Calibration and validation of solar radiation-based equations to estimate crop evapotranspiration in a semi-arid climate.

The Abtew and Jensen-Haise solar radiation-based equations were used to estimate evapotranspiration, considering the limited climatic data in many locations. Both equations were proven to successfully predict the potential evapotranspiration (ETO) compared with the standard Penman-Monteith (PM) method in two Mediterranean countries. Calibration of the constant coefficient k of the Abtew equation showed substantial differences compared to recommended values (1.22 vs. 0.53), with the highest values observed during September (1.46). Validation of ETO measurements using calibrated Abtew equation against the PM method indicated a high correlation coefficient (r2 = 0.97, RMSE = 0.61). Further, evapotranspiration requirements, using the calibrated empirical equation, were calculated for olives (449 mm) and citrus (807 mm) showing a good agreement with recommended values for dry climate regions. Therefore, the tested equations could be safely used to predict frequencies and doses of irrigation in semi-arid climates, considering limited climatic data availability.

Compost-assisted revegetation of highly phytotoxic sulfidic tailings with Medicago sativa L. plants grown from the seed to seedpod stage under greenhouse experimental mesocosms conditions.

The revegetation of highly phytotoxic sulfidic tailings is a challenging task which may often be successfully accomplished only following the addition of soil amendments. This study evaluated the use of green compost at increasing rates (10, 25 and 50% v/v) for the revegetation of extremely acidic sulfidic tailings of the North Mathiatis mine, Cyprus, with the use of alfalfa (Medicago sativa L.) plants, under greenhouse conditions. Alfalfa seeds were successfully germinated in tailings amended either with 25% or 50% (v/v) compost (52 and 85%, respectively). Plants managed to complete their life cycle and produce seeds only in the tailings amended with 50% (v/v) compost, since plants grown in tailings amended with lower rates of compost (i.e., 10 or 25% v/v) showed severe symptoms of phytotoxicity and eventually died. The amendment of tailings with 50% (v/v) green compost resulted in increased pH values, water holding capacity and organic content levels, soil respiration rates, as well as changes in soil elemental composition compared with tailings alone treatment, which in turn facilitated the growth and development of alfalfa plants during the whole experimental period (140 days). Plants managed to reach the late seedpod growth stage, indicating their potential regeneration and continual existence to the amended tailings, simultaneously uncovering the development of favorable conditions in the rhizosphere for the successful revegetation of studied tailings.

Estimating cucumber crop coefficients under different greenhouse microclimatic conditions.

This study aimed to determine cucumber crop coefficients under different greenhouse microclimatic conditions, parameterizing the Priestley-Taylor reference evapotranspiration model. Crop evapotranspiration was directly measured with the use of lysimeters, and crop coefficients were computed following the two-step climate FAO 56 methodology. Greenhouse compartments (i.e., cooled or uncooled) showed reference evapotranspiration differences of up to 12% in an autumn-winter crop. The results presented cucumber crop coefficient values from the initial to the late-season growth stages from 0.45 to 0.94 depending on the greenhouse climate. Based on the greenhouse hourly microclimatic variation of KC, it is recommended not to apply a KC as a constant for transpiration estimation even at greenhouses located within the same region Regression analysis relating crop coefficients with leaf area revealed very high correlation coefficients for the equations tested. The results indicated that evapotranspiration can be modeled satisfactory based on a significant relationship between crop coefficient and simple measurements of the leaf area index (i.e., KC = 0.447 × LAI).

Lead contamination of soils, sediments, and vegetation in a shooting range and adjacent terrestrial and aquatic ecosystems: A holistic approach for evaluating potential risks.

It is well accepted that shooting ranges constitute hotspots of Pb contamination. This study evaluated the degree of Pb contamination of soils, sediments and vegetation within the boundaries of a highly visited shooting range, as well as the fluvial transport and dispersal of Pb, and therefore the contamination of adjacent river and water reservoir. Soils in the shooting range were severely contaminated with Pb, as indicated by the values of enrichment and contamination factor. The concentration of Pb in these soils ranged from 791 mg kg-1 to 7265 mg kg-1, being several dozens or even hundreds of times higher compared with control background samples. A temporary stream being in close proximity was also polluted, though to a much lesser extent. The degree of Pb contamination was negatively correlated with the distance from the shooting range. To this effect, the degree of contamination of the river and the water reservoir being in the vicinity of the shooting range was negligible, as sediments and water samples preserved similar Pb concentrations with control samples. However, cultivated (olives) and wild native plant species grown in the area of the shooting range were found to uptake and accumulate high concentrations of Pb in their tissues (even 50 times higher compared with control samples). The severe contamination of soils, sediments and vegetation in the studied shooting range can provoke very high ecological risks. Overall, results suggest that management measures should be undertaken within the boundaries of the studied shooting range.

Uptake of hexavalent chromium by Lactuca sativa and Triticum aestivum plants and mediated effects on their performance, linked with associated public health risks.

Plants exposed to toxic Cr(VI) concentrations show reduced biomass production and yield. The present study examined (1) the impacts of increasing Cr(VI) exposure (0.05, 0.5, 1, 5 and 10 mg L-1 K2Cr2O7 in irrigation water) on the growth and development, yield, and stress physiology of two important crop species, such as wheat (Triticum aestivum L.) and lettuce (Lactuca sativa L.), and (2) the associated human health risks due to the consumption of these commodities. Plants in all Cr(VI) treatments preserved similar growth rates and phenotypes with control, untreated plants, with no remarkable modulations in biomass yield (fresh/dry weight, plant height, straw/grain weight). Grains harvested from plants exposed to all Cr(VI) treatments had increased size and 1000 grain weight, partially suggesting hormetic effect. Elevated K2Cr2O7 concentrations (5 and 10 mg L-1) resulted in increased photosynthetic pigments' levels in lettuce leaves. Lipid peroxidation and H2O2 content also revealed the absence of oxidative stress in lettuce plants. Non-carcinogenic (target hazard quotient) and carcinogenic risks from the consumption of these commodities grown under the conditions described in this study were found de minimis. However, more studies are needed in order to obtain more solid information on the safety of Cr(VI)-contaminated water irrigation.

Hexavalent chromium leads to differential hormetic or damaging effects in alfalfa (Medicago sativa L.) plants in a concentration-dependent manner by regulating nitro-oxidative and proline metabolism.

Chromium has been proven to be extremely phytotoxic. This study explored the impacts of increasing Cr(VI) exposure (up to 10 mg L-1 K2Cr2O7) on the growth and development of alfalfa plants and adaptation responses employed, in an environmentally relevant context. The threshold concentration of K2Cr2O7 in irrigation water beyond which stress responses are initiated is 1 mg L-1. Lower Cr(VI) exposure (0.5 mg L-1 K2Cr2O7) induced hormesis, evident through increased biomass and larger leaves, likely mediated by increased NO content (supported by elevated NR enzymatic activity and overexpression of NR and ndh genes). Elevated Cr(VI) exposure (5 and 10 mg L-1 K2Cr2O7) resulted in reduced biomass and smaller leaves, and lower levels of photosynthetic pigment (10 mg L-1 K2Cr2O7). Higher levels of lipid peroxidation, H2O2 and NO contents in these plants suggested nitro-oxidative stress. Stress responses included increased SOD and CAT enzymatic activities, further supported to some extent by MnSOD, FeSOD, Cu/ZnSOD and CAT transcripts levels. GST7 and GST17 gene expression patterns, as well as proline content, P5CS enzymatic activity and corresponding P5CS and P5CR gene expression levels emphasized the role of proline and GSTs in the adaptation responses. Results highlight the importance of managing Cr(VI) levels in irrigation water.

Comparative Analysis of the Nitrogen Effect of Common Agricultural Practices and Rotation Systems in a Rainfed Mediterranean Environment.

The nitrogen (N) effect of legumes is one of the main reasons for their inclusion in rotation systems and their success in rainfed agriculture of Mediterranean areas. The comparative analysis of this effect in relation to alternative systems or practices is essential for a comprehensive appreciation in their merit. This field experiment was comprised of four three-year rotation cycles. Wheat (Triticum turgidum durum) was seeded for two consecutive years after common vetch (Vicia sativa L.), treated in three different ways, and after fallow and compared with three wheat monocultures: the conventional one, the continuous straw incorporation, and the sewage sludge incorporation once every three years. Wheat grain and straw yields and N uptake were compared among treatments. Results showed that rotation systems that included vetch were the most promising for improving sustainability. Maximum N uptake and the greatest yield surpluses were obtained when wheat followed vetch incorporated during flowering. When vetch in the rotation was cut for hay or left to fill grains subsequent wheat showed also enhanced yields. Fallow affected the rotation system's fertility due to the incorporation of volunteer plants into the soil. Sewage sludge sustained production without the need for inorganic fertilization during three years. Straw incorporation always gave the smallest yields and N harvests, presumably due to soil N immobilization.