Marginal analysis of water productivity function of tomato crop grown under different irrigation regimes and mulch managements

During the winter season (November–March) of 2003–2004 and 2004–2005 a field study was carried out at the Research Farm of the University (Latitude 22°58′N, Longitude 88°31′E and altitude 9.75 m amsl), Gayeshpur, India. Aim of the study was to evaluate the sole and interactive effect of irrigation frequencies and mulches on performance and water productivity functions of tomato crop. The experiment was composed of three irrigation frequencies {rainfed (RF); CPE50 and CPE25 where irrigation was given at 50 and 25 mm of cumulative pan evaporation (CPE)}, kept in the main plots. The subplots consisted of four mulch managements {no mulch (NM), rice straw mulch (RSM), white polyethylene mulch (WPM) and black polyethylene mulch (BPM)}. Fruit yield under CPE25 was 39.4 Mg ha−1; it reduced by 7 and 30% respectively under CPE50 and RF condition. Different mulches increased fruit yield by 23–57% over non-mulch condition. Irrespective of mulching, water use efficiency (WUE), net evapotranspiration use efficiency (WUEET) and irrigation use efficiency (WUEI) were found to be the highest (22 kg m−3, 71 kg m−3 and 22 kg m−3 respectively) under moderately wet (CPE50) soil environment. Among different mulches, BPM recorded the highest WUE (25 kg m−3), WUEET (73 kg m−3) and WUEI (26 kg m−3) values. Critical values of seasonal evapotranspiration (SET) against maximum WUE and maximum yield were computed through marginal analysis of water productivity function. It was observed that the difference between these critical values was narrowed down under bio or polyethylene mulches compared to the bare situation.