the grain filling stage improved the leaf photosynthetic capacity and grain yield. We found that the tillering stage was most the susceptible to waterlogging in wheat; therefore, the maintenance of photosynthetic performance after anthesis could be a reasonable strategy for increasing grain yield.
The relay strip intercropping system of wheat-corn-soybean is widely used in southwest China. However, it is hard to produce soybean stably with this system, since the growth of soybean plants is slower under shading by corn at the seedling stage, and it is compensated by accelerated growth after the symbiotic stage. Soybean plants show excessive vegetative growth due to more rain during the flowering stage, which results in fallen petals, fallen pods and lower yield. This study investigated whether seed treatment with uniconazole powder (0, 2, 4 and 8 mg kg–1 seed) suppresses excessive vegetative growth of soybean plants during the flowering stage and delays senescence of photosynthetically active leaves at the pod-setting stage. If such events are correlated with changes in photosynthesis, they may affect dry matter accumulation and seed yield in the relay stripping system. Uniconazole promoted biomass accumulation from 31 (R3) to 61 (R5) days after flowering (DAF) and seed yield. Seed treatment with uniconazole raised the net photosynthetic rate, stomatal conductance, transpiration rate, and total chlorophyll and chlorophyll a contents. In contrast, uniconazole reduced leaf area index (LAI) from 1 DAF (R1) to 46 DAF (R4) with the increase in uniconazole concentration, whereas, uniconazole significantly increased LAI at 61 DAF, and the greatest promotion occurred at 2 mg kg–1 treatment. The study clearly showed that uniconazole effectively suppressed excessive vegetative growth of soybean during flowering stage, delayed senescence of photosynthetically active leaves at pod-setting stage and induced higher yield, which were related to the changes in photosynthetic rate, chlorophyll content, dry matter accumulation and LAI in the relay strip intercropping system.
Soybean is the most common resource of isoflavonoid in human food. Wide development of relay strip intercropped soybean has contributed to the soybean industry in China. Due to the shading from maize, growth and grain production of soybean is reduced. However, whether soybean isoflavonoid accumulation pattern is influenced in the relay strip intercropping system is still unclear. Here, we studied the accumulation patterns of soybean isoflavones in the relay strip intercropping system and sole cropping system at the per-harvest stage. The accumulation patterns of soybean isoflavones at the postharvest stage were also studied. The results indicated that accumulation patterns of soybean isoflavones of all varieties in leaf and seed in the two systems were similar, but the trend was delayed in the relay strip intercropping system compared with the sole cropping system. During the pod filling stage, the total content of isoflavone, M-type isoflavone content, G-type isoflavone content in seed in the relay strip intercropping system were lower than those in the sole cropping system. During the after-ripening period, seed isoflavone content, M-type isoflavone content, G-type isoflavone content in seed increased in both systems, but were higher in the relay strip intercropping system. The temperature and photosynthetically active radiation were significantly lower in relay intercropping than in sole cropping, while relative humidity showed the opposite trend. Path analysis showed that total isoflavone content in leaves and seeds showed a significantly positive correlation with temperature and photosynthetically active radiation, but significantly negative correlation with relative humidity. Correlation analysis between the highest isoflavone content in sole cropping or relay intercropping seeds and agronomic traits revealed a significant positive correlation between the number of both branches and pods with total isoflavone, M-type isoflavone and G-type isoflavone in both systems.
Soil chemistry and nutrient status of soil were surveyed in an attempt to improve the productivity of rainfed lowlands—which would include crop diversification and improved rice yields—in the semi-mountainous areas near Nameuang village (NV) and in the Vientiane plain (VP), Lao PDR. The soil survey revealed soil acidity, deficiency in exchangeable Ca and Mg and in available P despite the its being in a calcareous zone. The nitrogen; phosphorus and potassium fertilities in NV were not notably unique to those in the neighboring districts. In addition, it became apparent that in NV there was a risk of aluminum toxicity. In order to determine appropriate soil management, the effects of liming on non-rice crops and on rice plants were studied in pot experiments using soils collected from NV. Liming was usually effective for enhancing the growth of the tested non-rice crops. Under submerged conditions, soil pH increased naturally despite the strong pre-flooding acidity. Although liming plus chemical fertilizer was effective for increasing rice yields, the effect of liming was not positive when only liming was applied. Although soil amendments are required to mitigate aluminum toxicity on non-rice crops in lowland double cropping systems, it was necessary to consider the influence on rice yields, particularly under a condition without fertilization.
To ensure higher yields, farmers in China have increased cropping intensity with a large input of chemical fertilizer and livestock manure since 1980s, which has led to unsustainable agricultural productivity and environmental quality. This study aimed to evaluate the effects of intensive cropping on nutrient absorption and biomass production of crops and to determine the controllable source of residual nutrients in soil in the coastal area of Lake Dianchi, China. Soil and crops were sampled in 32 vegetable fields and four paddy fields; and simultaneously surveyed. In vegetable fields, cropping intensity and input to each crop were extremely high; and, 58, 72, and 20% of nitrogen, phosphorus, and potassium were not absorbed by the crop. Nitrogen absorption ratios of the vegetables were low. The amount of nitrogen absorbed from sources other than chemical fertilizer by vegetables, namely, from soil, manure, or irrigation water, in the fields with three to nine years cultivation duration was higher than those with zero to two years cultivation duration. Reduction of input should be more efficient than enhancing output to decrease soil nitrogen, phosphorus, and potassium; and, reducing input of chemical fertilizer should be more efficient than reducing input of manure. These results should be helpful for reducing agricultural pollution in China.
The vertical profile of leaf nitrogen (N) content per unit leaf area (NLA) is important for increasing crop productivity via optimizing N use for canopy photosynthesis. To investigate the effects of plant height on the optimality, we analyzed the NLA profiles with respect to light gradient twice during vegetative growth in canopies of tall and dwarf cultivars of sorghum. The gradients of the NLA profiles relative to the light gradients were similar in the two cultivars although the vertical light gradient was steeper in the dwarf cultivar with doubled leaf area density (LAD). This suggests that light attenuation is more influential on the NLA profile than is plant height or LAD. The advantage of the observed NLA profile for the canopy CO2 uptake as compared to the uniform NLA profile was similar in the cultivars except when the N allocation rate to the canopy decreased relative to the leaf area expansion in the dwarf cultivar. These results suggested that the optimality of the advantage of the NLA gradient may not be directly influenced by the plant height, but by the balance between N allocation and leaf area expansion. The balance may be altered by the difference in the biomass allocation in the shoot between the tall and dwarf sorghum. These factors are to be taken into consideration in breeding programs that target stature in order to potentially increase production in sorghum.
Six cultivars of soybean were cultivated under various phosphorus (P) application levels, in pots and in fields to clarify the relationship between P accumulation and dry matter production, and that of varietal differences in soybeans. Dry matter production and yield components increased with the increase of P application, especially under P-deficient conditions, and there were varietal differences in dry matter production, yield components, and amount of P accumulation. However, there were significant relationships between dry matter production and P accumulation, and the relationships could be represented by the same regression line regardless of cultivar. There were varietal differences in dry matter production efficiency of accumulated P under a P-deficient condition. These results suggest that either high ability to accumulate P or efficient dry matter production of P is required for stable production under P-deficient conditions. Therefore, selection of cultivars that have high dry matter production efficiency or large root systems, or the development of agricultural management technology that increases the rate of P fertilizer absorption is required for stable production under P-deficient conditions.
The objectives of this study were to evaluate the varietal difference in the occurrence of delayed stem senescence (DSS) and cytokinin level in the xylem exudate in soybeans and the relationship between the occurrence of DSS and cytokinin level in the xylem exudate. Pot experiments were carried out in the experiment field at Nihon University in 2010, 2012 and 2013. In this experiment, we used 11 soybean varieties, which were cultivated in the Kanto region, Japan. The degree of DSS (DSS score) was positively correlated with the days from sowing to flowering stage (S-R2), and was higher in the varieties with a longer length of S-R2, though the correlation was not significant. Under some conditions, the DSS score was negatively correlated with S-R2. Moreover, the DSS score was positively or negatively correlated with the main stem diameter, total node number, stem dry weight and seed weight depending on the growth parameter or sowing date. Thus, we concluded that the DSS score was not correlated with the growth parameters. On the other hand, the level of cytokinins such as t-ZR and iPA shown by their amount in xylem exudate from a plant at the seed filling stage was negatively correlated with the DSS score. Thus, we consider that one of the reasons for varietal difference in DSS occurrence may be the difference in cytokinin content of stem and leaves after the seed filling stage.
Soybean has attracted increasing attention as a cash crop while subsistent maize production is the first priority for smallholder farmers in southern Africa. Our study examined the performance of maize-soybean intercropping system at three sites across northern Mozambique. Both monocropped and intercropped maize received three levels of N application, while soybean was grown without additional fertilization. The grain yield of monocropped maize applied N at three rates and that of monocropped soybean ranged 1.6 – 2.1 t ha–1 and 0.57 t ha–1, respectively, in Nampula; 1.7 – 3.9 t ha–1 and 1.87 t ha–1, respectively, in Gurue; and 2.8 – 4.5 t ha–1 and 2.01 t ha–1, respectively, in Lichinga. Relative to these values, maize-soybean intercropping demonstrated advantageous productivity over monocropping in terms of the land equivalent ratio (LER) at 1.15 – 1.49 across the experimental sites. LER above 1 was mainly attributed to the consistently superior growth of intercropped maize than the monocropped maize. Under moist field conditions, the LER values were particularly high in the non-fertilized plots because maize plants became more competitive and depressed the intercropped soybean yields to greater degrees with increasing N application rates. When exposed to a dry spell, intercropped soybean showed an apparent benefit in drought avoidance, as shown by the slow depletion of the soil water potential and leaf stomatal conductance and by the retention of the aboveground biomass relative to the monocropped soybean. These results indicate that maize-soybean intercropping can be beneficial to introduce soybean while ensuring subsistent maize production in the low-N-input and drought-prone environment that prevails in the region.
Recently, application of sewage sludge/effluents to soils as an alternative source of organic matter in arid/semiarid regions and as a practical approach to remove its sanitary adverse effects in urban and industrial regions is gaining increased attention. This may lead to high levels of nickel (Ni) in soil and plants. On the other hand, in these regions water shortage is a major constraint of plant productivity. To determine the combined effects of Ni and water stress on the nutritional status of canola, we studied the effect of five Ni levels (0, 0.05, 0.1, 0.5 and 1 mg Ni kg–1 soil as Ni(NO3)2) and two levels of water status (field capacity, FC, and 0.6 FC) on the contents of iron (Fe), manganese (Mn), zinc (Zn) and copper (Cu) in canola (Brassica napus L.) on two loamy and sandy clay calcareous soils in greenhouse conditions. Shoot/root dry matter yield (SDMY/RDMY), their Fe, Zn and Mn content decreased under 0.6 FC conditions; whereas, their concentrations increased. Shoot/root Cu concentration/content decreased in water-stressed plants. Application of > 0.05 mg Ni kg–1 to loamy soil increased SDMY, however Ni did not affect SDMY positively or even decreased it in sandy clay soil. Application of 0.01～0.5 mg Ni increased RDMY in loamy soil under FC conditions; whereas, higher levels of Ni decreased it. Nickel decreased RDMY in sandy clay soil, whereas did not affect micronutrient concentrations in the root. The concentration and content of Mn in the shoot followed different patterns in response to applied Ni. Although the highest level of applied Ni increased shoot Zn content. Application of 0.05 and 1 mg Ni decreased the Cu concentration in the shoot on loamy and sandy clay soils, respectively. However, Ni did not affect the Cu content of shoot. Nickel had different impacts on the content of each micronutrient and was not effective in mitigating the adverse effects of drought stress.
Intercropping and relay intercropping systems, which significantly improve land use efficiency, are used worldwide to increase crops yield. The wheat-maize-soybean relay intercropping system has been widely employed by famers in Southwestern China for years, but the detailed mechanisms through which the nitrogen fertilizer use efficiency reach the high level in this system remain unclear. In the present study, two separate pot experiments were performed by 15N isotope dilution (ID) labeling and direct 15N foliar feeding (FF) assays, and a solid barrier was employed to prevent the roots intergrowth and N movement among crops in the first experiment, using no barrier as the control. The results showed that, under the no-barrier condition, the grain yields, 15N uptake and 15N recovery efficiency of wheat and maize were significantly increased, but those measures in soybean were decreased compared to the solid barrier condition. Furthermore, bi-directional N transfer was detected during the co-growing stage of crops, the amount (Ntransfer) and percentage (%NT) of 15N transferred varied significantly with the fertilizer-N rate, and the maximum reached at 150 – 300 kg N ha–1 level. The Ntransfer from maize to wheat was 16.1% – 163.0% higher than that from wheat to maize; the Ntransfer from soybean to maize was 1.7 – 6.0 times higher than those from maize to soybean, while the %NT from soybean to maize were 6.7 – 22.2 times higher than those from maize to soybean. Conclusively, this study revealed that the interaction of the roots among crops significantly increased the uptake efficiency and recovery efficiency, and further, the positive N competition and bi-directional N transfer of each crops were the main contributors to improve the N use efficiency in the wheat-maize-soybean relay intercropping system.
The Kilimanjaro Agricultural Training Center (KATC) extension approach has disseminated cultivation techniques for irrigated rice across Tanzania. KATC provides training to extension officers and key farmers (KFs). It also helps subsequent farmer-to-farmer (FTF) extension from KFs to intermediate farmers (IFs) and then to other farmers (OFs). The long-term intensive training for irrigated rice was greatly simplified for the dissemination of NERICA1 that was recently released for rainfed rice fields. While the original approach involves a 12-day residential training and a season-long field follow-up, the simplified one only provides a 2-day residential training. Here, we investigated the extent to which the simplified approach diffused NERICA1. The FTF extension worked almost theoretically from KFs to IFs but not from KFs/IFs to OFs over three cropping seasons. However, the number of OFs gradually increased with little intervention, suggesting that this approach should have some mechanism that encourages participation of OF from an early dissemination stage.
Nursery management methods for elongating seedlings are needed for stabilization of early growth after transplanting in the semi-dwarf rice cultivar Hokuriku 193, unlike japonica commercial cultivars. This study aimed to investigate how keeping the plants at 28ºC for 5 d after sowing (H treatment) and nitrogen top-dressing (N treatment) affects seedling quality and early growth after transplanting. Control plants had seedling lengths of 6.5 cm to 10.9 cm at transplanting. The H and N treatments significantly increased the seedling length, and the increase was greater in the H-treated plants. The H × N treatment elongated seedlings by 2.5 – 3.7 cm compared to the control plants. The N treatments, but not the H treatments, improved biomass production and tillering early after transplanting owing to the high nitrogen concentration in the seedlings. Combining H and N treatments can contribute for improving seedling length and early plant growth after transplanting in Hokuriku 193.
Open-top chambers (OTC) equipped with solar-heated double funnels (SDF) were tested for high-temperature treatments under unstable wind conditions. OTC-SDFs have two types of funnel-shaped tunnels attached on opposite ends; OTC-SDF-A had SDFs of the same width, and the OTC-SDF-B had SDFs that were twice the width of the open end. The temperature rise in these OTC-SDFs were compared with that in OTC with solar-heated air introduction tunnel (OTC-SAT). The temperature increase in the OTC-SAT during the daytime was small and not flat, whereas that in OTC-SDF-A was higher than in OTC-SAT and almost flat. The temperature rise was further enhanced in the OTC-SDF-B. An increase in air exchange ability at the intake may account for this enhancement. The drop in temperature at night observed in OTC-SAT was less prominent in OTC-SDFs. Based on these data, OTC-SDFs are considered useful in areas where the wind speed and direction are unstable.