摘要:

Early growth of leucaena(Leucaena leucoceohala(Lam) de Wit) is often slow, especially on soils low in organic matter and total N. This study was conducted to determine whether small quantity of N fertilizer in combination with P will enhance early growth. Nitrogen as urea was applied at 0, 25, and 100 mg/kg soil with 50 mg P/kg soil as monocalcium phosphate or without P to leucaena seedlings in pots. All plants were inoculated with leucaena Rhizobium (LX 382). Growth rates declined from 0.3 cm/day at 14 to 0.22 cm/day at 42 days after planting (DAP) in no‐P plants. Fertilizer N and P application increased growth rates sharply thus hastening shoot and root dry matter accumulation. P uptake was enhanced with 25 mg N/kg soil at 42 and 84 DAP, but not at 126 DAP. It appears small amount of N applied with adequate P enhanced P uptake and hence early growth of leucaena.

ISSN:0010-3624    

DOI:10.1080/00103629109368390

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The use of acetylene (C2H2) in the inhibition of N2O to N2is widely used for measuring denitrification. The objective of this study was to determine the effectiveness of acetylene inhibition of N2O reduction for short‐term and prolonged incubation studies in soils of varying water saturation, and to find out the possible reasons for lower N2O recovery in continuously sealed incubations. Two experiments carried out in the laboratory reconfirmed that acetylene was very effective in inhibiting the reduction of N2O in denitrification even for the prolonged incubation period (up to 96 h) under moist to saturated soil water contents. With 90 and 120% water‐filled pore space (WFPS), the accumulated N2O in containers kept sealed throughout the study period, was 28 to 41% less than total headspace N2O produced in containers that were opened, flushed and fresh C2H2added every 24 h. Interpretation of our results suggest the lower N2O amount recovered from continuously sealed containers at high WFPS, as compared to short‐term incubations (flushed containers), resulted primarily from delayed N2O release from soil and not greater N2O dissolved in soil solution, lower rates of denitrification, or decomposition/loss of C2H2during prolonged incubation. Reduction of N2O diffusion from soil cores showed direct relationship with headspace concentration of N2O and soil WFPS. From these results it is concluded that to obtain quantitative recovery of N2O produced via denitrification, especially from soil with high WFPS soil cores should be vigorously shaken before head‐space N2O analysis.

ISSN:0010-3624    

DOI:10.1080/00103629109368391

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

To gain a better understanding of N availability in Mediterranean soils, 18 surface (0–20cm) soil samples were selected from soil groups of Syria for study of their N mineralization potentials. The chosen soils represented the predominant soil groups found in West Asia and North Africa,i.e.Inceptisols, Vertisols, Aridisols, Mollisols and Entisols. Soils were incubated in tubes at 25 ± 0.5°C after addition of N‐free nutrient solution according to the method used by Stanford and Smith (18). Mineralized N was recovered from tubes by leaching with nutrient solution at 2 week intervals up to 22 weeks of incubation; NH4and NO3nitrogen were analyzed in the leachates. The N mineralization potential (No) was estimated using three procedures: (i) application of the empirical linear equation suggested by Stanford and Smith (18) relating (No) to the slope of N mineralized (Nt) with the square root of time (t) i.e., No = 6.5 (δNt/δt1/2); (ii) the exponential equation Nt = No [(1‐exp (‐kt)], with calculation of No and k (the rate constant of mineralization) from best fit to experimental data using the BMDP non‐linear least square equation (NLLS); (iii) application of hyperbolic model equation (9) Nt = No.t/(t1/2+ t), where (t1/2) is the time required for half of No to mineralize. The NLLS equation was used to calculate t1/2and No.

ISSN:0010-3624    

DOI:10.1080/00103629109368392

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Some irrigation waters have a high Mg/Ca ratio. The objective of the experiment reported herein was to compare the effect of high Mg in combination with different anions and different EC levels on the growth of corn(Zea maysL.). Corn was grown in the greenhouse in a calcareous soil equilibrated and irrigated with the following waters: 1) tap water (check, EC = 0.078 dS/m, SAR = 0.1); 2) Mg(HCO3)2, EC=1 dS/m; 3) Mg(HCO3)2, EC = 3; 4) MgSO4)EC=1; 5) MgSO4, EC=3; 6) MgSO4, EC = 6; and 7) and 8) mixed salts (Ec = 3 & 6 dS/m, SAR = 5, Ca: Mg = 3: 1, Cl: SO4= 2: 1). Yield depressions of top growth caused by mixed‐salt waters (EC = 3 & 6) were 17 and 26%, respectively, compared to yields obtained with tap water. Single‐salt MgSO4waters (EC = 1, 3 & 6) reduced corn tops 19, 38, and 59%, respectively, more than the mixed‐salt solutions at equivalent soil salinity levels probably due to Mg‐induced Ca deficiency. The Mg(HCO3)2waters (EC = 1 & 3) reduced top growth 45 and 87% more than the mixed salt solutions. Thus Mg (HCO3)2was more than twice as depressive on corn top growth as MgSO4. Corn root growth depression was similar to top growth depression. Leaf Ca: Mg ratio was related to their ratio in the soil solution. The leaf Ca and Mg concentrations were almost the same for plants irrigated with Mg(HCO3)2or MgSO4at EC = 1. Therefore, Mg: Ca ratio of leaves did not explain the yield differences between the two Mg salts. Nutrient imbalances and a high pH of 9 were possibly responsible for the lower yields in the presence of Mg(HCO3)2.

ISSN:0010-3624    

DOI:10.1080/00103629109368393

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The effect of Mg/Ca ratio in irrigation water on growth of plants has not been studied to any extent. The objective of the experiments reported herein was to study such an effect. Corn(Zea mays) and wheat(Triticum aestivum) were grown in the greenhouse in a noncalcareous clay loam soil. They were irrigated with tap water (EC = 0.080 dS/m, SAR = 0.1, Mg/[Ca + Mg] = 20%) as the “check”; treatment and 18 synthetic waters prepared using three levels of salinity (2, 4, and 6 dS/m) and 6 ratios of Mg/[Ca + Mg] (30, 50, 70, 90, 95, and 100%) for corn and wheat grown in fall and winter, respectively, or 30, 50, 60, 70, 80, and 90% for corn grown in summer. Two‐thirds of anion equivalents in the waters was sulfate and the balance Cl. The soils were equilibrated with their respective irrigation waters before planting. A 50% leaching fraction (drainage water quantity: irrigation water quantity) was applied on the corn grown in the fall. A 25% leaching fraction was applied on the wheat grown in winter and corn grown in summer. Wheat grain yield was highest at 50% Mg treatment and was depressed when Mg/[Ca+Mg] exceeded 55–65%. Severe grain yield depression with Ca deficiency symptoms on grain heads were observed when Mg/[Ca + Mg] ratio was about 90%. The highest straw yield was obtained with tap water. Except for 100% Mg treatment, wheat straw yield did not decrease by salinity levels at a given Mg percentage. Total uptake of both Mg and Ca and their ratios increased as their soil solution concentrations and ratios increased for wheat and corn crops. The corn stover dry matter did not decrease with soil solution salinity up to 8 dS/m except at 100% Mg treatment and at an EC level of more than 6 dS/m when grown in winter. In summer corn stover dry matter yields were lower in saline soil solutions of about 8 to 19 dS/m than in the tap water check treatment with lowest yield in 100% Mg treatment at the highest EC. It was not possible for corn to produce grain under the experimental conditions. It is concluded that irrigating wheat grown in noncalcaerous soils with waters containing a Mg/[Ca+Mg] level of more than 50–65% can reduce grain yields due to Mg‐induced Ca deficiency.

ISSN:0010-3624    

DOI:10.1080/00103629109368394

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Partial acidulation of phosphate rock (PR) or compaction of PR with soluble P fertilizers represents a means of producing P fertilizers from indigenous PR sources that may otherwise be unsuited for use as a P fertilizer. In the present two greenhouse experiments, we compared the agronomic effectiveness using a relative agronomic efficiency (RAE) index for the following P fertilizer sources: (i) ground Togo PR; (ii) partially acidulated phosphate rock (PAPR) at 50% acidulation with H2SO4; (iii) PR compacted with triple superphosphate (TSP), urea, and KCl at P ratio of PR: TSP = 50: 50; and (iv) commercial‐grade single superphosphate (SSP). The soil used was an acid Bladen sandy loam (Typic Albaquult) limed to pH 5.5 prior to cropping with maize for 6 weeks or cowpeas grown to maturity. Rates of P applied were 0, 50, 100, 150, and 200 mg P/kg. All treatments received adequate rates of N and K, as well as secondary and micronutrients.

ISSN:0010-3624    

DOI:10.1080/00103629109368395

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

In soils under different land use in North‐Germany, sucrose inversion was used to characterize the temperature regime of natural and agricultural ecosystems. This method is suitable for a comparison of soils and shows significant differences of O.1°C with 3–5 replicates. As it is necessary to implement the method very carefully, a detailed working scheme is presented to prepare the samples for intersite measurement.

ISSN:0010-3624    

DOI:10.1080/00103629109368396

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The objective of this study was to evaluate the usefulness of measures of mineralized sulfur (S), soil sulfate‐sulfur (SO4‐S), concentration of S in plant tissue, and the N: S ratio in plant tissue as predictors of the need for S in a fertilizer program for corn(Zea maysL.). Data to evaluate the use of plant analysis for S as a predictor were obtained from ten sites where various rates of N and S were applied to corn. Regression analysis was used to relate the S concentration in the ear leaf tissue as well as the N: S ratio in the same tissue to relative yield when the rate of applied N was held constant at a rate of 168 kg/ha. These measures of S in plant tissue were not significantly related to relative yield at sites where there was no response to fertilizer S as well as sites where added S increased yield.

ISSN:0010-3624    

DOI:10.1080/00103629109368397

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Peanut (Arachis hypogaeaL.) 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.

ISSN:0010-3624    

DOI:10.1080/00103629109368398

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Minimum sufficiency levels of hull and seed Ca for maximum yield and grade of runner or Virginia type peanuts(Arachis hypogaeaL.) have not been established and there is limited information on single and combined effects of limestone and gypsum on production and quality of peanuts. Field experiments were conducted on runner and Virginia type peanuts to study single and combined effects of limestone and gypsum on yield and grade, and to attempt to establish minimum sufficiency levels of hull and seed Ca for maximum yield and grade of each type. Gypsum treatments, O, low, medium, and high rates, were superimposed on residual limestone rates on three sites with ‘Florunner’ (runner type) and on one site with ‘NC‐7’ (Virginia type) peanuts. Yield and grade of Florunner peanuts were not increased by limestone or gypsum treatments on any site even though soil Ca concentrations (Mehlich 1) ranged from 152 to 200 mg/kg among the sites. These levels were lower than the Georgia recommended minimum sufficiency value of 250 mg/kg. However, yield and grade of ‘NC‐7’ peanuts were increased by limestone or gypsum, but maximum yield occurred only where gypsum was applied even with soil Ca levels of 682 mg/kg. The minimum hull Ca level of 1.2 g/kg and seed Ca of 0.42 g/kg were sufficient for Florunner peanuts since yields and quality were not increased by limestone or gypsum application. Maximim yield and grade were achieved with Florunner at leaf, hull, and seed Ca concentrations of 13.2, 1.2, and 0.42 g/kg as compared with 26.0, 1.9, and 0.58 g/kg for NC‐7, respectively. These data show that NC‐7 has a higher Ca requirement than Florunner.

ISSN:0010-3624    

DOI:10.1080/00103629109368399

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor