BackgroundIn soils with a low phosphorus (P) supply, sugar beet is known to intake more P than other species such as maize, wheat, or groundnut. We hypothesized that organic compounds exuded by sugar beet roots solubilize soil P and that this exudation is stimulated by P starvation.ResultsRoot exudates were collected from plants grown in hydroponics under low- and high-P availability. Exudate components were separated by HPLC, ionized by electrospray, and detected by mass spectrometry in the range of mass-to-charge ratio (m/z) from 100 to 1000. Eight mass spectrometric signals were enhanced at least 5-fold by low P availability at all harvest times. Among these signals, negative ions with an m/z of 137 and 147 were shown to originate from salicylic acid and citramalic acid. The ability of both compounds to mobilize soil P was demonstrated by incubation of pure substances with Oxisol soil fertilized with calcium phosphate.ConclusionsRoot exudates of sugar beet contain salicylic acid and citramalic acid, the latter of which has rarely been detected in plants so far. Both metabolites solubilize soil P and their exudation by roots is stimulated by P deficiency. These results provide the first assignment of a biological function to citramalic acid of plant origin.

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The aim of this study was to compare the effects of foliar fertilization with a nitrogen (N) fertilizer containing nanoparticles (nN) with those of foliar fertilization with urea on the characteristics of pomegranate fruits cv. Ardestani. The experiment was carried out using a completely randomized block design with five treatments and four replications (trees) per treatment during two consecutive years, 2014 and 2015. Two foliar applications of nN (0.25 and 0.50 g N/L, equivalent to ≈1.3 and 2.7 g N/tree or 0.9 and 1.8 kg N/ha; nN1 and nN2, respectively) and urea (4.6 and 9.2 g N/L, equivalent to ≈24.4 and 48.8 g N/tree or 16.3 and 32.5 kg N/ha; U1 and U2, respectively) were applied at full bloom and 1 month later, and trees not treated with any N fertilizer were used as a control. Results show that foliar N fertilization increased fruit yield (by 17% to 44%) and number of fruits per tree (by 15% to 38%). The highest fruit yields (17.8 and 21.9 kg/tree) and number of fruits per tree (62.8 and 70.1/tree) were obtained with the treatment nN2 (1.8 kg N/ha), whereas the lowest fruit yields (12.4 and 16.2 kg/tree) and number of fruits per tree (45.5 and 55.3/tree) were recorded in the control trees. The treatments U1 and nN2 increased fruit length (the latter only in the second season), whereas the treatment U1 increased average fruit weight (10% to 11%). The treatment nN2 increased aril juice and total soluble solids (TSS) in both seasons and titratable acidity (TA) only in the first one, whereas the treatment U1 increased TSS in both seasons and aril juice and TA in the second season. Treatments nN2 and U1 also increased total sugars and decreased total anthocyanins. On the other hand, fruit diameter, fruit cracking, peel thickness, aril content, weight of 100 arils, juice pH, maturity index, antioxidant activity, and total phenolic compounds were unaffected by N fertilization. Nitrogen fertilization increased the leaf concentration of N, whereas the leaf concentrations of P, K, Mn, and Zn were unaffected. Results indicate that pomegranate fruit yield was improved similarly with two applications (at full bloom and one month later) of nN fertilizer at a rate of 1.8 kg N/ha and with two applications of urea at a rate of 16.3 kg N/ha. Furthermore, fruit quality was improved more with the nN fertilizer at a rate of 1.8 kg N/ha than with two applications of urea at a rate of 16.3 kg N/ha.

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A b s t r a c t. This study investigated the impact of monovalent cations on clay dispersion, aggregate stability, soil pore size distribution, and saturated hydraulic conductivity on agricultural soil in Iran. The soil was incubated with treatment solutions containing different concentrations (0-54.4 mmol l -1 ) of potassium and sodium cations. The treatment solutions included two levels of electrical conductivity (EC=3 or 6 dS m -1 ) and six K:Na ratios per electrical conductivity level. At both electrical conductivity levels, spontaneously dispersible clay increased with increasing K concentration, and with increasing K:Na ratio. A negative linear relationship between percentage of water-stable aggregates and spontaneously dispersible clay was observed. Clay dispersion generally reduced the mean pore size, presumably due to clogging of pores, resulting in increased water retention. At both electrical conductivity levels, hydraulic conductivity increased with increasing exchangeable potassium percentage at low exchangeable potassium percentage values, but decreased with further increases in exchangeable potassium percentage at higher exchangeable potassium percentage. This is in agreement with earlier studies, but seems in conflict with our data showing increasing spontaneously dispersible clay with increasing exchangeable potassium percentage. Our findings show that clay dispersion increased with increasing K concentration and increasing K:Na ratio, demonstrating that K can have negative impacts on soil structure.

In arid and semi‐arid regions of the world, agricultural production is greatly limited by water scarcity and inefficient water use. Water‐absorbent hydrogels are a technological solution that can retain soil water for plants. A lignin‐based hydrogel as a natural plant‐based water absorbent is prepared from lignin alkali polymers and poly(ethylene glycol) diglycidyl ether (PEGDGE) in adjusted alkali (NaOH) solution. The maximum swelling capacity of the hydrogel is achieved in 1.5 m NaOH with 0.5 mmol PEGDGE g lignin −1. Water swelling capacity is 34 g g Hydrogel −1 dry weight of hydrogel in distilled water, which is reduced to 53% and 64% in 0.1 m NaCl and 0.1 m CaCl2 solution, respectively. Biodegradability and phytotoxicity tests show that 6.5% of the sample mass decomposed after 40 days of incubation in soil solution media and the hydrogel is not phytotoxic to wheat seeds. These findings support the use of the lignin‐based hydrogel as an environmentally friendly additive to promote water retention in dry, saline soils. Due to the limitations of this study, further assessments are needed in order to understand the efficiency of lignin‐based hydrogel application in different soils with different biota.