Effects of soil acidity on the growth of sericea lespedeza

Field experiments were conducted in 1992 and 1993 to examine effects of soil acidity on growth and N₂ fixation by “Serala”; sericea lespedeza [Lespedeza juncea (L.F.) var. sericea (Mig.)]. Effects of acidified soil on N₂ fixation could not be determined because nodulation was suppressed, apparently by sufficient availability of N. Apparently‐suppressive, mean 1993 levels of KCl‐extractable NH₄ and NO₃ in zero nitrogen (N) control treatments were 20 and 13 mg‐kg^‐1, respectively. In soil acidified with sulfur (S), growth of sericiea lespedeza was significantly reduced (PO.05) when the concentration of water‐extractable Mn exceeded 1.3 mM or calculated Mn²⁺ activity exceeded 0.4 mM. This occurred at pH values of 4.1 to 4.3 depending on S treatment. At a given value of pH, shoot dry weight production was greater in S‐amended soil than in Al₂SO₄‐amended soil. Reduced growth in the latter did not appear to be directly related to higher measured levels of toxic Al but may have been caused by a combination of aluminum (Al), hydrogen (H), manganese (Mn), and phosphorus (P) effects. Lespedeza growth was lowest in nonacidified soil with pH values near 6.0, indicating a preference for acid soils by the variety “Serala.”; The demonstrated tolerance of sericea lespedeza to acid soils make it a valuable reclamation species. However, Mn may inhibit growth in acidic soils when the activity of water‐extractable Mn²⁺ exceeds 0.4 mM, and it may not fix appreciable N₂ unless available soil N is quite low.     

Differential responses of sericea lespedeza to aluminum stress

Toxic levels of aluminum can cause severe yield reductions in many crop species, but sericea lespedeza [Lespedeza cuneata (Dum.‐Cours.) G. Don] has demonstrated considerable tolerance. Aluminum tolerances of six sericea lespedeza cultivars (Am 312, Appalow, AU Lotan, Interstate, Interstate 76, Serala) representing a broad genetic base were evaluated in a Monmouth soil [26.2% Al saturation (pH 4.8) vs. 2.8% Al saturation (pH 5.7)] and in nutrient solutions (0 vs 111 μM Al; pH 4.5). The soil and nutrient culture studies were harvested 30 and 27 d after seeding, respectively.

Aluminum stress did not reduce root and shoot growth significantly, nor were the pooled Al stress x cultivar interactions significant. Cultivars differed significantly in mean shoot and root vigor in nutrient solutions but not in soil. R‐esponses in soil were only weakly correlated with responses in nutrient solutions. Am 312 and Appalow had the lowest relative weight values (dry weight stressed/dry weight unstressed) in both media and Interstate and Interstate 76 the highest. Interstate 76 exhibited a significant positive response (5% level) to Al when evaluated in nutrient solutions.     

Changing pH shifts the microbial sourceas well as the magnitude of N2O emission from soil

Here, we examine the effect of long-term pH differences and short-term pH change on N₂O emissions from soil, and the microbial source (ammonia oxidation versus denitrification) of ¹⁵N-N₂O emissions. ¹⁵N-fertiliser (20 g N m^?2; 10 atom% excess ¹⁵N) was applied to (1) a silt loam soil of pH 7 held at 50% and 65% water-filled pore space (WFPS) (experiment 1) and (2) a loamy sand soil maintained at pH 4.5 and pH 7 for over 40 years (experiment 2). Soils were limed with CaCO₃ or acidified with H₂SO₄, and comparisons were made with unadjusted soils. Ammonia oxidation was the main microbial source of ¹⁵N-N₂O in soils limed to pH 7.0–8.1, unadjusted pH 7.1 (Experiment 1) and long-term pH 7 (experiment 2) soils. Eighty percent of ¹⁵N-N₂O from the long-term pH 4.5 soil (experiment 2) was derived from denitrification suggesting a possible inhibition of N₂O reduction. Short-term acidification to pH 5.6 or 4.3 lowered N₂O emissions. Liming of the pH 4.5 soil resulted in over four times greater N₂O emission (11 mg ¹⁴⁺¹⁵N-N₂O m^?2 over 41 days) than from the long-term pH 7.0 soil (experiment 2), with an associated increase in ammonia oxidiser-N₂O and decrease in denitrifier-N₂O production. This is the first report of a pH-induced change in microbial source of N₂O. Our results highlight the importance of distinguishing between short- and long-term effects of pH management when predicting N₂O emissions from soil, as they exhibit predominance of different microbial groups in N₂O production, with likely adaptation of the microbial community.     

Comparative Studies on the Use of Binary and Ternary Combinations of Various Acidifying Agents for the Reduction of Soil pH

The present study deals with the effects of addition of sulfur along with other acidifying agents for their ability to lower and maintain the pH in a given range for a longer period of time. The chemicals were subjected to batch test individually and in combinations. Treatments were applied to three soils of different textures: sandy clay loam, clay loam, and silt loam. A 1:1 soil/water paste along with the added amendment was maintained at room temperature for 2 months. Most of the chemical treatments lowered the pH significantly. Combinations containing S/Al₂(SO₄)₃/H₂SO₄, S/Al₂(SO₄)₃/H₂O₂, and S/H₂O₂/H₂SO₄ were found to be very effective in lowering the pH. The soil pH remained acidic for 2 months, indicating the suitability of chemically amended soil for the plantations requiring acidic soil pH.     

Geospatial Soil and Plant Tissue Analysis of Sericea Lespedeza (Lespedeza cuneata) Invasion around Lake Issaqueena,South Carolina

This study was conducted to determine the chemical composition of sericea lespedeza (Lespedeza cuneata) as well as soil and landscape characteristics that correlate with its invasion. Geographic Information Systems (GIS) and Light Detection and Ranging (LiDAR) were used to determine the pattern of invasion and to quantify landscape metrics. Sericea lespedeza was distributed on both sides of the lake in Pacolet and Madison soil map units (Fine, kaolinitic, thermic Typic Kanhapludults) on average slopes of 17.5%. It was common along roads and trails with a preferred mean canopy cover of <50%. Plant tissue analysis revealed statistically higher concentrations of macronutrients nitrogen (N), phosphorus (P), potassium (K), magnesium (Mg), calcium (Ca) and sulfur (S) and selected micronutrients in leaves compared to stems and roots. Micronutrients copper (Cu), manganese (Mn) and iron (Fe) were significantly higher in stems and roots. Soil analysis results showed no statistical difference between control and invaded plots for measured soil chemistry parameters.     

A rapid and precise method for routine determination of organic carbon in soil

Abstract

A simple method for routine determination of organic carbon in soil by a modified Mebius procedure is described. It involves (a) digestion of the soil sample with an acidified dichromate (K₂Cr₂O₇‐H₂SO₄) solution for 30 minutes in a Pyrex digestion tube in a 40‐tube block digester preheated to 170°C and (b) estimation of the unreacted dichromate by titration of the cooled digest with an acidified solution of ferrous ammonium sulfate with use ofN‐phenylanthranilic acid as an indicator. The method is more rapid and precise than the Mebius procedure commonly used for routine analysis of soils for organic carbon, and the only equipment required for its use is equipment now commonly used for routine Kjeldahl analysis of soils for total nitrogen.     

Mycorrhizal inoculation effect in Acacia mangium grown in an acid oxisol amended with gypsum

Glomus aggregatum and Acacia mangium were interacted in an acid manganese (Mn)‐rich oxisol unamended or amended with hydrated lime [Ca(OH)₂] or gypsum (CaSO₄) at soil phosphorus (P) concentrations considered optimal for mycorrhizal host growth. Vesicular‐arbuscular mycorrhizal fungal (VAMF) colonization as well as VAMF function was significantly curtailed if soil was unamended with gypsum or lime. The highest mycorrhizal inoculation effect (MIE) was observed in the soil treated with gypsum at the rate of 0.32 g of calcium (Ca)/kg followed by the limed soil. Higher concentrations of gypsum deleteriously affected VAMF infectivity and effectivity. The first increment of gypsum compensated for part of the VAMF colonization and for all of the mycorrhizal inoculation effect that was lost due to low pH. The better MIE observed in the gypsum treated soil compared to that which was amended with lime suggests that the sensitivity of the acacia‐VAMF association to soil acidity was more a function of Ca inadequacy than it was of pH or associated increases in Mn concentration.     

Calculating changes of legume rhizosphere soil pH and soil solution phosphorus from phosphorus uptake

Abstract

Some legumes are known to reduce rhizosphere soil pH which in turn usually increases soil solution P, P_li and therefore increases P uptake. In an initial experiment with a nonlegume [corn (Zea mays L.)], observed P uptake agreed closely with predicted P uptake while with a legume [alfalfa (Medicago sativa L.)], observed P uptake was greater than predicted P because the rhizosphere was acidified, P_li increased, and more P was absorbed. Using a pot experiment, this investigation calculates the change in rhizosphere pH and P_li necessary to have predicted P uptake obtained with a mechanistic uptake model agree with observed P uptake. The pot experiment was conducted with alfalfa, faba bean (Vicia faba L.) and Austrian winter pea (Lathyrus hirsutus) grown on Chalmers silt loam (fine‐silty, mixed, mesic Typic Haplaquolls) limed to pH levels of 5.72, 6.30, 7.22 and 8.30. Predicted phosphorus uptake at each pH level was calculated with the uptake model using the data for bulk soil. The relation of predicted P uptake to initial soil pH was determined, then this relation was used with observed P uptake to calculate rhizosphere pH. Subsequently, P_li as a function of pH was determined and used to calculate rhizosphere P_li. In this study, the calculations indicate that legumes reduced rhizosphere soil pH by 0.39 to 0.77 units and increased P availability by 20.8 to 241.7%.     

Chemical effects of pH 3 sulphuric acid on a soil profile

Cores of podzolic soil (monolith lysimeters) were treated for 4.8 yr with 1500 mm yr^?1 of either 0.5 mM H₂SO₄ at pH 3, equivalent to 24 g S m^?2 yr^?1 (acid treated) or distilled water (controls). The acid treatment was about 37 times greater than the average annual input of H₃O⁺ from rain at the site from which the monoliths were taken. Acid treatment acidified the litter (from pH(CaCl₂)3.4 to pH(CaCl₂)2.6) and the mineral soil to a depth of 80 cm (mean pH(CaCl₂) decrease of 0.2 unit). In the litter and upper A horizon, ion-exchange reactions provided the main neutralizing mechanism, resulting in a decrease in the reserves of extractable (in 2.5 % acetic acid) Ca, Mg, and Mn of about 70 to 80 %. Dissolution of solid phase Al from hydrous oxides provided most neutralization below this depth. Al3⁺ was the principal soluble Al species throughout the profile. In the litter and upper A horizon, some of the mobilized Al³⁺ was retained on cation exchange sites resulting in an increase in exchangeable Al. Deeper in the profile, where the exchange sites were effectively saturated with Al³⁺, no increase in exchangeable Al occurred, and Al³⁺ was, therefore, available for leaching. Some reversible adsorption of SO₄ ^2?, associated with hydrous Al oxides, occurred in the Bs and C horizons. The results are discussed in relation to possible effects of acid deposition over regions of Europe and N. America.     

Predicting Liming Needs of Soybean Using Soil pH,Aluminum, and Manganese Soil Tests

Abstract

Whether a tropical soil should be limed or not for a particular crop is strongly dependent on the levels of soil aluminum (Al) which can be determined with soil tests. Soil pH is used to predict whether lime is needed in less‐weathered soils, although some evidence indicates a soil Al test would be more accurate. The objectives of this study were to determine and to compare the accuracies of four soil tests to separate soils requiring lime from those that do not, and to determine the cause of acid‐soil injury to soybean [Glycine max (L.) Merr.]. Soybean was grown in the greenhouse on four surface soils representing the major land resource areas of Louisiana and were amended with eight rates of lime, yields determined, and soils analyzed for soil pH, extractable Al, CaCl₂‐extractable Al, CaCl₂‐extractable manganese (Mn), and Al saturation. Acid‐soil injury in soybean grown on the Litro clay and Stough fsl was probably caused by soil‐Al effects while low soil calcium (Ca) and high soil Mn was likely responsible for lower yields from the Mahan fsl. Leaf Ca from the limed Mahan‐soil treatment was 5‐fold greater and leaf‐Mn 7‐fold less than control levels. Regression analyses’ R² values were similar for all soil tests except for CaCl₂‐extractable Mn, which was lower. Soil tests were compared across soil type by selecting treatments that had the same 85% relative yield. Using this data subset, there was no difference in the soil pH among the four soils, while there were significant differences among soils for all other soil test measurements indicating the superiority of soil pH for identifying acid‐soil injury. Critical test values were 5.1 soil pH, 30 mg kg^‐1 extractable Al, 7% Al saturation, 0.7 mg‐kg^‐1 CaCl₂‐extractable Al, and 9 mg‐kg^‐1 CaCl₂‐extractable Mn.     

Zinc,copper, and nickel availabilities as determined by soil solution and DTPA extraction of a sludge‐amended soil

Abstract

Extracting sludge‐amended soil with DTPA does not always give a reliable measure of plant‐available heavy metals. The major purpose of this greenhouse pot study was to help explain why. Two anaerobically digested sludges from sewages treated with either Ca(OH)₂or FeCl₃were applied to 3‐kg samples of a Mollic Albaqualf previously limed with Ca(OH)₂rates of 0, 2.5, and 10g/pot that resulted in pHs in the check pots of 5.4, 6.2, or 7.7 after the first harvest. Sludge rates provided 0, 200, 40, 800, and 1600 mg Zn kg^‐1of soil. Two consecutive crops of soybeans (Glycine MaxL.) were grown for 42 d each in the greenhouse. DTPA‐extractable, soil‐solution, and plant concentrations of Cu²⁺, Ni²⁺, and Zn²⁺were measured.

Dry matter yields were depressed due to salt toxicity, while DTPA‐extracted Cu²⁺correlated with plant uptake of Cu²⁺for both sludges. DTPA‐extracted Ni²⁺also correlated with plant Ni²⁺from the Ca(OH)₂‐sludge‐amended soil, although DTPA‐extracted Ni²⁺did not correlate with plant uptake of Ni²⁺from the FeCl₃‐sludge‐amended soil, DTPA‐extracted Zn did not correlate with plant uptake of Zn²⁺from any sludge‐amended soil. Soil‐solution composition correlated with plant uptake of Cu²⁺and Ni²⁺in both sludges; it also correlated with plant uptake of Zn²⁺from FeCl₃‐sludge‐amended soil but not from Ca(OH)₂‐sludge‐amended soil. DTPA extraction probably failed with Ni²⁺and Zn²⁺because of (i) its ineffectiveness at low pH, (ii) the inability of DTPA to buffer each soil extract near pH 7.3, and (iii) increased amounts of soluble chelated micronutrients at higher sludge rates and higher soil pHs. Soil‐solution composition seemed to fail only where micronutrient cations in solution probably were present largely as organic chelates     

Factors associated with annual ryegrass yield response to limestone

Abstract

Quantifying the effects of soil acidity on plant growth remains a challenging research topic as numerous soil and plant growth factors are influenced by pH and lime. In the field, annual ryegrass (Lolium multiflorum Lam. ‘Marshall') responded positively to the application of 3.8 Mg lime/ha on a strongly acid (pH 4.7) Lilbert loamy fine sand (loamy, siliceous, thermic, arenic Plinthic Paleudult) over three growing seasons. Dry matter yield in some cuttings, however, was better correlated with soil Al, P, Ca, Mg, and K than with pH. A greenhouse study was undertaken to quantitatively determine the effects of these five minerals plus Mo on ryegrass yield in limed and unlimed Lilbert soil material. Three ryegrass cuttings were obtained from unlimed (pH 4.8) or limed (1000 mg CaCO₃/kg) Lilbert soil which was also amended with five rates of Ca, K, Mg, Al, P, and Mo in combinations stipulated by central composite design methodology. Response surface models that fit yield to the applied treatments and soil test data were complex because all factors and many interactions were significant. Furthermore, the models were transformed as the plants matured and element availability changed due to mineral uptake. Most yield improvement derived from liming occurred as a result of the elimination of exchangeable Al with a concomitant increase in P efficiency. Applied Ca did not alleviate Al toxicity in unlimed soil. Chlorotic plants developed in all pots where Mg was excluded. Yield was increased by applied Mg and Mo in unlimed soil, but not in limed soil. Applied K improved yield only in limed soil. Although regression accounted for a large portion of the yield variability (R² values ranged from 0.75 to 0.95), these models were unable to accurately predict yield in control treatments.     

Sulfur mineralization in two soils amended with organic manures,crop residues,and green manures

The mineralization of sulfur (S) was investigated in a Vertisol and an Inceptisol amended with organic manures, green manures, and crop residues. Field‐moist soils amended with 10 g kg^—1 of organic materials were mixed with glass beads, placed in pyrex leaching tubes, leached with 0.01 M CaCl₂ to remove the mineral S and incubated at 30 °C. The leachates were collected every fortnight for 16 weeks and analyzed for SO₄‐S. The amount of S mineralized in control and in manure‐amended soils was highest in the first week and decreased steadily thereafter. The total S mineralized in amended soils varied considerably depending on the type of organic materials incorporated and soil used. The cumulative amounts of S mineralized in amended soils ranged from 6.98 mg S (kg soil)^—1 in Inceptisol amended with wheat straw to 34.38 mg S (kg soil)^—1 in Vertisol amended with farmyard manure (FYM). Expressed as a percentage of the S added to soils, the S mineralized was higher in FYM treated soils (63.5 to 67.3 %) as compared to poultry manure amended soils (60.5 to 62.3 %). Similarly the percentage of S mineralization from subabul (Leucaena leucocephala) loppings was higher (53.6 to 55.5 %) than that from gliricidia (Gliricidia sepium) loppings (50.3 to 51.1 %). Regression analysis clearly indicated the dependence of S mineralization on the C : S ratio of the organic materials added to soil. The addition of organic amendments resulted in net immobilization of S when the C : S ratio was above 290:1 in Vertisol and 349:1 in Inceptisol. The mineralizable S pool (S_o) and first‐order rate constant (k) varied considerably among the different types of organic materials added and soil. The S_o values of FYM treated soils were higher than in subabul, gliricidia, and poultry manure treated soils.     

红壤酸化及石灰改良影响冬小麦根际土壤钾的有效性

【目的】了解初始酸度对石灰改良红壤钾素有效性的效应,为酸化红壤改良提供依据和支撑。【方法】本试验以湖南祁阳典型的第四纪红土为基础,人为调节出土壤pH分别为4.0、4.5、4.8、5.2的土壤。每个酸度土壤的一半加石灰改良至pH 6.0 (石灰改良处理),另一半不变(酸化处理)。以该土壤进行了小麦盆栽试验。每个盆内放入一个尼龙网根袋,并添加供试红壤1.65 kg (根袋中加150 g)。小麦生长80天后收获,调查了小麦生物量和钾吸收量,测定比较了小麦根际和非根际土壤不同形态的钾含量变化。【结果】1)不同酸化土壤冬小麦生物量(地上部和根部)与初始pH显著正相关(P＜0.05),也与钾吸收量显著正相关(P＜0.05)。石灰改良处理冬小麦生物量均显著高于相应的酸化处理,也随初始pH升高而显著升高。2)不同酸化土壤冬小麦根际土壤速效钾随pH升高显著降低,非根际土壤的速效钾含量均显著高于相应的根际土壤(除pH 4.0外)。石灰改良处理根际土壤速效钾含量均显著低于相应的酸化处理,且非根际土壤显著高于对应根际土,非根际土壤速效钾含量随初始pH升高而显著下降。3)不同酸化土壤冬小麦根际土壤钾离子饱和度随pH升高而显著下降,非根际土壤钾离子饱和度则随pH升高呈增加趋势。石灰改良处理土壤各处理根际土钾离子饱和度均显著低于对应的非根际土,同时非根际土钾离子饱和度与酸化处理的变化趋势一致。4)不同酸化处理红壤冬小麦生物量与根际速效钾亏缺量呈极显著正相关(P＜0.01),冬小麦根际土壤速效钾亏缺率和冬小麦吸钾量及根际钾离子饱和度亏缺率均呈极显著正相关(P＜0.01);而石灰改良处理根际土壤速效钾亏缺率则与初始pH呈显著负相关(P＜0.05)。【结论】在本试验的pH范围内,酸化条件下,根际土壤速效钾含量随pH降低而升高,而冬小麦吸钾量及生物量均随pH升高而升高。表明酸化红壤影响冬小麦钾养分吸收的主导因素是土壤的酸度。施石灰降低了土壤的酸度,提高酸化红壤作物产量和吸钾量。红壤施用石灰校正酸化应在pH降到5.0之前进行。酸化红壤石灰改良后,还应注意适量补充钾肥。     

Emission of nitrous oxide and carbon dioxide and dynamics of mineral N in wastewater sludge,vermicompost or inorganic fertilizer amended soil at different water contents: A laboratory study

Liming or vermicomposting eliminates pathogens from wastewater sludge, but might affect CO₂ and N₂O emissions when added to soil. Soil incubated at 40%, 60%, 80% and 100% of its water holding capacity (WHC) was amended with limed or unlimed wastewater sludge, vermicompost or inorganic fertilizer, while emissions of N₂O and CO₂ and mineral N concentrations were monitored in aerobic incubation experiment for 7 days. Application of unlimed wastewater sludge significantly increased the emission of CO₂ compared to the unamended soil, but not the other treatments except when unlimed wastewater sludge was added to soil incubated at 60% WHC. The emission of CO₂, was generally largest in soil incubated at 60% WHC and lowest in soil incubated at 100% WHC. The emission of N₂O after 1 day was significantly larger in soil amended with unlimed wastewater sludge compared to the other treatments, but not when soil was incubated at 100% WHC. The emission of N₂O increased with increased soil water content. The concentration of NH₄⁺ was largest in soil amended with limed or unlimed wastewater sludge and lowest in the unamended soil and soil water content had no clear effect on it. In soil incubated at 40%, 60% and 80% WHC, the largest amount of NO₃⁻ was found in soil amended with inorganic fertilizer and vermicompost and the lowest in the soil amended with unlimed wastewater sludge. The concentration of NO₃⁻ in soil decreased when the soil water content increased in all treatments, except in the soil amended with unlimed wastewater sludge. It was found that water content affected the emission of CO₂ of N₂O and the concentration of NO₃⁻, but not the amount of NH₄⁺ and NO₂⁻ in soil. Application of unlimed wastewater sludge increased the emissions of CO₂ and N₂O and the concentrations of NH₄⁺, but decreased the amount of NO₃⁻ in soil.     

Long‐term phosphorus solubility in soils receiving poultry litter treated with aluminum,calcium, and iron amendments

Abstract

Phosphorus (P) runoff from poultry litter applied to fields can adversely impact water quality. The majority of P in runoff from poultry litter is soluble, so decreasing the solubility of P could lessen the impact of poultry litter on water quality. The objective of this study was to determine long‐term P solubility in soils receiving poultry litter treated with aluminum (Al), calcium (Ca), and iron (Fe) amendments at various soil pHs. Soil pH was adjusted to 4.0, 5.0, 6.0, 7.0, and 8.0 using elemental sulfur (S) or CaCO₃ with some soil left at its native pH. The pH‐adjusted soil was then incubated with either no litter (control), litter alone (litter control), or litter amended with alum, A1₂(SO₄)₃.16H₂O, (100 or 200 g/kg), Ca(OH)₂ (25 or 50 g/kg), or FeSO₄ .7H₂O (100 or 200 g/kg). The soil was then allowed to equilibrate in the dark at room temperature for 0, 7, 49, 98, and 294 days. After equilibration, soils were extracted with deionized water and soluble reactive P levels were determined. Water‐soluble P levels decreased with time in all treatments, including the control and litter control treatments. Soil pH also affected soluble reactive P levels, with the lowest levels generally observed at pH 8.0. Addition of both unamended and chemically‐amended litter to soil significantly increased P concentrations at all combinations of pH and sampling time. Addition of chemically‐amended litter to soil significantly reduced soluble reactive P compared to unamended litter. With all treatments, an apparent equilibrium was reached at 98 d after treatment. Amendment of litter with either FeSO₄ .7H₂O or alum resulted in the lowest soluble reactive P levels after 294 days. Use of chemical amendments to limit P solubility has potential and should be pursued as a means of reducing eutrophication of sensitive surface waters where poultry litter is applied as a fertilizer.     

Effect of ammonium sulfate,ammonium chloride and root‐zone acidity on inorganic ion content of tobacco

Tobacco plants (Nicotiana tabacum L. cv NC82) were supplied with (NH₄)₂SO₄, or NH₄Cl at root‐zone pH of 6.0 and 4.5 in hydroponic culture for 28 days. Dry matter accumulation, total N and C content, and leaf area and number were not affected by the NH₄ ⁺ source or root‐zone pH. Plants supplied with NH₄C1 accumulated up to 1.2 mM Cl g DW^‐1, but accumulated 37% less inorganic H₂PO₄ ^‐ and 47% less SO₄ ^2‐ than plants supplied with (NH)₂SO₄. The large Cl^‐ accumulation resulted in NH₄C1 –supplied plants having a 31% higher inorganic anion (NO₃ ^‐, H₂, PO₄ ^‐, SO₄ ^2‐, and Cl^‐) charge. This higher inorganic anion charge in the NH₄C1‐supplied plants was balanced by a similar increase in K⁺ charge. Plants supplied with NH₄Cl accumulated greater concentrations of Cl^‐ in leaves (up to 5.1% of DW) than plants supplied with (NH₄)₂SO₄ (less than ‐% DW). Despite the high Cl^‐ concentration of leaves in NH₄Cl supplied plants, these plants showed no symptoms of Cl^‐ toxicity. This demonstrates that toxicity symptoms are not due solely to an interaction between high Cl^‐ concentration in tissue and NH₄ ⁺ nutrition. The increase in root‐zone acidity to pH 4.5 from 6.0 did not induce toxicity symptoms.     

Biochar mitigates N2O emissions by promoting complete denitrification in acidic and alkaline paddy soils

Biochar is an efficacious amendment for mitigating nitrous oxide (N₂O) emissions in soils. Nevertheless, the underlying mechanisms responsible for reduced N₂O emissions by biochar in paddy soils remain inadequately elucidated. Here, using two typical paddy soils with contrasting pH values (5.40 and 7.56), the N₂ and N₂O fluxes and the associated functional genes were investigated in soil amended with varying amounts of biochar (0%, 0.5%, and 5%, weight/weight) via soil slurry incubation integrated with the N₂/Ar technique and qPCR analysis. The results showed that N₂O fluxes were significantly (p < 0.05) reduced by 0.65–3.64 times following biochar amendment, concomitant with a significant (p < 0.05) increase in N₂ fluxes (5.47–46.14%) in both acidic and alkaline paddy soils. As a result, the N₂O/(N₂O + N₂) ratios were significantly (p < 0.05) reduced by 1.53–4.65 fold in both soil types. In acidic paddy soils, the enhanced denitrification rates and the decreased N₂O/(N₂O + N₂) ratios exhibited a strong correlation with increased pH values. In alkaline paddy soil, these changes were ascribed to the enhanced nosZ Clade I gene abundance and nosZ/(nirS + nirK) ratio. Our findings reveal that biochar primarily mitigates N₂O emissions in paddy soils by promoting its reduction to N₂.     

Acid soil tolerance of leucaena species in greenhouse trials

Abstract

Lines of Leucaena leucocephala (Lam.) de Wit were grown in greenhouse pots of an acid, Al‐toxic Tatum subsoil (clayey, mixed, thermic typic Hapludult) treated with 0 or 3000 ppm CaCO₃ to give final soil pH values of 4.1 and 5.3, respectively. Lines of L. leucocephala, plus those of other Leucaena species, were also tested on an acid, Monmouth soil (clayey, mixed, mesic, typic Hapludult) treated with 0 or 1500 ppm CaCO₃ to give final soil pH values of 4.8 and 6.6, respectively. The major index of acid soil tolerance used was relative root yield (unlimed/limed %).

Relative root yields of 117 L. leucocephala lines on Tatum soil ranged from 34 to 246%. Hence, liming the soil from pH 4.1 to 5.3 was highly beneficial to some lines and highly detrimental to others. Because Tatum subsoil is 89% Al saturated at pH 4.1, line tolerance to unlimed soil indicates tolerance to Al. Causes of yield depression at pH 5.3 were not determined.

On Monmouth soil, in a test involving 148 lines of 6 Leucaena species, relative root yields (unlimed/limed %) ranged from 23 to 386%. The line showing highest tolerance to the acid soil (P.I. 279578) and that showing lowest tolerance (P.I? 281636) are both L,. leucocephala. The majority of lines used on Monmouth soil (124 of a total of 148) were from this species. Average performances of the 6 species indicated that L. diversifolia Benth. (5 lines) was most tolerant to the acid Monmouth soil and liming the soil from pH 4.8 to 6.6 actually decreased root yields. The species L.. leucocephala (124 entries) and L. pulverulenta Benth. (4 lines) were intermediate, and L. lanceolata S. Wats. (3 lines) and I., retusa Benth. (1 line) appeared more sensitive to acid Monmouth soil. The Al saturation of Monmouth soil at pH 4.8 was only 23% (compared with 89% for Tatum at pH 4.1). The major growth limiting factor in acid Monmouth soil is believed to be Al toxicity, but this soil has not been as throughly characterized as has Tatum, and other factors may well be involved in explaining differential tolerances of Leucaena lines on the unlimed versus limed soil.

Results of these studies indicate that Leucaena species and lines within species differ significantly in tolerance to acid soils having high levels of exchangeable Al. Acid soil tolerant lines of Leucaena may be useful in expanding the acreage of this crop on oxisols and ultisols of the tropics and subtropics.     

Evaluation of rhizobial strains nodulating lespedeza cuneata for improving n input into minesoil revegetation systems

Abstract

This study was designed to identify strains of Bradyrhizobium sp. (lespedeza) which could improve the plant performance and N status of Lespedeza cuneata (Dumont) G. Don (sericea lespedeza). Based upon preliminary screening for nodulation capability and acetylene reducing activity (ARA), six strains of rhizobia were chosen to be evaluated in the greenhouse for plant growth effects and N₂‐fixing ability.

The L. cuneata symbiosis with two strains, VPI 142 and VPI 163, resulted in the greatest plant growth, total N accumulation, and highest nodule nitrogenase activity (acetylene reduction activity). The high correlation (significant at the 1% level) of shoot dry weight with root dry weight (r = .94), nodule dry weight (r = .92), total shoot N (r = .98), total root N (r = .92), as related to nitrogenase activity of the nodule mass (r = .71), indicates that plant dry weight could be used as an easily determined measurement for screening isolates to be used with L. cuneata.

The identification of efficient rhizobial strains capable of increasing N input should benefit revegetation systems using L. cuneata as the principal legume.