Differential leaching of cations and sulfate in gypsum amended soils

Abstract

An adequate supply of available Ca in the soil solution of the pegging zone during fruit development is required for production of high yields of high quality peanuts (Arachis hypogaea L.). On low Ca soils, application of gypsum during early bloom is recommended in order to ascertain adequate availability of Ca. Reaction of gypsum in soils under leaching conditions vary considerably and play an important role in fruit development and yield of peanuts. A laboratory study was conducted in leaching soil columns to investigate the effects of one gypsum amendment on leaching of Ca, K, Mg, and SO₄ to a depth of 8 cm (fruiting zone of peanut). Six soils of varying physical and chemical properties representative of major peanut growing soils in Georgia were utilized. Following leaching with 15 cm water through gypsum‐amended soil columns, 50% to 56% and 74% to 77% of applied Ca and SO₄, respectively, were leached below 8 cm in the sandy‐Carnegie, Dothan, Fuquay and Tifton soils. The respective values for the sandy clay loam‐Greenville and Faceville soils were 28% to 36% and 58% to 69%. Lower initial Ca status and greater leaching of Ca from the applied gypsum in the sandy soils as compared to sandy clay loam soils suggest greater beneficial effects of supplemental gypsum application for peanut production in the former soils than in the latter soils. Leaching of K or Mg (as percentage of Mehlich 1 extractable K or Mg) in gypsum‐amended treatment was considerably greater in sandy soils than that in the sandy clay loam soils. In view of the reported adverse effects of high concentrations of soil K and Mg in the fruiting zone on the yield and quality of peanuts, greater leaching of K and Mg from the fruiting zone in gypsum amended sandy soils enable them to maintain a favorable cation balance for the production of high yields of quality peanuts.     

Effect of gypsum on soil potassium and magnesium status and growth of alfalfa

Abstract

Though surface‐applied gypsum has been shown to be useful in reducing the subsoil acidity syndrome, excessive application could reduce the availability of other essential cations in soil. This study was conducted to determine the effects of surface‐applied gypsum on the availability of potassium (K) and magnesium (Mg) in field soils. Field experiments were conducted on Davidson and Tifton series soils in the southeastern United States with 6 main ameliorant treatments (0, 2, 5, and 10 t gypsum/ha, soil profile mixed to 1 m without lime incorporation and, mixed with lime to 1‐m depth), and 2 levels of Mg (0 and 100 kg Mg/ha) and 4 levels of K (0, 125, 250, and 375 kg K/ha) in a split‐split plot configuration. Alfalfa was grown on the Tifton soil and sorghum on the Davidson soil. Yields of alfalfa and sorghum increased with 2 t gypsum/ha but were adversely affected above 5 t gypsum/ha. Gypsum amendment at 2 t/ha reduced topsoil exchangeable Mg and K in both soils. In the soil profile study, exchangeable Mg was reduced throughout the upper 52.5‐cm depth, while no reduction of K was observed below the 22.5‐cm depth in either soil. The study indicates that Mg is more susceptible to leaching loss than K after surface application of gypsum. It is also suggested that surface‐applied gypsum be used as a soil ameliorant along with proper management of Mg and K fertilizers.     

Gypsum material effects on peanut and soil calcium

Abstract

Adequate availability of calcium (Ca) in the upper 7–10 cm of soil is extremely important for pod development and therefore for production of quality peanut (Arachis hypogaea L.). Supplemental Ca is usually applied as gypsum, however, availability of Ca may depend on the type of gypsum. The objective of a laboratory study was to evaluate recovery of Ca in Mehlich I, 0.01 M NaNO₃ and deionized water extractants from seven gypsum materials which varied physically from fine and coarse powders to crystals, granules and pellets. Overall, recovery of Ca was much greater in Mehlich I (89.5–99.6% of total Ca) than in either 0.01 M NaNO₃ (81.0–98.4%) or deionized water (78.7–97.5%). However, for 3 sources, recovery of Ca was very similar in NaNO₃ solution and deionized water.

Field experiments were conducted on Lakeland sand (Mehlich I Ca = 127 kg/ha, 0–15 cm) and Tifton loamy sand (Mehlich I Ca = 665 kg/ha) soils to study the effects of the gypsum materials on Florunner peanut grade and yield. Effects of gypsum treatments on Mehlich I‐ and 0.01 M NaNO₃‐extractable soil Ca were also evaluated during peanut pod development. On the Lakeland soil, Mehlich I Ca increased from 127 to a range of 420–737 kg/ha following application of gypsum depending on the type of gypsum material. Percent sound mature kernels were significantly greater where gypsum was applied than in the control treatment, regardless of source. Total sound mature kernel yield and gross return were greatest for the more soluble sources. The yield vs. soil test Ca relationship 90 d after planting revealed that yield response was very minimal if soil Ca was greater than 290 and 85 kg/ha of Mehlich I and 0,01 M NaNO₃‐extractable Ca, respectively. Application of gypsum to the Tifton soil, regardless of type of material, had no significant effect on yield, grade or gross return because Mehlich I extractable Ca in the control treatment was well over 560 kg/ha; the critical soil test Ca for runner peanut according to the current Georgia soil test recommendation.     

Soil solution and extractable calcium in gypsumamended coastal plain soils used for peanut culture

Abstract

Peanut (Arachis hypogaea L.) fruits absorb Ca directly from the soil solution; therefore, the concentration of soil solution Ca in the fruiting zone (0–8 cm) is important in determining the availability of adequate Ca during fruit development. Since the critical period for Ca requirement for peanut fruit may extend from 25–65 d after flowering, a measure of extractable Ca (Quantity factor) is also important in determining the replenishment of soil solution Ca over the fruiting period. A laboratory study was conducted to evaluate the effects of varying soil moisture regimes on soil solution and extractable Ca in gypsumamended Bonifay sand (loamy, siliceous, thermic, grossarenic, Plinthic Paleudult) and Greenville sandy loam (clayey, kaolinitic, thermic, Rhodic Kandiudult) soils over a 70‐d period. Soil solution Ca increased in both soils with increasing soil moisture, 14 d after incubation of gypsum‐amended soils. Subsequently, the soil solution Ca decreased for all moisture regimes in the Bonifay soil, but only in the driest regime in the Greenville soil. Soil solution Ca concentrations were 1.0 and 3.2 cmolc/L in the Bonifay soil and 2.7 and 1.6 cmolc/L in the Greenville soil for the wettest and driest regimes, respectively, 70 d after incubation. Gypsum amendment also increased the concentrations of K and Mg in soil solution in both soils; therefore, leaching of excess K and Mg below the fruiting zone may be facilitated in field situations.     

Evaluation of three calcium extractants for coastal plain soils

Abstract

Mehlich 1‐Ca is used as an index to predict the Ca requirement for peanut (Arachis hypogaea L.) fruit development in major peanut growing states. Recently, some concern has been raised about the inadequacy of Mehlich 1 extractable Ca for that purpose. Possible use of alternative extractants for soil Ca has been suggested. In this study, relationships among Mehlich 1, 0.2 M NH₄Cl and 0.01 M NaNO₃ extractable Ca were examined in several Coastal Plain soils to which gypsum or lime had been applied. Variability in extractable Ca was much greater following lime treatment than following gypsum treatment. In Bonifay soil, the quantity of Ca extractable by the three extractants was similar in a gypsum treatment, but in a lime treatment (at an application rate equivalent to the gypsum treatment) Mehlich 1‐Ca was 2 and 5‐fold greater than NH₄Cl‐ and NaNO₃‐Ca, respectively. In Greenville soil, Mehlich 1‐Ca was 3 to 4‐fold greater than NaNO₃‐Ca regardless of gypsum or lime amendment.

For soil samples from a field experiment on Lakeland sand, where lime or gypsum was applied prior to planting, Mehlich 1‐Ca was 7.5 and 2.2‐fold greater than NaNO₃‐Ca for the lime and gypsum treatments, respectively. Greater variability in Mehlich 1‐Ca in lime than in gypsum treatments was due to possible inclusion of undissolved limestone in the soil samples, resulting in overestimation of Ca available for peanut fruits. Mehlich 1‐Ca appears to be an adequate index of soil Ca for prediction of supplemental Ca requirement for peanut if lime has not been applied or has been applied well in advance of planting, thus minimizing the inclusion of undissolved limestone with the soil sample taken from the fruiting zone (0–8 cm depth) 10–14 d after planting.     

Effects of certain cations on manganese absorption by excised rice roots

Abstract

The peanut requires a readily available source of Ca in the fruiting zone during fruit development. Field studies were conducted for three years on two soils to compare rates of fine and coarse gypsum material applied to peanuts shortly after planting and at early flowering in supplying Ca to the peanut fruit and its effect on yields. The fine and coarse gypsum was applied at three rates and at two different times in randomized complete block experiments. At approximately every four weeks, composite soil samples were collected at 0–5 and 5–10 cm depths and extracted with (0.05N HC1 + 0.025N H₂ SO₄) extractant. On the Lakeland soil fine gypsum applied at early flowering gave higher Ca levels at the 0–10 cm depth than coarse material applied shortly after planting or at early flowering. Yield data showed that at low rates coarse gypsum applied at planting was superior to early flowering application. In most instances on the Greenville soil, coarse gypsum applied at planting produced higher levels of Ca than fine or coarse gypsum applied at early flowering. There was no yield response to gypsum application.     

Potassium,magnesium, and irrigation effects on peanuts grown on two soils

Abstract

Research data are limited on K and Wg requirements of peanuts (Arachis hypogaea L.) grown on sandy soils either with or without irrigation. Purposes of this study were (1) to determine Mg, K, and irrigation effects on yield, sound mature kernels (SMK's), and diseases of ‘Florunner’ peanuts grown on two sandy soils and (2) to determine sufficient amounts of Mg and K in peanut leaves and soils. Field experiments were conducted for three years on a Lakeland sand (thermic, coated Typic Quartzipsainments) and a Fuquay loamy sand (siliceous, thermic, Arenic Plinthic Paleudults). Both soils initially tested low in Mehlich 1 extractable K and Mg, but Lakeland was lower than Fuquay in both K and Mg. Factorial treatments were 0, 67, 67 (split into three applications), and 134 kg Mg/ha as MgS0₄ and 0, 56, 112, and 224 kg K/ha as KC1.

Neither irrigation, K, nor Mg treatment affected number of diseased plants. (Sclerotium rolfsii) or pod rot on either soil. Also, yield and % SMK's were not affected by any treatment any year on Fuquay soil. On Lakeland soil, yields were increased by irrigation 60.3% in 1980 and 11.0% in 1982, by K rates of 56 kg/ha or more each year, and by Mg rates of 67 kg/ha or more in 1978 and 1982. Yields (3‐yr average) were increased 14.7% by Mg with K and 30.7% by K with Mg. Magnesium plus K increased yields 69.3% over the control. Treatments had no consistent effects on % SMK's. Concentrations of K and Mg in leaves and soils were increased by increased rates of application but were not affected by irrigation. Minimum sufficiency levels for maximum yield were 10 and 2.0 g/kg for leaf K and Mg and 20 and 11 ng/kg for soil K and Mg (0 to 30 cm depth), respectively.     

Downward Movement of Soil Cations in Highly Weathered Soils Caused by Addition of Gypsum

Abstract

Besides supplying calcium (Ca) and sulfur (S) to plants, gypsum has recently been used in agriculture to ameliorate some soil physical and chemical properties, especially to alleviate aluminum phytotoxicity in subsoils. When applied in large quantities, however, gypsum may leach significant amounts of nutrients from the plow layer. This study was conducted to assess the effect of gypsum addition to the soil on the magnitude of cation leaching as well as the relationship of leaching with some soil properties in a group of seven Brazilian soils. Rates of gypsum equivalents to 0, 5.0, 10, and 20 t ha^?1 (0, 2.5, 5.0, and 10 g kg^?1) were mixed with triplicate soil samples consisting of 3.0 kg of dry base soil. After 60 days of incubation at room temperature (15–25°C), the experimental units were packed into polyvinyl chloride leaching columns (32‐cm‐high×10 -cm-diameter) at a density of 0.9 g cm^?3. Thereafter, they were percolated once a week with a volume of distilled water equivalent to 1.5 times the total soil porosity over 11 weeks. Soil samples were collected before the first and after the last percolation, for chemical analysis. Averaged across soils, 11 percolation events leached about 26% of each Ca, magnesium (Mg), and potassium (K) from the treatment without gypsum. Averaged across soils and rates, addition of gypsum leached 41–94% of added Ca, 13–90% of exchangeable Mg, and 13–58% of exchangeable K, and the highest losses occurred on the sandiest soils. The relationship between soil parameters and Ca leaching varied with gypsum rate: in the treatments that received gypsum, leaching was negatively related to cation exchange capacity (CEC), clay, and organic matter, and positively correlated with sand; in the treatment with no gypsum, leaching correlated with the same parameters above, nevertheless, all coefficients presented opposite signs. Leaching of K caused by gypsum was negatively associated with clay and positively with sand, whereas leaching of Mg was poorly correlated with any soil parameter. Gypsum is a good source to promote high and fast downward movement of Ca in the soil profile, but rates must be cautiously chosen because of excessive leaching of Mg especially on soils with low CEC.     

Leaching and reclamation of calcareous saline‐sodic soil by moderately saline and moderate‐SAR water using gypsum and calcium chloride

Lysimeter experiments were conducted with sandy‐clay‐loam soil to study the efficiency of two amendments in reclaiming saline‐sodic soil using moderately saline and SAR (sodium‐adsorption ratio) irrigation water. Gypsum obtained from industrial phosphate by‐products and reagent grade Ca chloride were applied to packed soil columns and irrigated with moderately saline (ECe = 2.16 dS m^–1), moderate‐SAR water (SAR = 4.8). Gypsum was mixed with soil prior to irrigation at application rates of 5, 10, 15, 20, 25, and 32 Mg ha^–1, and Ca chloride was dissolved directly in leaching water at application rates of 4.25, 8.5, 12.75, 17.0, and 21.25 Mg ha^–1, respectively. The highest application rate in both amendments resulted in 96% reduction of total Na in soil. The hydraulic conductivity (HC) of soils receiving gypsum increased in all treatments. The highest HC value of 6.8 mm h^–1 was obtained in the highest application rate (32 Mg ha^–1), whereas the lowest value of 5.2 mm h^–1 was observed with the control treatment. Both amendments were efficient in reducing soil salinity and sodicity (exchangeable‐sodium percentage, ESP); however, Ca chloride was more effective than gypsum as a reclaiming material. Exchangeable Na and soluble salts were reduced with gypsum application by 82% and 96%, and by 86% and 93% with Ca chloride application, respectively. Exchangeable Ca increased with increasing amendment rate. Results of this study revealed that sodium was removed during cation‐exchange reactions mostly when the SAR of effluent water was at maximum with subsequent passage of 3 to 4 pore volumes. Gypsum efficiently reduced soil ESP, soil EC, leaching water, and costs, therefore, an application rate of 20 Mg ha^–1 of gypsum with 3 to 4 pore volumes of leaching water is recommended for reclaiming the studied soil.     

灌溉对哈萨克斯坦南部农业富镁土壤的影响

Irrational irrigation practices in the Arys Turkestan Canal command area in the southern part of Kazakhstan have led to the formation of soils with poor physical and chemical properties. To study whether irrigation and leaching practices and/or groundwater rise have contributed to the accumulation of Mg²⁺ on the cation exchange complex of these soils, historical changes in soil and groundwater quality were used as source data and the Visual MINTEQ model was applied to analyze the chemical composition of water and soils in the study area. The imposed irrigation regime and the leaching of light sierosem soils led to the dissolution and subsequent leaching of inherent gypsum and organic matter from the soil profile. Further, the domination of bicarbonate in the irrigation water promoted weathering of the carbonate minerals present as calcite. The higher concentrations of Mg²⁺ in comparison to Ca²⁺ in the irrigation water resulted in the replacement of Na⁺ by Mg²⁺ on the cation exchange complex. In the lower part of the command area, shallow groundwater has contributed to the accumulation of Na⁺ and to a large extent of Mg²⁺ on the cation exchange sites.     

脱硫石膏与灌溉耦合对滨海盐碱土化学性质的影响

脱硫石膏(CaSO4.2H2O)是火力发电厂石膏湿法烟气脱硫的副产物。对盐碱地施用脱硫石膏可以通过Ca2+置换盐土中的Na+,达到脱盐目的。通过盆栽试验研究天津滨海盐土施用脱硫石膏并配合灌溉淋洗改良盐碱土的效果。结果表明:对于表层土壤(0-10cm),施用脱硫石膏对Ca2+、Mg2+、K+、Na+、Cl-、SO24-离子含量有显著降低作用。10cm以下土壤,脱硫石膏的脱盐能力与施用量呈正相关。脱硫石膏与灌溉耦合时,脱硫石膏施用量为3 000kg/hm2以上时改良效果较好。随着脱硫石膏施用量的增加不但降低了土壤Na+含量与土壤pH值,对灌溉量的需求也有所降低。灌溉量为田间持水量的80%时脱硫石膏对土壤Ca2+、Mg2+与K+的降低作用与CK相比差异最显著。脱硫石膏施用量的增加提高了土壤全盐量,但随灌溉量增加这种影响逐渐降低。     

Effects of gypsum and Zn on uptake ratios of Na,K and growth-yield of rice grown on a coastal saline soil

Salinity reduced (reduction below control = RBC) grain yield of rice by 80 and 98% at 8 and 16 mS/cm levels of saline irrigation, respectively, below tap water (0.6 mS/cm). The adverse effect of salinity was more pronounced on grain yield (98% RBC at 16 mS/cm) than on straw yield (84% RBC). The combined application of gypsum and Zn at the rates of 160 and 5 kg/ha produced 49, 45, and 41% more grain yield above controls at 0.6, 8, and 16 mS/cm levels of salinity, respectively. The length of panicles, percentage of filled grains, and 1000-grain weight, protein concentrations of the rice grains, sum of Ca, Mg and K concentrations were reduced due to imposition of saline irrigation, but gypsum and Zn treatments significantly improved these parameters even at the highest (16 mS/cm) salinity stress. The combined application of gypsum and Zn was found to be effective to increase the protein concentrations in rice grains by 2–4% and to increase total concentrations of Ca, Mg and K, but reduced the Na/K ratios in plant tissues by 29.13, and 12% at 0.6, 8, and 16 mS/cm salinity, respectively, suggesting that the application of gypsum and Zn in parallel with irrigation of saline soils, would be effective to reduce the adverse effects of high Na/K ratios as well as to improve growth, yield, and nutritional balance in rice.     

中国东南部红壤施用石灰和石膏后底土酸性的减缓

Application of lime or gypsum is a common agricultural practice to ameliorate soils with low pH which prohibits crop production. Its integrated effect on soil properties in a red soil derived from Quaternary red clay in Southeast China is discussed in this paper. Application of gypsum in the topsoil without leaching raised soil pH and promoted the production of soil NH₄, but lime addition had a contrary effect. Generally, application of lime and/or gypsum has little effect on soil electrical properties. Gypsum had a little effect on soil exchange complex and its effect went down to 30 cm in depth. The effect of lime reached only to 5 cm below its application layer. With leaching, Ca transferred from top soil to subsoil and decreased exchangeable Al in subsoil. Gypsum application led to a sharp decrease in soil exchangeable Mg but had no effect on K.     

红壤交换性钙、镁和钾的分布及施肥对其影响

A leaching experiment was Carried out with repacked soil columns in laboratory to study the leaching process of a red soil derived from sandstone as affected by various fertilization practices.The treatments were CK(as a control),CaCO3,CaSO4,MgCO3,Ca(H2PO4)2,Urea,KCl,Multiple(a mixture of the above mentioned fertilizers) and KNO3,The fertilizers were added to the bare surface of the soil columns,and then the columns were leached with 120 mL deionized water daily through perstaltic pumps over a period of 92 days,At the end of leaching process,soils were sampled from different depths of the soil profiles ,i.o.,of 92 days,At the end of leaching process,soils were sampled from different depths of the soil profiles,I.e.0-5cm,5-10cm,10-20cm,20-40cm,and 40-60cm,The results showed when applying Ca,Mg,and K to the bare surface of the soil columns,exchangeable Ca^2 ,Mg^2 ,and K^ in the upper layer of the soil profile increased correspondingly,with an extent depending mainly on the application rates of Ca,Mg,and K and showing a downward trend,CaCO3,CaSO4,MgCO3,and Ca(H2PO4)2 treatments had scarcely and effect on movement of exchangeable K^ ,while CaCO3,and CaSO4 treatments singnificantly promoted the downward movement of exchangealble Mg^2 although these two treatments had no obvious effect on leaching losses of Mg,The fact that under Urea treatment,exchangeable Ca^2 and Mg^2 ,were higher as compared to CK treatment showed urea could prevent leaching of exchangeable Ca^2 and Mg^2 ,the obvious downward movement of exchangeable Ca^2 and Mg^2 was noticed in KCl treatment ,In Multiple treatment,the downward movement of exchangeable Ca^2 and Mg^2 was evident,while that of K^ was less evident,Application of KNO3 strongly promoted the downward movement of exchangeable Ca^2 and Mg^2 in the soil profile.     

Effects of consecutive applications of gypsum in equal,increasing, and decreasing quantities on soil hydraulic conductivity of a saline‐sodic soil

The objective of this study was to determine the effects of consecutive application of gypsum dissolved in leaching water on hydraulic conductivity of a saline‐sodic soil. Drainage type plastic columns with a 10 cm diameter were used in this laboratory experiment. Soil depth within columns was 30 cm with an average bulk density of 1.38 g cm^–3. Leaching water was applied in six equal portions. Total gypsum was applied at 1, 3, and 5 portions after dissolving in leaching water. In dissolution, equal (1.273 + 1.273 + 1.273 Mg ha^–1), increasing (0.637 + 1.273 + 1.910 Mg ha^–1) and decreasing (1.910 + 1.273 + 0.637 Mg ha^–1) quantities of gypsum were used. Results were compared with the control treatment, in which total amount of gypsum were mixed with surface layer of soil column before leaching. Hydraulic conductivity of soil increased in all treatments. The maximum hydraulic conductivity value was obtained at consecutive application of gypsum at decreasing quantities.     

Effect of leaching events on the fate of polyhalite nutrient minerals used for crop fertilization

Abstract

Polyhalite is a natural mineral containing potassium (K), calcium (Ca), magnesium (Mg) and sulfur (S) and is proposed as a fertilizer source for these essential nutrients. Application of polyhalite is expected to be most relevant in soils where the availability of these nutrients is low: in sandy soils, in highly leached soils, or in areas where crops are irrigated by water with low content of these nutrients or are rain-fed. A controlled lysimeter experiment investigated the efficacy of surface applied polyhalite as a fertilizer supplying K, Ca, Mg and S compared to soluble sulfate salts in two soils (sandy and loamy) with or without simulated rain leaching events through two cycles of cropping. In the first cycle, carrot response and nutrient uptake, transport, and loss through leaching were studied, while in the second cycle the residual effect of the fertilizer was considered on maize without additional fertilizer application or leaching. Polyhalite plus rain led to increased carrot yield due to augmented Ca uptake in sandy soil. In both soils, polyhalite behaved as a prolonged availability fertilizer with more nutrients retained in the top soil layer and not leached below the root zone. The treatments did not affect maize growth or nutrient uptake except for lower K and S uptake in soils where rain had been simulated for the previous crop. We conclude that polyhalite shows potential as a commercial fertilizer to supply K, Ca, Mg, and S nutrients under conditions of dryland agriculture where occasionally leaching by rainfall occurs.     

盐碱地咸水灌溉枸杞种植条件下土壤盐分变化

In order to utilize the wasted saline-sodic soils under shallow groundwater condition,a 3-year field study was carried in a field cropped with Lycium barbarum L.and irrigated by drip irrigation with saline groundwater under the water table depth of 30-40 cm in the northern Yinchuan Plain,China.Effects of cropping duration (one,two,and three years) on soil salinity,soil solution composition,and pH in three adjacent plots were investigated in 2008.Results showed that a high irrigation frequency maintained high soil water potential and subsequently facilitated infiltration and downward movement of water and salt in the crop root zone.Salt accumulated on the edges of the ridges,and soil saturated-paste electrical conductivity (ECe) was higher in the edge.Concentrations of Na+,Ca2+,Mg2+,Cl-,and SO42- in the soil increased with the soil depth as did the ECe,while HCO3- and pH had a relative uniform distribution in soil profile.As planting year increased,the ECe and soil salts in the field had a decreasing tendency,while in the root zone they decreased immediately after irrigation and then remained relatively stable in the following growing seasons.HCO3- and pH had little change with the planting year.Results suggested that the application of drip irrigation with saline water could ameliorate saline-sodic soil and provide a relatively feasible soil environment for the growth of salt-tolerant plant Lycium barbarum L.under the saline-sodic soils with shallow groundwater.     

我国东南部地区红壤表土养分的淋溶及再分布

The leaching and redistribution of nutrients in the surface layer of 4 types of red soils in Southeast China were studied with a lysimeter experiment under field conditions. Results showed that the leaching concentrated in the rainy season (from April to June). Generally, the leaching of soil nutrients from the surface layer of red soils was in the order of Ca > Mg > K > NO₃-N. In fertilization treatment, the total amount of soil nutrients leached out of the surface layer in a red soil derived from granite was the highest in all soils. The uptake by grass decreased the leaching of fertilizer ions in surface layer, particularly for NO₃-N. Soil total N and exchangeable K, Ca and Mg in the surface layer decreased with leaching and grass uptake during the 2 years without new fertilization of urea, Ca(H₂PO₄)₂, KCl, CaCO₃ and MgCO₃. Ca moved from the application layer (0~5 cm) of fertilizer and accumulated in the 10~30 cm depth in the soils studied except that derived from Quaternary red clay. The deficiency of soil exchangeable K will become a serious degradation process facing the Southeast China.     

微咸水膜下滴灌不同灌水下限对盐碱地土壤水盐运移及玉米产量的影响

为了研究盐碱地上微咸水膜下滴灌不同灌水下限对土壤水盐运移和玉米产量的影响,在长胜试验站开展了微咸水膜下滴灌玉米的大田试验。试验采用负压计指导灌溉,控制滴头下20cm深处的土壤基质势下限分别为-10,-20,-30,-40kPa,每个处理重复3次,按随机区组布置。结果表明:膜下滴灌湿润体形状在垂直于滴灌带的滴头所在竖直剖面上近似为半椭圆形,随着灌水下限的增大,湿润层土体含水率增大;玉米根部附近均出现盐分低值区,膜外表层均出现盐分高值区;-20kPa和-30kPa灌水下限适中,既能较充分淋洗膜内表层土壤盐分,又不会造成微咸水中的盐分滞留累积;在玉米生育期内,膜内、膜外地下100cm土体均积盐;-10kPa和-20kPa下限处理对应的湿润体垂直深度约为60cm;玉米收获后,地下100cm土体均积盐,需要进行秋浇或春汇,大量淋洗土壤盐分,保证耕地盐分不逐年累积;试验条件下,玉米产量随着灌水下限的降低而减少。     

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

ABSTRACT

The 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.