Keywords: rigid scheduling, small-scale irrigation, water-use efficiency, potatoes, NE Portugal
The effect of rigid scheduling on productivity and water-use of potatoes (Solanum tuberosum L.) grown under small-scale irrigation
This paper evaluates the results of a study highlighting the effect of rigid scheduling on crop water use and soil water extraction patterns, crop coefficients, crop response functions and water-use efficiency (WUE). The cumulative Penman potential evapotranspiration (Etp) at the end of the season reached around 400 mm and the total depth of water applied between planting and harvest through irrigation (I) and rainfall (P) varied from 68 mm in rain-fed treatments to 670 mm in the wettest treatment. Crop water-use (Etc) varied from about 120 mm to around 280 mm corresponding to a daily mean value of Etc at the maximum stage of growth (55 days after planting) from about 1.3 mm to around 5.6 mm for fully irrigated crops. Maximum crop coefficients (Kc) ranged from 0.46 for rain-fed crops to 1.2. Crop yield reached ca. 9.1 t ha-1; for rain-fed treatments and ca. 31.1 t ha-1; for irrigated crops. The relationship between the total tuber fresh weight (t ha-1;) and total water applied (P+I) yielded a polynomial quadratic function (r?=75%). By contrast, the relationship between the total tuber fresh weight (t ha-1;) and total water-use displayed a linear function (r?=66%). The WUE for total water applied ranged from ca. 0.14 t ha-1; mm-1; in rain-fed crops to ca. 0.04 t ha-1; mm-1; for well irrigated crops following a linear function (r?=84%). These results indicate that rigid scheduling under small scale irrigation affects productivity, water-use and water-use efficiency of potatoes with a considerable waste of resources.