Estimating yields of salt- and water-stressed forages with remote sensing in the visible and near infrared

In arid irrigated regions, the proportion of crop production under deficit irrigation with poorer quality water is increasing as demand for fresh water soars and efforts to prevent saline water table development occur. Remote sensing technology to quantify salinity and water stress effects on forage yield can be an important tool to address yield loss potential when deficit irrigating with poor water quality. Two important forages, alfalfa (Medicago sativa L.) and tall wheatgrass (Agropyron elongatum L.), were grown in a volumetric lysimeter facility where rootzone salinity and water content were varied and monitored. Ground-based hyperspectral canopy reflectance in the visible and near infrared (NIR) were related to forage yields from a broad range of salinity and water stress conditions. Canopy reflectance spectra were obtained in the 350- to 1000-nm region from two viewing angles (nadir view, 45 degrees from nadir). Nadir view vegetation indices (VI) were not as strongly correlated with leaf area index changes attributed to water and salinity stress treatments for both alfalfa and wheatgrass. From a list of 71 VIs, two were selected for a multiple linear-regression model that estimated yield under varying salinity and water stress conditions. With data obtained during the second harvest of a three-harvest 100-d growing period, regression coefficients for each crop were developed and then used with the model to estimate fresh weights for preceding and succeeding harvests during the same 100-d interval. The model accounted for 72% of the variation in yields in wheatgrass and 94% in yields of alfalfa within the same salinity and water stress treatment period. The model successfully predicted yield in three out of four cases when applied to the first and third harvest yields. Correlations between indices and yield increased as canopy development progressed. Growth reductions attributed to simultaneous salinity and water stress were well characterized, but the corrections for effects of varying tissue nitrogen (N) and very low leaf area index (LAI) are necessary.     

Enhancing the Ability of a Soil Moisture‐based Index for Agricultural Drought Monitoring by Incorporating Root Distribution

Agricultural drought differs from meteorological, hydrological, and socioeconomic drought, being closely related to soil water availability in the root zone, specifically for crop and crop growth stage. In previous studies, several soil moisture indices (e.g., the soil moisture index, soil water deficit index) based on soil water availability have been developed for agricultural drought monitoring. However, when developing these indices, it was generally assumed that soil water availability to crops was equal throughout the root zone, and the effects of root distribution and crop growth stage on soil water uptake were ignored. This article aims to incorporate root distribution into a soil moisture‐based index and to evaluate the performance of the improved soil moisture index for agricultural drought monitoring. The Huang‐Huai‐Hai Plain of China was used as the study area. Overall, soil moisture indices were significantly correlated with the crop moisture index (CMI), and the improved root‐weighted soil moisture index (RSMI) was more closely related to the CMI than averaged soil moisture indices. The RSMI correctly identified most of the observed drought events and performed well in the detection of drought levels. Furthermore, the RSMI had a better performance than averaged soil moisture indices when compared to crop yield. In conclusion, soil moisture indices could improve agricultural drought monitoring by incorporating root distribution.     

Analysis of irrigation systems using sustainability-related criteria

Sustainable agricultural development as a desired goal in irrigation management is a result of recent public awareness of the scarcity of water for food production. In order to incorporate sustainability-related criteria in the analysis of irrigation systems, the present study aims at introducing environmental indices that represent irrigation water conservation and satisfactory production and income for farmers under stress conditions. An experiment was conducted in Chania, Greece, during the irrigation periods of 1989 and 1990. The irrigation water delivered to 40 experimental plots and the relevant soil moisture content at the root zone were recorded. The data, collected in real time, were used for the calculation of the corresponding environmental indices. The variation of indices in time and space was high, and demonstrated that up to 13% of water was delivered to crops, 82% was yield loss, and 84% was economic return. The study indicated that environmental indices could be easily computed by means of routinely collected data, and could also be incorporated into decision-making approaches, such as compromise programming, in order to develop policies for irrigation water allocation.     

PREDICTIVE ASSESSMENT OF SEVERITY OF AGRICULTURAL DROUGHTS BASED ON AGRO-CLIMATIC FACTORS1

ABSTRACT: Past historical evidence indicates that droughts have had great impacts on human life. Drought (or scarcity of water) is assessed based on two key factors, namely, the estimated water demand, and the expected water supply. The formulation of these key factors for a region largely depends on the agro-climatic and economic conditions. Consideration of one such key factor is the relationship between the crop yield and water deficit in the assessment and prediction of agricultural droughts. The varying nature of this relationship from crop to crop adds to the complexity of agricultural drought analysis. To overcome this difficulty in analyzing agricultural droughts of a region, it is adequate to consider and place emphasis on a single crop (i.e., an index crop) grown homogeneously over the major area of the region. From one year to another year, the pattern of water requirement during the growing season of an index crop is rather stationary, and the water supply in arid and semi-arid area is mainly from seasonal random precipitation. In a region, grain yield of the index crop and, in turn, assessment of the severity of drought can reasonably be predicted as a function of the time of crop sowing and the distribution of rainfall, provided that temporal and spatial effects of other contributing factors (crop variety, soil fertility status, crop disease, pest control, cultivation practices etc.) on grain yield are considered to be uniformly distributed (i.e., stable). A predictive method of assessing agricultural droughts in an arid area of western India is presented. The major crop (Pearl Millet) of this region is grown from. July through September. The formulation of the proposed predictive method inherently implies that the grain yield of the main crop is a reliable indicator of agricultural drought. In the development of this predictive relationship (i.e., a regression type model) a number of potential yet simple variables affecting the grain yield in the region were investigated. The soil moisture index, although generally considered significant compared to the simple variables, has been found to account for insignificant variation in the grain yield. Results of our investigations suggest that it would be advisable to exclude the soil moisture index variable from the model. The proposed regression model can be used in the prediction of grain yield of the main crop several months ahead of crop harvesting operations and, in turn, the assessment of agricultural drought severity as mild, moderate, or severe. Such an assessment is expected to be helpful to planners for arranging appropriate measures to effectively combat agricultural drought situations.     

Assessment of Water Availability and Scarcity Based on Hydrologic Components in an Irrigated Agricultural Watershed Using SWAT

This study assesses the water availability and the water scarcity based on the hydrologic behavior under different weather conditions and crop coverages in an irrigated agricultural area of Rincon Valley in New Mexico using the SWAT (Soil and Water Assessment Tool) model. Two spatial crop coverages included normal (2008) and dry (2011) years with 14 different crop sets for each year. The SWAT was applied to generate the five essential indicators (surface flow, evapotranspiration, soil water, groundwater recharge, and irrigation water) to evaluate the integrated water availability based on hydrologic response units (HRUs) along with the Arrey Canal to supply irrigation water in the crop areas. The water availability index scores (0–1 range with 1 being the most available and 0 the least available) of alfalfa, corn, cotton, and pecans were 0.21, 0.56, 0.91, and 0.20, respectively, in the normal year and 0.16, 0.78, 0.88, and 0.24, respectively, in the dry year. In the dry year, water scarcity values were high in mostly alfalfa areas, whereas cotton areas have mostly no stress with good water availability. The major water users of crops, ranked in order, were alfalfa, pecans, cotton, and corn. During the dry year, water availability showed to be balanced in terms of water supply and demand by controlling crop patterns from reducing alfalfa acreage by 12% and increasing cotton acreage by 13%.     

NEW METHODS OF MODELING WATER AVAILABILITY FOR AGRICULTURE UNDER CLIMATE CHANGE: THE U.S. CORNBELT1

ABSTRACT: This paper reports on new methods of linking climate change scenarios with hydrologic, agricultural an water planning models to study future water availability for agriculture, an essential element of sustainability. The study is based on the integration of models of water supply and demand, and of crop growth and irrigation management. Consistent modeling assumptions, available databases, and scenario simulations are used to capture a range of possible future conditions. The linked models include WATBAL for water supply; CERES, SOYGRO, and CROPWAT for crop and irrigation modeling; and WEAP for water demand forecasting, planning and evaluation. These models are applied to the U.S. Cornbelt using forecasts of climate change, agricultural production, population and GDP growth. Results suggest that, at least in the near term, the relative abundance of water for agriculture can be maintained under climate change conditions. However, increased water demands from urban growth, increases in reservoir evaporation and increases in crop consumptive use must be accommodated by timely improvements in crop, irrigation and drainage technology, water management, and institutions. These improvements are likely to require substantial resources and expertise. In the highly irrigated basins of the region, irrigation demand greatly exceeds industrial and municipal demands. When improvements in irrigation efficiency are tested, these basins respond by reducing demand and lessening environmental stress with an improvement in system reliability, effects particularly evident under a high technology scenario. Rain-fed lands in the Cornbelt are not forced to invest in irrigation, but there is some concern about increased water-logging during the spring and consequent required increased investment in agricultural drainage. One major water region in the Cornbelt also provides a useful caveat: change will not necessarily be continuous and monotonic. Under one GCM scenario for the 2010s, the region shows a significant decrease in system reliability, while the scenario for the 2020s shows an increase.     

Assessing drought-related ecological risk in the Florida Everglades

In the winter-spring of 2001, South Florida experienced one of the worst droughts in its recorded history. Out of a myriad of ecological concerns identified during this time, the potential for catastrophic peat fire and negative impacts to wading bird reproduction emerged as critical issues. Water managers attempted to strike a balance between the environment and protection of water supplies for agriculture and urban interests. It became evident, however, that a broad-scale, integrated way to portray and prioritise ecological stress was lacking in the Florida Everglades, despite this being considered a necessary tool for addressing issues of environmental protection. In order to provide a framework for evaluating various water management operations using real-time information, we developed GIS-based indices of peat-fire risk and wading bird habitat suitability. These indices, based on real physical, chemical, and biological data, describe two ecological conditions that help define the physical and biological integrity of the Everglades. In addition to providing continuous, updated assessments throughout the drought period, we incorporated predictive models of water levels to evaluate how various water management alternatives might exacerbate or alleviate ecological stress during this time.     

IMPROVING IRRIGATION RETURN FLOW QUALITY WITH A WATER RENTAL MARKET1

ABSTRACT: Current policies for correcting the problem of irrigation return flow pollution tend to attack the symptoms of the problem, rather than its cause. The present institutional arrangement for allocating irrigation water is seen as the source of the problem. This paper examines the water quality benefits of altering the institutional arrangement to allow for irrigation water transfers through a rental market. It is conceptualized that by creating a water rental market an opportunity cost would be associated with the use of irrigation water such that profit maximizing farmers would be induced to use his water supply more efficiently and rent the surplus to other irrigators, thus reducing return flow pollution. It is shown that a water rental market could increase water quality in the Yakima River in southcentral Washington by 31 percent as well as increase farm incomes and crop production.     

VARIABILITY OF SOIL WATER PROPERTIES AND CROP YIELD IN A SLOPED WATERSHED1

ABSTRACT: Spatial distribution of soil and water properties and the correlations between them and crop yield were determined for a natural rainfall environment. Hydraulic conductivity, soil texture, water retention, and soil-water flux were variables used to investigate their relationship to crop yield using multiple regression techniques. Variations in crop yields on a watershed with a 3 to 4 percent slope and moderately erosive soils were related to soil-water characteristics and soil properties along slope and with depth. Climatic conditions to sustain crop growth and yield ranged from inadequate soil water in 1983 to adequate soil water in 1984. Crop yield was predicted with models using both available and measured soil-water content. Available water content provided a better model for the prediction of water yield and does not require field measurements of actual soil-water content. Soil water holding capacity was more significant for predicting crop yield in soils with moderate to high silt content than infiltrability of water into the soil.     

Identifying and Evaluating a Suitable Index for Agricultural Drought Monitoring in the Texas High Plains

Drought is a complex and highly destructive natural phenomenon that affects portions of the United States almost every year, and severe water deficiencies can often become catastrophic for agricultural production. Evapotranspiration (ET) by crops is an important component in the agricultural water budget; thus, it is advantageous to include ET in agricultural drought monitoring. The main objectives of this study were to (1) conduct a literature review of drought indices with a focus to identify a simple but simultaneously adequate drought index for monitoring agricultural drought in a semiarid region and (2) using the identified drought index method, develop and evaluate time series of that drought index for the Texas High Plains. Based on the literature review, the Standardized Precipitation‐Evapotranspiration Index (SPEI) was found to satisfy identified constraints for assessing agricultural drought. However, the SPEI was revised by replacing reference ET with potential crop ET to better represent actual water demand. Data from the Texas High Plains Evapotranspiration network was used to calculate SPEIs for the major irrigated crops. Trends and magnitudes of crop‐specific, time‐series SPEIs followed crop water demand patterns for summer crops. Such an observation suggests that a modified SPEI is an appropriate index to monitor agricultural drought for summer crops, but it was found to not account for soil water stored during the summer fallow period for winter wheat.     

Alternate wet and dry irrigation technology as a sustainable water management and disease vector control tool

Rising population and demands for rice as a staple food have created severe stress on freshwater availability for paddy cultivation. The literature suggests that conventional irrigation techniques are inadequate to overcome the water constraints arising from drought and extreme weather conditions. In the past few decades, there is an upsurge of scientific exploration of agricultural techniques in reinventing traditional methods of irrigation. Recently, alternate wet and dry irrigation (AWDI) method has shown great promise regarding profitable rice cultivation with limited water supply. The AWDI method is a trending water management system, which inundates rice fields with intermittent wet conditions followed by a dry period. This not only ensures adequate water supply but increases crop yield and water productivity index (WPI). The AWDI also helps in reducing parasitic mosquito population in the rice fields by minimizing the field flooding period and curtailing a major part of their life cycles. This review proposes a novel approach of emphasizing AWDI method as an important agricultural tool for supplementing rice fields with limited freshwater, increasing crop yield, and monitoring parasitic mosquito populations. The major objective of this study is to report the state-of-the-art scenario of AWDI method, critically analyze the research gaps related to conventional methods of irrigation and appreciate the futuristic long-term benefits of AWDI method. Literature survey was performed using search engines like Scopus, PubMed, Google Scholar, Research Gate, Science Direct, and Google Scholar. Comprehensive appraisal of resources (both offline and online) and critical evaluation of AWDI technicalities revealed that the AWDI reduced water usage by 45%, enhanced crop yield and improved WPI in paddy fields in the Asian sub-continent. The AWDI also curtailed the propagation of lethal mosquito species (Cx. tritaenorhynchus, Cx. vishnui, and Cx pseudovishnui) in rice fields. Therefore, the current study endorses AWDI as a promising substitute of conventional irrigation and a novel approach towards fulfilling water constraints that may be practiced anywhere in the world.     

农作物对微囊藻毒素耐受性差异的研究进展

微囊藻毒素进入农田后会对农产品安全产生潜在的危胁,并可能通过食物链危害人类健康。已有的众多研究结果表明,不同农作物对微囊藻毒素的耐受性存在较大差异,而这一差异为农业生产上合理规避微囊藻毒素污染风险提供了一种可能。本文就农作物对微囊藻毒素耐受性差异这一问题进行了综述,并在此基础上提出了今后的研究方向。     

MODELING HYDROLOGIC IMPACT OF WITHDRAWING THE GREAT LAKES WATER FOR AGRICULTURAL IRRIGATION1

ABSTRACT: Growing interest in agricultural irrigation in the Great Lakes basin presents an increasing competition to other uses of Great Lakes water. This paper, through a case study of the Mud Creek Irrigation District in the Saginaw Bay basin, Michigan, evaluates the potential hydrologic effects of withdrawing water for agricultural irrigation to the Great Lakes. Crop growth simulation models for corn, soybeans, dry beans, and the FAO Penman method were used to estimate the difference in evapotranspiration rates between irrigated and nonirrigated identical crops, based on climate, soil, and management data. The simulated results indicate that an additional 70–120 mm of water would be evapotranspirated during the growing season from irrigated crop fields as compared to nonirrigated identical plantings. Dependent upon the magnitude of irrigation expansion, an equivalent of about 1 to 5 mm of water from Lakes Huron-Michigan could be lost to the atmosphere. If agricultural irrigation further expands in the entire Great Lakes basin, the aggregated potential of water loss to the atmosphere through ET from all five Great Lakes would be even greater.     

Assessing the Effectiveness of Winter Cover Crops for Controlling Agricultural Nutrient Losses

A nutrient loss reduction strategy is necessary to guide the efforts of improving water quality downstream of an agricultural watershed. In this study, the effectiveness of two winter cover crops, namely cereal rye and annual ryegrass, is explored as a loss reduction strategy in a watershed that ultimately drains into a water supply reservoir. Using a coupled optimization-watershed model, optimal placements of the cover crops were identified that would result in the tradeoffs between nitrate-N losses reduction and adoption levels. Analysis of the 10%, 25%, 50%, and 75% adoption levels extracted from the optimal tradeoffs showed that the cover crop placements would provide annual nitrate-N loss reductions of 3.0%–3.7%, 7.8%–8.8%, 15%–17.5%, and 20.9%–24.3%, respectively. In addition, for the same adoption levels (i.e., 10%–75%), sediment (1.8%–17.7%), and total phosphorus losses (0.8%–8.6%) could be achieved. Results also indicate that implementing each cover crop on all croplands of the watershed could cause annual water yield reduction of at least 4.8%, with greater than 28% in the months of October and November. This could potentially be detrimental to the storage volume of the downstream reservoir, especially in drought years, if cover crops are adopted in most of the reservoir's drainage area. Evaluating water yield impacts, particularly in periods of low flows, is thus critical if cover crops are to be considered as best management practices in water supply watersheds.     

An Innovative Index for Evaluating Water Quality in Streams

A water quality index expressed as a single number is developed to describe overall water quality conditions using multiple water quality variables. The index consists of water quality variables: dissolved oxygen, specific conductivity, turbidity, total phosphorus, and fecal coliform. The objectives of this study were to describe the preexisting indices and to define a new water quality index that has advantages over these indices. The new index was applied to the Big Lost River Watershed in Idaho, and the results gave a quantitative picture for the water quality situation. If the new water quality index for the impaired water is less than a certain number, remediation—likely in the form of total maximum daily loads or changing the management practices—may be needed. The index can be used to assess water quality for general beneficial uses. Nevertheless, the index cannot be used in making regulatory decisions, indicate water quality for specific beneficial uses, or indicate contamination from trace metals, organic contaminants, and toxic substances.     

ASSESSMENT OF A STRESSED MACROINVERTEBRATE COMMUNITY1

ABSTRACT: The tolerance of a community to stress is dependent on the nature of the receiving system, and the nature and degree to which the stress is applied. However, where the stress is sufficient to cause a response, either the numbers of organisms or taxa, or both, will be affected. A simple method of ordination was used to assess the effects of stressed conditions on macroinvertebrate communities in the New River, Virginia, and compared to the diversity index (d) of Wilhm and Dorris. A principal of the method was that standing crop, as reflected by the total numbers of specimens and taxa collected, served as an indicator of community health. The most healthy situation in the study was defined as the one in which standing crop and niche partitioning were greatest.     

Assessment of vegetation stress using reflectance or fluorescence measurements

Current methods for large-scale vegetation monitoring rely on multispectral remote sensing, which has serious limitation for the detection of vegetation stress. To contribute to the establishment of a generalized spectral approach for vegetation stress detection, this study compares the ability of high-spectral-resolution reflectance (R) and fluorescence (F) foliar measurements to detect vegetation changes associated with common environmental factors affecting plant growth and productivity. To obtain a spectral dataset from a broad range of species and stress conditions, plant material from three experiments was examined, including (i) corn, nitrogen (N) deficiency/excess; (ii) soybean, elevated carbon dioxide, and ozone levels; and (iii) red maple, augmented ultraviolet irradiation. Fluorescence and R spectra (400-800 nm) were measured on the same foliar samples in conjunction with photosynthetic pigments, carbon, and N content. For separation of a wide range of treatment levels, hyperspectral (5-10 nm) R indices were superior compared with F or broadband R indices, with the derivative parameters providing optimal results. For the detection of changes in vegetation physiology, hyperspectral indices can provide a significant improvement over broadband indices. The relationship of treatment levels to R was linear, whereas that to F was curvilinear. Using reflectance measurements, it was not possible to identify the unstressed vegetation condition, which was accomplished in all three experiments using F indices. Large-scale monitoring of vegetation condition and the detection of vegetation stress could be improved by using hyperspectral R and F information, a possible strategy for future remote sensing missions.     

SOIL MOISTURE SENSING WITH AIRCRAFT OBSERVATIONS OF THE DIURNAL RANGE OF SURFACE TEMPERATURE1

ABSTRACT: Aircraft Observations of the surface temperature were made by measurements of the thermal emission in the 8-14 μm band over agricultural fields around Phoenix, Arizona. The diuranal range of these surface temperature measurnments were well correlated with the ground measurment of soil moisture in the 0-2 cm layer. The surface temperature indicating no moisture stress. These results indicate that for clear atmospheric conditions remoteley sensed sufrace temperatures can be a reliable indicator of soil moisture conditions and crop status.     

Runoff Curve Numbers for Small Grain Under German Cropping Conditions

The Curve Number (CN) method is used in many models to predict surface runoff depth and transport of dissolved agrochemicals. CNs were determined on 70 small plots at 8 sites and different crop stages with artificial rain. The measured CNs deviated greatly from the commonly used CNs in most cases. For growing crops, CN correlated closely with cover, regardless of whether the crop was spring or fall barley or rape. The CNs measured with artificial rain agreed well with CNs measured on larger plots with natural rain. A new table was developed that accounts for the resulting seasonal changes in CNs of different small grain crops. The use of this table will greatly improve runoff predictions under German cropping conditions. Predictions will be poor between harvest and subsequent plowing, because of the fast and unpredictable changes in CNs during this generally short period (average CN: 75; standard deviation: 15). On a very stony site, CNs were much lower than would be expected for the hydrological soil group A. If, however, stone cover (23–35%) was included in total cover, the CNs fell into the range of the regression developed for crop cover. In cases where stones are not embedded into a surface seal, but rather protect the soil as would a crop or mulch cover, they can similarly reduce runoff.     

The 2007‐2009 Drought in Athens,Georgia, United States: A Climatological Analysis and an Assessment of Future Water Availability1

Campana, Pete, John Knox, Andrew Grundstein, and John Dowd, 2012. The 2007‐2009 Drought in Athens, Georgia, United States: A Climatological Analysis and an Assessment of Future Water Availability. Journal of the American Water Resources Association (JAWRA) 48(2): 379‐390. DOI: 10.1111/j.1752‐1688.2011.00619.x Abstract: Population growth and development in many regions of the world increase the demand for water and vulnerability to water shortages. Our research provides a case study of how population growth can augment the severity of a drought. During 2007‐2009, a drought event that caused extreme societal impacts occurred in the Athens, Georgia region (defined as Clarke, Barrow, Oconee, and Jackson counties). An examination of drought indices and precipitation records indicates that conditions were severe, but not worse than during the 1925‐1927, 1954‐1956, and 1985‐1987 drought events. A drought of similar length to the 2007‐2009 drought would be expected to occur approximately every 25 years. Streamflow analysis shows that discharge levels in area streams were at a record low during 2007 before water restrictions were implemented, because of greater water usage caused by recent population increases. These population increases, combined with a lack of water conservation, led to severe water shortages in the Athens region during late 2007. Only after per capita usage decreased did water resources last despite continuing drought conditions through 2009. Retaining mitigation strategies and withdrawal levels such as seen during the height of the drought will be an essential strategy to prevent water shortages during future extreme drought events. The key mitigation strategy, independent local action to restrict water use in advance of state‐level restrictions, is now prohibited by Georgia State Law.