Phosphorus equilibria in soils [Topraklarda fosfor dengesi]

Some chemical and thermodynamical approaches on the study of processes such as adsorption-desorption and precipitation-dissolution which are effective in the transfer of phosphorus between solution and solid phases of soils have been rewieved. Methods of soil analysis for phosphorus and their field calibrations to be used in fertilizer recommendations, on the basis of their effectiveness under various conditions were evaluated and references were made to the innovative approaches, especially in determination of available phosphorus

Assessment of leaching risks of residual N fertilisers applied to wheat in a Mediterranean-type environment

Nitrogen fertiliser recovery of a wheat (Triticum aestivum) cultivar (Seri 82) and residual N remaining in soil after harvest were measured using 15N labelled fertilisers during four years of field experiments from 1994/95 to 1997/98. Urea, as N-fertiliser, was applied in two splits, a commonly used practice in the region, 1/3 at emergence and the remaining two thirds at tillering, at rates of 0, 80, 160 and 240 kg N ha-1. Recovery of fertiliser N by the wheat crop was 50-60%, indicating that a significant amount of N fertiliser (40-50%) applied to wheat remained unused in the soil or was lost. However, over 90% of the fertiliser-N applied could be accounted for in the crop or soil after harvest. Of the residual N-fertiliser remaining in the soil, over 50% was within the surface layers of 20 to 30 cm depth, and reached barely detectable levels (< 2.5 kg N ha-1) beyond 60 cm. Nitrate concentrations in soil-water samples collected at 90-cm did not show any significant increase with the split N applications in 1995/96, the wettest growing season, under commonly used rates of application, 160 kg N ha-1. The results therefore suggests that, for rainfed wheat grown on heavy textured soils (Eutric Vertisol) of the Mediterranean Region, leaching losses of fertiliser N below 90 cm (plant rooting depth) during the wheat growing season when evapotranspiration accounts for most of the seasonal average rainfall (500 to 600 mm), were essentially nil. However, further work is needed to assess how the N retained in the soil after harvest of wheat will effect N utilisation of subsequent crops and likely losses to environment in future years. © OECD 2003

Phosphorus adsorption of the soils of the Gaziantep Kayacik Plain [Gaziantep kayacik ovasi topraklarinda fosfor adsorpsiyonu]

The phosphorus adsorption characteristics of 11 widespread soil series from Gaziantep Kayacik Plain were investigated and these characteristics were evaluated with regard to various soil properties and phosphate minerals. Langmuir adsorption isotherms were used to determine the phosphorus-adsorption characteristics of the soils. The soils were equilibriated with solutions containing phosphorus at different concentrations at constant temperature, and the equilibrium phosphorus concentrations of the solution phases (C) and the amounts of adsorbed phosphorus (x/m) at these concentrations were determined. The adsorption maxima (b) and adsorption-energy coefficients (k) of the experimental soils were calculated from C and the x/m values using the linear form of the Langmuir adsorption isotherm. The calculated b values of the soils varied from 58.1 to 113.3 µg/g, and the k values varied from 9.1 to 153.5 ml/µg

Determination of phosphorus adsorption using various forms of isotherms in soils of adiyaman çamgazi plain [Adiyaman çamgazi ovasi topraklarinda fosfor adsorpsiyonunun degişik i·zotermlerle belirlenmesi]

Samples from 8 widespread soil series from Adiyaman Çamgazi Plain were equilibriated at a constant temperature with 16 different solutions containing 0 to 50 µg/ml phosphorus in batch-type experiments. The phosphorus concentrations of the equilibrium solutions and the amounts of phosphorus adsorbed by the soils at these concentrations were determined. These phosphorus-adsorption data were evaluated statistically for their suitability for adsorption isotherms in various concentration ranges

Modelling nitrogen uptake and potential nitrate leaching under different irrigation programs in nitrogen-fertilized tomato using the computer program NLEAP

PubMedID: 15736886Readily available nitrogen (N) sources such as ammonium nitrate with excessive irrigation present a potential hazard for the environment. The computer program Nitrate Leaching and Economic Analysis Package (NLEAP) is a mechanistic model developed for rapid site-specific estimates of nitrate-nitrogen (NO3-N) moving below the root zone in agricultural crops and potantial impacts of NO3-N leaching into groundwater. In this study, the value of NLEAP was tested to simulate N uptake by crops and NO3-N leaching parameters in large lysimeters under the tomato crop. Three seedlings of tomato variety of H-2274 (Lycopersicum esculentum L.) were transplanted into each lysimeter. N fertilizer at the rate of 140 kg N ha-1 was sidedressed in two split applications, the first half as ammonium sulphate and the second half as ammonium nitrate. The lysimeters were irrigated based on programs of C 0.75, 1.00, 1.25 and 1.50, C referring to class A-Pan evaporation coefficients. Parameters such as leaching index (LI), annual leaching risk potential (ALRP), N available for leaching (NAL), amount of NO3-N leached (NL) and amount of N taken up by the crops (NU) were estimated using the NLEAP computer model. To test the ability of model to simulate N uptake and NL, measured values were compared with simulated values. Significant correlations, R2 = 0.92 and P < 0.03 for the first year and R2 = 0.86 and P < 0.06 for the second year, were found between measured and simulated values for crop N consumption, indicating that the NLEAP model adequately described crop N uptake under the varied irrigation programs using an optimal N fertilization program for the experimental site. Significant correlations, R2 = 0.96 and P < 0.01 for the first year and R2 = 0.97 and P < 0.01 for the second year, were also found between measured and simulated values of NL, indicating that the NLEAP model also adequately predicted NL under the varied irrigation programs. Therefore, this computer model can be useful to estimate the NO3-N moving beyond the root zone under conditions in which the present experiment was carried out. Also, the NLEAP-estimated NAL values and other parameters can also be used to improve N management practices and N fertilizer recommendations that will help to decrease the adverse effect of N fertilizer on groundwater quality and farm profitability. © Springer Science + Business Media, Inc. 2005

Nitrogen fertiliser recovery and yield response of greenhouse grown and fertigated tomato to root - Zone soil water tension [Fertigasyon teknigi ile serada yetiştirilen dornatesin, kök bölgesi topraksuyu tansiyonuna verim tepkisi ve azotlu gübre alimi]

Tomatoes were grown in a plastic greenhouse under 2 irrigation programmes and four N-fertiliser concentrations (0, 100, 150 and 200 mg N 1-1) of irrigation water. P and K concentrations were kept constant at 30 and 200 mg 1-1, respectively, for all N treatments. A drip irrigation system with single laterals centred between the plant rows, spaced 50 cm apart was used for irrigation as well as for feeding fertiliser solution (i.e. fertigation) during the experiment. Tensiometers, installed in 3 replicates at 45 cm soil depth and centred mid-way between 2 plants in rows, were used for irrigation scheduling. Two irrigation programmes, controlled through continuous monitoring of root-zone soil-water tension, were used as irrigation treatments. In one of the treatments, irrigation scheduling was based on a maximum soil-water tension of 50 kPa during the entire season. In the second treatment, soil-water tension to initiate irrigation was initially high (70 kPa), until fruit stetting, and it fell down to 50 kPa, later in the season. 15N labelled urea was used in one of the N-concentration treatments (150 mg N 1-1) to estimate tomato N-fertiliser recovery. The results showed that tomato yield was not influenced significantly by irrigation treatments, although the irrigation treatment of low soil-water tension (? 50 kPa), maintained throughout the season, gave higher yield. Exposing tomatoes to high soil water stress during the early growth stage, first 70 kPa then dropping to 50 kPa, promotes proportionally higher uptake of soil N, and thus reduces the recovery of applied N-fertiliser. However, when low soil water tension (?50 kPa) was maintained throughout the season, N-fertiliser recovery was 22.4% higher compared with when high soil water-tension prevailed until mid season. As for the effects of N concentration of the feeding solution, tomatoes showed a statistically significant (P ? 0.05) fruit-yield response to varying N concentrations. The feeding-solution-N concentration giving the highest tomato fruit yield was about 120 mg N 1-1 as estimated using a N-concentration yield-response function

Formation, distribution and chemical properties of saline and alkaline soils of the Çukurova Region, southern Turkey

The salinity and alkalinity changes over the last 30 years in the Çukurova Region were studied using LANDSAT images, field trials and data obtained from earlier studies. Three categories of reclaimed land were determined for the region as follows: 1. 1. Totally reclaimed soils, including the Bajadas, River Terraces and Bottom Lands. 2. 2. Partially reclaimed soils, in the Delta and Saline Marshy areas. 3. 3. Soils with increased salinity, in the Sand Dunes and the Salinity Marshy areas. © 1991

Grain yield response and N-fertiliser recovery of maize under deficit irrigation

Grain yield response and nitrogen (N) fertiliser recovery of maize (Zea mays L. cv. Sele) were assessed as influenced by deficit irrigation that was imposed either using conventional deficit irrigation (DI) or partial root drying (PRD) practice. The two deficit irrigation treatments were compared with FULL irrigation, the control treatment where rooting zone soil-water content was increased to field capacity at each irrigation, whereas 50% deficit irrigation was applied to the deficit treatments, DI50 and PRD50. Under the PRD practice, one-half of the rooting zone was wetted while the other half was maintained partially dry, thereby reduced amount of irrigation water was needed. The wetted and partially dry sides were interchanged in the subsequent irrigations. Under conventional DI, plants again received reduced amounts of water but the water was uniformly applied to both sides of the plant row. A popular hybrid maize-cultivar Sele was planted, following harvest of wheat. The study was conducted for two consecutive years in 2001 and 2002. A composite fertiliser of N, P and K, all at 80 kg ha-1 was applied before planting. At the ninth leaf (V9) stage, a second application of N-fertiliser at 170 kg N ha -1 rate was made. Difference method (plots with or without N-fertiliser application) was used for estimation of plant N-uptake efficiency. Contrary to earlier reports, the PRD treatment did not result in any yield benefit compared to the conventional deficit irrigation. The range of grain yield reduction under deficit irrigation treatments, DI50 and PRD50, was 10-25% and significant (P ? 0.01), compared to FULL irrigation practice. Measurements, including xylem sap abscisic acid concentration, photosynthetic rate and stomatal conductance under DI50 and PRD50 treatments followed a nearly identical trend. The PRD irrigation practice had the highest N-fertiliser recovery among the irrigation treatments, with minimal mineral N residue left after maize harvest. The recoveries under FULL and DI50 treatments were 17 and 24% less, respectively, than the PRD treatment. The PRD irrigation practice was not only as effective as conventional deficit irrigation (DI) in saving water, but it should also be regarded as an environmentally friendly irrigation practice due to its association with low mineral N residue left in the soil. © 2004 Elsevier B.V. All rights reserved.European Commission: ICA3-CT-1999-00008The authors gratefully acknowledge that this work was funded by European Union, through INCO-MED RTD project (ICA3-CT-1999-00008). Thanks are due to the Staff of Department of Biological Sciences, University of Lancaster, UK, for their help in ABA analysis, and to Dr. J.S. Schepers in Agronomy Department, University of Nebraska, USA, for editing the paper and valuable comments

Prospects of partial root zone irrigation for increasing irrigation water use efficiency of major crops in the Mediterranean region

Field experiments were conducted for 3 years from 2000 to 2002 to assess proportional crop yield differences obtained under conventional deficit irrigation (CDI) and partial root zone irrigation (PRI) practices, compared with full irrigation (FULL) where plant water requirements were fully met. The experimental crops included vegetables (tomato and pepper), field crops (maize and cotton) and citrus. The fruit yield of greenhouse-grown tomato with FULL irrigation was higher than with PRI (7-22% lower) but was not significantly different. The PRI treatments had 7-10% additional tomato yield over CDI receiving the same amount of water. The yield of pepper, however, decreased in proportion to the level of irrigation deficit with no increase of irrigation water use efficiency (IWUE). No seed yield decrease was evident for cotton with the deficit treatments (PRI and CDI) compared with FULL irrigation. Similarly, the PRI treatment did not give any yield benefit for maize compared with CDI. The ranking of fruit yields of mandarin, FULL > PRI > CDI, was the same as that of other crops; however, the differences were not significant. Although the deficit treatments (PRI and CDI) had as high as 39% increase in IWUE, compared with FULL treatment, some adverse effects on fruit quality were evident such as smaller size of fruits under the deficit treatments. © 2007 Association of Applied Biologists