Assessing the benefit of satellite-based Solar-Induced Chlorophyll Fluorescence in crop yield prediction

Large-scale crop yield prediction is critical for early warning of food insecurity, agricultural supply chain management, and economic market. Satellite-based Solar-Induced Chlorophyll Fluorescence (SIF) products have revealed hot spots of photosynthesis over global croplands, such as in the U.S. Midwest. However, to what extent these satellite-based SIF products can enhance the performance of crop yield prediction when benchmarking against other existing satellite data remains unclear. Here we assessed the benefits of using three satellite-based SIF products in yield prediction for maize and soybean in the U.S. Midwest: gap-filled SIF from Orbiting Carbon Observatory 2 (OCO-2), new SIF retrievals from the TROPOspheric Monitoring Instrument (TROPOMI), and the coarse-resolution SIF retrievals from the Global Ozone Monitoring Experiment-2 (GOME-2). The yield prediction performances of using SIF data were benchmarked with those using satellite-based vegetation indices (VIs), including normalized difference vegetation index (NDVI), enhanced vegetation index (EVI), and near-infrared reflectance of vegetation (NIRv), and land surface temperature (LST). Five machine-learning algorithms were used to build yield prediction models with both remote-sensing-only and climate-remote-sensing-combined variables. We found that high-resolution SIF products from OCO-2 and TROPOMI outperformed coarse-resolution GOME-2 SIF product in crop yield prediction. Using high-resolution SIF products gave the best forward predictions for both maize and soybean yields in 2018, indicating the great potential of using satellite-based high-resolution SIF products for crop yield prediction. However, using currently available high-resolution SIF products did not guarantee consistently better yield prediction performances than using other satellite-based remote sensing variables in all the evaluated cases. The relative performances of using different remote sensing variables in yield prediction depended on crop types (maize or soybean), out-of-sample testing methods (five-fold-cross-validation or forward), and record length of training data. We also found that using NIRv could generally lead to better yield prediction performance than using NDVI, EVI, or LST, and using NIRv could achieve similar or even better yield prediction performance than using OCO-2 or TROPOMI SIF products. We concluded that satellite-based SIF products could be beneficial in crop yield prediction with more high-resolution and good-quality SIF products accumulated in the future.     

Influence of non-photosynthetic pigments on light absorption and quantum yield of photosynthesis in the western equatorial Pacific and the Subarctic North Pacific

Regional variations in the contribution of non-photosynthetic pigments (ā _np^*) to the total light absorption of phytoplankton (ā _ph^*) and its influence on the maximum quantum yield of photosynthesis (φ _m) were investigated. In the western equatorial Pacific, the surface ā _np^* : ā _ph^* ratio was higher in the western warm pool than that in the upwelling region. This difference appears to be attributable to severe nitrate depletion and higher percentage of prokaryotes, which can accumulate very high concentrations of zeaxanthin in the western warm pool. In the subarctic North Pacific, the ā _np^* : ā _ph^* ratio was expected to be higher in the Alaskan Gyre where the thermocline is sharper and iron limitation may possibly be more severe than in the Western Subarctic Gyre. However, the ratio was actually higher in the Western Subarctic Gyre, contradictory to our expectations. This east-west variation appears to be attributable to changes in the taxonomic composition; cyanobacteria were more abundant in the Western Subarctic Gyre. The values of ā _np^* : ā _ph^* and its vertical variations were relatively small in the subarctic North Pacific compared to those in the western equatorial Pacific. These inter-regional variations appear to be attributable to the lower solar radiation intensity, smaller percentage of cyanobacteria, and relatively strong vertical mixing in the subarctic North Pacific. The spatial variations in ā _np^* : ā _ph^* significantly influence φ _m. In comparison with φ _m based on the total light absorption (φ _{m ph}), the values corrected for the contribution of non-photosynthetic pigments (φ _{m ps}) showed an increase in both the western equatorial Pacific and the subarctic North Pacific.     

渭北苹果花期冻害气象指数保险设计

为科学设计渭北苹果花期冻害气象指数保险产品,提供气象指数保险技术参考。研究选取旬邑县作为陕西省渭北地区苹果代表县,利用1991—2020年气象、苹果花期物候、产量等数据,选取苹果花期冻害极端低温和过程累积危害指数作为备选气象指数,采用滑动平均〖CD*2〗灰色预测法分离苹果气象产量。通过气象指数与苹果减产率的相关分析,确定苹果花期冻害气象指数,构建苹果花期冻害气象指数与减产率之间的关系模型。利用苹果单产风险分布特点,选取6种分布模型利用参数分布法进行拟合,并根据Anderson Darling(A D)检验结果和概率密度函数图筛选最优分布。最后根据保险触发值,厘定不同赔付触发条件下的保险纯费率。结果表明：代表县苹果花期冻害过程累积危害气象指数Ts与减产率的相关性显著强于苹果花期冻害极端低温气象指数Tc;Ts与减产率之间存在正向线性关系模型;苹果单产风险分布符合柯西分布;当赔付触发条件对应2%、4%、6%、8%减产率时,旬邑县各乡镇苹果花期冻害气象指数保险产品纯费率区间为0.40%～1.84%。相较传统苹果农业保险产品,苹果花期冻害气象指数保险产品可实现差异化费率,有利于发挥气象指数保险优势。     

土壤渍水胁迫对华北冬小麦籽粒灌浆及干物质分配的影响

利用少雨旱区华北冬麦主产区河北固城站的电动防雨棚,遮去自然降水,通过人工控制灌水形成土壤渍水、高湿、干旱和对照,冬小麦花后通过测定籽粒灌浆进程和地上生物量以及产量构成要素,解析不受阴雨和低温胁迫影响下土壤渍水对冬小麦籽粒灌浆速率及产量形成的胁迫效应。结果表明,随土壤水分的减少,冬小麦灌浆速率降低,灌浆持续日数缩短;灌浆期土壤高湿有增产效应,理论产量增产5.87%,土壤渍水出现减产,理论产量减产1.50%;高湿和渍水的收获指数比对照略有提高,并均高于0.5000;〖JP2〗干旱胁迫下,收获指数比对照低0.1130～0.1633。〖JP〗北方旱区灌溉解除了气候干旱对作物需水胁迫,晴好天气光照充足,日较差大,作物产量提高,土壤水分是影响北方冬小麦挖掘光温生产潜力和提高单产的关键限制因素。研究结果为应对气候变化引起极端降水事件对农业生产的影响,尤其是科学评估旱、涝灾害对北方旱区农作物的影响有一定参考意义。     

A context for ecosystem-based fishery management: Developing concepts of ecosystems and sustainability

Ecosystems have been viewed both as chaotic, untamed nature, and as mechanical systems with predictable equilibrium states. A developing concept of ecosystems as “complex adaptive systems” lies between these extreme concepts, with recognizably patterned but not fully predictable behavior. Sustainability has also been redefined as humans have exploited and often depleted desirable natural resources. Fisheries management desires sustainable yield, but must rethink this concept within the ecosystem context. The most powerful union of “ecosystem” and “sustainability” acknowledges the defining characteristics of complex adaptive systems with the objective of identifying and sustaining healthy relationships within and between ecosystems, economies, and society.     

Fluctuation in Ommastrephe bartrami yield in the North Pacific

The fluctuation in Ommastrephe bartrami yield from 1995 to 2001 in the North Pacific was shown obvious, on which this study was conducted using data of sea surface temperature (SST), chlorophyll-a (chl-a) and statistical production. The study shows that, cool water and low food abundance caused by abnormal Kuroshio resulted in the reduction in abundance of O. bartrami, which was worsened by excessive catch and the unawareness to local fishery resources protection.     

Sediment delivery from hillslopes and the Universal Soil Loss Equation: some perceptions and misconceptions

The Universal Soil Loss Equation (USLE) or the revised USLE (RUSLE) are often used together with sediment delivery ratios in order to predict sediment delivery from hillslopes. In using sediment delivery ratios for this purpose, it is assumed that the sediment delivery ratio for a given hillslope does not vary with the amount of erosion occurring in the upslope area. This assumption is false. There is a perception that hillslope erosion is calculated on the basis that hillslopes are, in effect, simply divided into 22·1 m long segments. This perception fails to recognize the fact the inclusion of the 22·1 m length in the calculation has no physical significance but simply produces a value of 1·0 for the slope length factor when slopes have a length equal to that of the unit plot. There is a perception that the slope length factor is inappropriate because not all the dislodged sediment is discharged. This perception fails to recognize that the USLE and the RUSLE actually predict sediment yield from planar surfaces, not the total amount of soil material dislocated and removed some distance by erosion within an area. The application of the USLE/RUSLE to hillslopes also needs to take into account the fact that runoff may not be generated uniformly over that hillslope. This can be achieved by an equation for the slope length factor that takes account of spatial variations in upslope runoff on soil loss from a segment or grid cell. Several alternatives to the USLE event erosivity index have been proposed in order to predict event erosion better than can be achieved using the EI₃₀ index. Most ignore the consequences of changing the event erosivity index on the values for the soil, crop and soil conservation protection factors because there is a misconception that these factors are independent of one another. Copyright © 2007 John Wiley & Sons, Ltd.     

Variation Character of Grain Yield per Unit Area in Main Grain-producing Area of Northeast China

Based on the surveys and the statistic data during 1980-2003, the variation character of grain yield per unit area in Northeast China and its main factors have been discussed by the methods of statistics and grey correlation analysis. The results show that: 1) the grain yield per unit area has been taking on an increasing trend in the recent 20 years. It increased from 2519.80kg/ha in 1980 to 4216.11kg/ha in 2003, with an increasing rate of 67.32%; 2) the variation of grain yield per unit area is considerably prominent and its range is also very great, with the maximal increase rate of 42.59% and maximal decrease rate of 21.13%, respectively, which are far above the whole Chinese average level; 3) the variation of main crops' yield per unit area is remarkable, which takes on the character that the yield of corn is much higher than that of soybean and rice; and 4) the grey correlation analysis shows that the most important factors impacting the variation of grain yield per unit area are the total power of agricultural machinery, the consumption of chemical fertilizer and effective irrigated area. However, the influence of natural disaster and income level should not be ignored. Effective ways to improve grain yield per unit area are to construct farmland improvement groundwork, reclaim the middle- and low-yield farmland, etc.     

Post‐wildfire changes in suspended sediment rating curves: Sabino Canyon,Arizona

Wildfire has been shown to increase erosion by several orders of magnitude, but knowledge regarding short‐term variations in post‐fire sediment transport processes has been lacking. We present a detailed analysis of the immediate post‐fire sediment dynamics in a semi‐arid basin in the southwestern USA based on suspended sediment rating curves. During June and July 2003, the Aspen Fire in the Coronado National Forest of southern Arizona burned an area of 343 km². Surface water samples were collected in an affected watershed using an event‐based sampling strategy. Sediment rating parameters were determined for individual storm events during the first 18 months after the fire. The highest sediment concentrations were observed immediately after the fire. Through the two subsequent monsoon seasons there was a progressive change in rating parameters related to the preferential removal of fine to coarse sediment. During the corresponding winter seasons, there was a lower supply of sediment from the hillslopes, resulting in a time‐invariant set of sediment rating parameters. A sediment mass‐balance model corroborated the physical interpretations. The temporal variability in the sediment rating parameters demonstrates the importance of storm‐based sampling in areas with intense monsoon activity to characterize post‐fire sediment transport accurately. In particular, recovery of rating parameters depends on the number of high‐intensity rainstorms. These findings can be used to constrain rapid assessment fire‐response models for planning mitigation activities. Copyright © 2006 John Wiley & Sons, Ltd.     

Yield design of dry‐stone masonry retaining structures—Comparisons with analytical,numerical, and experimental data

Over the past few years, there has been a steady increase in the interest in dry‐stone walling not only to preserve existing constructions but also to build new ones. Yet, dry masonry's expansion is slowed down by the lack of scientific knowledge to assess its reliability. This study aims at contributing to the construction of this scientific frame using a simplified model based on yield design and homogenization, which can be directly exploited for engineering purposes. A new analytical expression of the ultimate load is thus established. Then, the validity of the method is assessed by comparisons with limit equilibrium analysis, distinct element method, and field trials. Finally, possible improvements of the model are discussed. Copyright © 2008 John Wiley & Sons, Ltd.