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[Objective] Gravel mulching combined with drip irrigation is an improved agronomic technique for crop production in northwestern China. The purpose of this study is to investigate the impact of dripping rate of the emitters on soil water and salt redistribution, as well as the growth and yield of watermelon. [Method] The field experiment had three treatments with the dripping rate controlled at 2 L/h (Q1), 3 L/h (Q2), or 4 L/h (Q3), respectively. In each treatment, we measured the spatiotemporal variation in soil water and salt, water use efficiency, as well as growth, yield and fruit quality of the watermelon. [Result] Horizontal advancement of the wetting front in the soil increased with dripping rate. After harvest, soil salt content in the 0~100 cm soil layer decreased, with the decreasing rate increasing as the dripping rate increased. Also, with the increase in dripping rate, the soluble sugar content in the fruits increased first followed by a decline. Of the three dripping rates we compared, Q2 increased the soluble sugar content in the fruit the most, up by 54.3% and 22.3%, respectively, compared to Q1 and Q3. With the increase in dripping rate, the vitamin C content in the fruits decreased first and then ramped up. Q3 gave the highest vitamin C content, increasing by 53.7% compared to Q2. Increasing dripping rate boosted both fruit yield and water use efficiency. Compared to Q1 and Q2, Q3 increased fruit yield by 6.20% and 3.56%, and water use efficiency by 6.49% and 3.72%, respectively. [Conclusion] Taking soil water and salt redistribution, as well as watermelon yield and quality into account, the optimal dripping rate for watermelon growth in the gravel-mulched soil was 4 L/h when using the local saline water for irrigation. [ABSTRACT FROM AUTHOR]

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]