Shu Geng

A simple method for generating daily rainfall data

Abstract In recent years, agricultural scientists have developed considerable interest in modeling and simulation of rainfall as new ways of analyzing rainfall data and assessing its impact on agriculture. Among the proposed methods, a combination of Markov chain and gamma distribution function is recognized as a simple approach and is demonstrated to be effective in generating daily rainfall data for many environments. Unfortunately, this method requires that many years of daily weather records be available for estimating the model parameters. Thus the availability of the weather data limits the applicability of the simulation method. When these model parameters are evaluated over time and at different places, however, certain general characteristics are revealed. First, the transitional probability of a wet day followed by a wet day tends to be greater but parallel to the transitional probability of a dry day followed by a wet day. This phenomenon leads to a linear relationship of the transitional probabilities to the fraction of wet days per month. Second, the beta parameter in a gamma distribution function, which is used to describe the amount of rainfall, is closely related to the amount of rain per wet day owing to the positive skewness of the rainfall distribution. Based on these relationships, a simple method is introduced, by which model parameters can be estimated from monthly summaries instead of from daily values. The suggested method, therefore, provides a convenient vehicle for applying weather simulation models to areas in which its use had been impossible because of the unavailability of long series of daily weather data.

Marginal Land‐based Biomass Energy Production in China

Fast economic development in China has resulted in a significant increase in energy demand. Coal accounts for 70% of Chinas primary energy consumption and its combustion has caused many environmental and health problems. Energy security and environmental protection requirements are the main drivers for renewable energy development in China. Small farmland and food security make bioenergy derived from corn or sugarcane unacceptable to China: the focus should be on generating bioenergy from ligno-cellulosic feedstock sources. As China cannot afford biomass energy production from its croplands, marginal lands may play an important role in biomass energy production. Although on a small scale, marginal land has already been used for various purposes. It is estimated that some 45 million hm(2) of marginal land could be brought into high potential biomass energy production. For the success of such an initiative, it will likely be necessary to develop multipurpose plants. A case study, carried out on marginal land in Ningnan County, Sichuan Province with per capita cropland of 0.07 ha, indicated that some 380,000 tons of dry biomass could be produced each year from annual pruning of mulberry trees. This study supports the feasibility of producing large quantities of biomass from marginal land sources.

Comparison of four crops for alcohol yield

Abstract does not appear. First page follows. Introduction An intensive investigation of the phloem of Vitis vinifera L., the grapevine, was previously reported in this Journal (Esau, 1948a).3 That study was centered on the development of the tissue, especially with reference to seasonal changes. It served as a background for the subsequent study of the effects of Pierce’s disease virus on grapevine (Esau, 1948b). In connection with the earlier study, samples of bark were collected from thirty species of Vitis, other than V. vinifera, growing in the experimental vineyard of the Department of Viticulture at Davis. The first part of the present paper reports on a survey of phloem of these species. After an electron microscope was installed on the Davis campus, the ultrastructure of phloem tissue became one of the important research projects in the Department of Botany at Davis. Vitis phloem was included in the studies and a considerable amount of information on this tissue was obtained during 1960-1962. This information constitutes the major part of the present paper. Methodology in submicroscopic research is still new and is changing rapidly. The ultrastructural data reported here are based on relatively early techniques. Nevertheless, these data expand the understanding of the structure and seasonal changes in the conducting element, the sieve element, and further differentiate this element from the associated nucleate cells. The present study has confirmed the interpretation of some previously recognized features but has also introduced new problems. Early ultrastructural investigations on plant material have emphasized meristematic or relatively undifferentiated parenchyma cells, especially those derived from root tips (see, for example, (Whaley et al., 1960), and the submicroscopic structure of such cells is relatively well understood. Interpretation of the fine structure of mature and highly specialized cells must therefore be made by comparison with the less-differentiated cells. Part of the present paper deals with the sieve element in the root tip, which was studied against the background of information on more or less meristematic parenchyma cells of the same parts of the root. These background observations are reported in full because they help to single out the specific characteristics of the sieve element. The literature pertinent to the subject matter is not reviewed under a separate heading. Certain references are mentioned in connection with individual observations in the main text, but the comprehensive comparison of data obtained with those reported in the literature appears only in the discussion. The specific terminology concerning the phloem tissue is explained in the previous Hilgardia article on Vitis phloem (Esau, 1948a), and that serving for the description of ultrastructural details has been reviewed by (Esau and Cheadle (1965)).

BIOCHEMICAL FEATURES AND BIOETHANOL PRODUCTION OF MICROALGAE FROM COASTAL WATERS OF PEARL RIVER DELTA

This study describes identification, cultivation, monitoring of carbohydrate accumulation and bioethanol production from microalgal strains from the coastal waters of Pearl River Delta. Eighteen identified strains belong to the families Chlorellaceae, Scotiellocystoidaceae, Neochloridaceae, Selenastraceae and Scenedesmaceae. Of isolated strains Mychonastes afer PKUAC 9 and Scenedesmus abundans PKUAC 12 were selected for further biomass and ethanol production analysis. Comparison of three cultivation modes (stationary, shaken and aerated) resulted in the highest biomass productivity obtained for aerated cultures that yielded 0.09 g and 0.11 g dry weight per day per litre of medium for M. afer PKUAC 9 and S. abundans PKUAC 12, respectively. Carbohydrate accumulation monitored by FTIR showed that early stationary phase is optimal for biomass harvest. Microalgal biomass was successfully used as a carbohydrate feedstock for fermentative bioethanol production. S. abundans PKUAC 12 was superior feedstock for bioethanol production when pre-treated with the combination of dilute acid treatment and cellulase.

Spectral prediction of Phytophthora infestans infection on tomatoes using artificial neural network (ANN)

Late blight (LB) is one of the most aggressive tomato diseases in California. Accurately detecting the disease will increase the efficiency of properly controlling the disease infestations to ensure the crop production. In this study, we developed a method to spectrally predict late blight infections on tomatoes based on artificial neural network (ANN). The ANN was designed as a back‐propagation (BP) neural network that used gradient‐descent learning algorithm. Through comparing different network structures, we selected a 3‐25‐9‐1 network structure. Two experimental samples, from field experiments and remotely sensed image data sets, were used to train the ANN to predict healthy and diseased tomato canopies with various infection stages for any given spectral wavelength (µm) intervals. Results of discrete data indicated different levels of disease infestations. The correlation coefficients of prediction values and observed data were 0.99 and 0.82 for field data and remote sensing image data, respectively. In addition, we predicted the field data based on the remote sensing image data and predicted the remote sensing image data with field data using the same network structure, and the results showed that the coefficient of determination was 0.62 and 0.66, respectively. Our study suggested an ANN with back‐propagation training could be used in spectral prediction in the study.

Quality-Control Programs for Seedborne Pathogens

Presentation de deux methodes de controle de qualite, pour des evaluations directes ou indirectes, pour la determination de la taille des echantillons necessaire permettant la detection des faibles niveaux de contamination avec une probabilite de succes garantie

Effects of Temperature and Water Vapor Pressure on Conidial Germination and Lesion Expansion of Sphaerotheca macularis f. sp. fragariae

Conidial germination in vitro and foliar lesion expansion were studied for Sphaerotheca macularis f. sp. fragariae. Detached strawberry (Fragaria × ananassa) leaves were inoculated, then held in controlled environments of constant temperatures (4 to 36°C) and relative humidity (RH, 32 to 100%) representing the range of these variables observed under California commercial production conditions. Percent germination and lesion expansion rate were determined by destructive subsampling over time. Conidia germinated at all temperatures by 6 h and reached a maximum by 48 h, with the optimum near 20°C. Lesions were marked with the aid of a microscope and measured by computer-assisted image-analysis to determine expansion rate. Maximal rates occurred at 25°C. Several growth models were fit to the expansion rate data with high significance. Predicted optima from these models ranged from 22 to 27°C and/or 17 to 27 mm Hg VPwater@100%RH. Neither RH, partial vapor pressure of water (VPwater), nor vapor pressure deficit (VPD) correlated with lesion expansion rate, adding to studies minimizing the importance of RH and VPD as determinants of asexual phase powdery mildew growth other than specifically at spore germination.

A Sustainable Agro-ecological Solution to Water Shortage in the North China Plain (Huabei Plain)

A highly seasonal rainfall pattern in the agriculturally productive region of Huabei Plain has been widely considered in China as a handicap to maximizing agricultural production. Enhancing this perception is the traditional policy of achieving provincial or regional self-sufficiency in grain production, which underlies Chinas production quotas. The Chinese government has decided to overcome this perceived handicap in order to meet the increasing water demands of urban populations and to achieving its grain quotas by constructing aqueducts to transport about 14 2 10 9 m 3 of water from the Dan Jiang Reservoir into the Huabei Plain. However, this engineering construction solution threatens the long-term market competitiveness of the region by driving up the cost of water relative to the value of the product, by taking too long to complete and by being unproven in its effectiveness. This solution also threatens the existing ecosystem by interfering with the natural hydrology, and it risks exacerbating the ongoing groundwater overdrafts that are contributing to the formation of numerous sinkholes and ground surface cracks in the region, as well as to the intrusion of sea water. A more certain, ecologically sound solution can be found in alternative agricultural practices and cropping systems. Reducing the winter wheat production by a relatively small acreage, combined with the increased use of water-saving irrigation systems, can more than replace the effectively usable 10 2 10 9 m 3 of water that the engineering construction project would transport via aqueducts. The recommended alternative cropping system would solve the water shortage problem immediately. This alternative would enable the government to allocate funds where they are more needed, such as to the clean-up of extensively polluted rivers and to ecological restoration, which bears on the sustainability of agriculture and food supply in China.

Potential for using Lecanicillium lecanii for suppression of strawberry powdery mildew

Augmenting native populations of the hyperparasite Lecanicillium lecanii suppressed powdery mildew of strawberry, caused by Sphaerotheca macularis f. sp. fragariae in California field trials. Repeated sprays significantly reduced disease compared to the untreated controls for periods of the fruit production season, suggesting possible use as a partial, but not total disease control strategy.

Impact of Climate and Land-Use Changes on Water Security for Agriculture in Northern China

Abstract North China is the most important food basket of China, where the majority of wheat and corn are produced. Most crops grown in North China are irrigated, thus water security is food security. Since the 1980s, drying has been frequently observed, as shown by a reduction in precipitation, cutoff in riverflow, and shrinkage of lakes. This increase in drying cannot be explained by climate change alone. We propose that intensive land-use in this area in recent decades has had a significant impact. The objectives of the study are to develop a quantitative model of the concurrent processes of climate change and land-use in North China, and to estimate the relative contributions of each on the observed drying. We integrated relevant socioeconomic data, land-use data, and climate data in the model, and carried out a detailed multitemporal (decade, year, day) analysis. Results showed that land-use has greatly changed since 1999. This change is mainly associated with an extremely important 1999 national policy of ?returning farmland and grazing land to forest and grassland?. We found an interesting interaction between climate change and land use policy on riverflow, runoff, and evapotranspiration. During 1970s and 1980s, climate change explained more than 80%, while the land-use change explained only 10% of the riverflow change. The relative contributions were 45 and 45% in the 1980s-1990s and 35 and 55% in the 1990s-2000s respectively for climate change and land-use change. Since the 1990s land-use change has also contributed more to runoff change than climate change. The opposite trend was found for changes in evapotranspiration. Water availability for agriculture in northern China is simultaneously stressed by extensive changes in land-use and rapid climate change. Adaptation of ecological principles, such as the ?returning farmland/grazing land to forest and grassland? policy, and other adjustments of economic developmental strategies can be effective tools to mitigate the water shortage problem in northern China and promote sustainable agricultural and food development.