Hai-Yan Wei

Effects of Nitrogen Application Levels on Ammonia Volatilization and Nitrogen Utilization during Rice Growing Season

Abstract We conducted field trials of rice grown in sandy soil and clay soil to determine the effects of nitrogen application levels on the concentration of NH4+-N in surface water, loss of ammonia through volatilization from paddy fields, rice production, nitrogen-use efficiency, and nitrogen content in the soil profile. The concentration of NH4+-N in surface water and the amount of ammonia lost through volatilization increased with increasing nitrogen application level, and peaked at 1-3 d after nitrogen application. Less ammonia was lost via volatilization from clay soil than from sandy soil. The amounts of ammonia lost via volatilization after nitrogen application differed depending on the stage when it was applied, from the highest loss to the lowest: N application to promote tillering > the first N topdressing to promote panicle initiation (applied at the last 4-leaf stage) > basal fertilizer > the second N topdressing to promote panicle initiation (applied at the last 2-leaf stage). The total loss of ammonia via volatilization from clay soil was 10.49-87.06 kg/hm2, equivalent to 10.92%-21.76% of the nitrogen applied. The total loss of ammonia via volatilization from sandy soil was 11.32-102.43 kg/hm2, equivalent to 11.32%-25.61% of the nitrogen applied. The amount of ammonia lost via volatilization and the concentration of NH4+-N in surface water peaked simultaneously after nitrogen application; both showed maxima at the tillering stage with the ratio between them ranging from 23.76% to 33.65%. With the increase in nitrogen application level, rice production and nitrogen accumulation in plants increased, but nitrogen-use efficiency decreased. Rice production and nitrogen accumulation in plants were slightly higher in clay soil than in sandy soil. In the soil, the nitrogen content was the lowest at a depth of 40-50 cm. In any specific soil layer, the soil nitrogen content increased with increasing nitrogen application level, and the soil nitrogen content was higher in clay soil than in sandy soil. In terms of ammonia volatilization, the amount of ammonia lost via volatilization increased markedly when the nitrogen application level exceeded 250 kg/hm2 in the rice growing season. However, for rice production, a suitable nitrogen application level is approximately 300 kg/hm2. Therefore, taking the needs for high crop yields and environmental protection into account, the appropriate nitrogen application level was 250-300 kg/hm2 in these conditions.

Suitable growing zone and yield potential for late-maturity type of Yongyou japonica/indica hybrid rice in the lower reaches of Yangtze River, China

Abstract Late-maturity type of Yongyou japonica/indica hybrids series (LMYS) have shown great yield potential, and are being widely planted in the lower reaches of Yangtze River, China. Knowledge about suitable growing zone and evaluation of yield advantage is of practical importance for LMYS in this region. Fifteen LMYS, two high-yielding inbred japonica check varieties (CK-J) and two high-yielding hybrid indica check varieties (CK-I) were grown at Xinghua (119.57°E, 33.05°N) of Lixiahe region, Yangzhou (119.25°E, 32.30°N) of Yanjiang region, Changshu (120.46°E, 31.41°N) of Taihu Lake region, and Ningbo (121.31°E, 29.45°N) of Ningshao Plain in 2013 and 2014. The results showed that maturity dates of the 15 were later than the secure maturity date at Xinghua and 6, 14 and 15 LMYS were mature before the secure maturity date at Yangzhou, Changshu and Ningbo, respectively. One variety was identified as high-yielding variety among LMYS (HYYS) at Yangzhou, 8 HYYS in 2013 and 9 HYYS in 2014 at Changshu, 9 HYYS at Ningbo. HYYS here referred to the variety among LMYS that was mature before the secure maturity date and had at least 8% higher grain yield than both CK-J and CK-I at each experimental site. Grain yield of HYYS at each experimental site was about 12.0 t ha−1 or higher, and was significantly higher than CK varieties. High yield of HYYS was mainly attributed to larger sink size due to more spikelets per panicle. Plant height of HYYS was about 140 cm, and was significantly higher than check varieties. Significant positive correlations were recorded between duration from heading to maturity stage and grain yield, and also between whole growth periods and grain yield. HYYS had obvious advantage over check varieties in biomass accumulation and leaf area duration from heading to maturity stage. Comprehensive consideration about safe maturity and yield performance of LMYS at each experimental site, Taihu Lake region (representative site Changshu) and Ningshao Plain (representative site Ningbo) were thought suitable growing zones for LMYS in the lower reaches of Yangtze River. The main factors underlying high yield of HYYS were larger sink size, higher plant height, longer duration from heading to maturity stage and whole growth periods, and higher biomass accumulation and leaf area duration during grain filling stage.

Difference of Root Morphological and Several Physiological Characteristics between Indica and Japonica Super Rice Varieties

The objective of this study was to reveal the difference of dry matter accumulation and its distribution, and the main morphological and physiological characteristics in roots between indica and japonica super rice, and their relationship with yield formation. A field experiment was conducted using two main representative super hybrid indica combinations and two conventional japonica super rice varieties in wheat-rice double cropping regions. Dry weight of root, total root length, root number, root volume, root absorbing area, root germination ability and root bleeding intensity after heading for both single stem and population, root-shoot ratio, single root length, root diameter, root density, root bleeding per spikelet, root distribution in the soil at heading and yield components were analyzed systematically. Results showed as follows:(1) For the whole growth duration, root-shoot ratio, single root length, root germinating number, root germinating volume, root germinating dry weight, root bleeding per spikelet, number of panicles, total spikelets, seed-setting rate, and grain yield of japonica rice were higher than those of indica rice, while root diameter, spikelets per panicle and 1000-grain weight followed an opposite tendency, with root-shoot ratio, single root length, root bleeding per spikelet, number of panicles, spikelets per panicle, seed-setting rate and grain yield being a significantly different.(2) Before heading, dry weight of root, total root length, root number, root volume and total absorbing surface area of root per stem and root density of japonica rice were lower than those of indica rice, though not significantly, and higher than those of indica rice significantly at maturity.(3) Before jointing, active absorbing surface area per stem and ratio of active absorbing surface area to total absorbing surface area in japonica rice were less than those in indica rice significantly, which showed an opposite trend after jointing.(4) Population indicators of morphological and physiological characteristics of japonica rice except for population root dry weight at jointing and root number of population at jointing and heading were higher than those of indica rice significantly.(5) Root bleeding intensity during 0–35 d after heading was higher in japonica rice than in indica rice significantly whether it was based on a single stem or population.(6) Ratio of root dry weight in the 0–10 cm layer to total root dry weight was lower in japonica rice than in indica rice significantly, with an opposite trend for the 10 cm layer, which indicated the deep-rooted characteristic of japonica rice can strengthen its resistance to lodging and premature senescence. Compared with super hybrid indica rice, root growth advantages of conventional japonica super rice after heading were increased, especially for population growth advantages, and all the root morphological and physiological characteristics indicators of japonica rice at maturity were better than those of indica rice, which is the important cause and assurance for high-yielding formation of japonica rice.

Morphological and physiological traits of large-panicle rice varieties with high filled-grain percentage

Abstract Understanding the morphological and physiological traits associated with improved filling efficiency in large-panicle rice varieties is critical to devise strategies for breeding programs and cultivation management practices. Information on such traits, however, remains limited. Two large-panicle varieties with high filled-grain percentage (HF) and two check large-panicle varieties with low filled-grain percentage (LF) were field-grown in 2012 and 2013. The number of spikelets per panicle of HF and LF both exceeded 300, and the filled-grain percentage (%) of HF was approximately 90, while that of LF was approximately 75 over the two years. The results showed that when the values were averaged across two years, HF yielded 12.9 t ha−1, while LF yielded 11.0 t ha−1. HF had a greater leaf area duration, biomass accumulation and transport of carbohydrates stored in the culm to the grains from heading to maturity compared with LF. HF exhibited a higher leaf photosynthetic rate, more green leaves on the culm, and higher root activity during filling phase, especially during the middle and late filling phases, in relative to LF. The length of HF for upper three leaves was significantly higher than that of LF, while the angle of upper three leaves on the main culm was less in both years. Meanwhile, specific leaf weight of HF was significantly higher when compared with LF. In addition, the grain filling characteristics of HF and LF were investigated in our study. Our results suggested that a higher leaf photosynthetic rate and root activity during filling phase, greater biomass accumulation and assimilate transport after heading, and longer, thicker and more erect upper three leaves were important morphological and physiological traits of HF, and these traits could be considered as selection criterion to develop large-panicle varieties with high filled-grain percentage.

Photosynthetic Characteristics of Flag Leaf in Rice Genotypes with Different Nitrogen Use Efficiency

Abstract To identify the photosynthetic mechanism of nitrogen (N) absorption and utilization in different rice (Oryza sativa L.) genotypes, relationships between photosynthetic characteristics of flag leaf and N use efficiency were investigated in 6 N-efficient and 6 N-inefficient rice genotypes with variable N use efficiency. The abilities of seed setting of the genotypes were also analyzed. The N application rate was 225 kg ha−1 for all genotypes. During grain filling, chlorophyll content, N content, net photosynthetic rate, photosynthetic function duration, maximum photochemical efficiency (Fv/Fm), potential photochemical efficiency of photosystem II (Fv/Fo), actual photochemical efficiency of photosystem II (ΦPSII), photochemical quenching coefficient (qP), and nonphotochemical quenching coefficient (qN) of flag leaf were obviously higher in the N-efficient genotypes than those in the N-inefficient genotypes. All these indexes were positively correlated with N use efficiency and seed-setting ability. Compared with the N-inefficient genotypes, the N-efficient genotypes had more favorable characteristics of photosynthesis and longer photosynthetic function duration. Besides, their PSII was steady for the large potential of converting light energy into electrochemical energy, and nonphotochemical quenching could also protect the photosynthetic apparatus. The accumulation of photosynthate and the seed-setting ability were enhanced in the N-efficient genotypes compared to the N-inefficient genotypes. Simultaneously, the N absorption and utilization of N efficient genotypes were improved through feedback regulation of roots and shoots.

Effect of Nitrogen Management on the Structure and Physicochemical Properties of Rice Starch

Nitrogen management (nitrogen application ratio at transplanting, tillering, and panicle initiation growth stages) is an important parameter in crop cultivation and is closely associated with rice yield and grain quality. The physicochemical and structural properties of starches separated from two rice varieties grown under three different nitrogen management ratios (9:1; 7:3; 6:4) were investigated. As the percentage of nitrogen used in the panicle initiation stage increased, the content of small starch granules improved, whereas the content of large granules decreased. Amylose content decreased with increasing nitrogen ratio at the panicle initiation stage, thereby resulting in high swelling power, water solubility, gelatinization enthalpy, and low retrogradation. The X-ray diffraction patterns of the starches were found to be A type. The present study indicated that the best nitrogen management ratio for the cultivation of rice with the highest yield, desirable starch physicochemical properties for high quality cooked rice, and a moderate protein level is 7:3.

Comparison of Culm Characteristics with Different Nitrogen Use Efficiencies for Rice Cultivars: Comparison of Culm Characteristics with Different Nitrogen Use Efficiencies for Rice Cultivars

The morphological and physiological characteristics of low-yielding and low N-efficiency,high-yielding and medium N-efficiency,high-yielding and high N-efficiency of rice cultivars were investigated using six representative japonica varieties under their respective optimal N application levels.The results showed that compared with low-yielding varieties,high-yielding varieties showed shorter basal 1st internodes,longer basal 6th internodes,increased plant height,larger culm diameter and wall thickness,significantly higher dry weight of stem and sheath,obviously increased K and Si content in culm and sheath,and a higher ratio of Si to N.As a result of their improved stalk physical characteristics and the different chemical compositions,the comprehensive breaking resistance of the culm of high-yielding cultivars was improved evidently,and the lodging index reduced as well.The cultivars with different N-efficiencies displayed diverse culm morphological and physiological characteristics even though they were all in one high-yielding level.Comparing with medium N-efficiency genotypes,the high N-efficiency ones had longer 4th and 5th internode lengths,increased culm wall thickness,in spite of slightly decreased culm diameter,resulted in higher dry weight and strengthened plumpness status of culm,significantly decreased content of Si in stem and sheath,decreased N content,and remarkably unchanged K content.Given these results,for the purpose of further increasing the nitrogen fertilizer use efficiency of the high-yielding varieties,it would be favorable to properly increase 4th and 5th internode length,thus improving top three leaves configuration,to appropriately reduce the culm diameter while increasing wall thickness and filling degree for the sake of stalk breaking resistance and transporting capability,and to properly reduce the content of Si in culm and sheath tofacilitate the translocation of nitrogen.

Characteristics of Dry Matter Accumulation and Translocation in Rice Cultivars with High Yield and High Nitrogen Use Efficiency

The difference of dry matter production and translocation characteristics in low-yielding and low N-efficiency, high-yielding and medium N-efficiency, high-yielding and high N-efficiency rice cultivars was investigated using six representative japonica varieties under their optimum N supply levels, respectively. The results indicated that: with the increase of rice productivity, the total dry matter production amount significantly increased by 20.29% on average, and the dry matter accumulation amount and population growth rate increased on average by 15.05%, 27.04%, 24.75% and 15.05%, 28.38%, 23.00%, during the period before N-n (critical stage of productive tillering), from jointing to heading, and from heading to maturing, respectively, and decreased during the period from N-n to the jointing. Among the high-yielding varieties, with the nitrogen use efficiency increased, the tiller number per unit area at each growth stage showed a downward trend, and significantly reduced on average by 5.76%, 11.61%, 7.01%, and 5.70% at N-n, jointing, heading and maturing, respectively, but ratio of productive tillers to total tillers significantly increased. At each growth stage, the dry matter accumulation amount showed a declined tendency, and reduced on average by 12.18%, 10.54%, 8.29%, and 5.01% at N-n, jointing, heading and maturity, respectively, but harvest indexsignificantly increased. During the period from heading to maturing, dry matter accumulation rate increased on average by 5.40%, the population growth rate increased on average by 5.19%. The results above showed that proper control for population growth before heading, maintaining a high growth rate after heading and a higher harvest index were the important dry matter accumulation characteristics of the cultivars with high-yielding and high nitrogen use efficiency.

Characteristics of Super-high Yield Population in Yongyou Series of Hybrid Rice

A field experiment was conducted using the representative indica-japonica hybrid rice Yongyou 11, Yongyou 12,Yongyou 13, Yongyou 15, and Yongyou 17 to compare between super-high and high yield populations formed by the regulation of cultivation measures. The results showed that the spikelets of the super-high yield population was higher than that of high yield population, with difference very significant, but the seed-setting rate and 1000-grain weight of the super-high yield population were lower than those of high yield population. The average spikelets per panicle was significantly higher than that of high yield population, meanwhile the number of the primary and secondary branches and total grains were higher than those of high yield population, showing a significant or very significant difference. The dry matter accumulation of the super-high yield population was a little lower than that of the high yield population at the jointing stage, but higher at heading and maturity stages. From the critical leaf-age for productive tillers to jointing stage, the super-high yield population had a steady growth with less ineffective tillers and lower peak number of tillers after jointing stage, the super-high yield population had a steady decline in number of tillers and had higher productive tillers rate, leaf area index, photosynthetic potential and dry matter accumulation, compared with the high yield population. The super-high yield population had higher culm diameter and culm wall thickness in the basal first, second and third internodes, as well as higher bender moment and anti-broken strength, and lower lodging index than the high yield population.

Response of iron content in milled rice to nitrogen levels and its genotypic differences.

To investigate the effect of nitrogen (N) level on iron (Fe) content in milled rice, a field experiment was carried out under three N application levels including 0, 150 and 300 kg/hm2 by using 120 rice genotypes. In addition to the genotypic differences of iron content in milled rice, grain yield, 1000-grain weight and N content in grains under the same N level, there were also variations in the response of Fe content in milled rice to N levels. Based on the range and variation coefficient of Fe content in milled rice under the three N levels, the response of Fe content in milled rice to N levels could be classified into four types including highly insensitive, insensitive, sensitive and highly sensitive types. A significant quadratic correlation was found between the Fe content in milled rice and 1000-grain weight or the N content in grains. However, no significant correlation between the Fe content in milled rice and grain yield was detected. In conclusion, there are genotypic differences in the effects of N levels on Fe content in milled rice, which is favorable to breeding of Fe-rich rice under different N environments. Furthermore, high yield and Fe-rich rice could be grown through the regulation of nitrogen on Fe content in milled rice, 1000-grain weight and N content in milled rice.