Wheat response to combined application of nitrogen and phosphorus in a saline sandy loam soil

Fertilization with nitrogen (N) or phosphorus (P) can improve plant growth in saline soils. This study was undertaken to determine wheat (Triticum aestivum L; cv Krichauff) response to the combined application of N and P fertilizers in the sandy loam under saline conditions. Salinity was induced using sodium (Na⁺) and calcium (Ca²⁺) salts to achieve four levels of electrical conductivity in the extract of the saturated soil paste (EC_e), 2.2, 6.7, 9.2 and 11.8?dS?m^?1, while maintaining a low sodium adsorption ratio (SAR; ≤1). Nitrogen was applied as Ca(NO₃)₂?·?4H₂O at 50 (N50), 100 (N100) and 200 (N200)?mg?N?kg^?1 soil. Phosphorus was applied at 0 (P0), 30 (P30) and 60 (P60)?mg?kg^?1?soil in the form of KH₂PO₄. Results showed that increasing soil salinity had no effect on shoot N or P concentrations, but increased shoot Na⁺ and chlorine ion (Cl^?) concentrations and reduced dry weights of shoot and root in all treatments of N and P. At each salinity and P level, increasing application of N reduced dry weight of shoot. At each salinity and N level P fertilization increased dry weights of shoot and root and shoot P concentration. Addition of greater than N50 contributed to the soil salinity limiting plant growth, but increasing P addition up to 60?mg?P?kg^?1 soil reduced Cl^? absorption and enhanced the plant salt tolerance and thus plant growth. The positive effect of the combined addition of N and P on wheat growth in the saline sandy loam is noticeable, but only to a certain level of soil salinity beyond which salinity effect is dominant.     

Effects of Silicon Application on Wheat Growth and Some Physiological Characteristics under Different Levels and Sources of Salinity

We investigated the effects of silicon (Si) and the levels and sources of salinity on the growth and some physiological properties of wheat (Triticum aestivum cv. Chamran) in a sandy loam soil under greenhouse conditions. Treatments comprised four Si levels (8, 50, 100 and 150 mg kg^?1 soil), four salinity levels (0.46, 4, 8 and 12 dS m^?1) and two salinity sources (sodium chloride (NaCl) and four-salt combination). Salts combination included NaCl, sodium sulfate (Na₂SO₄), calcium chloride (CaCl₂) and magnesium sulfate (MgSO₄) at a molar ratio of 4:2:2:1. The experiment was arranged as a completely randomized design in a factorial manner, with three replications. Increasing salinity level resulted in a significant decrease in shoot dry weight, chlorophyll content and catalase (CAT) activity, and it caused a marked increase in proline and glycine betaine (GB) concentrations and superoxide dismutase (SOD) enzyme activity. The stimulating effect on GB accumulation and SOD activity was more intense in NaCl-treated plants. However, the source of salinity had no significant effect on shoot dry weight, chlorophyll and proline concentrations, and CAT activity. Si application enhanced all the above-mentioned parameters, except for proline. The suppressing effect of salinity on shoot dry weight, chlorophyll concentration and CAT activity was alleviated by Si supplementation. The stimulating effects of Si fertilization on shoot dry weight and chlorophyll concentration became more pronounced at higher salinity levels. It could be concluded that a decrease in soil osmotic potential, nutrient imbalance and increasing reactive oxygen species (ROS) in salt-treated plants caused growth suppression, while Si supply decreased the deleterious effects of excess salt on wheat growth. Consequently, it appears that when wheat plants are to be grown in salt-affected soils, it is highly recommended to supply them with adequate available silicon (Si).     

Measurement of pH at the root surface of red clover (Trifolium pratense) grown in soils differing in proton buffer capacity

Summary Measurements of pH were made at the root surface of Trifolium pratense, using Sb electrodes. Nodulated plants were grown in rhizotrones on a sandy soil free of carbonate and on a clay soil rich in carbonate. In the sandy soil, pH at the surface of root laterals was about 1 unit lower than in the bulk soil. The lowest pH values were found at the root tips. In the calcareous soil, pH measured at the root surface did not differ from pH in the bulk soil. This soil had a much higher H⁺ buffer capacity than the sandy soils. It seems likely that H⁺ ions excreted from the roots grown in the calcareous soil were directly neutralized by soil carbonate.     

Effects of water and organic manure coupling on the immobilization of cadmium by sepiolite

Purpose

Natural sepiolite (SP) has proven effective on the in-situ immobilization remediation of Cd-contaminated soils. But the practical remediation effect may largely influenced by water management and the application of organic manure. The effects of chicken manure (CM) on SP-amended soils were investigated under normal and saturated water conditions using a pot experiment with Brassica campestris L.

Materials and methods

Cd-contaminated paddy soils were amended with CM, SP, and CM?+?SP with no amendment as control. The amount of sepiolite was 0.5% (w/w, the same below) either in SP or CM?+?SP amended soils, while the amount of CM was 0.5, 1.0, and 2.0% in CM and CM?+?SP-amended soils. The plant metal contents, fresh weight, and soluble sugar content of plant edible parts were measured on harvest. Soil Cd was extracted by diethylenetriaminepentaacetic acid (DTPA) and HCl to estimate the mobility of heavy metal. Soil pH and dissolved organic matter (DOM) of rhizosphere soil were determined. The electronegative charges of soils were also measured using the zeta potential.

Results and discussion

The application of CM and increasing soil moisture on SP-amended soil increased plant growth to a greater extent than the application of SP alone. The application of CM along with the increase of soil moisture decreased Cd uptake and translocation in plants grown on SP-amended soil compared to the application of SP alone. Cd content of edible plant parts reached a minimum of 0.24 mg kg^?1 with the application of 2.0% CM on SP-amended soils under water-saturated conditions, which was approximately 50% lower than the Cd concentration found when applying SP alone.

Conclusions

The results of this study suggest that the application of sepiolite on Cd contaminated soil can effectively reduce Cd uptake by B. campestris L., and the addition of CM combined with effective water management also appears to further reduce Cd absorption and accumulation.

     

Effect of Induced Soil Compaction on Changes in Soil Properties and Wheat Productivity under Sandy Loam and Sandy Clay Loam Soils: A Greenhouse Experiment

The continuous use of heavy machinery and vehicular traffic on agricultural land led to an increase in soil compaction, which reduces crop yield and deteriorates the physical conditions of the soil. A pot experiment was conducted under greenhouse conditions to study the effects of induced soil compaction on growth and yield of two wheat (Triticum aestivum) varieties grown under two different soil textures, sandy loam and sandy clay loam. Three compaction levels [C₀, C₁, and C₂ (0, 10 and 20 beatings)], two textural classes (sandy loam and sandy clay loam), and two genotypes of wheat were selected for the experiment. Results indicated that induced soil compaction adversely affected the bulk density (BD) and total porosity of soil in both sandy loam and sandy clay loam soils. Compaction progressively increased soil BD from 1.19 Mg m^?3 in the control to 1.27 Mg m^?3 in C₁ and 1.40 Mg m^?3 in C₂ in sandy loam soil while the corresponding increase in BD in sandy clay loam was 1.56 Mg m^?3 in C₁ and 1.73 Mg m^?3 in C₂ compared to 1.24 Mg m^?3 in the control. On the other hand, compaction tended to decrease total porosity of soil. In case of sandy loam, porosity declined by 5% and 17% in C₁ and C₂, respectively, and declined in sandy clay loam by 29% and 54%, respectively. Averaged over genotypes and textures, shoot length decreased by 15% and 26% at C₁ and C₂, respectively, and straw yield decreased by 21% and 61%, respectively. The compaction levels C₁ and C₂ significantly decreased grain yield by 12% and 41%, respectively, over the control. The deleterious effect of compaction was more pronounced on root elongation and root mass, and compaction levels C₁ and C₂ decreased root length by 47% and 95% and root mass by 41% and 114%, respectively, over the control. Response of soil texture to compaction was significant for almost all the parameters, and the detrimental effects of soil compaction were greater in sandy clay loam compared to sandy loam soil. The results from the experiment revealed that soil compaction adversely affected soil physical conditions, thereby restricting the root growth, which in turn may affect the whole plant growth and grain yield. Therefore, appropriate measures to avoid damaging effects of compaction on soil physical conditions should be practiced. These measures may include soil management by periodic chiseling, controlled traffic, conservation tillage, addition of organic manures, and incorporating crops with deep tap root systems in a rotation cycle.     

Effect of cobalt treatments on dry matter production of wheat and DTPA extractable cobalt content in soils

Abstract

The effect of different concentrations of cobalt added to two soil types, a sandy and a sandy loam soil, was studied on growth performance and tissue cobalt concentration of wheat plants. DTPA‐extractable cobalt was significantly higher in the sandy soil than in the sandy loam soil. Plants grown in the sandy soil accumulated significantly higher amount of cobalt in comparison to plants grown in the sandy loam soil. Roots were significantly richer in cobalt than shoots in both the soil types. Lower (1 μg g^‐1) administration of cobalt resulted in an enhancement in the growth whereas higher (5–625 μg g^‐1) addition inhibited growth. A significant inverse relationship between relative wheat yield and tissue cobalt concentration was observed. The results indicate a possible requirement of cobalt for higher plants.     

Sulfuric acid effects on iron and phosphorus availability in two calcareous soils

An attempt was made to study the effects of sulfuric acid additions to iron (Fe)‐ and phosphorus (P)‐deficient calcareous soils. Several greenhouse experiments were conducted with sorghum (Sorghum bicolor L.) grown in two calcareous soils. Addition of sulfuric acid to soils increased soil acidity, salinity, DTPA‐extractable Fe, available P (NaHCO₃‐extractable), and crop yield. The change in soil pH is the primary cause of increased nutrient availability and thus crop yield. Leaching after acid application is highly beneficial in decreasing salinity during germination and seedling stages and therefore has a direct impact on the yield. The beneficial effects of acid carried over for at least two greenhouse cropping seasons (approximately 4.5 months).     

Interactive effects of salinity and two phosphorus fertilizers on growth and grain yield of Cicer arietinum L.

Chickpea is considered among the most sensitive grain legumes to salinity. The improvement of tolerance of lines in combination with tolerant rhizobial strains depends on various environmental and cultural conditions such as soil properties. This investigation was undertaken to evaluate the effect of phosphorus fertilization (0, 90 and 200 kg ha^?1 of P₂O₅) on biomass, nodular traits and grain yield (GY) of chickpea (cv. Flip 84-79C) growing under salinity (0 and 150 mM NaCl). The trial was laid out following a randomized block design with three replicates during 2010–2012, at the experimental farm of Oued Smar (Algiers). Salinity did not significantly decrease the dry biomass of the plants but the relative shoot growth was more affected than control, P and SP1 treatments. Besides, salinity significantly reduced GY (?20%) and nodulation traits compared to the control plants while an inversely proportional relationship was found between protein, leghemoglobin and MDA content, K/Na ratio and the increase in salt concentration. Application of two P levels to saline soil enhanced growing conditions of plants. Particularly, the (90?kg?ha^–1 of P ×?150?mM?NaCl) combination significantly increased leghemoglobin (92%), reduced proline content (?69%) and protected membranes against peroxydation compared to saline conditions. A significant increase was observed in the GY (about 30%) of plants at both P doses combined with salt stress compared to other cases. Statistically, the low P level combined with salinity induced similar responses of plants and sometimes better responses to control plants. Finally, our results support the roles of phosphorus fertilizer in the alleviation of salt stress and enhancing the soil quality for better symbiosis efficiency and yield of chickpea.     

Effects of earthworm casts and compost on soil microbial activity and plant nutrient availability

Vermicomposting differs from conventional composting because the organic material is processed by the digestive systems of worms. The egested casts can be used to improve the fertility and physical characteristics of soil and potting media. In this study, the effects of earthworm casts (EW), conventional compost (CP) and NPK inorganic fertilizer (FT) amendments on N mineralization rates, microbial respiration, and microbial biomass were investigated in a laboratory incubation study. A bioassay with wheat (Triticum aestivium L.) was also conducted to assess the amendment effects on plant growth and nutrient uptake and to validate the nutrient release results from the incubation study. Both microbial respiration and biomass were significantly greater in the CP treatment compared to EW treatment for the initial 35 days of incubation followed by similar respiration rates and biomass to the end of the study at 70 days of incubation. Soil NO₃⁻ increased rapidly in the EW and CP treatments in the initial 30 days of incubation, attaining 290 and 400 mg N kg⁻¹ soil, respectively. Nitrate in the EW treatment then declined to 120 mg N kg⁻¹ soil by day 70, while nitrate in the CP treatment remained high. While ammonium levels decreased in the CP treatment as nitrate level increased with increasing incubation time, a low level of ammonium was maintained in the EW treatment throughout the incubation. The wheat bioassay study included two additional cast treatments (EW-N and EW2) to have treatments with higher levels of N input. Plants grown with CP or FT treatment had a lower shoot biomass and higher shoot N content than in EW-N and EW-2 treatments, and also showed symptoms of salinity stress. Ionic strength and other salinity indicators in the earthworm cast treatments were much lower than in the CP treatment, indicating a lower risk of salinity stress in casts than in compost. All cast and compost amendments significantly increased wheat P and K uptake compared to either the non-amended control or the mineral fertilizer treatment. The results show that casts are an efficient source of plant nutrients and that they are less likely to produce salinity stress in container as compared to compost and synthetic fertilizers.     

Effects of soil type,mineral nutrition and salinity on greenhouse‐grown muskmelon in winter 1

Greenhouse experiments under winter conditions were conducted to examine the effects of soil type, mineral nutrition and salinity on vegetative growth and. fruit yield of ‘Galia’ muskmelon (Cucumis melo L.). Growth in a calcareous soil or in sand, under low nutrition level or with 200 mM NaCl added during fruit maturation, imposed significant stresses on the plants expressed by (a) a decrease in dry matter accumulation in vegetative organs, in fruit number and size, and (b) an increase in dry matter percentage in leaf blades and stems. Despite the significant differences in vegetative growth of plants grown in heavy soil vs sandy soil, and in high nutrition vs low nutrition levels, the distribution of dry matter among vegetative organs (leaves, stems and roots) was affected only slightly. Sandy soil, low nutrition and high salinity decreased branching, and thus the distribution of dry matter between the main shoot and the branches. Dry matter percentage in leaf blades and stems was a sensitive parameter which increased under soil, nutrition or salinity stresses. Fruit netting and total soluble solids (TSS) content were significantly decreased by sandy soil and low nutrition level. Application of salinity during fruit growth increased both netting and TSS.     

Effect of water stress and nickel application on yield components and agronomic characteristics of canola grown on two calcareous soils

A greenhouse experiment (5 × 2 × 2 factorial arranged in randomized-complete-design with three replicates) was conducted to assess the combined effects of nickel (Ni) and drought stress on growth and yield parameters of canola (Brassica napus L. var. Talaye) grown on two calcareous soils of loamy and sandy clay textures. Treatments consisted of five Ni levels (0, 0.05, 0.1, 0.5 and 1 mg Ni kg^?1 soil) and two levels of water status 100% and 60% field capacity (FC and 0.6FC, respectively). Growth parameters and yield components of plants decreased at drought-stress conditions. Almost all of the studied growth/yield parameters of canola grown on loamy soil were significantly more than those of the sandy clay soil, probably due to the increased capability of loamy soil for supplying the plant water/nutrient requirements. Nickel could positively affect some of the mean growth and yield parameters (e.g., grain yield) over both of the water status conditions. Nevertheless, some of the traits not only increased by Ni fertilization but also decreased compared to that of the control. The positive responses of canola was observed with higher amounts of applied Ni in the sandy clay soil than in loamy soil, e.g., the maximum grain yields of canola grown on loamy and sandy clay soils were obtained with applications of 0.5 and 1 mg Ni kg^?1, respectively. Generally, results demonstrated that Ni could not mitigate the negative effects of drought stress on canola growth or yield components.     

Underestimation of Available Phosphorus by Resin–Bicarbonate and Olsen Tests in Calcareous Soils treated with Gypsum

In the present study, Olsen [0.5 M sodium bicarbonate (NaHCO₃), pH 8.5] and resin–bicarbonate (HCO₃) tests underestimated available phosphorus (P) in calcareous soils treated with gypsum (CaSO₄). The reaction of CaSO₄ and HCO₃ ^? ion or resin–HCO₃ to form calcium carbonate (CaCO₃) precipitate reduced the strength of the Olsen NaHCO₃ extractant and resin–HCO₃ strip for P extraction. The iron (Fe) oxide–impregnated filter paper (Pi strip) was independent of CaSO₄ influence and thus correctly estimated soil‐available P with respect to plant response to soil‐available P. Two greenhouse experiments were conducted with maize and wheat grown on calcareous soils treated with different rates of CaSO₄. The results confirmed that Olsen and resin–HCO₃ tests should not be used to measure available P or labile P in the P fractionation scheme in the calcareous soils containing significant amounts of gypsum.     

Phosphorus source,organic matter,and arbuscular mycorrhiza effects on growth and mineral acquisition of chickpea grown in acidic soil

Abstract

Plants grown in acidic soil usually require relatively high amounts of available phosphorus (P) to optimize growth and productivity, and sources of available P are often added to meet these requirements. Phosphorus may also be made available at relatively high rates in native soil when roots are colonized with arbuscular mycorrhizal fungi (AMF). Addition of P to soil usually reduces root‐AMF colonization and decreases beneficial effects ofAMF to plants. In glasshouse experiments, soil treatments of P [0 P (Control), 50 mg soluble‐P kg^?1 as KH₂PO₄ (SP), and 200 mg P kg^?1 as phosphate rock (PR)], organic matter (OM) at 12.5 g kg^?1, AMF (Glomus darum), and various combinations of these (OM+SP, OM+PR, AMF+SP, AMF+PR, AMF+OM, AMF+OM+SP, and AMF+OM+PR) were added to steam treated acidic Lily soil (Typic Hapludult, pH_w=5.8) to determine treatment effects on growth and mineral acquisition by chickpea (Cicer areitinum L.). The various treatment applications increased shoot dry matter (DM) above the Control, but not root DM. Percentage AMF‐root colonization increased 2‐fold or more when mycorrhizal plants were grown with AMF, OM+SP, and OM+PR. Regardless of P source, plant acquisition of P, sulfur (S), magnesium (Mg), calcium (Ca), and potassium (K) was enhanced compared to the Control, and mineral enhancement was greater in PR compared to SP plants. Mycorrhizal plants also had enhanced acquisition of macronutrients. OM+SP and OM+PR enhanced acquisition of P, K, and Mg, but not Ca. Concentrations of Fe, Mn, Cu, and Al were generally lower than Controls in SP, RP, AMF+PR, AMF+SP, and OM plants, and mycorrhizal plants especially had enhanced micronutrients. Relative agronomic effectiveness values for shoot DM and shoot P, Ca, and Mg contents were considerably higher for PR, including OM+PR, AMF+PR, and AMF+OM+PR, than for SP. PR and OM applications to AMF plants are low‐cost attractive and ecologically sound alternatives to intensive use of P fertilizers for crops grown in acidic soils.     

The influence of rhizosphere microflora on the availability of 32P-myoinositol hexaphosphate phosphorus to wheat

Experiments with wheat grown in nutrient solution and in a sandy soil showed that ³²P activity, supplied as ³²P-myoinositol hexaphosphate (IH ³²P), was translocated to the tops of aseptic plants. The proportion of the added ³²P activity recovered in the tops of solution grown plants was influenced by the concentration of IH ³²P, decreasing from 8 per cent with 10 μg P/ml to 0.4 per cent with 0.2 μg P/ml.With concentrations of IH ³²P equivalent to 0.2 parts/10⁶ P, inoculation of the root zone of soil grown plants with soil bacterial isolates shown to possess phytase activity, or with a mixed rhizosphere flora had no effect on the incorporation of ³²P into the wheat plants. It is considered unlikely, with the concentration of inositol hexaphosphates normally present in soil solution, that soil microflora will increase the dephosphorylation of these compounds at root surfaces above the activity due to plant enzymes.     

Effect of tillage and residue management on properties of two coarse-textured soils and on yield of irrigated wheat and groundnut

Changes in soil properties and yield response in relation to tillage and residue management treatments in an irrigated groundnut (Arachis hypogea L.)—wheat (Triticum aestivum, L.) rotation on a sandy soil (1972–1974) and on a sandy loam soil (1974–1976) were evaluated. Tillage treatments (T₁ and T₂) did not cause significant changes in soil properties. Incorporation of crop residues (5 t residue per ha per crop, T₃) caused a substantial increase in organic C, available N, and NaHCO₃ -extractable P contents in the top 15 cm of both soils. Residue management treatments (T₃, T₄ and T₅) showed no significant effect on soil bulk density and exchangeable K. Crop yields under no-tillage (T₁) and conventional tillage (control, T₂) were comparable on sandy soil but on the sandy loam soil, no-tillage yielded significantly lower than conventional tillage. Compared with the control, incorporation of crop residues (T₃) caused higher yields on sandy soil for groundnut and wheat by 34.1 and 47.4%, respectively, and on sandy loam by 17.1 and 7.2%, respectively. Mulching with crop residues conserved soil moisture and reduced maximum soil temperature (1.5–5.3°C in groundnut and 1.5–2.9°C in wheat) but other measured soil properties were not significantly affected. Significant yield increase due to residue mulching (T₄) was observed in sandy soil but it was significantly less than when total crop residue was incorporated (T₃). Increased wheat root-weight density in the top 15 cm soil with residue mulching was not reflected in grain yield. Compared with the incorporation of the total amount of crop residue (T₃), incorporation of half the amount and application of the other half as mulch (T₅) caused lower yields — on sandy soil for groundnut and wheat by 31.5 and 15.7%, respectively, and on sandy loam by 4.8 and 3.6%, respectively.     

Kinetics of phosphorus release from calcareous soils under different land use in Iran

The rate of phosporus (P) release from soils can significantly influence P fertility of soils. The objectives of this study were to investigate the effects of land‐use types on the kinetics of P release under different management practices and the relationship between kinetic parameters and soil physical and chemical properties from calcareous soils. The kinetics of P release in 0.01 M CaCl₂ was studied in surface samples of 30 calcareous soils planted to garlic, garden, pasture, potato, vegetables, and wheat. Trend in P‐release kinetics was similar between land‐use types. Significantly different quantities of P were released under different land use. The maximum amount (average of five soils) (46.4 mg kg^–1) of P was released in soil under potato and the minimum amount (10.4 mg kg^–1) under pasture. The kinetics of P release from soils can be described as an initial rapid rate followed by a slower rate. Different models were used to describe P release. In general, parabolic diffusion and power equation were found to be appropriate for modeling P release. The P‐release rate for the soils was estimated by parabolic equation for the studied land‐use types. The constant b was lower for pasture and wheat than for garlic and potato. The relationship between the rate of P release with Olsen‐P was linear, while it was curved with respect to the CaCl₂‐P, indicating that release of P was diffusion‐controlled. When the kinetic parameters of models were regressed on soil properties, CaCl₂‐P and CaCO₃ appeared to be the most important soil properties influencing P‐release rates in these soils.     

Available N and P,Microbial Activity,and Biomass in Saline Sandy and Clayey Soils Amended with Residues of Wheat and Alfalfa

Salt accumulation has a negative effect on microorganisms, but plant residues may enhance the microbial activity and biomass. An experiment was conducted over 50 days to evaluate the effect of wheat and alfalfa residues on microbial activity and biomass and nitrogen (N) and phosphorus (P) availability in sandy and clayey soils at different salinity levels. Equivalent amounts of calcium (Ca⁺²) and sodium (Na⁺) salts were added to both soils. Values of electrical conductivity (EC_1:5), denoted S1, S2, and S3 in each soil, were 0.16, 1.10 and 1.98 dS m^?1 in the sand and 0.19, 0.82 and 1.75 dS m^?1 in the clay. Residues of wheat and alfalfa were added at 2% (w/w). Cumulative respiration and microbial biomass decreased with increasing salinity, but with residue addition they increased with a greater rate in amended sandy soil than in clay soil, with a more pronounced effect for alfalfa than for wheat residue. After 10 days, with wheat residue available N values were 113, 86, and 71 μg in the clay and 144, 114, and 94 μg g^?1 soil in the sand in S1, S2, and S3, respectively. Relative to wheat residue, alfalfa residue increased N availability by 9, 13, and 19% and 22, 24, and 24% in the clay and in the sand in S1, S2, and S3, respectively. Compared to the control, in the clay P availability increased by 33, 57, and 100% with wheat residue and by 58, 128, and 175% with alfalfa residue, whereas in the sand it increased by 92, 45, and 40% with wheat residue and by 130, 145, and 280% with alfalfa residue in S1, S2, and S3, respectively. Availability of N and P increased from day 10 to day 50 in both soils, but with different magnitudes. Residue addition can increase microbial activity and nutrient availability in saline soils, particularly in coarser textured soils.     

不同农业土壤中有效磷的变化与磷平衡的关系

Maintaining soil phosphorus(P) at adequate levels for plant growth requires assessing how the long-term P balance(viz., the difference between P inputs and outputs) results in changes in soil test P. The hypothesis that routinely measured soil properties can help predict the conversion factor of P balance into Olsen P was tested at 39 sites in agricultural areas of the Mediterranean region in Spain. A set of soil samples from each site was analyzed for Olsen P, inorganic P(P extracted using 0.5 mol L~(-1) H_2SO_4), pseudototal P(P extracted using 0.5 mol L~(-1) H_2SO_4 following ignition at 550℃), and organic P(the difference between pseudototal P and inorganic P). Organic and Olsen P were uncorrelated in most of the 39 soil sets, which suggests that organic P content changed little with P inputs and outputs. The slopes of the regression lines of Olsen P against pseudototal and inorganic P, which were used as two different measures of the conversion factor, ranged widely(from 0.03 to 0.25 approximately), with their average values(about 0.10) being similar to those found in long-term experiments conducted in temperate areas. Neither conversion factor was significantly correlated with any routinely measured soil property; however, the conversion factor for inorganic P was significantly lower for calcareous soils than for noncalcareous soils. Our negative results suggest the need to isolate the influence of soil properties from that of management systems and environmental factors relating to P dynamics in future studies.     

Silicon-Induced Growth and Yield Enhancement in Two Wheat Genotypes Differing in Salinity Tolerance

Silicon (Si) is known to alleviate a number of abiotic stresses in higher plants including salinity stress. Two independent experiments were conducted to evaluate the role of Si in alleviating salinity stress in two contrasting wheat (Triticum aestivum L.) genotypes, Auqab-2000' (salt sensitive) and SARC-3 (salt tolerant). In the first experiment, genotypes were grown in hydroponics with two levels of salinity (0 and 60 mM NaCl) with and without 2 mM Si in a completely randomized design with four replications. Salinity stress significantly (P < 0.01) decreased all of the growth parameters, increased sodium (Na⁺) concentration, and decreased potassium (K⁺) concentration in shoots of both genotypes grown in hydroponics. Silicon significantly improved growth of both genotypes. The increase in growth was more prominent under salt stress (75%) than under normal condition (15%). In the second experiment, both genotypes were grown in normal [electrical conductivity (EC) = 1.23 d Sm^–1] and natural saline field (EC = 11.92 d Sm^–1) conditions with three levels of Si (0, 75, and 150 g g^–1 Si) with three replications in a randomized complete block design. Silicon significantly (P < 0.05) decreased growth reduction in both genotypes caused by salinity stress. The grain yield under salt stress decreased from 62% to 33% and from 44% to 20% of the maximum potential in Auqab-2000 and SARC-3, respectively, when 150 g g^–1 Si was used. Auqab-2000 performed better in normal field conditions, but SARC-3 produced more straw and grain yield in saline field conditions. Addition of Si significantly (P < 0.05) improved K uptake and reduced Na⁺ uptake in both of wheat genotypes and increased the K⁺/Na⁺ ratio in shoot. Enhanced salinity tolerance and improved growth in wheat by Si application was attributed to decreased Na⁺ uptake, its restricted translocation toward shoots, and enhanced K⁺ uptake.     

Fate of 15N-Labeled Potassium Nitrate in Different Citrus-Cultivated Soils: Influence of Spring and Summer Application

The fate of ¹⁵N-labeled potassium nitrate (8.5% ¹⁵N excess) was determined in 3-year-old Valencia orange trees grown in 1-m³ containers filled with different textured soils (sandy and loamy). The trees were fertilized either in spring (24 March) or summer (24 July). Spring fertilized trees gave higher fruit yields in sandy than in loamy soils, which exceeded summer fertilized trees in both cases. Summer fertilized trees had greater leaf biomass than spring fertilized trees. Fibrous root weight was 1.9-fold higher in sandy than in loamy soil. At the end of the cycle, tree N recovery from spring application was 45.7% for sandy and 37.7% for loamy soil; from summer fertilization, N recovery was 58.9% and 51.5% for sandy and loamy soils, respectively. The ¹⁵N recovered in the inorganic soil fraction (0?C90?cm) was higher for loamy (1.3%) than for sandy soil (0.4%). Fertilizer N immobilized in the organic matter was lower in sandy (2.5%) than in loamy soil (6.0%). Potential nitrate leaching from fertilizer (¹⁵NO ₃ ^? ?CN in the 90?C110-cm soil layer plus ¹⁵NO ₃ ^? ?CN in drainage water) was 34.8% higher in sandy than in loamy soil. The low N levels in sandy soil resulted from both higher NO ₃ ^? ?CN leaching losses and higher N uptake of plants grown in the former. The great root mass and higher soil temperatures could account for raised plant N uptake in sandy soil and in summer, respectively.