Plant available silicon in bare fallow soils after 90 years of annual supplies of manure, lime and fertilizers

<p>Silicon (Si), non-essential but beneficial to plants, plays a crucial role in maintaining plant functions by alleviating a number of biotic and abiotic stresses. Applying manure, lime and chemical fertilizers to soils may impact the pool of plant available Si, but their impact over decades to century is unknown.</p><p>Here, we determined the evolution of the content of plant available Si in a silty soil derived from Quaternary loess (Haplic Luvisol), submitted to a long-term bare fallow experiment initiated in 1928 in Versailles (INRA, France). On this bare fallow soil, different treatments were applied annually since 1929, among which, manure, lime (CaCO<sub>3</sub>), NaNO<sub>3 </sub>and (NH<sub>4</sub>)<sub>2</sub>SO<sub>4</sub>) and compared to control soil. Archived soil samples were already characterized for their basic properties (pH, CEC, OC, N, oxalate-extractable Al, Fe and Si, DCB extractable Fe, particle size distribution, elemental analysis). Here, we computed the total reserve in bases (TRB), and we determined the content of plant available Si (CaCl<sub>2</sub>-Si) through a kinetical extraction using 0.01 M CaCl<sub>2</sub>.</p><p>TRB was 110 cmol (+) kg<sup>-1</sup> in 1929. During the 90 years period, TRB (cmol (+) kg<sup>-1</sup>) remained constant in manured plots, decreased to 96 in control/NaNO<sub>3</sub> plots and to 84 in the (NH<sub>4</sub>)<sub>2</sub>SO<sub>4</sub> plot whereas it increased to 160 in the CaCO<sub>3</sub> plot. The initial CaCl<sub>2</sub>-Si content did not differ between the treatments, as it ranged between 25 and 30 mg kg<sup>-1</sup> in 1929. Annual manure supply resulted in the progressive increase of CaCl<sub>2</sub>-Si up to 60 mg kg<sup>-1</sup>. In this treatment, CaCl<sub>2</sub>-Si (30 to 60 mg kg<sup>-1</sup>) and OC (18 to 40 g kg<sup>-1</sup>) contents were strongly and positively correlated, suggesting the continuous silicon through manure supply (probably phytoliths), and their dissolution at pH 6.6-7.6. In the four other treatments, OC content regularly decreased from 18 to 5 g kg<sup>-1</sup> from 1929 to 2019, but CaCl<sub>2</sub>-Si largely differed between them. Our data suggest a strong impact of pH on CaCl<sub>2</sub>-Si as well as the occurrence of two sources of bioavailable Si: phytoliths in limed plots (pH 6.6 to 8.8) and clay minerals in acidified plots submitted to annual (NH<sub>4</sub>)<sub>2</sub>SO<sub>4</sub> application (pH from 6 to 3.5).</p><p>Our preliminary results show that, in a given soil type, the pool of bioavailable silicon is strongly affected by soil properties, especially soil pH, OC content and weathering stage.</p>

A field survey of soil pH and extractable aluminium in the Ashburton Lakes Catchment, Canterbury, New Zealand.

Soil extractable aluminium (Al) concentrations have a strong impact on the establishment, growthand persistence of pasture legumes. A survey of 21 soil profiles in the Ashburton Lakes catchmentwas conducted to determine the key factors driving extractable Al concentrations. The mean Al (0.02 MCaCl2) concentration was 7.8 mg/kg with the highest values in the top 50 cm of the soil profile. However,there was considerable variation among sites. Landform age, rainfall and depth were all important variables forextractable Al (but R2 was low), while landform type was not. The highest Al concentrations in the 20 cm depthzone were found at the wettest sites in the catchment where rainfall was ≥ 1266 mm and where pH was lowest.Farmers in this catchment could use this knowledge to determine which areas of their farms are most susceptible to elevated Al concentrations and at what depth. This would assist in determining which areas could be targeted for development and which are unsuitable.

Aluminium toxicity on cowpea genotypes and its effect on plant and soil characteristics

In order to observe the effect of aluminium toxicity on plant and soil parameters investigation was carried out on twenty cowpea genotypes grown in pots with four aluminium levels i.e. 0, 20, 40, 60 ppm with three replications following factorial complete randomized design. After five weeks of growth, individual, main effect and their interaction were studied for uptake of Aluminium and Manganese by root and shoot, post-cropping parameters of soil (pH, available P, extractable Al and extractable Mn) were observed. Genotypes of cowpea and aluminium treatments exhibited significant differences for all characters. However, interaction effect was found significant for all studied character except manganese content in soil. The genotypes G2, G3, G5 and G15 were found superior for studied character.

Effect of elevated Al and pH on the growth and root morphology of Al-tolerant and Al-sensitive wheat seedlings in an acid soil .

Aluminium ion (Al³⁺) toxicity and hydrogen ion (H⁺) activity are the major constraints for plant growth in acid soil. This study was undertaken to determine the effect of pH and Al on the growth response and changes in root morphology of Al-tolerant (ET8) and Al-sensitive (ES8) wheat seedlings. Different levels of AlCl₃ and CaCO₃ were added to the soils to manipulate soil pH and extractable Al. The results showed that the bulk soil pH remained constant at pH 4.1 with further applications of AlCl₃, and that the seedlings died at the 200 mg AlCl₃/kg treatments. The ET8 seedlings responded better than the ES8 seedlings in both low and high Al and pH. The ET8 seedlings had higher root surface areas and root tip numbers than the ES8 seedlings in the Al treatment. In contrast, the ES8 had higher root diameters than the ET8 seedlings due to the elevated Al supply. Apoplast Al increased with the increase of soil available extractable Al, and declined with the decrease of soil extractable Al. The ET8 seedlings accumulated more Al in their apoplast than the ES8 seedlings. This study concluded that accumulation of Al in the apoplast is also involved in Al tolerance mechanism with the addition of organic acid exudation.

Extractable Al and Soil Solution Ionic Concentrations in Strongly Leached Soils from Northwest Iberia: Effects of Liming

Strongly leached soils occurring in Northwest Iberia contain high concentration of Al which may affect crop growth. Information regarding the extractability of Al and lime required to eliminate toxic Al species in the soil solution is scarce. In this context, the extractability of Al on these soils was determined using 1 M KCl, 0.33 M LaCl3 and 0.5 M CuCl2. The effects of lime on the concentration and activity of Al species in soil solution, using the GEOCHEM program was also evaluated. Extractability of Al was in the order: 1 M KCl < 0.33 M LaCl3 < 0.5 M CuCl2, with ranges from 0.7–3.3, 1.3–4.4, and 1.8–13.5 cmolc kg-1, respectively. These values were positively correlated with cation exchange capacity and organic C, clay, Alo and Feo contents. Application of 6 t CaCO3 ha-1 increased the total concentrations of Ca+2, Mg+2, K+, and Na+ ions in soil solution, whereas, application of 2 t CaCO3 ha-1 reduced the concentration and activity of Fe+3, Al+3, Mn+2, Zn+2, Cu+2, SO4-2, and PO4-3 ions,and eliminated toxicity threshold of free Al+3 and Al soluble complexes in the soil solution. Application of low amounts of lime may prevent the negative effects of soluble Al on crops.

Relationship between soil oxidizable carbon and physical, chemical and mineralogical properties of umbric ferralsols

The occurrence of Umbric Ferralsols with thick umbric epipedons (> 100 cm thickness) in humid Tropical and Subtropical areas is a paradox since the processes of organic matter decomposition in these environments are very efficient. Nevertheless, this soil type has been reported in areas in the Southeast and South of Brazil, and at some places in the Northeast. Aspects of the genesis and paleoenvironmental significance of these Ferralsols still need a better understanding. The processes that made the umbric horizons so thick and dark and contributed to the preservation of organic carbon (OC) at considerable depths in these soils are of special interest. In this study, eight Ferralsols with a thick umbric horizon (UF) under different vegetation types were sampled (tropical rain forest, tropical seasonal forest and savanna woodland) and their macromorphological, physical, chemical and mineralogical properties studied to detect soil characteristics that could explain the preservation of high carbon amounts at considerable depths. The studied UF are clayey to very clayey, strongly acidic, dystrophic, and Al-saturated and charcoal fragments are often scattered in the soil matrix. Kaolinites are the main clay minerals in the A and B horizons, followed by abundant gibbsite and hydroxyl-interlayered vermiculite. The latter was only found in UFs derived from basalt rock in the South of the country. Total carbon (TC) ranged from 5 to 101 g kg-1 in the umbric epipedon. Dichromate-oxidizable organic carbon represented nearly 75 % of TC in the thick A horizons, while non-oxidizable C, which includes recalcitrant C (e.g., charcoal), contributed to the remaining 25 % of TC. Carbon contents were not related to most of the inorganic soil variables studied, except for oxalate-extractable Al, which individually explained 69 % (P < 0.001) of the variability of TC in the umbric epipedon. Clay content was not suited as predictor of TC or of the other studied C forms. Bulk density, exchangeable Al3+, Al saturation, ECEC and other parameters obtained by selective extraction were not suitable as predictors of TC and other C forms. Interactions between organic matter and poorly crystalline minerals, as indicated by oxalate-extractable Al, appear to be one of the possible organic matter protection mechanisms of these soils.

Drinking water treatment residuals as an amendment to alkaline soils: Effects on bioaccumulation of heavy metals and aluminum in corn plants

An alum-based drinking water treatment residue (DWTR) is the by-product from the production of potable water. Land application of DWTR has received a considerable attention for its potential as a low-cost disposal alternative. A greenhouse experiment was conducted to quantify the effects of DWTR on bioaccumulation of some heavy metals in plant tissue and to determine the effects of the DWTR on soil aluminum and aluminum phytotoxicity for the corn plants in alkaline soils. The results indicated that land application of DWTR significantly decreased extractable heavy metals in all studied soils. Combined analyses of all soils and rates of DWTR application showed significant relationship between DTPA-extractable heavy metals and heavy metals uptake of corn plants. Addition of DWTR with different rates (10, 20, 30 and 40 g/kg) to different soil types did not cause aluminum phytotoxicity symptoms for corn plants grown in all studied alkaline agricultural soils because the application rates of DWTR did not increase extractable Al in amended soils > 8 mg Al/kg and the Al phytotoxicity may occur below pH 5.5. Extractable Al is associated with pH of the studied soils, combined analyses of all soils and rates of DWTR application showed a significant relationship between extractable Al and pH. Based on the results of current study, the DWTR is considered an ameliorating material for heavy metals removal from soils; however, additional studies are necessary to confirm these results under field conditions.