Water footprint in rainfed summer and winter crops: The role of soil moisture

Abstract

Argentina is one of the main producers and exporters of grains and oilseeds, ranking third in soybean exports and fourth in barley ones. The 90% of this production occurs within the Argentine Pampas region (APR) under rainfed conditions, but its water consumption and pollution has not been studied in depth. Likewise, the link between soil moisture (SM) and Water Footprint (WF) generation is poorly studied at the global level. And yet, SM is a critical factor for the development of rainfed crops. This study aims to evaluate, at plot scale, the role of SM in the generation of the green (WFgreen) and grey (WFgrey) (WF). Additionally, it estimates the WF for rainfed barley and soybean crops in the Southeast of APR, where there are no reference values. Yields, water consumption and nitrogen (N) pollution load were estimated for different campaigns. Field data (weather, crop and production management) recorded in the study plots were used. Results indicated an average WFgreen of 1236 m3/t for soybeans and a WFgreen of 349 m3/t and WFgrey of 547 m3/t for barley. The study highlights the critical role of SM in both WF sub-indicators. Soil water availability, based on the evaporative fraction during critical growth stages, influenced yields and final WFgreen volumes. In addition, there was an effect on N uptake by crops. In the driest barley campaign, WFgrey increased by 234%. Insufficient SM restricted nutrient uptake, reducing yields and increasing N with the potential to leach or runoff. Consequently, it is suggested to adjust the WFgrey methodology incorporating SM fluctuations and unaccounted N losses. The study contributes to understand the WF drivers and highlights the need to assess them accurately. In particular, it aims to reduce the gaps surrounding the water consumption of rainfed crops, thereby supporting resource conservation and grain provisioning efforts.