A phenology-based vegetation index for improving ratoon rice mapping using harmonized Landsat and Sentinel-2 data

Ratoon rice,which refers to a second harvest of rice obtained from the regenerated tillers originating from the stubble of the first harvested crop,plays an important role in both food security and agroecology while requiring minimal agricultural inputs.However,accurately identifying ratoon rice crops is challenging due to the similarity of its spectral features with other rice cropping systems(e.g.,double rice).Moreover,images with a high spatiotemporal resolution are essential since ratoon rice is generally cultivated in fragmented croplands within regions that frequently exhibit cloudy and rainy weather.In this study,taking Qichun County in Hubei Province,China as an example,we developed a new phenology-based ratoon rice vegetation index(PRVI)for the purpose of ratoon rice mapping at a 30 m spatial resolution using a robust time series generated from Harmonized Landsat and Sentinel-2(HLS)images.The PRVI that incorporated the red,near-infrared,and shortwave infrared 1 bands was developed based on the analysis of spectro-phenological separability and feature selection.Based on actual field samples,the performance of the PRVI for ratoon rice mapping was carefully evaluated by comparing it to several vegetation indices,including normalized difference vegetation index(NDVI),enhanced vegetation index(EVI)and land surface water index(LSWI).The results suggested that the PRVI could sufficiently capture the specific characteristics of ratoon rice,leading to a favorable separability between ratoon rice and other land cover types.Furthermore,the PRVI showed the best performance for identifying ratoon rice in the phenological phases characterized by grain filling and harvesting to tillering of the ratoon crop(GHS-TS2),indicating that only several images are required to obtain an accurate ratoon rice map.Finally,the PRVI performed better than NDVI,EVI,LSWI and their combination at the GHS-TS2 stages,with producer's accuracy and user's accuracy of 92.22 and 89.30%,respectively.These results demonstrate that the proposed PRVI based on HLS data can effectively identify ratoon rice in fragmented croplands at crucial phenological stages,which is promising for identifying the earliest timing of ratoon rice planting and can provide a fundamental dataset for crop management activities.

The underlying mechanism of variety–water–nitrogen–stubble damage interactions on yield formation in ratoon rice with low stubble height under mechanized harvesting

Agronomic measures are the key to promote the sustainable development of ratoon rice by reducing the damage from mechanical crushing to the residual stubble of the main crop, thereby mitigating the impact on axillary bud sprouting and yield formation in ratoon rice. This study used widely recommended conventional rice Jiafuzhan and hybrid rice Yongyou 2640 as the test materials to conduct a four-factor block design field experiment in a greenhouse of the experimental farm of Fujian Agricultural and Forestry University, China from 2018 to 2019.The treatments included fertilization and no fertilization, alternate wetting and drying irrigation and continuous water flooding irrigation, and plots with and without artificial crushing damage on the rice stubble. At the same time, a 13C stable isotope in-situ detection technology was used to fertilize the pot experiment. The results showed significant interactions among varieties, water management, nitrogen application and stubble status.Relative to the long-term water flooding treatment, the treatment with sequential application of nitrogen fertilizer coupled with moderate field drought for root-vigor and tiller promotion before and after harvesting of the main crop, significantly improved the effective tillers from low position nodes. This in turn increased the effective panicles per plant and grains per panicle by reducing the influence of artificial crushing damage on rice stubble and achieving a high yield of the regenerated rice. Furthermore, the partitioning of 13C assimilates to the residual stubble and its axillary buds were significantly improved at the mature stage of the main crop, while the translocation rate to roots and rhizosphere soil was reduced at the later growth stage of ratooning season rice. This was triggered by the metabolism of hormones and polyamines at the stem base regulated by the interaction of water and fertilizer at this time. We therefore suggest that to achieve a high yield of ratoon rice with low stubble height under mechanized harvesting, the timely application of nitrogen fertilizer is fundamental,coupled with moderate field drying for root-vigor preservation and tiller promotion before and after the mechanical harvesting of the main crop.

Improved Yield Prediction of Ratoon Rice Using Unmanned Aerial Vehicle-Based Multi-Temporal Feature Method

Pre-harvest yield prediction of ratoon rice is critical for guiding crop interventions in precision agriculture.However,the unique agronomic practice(i.e.,varied stubble height treatment)in rice ratooning could lead to inconsistent rice phenology,which had a significant impact on yield prediction of ratoon rice.Multi-temporal unmanned aerial vehicle(UAV)-based remote sensing can likely monitor ratoon rice productivity and reflect maximum yield potential across growing seasons for improving the yield prediction compared with previous methods.Thus,in this study,we explored the performance of combination of agronomic practice information(API)and single-phase,multi-spectral features[vegetation indices(VIs)and texture(Tex)features]in predicting ratoon rice yield,and developed a new UAV-based method to retrieve yield formation process by using multi-temporal features which were effective in improving yield forecasting accuracy of ratoon rice.The results showed that the integrated use of VIs,Tex and API(VIs&Tex+API)improved the accuracy of yield prediction than single-phase UAV imagery-based feature,with the panicle initiation stage being the best period for yield prediction(R^(2) as 0.732,RMSE as 0.406,RRMSE as 0.101).More importantly,compared with previous multi-temporal UAV-based methods,our proposed multi-temporal method(multi-temporal model VIs&Tex:R^(2) as 0.795,RMSE as 0.298,RRMSE as 0.072)can increase R^(2) by 0.020-0.111 and decrease RMSE by 0.020-0.080 in crop yield forecasting.This study provides an effective method for accurate pre-harvest yield prediction of ratoon rice in precision agriculture,which is of great significance to take timely means for ensuring ratoon rice production and food security.

Optimal management of nitrogen fertilizer in the main rice crop and its carrying-over effect on ratoon rice under mechanized cultivation in Southeast China

This study attempted to clarify the carrying-over effect of different nitrogen treatments applied to the main crop on the crop population growth and yield formation of ratoon rice under mechanized cultivation in Southeast China.Based on the constant total nitrogen application amounts(225.00 kg ha;)in the main crop,an experiment with different ratios of basal and topdressing nitrogen fertilizer(the ratio of basal fertilizer:primary tillering fertilizer:secondary tillering fertilizer:booting fertilizer at 3:1:2:4(N1),3:2:1:4(N2),3:3:0:4(N3),and 4:3:0:3(N4),respectively,and a control without nitrogen treatment(N0))was set up across two consecutive years in field using hybrid rice variety Yongyou 1540 as the test materials.The results showed that the total tiller number and effective tillering percentage increased in the main crop under the N1 treatment,more nitrogen fertilizer applied in late growth stage of the main crop,and its effective tillering percentage of the main crop was the highest at up to 70.18%,which was 9.15%higher than that of conventional fertilization treatment(N4),more nitrogen fertilizer applied in early growth stage of the main crop.The same tendency was observed in leaf area index(LAI)value of the main crop and its subsequent ratoon rice,which were 16.52 and 29.87%higher,respectively,in the N1 treatment than that in the N4 treatment at the full heading stage.The same was true in the case of the transport rates of stem and sheath dry mater and the canopy light interception rates in both the main and its ratoon crops.The transport rate of stem and sheath in main crop rice under N1 treatment increased by 50.57%compared with N4 treatment.The canopy light interception rate of N1 treatment increased by 5.07%compared with N4 treatment at the full heading stage of the ratoon crop.Therefore,the total actual yield was the highest in the main and its ratoon crops under N1 treatment,averaging 17351.23 kg ha;in two-year trials,which was 23.00%higher than that in the conventional fertilization treatment(N4).The results showed that appropriate nitrogen treatment was able to produce a good crop stand in the main crop,which was essential for producing a good ratoon crop population and high yield especially under mechanized cultivation with low stubble height of the main crop.The study suggested that shifting the proper nitrogen application amounts to the late growth stage of the main crop,such as N1 treatment,not only had a higher productive effect on ensuring the yield of the main crop,but also had a positive effect on the axillary bud sprouts from the stubbles for ratoon rice,resulting in an increased percentage of productive panicles and achieving the goal of one planting with two good harvests under the conditions of our study.

Effect of Different Sowing Dates in South Henan 's Rice-growing Areas on the Growth and Yield of Ratoon Rice

In order to determine the optimal sowing date of ratoon rice in South Henan's rice-growing areas,this paper performs a comparative analysis of rice growth process,seedling quality and yield of first season rice and ratoon rice under different sowing date treatments. The results show that under climatic conditions( 2014),by using dry seedling cultivation in a small plastic shed,the growth of seedling sown on February21 was affected,while the sowing treatments from March 1 to April 11 can breed normal seedlings,and in this period,the maturity period of first season rice was delayed with prolonged sowing date,and ratoon rice yield declined with prolonged sowing date( total production of rice sown on 11 March reaching a peak). Thus,it is considered that the optimal sowing date of ratoon rice in South Henan's rice-growing areas is mid-March.

Amylose Content,Morphology,Crystal Structure,and Thermal Properties of Starch Grains in Main and Ratoon Rice Crops

Rice ratooning,or the production of a second rice crop from stubble after the harvest of the main crop,is considered to be a green and resource-efficient rice production system.The present study was conducted to examine variance in amylose content(AC),grain morphology,crystal structure,and thermal properties of starch between main-and ratoon-season rice of seven varieties.Ratoon-season rice grains had higher ACs and significantly lower transition gelatinization temperatures(To,Tp,and Tc)than did main-season rice grains.The relative crystallinity and lamellar peak intensity of ratoon-season rice starch were 7.89%and 20.38%lower,respectively,than those of main-season rice starch.In addition,smaller granules with smoother surfaces and lower thermal parameters were observed in the starch of ratoon-season rice.The relative crystallinity and lamellar peak intensity of starch correlated negatively with the AC and positively with transition gelatinization temperatures.These results suggest that the superior cooking quality of ratoon-season rice is attributable to the moderate increase of grain AC,which reduces the relative crystallinity,weakens the crystal structure,and lead to a decrease in the gelatinization temperature.

Factors Affecting Yield and Yield Components of Main and Ratoon Rice：A Review

Rice ratooning refers to the production of second crop from the stubble after the harvest of main crop. Main and ratoon rice growth and development are affected by different factors. These factors include varieties selection, water management,fertilizer management, stubble height, plant protection practices and external environmental factors such as temperature and light.In this review, we discussed the different factors affecting the yield and yield components of main and ratoon rice. Among these factors the most important and first one is varietal selection. Varieties should be selected according to the requirement of specific area and prefer varieties resistant to insects/pests and diseases. Sufficient amount of water and fertilizer should be supplied.Stubble height of 10-20 cm will resulted in high production of ratoon rice. Too low or too high temperature and light would reduce the grain yield and quality of rice. Optimal temperature is useful for higher yield. It was concluded that by keeping the management practices more efficiently, the yield of main rice as well as ratoon rice could be increased. There is a need of more studies focusing on improvement of the quality of ratoon rice.

Integrated assessment of yield,nitrogen use efficiency and ecosystem economic benefits of use of controlled-release and common urea in ratoon rice production

Controlled-release urea(CRU)is commonly used to improve the crop yield and nitrogen use efficiency(NUE).However,few studies have investigated the effects of CRU in the ratoon rice system.Ratoon rice is the practice of obtaining a second harvest from tillers originating from the stubble of the previously harvested main crop.In this study,a 2-year field experiment using a randomized complete block design was conducted to determine the effects of CRU on the yield,NUE,and economic benefits of ratoon rice,including the main crop,to provide a theoretical basis for fertilization of ratoon rice.The experiment included four treatments:(i)no N fertilizer(CK);(ii)traditional practice with 5 applications of urea applied at different crop growth stages by surface broadcasting(FFP);(iii)one-time basal application of CRU(BF1);and(iv)one-time basal application of CRU combined with common urea(BF2).The BF1 and BF2 treatments significantly increased the main crop yield by 17.47 and 15.99%in 2019,and by 17.91 and 16.44%in 2020,respectively,compared with FFP treatment.The BF2 treatment achieved similar yield of the ratoon crop to the FFP treatment,whereas the BF1 treatment significantly increased the yield of the ratoon crop by 14.81%in 2019 and 12.21%in 2020 compared with the FFP treatment.The BF1 and BF2 treatments significantly improved the 2-year apparent N recovery efficiency,agronomic NUE,and partial factor productivity of applied N by 11.47-16.66,27.31-44.49,and 9.23-15.60%,respectively,compared with FFP treatment.The BF1 and BF2 treatments reduced the chalky rice rate and chalkiness of main and ratoon crops relative to the FFP treatment.Furthermore,emergy analysis showed that the production efficiency of the BF treatments was higher than that of the FFP treatment.The BF treatments reduced labor input due to reduced fertilization times and improved the economic benefits of ratoon rice.Compared with the FFP treatment,the BF1 and BF2 treatments increased the net income by 14.21-16.87 and 23.76-25.96%,respectively.Overall,the one-time blending use of CRU and common urea should be encouraged to achieve high yield,high nitrogen use efficiency,and good quality of ratoon rice,which has low labor input and low apparent N loss.

Border effects of the main and ratoon crops in the rice ratooning system

The border effect(BE)is widely observed in crop field experiments,and it has been extensively studied in many crops.However,only limited attention has been paid to the BE of ratoon rice.We conducted field experiments on ratoon rice in Qichun County,Hubei Province,Central China in 2018 and 2019 to compare the BE in the main and ratoon crops,and to quantify the contribution of BE in the main crop to that in the ratoon crop.The BE of two hybrid varieties was measured for the outermost,second outermost,and third outermost rows in each plot of both crops.To determine the contribution of BE between the two crops,portions of hills in the outermost and second outermost rows were uprooted during the harvest of the main crop so that the second and third outermost rows then became the outermost rows in the ratoon crop.Overall,the BE on grain yield was greater in the main crop than in the ratoon crop.In the main crop,the BE on grain yield was 98.3%in the outermost row,which was explained by the BE on panicles m^(–2),spikelets/panicle,spikelets m^(–2),and total dry weight.In the ratoon crop,the BE on grain yield was reduced to 60.9 and 27.6%with and without the contribution of the BE in the main crop,respectively.Consequently,55.1%of the BE on grain yield in the ratoon crop was contributed from the main crop.High stubble dry weight and non-structural carbohydrate(NSC)accumulation at the harvest of the main crop were responsible for the contribution of BE in the main crop to that in the ratoon crop.Our results suggest that increases in stubble dry weight and NSC accumulation at the harvest of the main crop could be important strategies for developing high-yielding cropping practices in the rice ratooning system.

Heavy soil drying during mid-to-late grain filling stage of the main crop to reduce yield loss of the ratoon crop in a mechanized rice ratooning system

Yield loss(Y_(Loss)) in the ratoon crop due to crushing damage to left stubble from mechanical harvesting of the main crop is a constraint for wide adoption of mechanized rice ratooning technology.Soil drying before the harvest of the main crop has been proposed to overcome this problem.The objective of this study was to determine the effect of soil drying during the mid-to-late grain filling stage of the main crop on grain yield of the ratoon crop in a mechanized rice ratooning system.Field experiments were conducted to compare Y_(Loss) between light(LD) and heavy(HD) soil drying treatments in Hubei province,central China in 2017 and 2018.Y_(Loss) was calculated as the percentage of yield reduction in the ratoon crop with the main crop harvested mechanically,relative to the grain yield of the ratoon crop with the main crop harvested manually.In comparison with LD,soil hardness was increased by 42.8%-84.7% in HD at the 5-20 cm soil depth at maturity of the main crop.Soil hardness at 5 and 10 cm depths reached respectively 4.05 and 7.07 kg cm^(-2) in HD.Soil drying treatment did not significantly affect the grain yield of the main crop.Under mechanical harvesting of the main crop,HD increased the grain yield of the ratoon crop by 9.4% relative to LD.Consequently,Y_(Loss) was only 3.4% in HD,in contrast to 16.3% in LD.The differences in grain yield and Y_(Loos) between the two soil drying treatments were explained mainly by panicles m^(-2),which was increased significantly by HD in the track zone of the ratoon crop compared with LD.These results suggest that heavy soil drying practice during the mid-to-late grain filling stage of the main crop is effective for reducing Y_(Loss) of the ratoon crop in a mechanized rice ratooning system.

Development of a new index for automated mapping of ratoon rice areas using time-series normalized difference vegetation index imagery

Over recent decades, the global demand for food has continued to grow, owing to population growth and the loss of arable land. Rice ratooning offers new opportunities for increasing rice production and has received renewed interest because of the minimal additional labor input required for its adoption. Regular, regional-scale monitoring of the spatial patterns of both traditional and ratoon rice cropping systems provides essential information for agricultural resource management and food security studies. However, the similar phenological characteristics of traditional double rice and ratoon rice cropping systems make it challenging to accurately classify these cropping practices based on satellite observations alone. In this study, we first proposed an improved phenology-based rice cropping area detection algorithm using moderate resolution imaging spectroradiometer (MODIS) normalized difference vegetation index (NDVI) imagery. A new index, ratoon rice index, was then developed to automatically delineate ratoon rice cropping areas with the aid of a base map of rice in Hubei Province, China. The accuracy assessment using ground truth data showed that our approach could map both traditional and ratoon rice cropping areas with high user accuracy (91.25% and 91.43%, respectively). The MODIS-retrieved rice cropping areas were validated using annual agricultural census data, and coefficient of determination (R2) values of 0.60 and 0.41 were recorded for traditional and ratoon rice cropping systems, respectively. The total area of ratoon rice was estimated to be 1 283.6 km2, 5.0% of the total rice cropping area, in Hubei Province in 2016. These demonstrated the feasibility of extracting the spatial patterns of both traditional and ratoon rice cropping systems solely from time-series NDVI and field survey data and strides made in facilitating the timely and routine monitoring of traditional and ratoon rice distribution at subnational level. Given sufficient historical satellite and phenology records, the proposed algorithm had the potential to enhance rice cropping area mapping efforts across a broad temporal scale (e.g., from the 1980s to the present).

Effects of Different Slow-release Fertilizers on Growth and Yield of Ratooning Rice

The effect of slow-release fertilizer application on reducing the fertilization times of ratooning rice was explored by carrying out plot experiments using different slow-release fertilizer formulas.The results showed that compared with conventional fertilization of farmers(TCK),there were no significant differences in plant heights of the first rice crop and ratoon rice crop and the number of tillers was slightly increased,by applying different ratios and types of slow-release fertilizers,indicating that reducing fertilization times did not affect rice growth.Compared with the TCK,the yields of treatments T1,T2,T3 and T4 of slow-release fertilizers increased to a certain extent.The yield of the first rice crop increased by 14.7%,16.7%,23.5% and 17.5%,respectively,the yields of the ratoon rice crop increased by 6.3%,5.8%,7.4% and 8.1%,respectively,and the yields of the two rice crops increased between 10.8% and 16.1%,indicating that reasonable combined application of slow-release nitrogen and fast-acting nitrogen fertilizer could meet the nutrient requirements of ratooning rice at different growth stages,and the application of slow-release fertilizers could reduce the fertilization times of ratooning rice.Based on the combination of rice yield and slow-release fertilizer cost in the first rice crop and ratoon rice crop,the T 3 formula was preferred,that is,urea-formaldehyde slow-release nitrogen fertilizer was used as the base and tillering fertilizer,and polyurethane-coated slow-release nitrogen fertilizer was used as the panicle-sprouting fertilizer.

江汉平原典型种植模式稻田土壤中农药残留特征

在江汉平原中稻-油菜/小麦轮作田、一季中稻田及再生稻田3种种植模式稻田采集土壤样品86个。调查了土壤样品中滴滴涕(DDTs,包括o,p′-DDT、p,p′-DDT、p,p′-DDE、p,p′-DDD)、六六六(HCHs,包括α-HCH、β-HCH、γ-HCH、δ-HCH)、甲胺磷、甲基对硫磷、氧乐果、乐果、敌敌畏、乙酰甲胺磷、毒死蜱、氯虫苯甲酰胺、吡蚜酮、吡虫啉、啶虫脒、三环唑、戊唑醇、氰氟草酯、二氯喹啉酸、乙草胺及异丙甲草胺等25种农药及其代谢产物的残留。结果表明,检出率最高的3种农药为当前常用杀虫剂氯虫苯甲酰胺(87.21%),杀菌剂三环唑(91.86%)及戊唑醇(72.09%),其残留均值分别为0.0397、0.0734 mg/kg及0.0276 mg/kg;已经禁用的有机氯农药滴滴涕(o,p′-DDT、p,p′-DDT、p,p′-DDE、p,p′-DDD)仍能检出,检出率为36.05%~66.28%。3种模式田块中检出的滴滴涕主要来源于历史上滴滴涕的使用。杀虫剂吡蚜酮及杀菌剂三环唑在再生稻田的残留量均值显著高于中稻-油菜/小麦轮作田及一季中稻田;但其他农药在不同种植模式稻田中的残留没有显著差异。本研究为江汉平原农药残留的治理及农药的合理使用提供了参考信息。

气候变化对川渝地区再生稻产业的影响与建议——以富顺县为例

2022—2023年以田间调查、电话访谈、文献查阅和专家座谈等方式对川渝地区再生稻生产情况进行了调研,统计分析了气候变化下川渝再生稻种植区生产格局变化和发展趋势,以富顺县为例,剖析了川渝地区再生稻产业发展的潜力和面临的挑战,并就如何提升再生稻气候韧性提出5条建议。调研显示,在气候变暖情况下,川渝地区秋季热量资源更加丰富,再生稻种植呈现适生区、优生区面积不断增加、产量稳步提高等有利变化;但气象灾害呈重发趋势,再生稻生产气候风险增高。富顺县为再生稻种植优生区,具有自然条件、技术、品种、历史、品牌、需求和政策等优势。随着再生稻产业的迅猛发展和极端天气频发重发,提高应对气候变化能力、加强再生稻气候韧性建设,对加快推进川渝地区再生稻产业发展和品牌建设具有重要的现实意义。

稻—再生稻—小龙虾稻田综合种养经济效益分析

为充分利用光温资源,在稻—小龙虾种养模式的基础上,进行稻虾综合种养,与再生稻种植相结合,开展稻—再生稻—小龙虾综合种养技术模式研究。设置4种种养模式,分别是种植中稻(MR)、种植再生稻(RR)、中稻—小龙虾综合种养(MRC)和稻—再生稻—小龙虾综合种养(RRC),分析不同种养模式对稻虾产量和经济效益的影响。结果表明,(1)RR的全年水稻产量均高于MR产量,再生季稻的产量约为头季稻产量的1/4,RRC模式水稻产量最高。(2)MRC和RRC模式养虾田水稻产量的提高主要通过较高的穗粒数和千粒重来实现。(3)稻—再生稻—小龙虾综合种养模式的产值、利润和产投比均最高,分别为102754元//hm^(2)、64704元//hm^(2)和2.70。综合来看,稻虾综合种养模式与再生稻模式相结合,能提高稻谷总产量,降低生产成本,具有较好的经济效益,是一种资源高效型、环境友好型的种养方式。

浙江省再生稻生产现状与发展策略

再生稻具有一种两收、省种省工、减肥减药、增产增效等优势,是增加复种指数和提高水稻总产的一种种植模式。浙江是长江中下游重要的水稻生产区。本文依据种植品种的类型将浙江再生稻的发展历程分为3个阶段,分别是以籼型早稻为主的起步阶段、以甬优1540为主的转变阶段和以甬优系列品种为主的快速发展阶段。以衢州市为例,再生稻的种植面积和产量在这3个阶段中不断提高,生产效益相较于单季稻和双季稻显著提升。在此基础上,进一步分析了浙江省再生稻发展前景以及高产稳产技术体系缺乏、农机农艺不配套、扶持力度低、品牌创建乏力等问题,并提出了相应的发展策略,以期为浙江省水稻生产方式转型升级提供参考。

甬优籼粳杂交稻作再生稻种植的再生特性及产量形成分析

为探究甬优籼粳杂交稻作再生稻种植时的再生特性及产量形成特点,以生产上应用广泛的甬优籼粳杂交稻品种甬优1540和甬优4949为试验材料、籼型杂交稻品种隆两优534为对照材料作再生稻种植进行了田间试验。结果显示:籼粳杂交稻和籼型杂交稻2个类型品种的再生特性存在显著差异;籼粳杂交稻甬优1540和甬优4949的优势再生节位为低节位的倒5节和倒4节,2个节位的再生苗有效穗占比之和分别为81.9%和68.9%,产量贡献率之和分别为89.6%和72.5%;2个节位再生稻的穗长、每穗粒数显著高于倒3节和倒2节,并呈现出从下往上节位逐步变小的趋势;而籼型杂交稻品种隆两优534的优势再生节位则是高节位的倒2节和倒3节,2个节位的有效穗占比和产量贡献率之和分别为71.5%和72.5%;甬优4949头季稻收割后1~7 d内的再生苗的成穗率、有效穗占比和产量贡献率分别为89.4%、74.6%和79.2%,均显著高于收割后8~12 d和12 d以上的再生苗;甬优1540和甬优4949再生稻的穗长、每穗粒数均要显著大于隆两优534,产量分别增产21.6%和17.3%。结果表明甬优籼粳杂交稻的低节位强再生力和再生苗穗大粒多的再生特性是其作再生稻种植时易获得高产的主要因素。

根际微生物响应再生稻衰老的演变特征及其延效机制

探索根际微生物响应再生稻生育后期植株衰老进程的菌群演变规律及其生态对策是防止作物早衰发生,促进耕地土壤肥力和作物生产力协同提升的关键。本研究选用2个具有亲缘关系的常规再生稻品种黄华占(Huanghuazhan,HHZ)和丰华占(Fenghuazhan,FHZ)为供试材料,采用高通量测序等方法研究再生稻生育后期根际菌群随植株衰老进程而发生的多样变化、菌群演变生态策略和物种间生态位关系。结果表明,2个具有紧密亲缘关系的供试品种其生育后期的自然衰老变化趋于一致。但在同等施肥条件下,丰华占生育后期的所有相关生理指标衰败速度均明显高于黄华占,即呈现早衰现象,并显著影响其头季和再生季稻的干物质积累与籽粒灌浆结实,进而减产。进一步分析结果证实,根际微生物多样性与再生稻植株的衰老进程紧密关联,具体表现在随着再生稻生育后期的推进,FHZ根际微生物多样性Chao 1指数和Shannon指数下降幅度更大,根际微生物生态位宽度变小。进一步分析发现,HHZ头季稻成熟期较FHZ头季稻成熟期根际土壤显著提高了地杆菌属(Geobacter)、卤囊菌属(Haliangium)、亚硝酸盐氧化菌属(Candidatus_Nitrotoga)以及硝化螺菌属(Nitrospira)的相对丰度(0.61%、0.17%、0.42%和0.045%);而在慢生根瘤菌属(Bradyrhizobium)、鞘脂单胞菌属(Sphingomonas)以及芽单胞菌属(Gemmatimonas)上HHZ较FHZ显著下降了0.29%、0.76%和0.15%;HHZ根际上调的微生物在土壤的营养循环和有效性转化上起到重要功能作用,其根际土壤微生物生态位宽度比FHZ高36.81%,反映了根际微生物对资源利用的差异,是微生物适应土壤胁迫环境的生物印迹。本研究认为植物早衰发生是根际微生物生态对策的结果,再生稻头季植株根际土壤微生物群落结构差异对其再生季具有显著的延效作用。因此,加强再生稻头季后期的根际调控,强化根际土壤微生物菌群的合理构建,促进根际正效应形成,是活化土壤营养环境,防止再生稻早衰发生,进一步提升再生季稻产量的关键。

主季减氮增密对再生稻产量形成特性的影响

为探明减氮增密对再生稻产量形成特性的影响,以杂交稻品种创两优669为材料,在3个施氮水平(N1:180 kg/hm^(2);N2:153 kg/hm^(2);N3:126 kg/hm^(2))与2个株行距(M1:20.0 cm×16.7 cm;M2:16.7 cm×16.7 cm)条件下开展了2 a大田试验。结果表明,减氮降低再生稻叶面积指数(LAI),但合理减氮范围内增密可提高主季和再生季的LAI,互作处理N1M2与N2M2的LAI较高;减氮和增密均降低再生稻叶片SPAD值,但密度影响不显著;减氮导致干物质质量下降,而增密可显著提高干物质质量,互作处理N1M2与N2M2干物质质量较高。减氮降低再生稻产量,但在合理减氮范围内增密可提高产量,互作处理N1M2与N2M2产量较高。减氮显著降低主季有效穗数、穗粒数和再生季再生率、有效穗数,但增密对穗数有弥补作用,合理减氮增密(N2M2)能够协调产量构成因素的关系,从而获得较高产量。相关分析表明,合理减氮增密主要通过提高主季和再生季的LAI和干物质质量,提高主季的有效穗数和穗粒数以及再生季的有效穗数,进而提高再生稻产量。综合来看,减氮增密处理N2M2(施N 153 kg/hm^(2)、株行距16.7 cm×16.7 cm)可以节氮15%,并可获得较高产量。

头季稻刈割时期对粮饲型再生稻饲草和再生稻产量、品质及经济效益的影响

【目的】探究头季稻不同刈割时期对粮饲型再生稻饲草和再生稻产量、品质及经济效益的影响,为粮饲型再生稻的高产优质高效种植及南方稻区解决粮饲争地、实现粮饲统筹提供理论依据和技术支撑。【方法】以我国南方稻区大面积作为再生稻种植的品种两优6326和桃优香占为试验材料,设开花期、乳熟期和蜡熟期3个头季刈割时期,分析头季饲草和再生季稻米的产量和品质差异,并对粮饲型再生稻模式的经济效益进行综合评价。【结果】随着刈割时期的推迟,头季干饲草产量逐渐增加,在蜡熟期刈割时最高,两优6326和桃优香占分别达9.17和10.35 t/ha。青贮饲草的饲用品质变化趋势与干饲草产量一致,刈割时期越晚,发酵品质越优,相对饲用价值越高,且在蜡熟期刈割时青贮饲草的中性洗涤纤维含量等发酵品质指标均达GB/T 25882—2010《青贮玉米品质分级》优质二级标准。再生季水稻产量在开花期刈割时最高,两优6326和桃优香占分别达8.94和8.92 t/ha,之后随着刈割时期的推迟逐渐降低。随刈割时间推迟,再生季稻米各品质指标变化趋势不尽相同,但各刈割处理下的整精米率、直链淀粉含量和垩白度表现达到或接近GB/T 17891—2017《优质稻谷》二级标准。再生季稻谷经济收益大幅高于头季饲草,2个品种的总收益、净收益和产出投入比在开花期刈割时最高,平均分别达36755元/ha、17450元/ha和1.90,并随着刈割时期的推迟逐渐降低。【结论】以高产优质饲草生产为目的,头季宜在蜡熟期刈割;以高产优质稻米生产为目的,头季宜在开花期刈割,且该模式在开花期刈割时的总体经济效益最高。