Effect of Selenium on Mineral Content and Nutritive Value of Melilotus officinalis L.

Plants of Melilotus officinalis L. were subjected to two different treatments: a) no selenium (Se), and b) addition of 3 mg Se L^?1 irrigation water for 45 days and samples of leaves, stems and roots were analyzed for Se, potassium (K), sodium (Na), magnesium (Mg), iron (Fe), copper (Cu), calcium (Ca), manganese (Mn) and zinc (Zn). Crude protein (CP) content, neutral detergent fiber (NDF), acid detergent fiber (ADF) and in vitro organic matter digestibility (IVOMD) were also estimated for the aerial plant tissues. In Se-treated plants Se mainly accumulated in leaf tissues, various changes in macronutrient concentrations were detected, while the micronutrient content decreased significantly. In addition, leaf CP, NDF and ADF content decreased, while IVOMD increased, possibly indicating ameliorated nutritive value. According to our findings, M. officinalis could be used either as a dietary supplement, in mixture with non-accumulator species, for livestock feed deficient in Se or for restoration of grasslands in seleniferous soils.     

Strontium Absorption by Two Trifolium Species as Influenced by Soil Characteristics and Liming

Strontium absorption by plants is specific to individual species and also depends on the underlying soil properties. The purpose ofthis study was to evaluate the effect of certain soil characteristics and liming on Sr absorption by twoTrifolium species. One-liter volume of two inorganic and three organic soilswere treated with a combination of three CaCO₃ levels, 0, 3.6 and 7.2 g, × two Sr levels, 50 and 100 mg, (treatments) in four replications. Trifolium repens L. was grown in thetreated soils, in pots, harvested twice, and Sr in theabove-ground biomass of each harvest and soil exchangeable Caof each treatment were determined. The experiment was repeatedwith Trifolium subterraneum L., harvested once. For bothspecies, Sr transfer factor (T.F.) values of the varioustreatments were calculated. Shoot Sr concentrations weresignificantly affected by soil characteristics and Sr additionrates and were greater in T. repens. In all cases, theSr concentrations of plants grown in the organic soils, whichwere characterized by higher exchangeable Ca and cationexchange capacity (C.E.C.) values, were lower than those ofplants grown in the inorganic soils. Among the organic soils,Sr concentrations of the plants grown in the soil with thehighest values of C.E.C., organic matter and exchangeable Cawere the lowest. Liming decreased significantly the Srconcentrations in T. repens and T. subterraneumgrown in the two acid soils, while the pH and exchangeable Cawere increased. Shoot Sr concentration (log scale) wassignificantly, negatively correlated with soil exchangeable Ca. Strontium T.F. values were quite similar between the two Sr application rates and were affected by the same soil characteristics.     

Assessment of nickel's sufficiency critical levels in cultivated soils,employing commonly used calibration techniques

Although Ni has been officially recognized as an essential micronutrient for all higher plants since 2004, research on assessing its sufficiency critical levels with different soil tests is missing in the literature. The objective of the study was to determine Ni critical levels in unpolluted cultivated soils utilizing four methods, employing three commonly used calibration techniques. Ten soils with different physical–chemical properties and low Ni content were treated with Ni at rates of 1, 2, 4, and 8 mg kg^?1. After equilibration for one month, the soils were analyzed for extractable Ni by four methods, namely DTPA, AB‐DTPA, AAAc‐EDTA, and Mehlich‐3. Response to soil‐applied Ni was assessed by a greenhouse pot experiment, with the untreated and Ni‐treated soils in three replications, using ryegrass (Lolium perenne L.). The aboveground biomass of ryegrass was harvested two months after sowing, dry weight of biomass was measured and relative biomass yield was calculated. Nickel's critical levels were determined employing the: (a) graphical technique of Brown and co‐workers, (b) Mitscherlich–Bray equation, and (c) Cate and Nelson graphical technique. According to the first technique, Ni critical levels were ≈ 2 mg kg^?1 for the DTPA and AB‐DTPA methods, and 6.0 and 5.3 mg kg^?1 for the AAAc‐EDTA and Mehlich‐3 methods, respectively. Similar levels were obtained by the Mitscherlich–Bray equation. However, the critical levels assessed by the Cate and Nelson technique were lower and ranged from 0.5 to 1.3 mg kg^?1 for all four methods. Conclusively, Ni sufficiency critical levels for all four methods are expected to range at levels of a few mg Ni kg^?1 of soil. As far as the three calibration techniques are concerned, a distinct boundary between Ni response and non‐response was accomplished by none. However, the fact that 60–74% of the soils were correctly separated into responsive and non‐responsive to added Ni by the graphical technique of Brown and co‐workers suggests that this is the most suitable technique.     

Evaluation of sodium tetraphenylboron (NaBPh4) as a soil test of potassium availability

Non-exchangeable potassium (K_nex) contributes to soil K availability and several extractants are used to access its contribution. This study evaluated sodium tetraphenylboron (NaBPh₄) as a soil test of K availability in 20 soils from Northern Greece. Winter wheat (Triticum aestivum L. var. ‘Yecora’) was sown in a greenhouse pot experiment and five cropping cycles were carried out until K-depletion. Soils were analyzed with NH₄OAc and NaBPh₄ (1 and 5 min incubation periods). Critical levels of K ranged between 130–140 and 330–340 mg K kg^?1 of soil for NH₄OAc and NaBPh₄ (1 min incubation period), respectively, and between 32 and 35 g K kg^?1 of wheat dry matter. NaBPh₄-K (1 min) related better with K concentration and uptake compared to NH₄OAc for each cropping cycle (r² = 0.45–0.83 and 0.44–0.89) and for all soils (r² = 0.58 and 0.51). Similar results obtained in soils low in exchangeable K (r² = 0.41 and 0.39). Correlation between NH₄Oac- and NaBPh₄-extractable K was weaker among soils below the critical level (r = 0.70) compared to those above (r = 0.93). Inclusion of illitic K and cation exchange capacity in a multiple linear regression between NH₄OAc- and NaBPh₄-extractable K showed that they significantly contributed to NaBPh₄-extractable K.     

Contribution of non-exchangeable potassium on its quantity-intensity relationships under K-depleted soils

ABSTRACT

Quantity-Intensity (Q/I) parameters were used for elucidating the role of buffering properties of soils through K depletion. Winter wheat was sown in a greenhouse pot experiment until K-depletion and soils were analyzed with NH₄OAc and NaBPh₄ (1 min incubation period). Q/I isotherms (partitioned in exchangeable and non-exchangeable form) were constructed for the soils before and at the end of the K-exhaustion experiment. Results showed that NaBPh₄-K correlated better than NH₄OAc-K with intensity parameter (AR_e^K) or labile K (-ΔΚ₀) in K-depleted soils (r = 0.41 and 0.70), indicating the importance of non-exchangeable K in K dynamics. The latter was confirmed from the comparison of buffering characteristics between initial and K-depleted soils which showed that among the soils studied there was a group whose increase in buffering capacity (PBC^K_t) was due to non-exchangeable K fixation. Furthermore, NaBPh₄-K was well predicted by the sum of exchangeable K and the quantity of K that has to be applied to achieve K balance as derived from Q/I isotherms (EK₀ + CK₀). Finally, relationships were found between Q/I parameters of the initial soils (-ΔΚ_0i, ΕΚ_0i, ΕΚ_ri, CK_0i) and the K-depleted ones (ΕΚ_rd, ΕΚ_0d, CK_0d, CK_rd) which allowed corresponding prediction of the initial parameters (r² = 0.78–0.87).     

Micronutrient Levels in Sugar Beet in Soils of Greece

A survey was conducted in order to estimate micronutrient levels in plants and soils of 215 farms in Greece cultivated with sugar beet. Soils were analyzed for particle-size distribution, pH, organic carbon (C), CaCO₃, and DTPA-extractable copper (Cu), zinc (Zn), iron (Fe), and manganese (Mn). Sugar beet leaves were analyzed for the same metals. Also, aboveground biomass (top), root, and raw sugar yields were recorded. DTPA-extractable Fe and Mn were above critical levels in all cases, whereas Cu and Zn were above critical levels in 49% and 24% of the soil samples, respectively. Concentrations of the four metals in plant tissue were similar or higher than the sufficiency range. Concentrations of DTPA-extractable Fe and Mn, and plant Zn and Mn, were significantly and negatively correlated with soil pH. Soil pH and DTPA-extractable Fe seemed to have a significant positive impact on root, top, and raw sugar yields. However, in all cases, less than 14% of the variance of the sugar beet parameters was explained by soil characteristics.