Drought challenges in a context of soil use sustainability

Droughts are natural but temporary imbalances of water availability, consisting of a persistent lower-than-average precipitation, of uncertain frequency, duration and severity, of unpredictable or difficult to predict occurrence, resulting in diminished water resources availability and impacts on natural and man-made ecosystems. To successfully cope with drought there is a need to understand the characteristics and consequences of related phenomena; however, differences in the perception of drought lead to difficulties in adopting risk management. The effectiveness of drought risk management depends upon drought monitoring, drought prediction and warning capabilities, and means to provide information to users, as well as on related awareness of populations. For drought monitoring and warning, drought indices are useful. The SPI has been extensively used in Portugal and stochastic methods have been developed for prediction of drought class transitions to be used for early warning. For agricultural purposes, the PDSI was modified and successfully referred to the rainfed olive crop, thus originating the MedPDSI. Its evaluation against the SPI and PDSI shows the appropriateness of this index. Relative to information systems, a variety of approaches were used to support deficit irrigation. However, its economic feasibility is questionable and more studies are required to assess ways to improve irrigation under droughtinfo:eu-repo/semantics/publishedVersio

Irrigation scheduling for furrow-irrigated maize under climate uncertainties in the Thrace plain, Bulgaria

Research Paper: SW - Soil and WaterClimate change creates uncertainties for irrigation management. To cope with them, simulations were performed for the present and scenario-built weather conditions that include a pessimistic scenario of precipitation decrease in the next 25 years. In a former study, the irrigation scheduling simulation model ISAREG was calibrated for two maize varieties: the water stress-resistant hybrid Kn-2L-611 and the water stress-sensitive hybrid H708. Both are subjects of this study, which compares four irrigation scheduling alternatives: (1) refilling the soil reservoir and adopting a management-allowed depletion fraction (MAD) of 0.47; (2) refilling the soil reservoir and adopting MAD ¼ 0.33; (3) partially refilling the soil reservoir and adopting MAD ¼ 0.47; and (4) crop without irrigation. For the very dry year and the present climate all alternative irrigation schedules behave similarly but for the average year, alternatives 1 and 3, allowing a larger soil water depletion with MAD ¼ 0.47, require less water than the alternative with MAD ¼ 0.33. However, analysis of impact on yields using simulations relative to every year during 1970–1992 shows that alternative 2 leads to less impact on yields. The results of simulations were compared with irrigation schedules presently advised in the region and show that the latter do not fully cover crop requirements in dry seasons, when some yield decrease occurs. Simulations for the pessimistic scenario show that all three irrigation scheduling alternatives can easily accommodate the foreseen changes mainly by selecting suitable irrigation dates. The results of simulations do not allow selecting one among the three alternatives as the best irrigation scheduling strategy but are useful for later building an information system for farmers using actual weather data. Relative to the rainfed crop, the results indicate that yield impacts highly increase for the pessimistic scenario, particularly for the water stresssensitive hybrid H708. The results indicate that vulnerability to climate change is higher for non-irrigated crops and that coping with possible rainfall decreases requires adopting less sensitive crop varieties, including when deficit irrigation would be applied for water saving

Innovation issues in water, agriculture and food

EditorialThe main challenge faced by agriculture is to produce enough food for a continued increase in population, however in the context of ever-growing competition for water and land, climate change, droughts and anthropic water scarcity, and less-participatory water governance. Such a context implies innovative issues in agricultural water management and practices, at both the field and the system or the basin scales, mainly in irrigation to cope with water scarcity, environmental friendliness, and rural society welfare. Therefore, this special issue was set to present and discuss recent achievements in water, agriculture, and food nexus at di erent scales, thus to promote sustainable development of irrigated agriculture and to develop integrated approaches to water and food. Papers cover various domains including: (a) evapotranspiration and crop water use; (b) improving water management in irrigated agriculture, particularly irrigation scheduling; (c) adaptation of agricultural systems to enhance water use and water productivity to face water scarcity and climate change; (d) improving irrigation systems design and management adopting multi-criteria and risk approaches; (e) ensuring sustainable management for anthropic ecosystems favoring safe and high-quality food production, as well as the conservation of natural ecosystems; (f) assessing the impact of water scarcity and, mainly, droughts; (g) conservation of water quality resources, namely by preventing contamination with nitrates; (h) use of modern mapping technologies and remote sensing information; and (i) fostering a participative and inclusive governance of water for food security and population welfareinfo:eu-repo/semantics/publishedVersio

Assessing economic impacts of deficit irrigation as related to water productivity and water costs

Research Paper:SW-Soil and WaterThis study aims at assessing the feasibility of deficit irrigation of maize, wheat and sunflower through an analysis of the economic water productivity (EWP). It focuses on selected sprinkler-irrigated fields in Vigia Irrigation District, Southern Portugal. Various scenarios of water deficits and water availability were considered. Simulations were performed for average, high and very high climatic demand. The potential crop yields were estimated from regional climatic data and local information. Using field collected data on yield values, production costs, water costs, commodity prices and irrigation performance, indicators on EWP were calculated. Results show that a main bottleneck for adopting deficit irrigation is the presently low performance of the irrigation systems used in the considered fields, which leads to high water use and low EWP. Decreasing water use through deficit irrigation also decreases the EWP. Limited water deficits for maize are likely to be viable when the irrigation performance is improved if water prices do not increase much, and the commodity price does not return to former low levels. The sunflower crop, despite lower sensitivity to water deficits than maize, does not appear to be a viable solution to replace maize when water restrictions are high; however it becomes an attractive crop if recently high commodity prices are maintained. With improved irrigation performance, wheat deficit irrigation is viable including when full water costs are applied, if former low prices are not returned to. However, under drought conditions full water costs are excessive. Thus, adopting deficit irrigation requires not only an appropriate irrigation scheduling but higher irrigation performance, and that the application of a water prices policy would be flexible, thus favouring the improvement of the irrigation systems

Multicriteria analysis for design of microirrigation systems. Application and sensitivity analysis

This paper presents a practical application of the DSS MIRRIG for the design of a microirrigation system for a citrus orchard in Algarve (Portugal). Several alternatives were considered using different emitter types (drippers, sprayers, pressure-compensating and non-pressure compensatingemitters), different pipe sizesandlayouts withand without pressure regulation valves, as well as different pressure head and discharge at the upstream end of the systems. This application is described and the ranking of alternative designs is analysed using the weights given by the farmer to the hydraulic, economic and environmental criteria. An analysis of impacts resulting from selecting different weights is presented aimed at understanding the sensitivity of the model in relation to those criteria. In addition, a sensitivity analysis is performed to test the robustness of the algorithms used for ranking with respect to changes in concordance and discordance threshold values, which show that the values selected by the model are those providing for a more clear ranking of design alternatives

Decision support system for surface irrigation design

The SADREG decision support system was developed to help decision makers in the process of design and selection of farm surface irrigation systems to respond to requirements of modernization of surface irrigation—furrow, basin, and border irrigation. It includes a database, simulation models, user-friendly interfaces, and multicriteria analysis models. SADREG is comprised of two components: design and selection. The first component applies database information, and through several simulation and computational tools, produces a set of design alternatives in agreement with the user options. These alternatives are characterized by several hydraulic, economic, and environmental indicators that allow appropriate selection and ranking. The selection component bases upon multicriteria analysis using composite programming and ELECTRE II ranking models, which support the decision maker to select the best alternative. The decision maker participates in all decision processes through a user-friendly interface that allows expressing design options and priorities. SADREG was tested with data collected from field experiments. In addition to describing the modeling approach, an application to a sector of the Lower Mondego Irrigation Project, Portugal, is presente

Estimating crop coefficients from fraction of ground cover and height

The FAO-56 procedure for estimating the crop coefficient Kc as a function of fraction of ground cover and crop height has been formalized in this study using a density coefficient Kd. The density coefficient is multiplied by a basal Kc representing full cover conditions, Kcb full, to produce a basal crop coefficient that represents actual conditions of ET and vegetation coverage when the soil surface is dry. Kcb full is estimated primarily as a function of crop height. Kcb full can be adjusted for tree crops by multiplying by a reduction factor (Fr) estimated using a mean leaf stomatal resistance term. The estimate for basal crop coefficient, Kcb, is further modified for tree crops if some type of ground-cover exists understory or between trees. The single (mean) crop coefficient is similarly estimated and is adjusted using a Ksoil coefficient that represents background evaporation from wet soil. The Kc estimation procedure was applied to the development periods for seven vegetable crops grown in California. The average root mean square error between estimated and measured Kc was 0.13. The Kc estimation procedure was also used to estimate Kc during midseason periods of horticultural crops (trees and vines) reported in the literature. Values for mean leaf stomatal resistance and the Fr reduction factor were derived that explain the literature Kc values and that provide a consistent means to estimate Kc over a broad range of fraction of ground cove

Effects of Biochar in Soil and Water Remediation: A Review

In the last decades increased global environmental concerns to water and soils pollution. The main concerns are related to the contamination of the ecosystem, food security, and human health since many of the contaminants present in soil and water (residues of pesticides and antibiotics, genes of resistance to antibiotics, and heavy metals) are absorbed by plants and enter the food chain. Remediation of the contaminated water and soil to ensure sustainable water supply and food production is urgently needed. The use of biochar can have a positive effect on this remediation process. There are several studies that demonstrate the biochar’s ability to block/reduce the contaminating effect of pesticides, antibiotic residues, antibiotic resistance genes, and heavy metals. The objective of this chapter is to carry out a comprehensive review of the effect of using biochar on the availability/transmission of these contaminants to the soil and food supply chain.info:eu-repo/semantics/publishedVersio

Stochastic prediction of drought class transitions

This paper aims at the stochastic characterization of droughts applying Markov chains modeling to drought class transitions derived from SPI time series. Several sites in Southern Portugal having updated data on precipitation available were considered. The drought class probabilities, the expected residence time in each class of severity, the expected time for the transition between drought classes and the drought severity class predictions 1, 2, or 3 months ahead have been obtained. Those predictions are then compared with observed drought classes for the recent drought periods of 2003–2006. In addition, the estimation of the cumulated precipitation deficits, amount of monthly precipitation needed to decrease drought severity, and foreseen SPI values depending on different precipitation scenarios are also presented as complementing the prediction of drought class transitions

Defensive role of allelopathic secondary compounds in plants: a review of data on two independent general hypotheses

This review examines and whenever appropriate, reanalyses published literature related to two general and independent hypotheses having the underlying assumption that phytoactive secondary compounds produced by plants evolved primarily as plant defences against competitor plant species. The first hypothesis is that production and the main way of release of phytoactive compounds reflect an adaptive response to climate conditions. Thus, higher phytoactivity by volatile-compounds should prevail in plants of hot, dry environments whereas higher phytoactivity by water- solubles should be preponderant in plants from wetter environments. The second hypothesis is that the synergy between phytoactive compounds of plants should be widespread while antagonism or absence of interaction of effects should be rare because of the higher efficiency of energy and use of resources provided by synergy. Published literature does not support either hypotheses. We found no pattern of association between higher phytoactivity in volatile compounds in plants from drier environments or in water-soluble compounds in plants from wetter environments. Neither did we found evidences for the predominance of synergy. On the contrary, antagonism or no interaction of effects among allelopathic compounds largely prevailed