Physiological N Use Efficiency Research Articles

Seasonal Plant Nitrogen Use and Soil N pools in Intermediate Wheatgrass (Thinopyrum intermedium)

Intermediate wheatgrass (Thinopyrum intermedium; IWG) is a perennial grass under development as a grain and forage crop. Although IWG is known for its ability to take up nitrate and improve water quality, seasonal nitrogen (N) demand and uptake by IWG is not well known. We measured IWG shoot, root, and grain production, tissue N concentration, and soil mineral N at multiple plant growth stages in 1- and 2-year-old IWG stands fertilized with various rates of N: (1) 80 kg N ha−1 applied at spring regrowth (spring), (2) 40–40 kg N ha−1 applied at spring regrowth and anthesis (split), and (3) an unfertilized control. We also calculated nitrogen use efficiency and biomass N yield. Soil mineral N, N-mineralization rates, and plant N concentration increased with fertilization, and lodging increased with spring fertilization, while root physiological N use efficiency (PNUE) declined with fertilization. Seasonally, shoot and root N concentration declined at physiological maturity, while shoot PNUE was highest at maturity, suggesting either that surplus N was allocated to grain or that more biomass was being produced per unit N taken up. In the 1-year-old stand, during fall regrowth, soil mineral N levels were among the lowest; however, the total soil N was highest compared with other sampling times, suggesting a large influx of organic N between physiological maturity and fall regrowth. Based on our results, IWG is well suited to use nitrogen inputs and avoid excess N leaching into groundwater, but it is also clear that IWG has strong seasonal N allocation patterns that should be taken into consideration with N recommendations and best practices.

Straw return and nitrogen fertilization regulate soil greenhouse gas emissions and global warming potential in dual maize cropping system

Abundant nitrogen (N) fertilization is needed for maize (Zea mays L.) production in China because of its huge residual biomass return. However, excessive N fertilization has a negative impact on the soil ecosystem and environment, which contributes to climate change. Soil incorporation of maize residues is a well-known practice for reducing chemical N fertilization without compromising maize yield and soil fertility. Thus, residues incorporation has the capacity to minimize N fertilization uses and hence mitigate soil greenhouse gas emissions by improving plant N uptake and use efficiency. There is still a research gap regarding the effects of maize residues incorporation on maize yield, soil fertility, greenhouse gas emissions, and plant N and carbon (C) contents. Therefore, we conducted a field experiment during spring and autumn involving four different N fertilization rates (N0, N200, N250, and N300 kg N ha−1), with and without maize residues incorporation, to evaluate grain yield, soil fertility, plant N and C contents, and greenhouse gas emissions (GHGs). Compared to N0, N fertilizer application at 300 kg N ha−1 with residues incorporation significantly increased area-scaled global warming potential (GWP) compared to other N fertilization rates in both spring and autumn seasons, but soil nutrient contents and plant N and C contents were not statistically different from the N250 treatment. In contrast, the N recovery use efficiency (NRUE), physiological N use efficiency (PNUE), and agronomic N use efficiency (ANUE) were significantly lower in the N300 treatment than in the lower N treatment groups. Nitrous oxide (N2O) and carbon dioxide (CO2) fluxes, area-scaled GWP, and greenhouse gas intensity (GHGI) were significantly lower in the N200 treatment with straw incorporation than the N250 and N300 treatments of the traditional planting system. Thus, we concluded that N200 treatment with residues incorporation is optimal for improving grain yield, soil fertility, plant N uptake, and mitigating greenhouse gas emissions.

The difference method is not necessarily reliable for comparing the nitrogen use efficiency of hybrid rice cultivars with different tolerance to low nitrogen conditions

The difference method is one of the most commonly used methods to measure crop nitrogen (N) use efficiency. This study aimed to test the reliability of using this method to evaluate the N use efficiency of low-N tolerant hybrid rice. Two years of N fertilization experiments were conducted to compare yield attributes and N use efficiency measured by the difference method between two hybrid rice cultivars with contrasting tolerance to low N conditions, i.e. Deyou 4727 (D4727) with higher tolerance and Y-liangyou 900 (Y900) with relatively lower tolerance. Results showed that D4727 produced 17–24% higher grain yield than Y900 under zero-N fertilization conditions, confirming the higher tolerance of D4727 to low N conditions. Higher grain weight, harvest index, and internal N use efficiency were responsible for the higher grain yield in D4727 than in Y900. However, recovery efficiency of N determined by the difference method was not consistently different between D4727 and Y900, and physiological N use efficiency (PEN) and agronomic N use efficiency (AEN) determined by the difference method were 31–68% lower in D4727 compared to Y900. The lower PEN and AEN in D4727 than in Y900 were mainly due to a higher grain yield in D4727 than in Y900 under unfertilized conditions. This study suggests that the difference method is not necessarily reliable for comparing the N use efficiency of rice cultivars with different tolerance to low-N conditions, and both crop performance under unfertilized conditions and N responses under fertilized conditions should be considered when using this method to evaluate the N use efficiency of rice.

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.

Inoculation of nitrogen fixing bacteria in conjugation with integrated nitrogen sources induced changes in phenology, growth, nitrogen assimilation and productivity of wheat crop

Numerous strains of plant growth-promoting bacteria are used as biofertilizers to minimize the utilization of synthetic fertilizers, improve nutrients use efficiency, crop productivity and to reduce environmental pollution. This study was planned with the aims to assess the effects of seeds inoculation with different strains of nitrogen (N)-fixing bacteria in conjugation with N fertilization from various combinations of farmyard manure (FYM) and urea on days to anthesis, days to physiological maturity, leaf area duration (LAD), crop growth rate (CGR), net assimilation rate (NAR), physiological N use efficiency (PNUE), apparent N re-translocation (ANR), relative N accumulation rate (RN), N harvest index (NHI) and grain yield of wheat crop under the environmental conditions of Northern Pakistan. The experiment was carried out in RCB design with a factorial arrangement of treatments. Wheat seeds were inoculated with N-fixing bacterial strains viz. Azotobacter sp., Azospirillum ER-20, Rhizobium SK-8 and Pseudomonas K-1, and N were applied from three different combinations of FYM and urea i.e. 100% urea, 75% FYM and 25% urea, and 50% FYM and 50% urea. The results showed that days to anthesis (122), days to physiological maturity (162), CGR (10.31 g. m −1 . day −1 ), grain yield (4016 kg ha −1 ), PNUE (43.1 kg grain kg −1 N uptake), ANR (9.1 g kg −1 DM), NHI (79.4) and RN (0.1046 day −1 ) were increased (P < 0.05) by Azospirillum Er-20 and Pseudomonas K-1 inoculation, while maximum (P < 0.05) LAD (76 m. day −1 ) and NAR (0.19 g. m −1 . day −1 ) were attained on Rhizobium SK-8 inoculation with N from 50% FYM and 50% urea, as compared to control. The grain yield revealed a significant (P < 0.001) correlation with CGR (0.76), NHI (0.72) and PNUE (0.68). The regression analysis exhibited a good estimate for grain yield (R 2 = 0.83) and CGR (R 2 = 0.57) in response to soil mineral N content. In conclusion, bacterial inoculation in conjugation with an equal ratio of N from the integrated sources improved the phenological and growth traits as well as N assimilation and grain yield of wheat crop. Therefore, it is suggested to plan long-term experiments to explore the potential of N-fixing bacteria in conjugation with integrated N-sources under different agronomic conditions for attaining sustainability in the wheat cropping systems.

Proximal Sensing of Nitrogen Needs by Spring Wheat

Canopy nitrogen (N) status relates strongly to canopy chlorophyll content and the strength of green color. Proximal photograph by RGB camera was used to select green features that has the potential to assess N content at leaf of plant as a function of its the greenness. We proposed the development of it as a tool for sensing nitrogen content in spring wheat (Triticum aestivum). Image processing algorithm was programed calibrated and validated wheat %N%N. Nitrogen uptake =%N × canopy dry matter was harvested and calculated using simulated dry matter by DSSAT model. The data replicated laboratory measurements. A linear Lab vs Camera model displayed a unit slope with r2 = 0.93. Increase of dry matter was successfully surrogated by days after emergence and used as abscissa for inverse logistic model of critical nitrogen level. It decreased gradually from about 6% to 2% as days after emergence increased from 0 to 110 days. Maximum N uptake calculated from photo and laboratory was 324 Kg ha−1 and 318 Kg ha−1 respectively suggesting insignificant difference. Physiological N-use efficiency (i.e., canopy weight/N weight) was 52 and 78 kg canopy dry weight per 1 kg N for early and late-ripening cultivars, respectively. The determination of N application based on the smartphone photograph proved to be useful by saving on time and expenses for growers who have access to smartphones and can use them for N application and management.

Carbon dioxide and/or temperature elevation effect on yield response, nutrient partitioning and use efficiency of applied nitrogen in wheat crop in central India

Despite several implications of excessive nitrogen (N) use on environment, information on effect of elevated carbon dioxide (CO2) and/or temperature on recovery and use efficiency of applied N are limited. Hence, this field study was carried out for three consecutive seasons of wheat crop during 2016−17 to 2018−19 in Open Top Field chambers (OTCs) under four climate conditions, viz. ambient, elevated CO2 (∼550 μmol mol−1), elevated temperature (∼ 2.0 °C above ambient) and co-elevation of both CO2 and temperature. Interaction of climate and year was found non-significant (P > 0.05) for the studied parameters, but, significant effect of climate was observed in most of the parameters except straw N uptake. Pooled data analysis of three consecutive crop years indicated CO2 elevation significantly enhancing above ground biomass and grain yield and also N uptake in grain. The CO2 mediated grain yield response was to the extent of 15% (P < 0.0001) as compared to ambient, however, the yield advantage was partly offset with co-elevation of temperature. Elevation in CO2 produced 16% higher total N uptake than ambient. Co-elevation of CO2 and temperature showed a higher N uptake by about 10% as compared to ambient. In absolute terms, 25 and 15 kg ha−1 of additional N uptake was observed under elevation of CO2, and with co-elevation of temperature, respectively. Agronomic (AEN) and physiological N use efficiency (PEN), recovery of applied fertilizer N (REN) and partial factor productivity (PFPN) were significantly higher under CO2 elevation. Co-elevation of temperature caused significant depletion in REN and PFPN compared to CO2 elevation. The three years’ study clearly indicated significant advantage in yield and recovery of applied fertilizer N with CO2 elevation, at the cost of significantly higher N uptake. Significantly higher N removal and trend of declining soil mineral N content under elevated CO2 indicates possible N mining and N limitations may constrain the long-term plant response to CO2 elevation. The study has significance in N management for sustaining productivity and maintaining soil nutrient pool under changing climate.

Optimizing nitrogen application rate and plant density for improving cotton yield and nitrogen use efficiency in the North China Plain.

Plant population density (PPD) and nitrogen (N) application rate (NAR) are two controllable factors in cotton production. We conducted field experiments to investigate the effects of PPD, NAR and their interaction (PPD × NAR) on yield, N uptake and N use efficiency (NUE) of cotton using a split-plot design in the North China Plain during 2013 and 2014. The main plots were PPDs (plants m−2) of 3.00 (low), 5.25 (medium) and 7.50 (high) and the subplots were NARs of 0 (N-free), 112.5 (low), 225.0 (moderate) and 337.5 (high). During both 2013 and 2014, biological yield and N uptake of cotton increased significantly, but harvesting index decreased significantly with NAR and PPD increasing. With NAR increasing, internal nitrogen use efficiency(NUE) decreased significantly under three PPDs and agronomical NUE, physiologilal NUE, nitrogen recovery efficiency(NRE) and partial factor productivity from applied nitrogen (PFPN) also decreased significantly under high PPD between two years. Lint yield increment varied during different PPDs and years, but NAR enhancement showed less function under higher PPD than lower PPD in general. Taken together, moderate NAR under medium PPD combined higher lint yield with higher agronomic NUE, physiological NUE, and NRE, while low NAR with high PPD would achieve a comparable yield with superior NRE and PFPN and high NAR under high PPD and medium PPD produced higher biological yield but lower harvest index, lint yield and NUE compared to moderate NAR with medium PPD. Our overall results indicated that, in this region, increasing PPD and decreasing NAR properly would enhance both lint yield and NUE of cotton.

Rice Yield and the Fate of Fertilizer Nitrogen as Affected by Addition of Earthworm Casts Collected from Oilseed Rape Fields: A Pot Experiment.

The mechanism associated with improvement of soil nutritional status by oilseed rape crop, leading to better performance of rice crop, in rice-oilseed rape cropping systems is little known. The present study was aimed to test the hypothesis that earthworm casts produced during oilseed rape-growing season have positive effects on grain yield and fertilizer nitrogen (N) utilization in the subsequent flooded rice crop. A 15N-tracing pot experiment was conducted to determine the effects of earthworm casts collected from oilseed rape fields on yield attributes in rice and the fate of fertilizer N. Soil treated with earthworm casts (soil: earthworm casts = 4: 1, w/w) (EC1) produced 39% higher grain yield than soil only (EC0). EC1 had 18% more panicle number and 10% higher spikelet filling percentage than EC0. Aboveground biomass and harvest index were higher in EC1 than in EC0 by 20% and 15%, respectively. SPAD values in flag leaves were 10% and 22% higher under EC1 than EC0 at 15 and 20 days after heading, respectively. EC1 had 19% higher total N uptake and 18% higher physiological N-use efficiency than EC0. These positive effects of earthworm casts on yield attributes offset negative effects of decreasing N rate from 0.74 g pot–1 (equivalent to the recommended field rate of 150 kg ha–1) to 0.44 g pot–1 (equivalent to 60% of the recommended rate). Fertilizer N retention rate was 7% higher while fertilizer N loss rate was 6% lower in EC1 than in EC0. Our study suggests that earthworm casts produced during oilseed rape-growing season are expected to have the following benefits on the subsequent flooded rice system: (1) improving growth and physiological processes in rice plants and consequently increasing rice grain yield, and (2) increasing fertilizer N retention rate and hence decreasing fertilizer N loss rate and reducing environmental risk.

Biomass Yield and Nutrient Uptake of Energy Sorghum in Response to Nitrogen Fertilizer Rate on Marginal Land in a Semi-Arid Region

Energy sorghum tolerates adverse climatic and edaphic conditions and has great potential as biofuel feedstock in marginal land. This study investigates the potential energy sorghum biomass production and uptake of nitrogen (N), phosphorus (P), and potassium (K) on a sandy loam marginal land in a semi-arid region, in order to define optimum N fertilizer rate to produce the highest biomass yield with minimal nutrient elimination. Five N rate treatments (0, 60, 120, 180, and 240 kg ha−1) and two sorghum varieties (sweet type Guotian-8 (GT-8) and biomass type Guoneng-11 (GN-11)) were used. Yield increment was observed as N level increased, but the standout treatment appeared to be N rate of 60 kg ha−1 which significantly increased biomass yield vs. controls by 68.8% in 2014 and 64.1% in 2015. Biomass yield exhibited non-significant differences between N rate treatments from 60 to 240 kg ha−1, although the highest biomass yield (9.2–11.9 t ha−1) was observed in the 120 kg N ha−1 treatment. Nutrient analysis showed that N, P, and K accumulation in aboveground plants increased with N rate increase, ranging between 32.2 and 119.1, 7.9 and 19.2, and 22.1 and 94.0 kg ha−1, respectively, for the highest N rate of 240 kg ha−1. Substantial amounts of N were extracted from the soil in control and 60 kg N ha−1 treatments, despite the low fertility and organic matter content of the soil. Moreover, nitrogen (N) use efficiency (NUE) was maximized at lower N rates. A decline in physiological N use efficiency (PNUE) resulted in decreased agronomic N use efficiency (ANUE) at higher N rates. Hence, it is concluded that N fertilizer rate between 60 and 120 kg ha−1 would be the optimal N requirement to facilitate sustainable production of energy sorghum on a sandy wasteland.

Efficient rates of nitrogenous fertiliser for irrigated sweet sorghum cultivation during the post-rainy season in the semi-arid tropics

Sorghum (Sorghum bicolor (L.) Moench) is a multipurpose crop with high tolerance to environmental stresses. To meet the increased demand for food and biofuel, current agricultural practices rely on the excessive use of inorganic nitrogen (N) fertiliser. However, excessive N fertiliser has resulted in negative environmental effects. In view of the varied N use efficiency (NUE) of plants under different environmental conditions, the aim of this study was to evaluate the efficient rates of N fertiliser in semi-arid tropics for sweet sorghum cultivation during post-rainy season by maximising NUE without compromising yield. Field experiments were conducted on two sweet sorghum cultivars with four different N fertilisation rates (0, 63, 90 and 150kgNha−1) during the post-rainy season in India. Grain and stalk yields increased with N fertiliser, but significantly only up to 90kgNha−1. The observed increases in grain yield were attributed by increases in kernel numbers. Corresponding with the differences in biomass, both relative growth rate (RGR) and crop growth rate (CGR) increased with N fertilisation rate up to 90kgNha−1. Component analyses of RGR and CGR revealed that both net assimilation rate (NAR) and leaf area index (LAI) significantly contributed with increasing rates of N fertiliser applications. Furthermore, studies of NUE indices showed that agronomic N use efficiency (ANUE, indicating yield production per unit of fertiliser N) responded comparably up to 90kgNha−1, and decreased significantly thereafter. Analysis of ANUE components showed that the decline in ANUE at 150kgNha−1 was due to a decrease in physiological N use efficiency (PNUE), indicating that the absorbed N was not utilised efficiently for biomass and yield production, but merely accumulated. These results together suggest that 90kgNha−1 is an efficient N fertilisation rate suggested among the tested treatments for sustainable sweet sorghum cultivation during the post-rainy season in the semi-arid tropics.

Improving physiological N-use efficiency by increasing harvest index in rice: a case in super-hybrid cultivar Guiliangyou 2

Field experiments were conducted in 2013 and 2014 to compare grain yield, yield attributes and physiological N-use efficiency between two super-hybrid rice cultivars: (1) with the potential of high harvest index and physiological N-use efficiency (Guiliangyou 2) and (2) a representative super-hybrid rice cultivar (Y-liangyou 1). No significant difference in grain yield was observed between Guiliangyou 2 and Y-liangyou 1, whereas there were obvious differences in yield attributes between the two cultivars. Compared with Y-liangyou 1, Guiliangyou 2 had 8–10% lower biomass production but 14–18% higher harvest index. Consequently, physiological N-use efficiency was 18–20% higher in Guiliangyou 2 than in Y-liangyou 1. The higher harvest index in Guiliangyou 2 was mainly attributed to enhanced remobilization of stored reserves in the growing grain than in Y-liangyou 1. Larger panicle neck diameter and thinner leaves were partially responsible for the enhanced remobilization of stored reserves in Guiliangyou 2 as compared to Y-liangyou 1. Our results suggest that Guiliangyou 2 is a unique super-hybrid rice cultivar that achieves high grain yield by increasing harvest index and N-use efficiency.

Enhancing Grain Yield and Nitrogen-Use Efficiency in Rice through Foliarly Applied Gibberellic Acid in Dry-Direct-Seeded Rice

Dry-direct-seeded rice (Oryza sativa L.) (DSR) is an emerging production system in northwest India. We hypothesized that gibberellic acid (GA3) affects nitrogen (N) metabolism and N redistribution in plants and improves N-use efficiency (NUE) through better utilization of soil-derived N in DSR. The objective of the study was to determine if foliarly applied GA3 could enhance the performance of DSR. Sixteen treatments arranged in a split-plot design, i.e., four doses of N (0, 120, 150, and 180 kg ha−1) assigned to main plots and four foliar sprays (unsprayed, water spray, and GA3 20 and 40 mg kg−1) assigned to subplots, were tested. Foliar spray of GA3 was applied at panicle initiation and flowering stages of the crop. In the unfertilized (0 N) plots, foliar spray of 20 (5.45 t ha−1) and 40 mg kg−1 GA3 (5.48 t ha−1) resulted in higher grain yield as compared with unsprayed plots (4.83 t ha−1). A similar response was observed at 120 kg N ha−1, where foliarly applied GA3 at 20 and 40 mg kg−1 resulted in 22% and 26% higher grain yield, respectively, as compared with the unsprayed treatment. Foliar spray of GA3 (20 and 40 mg kg−1) in the unfertilized plots (0 N) provided similar grain yield as with 120 kg ha−1 of N application. The GA3-treated plants showed enhanced physiological NUE, milling, and head-rice recovery. However, results could be variety-specific, and physiological basis of this effect remains unknown.

Effects of Controlled-Release Fertiliser on Nitrogen Use Efficiency in Summer Maize

Nitrogen (N) is a nutrient element necessary for plant growth and development. However, excessive inputs of N will lead to inefficient use and large N losses to the environment, which can adversely affect air and water quality, biodiversity and human health. To examine the effects of controlled-release fertilisers (CRF) on yield, we measured ammonia volatilisation, N use efficiency (NUE) and photosynthetic rate after anthesis in summer maize hybrid cultivar Zhengdan958. Maize was grown using common compound fertiliser (CCF), the same amount of resin-coated controlled release fertiliser (CRFIII), the same amount of sulphur-coated controlled release fertiliser (SCFIII) as CCF, 75% CRF (CRFII) and SCF (SCFII), 50% CRF (CRFI) and SCF (SCFI), and no fertiliser. We found that treatments CRFIII, SCFIII, CRFII and SCFII produced grain yields that were 13.15%, 14.15%, 9.69% and 10.04% higher than CCF. There were no significant differences in grain yield among CRFI, SCFI and CCF. We also found that the ammonia volatilisation rates of CRF were significantly lower than those of CCF. The CRF treatments reduced the emission of ammonia by 51.34% to 91.34% compared to CCF. In addition, after treatment with CRF, maize exhibited a higher net photosynthetic rate than CCF after anthesis. Agronomic NUE and apparent N recovery were higher in the CRF treatment than in the CCF treatment. The N uptake and physiological NUE of the four yield-enhanced CRF treatments were higher than those of CCF. These results suggest that the increase in NUE in the CRF treatments was generally attributable to the higher photosynthetic rate and lower ammonia volatilisation compared to CCF-treated maize.

Genotypic Variation in Nitrogen Uptake during Early Growth among Rice Cultivars under Different Soil Moisture Regimes

In order to enhance rice productivity under water-deficient conditions, it is essential to improve nitrogen (N) uptake ability or its use efficiency. The objectives of the present study were to examine the genotypic variation in N uptake ability and physiological N use efficiency (PNUE) among 70 rice cultivars, and to clarify its association with biomass production and water uptake ability. Plants were grown under three soil moisture regimes: flooded and two non-flooded (−0.10 and −0.52 MPa soil water potential) conditions. A substantial genotypic variation in the amount of aboveground N uptake was observed, and the amount bore a positive correlation with aboveground biomass production regardless of soil moisture regime, whereas PNUE showed a negative if any correlation with biomass production depending on soil moisture regime. A significant interactive effect on the amount of aboveground N uptake between cultivars and soil moisture regimes was observed; there existed cultivars that exhibited superior N uptake only under non-flooded conditions. N uptake ability was closely correlated with water uptake ability, while a substantial genotypic variation in N uptake per unit water uptake was found in the two non-flooded regimes. These results indicate that a substantial genotypic variation in N uptake ability under water deficient conditions exists among diverse rice genetic resources, and that the variation is associated with water uptake ability and biomass production under the water-limited conditions at the early growth stage.

Lint yield and nitrogen use efficiency of field-grown cotton vary with soil salinity and nitrogen application rate

Understanding salinity and fertilizer interaction is of great economic importance to improving crop yield and fertilizer use efficiency. The objective of this study was to investigate the effects of nitrogen (N) rate on cotton yield and N use efficiency (NUE), and relate this to the optimum N fertilizer rate under saline field conditions. To achieve this goal, we conducted a two-year experiment in two nearby fields with similar fertility but varying salinity, using a split-plot design in the Yellow River Delta of China. The main plots were assigned to moderate (electrical conductivity of soil saturated paste extract, ECe=6.3dS/m) and high (ECe=12.5dS/m) salinity levels, while N-free (0kg/ha), low (120kg/ha), moderate (210kg/ha) and high (300kgN/ha) nitrogen rates were assigned to the subplots. The high-salinity soil produced 35% lower biological yield but 8.9% higher harvest index than the moderate-salinity soil. Biological yields were increased by 30% at low N rate, 35% at moderate N rate and 37% at high N rate. Under moderate salinity, moderate N rate produced more lint than other N rates; under the high salinity field, the low N rate produced lint yield comparable to the high- and moderate-N rates, being about 33% greater than that from 0-N rate. Moderate N rate was superior to high N rate but comparable to low rate based on agronomic NUE (aNUE), physiological NUE (pNUE), internal NUE (iNUE) and N recovery efficiency (NRE) under moderate salinity; under high salinity, the low N rate produced the greatest aNUE and NRE, and higher pNUE and iNUE than high N rate. Our overall results supported the use of moderate N rate for moderate salinity cotton fields and low N rate for high salinity fields in the saline Yellow River Delta and other cotton-growing areas with similar ecologies.

A large-grain rice cultivar, Akita 63, exhibits high yields with high physiological N-use efficiency

A new large-grain cultivar, Akita 63, of japonica-type rice exhibited high yields with high physiological nitrogen (N)-use efficiency for grain production. Akita 63 and three reference cultivars, Yukigesyou, Toyonishiki and/or Alitakomachi were grown in a field with different levels of N supply for three years. The grain yield of Akita 63 was 22–58% greater than that of the reference cultivars. The highest yield was 9.83 t ha −1 of brown (hulled) rice (approximately 12.3 t ha −1 of rough (unhulled) rice). The dry weight of the aboveground part and the number of spikelets at harvest, and the total leaf area (LAI) at the full-heading stage for a given amount of N accumulated in the aboveground part (plant N) did not differ between Akita 63 and the reference cultivars. The grain yield or panicle dry weight for a given amount of plant N at harvest and for a given unit of LAI were, however, greater in Akita 63 (superior in physiological N-use efficiency) than in the reference cultivars because of a higher proportion of dry matter partitioning into panicles in Akita 63 than in the reference cultivars. As the grain size of Akita 63 was about 35% larger than that of the reference cultivars, the sink capacity (the number of spikelets per unit land area × grain size) for a given amount of plant N was much larger in Akita 63. Reaccumulation of starch in the culms and leaf sheaths was very limited in Akita 63, but remarkable in the reference cultivars in the late stage of grain filling. When pot-grown Akita 63 and the reference cultivar, Toyonishiki, at different stages of ripening were fed with 13CO 2 and 13C partitioning into constituent organs was examined at harvest, the proportion of 13C partitioned into panicles was much higher in Akita 63 throughout the ripening period. These results indicate that Akita 63 is a new type of high yielding cultivar of japonica-type rice, superior in physiological N-use efficiency.

Organic Amendment and Soil Type Effects on Dry Matter Accumulation, Grain Yield, and Nitrogen Use Efficiency of Rice

ABSTRACT Research to improve and encourage the use of organic materials for lowland rice (Oryza sativa L.) production in the West African sub-region has received little attention. Experiments were conducted during two seasons in 2002 in Kumasi, Ghana, to evaluate the response of rice to a range of organic materials in three lowland soils classified as Eutric Vertisol, Eutric Fluvisol, and Haplic Gleysol. The organic materials were humified sludge, poultry manure, and cattle manure. Organic amendments to all the soils improved grain yield. The best grain yield (71.5 g pot− 1) was recorded in the second season in Vertisol amended with humified sludge. Grain weight was not much affected by soil type, but organic amendment influenced it to some extent. Uptake of nitrogen (N) was enhanced significantly by nutrient amendments, with humified sludge and poultry manure superior to cattle manure during the second season. Soil type and nutrient amendment had little effect on both physiological N use efficiency (PNUE) and nitrogen harvest index (NHI). Among the soil types, the highest N uptake was observed in Gleysol during the first season. Agronomic N use efficiency (ANUE) followed the order Vertisol > Gleysol > Fluvisol in the second season. The observed differences in N uptake and ANUE may be due partly to differences in native N fertility of the soils used for the experiment.

Photosynthetic efficiency and nitrogen distribution under different nitrogen management and relationship with physiological N-use efficiency in three rice genotypes

Nitrogen fertilization strategies were widely adopted to enhance grain production and improve nitrogen utilization in rice all over the world. For fertilization timing strategy, ear fertilization was usually employed in recent years. For fertilization amount strategy, nitrogen fertilization would continually increase to meet the demands of increasing people for food. However, under heavy ear fertilization as well as great nitrogen amount (NA), physiological N-use efficiency (PE, defined as grain production per unit nitrogen uptake by plants) decreased. Under three NA and two ratios of fertilization given during ear development period to total NA (ear fertilization distribution ratio, EFDR), net photosynthetic rate (Pn), Pn to nitrogen content per unit area (photosynthetic N-use efficiency, Pn/N), nitrogen accumulation in plant tissues and PE of three rice (Oryza sativaL.) genotypes, Jinyou 253, Liangyoupeijiu and Baguixiang were screened in the first and second seasons in 2002 so as to understand the fluctuation patterns of Pn/N and nitrogen distribution in leaf blades under great NA & EFDR and relationship with PE in rice. Results showed that under greater NA & EFDR, Pn in flag leaves at heading and plant nitrogen accumulation at maturity always increased and PE & Pn/N always decreased in spite of increased grain production. Rice distributed more nitrogen in leaf blade under greater NA and EFDR. PE indicated significantly (P < 0.05) positive relationship with Pn/N and negative relationship with nitrogen distribution ratio in leaf blades at heading and maturity, and no association with Pn in two growing seasons. Results suggested that low PE in rice under great NA and heavy ear fertilization is associated to more nitrogen distribution in leaf blades and decreases in photosynthetic efficiency.

Characterizing physiological N-use efficiency as influenced by nitrogen management in three rice cultivars

Improving physiological N-use efficiency (PE) in rice must be based on an understanding of rice responses to nitrogen management. Field experiments were conducted to investigate the effects of nitrogen management on PE in relation to accumulation and redistribution of dry matter and nitrogen in three rice cultivars, Baguixiang, Liangyoupeijiu and Jinyou 253. The rice plants were grown in spring and summer seasons in 2002 with three N rates of 0, 99 and 157 kg ha −1 and two panicle nitrogen fractions (PNF) of 1/3 and 2/3. Grain yield, dry weights and nitrogen contents of plants were measured at heading and maturity, respectively. Grain yield exhibited highly significant differences among cultivars and among N rates, but no significant difference between two PNFs. Increasing N rates increased pre- and post-heading and total dry matter accumulation in cultivars except Baguixiang at N rate of 157 kg ha −1 in the first season and increased pre-heading and total nitrogen accumulation in all three cultivars. In contrast, post-heading N accumulation varied markedly with cultivars, N rates and growing seasons. High PNF increased pre-heading and total dry matter accumulation in Jinyou 253 and Liangyoupeijiu, and post-heading dry matter accumulation in the three cultivars, while reduced pre-heading and total dry matter accumulation in Baguixiang. High PNF increased pre-heading and total nitrogen accumulation, and reduced post-heading nitrogen accumulation for all three cultivars. As a result, increasing N rate and PNF reduced pre-heading N-use efficiency, post-heading N-redistribution efficiency, physiological N-use efficiency for grain (PE-grain), and physiological N-use efficiency for biomass (PE-biomass). It can be concluded that PE of three cultivars showed similar responses to N rates and PNFs although accumulation and redistribution of dry matter and nitrogen indicated considerable differential responses to N management. In addition, improvement in PE should focus on increasing pre-heading nitrogen accumulation, post-heading dry matter accumulation and post-heading nitrogen redistribution in rice.