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Knowledge regarding uptake of water and nutrients as a function of their status in the soil is critical for smart fertigation management. Of particular interest is the uptake of water and potassium (K), each as a function of root zone salinity. The objective of this study was to quantify the response of tomato water uptake (transpiration) and K uptake to varied levels of K availability combined with salinity. Two independent lysimetric experiments were conducted and used to calibrate and validate models for water and K uptake under varied soil salinity. Tomato water and K uptake were determined by water and nutrient balance using the measured soil water content and K concentration in soil and drainage solution. Tomato water uptake was affected by root zone soil K and salinity. Salinity was the dominant factor driving uptake when irrigation solution had NaCl concentration of over 3 g L–1. Potassium uptake of tomato decreased with decreasing soil K content and increasing soil salinity. The linear relationship between tomato water uptake and K uptake rate was not influenced by soil salinity, indicating that the inhibition of K uptake was probably due to passive uptake of K with the flux of water from soil to roots decreased due to salinity. Tomato water and K uptake were simulated considering the effect of soil solution K concentration under simultaneous K and salinity stresses. Simulated daily average water and K uptake rates agreed well with measured values, with root mean squared error, normalized root mean squared error, and index of agreement of 144 cm3 d–1, 20.13% and 0.99 for average daily water uptake; and 24.43 mg d–1, 29.78% and 0.98 for K average daily uptake rate, respectively. These findings can be used to predict crop water and K requirements under combined salinity and K status conditions, which should contribute to efficient and sustainable fertigation scheduling. [ABSTRACT FROM AUTHOR]

A four-year trial was set up to test the feasibility of growing oleic sunflower in a very strongly saline wasteland with drip irrigation in the Ningxia plain of Northwest China. The soil salinity expressed as electrical conductivity of the saturation paste extract (EC) was around 28 dS/m, and soil nutrient was deficient in the upper 120 cm depth. The experiment included five soil matric potential (SMP) treatments, with the SMP at 20-cm depth immediately under the emitters maintained to be higher than −5, −10, −15, −20 and −25 kPa after sunflower establishment. Drip irrigation consistently created a favourable soil moisture and low-salinity region in the root zone when the SMP was maintained higher than −25 kPa. The sunflower dry seed yield decreased by 3.8 % for each unit increase in seasonal average soil salinity in the root zone. Plant vegetative growth, yield characteristics, irrigation frequency and irrigation amount all increased with the increase in SMP from −25 to −5 kPa, and the highest irrigation water use efficiency was available when the SMP was between −10 and −15 kPa (the amount of applied water was around 750 mm). Leaching of salts by drip irrigation gradually turned the very strongly saline soil into a moderately saline soil. This research suggests that drip irrigation can be successfully used in oleic sunflower cultivation in this highly saline soil and a SMP threshold between −10 and −15 kPa is suggested for irrigation scheduling. [ABSTRACT FROM AUTHOR]