Green, blue and greay water footpring reduction in irrigated crop production

Abstract

In the face of increasing water scarcity, reducing the consumptive and degradative water use of crop production is important to produce more food and/or for the environment. The thesis explores the potential for reducing the green, blue and grey water footprint (WF) of irrigated crop production by model-based assessment of different (combinations of) field management practices. First, the effect of management practices on ET and/or nitrogen(N) load to freshwater, and on crop yield are simulated (using AquaCrop or APEX models). The ET is partitioned into its green and blue part by applying a shadow water-balance method, which is developed in the thesis. Then green, blue and grey WF of crop production resulting from different management practices are calculated using the global WF accounting standard. The field management practices considered in this thesis are: four irrigation techniques, four irrigation strategies, three mulching practices, different N-application rates, two forms of nitrogen, and two tillage practices. We analyse various cases, including three crops, four different environments, different hydrologic years (dry to wet), and different soil types. The results show that compared to the reference (furrow and full irrigation without mulching), the maximum reduction in the blue and consumptive WF of crop production can be achieved by practicing drip/subsurface drip with deficit irrigation and synthetic mulching. Reducing the N-application rate will generally result in a higher reduction of the grey WF per tonne than changing the form of N applied, the tillage practice or the irrigation strategy. For reducing both consumptive WF and grey WF per tonne, one can best apply manure-N instead of inorganic-N, and deficit instead of full irrigation. Trade-offs between crop yield, blue and grey WF are likely: increasing the N-application rate to increase the crop yield to its maximum, decreases the blue WF per tonne, and increases the grey WF per tonne. Aiming at cost-effective consumptive WF reduction, application of marginal cost curves shows that, one can best improve the irrigation strategy first, next the mulching practice can best be changed from no mulching to organic mulching, and finally the irrigation technique from furrow or sprinkler to drip irrigation.