Effect of soil pH and N fertilization oh uptake and fractions of Ca and Mg in two barley cultivars

Abstract

A study has been made of the amounts of Ca and Mg removed from dry matter of young barley plants by sequential extraction with water, M NaCl, 0.4 M acetic acid and 0.6 M HCl. Two contrasting cultivars were examined and other factors included the effects of the soil pH in which the plants were grown and the form of N‐fertilizer used. The distribution of total Ca and Mg and the different fractions between young and old tissues was also examined.

Water and NaCl between them removed the bulk of the Ca and Mg (between 80 and 90%) and broadly, where uptake of total Ca or Mg increased with increase in soil pH, there was little change in the percentage of either cation appearing in the fractions, indicating a constant removal by the extractants, irrespective of content.

Only about a third of the total Ca was found in the upper half of the plants, against over 60% in the case of Mg and the same distribution was found for the percentages of the water‐soluble and the exchangeable fractions.

Small differences between cultivars and between N forms in respect of fractions and their distribution in the plant were found, but these did not affect the overall general pattern.     

Growth and composition of corn,alfalfa, and orchardgrass grown on soils contaminated with airborne dust containing Ca and Mg

Abstract

A greenhouse experiment was conducted with soils allegedly contaminated with airbourne dust containing Mg and Ca oxides and carbonates to study the growth and composition of corn, orchardgrass, and alfalfa plants. Soils were obtained from sites varying in distance from the alleged source of airbourne dust.

Soil pH values ranged from 6.2 to 8.7. Plant yields decreased only when the soil pH increased above 7.7. There was no apparent relationship between the observed yield decrease and the N, P, K, and B concentrations in the plants. Although the Mn and Zn concentrations generally decreased with increasing soil pH, the decrease was not great enough to account for the yield depressions. The obviously minor symptoms occurring on the plants growing on the most affected soils could not be associated with a deficiency or excess of any other element.

The Ca/Mg ratio in the alfalfa plants decreased as soil pH increased over the range from 6.2 to 8.7. However, the Ca/Mg ratios in the corn and orchardgrass plants decreased only when the soil pH values increased above 7.7. The apparent imbalance of Ca and Mg in the tissues may account for the yield depressions.     

Effects of Boron and Calcium Supply on Calcium Fractionation in Plants and Suspension Cells of Rape Cultivars with Different Boron Efficiency

Abstract

In this study, the effects of boron (B) and calcium (Ca) supply on Ca fractionation in suspension cells and different tissues of rape (Brassica napus L.) plants of two cultivars with different B efficiency were studied, with a purpose to elucidate the mechanism by which B affects Ca concentration in plants. As Ca supply increased in nutrient solution or culture medium, the relatively easily extractable Ca fractions, that is H₂O and 80% ethanol extractable Ca in leaves, 1 mol L^?1 NaCl extractable Ca in upper leaves, roots and suspension‐cell were significantly increased. While the recalcitrant Ca fractions extracted by 2% acetic acid, 0.6 mol L^?1 HCl and Ca in the residue were not affected by Ca supply. Increasing B supply in nutrient solution or culture media significantly reduced 1 mol L^?1NaCl extracted Ca in suspension cell and roots of both cultivars, which were most likely related to the alteration of cell wall metabolism. Calcium extracted by 2% acetic acid, 0.6 mol L^?1 HCl and Ca in residue in suspension‐cell and roots of B inefficient cultivar Bakow were easily improved by B deficiency as compared to that of B efficient cultivar Tezao16. Increasing of these relative recalcitrant Ca fractions was related to the different response of cultivars to the B deficiency, which may reflected different extent that Ca deposited in the two cultivars due to impaired membrane integrity under B deficiency. The effects of B on Ca concentration in lower and upper leaves of the two cultivars were quite different and were the integrated effects of B on Ca metabolism, Ca transport in plants and growth of certain organ. Increasing B supply increased total Ca concentration in upper leaves of Bakow and reduced that of Tezao16, which might relate to the different adaptability of the two cultivars to comparatively higher B supply.     

Soil and plant calibration for cucumbers grown in the mid‐Atlantic coastal plain

Abstract

Few soil test and plant tissue calibration data exist for cucumbers (Cucumis sativus L.). Two years of a singly‐replicated cucumber fertility study were conducted to develop soil and plant data for calibration purposes employing the Boundary Line Approach. Fertility treatments consisting of 4 K levels (as KC1), 3 Mg levels (as MgCl₂), 3 pH levels (as Calcitic limestone), and 4 N rates (as urea ammonium nitrate) were factorilly arranged and completely randomized to give 108 treatments in both 1987 and 1988. Analyses were performed upon leaf samples for N, P, K, Ca and Mg at early bloom and soil samples for Mehlich (M) 1‐ and 3‐ P, K, Ca and Mg, and pH. Cucumber yields were determined on early (two fruit pickings) and total (four fruit pickings) sampling periods. High‐yielding cucumbers were attained at soil K (Ml = 64 mg/kg) and Mg (Ml = 29 mg/kg) levels lower than currently recommended. No significant differences in correlation coefficients between either Mehlich (Ml, M3) extractant and cucumber leaf P, K, Ca and Mg concentrations were found. Co‐efficients of determination (R²) values for the relationships (in 1987, 1988) between Ml‐ and M3‐extractable P (0.53, 0.40), K (0.77, 0.64), Ca (0.81, 0.71) and Mg (0.89, 0.74) were all highly significant (P ≤ 0.01). No significant differences were noted between early and total high‐yielding cucumber leaf concentrations and ratios developed for use as preliminary sufficiency ranges and DRIS norms, respectively. A reevaluation of cucumber coastal plain soil test calibrations, especially with regard to K, appears necessary. This study provides further support for the conversion of Ml to M3 soil extraction methodology.     

Comparison of mehlich 1 and mehlich 3 extractants for P,K, Ca,Mg, Mn,Cu and Zn in atlantic coastal plain soils

Abstract

The Mehlich 3 (M3) extractant was introduced in 1981 to improve the efficiency of soil testing laboratories by eliminating the need for multiple extractants for P, K, Ca, Mg, Mn, Cu and Zn. The M3 was also intended to be suitable for a wide range of soils, perhaps to serve as a “universal”; soil test extractant. At present, regional soil testing committees throughout the U.S. are investigating the M3 in this regard.

Development of a field calibration data base for a new soil testing extractant is an essential, but expensive and time‐consuming process. An interim measure is the use of conversion equations between new and current extractant(s). These equations allow for use of the new extractant with existing field calibration data. The objectives of this study were (i) to develop conversion equations for the Mehlich 1 (M1) and M3 extractants for Atlantic Coastal Plain soils, and (ii) to determine the influence of soil pH and organic matter content on the relative extractability of P, K, Ca, Mg, Mn and Zn by Ml and M3.

Four hundred soil samples, obtained from field plots and commercial crop samples submitted to the University of Delaware Soil Testing Laboratory were analyzed for P, K, Ca, Mg, Mn, Cu and Zn by M1 and M3. Highly significant correlations between M3 and M1 were found for all nutrients (r=0.92*** to 0.97***) and, except for Cu and Mn, soil pH and OM did not markedly improve the linear regression equations developed for conversion between M3 and M1. Inclusion of OM in a multiple regression equation between M3 and M1 extractable Cu increased R² from 0.46** to 0.71***; R² for Mn+(pH+OM) was 0.48***, relative to 0.35*** for extractable Mn alone. Critical values for M3 P, K, Ca, and Mg, based on conversion equations restricted to soils testing less than high with the M1 extractant, were 41, 49, 295 and 45 mg.dm^‐3, respectively. For Mn and Zn, at a pH of 6.2, M3 critical values were 9.5 and 0.6 mg.dm^‐3, while for Cu, the M3 critical value ranged from 0.5 to 1.1 mgdm^‐3 for soil OM of 2 to 8%.     

Adsorption‐desorption of zinc in mollisols and their relationship with uptake of fertilizer‐applied zinc by rice

Abstract

Zinc (Zn) adsorption in mollisols conformed to the linear form of Freundlich equation. The log K values were positively correlated with silt, clay, and carbonate contents and soil pH, but negatively correlated with sand content. Sequential desorption of adsorbed Zn in 0.05M Ca(NO₃)₂, 0.1M Mg(NO₃)₂, 0.005M DTPA, and 0.1M HCl revealed that weakly and specifically bound fractions of added Zn, which could easily equilibrate with soil solution, were low and decreased with silt and carbonate contents and soil pH. Weakly bound fraction increased with sand content. Strongly bound and complexed fraction of applied Zn was the maximum and increased with clay, soil organic carbon and carbonate contents and specific surface area, but decreased with sand content. The mineral bound fraction of applied Zn was intermediate and increased with silt, clay and carbonate contents, and soil pH and specific surface area. Zinc uptake due to added Zn fertilizer by rice crop (Y) negatively correlated with log K, but positively related to Zn content in the equilibrium soil extract and Zn desorbed in 0.05M Ca(NO₃)₂. Both log K and l/n values together explained 59.5% of the total variation in Y, while Zn content in the equilibrium soil extract, Zn desorbed in 0.05M Ca(NO₃)₂, 0.005M DTPA and 0.1M HCl collectively accounted 79.6% of the total variation in Y.     

Effect of manganese on concentrations of Zn,K, Ca and Mg in two bush bean cultivars grown in solution culture

Two bush bean cultivars [Phaseolus vulgaris L. cv. ‘Wonder Crop 2’ (WC‐2) and ‘Green Lord’ (GL)], differing in Mn toxicity, were grown in a growth chamber for 12 days in Hoagland No. 2 nutrient solution containing 0.05 to 1 ppm Mn as MnCl₂4H₂O with 1 ppm Fe as Fe‐EDTA, at an initial pH 5.00. Concentrations of Zn, K, Ca and Mg in the tissues of two bush bean cultivars were examined in relation to Mn toxicity.

The concentration of Zn in the leaves of Mn‐sensitive WC‐2 increased significantly with increasing Mn concentration in the solution, but such levels were not toxic to the plants.

The percent distribution of Zn and K in Mn‐sensitive WC‐2 plants (% of total uptake) significantly increased in the tops and decreased in the roots with increasing Mn concentration in the nutrient solution; however, Mn treatment had no effect on distribution of either Ca or Mg in WC‐2. External Mn concentration had little or no effect on the K, Ca, or Mg concentration in the tops of Mn‐tolerant GL.     

Maize growth and mineral acquisition on acid soil amended with flue gas desulfurization by‐products and magnesium

Abstract

The large amounts of coal combustion by‐products (CCBs) generated by coal burning power plants must be utilized or discarded, and beneficial use of these materials are desired. One beneficial use of CCBs could be application to agricultural land. Information about the use of one kind of CCB (flue gas desulfurization by‐product, FGD‐BP) on soil is limited. Maize (Zea mays L.) was grown (greenhouse) on an acid soil [Umbric Dystrochrept, pH_Ca (1:1, soil: 10 mM CaCl₂) 4.2] amended with two high CaSO₄ FGD‐BPs (5 and 15 g#lbkg^‐1 soil) and CaCQ₃ (2.5 and 5.0 g#lbkg^‐1 soil) at varied calcium/magnesium (Ca/Mg) equivalency ratios (0/0, 1/0, 1/0.01, 1/0.05, 1/0.1, and 1/0.5) to determine treatment effects on growth traits [shoot and root dry matter (DM) and total and specific root length (RL)], mineral concentrations in leaves, and soil pH and electrical conductivity [(EC) 1:1, soil:water]. Magnesium deficiency symptoms were induced on leaves of plants grown with and without low Mg, and the Mg to Ca ratio in each amendment needed to be about 1 to 20 to alleviate Mg deficiency. Shoot and root DM and total RL of plants grown with FGD‐BPs became higher as Mg increased. Specific RL (total RL/root DM, root fineness) was not affected by FGD‐BP and only slightly by Ca/Mg ratio. Shoot concentrations of Mg increased; Ca, phosphorus (P), and manganese (Mn) decreased; and potassium (K), sulfur (S), iron (Fe), zinc (Zn), and copper (Cu) remained relatively constant as amendment and Mg increased. On unamended soil, aluminum (A1) and Mn concentrations in shoots were above normal. Enhancement of growth was closely related to increased soil pH compared to added Mg for CaCO₃ amended soil and to increased Mg compared to increased soil pH for FGD‐BP amended soil. Except at the highest level of Mg where soil pH increased, added FGD‐BPs and Mg had only limited effect on increasing soil pH. Soil EC increased from added FGD‐BPs but not from added Mg, and EC was not sufficiently high to be detrimental to plants. Maize grown on this acid soil amended with FGD‐BPs received benefits when caution was used to alleviate mineral deficiencies/toxicities inherent in the soil.     

Spatial variability of plant analysis calcium and magnesium levels before and after liming

Abstract

Plant samples were taken in an 82.5 ft grid at an early and late sampling date in both 1991 and 1992 from a forty acre field in Illinois. Calcium (Ca) and magnesium (Mg) were analyzed on each sample and maps were made showing the levels of each nutrient within the field. Soil pH measurements were also made from each of the same sampling locations following each year of plant sampling. In the fall of 1991, a calcitic lime application was made using soil pH informations from the 1991 soil sampling to determine the boundaries and rate of the application. Calcium and Mg levels in 1991 roughly defined the area of low pH, except for the early sampled Mg levels. However, low Ca and Mg levels did not always indicate low pH levels. High Ca and Mg levels did not always indicate high pH levels. Following liming, plant Ca levels correlated better with soil pH and represented areas of high and low pH better than plant Mg. Other factors which influenced Ca and Mg levels may have been high levels of competitive cations, disease injured plants, and subsoil pH not described by surface pH measurement.     

Grass species and cultivar differences in magnesium concentration

Abstract

Two rates of Mg, 0 and 56 kg/ha, were randomized within each of 43 cultivars that had previously been established in a randomized complete block design. The 43 cultivars consisted of 6 species. Forage samples were obtained in early spring and chemically analyzed for content of Ca, Mg and K.

Grass species and cultivars with species significantly differed in content of Ca, Mg and K and in the ratio meq K/(meq Ca + meq Mg). Significant interactions of Mg with species and Mg with cultivars within species were observed. At the relatively low level of soil Mg and Mg rate, no cultivar contained 0.20% Mg, a value often used to identify proneness to grass tetany. However, no cultivar had an average meq ratio, K/(Ca + Mg), greater than 2.2, a value often used in diagnosing potential tetany problems that might be associated with intake of low Mg forage.

The interaction of cultivar with Mg rate indicates that fertilizer Mg level influenced cultivar content of Mg, and that the effect was not consistent for all cultivars.     

Response of two sorghum genotypes to soil lime and sodium chloride amendments

Abstract

Salinity affects plants by interaction between sodium (Na) and calcium (Ca). Two sorghum (Sorghum bicolor) genotypes ('Hegari’ and ‘NB‐9040') were studied for the Na x Ca interaction in a soil amended with 2% calcium carbonate (CaCO₃) and with 0, 12.3, 24.6, and 36.9 mmol sodium chloride (NaCl)/kg soil. The two genotypes were similar in their response to soil NaCl in their shoot and root growth but differed in response to lime. The salinity‐tolerant Hegari was suppressed by high Ca concentration in the soil, mainly in the low‐NaCl treatments, and responded by a lower concentration of potassium (K) and magnesium (Mg) in the leaves, which was associated with leaf‐chlorosis. Since Na uptake was reduced by Ca, the main effect of salinity on plant growth was by the accumulation of chloride (Cl) in the leaves.     

Comparison of mehlich 3, mehlich 1, ammonium bicarbonate‐DTPA, 1.0M ammonium acetate,and 0.2M ammonium chloride for extraction of calcium,magnesium, phosphorus,and potassium for a wide range of soils

Abstract

Extractants employed for routine soil analysis vary from one laboratory to another. Lack of a universal soil extractant is a serious limitation for interpretation of analytical results from various laboratories on nutritional status of a given soil. This limitation can be overcome by developing functional relationships for concentrations of a given nutrient extractable by various extradants. In this study, extractability of Ca, Mg, P, and K in a wide range of soils (0–15 cm) from citrus groves in Florida representing 21 soil series, with varying cultural operations, were compared using Mehlich 3 (M3), Mehlich 1 (M1), ammonium acetate (NH₄AOc), pH = 7.0 (AA), 0.2M ammonium chloride (NH₄Cl), and ammonium bicarbonate‐DTPA (AB‐DTPA) extractants. Soil pH (0.01M CaCl₂) varied from 3.57 to 7.28. The concentrations of Ca or Mg extractable by M3, M1, AA, and NH₄Cl were strongly correlated with soil pH (r² = 0.381–0.482). Weak but significant correlations were also found between AB‐DTPA extractable Ca or Mg and soil pH (r² = 0.235–0.278). Soil pH relationships with extractable K were rather weak (r² = < 0.131) for M1 and NH₄Cl but non‐significant for M3, AB‐DTPA, and AA. Concentrations of Ca, Mg, and K extractable by M3 were significantly correlated with those by either M1, AA, or NH₄Cl extractants. Mehlich 3‐P was significantly correlated with P extractable by M1 extractant only. Mehlich 3 versus AB‐DTPA relationship was strong for K (r² = 0.964), weaker for Mg and P (r² = 0.180–0.319), and non‐significant for Ca. With the increasing emphasis on possible use of M3 as an universal soil extractant, data from this study support the hypothesis that M3 can be adapted as a suitable extractant for routine soil analysis.     

Effects of Sodium Chloride-Induced Salinity on Mineral Nutrients and Soluble Sugars in Three Commercial Cultivars of Pomegranate

Abstract

The effect of sodium chloride (NaCl)-induced salinity on concentration and translocation of ions and soluble sugars in three commercial cultivars, ‘Alak Torsh,’ ‘Malas Torsh,’ ‘Malas Shirin,’ of pomegranate (Punica granatum L.) was studied. After rooting of cuttings, they were planted in the plastic pots contained sand:perlite (1:1) medium and irrigated with complete Hoagland^’s solution immediately. After three weeks, plants were treated with different concentration (0, 40, 80, and 120 mM) of NaCl solution. These treatments continued during 80 days with irrigation water. Finally, uptake and transport of ions [Na, potassium (K), calcium (Ca), magnesium (Mg), nitrogen (N), and Cl) and soluble sugars in these three cultivars were measured. With increasing NaCl concentration in irrigation water, the amount of Na, Cl, and K of the tissues increased, but amount of Ca, Mg, and N of the tissues decreased. No cultivar differences were observed in the rate of uptake of tested minerals. Soluble sugars decreased as NaCl concentrations in irrigation water increased.     

Effects of low aluminium levels on growth and nutrient relations in three rice cultivars with different tolerances to aluminium

Reports on varietal diversity of upland rice in relation to relatively low aluminium (Al) levels are limited. Therefore, effects were examined of 35, 70, and 140 μM Al on plant growth and uptake of macro‐ and micro‐nutrients (K, P, Ca, Mg, Fe, Zn, Cu, and Mn) and their distribution in three upland rice (Oryza saliva L.) cultivars (BG35, DA14, and IR45) with different Al sensitivity. After an initial growth period of 5 days without Al, the plants were grown for 21 days in nutrient solutions containing Al at pH 4.1. Cultivar BG35 showed the highest and IR45 the lowest tolerance to Al when fresh weights of shoots or roots were considered. Except for IR45 at 140 μM Al, total dry weight was unaffected by Al, and the cultivars could not be clearly distinguished with respect to Al tolerance. Net Al uptake rate was higher in Al tolerant BG35 than in DA14 or IR45. Conversely, in IR45 the absorbed Al was rapidly transported to the shoots and accumulated there. In BG35, net P and Ca uptake rates in Al‐treated plants were high enough to maintain the P and Ca status of the shoots at all Al levels. Irrespective of Al sensitivity, there was a general depression of internal Mg concentration in Al‐reated plants. The Fe, Zn, Cu, and Mn concentrations of the plants were not negatively affected by Al in any of the cultivars.     

A simple rapid method for the measurement of exchangeable cations and effective cation exchange capacity

Abstract

A simple single‐extraction procedure for measuring exchangeable cations and effective CEC (ECEC, the CEC at natural pH and ionic strength) has been developed for routine advisory soil analysis. The method is based on the use of Sr (1.26M SrCl₂) to displace exchangeable cations and effective CEC is taken as the sum of the exchangeable cations. A ten minute shaking time at 5 g:80 ml, soil solution ratio, was found to be optimum. Good agreement was found between the proposed method and the standard neutral IN ammonium acetate leaching procedure with correlation coefficients (r) for the individual cations Mg, Ca, Na and K of 0.99***, 0.99***, 0.83*** and 0.96*** respectively. Strontium chloride extracted more Al but less Mn (P<0.01) than IN KC1, but because of the low levels of these cations in relation to the total cations present, there was still a good relationship (r= 0.99) between ECEC determined by 1.26M SrCl₂ and that determined as the sum of ammonium acetate extractable Mg, Ca, Na and K plus IN KCl‐extracted Al and Mn.     

Manganese toxicity in tomato plants: Effects on cation uptake and distribution

Two experiments are described in which tomato plants (Lycopersicon esculentum L. var Ailsa Craig) were grown in water culture supplied with 10–300 μM Mn. Toxicity symptoms associated with a yield reduction were observed only in treatments in excess of 50 μM Mn indicating that this species is relatively tolerant of high Mn supply. Dark brown/black spots appeared first in the cotyledons. Similar symptoms were observed in the leaves, progressively from the oldest leaf. Manganese concentration in the shoot tissues ranged from 286 to 4240 μg. g^‐1 dry weight. The high Mn concentration values found in the shoot tissues of the toxic plants indicate that Mn was highly mobile in the xylem as confirmed by xylem sap analysis.

The concentrations of both Ca and Mg were lower in the smaller Mn toxic plants. Not only was uptake of Ca and Mg retarded but so also was the distribution of Ca and Mg to the younger tissues as illustrated by measurements of Ca and Mg concentrations along a leaf age sequence. This is in accord with the cation‐anion balance of the xylem exudates collected from decapitated plants.

Higher cation exchange capacity (CEC) was found in the leaf tissues of toxic plants particularly in the older leaves but similar values of C.E.C were recorded for the younger leaf tissues of both control and toxic plants.     

Leaf mineral element concentrations and growth of sweet sorghum subjected to acid soil stress

Abstract

The nutritional profile of sweet sorghum [Sorghum bicolor (L.) Moench] cultivars grown under acid soil field stress conditions is a critical consideration when developing plants which are adapted to these infertile soils. Uptake and accumulation of macro‐ and micronutrients vary among genotypes and ultimately Influence plant growth and development. This study compared fourteen sweet sorghum germplasm lines and varieties for their Individual patterns of leaf nutrient concentrations and productivity when grown under acid soil field conditions (pH 4.45 to pH 4.85) at three locations over a two‐year period. Significant year x location interactions were found for Fe, K, and Ca concentrations at both Blairsville and Calhoun and for Mn and P levels at Blairsville and Calhoun, respectively. Data from Calhoun on plant height, dry weight, visual stress ratings, and rainfall indicate a possible association between drought tolerance and acid soil tolerance in sorghum. No significant differences in A1 concentrations were found among these sweet sorghum lines and varieties, which indicate that their acid soil tolerance mechanisms are probably not related to A1. MN 1054 accumulated the highest levels of Mn in the three acid soils. The highest concentrations of Mg and P were found in Brandes. MN 960 had the highest visual stress ratings (highest susceptibility) while Brandes, Ramada, Roma, and Wray were the most tolerant. All fourteen cultivars apparently have some tolerance to acid soil stress conditions.     

Soil pH,extractable aluminum and tree growth on acid minesoils

Abstract

Paper birch and hybrid poplar were grown in acid minesoils amended with different rates and types of lime. Growth of the trees was correlated with soil pH, Ca, Mg, K, P and three measures of extractable Al ‐ 1 N KCl, 0.01 M CaCl₂ and H₂O extractable Al. Correlations between soil pH and extractable Al and between the three measures of extractable Al were also determined. Soil pH accounted for the largest share of the total variation in root and shoot growth of both species over all soils. Correlations between tree growth and extractable Al for all soils combined were low and generally non‐significant. Significant correlations were obtained between soil pH and extractable Al and between the three measures of extractable Al, however, the relationships varied among soils.     

Effect of External Nitrogen and Potassium Supply on Xylem Sap Composition of Sugarcane

ABSTRACT

This study was conducted to evaluate the effect of nitrogen (N) and potassium (K) availability on root exudate composition of two sugarcane cultivars known to differ with regard to their resistance to drought and salinity stress. The plants were hydroponically grown in a greenhouse and subjected to three levels of N (0.1, 1.0, and 10 mM N) and three levels of K (0.02, 0.2, and 2 mM K). Nitrogen and K stress altered the xylem sap composition. Nitrogen stress significantly reduced nitrate (NO₃ ^?), ammonium (NH₄ ⁺), calcium (Ca), magnesium (Mg), and amino acid content and increased the pH, phosphorus (P), and K content. Whereas, K stress significantly decreased pH, K, NH₄ ⁺, and amino acid content but increased Ca, Mg, and P content. Nitrogen and K stress had opposing effects on xylem sap pH and osmolality. Results indicated that sugarcane plants recycle compounds between the phloem and xylem. The results also suggested that the NO₃ ^? and K concentration of xylem sap could be effectively used to estimate the N and K status of the soil solution.     

Use of exchangeable and nonexchangeable forms of calcium,magnesium, and potassium in soils without fertilization after successive cultivations with Pinus taeda in southern Brazil

Purpose

The aim of this study was to quantify the contents and stocks of exchangeable and nonexchangeable fractions of potassium (K), calcium (Ca), and magnesium (Mg) after one and three successive Pinus taeda crops without fertilization and to predict the soil supply for further cultivations.

Materials and methods

The soil was analyzed in layers up to 80 cm in two Pinus forests, one at the end of the first cultivation and other at the end of the third successive crop, in a subtropical region in southern Brazil. Stocks of exchangeable and semi-total fractions of K, Ca, and Mg in the soil were calculated, and the potential number of crop rotations of Pinus without fertilization was estimated.

Results and discussion

After three Pinus crops, there was an average reduction of 46.9, 90.8, and 45.5% of exchangeable K, Ca, and Mg fractions respectively. Semi-total Ca content reduced in all depths, and semi-total K contents, in turn, only decreased until 20 cm of depth. The semi-total Mg contents have not been modified over the cultivations. Considering crop management with the export of plant twigs and needles and relying just on the availability of exchangeable Ca, the stocks of these nutrients in the soil would be sufficient for only one more Pinus cultivation, even when considering the absorption of nutrients on an 80-cm soil depth profile.

Conclusions

The management adopted in the region must be modified, replacing the nutrients exported via harvesting, especially Ca. Thus, the establishment of new cultivation of Pinus without fertilization may have its yield impaired, especially by the Ca availability.