Water and nitrogen use efficiency of potato grown in a sub-humid area

Rational use of natural resources, especially water and nutrients, is one of the most important objectives in the sustainable management of cropping systems. To achieve this goal it is useful to consider some efficiency indexes in order to optimise the scheduling of water and nitrogen. Water and nitrogen use efficiency (WUE and NUE) were calculated on the basis of the results of a lysimeter experiment in which a ETc 100% drip irrigation control was compared with treatments providing for early or late water stress or over-watered conditions (ETc 120%). In a field experiment the effects of three treatments (Rainfed, ETc 100%, ETc 100% followed by ETc 70%, with a change of irrigation regime at an average tuber diameter of 35 mm) on four varieties (one determinate and three indeterminate) were compared. In the field the WUE of the irrigated plots was 38% lower than under rainfed conditions, depending on rain distribution during the growth cycle and whether calculated on fresh matter or on dry matter (DM). NUE was found to be related to water availability and increased up to 22% for the 100% ETc treatment. Water supplies of approximately 300 mm y-1 resulted in highest yields both of fresh tubers and tuber dry matter. In terms of profitability WUEDM and NUEDM were optimal when the total available water was approximately 250 mm y-1. The indexes calculated in the field trial experiment were compared with those resulting from the lysimeter observations. © ISHS.