Quantifying and reducing the water footprint of rain-fed potato production part II: a hydrological assessment using modelling supported by measurements

Water footprinting (WF) is mooted to quantify the impacts of production on water resources. The impact of the rain-fed potato (Solanum tuberosum) production on water resources was assessed for a kilogram of potatoes at the packhouse gate. The hydrological water-balance method was used and this accounts for all inflows and outflows to quantify the net use of groundwater as the blue WF, and that of the soil-water store as the green WF. The green WF was found to be negligible. The blue WF was negative at −67 L/kg. Thus rain-fed potato production here has no deleterious impacts on the water quantity. ey WF, the water required to ‘dilute’ NO3–N in the drainage to meet the drinking water standard, was 61 L/kg, of which 56 L/kg was from the cropping stage. The impact of the packhouse phase and the background system was found to be small. However, the average leached NO3–N concentration of 11.3 mg/L, which is just at the drinking water standard, and the loading of 27.8 kg-N/ha/y during cultivation indicate that a single application of fertilizer at the time of planting has impacts on water quality. Our modelling of different fertilizer application scenarios of two splits, three splits and a late application at 55 days after planting reduced the annual average NO3–N concentrations to 10.5, 10.3 and 9.5 mg/L respectively. Potato yield was not compromised. The grey WF would be reduced to 50.6, 50.9 and 48.9 L/kg respectively for these fertilizer scenarios.