JWSS - Journal of Water and Soil Science

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High-yielding rice varieties are prevailing in Guilan Province which is one of the most important rice producing regions in Iran. However, little is known about K status in this region and no suitable extraction method can yet be introduced to the farmers. This experiment was carried out to determine the available K by 15 chemical extractants and also to examine the critical K levels in paddy soils of the region. The treatments included 23 soils and 2 K levels (0 and 300 mg/kg as KCl) in a factorial experiment in a randomized complete block design with three replications.

 Results indicated that K application increased grain and straw yields, K concentration in straw as well as K uptake by rice. High correlation coefficients were observed between MgOAc, H₂SO₄, Morgan and 0.01 M CaC_l2 methods with K concentration in straw (0, 0.83, 0.78, 0.8 and 0.78, respectively) and with K concentration in plant tops (0.79, 0.76, 0.75 and 0.73, respectively). Similarly, high correlation coefficients were observed between the same extraction methods with K absorbed by straw (0.83, 0.82, 0.78 and 0.76, respectively) and with total plant K uptake (0.79, 0.83, 0.74 and 0.71, respectively). Potassium critical levels by different extracting solutions were determined by Cate-Nelson procedure and were 38, 74, 160, 111, 36, 112 and 100 mg kg^-1 for MgOAc, Morgan and Kelowana methods, Texas method H₂SO₄ 0.01 M CaCl₂ and NH₄OAc without and with submergence of soil samples, respectively. In this study, available K was below the critical level in almost 75% of the soils.

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Evaluation of nutrient status in soil is important from nutritional, environmental and economical aspects. Potassium is a very important plant nutrient not only because of its large demand, but also because of its important physiological and biochemical functions in plant. In order to evaluate K availability and common K extractants in the central region of Isfahan Province, surface soil samples from 26 important soil series were taken, out of which 16 soil samples were selected for further study based on their ammonium acetate extractable K and texture. Available K was extracted from the soil samples by NH₄OAC (4 methods), CaCl₂ (2 methods), NaCl (2 methods), NaOAC, AB-DTPA, Mehlich I, Mehlich III, Morgan-Wolf and HNO₃. A green house experiment using corn (Zea mays L.) variety Single-cross 704 as the test plant with 2 treatments (zero and 150 mg/kg K) and three replications was performed with the 16 selected soils to correlate K uptake with K extracted by different extractants.

 From XRD analysis, the dominant clay mineral was found to be Illite. Based on the amount of potassium extracted by these extractants from the soils the extractants used in this research may be divided into three groups: relatively weak extractants including CaCl₂, Mehlich I and Morgan-Wolf relatively strong extractants including NH₄OAC, NaCl (2N), Mehlich III, AB-DTPA, NaOAC and NaCl (1N), the strongest and weakest extractants in this group were NH₄OAC and NaCl (1N), respectively and finally, a very strong extractant which includes only HNO₃. In each group, the quantities of extracted K showed high correlation with each other. A high and significant correlation was observed between the quantities of K extracted by NH₄OAC, AB-DTPA and HNO₃. The amount of K extracted by 2N NaCl, 1N NaOAC, 1N NH₄OAC, and AB-DTPA was significantly correlated with K taken up by plant and its K concentration. 2N NaCl and 1N NaOAC were selected as the most suitable extractants for K based on their high correlation coefficients with plant uptake (0.79** and 0.72**, respectively) and K concentration in plant (0.86** and 0.85**, respectively). Yield, relative yield and plant response were not significantly correlated with K extracted by different extractants indicating that available K of the selected soils was not a limiting factor for corn growth therefore, it was impossible to determine the critical level of K for corn by the selected extractant.

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In a 3×3 factorial experiment, 90 72-week-old native breeder hens of Isfahan were kept in cages (one bird/cage). The effect of three levels of dietary calcium (3.27, 2.62, and 1.96%) and three levels of dietary available phosphorus (0.25, 0.20, and 0.15%) on egg production and egg shell traits were investigated. Each treatment contained five replicates of two birds (10 birds per treatment). The experimental diets were fed 8 weeks (from 72 to 80 weeks of age). Dietary calcium and available phosphorus levels had no significant effects on feed consumption, shell thickness and shell breaking strength. Decreasing dietary calcium or available phosphorus levels (1.96% calcium and 0.15% available phosphorus) caused a significant (P<0.05) linear increase in egg production, egg weight and improvement in feed conversion. The results from this study showed that high egg production, maximum calcium retention in the shell and optimum feed conversion were observed in native breeder hens during late growing period with 1.96% calcium and 0.15% available phosphorus.

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In order to investigate variations of spore population, root colonization and also to determine mycorrhizal symbiosis in the root and rhizosphere of Pistachio trees (Pistacia vera) in natural forests, two study stations in Kalat (Chachaeh) and Sarakhs (Shorlogh) regions were selected. Sampling from soil and root of the trees were taken from under the canopy and from a depth of 30 cm. On a monthly basis. The roots were stained and the colonization rate and the variations of spore population were measured. Some soil characteristics including pH, moisture, organic material percentage and available phosphorus were determined, The correlation coefficients between the measured factors were calculated. The results indicated that vesicular – arbuscular mycorrhiza (VAM) was the only symbiotic mycorriza of pistachio trees. Average amounts of root colonization were 13% and 11% in Chahchaheh and Shorlogh stations, respectively. Also, average numbers of spores per 1 gram of dry soil in the above stations were 12 and 10, respectively. The correlation between the variation of spore population and colonization levels was positive but the correlation between spore population and soil moisture, organic material, available phosphorus and pH was negative.

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Potassium is one of nutritional element that has an important effect on the quantity and quality of rice plant. Knowledge about the K critical level and plant response to different application rate of K, can effectively help with the proper use of this element. Therefore, in this study potassium (K) critical level for rice (Khazar variety) and prediction equation for grain yield were determined in 21 rice fields of Guilan provience during 2001-2002. After land preparation, 6 experimental plots (4×5m) were constructed in each selected field. Nitrogen and phosphorus were applied before transplanting, based on soil test from urea and triple superphosphate, respectively. Potassium was applied in different rates including 0, 100, 200, 300, 400, and 500 kg ha^-1 of K₂O as muriate potassium. Khazar variety was transplanted in a space of 25×25cm, just after fertilizing of plots. Plots were harvested in 5 m² at the end of maturity stage from the first node above the ground, and grain and straw were measured separately. Statistic analysis was done on grain weight based on 14% moisture. The results showed, that effect of different K fertilizer application in 5% and the effect of soil type in 1% were statistically significant on the grain yield. The mean increase of grain yield in responsive fields to K application was 982 kg ha^-1. The results also showed that the responses of rice fields with available K less than 100 mg kg^-1, 100-160, and more than 160 mg kg^-1 to KCl application were high, moderate and low, respectively. Potassium critical level based on 90% relative yield was determined as 110 mg kg^-1 of soil . In final relative yield, prediction equation, available potassium, potassium content of irrigation water, and rate of KCl fertilizer application entered positively in the equation, while available phosphorus showed negative effect on relative yield.

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Hamadan province is one of the most important alfalfa (Medicago sativa) producing regions in Iran. However, little is known about P status in this region and no suitable extraction method has yet been introduced. This experiment was carried out to determine the available phosphorus by nine chemical extractants in some soils of the Hamadan region. The treatments consisted of 15 soils and 2 P levels (0 and 200 mg P kg^-1 as Ca(H₂PO₄)₂.H₂O ) in a factorial experiment in a randomized design with three replications. Alfalfa plant were harvested in three cutting. The results indicated that the amount of extractable phosphorus decreased in the following order: Collwell>Bray 2>0.1 N HCl>Bray 1>Olsen>AB-DTPA>Mehlich 1>Mehlich 2 > 0.01 M CaCl₂ The amounts of P extracted by all methods except that by 0.01 M CaCl₂ method, showed significant correlation. The results of correlation studies showed that in the first cutting, Collwel method, in the second cutting AB-DTPA, Olsen, Collwel, Bray 1, Bray 2 and Mehlich 2 and in the third cutting, AB-DTPA, Olsen, Collwel, Bray 1, and Mehlich 2 methods seems to be suitable extractants for assessing available P of soils in Hamadan province.

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Study of phosphorus reactions over time and the role of organic matter in the calcareous soils are important for the development of P fertilizer and manure management practices. The objective of this study was to determine the effect of applied manure on P availability and its chemical forms in the soil, over time. Eight samples were collected from semi-arid calcareous soils of Mashhad plain. The samples were treated with two levels of inorganic P (0 and 300 mg P kg^-1 soil as KH₂PO₄) and two levels of organic matter (0 and 1% cattle manure). The experiment was conducted in a completely randomized design with factorial arrangement. The treated soil samples were incubated for 2, 5, 10, 30, 60, 90 and 150 days, then analyzed for available P (Olsen-P). The result showed that only 17% of added phosphorus was available in P treatment at the end of experiment. In manure treated soils, this figure reached 34% for the same period of time. Application of manure along with P increased the recovery of applied P and CBD-P (Citrate-Bicarbonate-Dithionite). This may be due to the formation of P-organic complexes with Fe oxides. Application of manure in soil increased NaCl-NaOH-P considerably compared with P and P+OM treatments. It can be concluded that P originating from manure compared with inorganic-P may be more available for plants over the time.

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Phosphorus is often considered the most limiting soil nutrient for plant productivity. Several extractants have been typically used to measure available P. Organic and inorganic P fractions are not measured by common soil test, and thus fractionation schemes using various extractants have been developed over years to quantify the different chemical forms of P in soils. The objectives of this research were: i) to investigate the effect inorganic P fractions on Phosphorus availability ( Olsen procedure), and ii) to evaluate the relationships between these P fractions and Garlic (Allium sativum) plant indices. Soil inorganic P fractions were determined in 30 surface soil samples (0-30 cm) from various regions of Hamedan Province. Inorganic P fractions included dicalcium phosphate (Ca2-P), octa calcium phosphate (Ca8-P), P adsorbed by Al oxide (Al-P), P adsorbed by Fe oxide (Fe-P), P incorporated into Fe oxide (O-P), and apatite (Ca10-P). Total P and Organic P were measured in these soils. In order to evaluate the availability of different forms of P to plant, a pot experiment was conducted on Garlic plant. The treatments including two rates of P (zero and 150 mg kg-1) and 9 soils from 30 soil samples were arranged in a factorial experiment in a completely randomized design with three replicates. The results showed the total P with an average of 1501 mg kg-1 soil, and organic P comprised 19 % of the total P. The inorganic P fractions (Ca2-P), (Ca8-P), (Al-P), (Fe-P), (O-P), (Ca10-P) and residual phosphate (Res-P) comprised 4.7, 20, 8.7, 3.0, 2.8, 24 and 18 % of total P, respectively. Most of the inorganic P occurred as Ca-P and comprised 49% of total P. The correlation study between different P fractions showed that Ca2-P, Ca8-P, Ca10-P, and Al-P were significantly correlated with Olsen-P. This suggested that probably Olsen procedure essentially removed some P from these fractions. The results of pot experiment indicated that plant indices (relative yield and Yield efficiency) were significantly correlated with Ca2-P, Ca8-P and Olsen-P (P ≤ 0.05). P availability in the studied soils was influenced by Ca2-P and Ca8-P which could be used in a long period of time by plant.

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Phosphorus behavior in waterlogged soils is significantly different from non-waterlogged soils. Changes in available phosphorus and inorganic phosphorus fractions after waterlogging in the paddy soils of north of Iran were studied in a laboratory research. A factorial experiment in a completely randomized design with two replications was performed with factors of soil at 14 levels (10 alkaline-calcareous and 4 non-calcareous or acid soils) and duration of waterlogging period at three levels (0, 30, 90 days). At the end of waterlogging period, phosphorus fractions in calcareous soils by Jiang and Gu method and in non-calcareous soils by Kuo method and available-P by Olsen method were determined. The results showed that the level of available-P in all soils was increased 90 days after waterlogging (on the average 2.3 times). In general, all P fractions were changed significantly after waterlogging and the amount of change was different depending on P fraction, soil type, and duration of waterlogging period. These results indicated the complex behavior of P in soils. The Al-phosphates were increased in 12 out of 14 calcareous and non-calcareous soils 90 days after waterlogging compared with air-dry soil. The Fe-phosphates were decreased in 9 out of 10 calcareous soils 90 days after waterlogging compared with air-dry soil while the effect of duration of waterlogging period on the Fe-phosphates in non-calcareous soils was not significant. The readily soluble-P in non-calcareous soils increased 30 and 90 days after waterlogging. The results indicated that some inorganic P fractions transformed into other fractions and probably organic P transformed into inorganic P during soil waterlogging period.

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The ability of different soil tests in predicting soil phosphorus (P) is important in soils amended with municipal sewage sludge. The objective of the present study was to evaluate several chemical extractants to estimate available P for bean growing in 10 calcareous soils amended with municipal sewage sludge from Chaharmahal-Va-Bakhtiari province under the greenhouse conditions. For this purpose, the soil samples were incubated with sludge at a rate of 39-ton sludge ha–1. The amount of available P of the soil samples was determined by Olsen, Colwell, ammonium bicarbonate-DTPA, 0.01 M calcium chloride, BrayІ, ІІ, Mehlich І and ІІ methods. A pot experiment in a completely randomized design was conducted to evaluate the bean plant indices. The results showed that the amount of extractable P with the above methods decreased in the following order: Colwell> Bray ІІ> Mehlich ІІ> Olsen> Ammonium bicarbonate DTPA> Mehlich І> Bray І> 0.01M chloride calcium. The extractable P with 0.01M chloride calcium, Mehlich І, ІІ Colwell and Olsen methods correlated significantly with plant indices (P concentration and P uptake). Thus, mentioned methods could be used to estimate plant-available P in the soils amended with sewage sludge.

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