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【Objective】 Brackish water has been used as a supplementary irrigation resource in some arid and semi-arid regions in northwestern China, but the impact of its long-term application on soil environment and crop growth and quality is not well understood. The objective of this paper is to fill this knowledge gap using watermelon as an example. 【Method】 The experiment was conducted in fields with sand mulch, where brackish water has been used as a supplementary irrigation resource for varying periods ranging from 2 to 14 years. During the experiment, we measured the distribution of soil water and salt in the 0~60 cm soil layer, soil bulk density, as well as the yield and quality of watermelon. An uncultivated piece of land nearby was used as the control. 【Result】 Soil salt content increased with the increase in duration of brackish water irrigation in both tendril elongation and harvest stage. The highest soil salt content was in the 20~40 cm soil layer for the control, and in the 40~60 cm soil layer for the sand-mulched field. The supplementary brackish water irrigation increased the soil moisture content in flowering and fruit-setting stages, but the increase varied in that with the increase in the duration of the brackish water irrigation, the soil water content increased first and then declined. The highest soil moisture content in the sand-mulched field was in the surface layer (0~10 cm), while for the control it was in the 10~20 cm soil layer. Sand mulch increased soil bulk density in the 0~40 cm soil layer and soil compaction in the 0~8 cm soil layer. It was also found that with the increase in length of brackish water irrigation, the yield and soluble solids content in the watermelon decreased, while the fruit quality improved first followed by a decline. 【Conclusion】 Long-term use of brackish water for supplementary irrigation in the sand-mulched fields increased soil bulk density and compaction in the upper soil layers, as well as soil moisture and salt content. As the years of brackish water irrigation increased, the yield of watermelon decreased while the quality of its fruits showed an initial improvement before deteriorating.

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]

Schematic representation of the effects of salinity on root structural traits. Namely; enlarged root diameter and periderm tissue while stele smaller with larger xylem vessels. • Roots modified their structural traits to enhance salt compartmentation and exclusion. • Salts accumulated in enlarged periderm tissue allowing greater compartmentation. • Two putative apoplastic barriers were identified: around the periderm and the stele. • Xylem vessel diameter distribution shifted to allow higher hydraulic conductivity. Roots are the first plant organ to encounter, sense, and respond to soil salinity. Like for many moderately salt tolerant species, roots of olive (Olea eurpaea) trees are the principal players in salt tolerance. We studied roots of mature olive trees in order to illuminate the yet vague mechanism(s) of root salt exclusion. Root structural traits were examined in olive trees grown in lysimeters and from a long-term salinity field trial. The distribution of salts was detected in root cross-sections using scanning electron microscopy combined with energy dispersive spectroscopy. Increased soil salinity caused a continuous decline in specific root length and an increase in root diameter, periderm thickness, and specific hydraulic conductivity. While periderm cell number was not modified, cell diameter increased linearly by a total of 50 % as root zone salinity increased nearly eight-fold. Strong compartmentation of Na within the periderm was found, with highest content in the outer periderm layer and lowest content in the stele. Increase in soil salinity was associated with decrease in stele area, yet, hydraulic conductivity was doubled due to higher fraction of large diameter xylem vessels. Our results indicate significant root structural plasticity, which underlies the salt resistance mechanisms. The dominant trait enabling salt tolerance of olive trees is the enlarged periderm serving as an apoplastic barrier that enhances salt compartmentation and exclusion from the vascular tissues. [ABSTRACT FROM AUTHOR]

Abstract: A 4-year trial was set up to test the feasibility of growing waxy corn (Zea mays L. var. ceratina Kulesh) in a highly saline wasteland with drip irrigation in the Ningxia plain, northwest China. The original soil salinity expressed as electrical conductivity of the saturation paste extract (EC e ) averaged 28dS/m in the 0–120cm depth. The experiment included five soil matric potential (SMP) treatments in which the SMP at 20cm depth below the drip emitters was controlled higher than −5, −10, −15, −20 and −25kPa after waxy corn establishment. The results showed that drip irrigation created a favorable soil condition for waxy corn growth through forming and maintaining a high moisture and low salinity region in the root zone when the SMP was maintained higher than −25kPa. Waxy corn growth and yield parameters increased with the increase of SMP from −25kPa to −5kPa, but their responses to SMP decreased with the prolonged period of cultivation. Irrigation frequency and irrigation amount decreased significantly as SMP decreased from −5kPa to −25kPa, and the highest irrigation water use efficiency (IWUE) was available when the SMP was around −15kPa in 2005, and was between −20kPa and −25kPa in successive years. After years of cultivation and drip leaching, the highly saline soil gradually changed to a moderately saline soil. This research suggests that drip irrigation can be successfully used in growing waxy corn in dry and highly saline conditions after appropriate management strategies are adopted. [Copyright &y& Elsevier]