Environmental and agricultural relevance of humic fractions extracted by alkali from soils and natural waters
. Journal of Environmental Quality 2019
, 217-232. Publisher's VersionAbstract
To study the structure and function of soil organic matter, soil scientists have performed alkali extractions for soil humic acid (HA) and fulvic acid (FA) fractions for more than 200 years. Over the last few decades aquatic scientists have used similar fractions of dissolved organic matter, extracted by resin adsorption followed by alkali desorption. Critics have claimed that alkali-extractable fractions are laboratory artifacts, hence unsuitable for studying natural organic matter structure and function in field conditions. In response, this review first addresses specific conceptual concerns about humic fractions. Then we discuss several case studies in which HA and FA were extracted from soils, waters, and organic materials to address meaningful problems across diverse research settings. Specifically, one case study demonstrated the importance of humic substances for understanding transport and bioavailability of persistent organic pollutants. An understanding of metal binding sites in FA and HA proved essential to accurately model metal ion behavior in soil and water. In landscape-based studies, pesticides were preferentially bound to HA, reducing their mobility. Compost maturity and acceptability of other organic waste for land application were well evaluated by properties of HA extracted from these materials. A young humic fraction helped understand N cycling in paddy rice (Oryza sativa L.) soils, leading to improved rice management. The HA and FA fractions accurately represent natural organic matter across multiple environments, source materials, and research objectives. Studying them can help resolve important scientific and practical issues. Copyright © American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America.
Olive tree survival and adaptation to the harsh growing conditions in the arid desert environment of the Negev Highlands, Southern Israel
. Israel Journal of Plant Sciences 2019
, 147-152. Publisher's VersionAbstract
Twenty-three olive trees were found to grow in traditional orchard sites in the Negev Highlands desert, southern Israel. Their location was marked on maps, and their growth, morphology, biology, preservation and survival was monitored. Some of them are presently maintained by the Bedouin population of the Negev, whereas others seemed to have survived from earlier periods. The average annual rainfall in this region is 90-130 mm. Most of the orchards were deliberately planted in preexisting agricultural plots, built during the Byzantine and Early Muslim era (3rd-8th centuries CE). They were irrigated by harvesting runoff water. The Byzantine era was the most populated period in the Negev Highlands, when wine and olive oil were the main horticultural products. A variety of domesticated fruit trees are found in the present abandoned orchards: olive, fig, grapevine, pomegranate, almond, date palm, carob, pistachio and bitter orange. The trees have not been artificially irrigated for at least seven decades. Nevertheless, most of them continue to flourish and bear fruit. We focused on understanding the abandoned olive trees' survival and adaptation mechanisms. Olive trees growing was a favorite crop to Byzantine farmers due to the significant economic value of olive oil and good adaptation to the environmental conditions in the Negev Highlands. © Koninklijke Brill NV, Leiden, 2018.
Using humic fractions to understand natural organic matter processes in soil and water: Selected studies and applications
. Journal of Environmental Quality 2019
, 1633-1643. Publisher's VersionAbstract
Natural organic matter (NOM) plays key environmental roles in both aquatic and soil systems. A long-standing approach for evaluating NOM composition and activity is to extract soils with alkali solutions to obtain humic substances, namely humic acids (HA), and fulvic acids (FA), or to briefly expose isolated fractions of dissolved organic matter to alkali. Critics have claimed these methods create laboratory artifacts and are thus unsuitable for studying NOM behavior in field conditions. In response, we describe case studies in which humic fractions were analyzed to identify significant processes in environmental or agricultural issues. Specifically, humic fractions played a key role in maintaining toxic levels of arsenic (As) in drinking water supplies in South and Southeast Asia. Elsewhere, binding reactions of FA and HA with prions were shown to provide a plausible mechanism for variable persistence of prion infectivity across soil types. Humic substances were also shown to enhance iron (Fe) uptake by plants in solution culture and field conditions. Their specific binding sites for mercury (Hg) as determined in laboratory conditions enabled accurate modeling of soil Hg binding under varying conditions. A young HA fraction reproduced in controlled conditions the capacity of animal manure to maintain potassium (K) availability in strongly K-fixing field soils, leading to development of a commercially successful humic-K fertilizer. Humic fractions accurately represented NOM across multiple settings and research objectives while providing novel opportunities for advanced analyses. The study of humic fractions has helped resolve scientific and practical issues in aquatic and soil systems. © 2019 The Author(s).
The vitality of fruit trees in ancient Bedouin orchards in the Arid Negev Highlands (Israel): Implications of climatic change and environmental stability
. Quaternary International 2019
. Publisher's VersionAbstract
Thirty-seven sites with fruit tree orchards were found in the arid Negev Highlands of southern Israel. A variety of domesticated fruit trees were planted in these orchards, including date palm, fig, olive, pomegranate, almond, carob, pistachio, grapevine and bitter orange. The orchards were irrigated only by runoff water accumulating in runoff-harvesting systems built during the Byzantine and Early Muslim eras, some 1000–1500 years ago, which, despite their antiquity, are still vivid and occasionally fruit bearing today. The oldest olive trees seem to be direct descendants of trees planted during Byzantine times, whereas the youngest trees were planted by the Bedouin population of the Negev Highlands in the last few decades. The fact that the Bedouin population, with very little experience in agriculture, has succeeded to cultivate a large variety of fruit trees in the present harsh arid climate utilizing the historical agricultural installations has important environmental implications. It indicates that the original builders of the desert agriculture systems were highly sophisticated in transforming desert soil into arable land. However, this was achieved through hard labor, involving the construction of a vast number of stone dams and agricultural terraces to divert channels, and the clearing of rocky surfaces. This huge effort indicates that the climate and environment prevailing during the Byzantine–Early Muslim eras was equally harsh and arid; otherwise, the invested labor would not have been justified. We conclude that the Byzantine farmers, with their greater agricultural experience and long heritage in dry land agriculture, have achieved greater success than today Bedouin population, at cultivating of fruit trees under the harsh conditions of the Negev Highlands. Therefore we deduce that the ancient desert agriculture was not the outcome of better climate; rather, the climate prevailing during the relevant historical times was probably dry and harsh, much like today. The fact that the Bedouin population in that geograghical area is cultivating orchards utilizing the same constructions, and technologies indicates that the present environmental and climatic conditions were are suitable for practicing desert agriculture and have hardly changed since the Byzantine era. © 2019 Elsevier Ltd and INQUA