NUTRIENT AND GROWTH RESPONSES OF LEERSIA ORYZOIDES,RICE CUTGRASS,TO VARYING DEGREES OF SOIL SATURATION AND WATER NITROGEN CONCENTRATION

Leersia oryzoides (rice cutgrass) is an obligate wetland plant common to agricultural drainage ditches. The objective of this greenhouse study was to expose plants to various flooding and aqueous nitrogen (N) concentrations and then to quantify the allocation of nutrients and biomass to plant components. Plants in the continuously flooded treatment (CF) had the highest tissue concentrations of copper (Cu), sulfur (S), zinc (Zn), potassium (K), sodium (Na), and manganese (Mn) in one or more plant components. Plants in the partially flooded treatment (PF) had the highest concentrations of magnesium (Mg) in leaves. The N input affected phosphorus (P) and S concentrations in roots. Leaf, stem, and root biomass were highest in PF plants. Rhizome biomass was the lowest in CF plants. These results indicate that L. oryzoides may significantly affect elemental concentrations in surface waters by its ability to uptake various elements and subsequent sequestration in various biomass components.     

Evolution and phosphorus fractionation in saline Spolic Technosols flooded with eutrophic water

Purpose

The aim of this study was to evaluate the behaviour of P in saline Spolic Technosols flooded with eutrophic water, with and without plant rhizosphere, in order to assess the role of these soils as sinks or sources of this nutrient.

Materials and methods

Samples were taken from basic (pH?~7.8), carbonated and acidic (pH?~6.2), de-carbonated soils of salt marshes polluted by mine wastes. Three treatments were assayed: pots with Sarcocornia fruticosa, pots with Phragmites australis and pots without plants (bare soil). The pots were flooded for 15?weeks with eutrophic water (PO ₄ ^3? ~6.92?mg?L^?1) and pH, Eh and water-soluble organic carbon and PO ₄ ^3? concentrations were monitored in the soil solution. A soil P fractionation was applied before and after the flooding period.

Results and discussion

The PO ₄ ^3? concentration in the soil solution decreased rapidly in both soils, with and without plant, being diminished by 80?C90?% after 3?h of flooding. The Fe/Mn/Al oxides and the Ca/Mg compounds played an important role in soil P retention. In pots with S. fruticosa, the reductive conditions due to flooding induced P release from metal oxides and P retention to Ca/Mg compounds. In turn, P. australis may have favoured the release of P from carbonates, which was transferred to Fe/Mn/Al compounds.

Conclusions

The retention of P by the soil was the main mechanism involved in the removal of PO ₄ ^3? from the eutrophic flooding water but to evaluate the capacity of these systems as long-term P sinks, the combined effect of metals, Ca/Mg compounds and specific plant species should be considered.     

Influence of temporary flooding at three growth stages on soybeans grown on a clayey soil

Abstract

Knowledge of crop response to temporary waterlogging is important in the development of effective water management practices. A field study was conducted to determine the response of soybean [Glvcine max. (L.) Merr] grown on a poorly drained, clayey soil to temporary flooding at three growth stages. The four treatments were soybean flooded for seven consecutive days at either VI, V4 or R2 growth stages at a flood height of 0.03 m above the soil surface and a well‐watered control. Flooding for seven consecutive days wetted but did not saturate the lower parts of the soil profile. This was attributed to the swelling by the montmorillonitic clay and subsequent sealing of the soil near the surface. In general, Eh and ODR decreased gradually during the flood, but increased as the soil dried upon removal of the flood. Canopy heights and dry weights of the flooded soybeans were dependent on plant growth stage at flooding and time of measurement but were lower than the control. When flooded at the VI or V4 growth stages, concentrations of N and K in the above‐ground plants were lower than the control after the flood. Three weeks after the flood was removed higher concentrations of these elements were found. When flooded at R2, concentrations of N and K were lower than in the control. Few differences were found in the plant concentrations of Ca, Mg, Mn, Fe, Al, and Na in the plant due to the flood, but by the end of the growing season, concentrations of Mn, Fe and Al were higher in the R2 flooded soybeans than in the other treatments. Seed yield response of the soybeans depended upon plant growth stage at flooding. The soybeans were particularly sensitive to the seven days of continuous flood at the R2 growth stage. Values of relative seed yield were 88, 83, and 44 % of the well watered‐control for the VI, V4 and R2 growth stages, respectively. Differences in seed yield were found with cultivar and with cultivar?flood treatment.     

Influence of pH on the redox chemistry of metal (hydr)oxides and organic matter in paddy soils

Purpose

The primary purpose of this study was to determine how flooding and draining cycles affect the redox chemistry of metal (hydr)oxides and organic matter in paddy soils and how the pH influences these processes. Our secondary purpose was to determine to what extent a geochemical thermodynamic equilibrium model can be used to predict the solubility of Mn and Fe during flooding and draining cycles in paddy soils.

Material and methods

We performed a carefully designed column experiment with two paddy soils with similar soil properties but contrasting pH. We monitored the redox potential (Eh) continuously and took soil solution samples regularly at four depths along the soil profile during two successive flooding and drainage cycles. To determine dominant mineral phases of Mn and Fe under equilibrium conditions, stability diagrams of Mn and Fe were constructed as a function of Eh and pH. Geochemical equilibrium model calculations were performed to identify Mn and Fe solubility-controlling minerals and to compare predicted total dissolved concentrations with their measured values.

Results and discussion

Flooding led to strong Eh gradients in the columns of both soils. In the acidic soil, pH increased with decreasing Eh and vice versa, whereas pH in the alkaline soil was buffered by CaCO₃. In the acidic soil, Mn and Fe solubility increased during flooding due to reductive dissolution of their (hydr)oxides and decreased during drainage because of re-oxidation. In the alkaline soil, Mn and Fe solubility did not increase during flooding due to Mn(II) and Fe(II) precipitation as MnCO₃, FeCO₃, and FeS. The predicted levels of soluble Mn and Fe in the acidic soil were much higher than their measured values, but predictions and measurements were rather similar in the alkaline soil. This difference is likely due to kinetically limited reductive dissolution of Mn and Fe (hydr)oxides in the acidic soil. During flooding, the solubility of dissolved organic matter increased in both soils, probably because of reductive dissolution of Fe (hydr)oxides and the observed increase in pH.

Conclusions

Under alternating flooding and draining conditions, the pH greatly affected Mn and Fe solubility via influencing either reductive dissolution or carbonate formation. Comparison between measurements and geochemical equilibrium model predictions revealed that reductive dissolution of Mn and Fe (hydr)oxides was kinetically limited in the acidic soil. Therefore, when applying such models to systems with changing redox conditions, such rate-limiting reactions should be parameterized and implemented to enable more accurate predictions of Mn and Fe solubility.     

Effect of Lime and Flooding on Phosphorus Availability and Rice Growth on Two Acidic Lowland Soils

Abstract

Loss of soil‐water saturation may impair growth of rainfed lowland rice by restricting nutrient uptake, including the uptake of added phosphorus (P). For acidic soils, reappearance of soluble aluminum (Al) following loss of soil‐water saturation may also restrict P uptake. The aim of this study was to determine whether liming, flooding, and P additions could ameliorate the effects of loss of soil‐water saturation on P uptake and growth of rice. In the first pot experiment, two acid lowland soils from Cambodia [Kandic Plinthaqult (black clay soil) and Plinthustalf (sandy soil)] were treated with P (45 mg P kg^?1 soil) either before or after flooding for 4 weeks to investigate the effect of flooding on effectiveness of P fertilizer for rice growth. After 4 weeks, soils were air dried and crushed and then wet to field capacity and upland rice was grown in them for an additional 6 weeks. Addition of P fertilizer before rather than after flooding depressed the growth of the subsequently planted upland rice. During flooding, there was an increase in both acetate‐extractable Fe and the phosphate sorption capacity of soils, and a close relationship between them (r²=0.96–0.98). When P was added before flooding, Olsen and Bray 1‐extractable P, shoot dry matter, and shoot P concentrations were depressed, indicating that flooding decreased availability of fertilizer P. A second pot experiment was conducted with three levels of lime as CaCO₃ [to establish pH (CaCl₂) in the oxidized soils at 4, 5, and 6] and four levels of P (0, 13, 26, and 52 mg P kg^?1 soil) added to the same two acid lowland rice soils under flooded and nonflooded conditions. Under continuously flooded conditions, pH increased to over 5.6 regardless of lime treatment, and there was no response of rice dry matter to liming after 6 weeks' growth, but the addition of P increased rice dry matter substantially in both soils. In nonflooded soils, when P was not applied, shoot dry matter was depressed by up to one‐half of that in plants grown under continuously flooded conditions. Under the nonflooded conditions, rice dry matter and leaf P increased with the addition of P, but less so than in flooded soils. Leaf P concentrations and shoot dry matter responded strongly to the addition of lime. The increase in shoot dry matter of rice with lime and P application in nonflooded soil was associated with a significant decline in soluble Al in the soil and an increase in plant P uptake. The current experiments show that the loss of soil‐water saturation may be associated with the inhibition of P absorption by excess soluble Al. By contrast, flooding decreased exchangeable Al to levels below the threshold for toxicity in rice. In addition, the decreased P availability with loss of soil‐water saturation may have been associated with a greater phosphate sorption capacity of the soils during flooding and after reoxidation due to occlusion of P within ferric oxyhydroxides formed.     

土壤溶液动态变化和CdCO3, CdS的平衡研究

土壤渍水后带来了一系列的电化学和化学变化,pH、氧化还原电位(Eh)、电导(EC)、离子交换、吸附和解吸、化学动力学和化学平衡等都有着显著的改变^[9,11,13],它们影响着土壤肥力状况和植物对毒性元素的吸收。本文报道了在添加Cd,P,Zn化合物的情况下土壤溶液动态变化和CdCO₃,CdS平衡研究的结果。     

Sour Orange (Citrus Aurantium L.) Growth is Strongly Mycorrhizal Dependent in Terms of Phosphorus (P) Nutrition Rather than Zinc (Zn)

The partial sterilization of soil eliminates useful microorganisms, resulting in the reduced growth of mycorrhizae-dependent citrus plants, which are often unresponsive to the application of fertilizer. Research was conducted to test the hypothesis that indigenous mycorrhizae (IM) inoculation is as efficient as selected mycorrhizal inoculation under sterile and non-sterile soil conditions. Rhizophagus clarus and indigenous mycorrhiza spores, isolated from citrus orchards, were used as arbuscular mycorrhizae fungi under greenhouse conditions with sterile and non-sterile Çanakçi series (Typic xerofluvent) soils with low phosphorus (P) fertility. Different P (0 and 100 mg kg^?1) and zinc (Zn) (0, 5 and 10 mg kg^?1) concentrations were used at the start of the experiments. The shoot, root dry weight (RDW), root colonization, and P, Zn, iron (Fe), copper (Cu) and manganese (Mn) concentrations of the shoot were determined; mycorrhizae dependency (MD) was also calculated.

The results indicate that R. clarus and indigenous mycorrhiza in sterile and non-sterile soil conditions considerably increased the growth of citrus plants. Owing to existing beneficial indigenous rhizosphere microorganisms, citrus plant growth without inoculation was better in non-sterile soils than in the sterile soils. In non-sterilized soil, the plant growth parameters of R. clarus-inoculated soils were higher than those of indigenous mycorrhiza-inoculated soils. Mycorrhizae infection increased certain citrus plant growth parameters, such as root infection, biomass and nutrient uptake (P, Zn, Fe, Mn and Cu). In sterile soil, the addition of up to 5 mg kg^?1 soil Zn and the inoculation of R. clarus significantly increased plant growth; inoculation with indigenous mycorrhiza produced more dry weight upon the addition of up to 100 mg kg^?1 phosphorus pentoxide (P₂O₅). Under sterile soil conditions, without considering fertilizer addition, MD was found to be higher than that of non-sterile soils. In general, the contribution of the indigenous soil spores is significant. However, indigenous soil mycorrhizae may need to be managed for better efficiency in increasing plant growth and nutrient uptake. The major finding was that the inoculation of citrus seedlings with mycorrhiza is necessary under both sterilized and non-sterilized soil conditions.     

Immobilization of Zinc Fertilizer in Flooded Soils Monitored by Adapted DTPA Soil Test

Zinc (Zn) deficiency is a persistent problem in flooded rice (Oryza sativa L.). Severe Zn deficiency causes loss of grain yield, and rice grains with low Zn content contribute to human nutritional Zn deficiencies. The objectives of this study were to evaluate the diethylenetriaminepentaacetic acid (DTPA) extraction method for use with reduced soils and to assess differences in plant availability of native and fertilizer Zn from oxidized and reduced soils. The DTPA‐extractable Zn decreased by 60% through time after flooding when the extraction was done on field‐moist soil but remained at original levels when air‐dried prior to extraction. In a pot experiment with one calcareous and one noncalcareous soil, moist‐soil DTPA‐extractable Zn and plant Zn uptake both decreased after flooding compared with the oxidized soil treatment for both soils. In the flooded treatment of the calcareous soil, both plant and soil Zn concentrations were equal to or less than critical deficiency levels even after fertilization with 50 kg Zn ha^?1. We concluded that Zn availability measurements for rice at low redox potentials should be made on reduced soil rather than air‐dry soil and that applied Zn fertilizer may become unavailable to plants after flooding.     

Impacts of flooding,nitrogen-fertilization,and soil-depth on sugarcane nutrients grown on Histosols

Abstract

Sustainable production in the Everglades Agricultural Area (EAA) is confounded by decreasing soil depth and high annual rainfall. Formerly a sawgrass marsh, Histosols predominate much of the EAA and these soils have frequently flooded following their drainage in the early 20th century. Subsidence has increased inundation frequency as soil depth has decreased to less than 25?cm in many locations. A 2-year lysimeter study was conducted to examine alternative management practices for improved agricultural sustainability given frequent flooding and reduced oxidation rates on Histosols. Specific management factors examined included water-table, soil depth, and nitrogen (N) fertilizer effects on sugarcane leaf nutrient concentrations and soil nutrient cycling. The trial utilized soil depths of 13 and 25?cm, water tables of constant and periodically flooded, and N fertilizer rates of 0 and 168?kg ha^?1?year^?1. Periodic flooding increased plant uptake of manganese (Mn), silicon (Si), and boron (B). Yield increases associated with additional N indicate a potential need to develop fertilizer rate recommendations for shallow Histosols. Soil depth impacted sugarcane nutrient uptake with 25?cm of soil depth significantly affecting examined leaf nutrient concentrations except iron (Fe). Sugarcane yield may benefit if additional N and potassium (K) are added at rates specific to soil depth. Proximity to bedrock led to excessive calcium (Ca) uptake and low K and Fe DRIS (Diagnosis and Recommendation Integrated System) values were below recommendations. Data from this study can assist development of precision agricultural practices in the EAA that utilize soil depth.     

Impacts of biochar and processed poultry manure,applied to a calcareous soil,on the growth of bean and maize

Direct use of poultry manure on agricultural lands may cause environmental concerns, so there is a need to establish the suitability of the application of biochar derived from poultry manure for calcareous soil chemical properties and plant growth. The purpose of this study was to evaluate the effects of processed poultry manure (0, 5, 10 and 20 g/kg) and its biochar (0, 2.5, 5, 10 and 20 g/kg) on soil chemical properties of a calcareous soil and growth of bean (Phaseolus vulgaris) and maize (Zea mays) plants. In the incubation experiment, both processed poultry manure (PPM) and biochar decreased pH and the concentration of plant‐available Fe of soil but increased plant‐available P, Zn, Cu and Mn concentrations. PPM and biochar increased the concentrations of exchangeable cations (K, Ca and Mg) in soil. PPM and biochar applications increased the growth of maize and bean plants. PPM and biochar resulted in increased concentrations of N, P, K, Ca, Fe, Zn, Cu and Mn in bean plants. In maize plants, PPM and biochar applications increased the N, P, K, Zn, Cu and Mn but decreased the Ca and Mg concentrations. Results of this study reveal that poultry manure biochar can be used effectively for agricultural purposes.     

Effects of slag silicate fertilizer on silicon content of rice plants grown in paddy fields on the Shounai Plain,Yamagata, Japan

Abstract

Slag silicate fertilizer (SSF) is applied to paddy fields with different soil chemical properties to increase silicon (Si) concentration in rice (Oryza sativa L.) plants. However, the effects of soil chemical properties on Si availability of SSF to rice Si uptake is poorly understood. To investigate the relationships between chemical properties of soils and the effects of SSF application on the Si concentration in rice plants, a field experiment was conducted in 2007 and 2008 at 18 paddy fields on the Shounai Plain, Yamagata, Japan. Two treatments were implemented: SSF applied at 1.5 t ha^?1 and a no-SSF control. The Si concentrations of rice tissues were measured at the tillering and ripening stages. The difference in the Si concentrations of rice tissues between treatments (ΔSi concentration) was used to evaluate the effect of SSF. The Si concentrations in the shoots and aboveground parts of the rice plants were significantly increased by the SSF application in six or more of the fields at the two growth stages, whereas the Si concentrations in the panicles of the rice plants at the ripening stage were not increased significantly in most fields. Results of two-way analysis of variance evidenced a significant effect of field on the ΔSi concentrations in the shoots and aboveground parts at both growth stages. Furthermore, the ΔSi concentrations in the same rice plant tissues and at the same growth stages in the first year and in the second year were found to be positively correlated. These results indicate that the effect of SSF on the Si concentration in shoots and aboveground parts of rice plants varies from field to field. The ΔSi concentrations in shoots and aboveground plant parts at both growth stages were also found to be negatively correlated with soil chemical properties, i.e., available Si, Si adsorption capacity, contents of Si adsorbents (acid oxalate-extractable iron and manganese) and the pH under flooded soil conditions. These findings imply that those soil chemical properties of paddy fields should be taken into account for better prediction of ΔSi concentration of rice plants.     

Influence of phosphorus limitations on the growth,nutrient partitioning and physiology of mahogany (Swietenia macrophylla King) seedlings

The effects of four rates of phosphorus (P) fertilization (0, 0.56, 5.6 and 56.0 mg l^?1) in soilless medium on the growth and physiology of mahogany seedlings were examined. The greatest response occurred at the 56 mg l^?1 rate, with relatively small differences between other treatments. Biometric parameters increased at the 56 mg l^?1 compared to 0 mg l^?1 rate except root dry mass. Both the concentration and the total content of P and Kjeldahl nitrogen (N) increased in leaves, stems and roots with P application rate. Foliar concentrations of potassium (K), calcium (Ca), magnesium (Mg), manganese (Mn) and sulfur (S) declined, and boron (B) and copper (Cu) increased with P limitations; zinc (Zn) and iron (Fe) were unaffected. Physiological adaptations of mahogany to P limitations include the preferential allocation of carbon (C) to plant roots, and increases in P utilization efficiency, P acquisition efficiency and the concentration of organic acids in xylem fluid. Root phosphatase activity was not influenced by P fertilization.     

Effects of soil flooding and organic matter addition on plant accessible phosphorus in a tropical paddy soil: an isotope dilution study

Plant growth experiments were conducted to reveal the mechanism by which organic matter (OM) and soil flooding enhance phosphorus (P) bioavailability for rice. It was postulated that reductive dissolution of iron‐(III) [Fe(III)] oxyhydroxides in soil releases occluded phosphate ions (PO₄), i.e., PO₄ that is not isotopically exchangeable in the original soil prior to flooding. Rice was grown in P‐deficient soil treated with factorial combinations of addition of mineral P (0, 50 mg P kg^?1), OM (0, ≈ 20.5 g OM kg^?1 as cattle manure +/– rice straw) and water treatments (flooded vs. non‐flooded). The OM was either freshly added just before flooding or incubated moist in soil for 6 months prior to flooding; nitrogen and potassium were added in all treatments. The soil exchangeable P was labeled with ³³PO₄ prior to flooding. The plant accessible P in soil, the so‐called L‐value, was determined from the ³³P/³¹P ratio in the plants. The L‐values were inconsistently affected by flooding in contrast with the starting hypothesis. The OM and P addition to soil clearly increased the L‐value and, surprisingly, the increase due to OM application was larger than the total P addition to soil. An additional isotope exchange study in a soil extract (E‐value) at the end of the experiment showed that the E‐value increased less than the total P addition with OM. This suggests that plants preferentially take up unlabeled P from the OM in the rhizosphere compared to labeled labile inorganic P. The effects of soil flooding on P bioavailability is unlikely related to an increase of the quantity of bio‐accessible P in soil (L‐value) but is likely explained by differences in P mobility in soil.     

The earthworm (Aporrectodea caliginosa) primes the release of mobile and available micronutrients in soil

The objectives of our study were to quantify the impact of endogeic earthworms Aporrectodea caliginosa (Savigny) on iron (Fe), manganese (Mn) and zinc (Zn) mobility and availability in soil. Dried rye straw (Cecale cereale L.), clover aboveground parts (Trifolium pratense L.) or calcium carbonate were added to determine the effects on soil micronutrient mobility. To test the importance of soil–water saturation mediated by earthworms, soil samples were modified to 60% (control) and 100% (as in casts) water holding capacity (WHC). To assess availability of micronutrients, a cucumber plant (Cucumis sativus L.) bioassay were used. Earthworm casts had generally higher amounts of water-soluble micronutrients compared with bulk soils regardless of their moisture contents. The increased micronutrient mobility was more pronounced in casts from soil samples amended with plant residues (especially with straw) and was significantly higher than mobility in control soil for at least 1 week after the casts were deposited. Pre-incubation of soils amended with clover or straw with living earthworms for 4 weeks produced an increase in both shoot biomass and translocation rate of micronutrients (Mn, Zn) into xylem sap of cucumber compared to soils not worked by earthworms. The earthworm-mediated plant performances were determined 4 weeks after the earthworms were removed. The results demonstrated that earthworms can significantly impact the formation of mobile and available micronutrients in a soil. The relationship between micronutrient availability to cucumber plants and earthworm contribution to nitrogen (N) mineralization and micronutrient mobility are discussed.     

Chemical analysis of Teucrium species (Lamiaceae) growing on serpentine soils in Bulgaria

Trace elemental concentrations (Fe, Ni, Mn, Cr, Co, Cu, Zn, Pb, Cd, and As) in aerial biomass (stems, leaves, and flowers) of the medicinal plants Teucrium chamaedrys, T. montanum, and T. polium growing on serpentine soils in Bulgaria were examined in relation to the total element contents in their respective rhizospheric soils. The objectives of the study were to evaluate: (1) elemental concentrations in plant tissues and associated soil samples together with the plants ability to tolerate/accumulate metal concentrations; (2) correlations between total metal concentrations in plants and their rhizospheric soils. Metal concentrations varied across species and sites. Their levels in plant tissues from nonserpentine sites were always lower compared to those from serpentine ones. The highest concentrations for Fe, Ni, Mn, Cr, As, Cu, and Pb were found in T. polium. Positive correlation coefficients were established between Ni, Cr, Fe, Co, and Cu in plants and Ca in the soil. None of the species tested hyperaccumulated metals although the metal concentration in some of them exceeded the range naturally found in plants. The Teucrium species can be considered as “excluders”, containing relatively low metal concentrations in their aerial parts (stems, leaves, and flowers) even in cases of high elemental concentrations in the rhizospheric soil. In all three medicinal plants, metal concentrations for toxic elements were above the permissible limits for pharmaceutical purposes. Therefore, plants found on serpentine bedrock are not recommended to be collected for pharmaceutical purposes.     

Beneficial effects of glycine on growth and leaf nutrient concentrations of coriander (Coriandrum sativum) plants

Abstract

In this study, the effect of glycine amino acid was evaluated on growth characteristics and nutrient uptake of coriander plants under greenhouse conditions. The treatments were soil application of glycine in two concentrations of 300 and 600?mg kg^?1 soil, foliar application of glycine (in 0.05% concentration), soil application of mix NPK fertilizer and no fertilizer control. The growth parameters of plant height, leaf SPAD value, shoot and root fresh weights were significantly improved by soil application of glycine, particularly in higher concentration. Soil application of glycine also reduced the number of flowered plants, while it increased soluble solids (TSS) and vitamin C of plant leaf extracts than control plants. Leaf nutrient concentrations of nitrogen (N), calcium (Ca), potassium (K), phosphorus (P), iron (Fe), and zinc (Zn), but not magnesium (Mg) and manganese (Mn), were significantly increased by soil application of glycine, whereas soil applied NPK significantly increased P and Ca of leaves than unfertilized control plants.     

Effects of soil flooding on P transformations in soils of the Mesopotamia region,Argentina

In the Mesopotamia region (Argentina), rice is cropped on a wide range of soil types, and the response of rice to fertilizer application has been inconsistent even in soils with very low levels of available phosphorus. Phosphorus transformations in flooded soils depend on soil characteristics that may affect phosphorus availability. This study was conducted to determine which soil characteristics were related to the changes in P fractions during soil flooding. Soils were chosen from ten sites within the Mesopotamia region that are included in five different soil orders: Oxisols, Ultisols, Alfisols, Mollisols, and Vertisols. Soil phosphorus (P) was fractionated by a modified Hedley method before and after a 45 d anaerobic‐incubation period. Changes in the inorganic P extracted with resin depended on soil pH and were related to the exchangeable‐Fe concentration of soils (extracted with EDTA). Inorganic P extracted with alkaline extractants (NaHCO₃ and NaOH) increased due to soil flooding. This increase was related to the organic‐C (OC) percentage of soils (r² = 0.62, p < 0.01), and ranged from 13 to 55 mg kg^–1. Even though previous studies showed that P associated with poorly crystalline Fe played an important role in the P nutrition of flooded rice, in this study, there was no relationship between ammonium oxalate–extractable Fe and P changes in soils due to flooding. Our results suggest that in the Mesopotamia region, changes in P fractions due to soil flooding are related to soil OC, soil pH, and soluble and weakly adsorbed Fe.     

Effect of excess zinc and arbuscular mycorrhizal fungus on bioproduction and trace element nutrition of Tomato (Solanum lycopersicum L. cv. Micro-Tom)

ABSTRACT

The effect of excess Zn and arbuscular mycorrhizal (AM) fungus on bioproduction and trace element nutrition were investigated in tomato. In a completely randomized factorial design, the experimental treatments – Zn addition at 0 (normal) and 300 (excess) mg Zn kg^?1 soil, and AM inoculation (non-AM and Rhizophagus irregularis) – were set up in a growth chamber for 10 weeks. Generally, AM effects on the available Zn, Mn, Cu, and Fe in the rhizosphere soil were in tandem with the effects in host tissues. Under normal Zn condition, AM enhanced Cu availability in the rhizosphere, optimized the Cu:Zn balance in shoots, and increased the host biomass production. Excess Zn reduced mycorrhizal colonization in AM plants and the total plant biomass in both AM and non-AM plants. Although AM decreased the Zn concentrations in soil and host tissues under excess Zn, the distortions in host TE balance were not significantly ameliorated by the fungus. While Zn in fruit was within the safety threshold, Mn deficiency in the fruit was observed under excess Zn, alongside increased root-to-fruit Fe and Cu translocations. Mycorrhizal reductions in soil and tissue Mn concentrations were considered a minus in terms of probable symbiont amelioration of Mn:Zn in-balance under excess Zn. Additional microbe(s) that can enhance Mn homeostasis might be helpful in tomato under elevated soil Zn.     

酸性土壤活性锰与pH、Eh关系及其生物反应

以灰潮土为对照研究了湖北省 3种有代表性的酸性土壤在盆栽条件下 ,不同酸化处理土壤pH、Eh与活性锰的动态变化关系。结果表明 ,供试的棕红壤和黄棕壤酸化后 ,在盆栽油菜生长的前 70d内 ,土壤交换性锰含量增加 ,土壤交换性锰与碳酸盐结合态锰呈一定负相关 ,且交换性锰含量增加明显滞后于碳酸盐结合态锰的增加 ;30～90d内 ,碳酸盐结合态锰与易还原性锰呈一定正相关。虽然土壤pH和Eh在作物生长季节不断变化 ,但其 pe +pH仍维持不变。土壤 pH、Eh与交换性锰的关系能较好地反映土壤锰的转化机制 ,在进一步酸化时 ,供试的棕红壤MnO2/Mn2+电对是该土壤锰化合物变化的主要形式 ,MnO2是变化过程的电子受体。供试的黄棕壤则以MnOOH MnO电对为其锰化合物氧化还原的主要形式 ,土壤酸化对其锰电对电位的影响没有直接引起Mn2+ 的变化 ;Mn2+的增加可能是MnO在该过程中进一步溶解所致。试验结果还表明 ,油菜体内的锰铁比随锰中毒程度的加强而急剧增加 ,这一趋势远高于土壤锰铁比的增加。     

Observations on Manganese Deficiency and Toxicity in Some Australian Native Plants

Analysis and research on the nutrition of some Australian native plants as well as diagnostic analysis of failed native plant gardens reinforces the view that manganese (Mn) availability is a major factor in the edaphology and cultivation of Australian native species. Yellow Kandosol soils on sandstone show a unique endemic floral assemblage. These soils show low total soil Mn levels of only 20–30 mg/kg. Despite this, endemic species such as Eucalyptus haemastoma and Acacia suaveolens show greater foliar Mn levels (around 291 and 389 mg/kg, respectively) than iron (Fe) levels, with Fe/Mn ratios as low as 0.14 and 0.27. During pot trial work on artificial soils created from crushed sandstone and green waste compost that were designed to research phosphorus (P) and calcium (Ca) nutrition, some interesting data on Mn uptake were collected. Levels of foliar Mn as high as 1250 and 389 mg/kg, respectively, accumulated in E. haemastoma and A. suaveolens when soils were artificially acidified to pH 4.7 (CaCl₂) using ferrous sulfate. These Mn levels were associated with visible toxicity symptoms in foliage of E. haemastoma but not in A. suaveolens. Foliar Mn in both species showed a strong inverse correlation (R² > 0.93) with soil pH. Previous research has shown that eucalypts from this floral assemblage are prone to Mn toxicity when grown in conditions of high soil Mn availability. Diagnostic analysis of soils and foliage for a client with horticultural problems in a native plant landscape showed severe chlorosis in a wide range of native species due to Mn deficiency induced by neutral soil pH (around 7.0 in CaCl₂). Such soil pHs are considerably greater than those of the plant’s natural distribution. Despite apparently elevated soil P and the appearance of what looked like P toxicity, foliar P levels were not sufficiently elevated to conclude acute P toxicity but rather simple and severe Mn deficiency. The work suggests that induced Mn deficiency and toxicity may be underdiagnosed problems in the cultivation of many Australian native plants.