Optimisation of Irrigation Regime for Early Potatoes, Late Cauliflower, Early Cabbage and Celery

Abstract

Qualified management of irrigation regimes of crops is one of the basic conditions of irrigation profitability. It brings about great savings of irrigation water, electrical power and nitrogen fertilisers, and it enables to achieve optimum and high-quality marketable yields of crops and to reduce a risk of groundwater contamination by nitrates, pesticide residues and other xenobiotic compounds. SANFORD (2003) stated that the management of irrigation regime could reduce energy consumption per unit yield by 7-32% in relation to the crop. The importance of energy savings increases with the growth of its prices that has been, and will probably be, marked. Abstract: The paper deals with optimisation of threshold suction pressure of soil water on light soils for early potatoes, early cabbage, late cauliflower and celery on the basis of results of small-plot field experiments with differentiated irrigation regime. Experiments were conducted in 2003-2005. Threshold suction pressures of soil water were identical for all crops: 15 kPa in treatment I, 30 kPa in treatment II, 60 kPa in treatment III, and 120 kPa in treatment IV. Precipitation, air temperature and relative humidity, global solar radiation, wind speed and direction were measured by an automated meteorological station. Reference and actual evapotranspiration was determined for the experimental crops according to FAO Paper No. 56 and by means of a biological curve (BC) in 2003-2005. To compare these two methods of calculation of actual evapotranspiration the soil moisture balance was found out. Based on the influence on marketable yield and proportion of the crop quality grades it is possible to determine the optimum threshold suction pressure on light loamy-sand soils in early potatoes, late cauliflower and cabbage 30 kPa and in celery 15 kPa. 80% of available soil water capacity (ASWC) corresponds to the threshold suction pressure 30 kPa, and as much as 96% of ASWC corresponds to 15 kPa. The seasonal irrigation depths determined on the basis of soil moisture balance, in which the crop evapotranspiration (ET c) is calculated either according to FAO 56 or by the BC, are substantially different from the really achieved irrigation depths in the treatments where optimal suction pressure is maintained. For potatoes, the really achieved values of seasonal irrigation depths are nearer to the depths calculated by the BC, while for the other vegetables (cauliflower, cabbage and celery) they are more similar to the depths calculated by FAO 56 methodology. The theoretical irrigation depths calculated by the BC method sometimes differ substantially from those based on FAO 56. These differences are at maximum for cauliflower and celery and at minimum for cabbage and decrease with the decreasing irrigation depths.