Physiological Nitrogen Use Research Articles

Influence of cultivation techniques on dry matter partitioning, nitrogen distribution pattern and yield of super hybrid rice Liangyoupeijiu

Liangyoupeijiu was grown under different crop cultivation techniques viz: conventional tillage and transplanting (CTTP), no tillage and transplanting (NTTP), conventional tillage and direct seeding (CTDS) and no- tillage and direct seeding (NTDS) during 2011 and 2012. Results showed that, CTTP had higher leaf dry weight than NTTP. Maximum leaf dry weight reduced in direct seeded than transplanted rice. Shoot dry weight reduced by 6% both in transplanted and direct seeded rice from heading to 12 days after heading (DAH) in both the years. No tillage and transplanting had higher export percentage of dry matter and transport percentage of dry matter among the cultivation techniques in both the years. At heading, leaf nitrogen concentration (%) and nitrogen uptake (g m-2) were higher in transplanted than direct seeded rice and significantly higher nitrogen uptake was observed under conventional tillage and transplanting in both the years. The physiological nitrogen use efficiency was higher in no-tillage than conventional tillage in both the years. Total nitrogen (kg ha-1) uptake was higher in conventional tillage than no tillage either in transplanted or in direct seeded rice and was higher under conventional tillage and transplanting among the cultivation techniques in both the years. Grain yield was closely associated with uptake of total nitrogen at heading. Although, direct seeded rice had more than 23% higher panicle number than transplanted rice but conventional tillage and transplanting produced higher grain yield due to higher uptake of nitrogen by grain at maturity and bigger sink size. Bangladesh Rice J. 26 (2): 51-62, 2022

The Fraction of Intercepted Radiation to Nitrogen Absorption as an Indicator for Assessing Physiological Nitrogen Use Efficiency in Rice

Improving nitrogen (N) use efficiency is important for achieving sustainable rice production in China. Physiological N use efficiency (PNUE) is a measure of a plant’s ability to convert absorbed N into biomass, and can be calculated as the product of the fraction of intercepted radiation to N absorption (FIRNA) and radiation use efficiency (RUE). This study evaluated the relationships between PNUE with FIRNA and RUE in three widely grown, high-yielding rice varieties using data obtained from two N fertilization experiments conducted in 2020 and 2021. The results show that PNUE was significantly positively related to FIRNA, but not significantly related to RUE in all three rice varieties. PNUE increased by 7.4–10.3 g g−1 for each 10 MJ g−1 increase in FIRNA. These results suggest that FIRNA can serve as an indicator for assessing PNUE in rice, which has implications for the phenotypic identification of rice varieties with high PNUE.

Modulation of Growth Duration, Grain Yield and Nitrogen Recovery Efficiency by EMS Mutagenesis under OsNRT2.3b Overexpression Background in Rice

Growth duration is an important agronomic trait that determines the season and area of crop growth. Previous experiments showed that overexpression of nitrate transporter OsNRT2.3b significantly increased rice yield, nitrogen use efficiency, and growth duration. Through screening, we obtained four ethyl methanesulfonate (EMS)-mutagenized mutants with shorter growth duration compared with O8 of OsNRT2.3b overexpression line. The nitrogen translocation efficiency and physiological nitrogen use efficiency of the mutants were not significantly different from O8, which were increased by 24.4% and 14.2%, respectively compared with WT, but the growth duration of the mutant was significantly lower than O8. Analysis of O8 and mutants showed that the growth duration positively correlated with grain weight per panicle, grain yield, and nitrogen recovery efficiency. In conclusion, our results provide a new idea for balancing rice yield and growth duration.

Crop Establishment Methods and Integrated Nutrient Management Improve: Part II. Nutrient Uptake and Use Efficiency and Soil Health in Rice (Oryza sativa L.) Field in the Lower Indo-Gangetic Plain, India

Rice, the predominant food crop in India, is being grown traditionally with improper plant nutrient management mostly under the flooded situation. Recent advancement in research on crop science focuses on water-saving rice technologies for maximization in crop and water productivity under the backdrop of a shrinking water resource base for ensuring environmental and agricultural sustainability. Under this situation, an experiment was conducted in two consecutive years in a split-plot design keeping rice cultivation methodologies, viz., aerobic culture, System of Rice Intensification (SRI), and conventional flooded culture in main plots and integrated plant nutrient management (INM) treatments in sub-plots. The experiment was aimed at understanding the effects of different rice production systems and INM on nutrient content, uptake, and use efficiency. The change in soil quality parameters was also studied to understand the impact of crop establishment methods (CEM) and INM options. Significant reduction (p ≤ 0.05) in nutrient uptake and use efficiency was observed under aerobic culture compared to SRI and flooded method, although aerobic culture showed the highest physiological nitrogen use efficiency. Post-harvest available Fe status was significantly lower in aerobic rice (mean 10.39 ppm) compared to other crop establishment technologies; however, Zn status was higher in aerobic rice over the flooded situation. Although available potassium was not affected due to rice cultivation methods, available nitrogen and phosphorus status were influenced remarkably. Soil microbial quality was improved in aerobic rice in comparison to flooded rice. SRI proved to be the most efficient rice establishment method for enhancement in nutrient uptake, use efficiency, and enrichment of soil chemical and microbiological quality. Irrespective of crop culture, integrated plant nutrition in rice improved the nutrient uptake, use efficiency, and soil quality parameters. The study revealed that, under the alluvial soils of the Indo-Gangetic Plains of Eastern India, SRI can be considered as a water-saving rice production method. The method can also improve nutrient uptake, efficiency, and soil quality parameters if proper INM is adopted.

Evaluation of Assam rice (Oryza sativa) genotypes for nitrogen use efficiency

We assessed genetic diversity in 26 rice genotypes including 21 landraces and five improved varieties grown in three different nitrogen doses, viz. 0, 40, and 60 kg/ha during kharif 2014-15, and identified superior nitrogen use efficient genotypes for lowland rice ecosystem. The presence of significant genotypic differences was registered for 12 quantitative traits of nitrogen use efficiency, grain yield, and its related traits. Mahalanobis distance-based clustering grouped the genotypes into seven clusters. The maximum contribution towards divergence was due to flag leaf area followed by physiological nitrogen use efficiency and grain yield/plant. Principal component analysis performed on the 12 quantitative traits revealed that the first four principal components accounted for 83.57% variance among the genotypes. Grain yield/plant (0.43), nitrogen utilization efficiency (0.39), and nitrogen harvest index (0.37) accounted most for principal component 1. The genotypes namely Lothabor, Betguti Sali, and Luhasali were found to be suitable for the lowland rice ecosystem.

Differences in yield and nitrogen absorption and utilization of <italic>indica-japonica</italic> hybrid rice varieties of Yongyou series

<p indent=0mm>A field experiment was conducted with 24 <italic>indica-japonica</italic> hybrid rice varieties (lines) of Yongyou series, from which three types (high yield and high AE (agronomic nitrogen use efficiency) [HH], high yield and medium AE [HM], medium yield and medium AE [MM]) were selected to explore the characteristics of varieties with high yield and high AE. The yield of HH type was 4.04%–4.38% and 13.37%–13.41% higher than that of HM type and MM type respectively, owing to the larger number of total spikelets, which was 5.87×10⁸–6.20×10⁸ hm^–2. Compared with HM and MM type, HH type had a high percentage of tiller rate, which was 68.83%–70.05%. The LAI of HH type was maximum at heading stage and declined slowly after heading. As a result, the LAI of HH type was above 3.85 at maturity stage. The dry matter accumulation of HH type was <sc>7.91–7.99 t</sc> hm^–2 from heading to maturity, which was the highest in three types, and its dry matter accumulation was more than <sc>21.15–21.46 t</sc> hm^–2 in the whole growth period. The total nitrogen uptake of HH type showed 5.07%–5.14% and 4.50%–5.96% increase than that of HM type and MM type respectively at maturity stage. The nitrogen sbsorption rate from jointing to heading stage and from heading to maturity stage showed HH type > HM type > MM type, as well as NTSH (N transportation from stem after heading), NIPH (N increase in panicle after heading) and NHI (N harvest index). HH type had the highest NRE (nitrogen recovery use efficiency), AE, PE (physiological nitrogen use efficiency) and PFP (partial factor productivity of applied N). Expect for NRE and NRG (nitrogen requirement for <sc>100 kg</sc> grain), all the other nitrogen utilization indexes of HM type were higher than that of MM type.

Integrated soil-cotton management system enhances nitrogen use efficiency under different soil fertility levels

ABSTRACT An integrated soil-cotton management system integrated with optimal management practices is projected to replace the conventional management system for enhancing nitrogen use efficiency. Field experiment was conducted in the more and less fertile soil with two treatments. Results showed that compared with conventional management system, integrated soil-cotton management system increased 9.5–21.2% soil-available nitrogen during the middle and later growth stages, in addition, improved average and maximum accumulation rate of nitrogen by 30.4–36.2% and 39.9–45.1%, and postponed the start time of the fast nitrogen accumulation phase by 3–6d, resulting in 32.5–38.3% higher final nitrogen accumulation. Furthermore, the increased nitrogen accumulation improved leaf area index, leaf area duration and boll number, finally enhanced agronomic nitrogen use efficiency and recovery nitrogen use efficiency. We suggest the nitrogen-based fertilizer of integrated soil-cotton management system could be omitted completely in the more fertile soil to enhance physiological nitrogen use efficiency ultimately by optimizing leaf area index. In addition, the decrement of nitrogen use efficiency was diminished under integrated soil-cotton management system. These results demonstrate ISMS might be a more profitable pattern for nitrogen use efficiency of cotton, especially to meet the challenge of soil degradation in future.

Four-year effects of soil acidity amelioration on the yields of canola seeds and sweet potato and N fertilizer efficiency in an ultisol

A four-year field experiment was conducted in Langxi, Anhui province, China to investigate the ameliorated effects of various amendments on soil acidity, soil fertility properties, yields of canola seeds and sweet potato, nutrients uptake, and nitrogen utilization efficiency by the crops. The nine treatments used were control, lime, alkaline slag (AS), peanut straw (PS), canola straw (CS), organic manure (OM), AS + PS, AS + CS, AS + OM. The chemical fertilizers with 150.0 kg ha−1 N, 150.0 kg ha−1 P2O5, and 150.0 kg ha−1 K2O were applied for all treatments in canola season, while 90.0 kg ha-1 N, 90.0 kg ha−1 P2O5, and 90.0 kg ha−1 K2O in sweet potato season. Application of lime, AS, AS + PS, AS + CS, and AS + OM increased soil pH and decreased soil exchangeable Al3+. AS + OM showed the greatest ameliorating effect on soil acidity, and soil pH of the treatment increased by 0.45 compared with control. Application of AS + OM also led to greater reduction in soil exchangeable Al3+ and greater increase in soil exchangeable calcium and magnesium compared with lime, AS, AS + PS, and AS + CS. Applying amendments alone and combined promoted the physiological nitrogen use efficiency (PNUE) and nitrogen partial factor productivity (PFPN) of canola and sweet potato, thus increased the uptake of N, P, K, Ca, and Mg by the crops, and the yields of canola seeds and sweet potato. The application of AS + OM showed the greatest effect on the PFPN of canola among the treatments, while AS + CS was the best treatment for sweet potato in this aspect. The yield of canola seeds in AS + OM treatment was 2.61 Mg ha-1, and 5.84 times greater than that of control, while that of sweet potato in AS + CS treatment was 8.07 Mg ha-1, and 32% greater than control. In conclusion, AS + CS, AS + PS, and AS + OM were the good way to ameliorate soil acidity, increase use efficiency of nutrients and promote crop production and the AS + OM is the best one in these treatments.

Late harvest improves yield and nitrogen utilization efficiency of summer maize

The farmers are accustomed to harvesting summer maize around September 20, but the maize has not yet reached physiological maturity in the Huang-Huai-Hai region, which is adverse for grain yield and mechanized harvest. In order to explore the effect of harvest date on grain yield and nitrogen utilization of summer maize, two treatment in 2016 (CK and 10d) and four treatments in 2017 (CK, 3d, 6d, 10d) were conducted. The sowing dates of all treatments were June 13, and the harvest dates of CK, 3d, 6d and 10d were September 20, 23, 26 and 30, respectively. We found that grain yield and thousand-kernel weight of 10d significantly increased by 17.4–19.8% and 16.8–19.6%, respectively, compared to CK. And partial factor productivity of nitrogen of 10d was 17.4–19.7% higher than that of CK. The grain nitrogen concentration of 3d, 6d and 10d increased by 5.4%, 9.0%, and 9.3–10.8% compared to CK, which promoted nitrogen harvest index, physiological nitrogen use efficiency and partial factor productivity of nitrogen. The reason why nitrogen utilization efficiency increased was that late harvest promoted nitrogen accumulation after tasseling and nitrogen translocation to grain. The nitrogen translocation of 6d was 10.0% in 2017 higher, and that of 10d was 25.1% in 2016 and 15.3% in 2017 higher, respectively, compared to CK. The nitrogen accumulation of 10d increased by 39.0% in 2016, and that of 3d, 6d and 10d increased by 46.5%, 51.3% and 57.3% in 2017, compared to CK. In conclusion, the thousand-kernel weight increased with the delay of harvest date, resulting in increases in grain yield of summer maize. The late harvest promoted nitrogen utilization efficiency resulting from higher nitrogen accumulation after tasseling and higher nitrogen translocation to grain. The contribution of nitrogen translocation to grain yield appeared in the mid-late period (September 23–30), while the contribution of nitrogen accumulation after tasseling did in the early and middle period (September 20–26). Considering annual production of winter wheat-summer maize, the optimized harvest date for summer maize is 6–10 days later than the conventional pattern in this study, that is the cumulative growing degree-days after tasseling reach 613.2–711.5 °C at least.

水稲極長稈育成系統TAT-26のバイオマス生産，窒素蓄積，および生理的窒素利用効率の特性

水稲極長稈育成系統TAT-26のバイオマス生産，窒素蓄積，および生理的窒素利用効率の特性

Physiological analyses of nitrogen use efficiency and yield traits of rice genotypes

Nitrogen (N) is a vital element for plant development and growth, and the application of N fertilizer could significantly increase yield formation in rice. One potential approach to reduce N fertilizer application in rice production is the development of varieties with improved nitrogen use efficiency. This study was investigating the genotypic differences of rice in the physiological nitrogen use efficiency and yield traits under different nitrogen levels. The photosynthetic rate was recorded higher (36.91 μmol CO2 m−2 s−1) in the treatment of 150% of recommmended nitrogen with rice genotype CB-08-513 at 50% flowering stage. The higher SPAD meter value (44.23) and leaf thickness (0.87 mm) were recorded in the recommended nitrogen with the genotype of CB-08-513. Regarding nitrogen content, the leaf nitrogen (5.43%) and total nitrogen content (1.86%) was recorded higher in medium duration genotypes under 150% of recommmended Nitrogen level at panicle initiation stage. The Nitrogen Uptake Efficiency (1.73), Physiological Nitrogen Use Efficiency (29.39), Nitrogen Utilization Efficiency (3.17), photosynthetic nitrogen use efficiency (4.74) were lower in medium duration genotypes when treated with 150% of recommmended Nitrogen. The maximum grain yield of 9160 kg ha−1 was registered in medium duration genotype CO 50 under 150% of recommmended Nitrogen with increase of 20.62% over control. However, in short duration genotype CB-08-504 was recorded maximum grain yield of 8449 kg ha−1 under 150% of recommmended Nitrogen with increase of 21.41% compared to 50% of recommmended Nitrogen.

Interactive effects of plant growth regulators and nitrogen on corn growth and nitrogen use efficiency

ABSTRACTOur objective was to determine the combined effect of some plant growth regulators and nitrogen (N) on corn growth, yield and nitrogen use efficiency. A potted experiment was conducted with two levels of growth regulators [i.e. with or without treatment with Seed king (Kinetine), Root king (Indole-butyric acid) and More king (Chitosan)], two maize cultivars (Calabar White and Obatanpa-98 and three nitrogen rates (0, 90 and 180 kg/ha in the form of urea). The measured parameters were growth attributes, nitrogen uptake, dry matter yield, harvest-index, shoot to root ratio, yield attributes and agronomic and physiological nitrogen use efficiency. Calabar White had taller plants (154.53 cm) more leaves (12.00) and larger leaf area (466.98 cm2) than obatanpa-98 at 6 weeks after sowing. The dry matter yield of both leaf and stem increased significantly (P ≤ 0.05) with increasing N rates but the growth regulators significantly (P ≤ 0.05) increased only the leaf dry matter. The interaction between growth regulators and nitrogen significantly affected the leaf dry matter but not the stem dry matter. There was a considerable (P ≤ 0.05) increase in harvest-index (HI) at the 90 kg/ha N rate with growth regulators and Obatanpa-98 had better HI (30.81%) than Calabar White (27.41%). Obatanpa 98 also had much (P ≤ 0.05) higher grain yield (87.42 g/plant) than Calabar White (65.40 g/plant) but for both cultivars, the grain yield increased progressively with increasing N rate. The uptake of N differed significantly (P ≤ 0.05) among the different partitions of maize (leaves, stems and grains) at various growth stages. Calabar White had the highest N uptake in the leaves and stem whether at silking or at harvest. Obatanpa-98 partitioned more N to the grains than Calabar White. Agronomic nitrogen use efficiency (ANUE) was highest (21.31 gg−1) at the 90 kg/ha N rate with Obatanpa-98 having a superior (20.26 gg−1) ANUE to Calabar White (15.94 gg−1). The physiological nitrogen use efficiency (PNUE) was also highest (8.14 g/kg) at the 90 kg/ha N rate with Obatanpa-98 being more efficient (8.08 gkg) than Calabar White (6.26 g/kg). Thus, both cultivars treated with 90 kgN/ha with or without growth regulators would best optimize nitrogen fertilizer use. However, the growth regulators increased the yield of Calabar White significantly only when no N was applied. In contrast, they increased the yield of the hybrid Obatanpa-98 at all N rates especially at the 180 kgN/ha rate. Thus, under the low input cropping common with Calabar White, treatment with the growth regulators would boost yield. A combined treatment of 180 kg N/ha with the growth regulators would ensure the best yield of Obatanpa-98.

Physiological evaluation of nitrogen use efficiency and yield attributes in rice (Oryza sativaL.) genotypes under different nitrogen levels

Nitrogen use efficiency, more specifically physiological nitrogen use efficiency depends primarily on management of N, one of the major essential nutrients. It is required in increased agricultural production and may possibly cause soil toxicity if fed in excess. Rate of N fertilizer application in fertile agricultural field and improved productivity in sterile soils require the improvement of NUE. A field experiment was therefore conducted to evaluate the effect of different N levels (N0, N50, N100 and N200) on rice genotypes. Vegetative plant growth was found to be reduced under N0 while improved at N200 level. Among the genotypes, highest PNUE (34.94) and correspondingly higher yield (7.15 ton ha−1) was observed for Krishna Hamsa. The other traits viz. plant height, no. of productive tillers and LAI exhibited higher values for Krishna Hamsa as well. Hence these can be utilized as physiological markers for the selection of rice genotypes efficient in N use.

Rhizosphere Nitrification and Nitrogen Nutrition of Rice Plants as Affected by Water Management

Redox status shapes the biogeochemistry and dominant biogeochemical processes in soil environment. Nitrification is a microbiologically mediated transformation affected by the oxygen availability in soil. Nitrification rate often determines the agronomic N use efficiency (NUE) since it affect the pool size of plant available N forms (NH 4 + ) and NO 3 - ) in soil. A mesocosm experiment was conducted using three rice varieties (PI312777, IR55423 and IR80508) to test the effect of soil water status on plant characters and nitrification in the rhizosphere. Two irrigation treatments as aerobic cultivation (AC) and continuously flooded condition (CF) were imposed. Plants were grown until 50 days after germination (DAG). At harvest, leaf nitrate reductase activity, physiological nitrogen use efficiency (PNUE), air-filled pore-space of roots, and biomass accumulation were determined. Also potential nitrification rate in the rhizosphere, soil moisture, pH, and NH 4 + and NO 3 - contents at three soil depths were determined. Biomass production was nearly 50% lower under AC than under CF. Rooting depth and rhizosphere nitrification were significantly higher under AC than CF. Rice variety and water management affected the activity of nitrifies in the rice soils. Measured soil properties and plant traits correlated significantly (p Tropical Agricultural Research Vol. 24(1): 1-11 (2012) DOI: http://dx.doi.org/10.4038/tar.v24i1.7984

Growth, yield, and nitrogen use in the wheat/maize intercropping system in an arid region of northwestern China

Relay intercropping of spring wheat and maize is practiced on a large scale in northern China. In order to provide information on productivity and nitrogen use for spring wheat/maize intercropping, a two-year experiment under three N levels and three cropping systems (monocultured wheat, monocultured maize, and intercropped wheat and maize) was carried out in the Hetao Irrigation District of the Inner Mongolia Autonomous Region, to quantify and characterize the growth and yield of the wheat and maize and determine the uptake and use efficiency of nitrogen in two crops.The land equivalent ratio (LER) of the wheat/maize intercropping system ranged from 1.01 to 1.19, and thus land use efficiency was significantly enhanced by this intercropping system. The dry-matter yield and LAI (leaf area index) of wheat were higher in border rows than in inner rows and monocultured rows, indicating an effect of border rows in the intercropping system. The LAI was considerably lower for the intercropped than the monocultured maize, indicating that intercropping limited the vegetative growth of maize.The grain yield and nitrogen uptake of both wheat and maize in two cropping systems were significantly improved with increasing amounts of N application. The LER of intercropping system tended to increase at higher N levels.The patterns of maize growth in the monocultures and intercrops were characterized by fitting expolinear growth equations to periodic harvest data. Fitted parameters indicated a growth delay in the intercropped maize ranging from 2.39 to 8.24d relative to the maize monoculture. The growth delays were shortest at the moderate N rate among three N levels (2.39d in 2012 and 2.57d in 2013). This result could be interpreted in terms of the competitive effect of wheat during the seedling phase of maize, which was weakest at the moderate N rate, causing a comparatively short growth delay. The estimated growth rate during the linear growth phase was highest in the intercrop in the high N treatment (417.5kgha−1d−1 in 2012 and 376.7kgha−1d−1 in 2013).The physiological nitrogen use efficiency (IE) was more favorable for monocultured wheat and intercropped maize and decreased as N rates increased. The efficiency of the use of N for the entire system was assessed by comparing the relative nitrogen yield total to the relative yield total. The relative nitrogen yield total ranged from 1.06 to 1.23, while the relative yield total ranged from 1.01 to 1.19, indicating that the intercrop used more nitrogen per unit production than did the monocultures.

Interaction of cyanide uptake by sorghum and wheat with nitrogen supply

Cyanide occurs naturally in soils, arising from biological cyanogenesis and also in some cases from anthropogenic contamination. Plant utilization of cyanide at non-toxic concentrations as a supplemental source of nitrogen has been a topic of recent scientific interest and it was investigated here using sorghum (Sorghum bicolor L.) and wheat (Triticum aestivum L.). The accumulation of cyanogenic nitrogen in plant tissues was assessed under nitrogen regimes with specific combinations of cyanide, ammonium, and nitrate or each nitrogen source alone. Cyanogenic nitrogen accumulated in plant tissues when in combination with nitrate and accumulation of cyanogenic nitrogen decreased when ammonium was present. A greater increase of nitrogen in tissue from cyanide was observed in both species when cyanide was substituted for ammonium, but accumulation of cyanogenic nitrogen decreased when ammonium was present. A reciprocal nitrogen labeling experiment showed that nitrogen from nitrate and ammonium was accumulated preferentially over cyanogenic nitrogen. Differences in biomass and relative growth rate were observed in response to the treatments where plants were grown with nitrate, ammonium, or cyanide as the sole nitrogen source, but not when cyanide was present along with ammonium and nitrate. Physiological nitrogen use efficiency did not differ significantly within a species for any treatment imposed. The results suggest that cyanide as a nitrogen source can potentially support plant growth and development for up to eight weeks, but more effectively in combination with ammonium and nitrate.

Effects of narrow plant spacing on root distribution and physiological nitrogen use efficiency in summer maize

The objective of this study was to understand the effects of plant spacing on grain yield and root competition in summer maize (Zea mays L.). Maize cultivar Denghai 661 was planted in rectangular tanks (0.54m×0.27m×1.00m) under 27cm (normal) and 6cm (narrow) plant spacing and treated with zero and 7.5g nitrogen (N) per plant. Compared to normal plant spacing, narrow plant spacing generated less root biomass in the 0–20cm zone under both N rates, slight reductions of dry root weight in the 20–40cm and 40–70cm zones at the mid-grain filling stage, and slight variation of dry root weights in the 70–100cm zone during the whole growth period. Narrow plant spacing decreased root reductive activity in all root zones, especially at the grain-filling stage. Grain yield and above-ground biomass were 5.0% and 8.4% lower in the narrow plant spacing than with normal plant spacing, although narrow plant spacing significantly increased N harvest index and N use efficiency in both grain yield and biomass, and higher N translocation rates from vegetative organs. These results indicate that the reductive activity of maize roots in all soil layers and dry weights of shallow roots were significantly decreased under narrow plant spacing conditions, resulting in lower root biomass and yield reduction at maturity. Therefore, a moderately dense sowing is a basis for high yield in summer maize.

Differences of Nitrogen Absorption and Utilization in Rice Varieties with Different Productivity Levels

The field experiment was carried out using 50 early-maturing late Japonica rice varieties, adopted in the region of Yangtze River, with seven nitrogen application levels (0, 150.0, 187.5, 225.0, 262.5, 300.0, 337.5 kg ha–1) to investigate the differences of the nitrogen absorption and utilization. We defined the highest rice yields under different nitrogen levels as the highest population productivity of N fertilization (HPPNF). The main results indicated that the top-and high-level yielding varieties had extremely significant larger amount of population spikelets than the middle- and low-level yielding varieties, and this superiority of total spikelets was mainly due to the extremely remarkable increase of spikelets per panicle. The nitrogen content and nitrogen absorption rate in plant at jointing, heading and maturity were all significantly increased with increasing productivity level. In transplanting to jointing and jointing to heading stages, there were no significant differences in ratio of nitrogen accumulation among four productivity levels, but a trend of decrease with the increase of productivity level. In heading to maturity stages, the ratio of nitrogen accumulation was significantly increased with increasing productivity level, which was 14.94% for top-level yielding cultivars. With the productivity level increasing, the apparent nitrogen recovery efficiency, agronomic nitrogen use efficiency and physiological nitrogen use efficiency were significantly increased. Taking into consideration of the production capacity and the apparent nitrogen recovery efficiency of all 50 rice varieties, 13 varieties with high yield and high nitrogen efficiency were selected and recommended.

Precise Postponing Nitrogen Application and Its Mechanism in Rice

Leaf ages of nitrogen application for high yield and apparent nitrogen recovery efficiency were specified through applying nitrogen fertilizer once in middle stage of growth and development using early-maturing and late japonica rice-Wuyunjing 7, Wuxiangjing 14, Changyou 1 as materials. Based on this, we studied precise postponing nitrogen application and its mechanism. Results showed that leaf ages of nitrogen application to high yield and apparent nitrogen recovery efficiency were 3rd leaf and fourth leaf from the top in early-maturing and late japonica rice. Using nitrogen in 3rd and 4th leaf from the top, made more panicles and spikelets per panicle, larger total spikelets and stable filled-grain percentage and 1000-grain weight, and lower max number of stems and tillers, higher ratio of productive tillers to total tillers, higher nitrogen accumulation, max LAI, LAD and dry matter weight in population growth and development. Yield with "PPM" (precise promoting in the middle phase) of nitrogen was significantly more than that of CK. Compared to CK, there were more significantly apparent nitrogen recovery efficiency, physiological nitrogen use efficiency, agronomic nitrogen use efficiency and yield of ear nitrogen, but lower nitrogen requirement for 100 kg grain in "PPM" of nitrogen. Mechanism of high yield and apparent nitrogen recovery efficiency in "PPM" of nitrogne was that high ratio of productive tillers to total tillers and enough population panicles were formed through consolidating population panicles and controlling non productive tillering and low effective tillering; high grain-leaf ratio (filled grains per cm2 leaf area, grain weight per cm2 leaf area), enough quantity and good quality of dry matter in heading were obtained through forming large population spikeletes, high and appropriate LAI and fine canopy structure; intense source and smooth translocation, effective sink-filling ability were enlarged through enriching dry matter accumulation after heading and coordinating producton and translocation of dry matter from population stems and sheaths.

Agronomic performance of high-yielding rice variety grown under alternate wetting and drying irrigation

Alternate wetting and drying (AWD) irrigation has been proven to be an effective water-saving technology for irrigated rice system. There is limited information on the performance of “super” hybrid rice varieties under AWD conditions. This study was conducted to compare grain yield and other related traits between a “super” hybrid rice variety and a water-saving and drought-resistance rice (WDR) variety and to identify plant traits which were responsible for varietal difference in grain yield under AWD conditions. Yangliangyou 6 (YLY6, a “super” hybrid rice variety) and Hanyou 3 (HY3, a WDR variety) were grown under AWD and continuously flood-irrigated (CF) conditions across different levels of nitrogen input in Hubei, China in 2009 and 2010. Grain yield, yield attributes, total water input, water productivity, and nitrogen use efficiency were measured. AWD saved 24% and 38% irrigation water compared with CF in 2009 and 2010, respectively. There was insignificant difference in grain yield between AWD and CF. On average, YLY6 produced 21.5% higher yield than HY3 under AWD conditions. Like grain yield, YLY6 showed consistently higher water productivity and physiological nitrogen use efficiency than HY3. Both total dry weight and harvest index contributed to higher grain yield of YLY6. Among the yield components, large sink size which was caused by more spikelets per panicle was mainly responsible for high grain yield of YLY6 compared with HY3. These results suggest that high-yielding varieties developed for the continuously flood-irrigated rice system could still produce high yield under safe AWD experienced in this study. “Super” hybrid rice varieties do not necessarily require more water input to produce high grain yield. Increasing the number of spikelets per panicle should be a primary target of breeding high-yielding rice varieties for AWD conditions.