JWSS - Journal of Water and Soil Science

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Twenty-two surface soil samples (0-20 cm) from Fars province were extracted by five extractants (i.e., DTPA, 1.5 M NH₄H2PO₄, 0.1 NH₃PO₄, 0.05 MNa2EDTA, and 1% Na₂EDTA) and used in a 7-week greenhouse experiment which was a 22 × 3 factorial with 22 soils (clay 16-63% pH 7.8-8.2 electrical conductivity 0.32-1.78 dS m^-1 calcium carbonate equivalent 28-63% organic matter 1.1-4.9% cation exchange capacity 9-27 cmol kg^-1 and DTPA-extractable Mn 4-24 mgkg^-1), 3 levels of applied Mn (0, 10, 20 mg Mn kg^-1 as manganese sulfate), 3 replications, and soybean [Glycine max (L.) Merr., cv. Williams]. Application of Mn significantly increased top dry weight by 4 to 104%, averaging to about 12% over the control. But the increase in Mn concentration was not significant. Total Mn uptake also significantly increased but the apparent recovery of the applied Mn was very low (i.e., 0.05%). Soil pH, calcium carbonate equivalent, and clay content were found to be the properties influencing the extractability of Mn. The DTPA-extractable Mn, alone (with a critical level of 13 mg Mn kg^-1) or along with some soil properties, was the only form of Mn that could reasonably predict the plant responses.

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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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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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Sorghum (Sorghum bicolor L. Var. Speedfeed) is a major forage crop in Birjand Region, and phosphorus (P) plays an important role in its nutritional value. During a field campaign, eighty soil samples from the region were collected and analyzed. Among them, 24 samples varying in physico-chemical properties and available P were selected. Five extractants were used for measuring sorghum available P as follows: 1) 0.5 M NaHCO3, pH=8.5, shaken for 30 minutes (Olsen's method), 2) 0.5 M NaHCO3, pH=8.5, shaken for 16 hours (Colwel's method), 3) 0.0025 M Na2-EDTA, pH=7 (EDTA method), 4) 1 M NH4HCO3, 0.005 N DTPA (Soltanpour and Schwab's method), and 5) Water (Paauw's method). A greenhouse experiment using a completely randomized design was carried out with 24 soil samples, two treatments of 0 and 90 mg P/kg soil and three replicates. Results indicated that all five extractants are suitable for prediction of sorghum available phosphorus, but Olson and Paauw's methods are preferable. The results also show ed that the critical levels of soil phosphorus for sorghum by Olsen, Colwel, EDTA, Soltanpour and Schwab and Paauw methods are 17, 24, 14, 7 and 2.5 mg P/kg soil, respectively. Statistical analysis indicated that soil pH, clay percentage and organic carbon significantly affected sorghum available phosphorus.

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In order to assess the status of the iron (Fe) chlorosis of plane trees in green space of Isfahan city, the chlorosis intensity of 73 trees in different regions was recorded as (1): low (less than 5% of leaves), (2): moderate (less than 50% of leaves), (3): severe (more than 50% of leaves), and (4): very severe (more than 95% of leaves). The whole leaf (with petiole) samples were taken from the top and bottom of each tree, separately, during 2008 and 2009. Then selected chemical properties of the leaves were analyzed.  The results showed that in more than 95 and 71% of the young leaves, Fe concentration was less than the critical deficiency level (202 mg/kg). Concentration of Fe in the older leaves of all plane trees even those with slight symptoms of chlorosis was less than the critical level (382 mg/kg). No significant relationship was found between the leaf zinc concentrations and intensity of iron chlorosis. In more than 92 (in the first year) and 87% (in the second year) of the plane trees, Zn concentration of young leaves and in all trees, Zn concentration of old leaves were less than the critical deficiency concentration (23 mg/Kg). The comparison between concentrations of Cu in the leaves with its critical deficiency level showed that more than 90% of young and old leaves accumulated toxic levels of Cu in both sampling years. In regard with the sufficient range of P, about 79% of the trees in the first year and 53% in the second year accumulated excess levels of this nutrient in their young leaves. This condition was slightly modified for the older leaves so that excessive concentration of phosphorus in mature leaves was not observed in the first year and in the second year, only about 29% of the samples had concentrations higher than critical levels.