Management of nitrogen and water plays a significant role in increasing crop productivity. A large amount of nitrogen (N) may be lost through leaching if these resources are not well managed. Wetting front detectors (WFDs) and Chameleon soil water sensors were used to adapt water and nitrogen applications with the goal of increasing millet yields, as well as nitrogen and water use efficiency. The trials were laid out as a randomized complete block design with factorial combinations of water and N, and included the following treatments: irrigation to field capacity (fortnightly and weekly), adaptive-water application based on sensor response or rainfed, and N treatments included either fixed nitrogen levels (0, 45, 90 kg N ha⁻¹) or an adaptive-N rate, depending on N content of the soil solution extracted from WFDs. Adaptive management aims to steer water and nitrogen applications towards optimum crop requirements. Treatments that received both high water and nitrogen outperformed other treatments by 11% to 68% in terms of biomass production and 16% to 54% in grain yield, while water use efficiency and irrigation use efficiency values were also higher, ranging from 1.58 to 7.94 kg m⁻³ and 1.43 to 8.30 kg m⁻³. Results suggest that integrated adaptive water and nitrogen management should be considered to reduce high N losses and cost of crop production, without a meaningful yield penalty, relative to high production input management.

Water footprint (WF) accounting as proposed by the Water Footprint Network (WFN) can potentially provide important information for water resource management, especially in water scarce countries relying on irrigation to help meet their food requirements. However, calculating accurate WFs of short-season vegetable crops such as carrots, cabbage, beetroot, broccoli and lettuce presented some challenges. Planting dates and inter-annual weather conditions impact WF results. Joining weather datasets of just rainfall, minimum and maximum temperature with ones that include solar radiation and wind-speed affected crop model estimates and WF results. The functional unit selected can also have a major impact on results. For example, WFs according to the WFN approach do not account for crop residues used for other purposes, like composting and animal feed. Using yields in dry matter rather than fresh mass also impacts WF metrics, making comparisons difficult. To overcome this, using the nutritional value of crops as a functional unit can connect water use more directly to potential benefits derived from different crops and allow more straightforward comparisons. Grey WFs based on nitrogen only disregards water pollution caused by phosphates, pesticides and salinization. Poor understanding of the fate of nitrogen complicates estimation of nitrogen loads into the aquifer.