Surface Application Of Gypsum Research Articles

Effect of Gypsum and Coal fly ash on Germination and Stump Quality of Teak (Tectona grandis L. f. )

A nursery experiment was conducted to study the effect of gypsum and coal fly ash on germination and stump quality of teak seedling. The preconditioned 8 months-old teak drupes (fruit with seed) were placed for germination in the nursery bed. The experiment consists of seven treatments which were replicated thrice. On 28 and 60 days after sowing, the results revealed that the application of gypsum at 1.5 t ha-1 did not have any significant effect on number of seedlings/m2 of teak at 28 days after sowing, whereas, the significant influence were observed at 60 days after sowing. Significant differences were also observed in root length, shoot length, number of leaves/ seedlings, stump girth and drymatter production of stump at 6 months after sowing. From this study, it could be concluded that the surface application of gypsum at 1.5 t ha-1 in teak nursery bed enhanced the seedling growth and stump quality of 6 months-old teak nursery plants.

Dynamics of sulfate and basic cations in soil solution as affected by gypsum fertilization in an Ultisol of Southern Brazil

ABSTRACTThe objective of this study was to evaluate the short-term dynamics of chemical species of sulfate and the main basic cations in the soil solution affected by the application of different sulfur (S) rates using agricultural gypsum. The experiment was carried out in an Ultisol with 14% clay, managed under no-tillage for 14 yrs in Southern Brazil. Four rates of S (0, 5, 10 and 20 kg of S ha−1) were evaluated using agricultural gypsum (CaSO4) as S-source. The soil solution was collected using porous capsule lysimeters before and at 9, 17, 37, 60, 76 and 109 d after the gypsum application, at depths of 20 and 60 cm. Surface application of gypsum rapidly increases the sulfate concentration in the soil solution at 20 cm depth. However, in less than 30 d, the effect of the S rates on the soil solution at 20 cm was minimal, with an increase in sulfate concentration in the soil solution at 60 cm depth after 17 d. Sulfated fertilization via agricultural gypsum at rates greater than 10 kg ha−1 in sandy soil with low cation exchange capacity increased the mobility of Ca and Mg in the soil profile.

Can highly saline irrigation water improve sodicity and alkalinity in sodic clayey subsoils?

The concept of irrigating crops with saline irrigation water is not new, but impacts of this practice on soil properties remain debatable, particularly the use of highly saline water. In this work, key soil chemical properties were assessed to a depth of 300 cm following 2.5 years of application of highly saline irrigation to a sodic texture-contrast soil (Brown Sodosol) in south-eastern Tasmania, Australia. Control plots (rainfall only) were compared to irrigation treatments of low (0.8 dS/m) and high salinity (16 dS/m) waters at application rates of both 200 and 800 mm/year. Whilst significant increases in both electrical conductivity and chloride concentration occurred throughout the soil profile in the high salinity treatment, these values were well below those of the irrigation water, indicating effective deep leaching. In the upper soil profile, 0–50 cm, of the high salinity treatments both the exchangeable Na+ and its ratio to total base cations (ESP) were significantly increased whilst the lower soil profile between 50 and 200 cm, was improved via both reduced alkalinity and sodicity. Leaching of the exchangeable base cations Ca2+, Mg2+ and K+ was significant in the upper soil profile (0–50 cm). As expected, the low salinity treatment (0.8 dS/m) had minimal impacts on soil chemical properties. The upper topsoil (0–10 cm) total organic carbon was significantly reduced in the high salinity plots and was negatively correlated with Cl− concentration. The data confirms the general concerns about application of saline irrigation, namely increased whole profile salinisation and upper soil profile (0–50 cm) sodicity, but they also show unexpected and desirable reductions in the lower soil profile (> 50 cm) alkalinity and sodicity. It appears the Na+ ions present in the saline waters led to differential leaching of base cations from the rooting zone, especially Ca2+ which then ameliorate the alkalinity and sodicity deeper in the soil profile (> 50 cm). Thus, surface application of gypsum may help sustain the application of highly saline waters; alternatively, subsurface irrigation above the sodic clayey subsoils could be trailed.

Lime and gypsum application increases biological activity, carbon pools, and agronomic productivity in highly weathered soil

The application of lime and gypsum has been recognized as an important strategy for correcting soil acidity and for improving soil fertility, soil aggregation, and agronomic productivity in highly weathered soils. We hypothesized that the combined application of lime and gypsum would create favorable conditions for biological activity and result in increased SOC storage and agronomic productivity. Thus, the aim of this study was to evaluate the long-term (i.e., 15 years) impact of lime and gypsum application on the biological activity, SOC stocks, and agronomic productivity of plots under no-till soil management. The experiment was established in 1998 at a site with clayey Oxisol in southern Brazil, and was designed with a split-plot arrangement, completely randomized blocks, and three replicates. The main plot was subject to three lime treatments: (i) control (no lime); (ii) incorporated lime (IL):incorporation of 4.5Mglimeha−1 to a depth of 0–20cm by; and (iii) surface lime (SL): surface application of 4.5Mglimeha−1, which was equally divided among three annual applications during the first three years of the experiment. The subplots were comprised by surface applications of gypsum at 0, 3, 6, or 9Mgha−1. Soil samples were collected in 1998, before of the experiment, and in October 2013, in order to evaluate soil enzyme activities, SOC pool stocks, crop productivity, C-biomass input, and soil fertility attributes. Both forms of lime application significant improved the stocks of several SOC pools, crop productivity, biomass-C input rates, soil fertility attributes, and enzyme activity. The SOC stocks were positively correlated with Ca2+ content and biomass-C input, demonstrating the potential of calcium to improve C accumulation. Enzyme activities were significantly affected by both soil fertility and SOC pools, with increases in hot water extractable organic C yielding the greatest increases in enzyme activity. In addition, we also found that gypsum application significantly increased the stocks of labile SOC pools and arylsulfatase activity. However, effects of gypsum application were less apparent than those of lime application and the combination of surface lime (4.5Mgha−1) and gypsum (9Mgha−1) application yielded the greatest long-term increase in the stock of total organic C stock. Thus, the results of the present study suggest that lime and gypsum application, along with no-till management and biomass-C input, constitutes an efficient strategy for improving the biological activity, C stocks, and productivity of agricultural soils.

Foliar tissue, grain yield and economic return by surface application of gypsum and different number of soybean plants in precision seed drill

The gypsum has elevated calcium and sulfur in the soil, and there are reports of increased grain yield of soybean with reduced number of plants, being necessary in conjunction with economic return on investment. This study investigated the effect of application superficial of gypsum and different numbers of plants in precision seed drill in the nutritional aspect of the leaf tissue, grain yield of soybean cultivated in clayey Rhodic Hapludox and economic return on investment. Used in the experiment was a randomized block design in scheme tracks (4 × 4), with four doses of gypsum (0, 800, 1600 and 2400 kg ha-1) applied at the V4 stage of soybean Vmax RR (SYN 7059RR) and four variations in the number of plants (12, 14, 16 and 18 plants per meter), with four replications. Samples of leaf tissue were collected in the flowering stage of soybean in the 2011/2012 crop, and then determined the levels of Ca, Mg, K, P, S, Cu, Zn, Mn and Fe. At maturity the yield assessment was performed. The number of plants per meter with precision seed drill and superficial application of gypsum at the V4 stage do not affect the content of macro-and micronutrients leaf tissue of soybean cultivar SYN 7059RR. The application of gypsum at the V4 stage and reducing the number of plants per meter statistically do not affect the grain yield. Recommend lower number of plant (12 plants m-1) on soybean cultivar for SYN 7059RR. The economic returns using higher amount of seed (14, 16 and 18 plants m-1) is -283, -260 and -271% with investment of US$ 13.76, 29.24 and 44.72. Use of gypsum focused costs to only two cultures (soybeans and wheat) during the crop season provides residual soil of 104.43 kg ha-1 of S. Application 800 kg ha-1 gypsum provides US$ 14.56 profit with 44% economic return to payment half investment (US$ 33.32). Key words: No-till, fertilization, plant population, seeding rate, investment return

Improvement in Chemical Attributes of Oxisol Subsoil and Crop Yields under No‐Till

The natural chemical qualities of the subsoil of Oxisols often restrict root growth, water use efficiency, and crop yield. The practice of continuous no‐till farming creates a fertile topsoil but generally does not affect the subsoil. This study aimed to evaluate the effectiveness of gypsum in improving the chemical attributes of the subsoil and increasing crop yields. To this end, the experiment was conducted at two sites in distrophic Red Oxisols located in southern Brazil. The experimental design was a randomized complete block with three replications. Treatments consisted of broadcast gypsum rates of 0.0, 1.0, 2.0, 3.0, 4.0, 5.0, and 6.5 Mg ha–1. Soil samples were collected from the root zone at the beginning of the experiment and after six and 22 mo to evaluate soil pH and extractable P, K+, Ca2+, Mg2+, Al3+, and SO4–S concentrations. After 6 mo of gypsum application, an increase in exchangeable bases associated with a decrease in Al3+ concentrations in the subsoil was noted, and this improvement was intensified further by 22 mo. An increase in crop yields was related to the increase in base saturation and Ca2+ saturation and a decrease in Al3+ saturation in the 25‐ to 40‐cm soil depth. Surface application of gypsum was an effective method of improving the chemical quality of the rooting zone in Oxisols under continuous no‐till farming and resulted in a higher impact on corn (Zea mays L.) grain yield than soybean [Glycine max (L.) Merr.] yield.

Polyacrylamide coated Milorganite™ and gypsum for controlling sediment and phosphorus loads

Abstract The application of polymer for controlling erosion and the associated nutrient transport has been well documented. However, comparatively less information is available on the effect of polymer application together with soil amendments. In this study, the effect of polyacrylamide (PAM) in combination with surface application of gypsum and Milorganite™ (MILwaukee ORGAnic NITtrogEn) biosolid for reducing sediment and phosphorus transport under laboratory rainfall simulations was investigated. The treatments considered were bare soil, gypsum, Milorganite™, gypsum + Milorganite™, PAM-coated gypsum and PAM-coated Milorganite™. Application rates for gypsum and Milorganite™ were 392 kg ha −1 (350 lb/acre) and 726 kg ha −1 (650 lb/acre), respectively. The PAM was coated on gypsum and Milorganite™ at an application rate of 11.2 kg ha −1 (10 lb/acre) and 22.4 kg ha −1 (20 lb/acre), respectively. Rain simulation experiments were conducted using a rainfall intensity of 6.0 cm h −1 for 1 h on a 10% slope. Surface runoff was collected continuously from each soil box over 10 min intervals and leachate was collected continuously over the 60 min simulation. The reduction in runoff or in leachate for all treatments was not significantly different from the bare soil control. The sediment loss for PAM coated Milorganite™ was reduced by 77%, when compared to bare soil. However, the sediment loss was not significantly reduced for any other treatment compared to bare soil. The PAM-coated gypsum was not effective for erosion control in our study, and there appears to be a correlation between effectiveness and prill size. However, the gypsum (coated and uncoated) contributed about half of the dissolved reactive phosphorus (DRP) export (in the runoff) compared to bare soil. The PAM-coated Milorgante™ reduced the DRP and total phosphorus (TP) export to 0.3–0.5 times that of Milorganite™ and to levels similar to bare soil. The decreased sediment and phosphorus export for the PAM-coated Milorganite™ treatment is a signal for a potential management practice for controlling erosion and nutrient transport in fertilized agricultural landscapes.

Surface application of gypsum in low acidic Oxisol under no-till cropping system

The conditions in which a favorable response to a gypsum application can be expected on crop yields are not clear. A 3-year field trial was carried out to evaluate the effects of gypsum application on soil chemical attributes and nutrition and yield of corn (Zea mays L.) and soybean (Glycine max L. Merrill) on a clayey Typic Hapludox of high fertility and low acidity under no-till in Guarapuava, Parana State, Brazil. Treatments were arranged in a randomized complete block design with four replications, and consisted of gypsum application on the soil surface at 4, 8, and 12 Mg ha-1. Gypsum application increased the P content in the soil most superficial layer (0.0 - 0.1 m) and also the exchangeable Ca and S-SO4(2-) contents and the Ca/Mg ratio in the soil profile (0.0 - 0.6 m). Gypsum also caused leaching of Mg and K exchangeable in the soil. An increase in Ca concentrations in the corn leaves, and in P and S concentrations in the corn and soybean leaves occurred following the gypsum application. A yield response of corn to initial application of gypsum was found, but subsequent soybean crops did not respond. Gypsum application proved to be an effective practice to maximize no-till corn grain yield.

Potassium leaching in undisturbed soil cores following surface applications of gypsum

Displacement studies on leaching of potassium (K+) were conducted under unsaturated steady state flow conditions in nine undisturbed soil columns (15.5 cm in diameter and 25 cm long). Pulses of K+ applied to columns of undisturbed soil were leached with distilled water or calcium chloride (CaCl2) at a rate of 18 mm h−1. The movement of K+ in gypsum treated soil leached with distilled water was at a similar rate to that of the untreated soil leached with 15 mM CaCl2. The Ca2+ concentrations in the leachates were about 15 mM, the expected values for the dissolution of the gypsum. When applied K+ was displaced with the distilled water, K+ was retained in the top 10–12.5 cm depth of soil. In the undisturbed soil cores there is possibility of preferential flow and lack of K+ sorption. The application of gypsum and CaCl2 in the reclamation of sodic soils would be expected to leach K+ from soils. It can also be concluded that the use of sources of water for irrigation which have a high Ca2+ concentration can also lead to leaching of K+ from soil. Average effluent concentration of K+ during leaching period was 30.2 and 28.6 mg l−1 for the gypsum and CaCl2 treated soils, respectively. These concentrations are greater than the recommended guideline of the World Health Organisation (12 mg K+ l−1).

Aplicação de gesso agrícola e especiação iônica da solução de um Latossolo sob sistema plantio direto

O baixo teor de Ca e a toxicidade por Al são importantes limitações à produtividade das culturas em solos ácidos brasileiros. É possível aumentar o teor de Ca e reduzir a toxicidade por Al por meio da aplicação de gesso agrícola. No entanto, é importante melhor compreensão dos efeitos do gesso na especiação iônica da solução do solo. Avaliou-se a especiação iônica da solução do solo (extrato aquoso 1:1) de amostras de um Latossolo Vermelho distrófico textura argilosa, sob sistema plantio direto, cinco anos após a aplicação superficial de 3, 6 e 9t ha-1 de gesso agrícola. A especiação foi realizada com auxílio do programa computacional Visual Minteq em amostras coletadas nas profundidades de 0-0,05; 0,05-0,1; 0,1-0,2 e 0,2-0,4m. Para o Al, as principais espécies químicas foram os complexos com carbono orgânico dissolvido (Al-COD) e com F (Al-F), enquanto o par iônico AlSO4+ ocorreu em pequena proporção. O COD foi o principal ligante para Mg e Ca, mas em muito maior magnitude para este último, refletindo importante participação dos ânions orgânicos na dinâmica desses nutrientes. Em relação ao sulfato, apesar da formação dos pares iônicos com Ca, Mg e Al (CaSO4(0), MgSO4(0) e AlSO4+), houve a predominância da forma livre S-SO4-2, enquanto o fosfato apresentou forte interação com o Al em solução, formando a espécie química Al-HxPO4x.

Amending subsoil acidity by surface applications of gypsum, lime, and composts

Crop growth on many highly weathered soils could be severely restricted by the subsoil acidity, which is characterized by low calcium (Ca) and high aluminum (Al) at depths below the plow layer. Since surface applied lime may not improve subsoil conditions, alternatives must be sought. Thus, effects of composts alone or in combination with lime on increasing Ca and decreasing Al in subsoil were evaluated in a simulated soil profile. An acid Ultisol was packed in a 50-cm long column with the top 15 cm being amended with either lime (CaCO3), gypsum (CaSO4·2H2O), a yard waste compost, a bio-solids-based compost (Nitrohumus), or a combination of compost and lime. The column was leached with 40 mL deionized water daily at a rate of 10 mL per 15 min for 27 days (40 cm water). Thereafter, the column was dismantled and cut into 15, 10, 10, 10 cm layers from the top for chemical analysis. Results showed that lime markedly increased pH and reduced exchangeable Al of the surface layer, but had little effect on subsoil pH. Only 7.6% of the applied Ca from lime moved from the applied layer to the next 10-cm layer, while more than 60% of the applied Ca from gypsum moved past the applied layer. Composts effectively reduced exchangeable Al of the top layer, and of the top two layers when applied together with lime. More Ca was found in deeper soil layers when lime and the Nitrohumus compost were applied together than when either material was applied alone. The downward Ca movement was mainly assisted by SO4 2− even in the compost treatments.

A Comparison of Strategies for Ameliorating Subsoil Acidity I. Long‐Term Growth Effects

Subsoil acidity is an important yield‐limiting factor. Mechanical procedures of deep lime incorporation and surface applications of gypsum have been shown to be beneficial, but no long‐term comparisons of these strategies have been published. Without such information it is difficult to make appropriate management decisions. The work reported here was conducted toward this end. In a long‐term study with maize (Zea mays L.) on a strongly acidic Plinthic Paleudult, conventional moldboard incorporation of lime (15 Mg ha−1) was compared with (i) deeper incorporation of the same quantity of lime with plowing and subsoiling operations, and (ii) treatments where large additional quantities of lime were similarly introduced below normal plow depth. The efficacy of gypsum was tested by adding 10 Mg ha−1 to conventionally limed plots. For 11 seasons, the average grain yield benefit ranged from 5 to 17% in the case of mechanical strategies and was 25% in the case of gypsum. Yields were increased only marginally by extra lime applications and segmental (slotted) amelioration proved inferior to deep‐plowing procedures. The gypsum treatment proved profitable only in the fourth season, but by the eighth season had proved more profitable than the best mechanical procedure; and by the 11th season, the gypsum treatment had resulted in a cumulative yield advantage of 3.8 Mg ha−1 Long‐term superiority of the gypsum treatment was unquestionable in this study, but gypsum is often unavailable and acidic soils are frequently unresponsive to gypsum. In such situations, deep plowing should not, as is often the case, be discarded as impractical.

Plant Responses to Gypsum Amendment of Sodic Bentonite Mine Spoil

Abandoned bentonite mine spoils are extremely difficult to revegetate because of their high clay content, salinity, sodicity, low permeability, and the semiarid climate of the area where bentonite mining occurs. Recent research has led to the development of technology utilizing sawmill wastes (chips, bark, and sawdust) to enable the successful revegetation of these lands. The use of wood residue amendments increased water infiltration, leaching of soluble salts, and vegetation establishment; however, sodicity continued to be a problem and threatened to destroy the established vegetation. Surface application of gypsum was evaluated to determine its effectiveness in ameliorating the spoil sodicity and its effect on plant growth. In a 3-year field study, surficial gypsum amendment resulted in significant increases in perennial grass biomass (150%) and canopy cover (140%). These changes were not evident until the second or third year after gypsum amendment. Annual forb biomass did not respond to gypsum amendment; however, canopy cover did exhibit a significant increase in the second year at lower wood residue amendment rates. This research demonstrates that surface applied gypsum can be effective in ameliorating bentonite spoil sodicity when applied to established plant communities.

Amelioration of subsurface acidity in sandy soils in low rainfall regions .2. Changes to soil solution composition following the surface application of gypsum and lime

Two field trials were sampled to investigate the changes to soil solution chemical properties of a yellow sandplain soil with an acidic subsoil following the application of gypsum and lime to the soil surface in 1989. The soils were sandy textured and located in a region of low annual rainfall (300-350 mm). Soil was sampled annually to a depth of 1 m and changes in soil solution composition were estimated by extraction of the soil with 0.005 M KCl. Gypsum leaching caused calcium (Ca), sulfate (SO4) and the ionic strength to increase substantially in both topsoil and subsoil by the end of the first year. Continued leaching in the second year caused these properties to decrease by approximately one-half in the topsoil. Gypsum appeared to have minimal effect on pH or total Al (Al-T), although the amount of Al present as toxic monomeric Al decreased and the amount present as non-toxic AlSO+4 ion pairs increased. Magnesium (Mg) was displaced from the topsoil by gypsum and leached to a lower depth in the subsoil. In contrast, lime caused pH to increase and Al to decrease substantially in the topsoil, but relatively little change to any soil solution properties was observed in the subsoil. There was an indication that more lime may have leached in the presence of gypsum in the first year after application at one site. Wheat yields were best related to the soil acidity index Al-T/EC (where EC is electrical conductivity of a 1:5 soil:water extract), although the depth at which the relationship was strongest in the subsoil varied between sites. The ratio Al-T/EC was strongly correlated with the activity of monomeric Al species (i.e. the sum of the activities of Al3+, AlOH2+ and Al(OH)+2 in the soil solution. An increase in the concentration of sulfate in the subsoil solution (which increased the ionic strength, thereby decreasing the activity of Al3+, and also increased the amount of Al present as the AlSO+4 ion pair) was probably the most important factor decreasing Al toxicity to wheat. The results indicated that gypsum could be used to increase wheat growth in aluminium toxic subsoils in sandy soils of low rainfall regions and that a simple soil test could be used to predict responses.

Effect of surface‐applied Ca amendments and N on solonetzic soil properties and composition of Barley

Abstract A field study was conducted on a black Solonetzic soil in east‐central Alberta to determine the influence of surface applications of gypsum, lime, and ammonium nitrate, alone and in combinations, on soil chemical properties, grain yield, and chemical composition of barley. The Ca amendments were applied once in fall 1982; ammonium nitrate was applied each spring before sowing of barley in 1986, 1987, and 1988. Gypsum increased the concentration of soluble and extractable Ca in the Ap horizon, but the effect of lime was significant only on extractable Ca. Gypsum also reduced SAR (sodium adsorption ratio) and concentration of soluble and extractable Na. The effect of gypsum further increased when N was applied at the same time. The added N fertilizer increased grain yield of barley in two of the three years, the N concentration in the grain and the concentration of N and Zn in the flag leaf in all years and the Mn concentration in one year. Both gypsum and lime increased grain yield in only one yea...

Chemical Effects of Repeated Equilibrations of Variable-Charge Soils with Phosphogypsum Solution

Surface applications of gypsum or phosphogypsum (PG) to acid soils have resulted in improved crop growth as a result of amelioration of subsoil acidity; however, the mechanism involved is not clearly understood. The effects of repeated equilibrations of soils with PG solution on soil solution and extractable ion composition were investigated in this study. Cultivated and woodland Cecil Bt horizon (0.6–0.8 m depth) soil materials (clayey, kaolinitic, thermic Typic Kanhapludult) were sequentially equilibrated five times in the laboratory with 2 g L−1 PG solution at 40% (v/w) soil moisture content. With an increase in the number of equilibrations, the pH of the displaced soil solution increased in the cultivated soil, and initially decreased and then increased slightly in the woodland soil. On the basis of predictions of saturation indices by using the MINTEQ speciation model, the composition of displaced soil solutions showed no evidence of CaSO4 precipitation regardless of the number of equilibrations. The cumulative sorption of Ca and SO4 after five equilibrations with PG solution was 2.80 and 1.69 cmolc kg−1, respectively, in the cultivated soil, and 4.43 and 4.41 cmolc kg−1, respectively, in the woodland soil. For the cultivated soil, 83 and 71% of the final cumulative sorption of Ca and SO4 was reached after the second equilibration while, for the woodland soil, the values were 45 and 46%, respectively. The retention of Ca and SO4 following the equilibration of the soils with PG solution was attributable to a salt-sorption mechanism, as evident from the sorption of Ca and SO4 in equal proportions with negligible release of cations or anions into the displaced soil solution. Successive equilibration of the soils with PG solution resulted in a decrease in extractable Al, an increase in extractable Ca, and a net increase in cation-exchange capacity. These changes were much greater in the woodland soil than in the cultivated soil.

Amelioration of subsoil acidity

Abstract In highly weathered regions, acid, infertile subsoils limit productivity by preventing root proliferation and thereby increasing the likelihood of drought stress. An experiment on a Typic Hapludult involving surface application of gypsum and deep lime incorporation investigated the possibilities of ameliorating such subsoils. Yield responses to both treatments were highly significant and stemmed from reductions in subsoil Al and increases in Ca. Root measurements corroborated the fact that the responses were due to root proliferation in the subsoils and consequent resistance to drought stress. Redistribution of roots in the profile in ameliorated subsoils resulted in P insufficiencies being recorded despite high soil test levels of P probably the result of a relatively smaller root surface in topsoil where P had been placed. These results confirm the feasibility of using gypsum and in particular, phosphogypsum as a subsoil ameliorant.

Amelioration of an Acid Soil Profile through Deep Liming and Surface Application of Gypsum

AbstractHighly weathered soils in the southeastern USA often have very acid, hard, infertile subsoils not readily penetrated by crop roots. An experiment on a Typic Hapludult involving deep liming, subsoil disturbance and mixing, and surface application of gypsum was conducted to investigate the possibilities of ameliorating such subsoils. Results with alfalfa (Medicago sativa L.) over 4 yr show that liming to 1 m can increase yields by 50% while merely mixing the subsoil without lime incorporation resulted in a substantial yield decline. Surface application of gypsum with sufficient time for it to penetrate the subsoil resulted in 25% yield increases. Deep liming resulted in the complete precipitation of soluble Al and increased the level of soluble Ca allowing roots to freely penetrate the subsoil. Gypsum resulted in a progressive reduction in soluble Al and an increase in soluble Ca creating a similar but lesser effect than liming. Water extraction patterns corroborated the fact that roots were penetrating chemically ameliorated subsoil. Saturation extract studies indicated that gypsum reduced the activity of Al3+ and increased that of Ca2+ substantially. These results suggest that by‐product gypsum from phosphate acid manufacture would be a feasible amendment for acid subsoils.

Amelioration of an Acid Soil Profile through Deep Liming and Surface Application of Gypsum

Amelioration of an Acid Soil Profile through Deep Liming and Surface Application of Gypsum

DYNAMICS OF PHOSPHORUS DURING RECLAMATION OF SODIC SOILS

This study describes the phosphorus status of sodic soils formed under the influence of sodium carbonate, aquic natrustalf, and its possible leaching during their reclamation. Uncultivated, barren sodic soils contained high amounts of Olsen's extractable phosphorus, which decreased with depth, and the amounts were highly correlated with the electrical conductivity of the soil. The incubation studies conducted at saturated moisture content with differential amounts of gypsum at 0, 25, 50, 100, and 200 percent of laboratory-determined gypsum requirement (GR) showed that Olsen's P decreased with increases in the rate of gypsum applied. The leaching studies conducted in the field showed that phosphorus in sodic soils moved down, along with other soluble salts, though the peak P concentration lagged behind the other salts. Leaching studies conducted in plexiglass columns in the laboratory brought out that substantial leaching of P, up to 60 ppm P, could occur when sodic soils are leached as such or after surface application of gypsum. It seems that under natural conditions, Na2CO3, which is the predominant salt in sodic soils, reacts with native calcium phosphate to form highly soluble sodium phosphates, which are leached during reclamation. Gypsum, mixed with soil at a rate of 100 percent GR and above, decreases the leaching of phosphorus. It seems due to (1) immobilization of soluble P by CaSO4 through the formation of less soluble Ca-P compounds; (2) common ion effect to decrease solubility of Ca-P compound; and (3) lowering of soil pH, which in turn decreases the soluble P in the pH range of 8.3 to 10.