Theib Oweis

Irrigation management under water scarcity

The use of water for agricultural production in water scarcity regions requires innovative and sustainable research, and an appropriate transfer of technologies. This paper discusses some of these aspects, mainly relative to on-farm irrigation management including the use of treated wastewater and saline waters. First, the paper proposes some concepts relative to water scarcity, concerning aridity, drought, desertification and water shortage, as well as policies to cope with these water stressed regimes. Conceptual approaches on irrigation performances, water use and water savings are reviewed in a wide perspective. This is followed by a discussion of supply management to cope with water scarcity, giving particular attention to the use of wastewater and low-quality waters, including the respective impacts on health and the environment as water scarcity is requiring that waters of inferior quality be increasingly used for irrigation. The paper then focuses on demand management, starting with aspects relating to the improvement of irrigation methods and the respective performances, mainly the distribution uniformity (DU) as a fundamental tool to reduce the demand for water at the farm level, and to control the negative environmental impacts of over-irrigation, including salt stressed areas. Discussions are supported by recent research results. The suitability of irrigation methods for using treated wastewaters and saline waters is analysed. Supplemental irrigation (SI) and deficit irrigation strategies are also discussed, including limitations on the applicability of related practices. The paper also identifies the need to adopt emerging technologies for water management as well as to develop appropriate methodologies for the analysis of social, economic, and environmental benefits of improved irrigation management.

Water-use efficiency and transpiration efficiency of wheat under rain-fed conditions and supplemental irrigation in a Mediterranean-type environment

Growth and water use were measured in wheat (Triticum aestivum L.) grown in northern Syria in a typical Mediterranean climate over five seasons 1991/92–1995/96. Water use was partitioned into transpiration (T) and soil evaporation (Es) using Ritchies model, and water-use efficiency (WUE) and transpiration efficiency (TE) were calculated. The aim of the study was to examine the influence of irrigation and nitrogen on water use, WUE and TE. By addition of 100 kg N ha-1, Es was reduced from 120 mm to 101 mm under rain-fed conditions and from 143 mm to 110 mm under irrigated conditions, and T was increased from 153 mm to 193 mm under rain-fed conditions and from 215 mm to 310 mm under irrigated conditions. Under rain-fed conditions, about 35% of evapotranspiration (ET) may be lost from the soil surface for the fertilized crops and 44% of ET for the unfertilized crops. Transpiration accounted for 65% of ET for the fertilized crops and 56% for the unfertilized crops under rain-fed. As a result of this, WUE was increased by 44% for dry matter and 29% for grain yield under rain-fed conditions, and by 60% for dry matter and 57% for grain yield under irrigated conditions. Transpiration efficiency for the fertilized crops was 43.8 kg ha-1 mm-1 for dry matter and 15 kg ha-1 mm-1 for grain yield, while TE for the unfertilized crops was 33.6 kg ha-1 mm-1 and 12.2 kg ha-1 mm-1 for dry matter and grain yield, respectively. Supplemental irrigation significantly increased post-anthesis water use, transpiration, dry matter and grain yield. Water-use efficiency for grain yield was increased from 9.7 to 11.0 kg ha-1 mm-1 by supplemental irrigation, although WUE for dry matter was not affected by it. Irrigation did not affect transpiration efficiency for grain yield, but decreased transpiration efficiency for dry matter by 16%. This was associated with higher harvest index as a result of good water supply in the post-anthesis period and increased transpiration under irrigated conditions.

Rainfed agriculture: unlocking the potential

1. Rainfed Agriculture - Past Trends and Future Prospects 2. Zooming in on the Global Hotspots of Rainfed Agriculture in Water Constrained Environments 3. Water Resource Implications of Upgrading Rainfed Agriculture - Focus on Green and Blue Water Trade-offs 4. Tectonics-climate Linked Natural Soil Degradation and its Impact in Rainfed Agriculture: Indian Experience 5. Determinants of Crop Growth and Yield in a Changing Climate 6. Yield Gap Analysis: Modeling of Achievable Yields at Farm Level 7. Can Rainfed Agriculture Feed the World? - An Assessment of Potentials and Risk 8. Opportunities for Improving Crop-water Productivity Through Genetic Enhancement of Dryland Crops 9. Water Harvesting for Improved Rainfed Agriculture in the Dry Environments 10. Supplemental Irrigation for Improved Rainfed Agriculture: In WANA Region 11. Opportunities for Water Harvesting and Supplemental Irrigation for Improving Rainfed Agriculture in Semi-arid Areas 12. Integrated Farm Management Practices and Up Scaling the Impact for Increased Productivity of Rainfed Systems 13. Challenges of Adoption and Adaptation of Land and Water Management Options in Smallholder Agriculture: Synthesis of Lessons and Experiences 14. Scaling-out Community Watershed Management for Multiple Benefits in Rainfed Areas.

Reducing peak supplemental irrigation demand by extending sowing dates

Abstract Supplemental irrigation (SI) is a common practice in the dry environments and aims at improving and stabilizing rainfed crops by adding small amounts of water to rainfed crops during times when rainfall fails to provide sufficient moisture for normal plant growth. Results from long-term research in experimental stations and farmer fields showed substantial increases in rainfed crop yields and water use efficiency in response to SI. Nevertheless, SI comes at a cost. The date of sowing winter wheat in a rainfed Mediterranean-type environment depends upon the onset of rainfall. The optimal date for achieving highest yield under rainfed conditions is around mid-November. However, farmers tend to sow wheat later than this date because of the delay and/or unreliability of initial rains. With SI, early sowing and crop establishment can be ensured. However, early sowing of all the fields’ results in higher water demand during a very short period in spring because all the fields will be at the peak use rate. Spreading out dates of sowing allows peak water demand to occur over a longer period, thus reducing the discharge and the size of irrigation system needed, and hence improves the economics of this practice. In this paper, the impact of adopting a multi-sowing date strategy on farm water demand and crop production is considered. A simplified optimization model solved by linear programming is presented. Four-years’ data (1992–1996) from field experimental research conducted on bread wheat in northern Syria have been used in the analysis. We showed that a multi-sowing date strategy has reduced the peak farm water demand rate by more than 20%, thus potentially reducing irrigation system capacity and/or size. Alternatively, the water demand rate of a larger area can be met with the same water supply. However, optimal sowing dates that minimize farm water demand rate do not always maximize total farm production. The outcome depends on crop water requirements and yield for each sowing date. Furthermore, this selection is greatly influenced by the level of water scarcity. The approach used can help in reducing the cost of irrigation and improving the efficiency of water use in SI.

Performance of Penman-Monteith FAO56 in a Semiarid Highland Environment

Reliable estimates of evapotranspiration are essential for irrigation and water resources planning and management. Although several methods are available for computing reference evapotranspiration ( ETo ) , the provision of complete and accurate climate data is often a problem. Therefore, weighing lysimeter data from a semiarid highland environment were used to evaluate the performance of six commonly used reference evapotranspiration estimation methods with different data requirements (Penman-Monteith-FAO56, Priestley-Taylor, Radiation-FAO24, Hargreaves, Blaney-Criddle, Class A pan). The lysimeter experiments were conducted at Ankara Research Institute of Rural Services in Turkey, during the April–October cropping seasons of the years 2000–2002. The average ETo for the three seasons, computed from the lysimeter data, was 964 mm. The Penman-Monteith-FAO56 method was also evaluated for cases where relative humidity, wind speed, solar radiation, or all three parameters would be missing. This resulted in a t...

Yield gap analysis: modelling of achievable yields at farm level

This chapter quantifies the potential yields and yield gaps between the potential and the actual yields obtained by the farmers for the major rainfed crops grown in the selected countries in South and South East Asia (India, Thailand and Vietnam), SSA and the West Asia and North Africa (WANA) region, where food security is increasingly threatened because of expected increase in population and degradation of natural resources. This analysis is expected to help identify the opportunities and constraints for yield improvement with the implementation of the improved crop production and natural resource management technologies for the rainfed regions.

A Participatory GIS Approach for Assessing Land Suitability for Rainwater Harvesting in an Arid Rangeland Environment

The dry rangelands of West Asia and North Africa are fragile and severely degraded due to low rainfall and mismanagement of natural resources. Rainwater harvesting (RWH) interventions are used to increase soil moisture content, vegetation cover, and productivity. However, adoption of rainwater harvesting by communities is slow. To understand adoption constraints and to develop options for sustainable integration of rainwater harvesting, a benchmark watershed was established in the dry rangelands of Jordan. The objective is to develop a methodology for identifying the suitability for different rainwater harvesting interventions using participatory GIS approach and field survey. The main biophysical parameters used to assess the suitability for rainwater harvesting were slope, soil depth, soil texture, and stoniness. Criteria for each parameter were integrated and a suitability map was produced using raster-based and polygon-based analysis. To integrate biophysical and socio-economic aspects, the land tenure was superimposed with the suitability map. Options for implementing different rainwater harvesting interventions were identified with the participation of the local communities. Field investigations indicated that the applied approach helped to select the most promising fields. Within two years, four types of rainwater harvesting were implemented in the fields of 41 farmers, covering 62.9 hectares, which helped to increase water productivity (kg/m3) four folds and reducing soil erosion five folds compared to fields without rainwater harvesting. The approach showed that participatory GIS approach may be used to integrate socio-economic and biophysical criteria and facilitate the participation of farmers to introduce rainwater harvesting interventions in dry rangeland systems to mitigate land degradation.

The potential of small-scale rainfed agriculture to strengthen food security in Arab countries

In most Arab countries, domestic agricultural production is insufficient. The gap between production and demand is likely to increase due to climate change and other factors. This review paper examines the challenges and possible solutions to ensuring food security in the future. It focuses on rainfed agriculture, which accounts for two-thirds of the region’s cropland, the bulk of its food staples, and almost all its rangelands. Given the scarcity of water and arable land, there are few opportunities in the region to expand cultivated area. But numerous effective, proven technologies are available that can increase productivity per unit area of land or volume of water. Crop technologies include, for example, new stress-tolerant varieties, supplemental irrigation and other techniques to increase water productivity, and conservation agriculture and other land management methods. Livestock nutrition and productivity could be increased with new forage or dual-purpose varieties, and greater use of alternative feed sources such as feed blocks made from crop by-products. The paper describes some of these technologies, and summarizes results obtained from on-station and on-farm testing. The key issue is poor adoption of available technologies. The priority for researchers and policy makers must therefore be to scale up investments in research and extension; encourage private sector participation; and create enabling policies to encourage technology adoption, market participation and more sustainable use of natural resources, by smallholder farmers.

Concepts and Applications of AquaCrop: The FAO Crop Water Productivity Model

Predicting attainable yield under water-limiting conditions is an important goal in arid, semi-arid and drought-prone environments. To address this task, FAO has developed a model, AquaCrop, which simulates attainable yields of the major herbaceous crops in response to water. Compared to other models, AquaCrop has a significantly smaller number of parameters and attempts to strike a balance between simplicity, accuracy, and robustness. Root zone water content is simulated by keeping track of incoming and outgoing water fluxes. Instead of leaf area index, AquaCrop uses canopy ground cover. Canopy expansion, stomatal conductance, canopy senescence, and harvest index are the key physiological processes which respond to water stress. Low and high temperature stresses on pollination and harvestable yield are considered, as is cold temperature stress on biomass production. Evapotranspiration is simulated separately as crop transpiration and soil evaporation and the daily transpiration is used to calculate the biomass gain via the normalized biomass water productivity. The normalization is for atmospheric evaporative demand and carbon dioxide concentration, to make the model applicable to diverse locations and seasons, including future climate scenarios. AquaCrop accommodates fertility levels and water management systems, including rainfed, supplemental, deficit, and full irrigation. Simulations are routinely in thermal time, but can be carried out in calendar time. Future versions will incorporate salt balance and capillary raise. AquaCrop is aimed at users in extension services, consulting firms, governmental agencies, NGOs, farmers associations and irrigation districts, as well as economists and policy analysts in need of crop models for planning and assessing water needs and use of projects and regions.

Simulation of Supplemental Irrigation Strategies for Wheat in Near East to Cope with Water Scarcity

The development of supplemental irrigation strategies that reduce water demand with acceptable impacts on yields is part of preparedness measures to cope with drought and water scarcity. The irrigation scheduling simulation model ISAREG, after appropriate validation, is used to simulate various irrigation schedules for wheat under average, high and very high climatic demand conditions to cope with limited water supplies. Surface and set sprinkler irrigation are considered. The study was performed with field data collected at the Tel Hadya research station of ICARDA, Aleppo, Syria. The alternative irrigation schedules are evaluated through the achieved reduction in demand for irrigation water and the consequent yield decrease. Results show that water saving strategies for supplemental irrigation of wheat are generally feasible.