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Applying nitrogen fertilizer is commonly used to increase yields of surface-irrigated crops, despite often low application efficiency (AE) and distribution uniformity (DU). Surface fertigation, the application of fertiliser dissolved in irrigation water, is a promising technique for improved on-farm performance. This study evaluated surface fertigation strategies in a field experiment and by modelling with WinSRFR. The field experiment was conducted in the North China Plain in 2017–2019. The aim was to test different practices and for model validation, then to develop optimisation scenarios. The study found, first, that conventional practices resulted in low AE of irrigation, around 40 % in wheat season and 60 % in maize season. DU, however, was satisfactory in both wheat and maize seasons, averaging 80 %. Second, surge border irrigation showed no significant advantage in terms of performance compared to the conventional practice of continuous border irrigation. Third, the WinSRFR model offered satisfactory accuracy compared to field-measured data; and soil infiltration parameters, such as the Kostiakov K, showed temporal variation during the crop seasons. Fourth, improved fertigation scenarios were developed by optimising the cut-off ratio in tandem with changes in border length and fertigation timing. The optimised strategies resulted in AE and DU increasing to some 90 %.

As global demand for food increases and impacts of climate-related extremes become more severe new governance mechanisms have become relevant. Individual and collective efforts by actors in water-for food governance could all contribute to sustainably managing the locally scarce water resources that are mobilized to meet the world's demand for food. This review synthesises insights from agricultural water management, water resources management and socio-hydrology to contribute to a knowledge base for informing joint efforts by networks of actors teaming up for sustainable water-for-food governance. The interpretation of water-for-food indicator values is complicated by spatiotemporal variations, different interests and perspectives. However, incorporating these complexities is crucial for governing a globalized food system that depends on water resources of which the availability varies in space and time.

Virtual water flows, incorporated in global food trade has increased the last decade. The drivers and consequences are complex. These complex relations between humans and water resources are studied from different perspectives. In this article, an overview of four such perspectives on water in global food production and trade is provided. These four perspectives are: (1) More crop per drop for increasing production, (2) Less drop per crop for reducing impacts, (3) National food security and import dependency; and (4) Local values and implications of water used in export food production. Each of the perspectives is valuable in the sense of representing different value frameworks, which represent contrasting norms and convictions, belief systems, and discourses; which are often incommensurable.

Despite its obvious advantages, pricing irrigation water is not widely practiced because it is not easy to deploy effectively. Water authorities require an understanding of the objectives they hope to gain from it, the performance different pricing instruments have and the preconditions that must be met to enable them to work. Also, pricing instruments work under assumptions that do not hold in an environment where multiple market failures exist and their introduction may lead to a number of unintended consequences those who operate irrigation systems never considered. The aim in this paper is to outline the difficulties that are associated with implementing pricing instruments in the irrigation sector.

Policies supporting rice production and investments in water infrastructure enabled intensification and diversification of farming systems in the Vietnamese Mekong Delta (VMD) over the past 20 years. Yet, demands of food security, economic development, and climate change continue to pose diverging and often conflicting challenges for water resources management in the upper, central, and coastal zones of the delta. The major changes effected in the VMD’s hydrological regime and land-use patterns are acknowledged in the literature, but few studies have examined the interplay between these dynamics at the delta scale. Based on time-series maps and statistical data on land-use, flooding, and salinity intrusion, we investigated the interrelations between land-use dynamics and changes in hydrological regime across the VMD in three representative periods. Land-use was found to be highly variable, changing by 14.94% annually between 2001 and 2012. Rice cropping underwent the greatest change, evolving from single cropping of traditional varieties towards double and triple cropping of high-yielding varieties. Aquaculture remained stable after rapid expansion in the 1990s and early 2000s. Meanwhile, flooding and salinity intrusion were increasingly controlled by hydrological infrastructure erected to supply freshwater for agriculture. Effects of this infrastructure became particularly evident from 2001 to 2012. During this period, spatial and temporal impacts on flooding and salinity intrusion were found, which extended beyond the rice fields to affect adjacent lands and livelihood activities. Unforeseen effects will likely be aggravated by climate change, suggesting a need to rethink the scale of planning towards a more integrated hydrologic approach.

Sustainable Development Goal indicator 6.4.1 is defined as the change in water use efficiency over time and measured as the change in the ratio of gross economic value added by irrigated agriculture, industry and the services sector to the volume of water withdrawn over time. The rationale behind this indicator is to decouple a country's economic growth from its water use. Yet, this unwittingly results in an economic distortion of the water balance, favouring increased water withdrawal in service of higher water-use efficiency, at the expense of environmental sustainability. This paper discusses three methodological flaws. First, aggregation of only economic values across all sectors ignores social and environmental values and is very sensitive to changes in the relative water use by agriculture versus industry and services. Second, the economic value derived from agriculture and from imports cannot in fact be decoupled from agricultural water use. Third, the indicator completely ignores the effects of diminished return flows to the environment due to increased re-use of water. A novel alternative, disaggregated WUE approach is therefore proposed, which links water consumption to the water balance. It is defined as the economic value of irrigated and rainfed agriculture combined with water consumption (ETa) by rainfed and irrigated agriculture per area based on earth observation data. It is measured as the change in the ratio of gross economic value added by irrigated and rainfed agriculture to the volume of water consumed by rainfed and irrigated agriculture over time. This approach is more consistent and objective, while being methodologically, hydrologically and environmentally sound. It acknowledges the coupling of economic growth and water depletion, and the need to strike a balance between opportunities for economic growth and environmental sustainability. This better serves the full breadth of the water and sanitation goal as defined in SDG 6.

A better use of land and water resources will be necessary to meet the increasing demand for food in the Nile basin. Using a hydro-economic model along the storyline of three future political cooperation scenarios, we show that the future of food production in the Basin lies not in the expansion of intensively irrigated areas and the disputed reallocation of water, but in utilizing the vast forgotten potential of rainfed agriculture in the upstream interior, with supplemental irrigation where needed. Our results indicate that rainfed agriculture can cover more than 75% of the needed increase in food production by the year 2025. Many of the most suitable regions for rainfed agriculture in the Nile basin, however, have been destabilized by recent war and civil unrest. Stabilizing those regions and strengthening intra-basin cooperation via food trade seem to be better strategies than unilateral expansion of upstream irrigation, as the latter will reduce hydropower generation and relocate, rather than increase, food production.

Although water harvesting is receiving renewed attention as a strategy to cope with increasing seasonal and inter-annual rainfall variability, many centuries-old local water-harvesting reservoirs (tanks) in India are rapidly deteriorating. Easy access to groundwater is seen as one of the major threats to their maintenance and functioning. Potentially, however, conjunctive use of water from rain, tanks and groundwater reserves, supported by proper monitoring, could improve the resilience and productivity of traditional tank irrigation systems. To date, few quantitative multi-annual analyses of such climate-smart systems have been published. To redress this, we assess the sustainability of a rehabilitated tank irrigation system, by monitoring all inputs and outputs over a period of six years (12 cropping seasons). Our results show that during the period considered, improved conjunctive use resulted in a more stable cropping intensity, increased economic water productivity and higher net agricultural income. Groundwater tables were not negatively affected. We argue that improved conjunctive use can considerably reduce the vulnerability of tank irrigation to rainfall variability and thus is a valuable strategy in light of future climate change.

Summary As irrigation water is an input into a production process, its demand must be ‘derived’. According to theory, a derived demand schedule should be downward sloping and dependent on the outputs produced from it, the prices of other inputs and the price of the water itself. Problems arise when an attempt is made to estimate the demand for irrigation water and the resulting own-price elasticity of demand, as the uses to which water is put are spatially, temporarily and geographically diverse. Because water is not generally freely traded, what normally passes for an estimate of the own-price elasticity of demand for irrigation water is usually a well argued assumption or an estimate that is derived from a simulation model of a hypothesized producer. Such approaches tend to provide an inadequate explanation of what is an extremely complex and important relationship. An adequate explanation of the relationship between the price and the quantity demanded of water should be one that not only accords with the theoretical expectations, but also accounts for the diversity of products produced from water (which includes the management practices of farmers), the seasons in which it is used and over the region within which it is used. The objective in this article is to present a method of estimating the demand curve for irrigation water. The method uses actual field data which is collated using the Residual Method to determine the value of the marginal product of water deployed over a wide range of crops, seasons and regions. These values of the marginal products, all which must lie of the input demand schedule for water, are then ordered from the highest value to the lowest. Then, the amount of irrigation water used for each product, in each season and in each region is cumulatively summed over the range of uses according to the order of the values of the marginal products. This data, once ordered, is then used to econometrically estimate the demand schedule from which the own-price elasticity of demand for irrigation water can be derived. To illustrate the method, the values of the marginal product of water deployed in the Musi catchment in India are used to determine an own-price elasticity of demand for irrigation water which has some positive value to producers of approximately −0.64. For water that is most highly valued, the elasticity was found to be highly elastic at −2.12, while less valued water used in agriculture was far more inelastic at −0.44. Finally, for almost 36% of water deployed in the catchment the elasticity was logically determined to be perfectly elastic.