Analysis of Water Non-limiting and Water Limiting Yields and Yield Gaps of Groundnut in India Using CROPGRO-Peanut Model

To assess the scope for enhancing productivity of groundnut (Arachis hypogaea L.) in India, well‐calibrated and validated CROPGRO‐Peanut model was used to assess potential yields (water non‐limiting and water limiting) and yield gaps of groundnut for 18 locations representing major groundnut growing regions of India. The average simulated water non‐limiting pod yield of groundnut for the locations was 5440 kg ha^?1, whereas the water limiting yield was 2750 kg ha^?1 indicating a 49 % reduction in yield because of deficit soil moisture conditions. As against this, the actual pod yields of the locations averaged 1020 kg ha^?1, which was 4420 and 1730 kg ha^?1 less than the simulated water non‐limiting and water limiting yields, respectively. Across locations, the simulated water non‐limiting yields were less variable than water limited and actual yields, and strongly correlated with solar radiation during the crop season (R² = 0.62, P ≤ 0.01). Simulated water limiting yield showed a significant positive, but curvilinear relationship (R² = 0.73, P ≤ 0.01) with mean crop season rainfall across locations. The relationship between actual yield and the mean crop season rainfall across locations was not significant, whereas across seasons for some of the locations, the association was found to be significant. Total yield gap (water non‐limiting minus actual yields) ranged from 3100 to 5570 kg ha^?1, and remained more or less unaffected by the quantity of rainfall received across locations. The gap between simulated water non‐limiting and water limiting yields, which ranged from 710 to 5430 kg ha^?1, was large at locations with low crop season rainfall, and narrowed down at locations with increasing quantum of crop season rainfall. On the other hand, the gap between simulated water limiting yield and actual farmers yield ranged from 0 to 3150 kg ha^?1. It was narrow at locations with low crop season rainfall and increased considerably at locations with increasing amounts of rainfall indicating that type of interventions to abridge the yield gap will vary with the rainfall regimes. It is suggested that improved agronomic management (such as high yielding cultivars, balance crop nutrition and control of pest and diseases) in high rainfall regimes and rainfall conservation and supplemental irrigations in low rainfall regimes will be essential components of the improved technologies aimed at abridging the yield gaps of groundnut.     

四川盆地小麦籽粒的灌浆特性

四川盆地小麦灌浆期长,粒重优势明显,但易受环境影响。2010-2011和2011-2012年连续2个小麦生长季,选用10个品种在3个地点进行灌浆特性研究,以揭示该区域小麦灌浆参数的基因型差异及环境效应。2年平均粒重48.25 g,灌浆分为渐增期(T₁)、快增期(T₂)和缓增期(T₃) 3个阶段,各阶段持续时间为T₃ (16.30 d)>T₁ (13.41 d)>T₂ (12.98 d),其灌浆速率分别为0.618、0.772和2.205 mg grain^-1 d^-1。3个阶段的干物质积累贡献率依次为21.21% (T₁)、58.27% (T₂)和20.53% (T₃),可见快增期结束时可以积累80%左右的干物质量。基因型、地点和年份对除粒重以外的所有灌浆参数均有显著影响,以年份的效应最大。同一年中,粒重、最大灌浆速率、平均灌浆速率、缓增期灌浆速率、渐增期灌浆速率和快增期灌浆速率主要受基因型的影响,而其他参数则以地点效应大于基因型效应。粒重与平均灌浆速率、最大灌浆速率、快增期灌浆速率和缓增期灌浆速率呈极显著正相关。10个参试品种中,川麦42、川育23和川麦56具开花期早、灌浆速率高、灌浆时间长、粒重大等特征。     

高产棉花太阳辐射能利用率及干物质分配规律研究

通过对1988～1989年高产棉花栽培试验结果进行分析发现,棉花的太阳辐射利用率在叶面积系数小于2.0时随叶面积系数的增加而线性增加,大于2.0时增加变缓。从生育时间看,7月中旬前太阳辐射利用率指数上升,7月中旬至8月底相对稳定在1.2～1.4克/兆焦左右,9月以后又不同程度线性下降。生长季内子棉太阳辐射经济效率1988和1989年分别为0.14和0.15克/兆焦。收获指数与最大叶面积系数呈显著负相关;盛花期之前棉株各器官之间的同伸关系或明显,盛花期后器官的生长相互间无明显的确定性关系。如能调节密度与叶面积系数的关系,使得既提高5～6月的辐射能利用率,同时使7～8月叶面积系数维持在3.0～3.5的适宜范围内,9～10月群体又不早衰,则有利于获得高产。     

Differential Response of Southern US Rice (Oryza sativa L.) Cultivars to Ultraviolet‐B Radiation

Elevated ultraviolet‐B (UV‐B; between 290 and 320 nm) radiation, because of depletion of the stratospheric ozone layer, is one of the major environmental factors influencing plant metabolic processes and yield. The southern US rice cultivars contribute greatly towards US rice production, but the effects of elevated UV‐B radiation on these cultivars are not well known. The objective of this study was to determine the effects of elevated UV‐B radiation on leaf photosynthetic rate (P_n), membrane stability, pollen viability, phenolic concentration and yield of eight commercially popular southern US rice cultivars (five inbred cultivars and three hybrids). Plants were grown in a temperature‐controlled greenhouse in Beaumont, TX, USA, and were exposed to UV‐B radiation of 0, 8 or 16 kJ m^?2 day^?1 for 90 days. For most of the cultivars, plants grown under 8 or 16 kJ UV‐B radiation showed significant decreases in P_n, membrane stability, pollen viability, and yield compared with the plants grown under an UV‐B‐free environment, whereas there was a significant increase in leaf phenolic concentration under 16 kJ UV‐B radiation. The hybrid ‘Clearfield XL729’ performed best among the selected southern US rice cultivars under 16 kJ UV‐B radiation.     

机插条件下低氮密植栽培对“早晚兼用”双季稻产量和氮素吸收利用的影响

为了缓解长江中下游双季稻区机插双季稻生育期不配套的矛盾,2014—2015年早晚两季均以常规早稻品种中嘉早17为材料,在大田栽培条件下研究机插密度(36.4、28.6、19.0穴m–2)与施氮量(0、110~140、176~189 kg N hm–2)对机插双季稻产量及氮肥利用率的影响。结果表明:采用"早晚兼用"机插双季稻栽培模式有利于早、晚2季周年高产,以"高密+高氮"处理产量最高,2年分别达到16.94 t hm–2和16.99 t hm–2,但与"高密+低氮"处理的产量差异不显著;氮肥利用率随氮肥用量增加而下降,随栽插密度增加而提高,以"高密+低氮"处理最高,2年4季分别为62.77%、55.75%、65.82%、64.37%,比"高密+高氮"处理分别提高12.11%、9.01%、8.49%、2.14%;"高密+低氮"处理与"低密+高氮"处理相比,群体干物质积累量及辐射利用率均有一定的优势。由此可见,在此模式下适当增加机插密度,减少氮肥用量,既可实现高产,又能显著提高氮素利用率。采用"早晚兼用"品种搭配模式,低氮、密植栽培可作为长江中下游双季稻区机插双季稻生产的关键技术。     

Yield Performance of Wheat Isolines with Different Dosages of the Short Arm of Rye Chromosome 1

Translocations of the short arm of rye (Secale cereale L.) chromosome 1 (1RS) in wheat (Triticum aestivum L. cv. Pavon 76) are known to increase root biomass. Such an increase enhances water and nutrient uptake and may improve grain yield. Two greenhouse experiments and a field experiment were carried out at the University of California, Riverside, in 2012 and 2013 under well‐watered and terminal drought treatments to evaluate phenotypic characters associated with varying dosages of 1RS, including grain yield. The genotypes used were cultivar Pavon 76 (R₀), Pavon 76/Pavon1RS.1AL (F₁ hybrid) with a single dosage of 1RS (R₁A), Pavon 1RS.1AL with two dosages of 1RS (R₂A), Pavon 1RS.1DL (R₂D) also with two dosages of 1RS and Pavon 1RS.1AL‐1RS.1DL (R₄AD) with four dosages of 1RS. There was a significant positive correlation between number of dosages of 1RS and root biomass. However, no correlation was found between root biomass and grain yield per plant. Drought in the field experiment reduced grain yield significantly. Under well‐watered field conditions, grain yield of R₂A (215.9 g plant^?1) was significantly greater than those of R₂D (191.8 g plant^?1) and R₄AD (161.7 g plant^?1). Also, grain yield of R₄AD was significantly less than those of F₁, Pavon 76 and R₂D under well‐watered conditions. Under drought field conditions, no significant differences were found among the genotypes for grain yield was found between F₁ (14.7 g plant^?1) and R₄AD (12.4 g plant^?1). Harvest index was significantly greater in well‐watered (44.2 %) than in drought (34.6 %) field conditions. On average, genotypes F₁ (42.3 %) and R₂A (40.6 %) had higher harvest index than R₂D (38.3 %) and R₄AD (35.5 %) in the field. Also, Pavon 76 (40.2) and R₂D (38.3) had higher harvest index than R₄AD. Drought tolerance was lowest for R₄AD due to its relatively lower grain yield potential. In general, Pavon 1RS.1AL carrying two dosages of 1RS showed higher grain yield under wet treatments. Pavon 1RS.1AL‐1RS.1DL carrying four dosages of 1RS produced the largest shoot and root biomasses, but the least grain yield.     

Genotypic Variation in the Response of Rice (Oryza sativa L.) to Increased Atmospheric Carbon Dioxide and its Physiological Basis

Increasing atmospheric carbon dioxide concentration (C_a) is one aspect of global change that will have a significant impact on the productivity of agricultural crops. Crop yields have been shown to increase with increasing C_a. The magnitude of yield response to increased C_a could vary depending on genotypic and environmental factors. The objective of this study was to determine the genotypic variation of yield response and its physiological basis in rice (Oryza sativa L.) through an initial varietal screening using 16 genotypes. The genotypes were grown under two concentrations of C_a, i.e. 370 ± 28 (ambient) and 570 ± 42 (elevated) μmol mol⁻¹, in open top chambers under lowland field conditions at the Rice Research and Development Institute in Sri Lanka (7°50′N, 80°50′E) from May to August 2001 (yala season) and from November 2001 to March 2002 (maha). C_a within chambers was maintained around target concentrations by a computer‐based real‐time data acquisition and control system. There was significant variation between genotypes in the response of yield to elevated C_a, with absolute increases up to 530 g m⁻² in yala and 347 g m⁻² in maha. In relative terms, percentage yield increases from ambient to elevated C_a ranged from 4 % to 175 % in yala and from 3 % to 64 % in maha. Genotypic variation in yield showed significant positive correlations with light‐saturated net photosynthetic rate of the flag leaf during the grain‐filling stage. This indicated that increased assimilate supply and its genotypic variation contributed to the observed genotypic variation in yield response to elevated C_a. Furthermore, the capacity to develop a larger reproductive sink through increased panicle number per m² and increased number of grains per panicle contributed to greater yield at elevated C_a. There was a significant genotype × season interaction with genotypes responding differentially to increased C_a in the two seasons. This was mainly due to inter‐seasonal variation in incident radiation during the grain‐filling stage. Our results demonstrate the significant genotypic variation that exists within the rice germplasm, in the response to increased C_a of yield and its correlated physiological parameters. A subset of genotypes from screening trials such as the present study can be used for more in‐depth analysis of the influence of elevated C_a on processes responsible for yield determination in rice and for molecular studies to elucidate the genetic basis of the response to increased C_a. This could pave the way for breeding genotypes which are more productive in a future high CO₂ environment, provided that genotypes with greater flexibility in their physiology are selected to counter the genotype × environmental interaction.     

Leaf K/Na ratio predicts salinity induced yield loss in irrigated rice

Salinity is a major constraint to irrigated rice production, particularly in semi-arid and arid climates. Irrigated rice is a well suited crop to controlling and even decreasing soil salinity, but rice is a salt-susceptible crop and yield losses due to salinity can be substantial. The objective of this study was to develop a highly predictive screening tool for the vegetative growth stage of rice to estimate salinity-induced yield losses. Twenty-one rice genotypes were grown over seven seasons in a field trials in Ndiaye, Senegal, between 1991 and 1995 and were subjected to irrigation with moderately saline water (3.5 mS cm^-1, electrical conductivity) or irrigation with fresh water. Potassium/sodium ratios of the youngest three leaves (K/Na_Leaves) were determined by flame photometry at the late vegetative stage. Grain yield was determined at maturity. All cultivars showed strong log-linear correlations between K/Na_Leaves and grain yield, but intercept and slope of those correlations differed between seasons for a given genotype and between genotypes. The K/Na_Leaves under salinity was related to grain yield under salinity relative to freshwater controls. There was a highly significant correlation (p < 0.001) between K/Na_Leaves and salinity-induced grain yield reduction: the most susceptible cultivars had lowest K/Na_Leaves and the strongest yield reductions. Although there were major differences in the effects of salinity on crops in both the hot dry season (HDS) and the wet season, the correlation was equally significant across cropping seasons. The earliest possible time to establish the relationship between K/Na_Leaves under salinity and grain yield reduction due to salinity was investigated in an additional trial in the HDS 1998. About 60 days after sowing, salinity-induced yield loss could be predicted through K/Na_Leaves with a high degree of confidence (p < 0.01). A screening system for salinity resistance of rice, particularly in arid and semi-arid climates, is proposed based on the correlation between K/Na_Leaves under salinity and salinity-induced yield losses. This revised version was published online in July 2006 with corrections to the Cover Date.     

Potential of gamma radiation enhancing the biosynthesis of tropane alkaloids in black henbane (Hyoscyamus niger L.)

Summary A productive yellow flowered mutant with high tropane alkaloid content was isolated in the M₂ generation of gamma irradiated (Co⁶⁰ at 40 kr) progenies ofHyoscyamus niger. Mutant progenies, on an average, were capable of synthetising more than twice crude alkaloid (0.147% to 0.221%) in M₃ through M₆ generations compared to the parental control (0.065 to 0.106%). In pilot scale trial (M₇), two elite lines, Y-15 and Y-17 were found to contain 0.390% and 0.318% crude drug in contrast to 0.211% in an improved inbred used as control. However, owing to conducive plant morphology, Y-17 registered high yield of dry biomass, hence gave more than double yield of crude drug than the improved control (inbred) (23 kg/ha against 11 kg/ha). Also being superior in hyoscyamine and hyoscine yields, it was redesignated as var.Aela, and released for commercial cultivation in India, thus signifying the efficiency of radiation breeding for crop improvement.     

生长季降水对黑龙江省水稻生产的影响

研究旨在分析寒地水稻洪涝的致灾因子—降水的变化趋势和特征及对水稻生长发育的影响,揭示其变化规率,以期水稻生产防灾减灾提供科学依据。利用黑龙江省水稻主产区气象观测站的降水量、发育期、产量资料及洪涝灾害资料,分析了水稻主产区夏季及关键生育期降水、暴雨量和暴雨日数变化特征,阐述了黑龙江省洪涝灾害的分布规率,分析了降水对水稻产量的影响。结果表明：1971-2016年稻区6-8月降水呈现西部和东部少、中部多的趋势,暴雨日数中西部多,东部少,暴雨量总体呈上升趋势;水稻关键期平均暴雨量为76.2毫米,总体呈小幅上升趋势,暴雨日数中西部多,东部少;1984-2010年黑龙江省洪涝灾害西北、东南、中部偏多,西南、东北偏少,总体呈逐年增加的趋势,且主要发生在夏季。制约黑龙江省各地区水稻生长发育及产量形成的降水阶段各地有所不同,北部主要在7月下旬,西部在7月下旬及9月下旬,南部在5月下旬、6月下旬及9月中旬,中部及东部稻区较为复杂,几乎贯穿整个生长季。     

Thermal characterization of a tropical rice soil in relation to puddling,flood-water depth and percolation rate

Effects of puddling, flood-water depth and percolation rate on the thermal properties of a tropical rice soil were studied under field and glass-house conditions. Puddling increased volumetric heat capacity (C_V), but decreased thermal conductivity (Kt), thermal diffusivity (Dt) and damping depth (D) compared to a nonpuddled soil. A percolation rate of 40 mm d⁻¹ showed higher Kt, Dt and D than zero percolation. The values of Kt, Dt and D were highest with 50 mm and lowest with 10 mm flood- water depth. The C_v did not change with different flood-water depths or percolation rates. Consequently, puddling, 40 mm d⁻¹ percolation and 50–100 mm submergence kept the maximum temperature of surface 100–150 mm soil at relatively low level under tropical conditions. These treatments also buffered soil against extreme diurnal temperature fluctuations. The time lag between maximum solar radiation and maximum temperature of submerged soil varied, on an average, between 1.2 hours at soil surface and 11.6 hours at 300 mm soil depth; which is more than that in an upland soil.     

黑龙江省水稻生长季极端降水及洪涝时空演变特征

为了合理规避极端降水带来的洪涝灾害,有效保障水稻安全生产。本研究基于黑龙江省69个气象台站1971—2016年降水资料和历史洪涝记载资料,利用方差分析和Mann-Kendall检验方法,分析了黑龙江省水稻生长季极端降水和洪涝时空演变特征。结果表明：（1）极端降水指数(EPI)5月、6月和9月在2010s最突出,7月和10月在1990s最突出,8月在1980s最突出;（2）根据典型因子,7月多雨时段为1990s,8月多雨时段为1980s;（3）水稻洪涝多发生在7月,7月和8月水稻洪涝历史高发时段分别为1990s和1980s。     

Deficit irrigation maintains maize yield through improved soil water extraction and stable canopy radiation interception

Deficit irrigation (DI) is an effective way to save irrigation water while maintaining sustainable yield in irrigated crops. However, limited information is available related to canopy structure and solar radiation use under DI condition. In this study, our objective was to assess maize hybrids for leaf development, photosynthetically active radiation (PAR) interception and water use under DI condition. Field experiments were conducted in 2016 and 2017 in four maize hybrids at well-watered (I₁₀₀, referring to 100% evapotranspiration [ET] requirement) and DI (I₇₅, referring to 75% ET requirement) water regimes. Compared to I₁₀₀, I₇₅ did not reduce maize biomass and grain yield. Although DI reduced the leaf appearance rates (1.5% in 2016 and 7.6% in 2017) and resulted in greater variations in leaf area index (LAI) among hybrids, the amount of PAR interception was not affected during the growing season. DI significantly reduced the seasonal ET in both years (19.8% in 2016 and 26.6% in 2017). All the hybrids extracted more soil water (29 mm in 2016 and 27 mm in 2017) at I₇₅ than at I₁₀₀. Maize plants at I₇₅ had greater water use efficiency (WUE) (1.68 kg m⁻³) than those at I₁₀₀ (1.41 kg m⁻³). However, DI did not affect radiation use efficiency (RUE). In conclusion, DI at I₇₅ maintained grain yield through improved soil water extraction and WUE but stable canopy radiation interception and RUE.     

长江中游不同玉稻种植模式产量及资源利用效率的比较研究

发展长江中游玉米生产是解决本区域玉米产需矛盾的根本途径。近年来随着长江中游玉米的快速发展,该地区出现了春玉米–晚稻、双季玉米和早稻–秋玉米等新型的一年两熟制种植模式,为探明其适应性和实用性,2013—2014年在湖北省武穴市设置了传统种植的双季稻(对照)、春玉米–晚稻、双季玉米和早稻–秋玉米共4种两熟制种植模式,分析比较其周年产量及光、温、水资源利用效率和经济效益。结果表明,春玉米–晚稻和双季玉米周年产量显著高于早稻–秋玉米和双季稻。与双季稻相比,春玉米–晚稻周年产量、光能生产效率、光能利用率、积温生产效率、水分利用率及经济效益分别提高18.3%、14.1%、23.4%、16.4%、37.2%和44.3%,双季玉米分别提高了13.5%、8.1%、26.1%、11.4%、88.8%和37.8%。春玉米其产量、积温生产效率、水分利用率及经济效益两年平均比早稻分别高出30.6%、29.5%、57.2%和96.1%,而秋玉米和晚稻之间产量无显著差异。不同玉稻模式周年产量差异主要源于第一季春玉米和早稻产量的差异。可见,春玉米–晚稻和双季玉米是适宜在长江中游推广的两熟制种植模式。     

Modelling Wheat Stomatal Resistance in Hourly Time Steps from Micrometeorological Variables and Soil Water Status

An accurate estimation of stomatal resistance (r_S) also under drought stress conditions is of pivotal importance for any process‐based prediction of transpiration and the energy budget of real crop canopies and quantification of drought stress. A new model for r_S was developed and parameterized for winter wheat using data from field experiments accounting for the influences of net radiation (R_Net), air temperature (T_Air) and vapour pressure deficit of the atmosphere (VPD) interacting with an average water potential in the rooted soil (ψ_RootedSoil). r_S is simulated with a limiting factor approach as maximum of the metabolic (related to photosynthesis) and hydraulic (related to drought stress) acting influences assuming that, if drought stress occurs, it will dominate stomatal control: r_S = max(r_S(T_Air), r_S(R_Net), r_S(VPD, ψ_RootedSoil)). This transitional approach is suited to reproduce measured daily time courses of r_S with a varying accuracy for the single measurement dates but performed satisfactorily for the whole data set (r² = 0.63, RMSE = 59 s m^?1, EF = 0.60). This new semi‐empiric approach calculates r_S directly from external environmental conditions. Therefore, it can be easily implemented in existing model frameworks as link between operational crop growth models that use the concept of radiation use efficiency instead of mechanistic photosynthesis modelling and soil–vegetation–atmosphere transport models.     

Toward yield improvement of early-season rice: Other options under double rice-cropping system in central China

Rice (Oryza sativa L.) grain yields vary considerably between seasons under subtropical irrigated conditions. Reports on comparisons of grain yield between early- and late-season rice in subtropical environments are lacking. In order to evaluate the role of climatic and physiological factors under double rice-cropping system in determining rice grain yield in farmers’ fields, six field experiments were conducted in both early and late seasons from 2008 to 2010 in Wuxue County, Hubei province, China. For early season crop, the attainable yield was highest under dense planting (38.5 hills m⁻²) when N was applied at a rate of 120–180 kg ha⁻¹. However, the effect of hill density on grain yield was relatively smaller for late season crop, while moderate hill density (28.1 hills m⁻²) and nitrogen rate (120 kg ha⁻¹) were advantageous in terms of grain yield and lodging resistance. Remarkably higher grain yields were achieved in late season crops compared with early season crops, as the former had superiority over the latter in sink size (sink capacity, such as spikelets per m²) and biomass production. The comparatively lower yield under early season mainly resulted from slower growth during the vegetative phase, which can be attributed to the lower temperature rather than reduced mean daily radiation. Summary statistics suggested that there was ample opportunity to improve rice yield in early season crops, compared with late season crops. Correlation analysis further showed that spikelets per m², panicles per m², leaf area index at panicle initiation and flowering, biomass at physiological maturity and biomass accumulation after flowering should be emphasized for increasing grain yield, especially in early season crops under the double rice-cropping system in central China. Current breeding programs need to target strong tillering ability, large panicle size and greater grain filling (%) for early season crops, and high yield potential and lodging-resistance for late season crops as primary objectives.     

Effect of Sesbania rostrata on Nitrogen Uptake and Yield of Lowland Rice

Nitrogen inputs into rice fields can be increased by cultivation of green manure crops. Many Sesbania species have been generally grown by the rice farmers in India and these green manures are capable of contributing significant amount of nitrogen in 45 to 90 days period by their association with the nitrogen fixing symbiotic bacterium – Rhizobium . Field experiments conducted at the Tamil Nadu Agricultural University, Coimbatore, India, during Dry and Wet seasons in 1987–88 with medium duration (145 days) rice variety CO 43. Sesbania rostrata produced higher biomass on 60th day after sowing and accumulated higher percentage of nitrogen. Application of fertilizer nitrogen with S. rostrata have increased the nitrogen uptake and yield of rice.     

不同播期密度对甜荞麦农艺性状及产量的影响

为了探讨甜荞麦适宜的种植密度和播种期。以当地主栽品种为材料,在田间试验的基础上,通过设置种植密度（B₁：45万/hm²、B₂：75万/hm²、B₃：105万/hm²、B₄：135万/hm²）和播期（A₁：7月28日、A₂： 8月7日、A₃：8月27日）2个处理因素,研究种植密度和播期对甜荞麦农艺性状及产量的影响。结果表明：播种密度对甜荞麦生育期、株高、主茎分枝数和主茎节数的影响不显著,而不同播期对甜荞麦生育期、株高和主茎节数有较大影响。其中,8月27日(A₃)播种的生育期比7月28日(A₁)、8月7日(A₂)播种的生育期长10天左右,株高比A₁、A₂平均矮9 cm和12 cm,主茎节数相应减少3.8节和2.7节,差异达到显著水平,但对主茎分枝数的影响不显著。不同的播期、密度对甜荞麦的产量及产量构成因素均有较为显著的影响,各处理间差异达到显著水平,其中,产量最高的为A₁B₄处理,其产量为3997.55 kg/hm²,比产量最低的A₂B₁处理增产134.25%;A₁B₃、A₁B₄、A₂B₄处理的产量分别为3970.25、3997.55、3970.20 kg/hm²,是本试验中较高的产量,可见,105万/hm²~135万/hm²的播种密度和适当提早播期（7月底到8月上旬）能获得较高荞麦产量。     

江苏不同熟期粳稻品种的齐穗期和安全播期预测

为明确当前江苏各地不同熟期粳稻品种的安全播期,以江苏的4个熟期类型的5个常规粳稻品种为材料,在江苏连云港(34°83′N)、淮安(33°34′N)、扬州(32°25′N)和苏州(31°18′N)等4地,进行自5月10日起每10天1期,共8个播期的播种试验,得出各播期的相应齐穗期。以齐穗期温光预测模型y=a＋b₁x₁＋b₂x₂拟合其实得的播期与齐穗期资料。用该模型拟合4个试验点、5个供试品种计20组数据,得出20个预测式,其拟合度R²在0.9927~0.9998之间,均达极显著水平。用各试点所在地近25年各年粳稻品种安全齐穗期及逐日平均温度,依齐穗期光温模型预测式经多次迭代推得各年的安全播期,进而求得90%保证率的安全播期并作各地生产应用分析。在江苏淮北的北部,麦稻两熟田水稻的可播栽始期为6月15日,中熟中粳的安全播期为6月21日,此类品种可用于该地直播;其他各熟期类型品种安全播期均早于当地可播栽始期,故不能用于直播。在淮北南部稻麦两熟田的可播栽始期为6月12日左右,中熟中粳和迟熟中粳的安全播期分别在7月4日和6月22日,此两类品种可用于该地麦茬直播;早熟晚粳安全播期在6月17日、18日,在大面积生产中因接茬时间过紧应慎用于麦茬直播;中熟晚粳的安全播期为6月8日,不可用于直播。在苏中南部,水稻可播栽始期为6月8至11日,中熟中粳、迟熟中粳、早熟晚粳类型两品种的安全播期分别在7月12日、3日、6月25日和28日,可用于该地直播;中熟晚粳的安全播期为6月11日,用于直播接茬时间太紧,不可应用。在苏南,水稻的可播栽始期为6月5日,供试4熟期类型品种的安全播期分别为7月18日、13日、9日至10日和7月3日,仅考虑安全齐穗各熟期类型品种均可用于麦茬直播,但因中粳类型品种直播稻生育期过短、产量不高,不宜应用。     

Field‐grown Cotton Exhibits Seasonal Variation in Photosynthetic Heat Tolerance without Exposure to Heat‐stress or Water‐deficit Conditions

Thermotolerance acclimation of photosystem II to heat and drought is well documented, but studies demonstrating developmental impacts on heat tolerance in field‐grown plants are limited. Consequently, climatic variables, estimated canopy temperature, predawn leaf water potential (Ψ_PD), and the temperature responses of maximum quantum yield of photosystem II (F_v/F_m), variable fluorescence (F_v/F₀), quantum yield of electron transport (φ_Eο) and efficiency of PSI electron acceptor reduction (REο/ABS) were characterized for Gossypium hirsutum at three sample times during the growing season (21 June, 2 July and 18 July 2013) under well‐watered conditions. The temperature decreasing a given photosynthetic parameter 15% from the optimum is referred to as T₁₅ and served as a standardized measure of heat tolerance. Ambient and estimated canopy temperatures were well within the optimal range for cotton throughout the sample period, and leaves were verified well watered using Ψ_PD measurements. However, T₁₅ varied with sample date (highest on July 2 for all parameters), being 2 °C (F_v/F₀) to 5.5 °C (φ_Eο) higher on July 2 relative to June 21, despite optimal temperature conditions and predawn leaf water potential on all sample dates. These findings suggest that even under optimum temperature conditions and water availability, heat tolerance could be influenced by plant developmental stage.