Norwegian Journal of Agricultural Sciences : irrigation of cereals, potato, carrot and onion on a loam soil at various levels of moisture deficit

Abstract

Field trials were performed on a morainic loam soil to delermine optimum irrigation strategy in cereals, potato, carrot and onion. lrrigation was given at deficits of 20, 40 and 60 mm, calculated using a water balance modeI. Rooting depth was estimated to be 60 cm and the available water capacity (AWC) was found to be 95 mm. Regression equations were derived of relative yield on relative evapotranspiration at different growth stages. Effects on various irrigation strategies on yields, water requirements and drainage losses were predicted over 25 years. Mean maximum responses to irrigation at an AWC of 110 mm were about 20% for potato and carrot and 12% for cereals and onion. At 70 mm AWC the figures were approx. 40% and 20%. Non-irrigated yields were greater than 95% ofthose with irrigation in half or one-third ofall years, and lower than 75% in about one-quarter or one-third on all years, at 110 mm and 70 mm AWC, respectively. Irrigation at 50% depletion of'AWC gave only slightly lower yields than more frequent irrigation, and considerable reductions in both the amounts ofwater required and in drainage losses.