نشریه پژوهشهای خاک (علوم خاک و آب)
سال بیست و پنجم شماره 3 (پاییز 1390)

Determining soil parameters variability is a great necessity for precision agriculture. To achieve higher yield with better management, knowledge of physico-chemical properties of soil and nutrients critical levels in the fields is essential. In this regard, geostatistics is one of the methods recently used for investigating the spatial variability of soil properties. In this study, 188 soil samples were taken from the eastern farms of Mazandaran Province and were analyzed for their pH, Organic Carbon (OC), CaCO3, P, K, Fe, Mn, Zn, Cu, and soil texture, in 2009. The spatial correlation of variable Zn and the best fitted model (Gaussian model) were determined by variogram. The effective range of this value was 40 km. In order to determine the distribution map, interpolation methods, including Kriging, Inverse Distance Weighted (IDW) and Splines were used. Moreover, the precision of these interpolation methods was calculated through mean base error (MBE), mean absolute error (MAE) and Root Mean Square Error (RMSE). A pot experiment with soil samples collected from 29 fields out of the 188 studied fields and containing different Zn concentration was conducted to determine the critical level of soil in response prediction of soybean (Glycine max L.) to Zn fertilization. The experiment was done in a factorial arrangement in randomized complete block design with three replications (174 pots), in the Agricultural Research Center of Mazandaran Province. Soil samples from 29 fields were considered as factor 1, and two Zn fertilizer treatments (0 and 10 mg Zn kg-1 as zinc sulfate) as factor 2. After harvesting and relative yield determination, the critical soil Zn concentration was found to be 1.40 mg Zn kg-1. This finding was based on pot study for obtaining 95% relative yield, using Cate-Nelson graphical method. Furthermore, using the probability map with Indicator Kriging method revealed that about 80 percent of soils in the studied region had Zn deficiency.

In recent years, the increment of atmospheric CO2, which is one of the main green house gases, has caused the global warming and climate changes. It has unfavorable effects on environment and humankind life on earth. Whereas forests and afforestation regions in degraded and uncultivated lands have significant influence on the carbon sequestration. This research was done in Robinia Pseudoacacia and Fraxinus rotundifolia stands and the surrounding degraded range as blank and the sequestrated carbon was measured. Besides, the relation between some physical and chemical properties of soil and soil organic carbon (SOC) was investigated. The results showed that total sequestrated carbon in unit area of Robinia Pseudoacacia and Fraxinus rotundifolia stands were, respectively, 78.19 and 48 ton/ha, while it was 10.8 ton/ha in degraded rangeland. The amount of SOC in the first layer of soil was more than the second layer in the two mentioned stands, but it was the opposite in the blank. Also, the results of step-wise regression analysis indicated that pH, sand, and nitrogen content were, respectively, the most important factors affecting soil organic carbon content. The results of correlation analyses showed that there was a positive significant relation between SOC with gravel and sand percentages, but it had a negative significant relation with pH, silt, and clay percentages. The economical value of this amount of carbon sequestration with the two mentioned stands was calculated at about 10.4 and 2.5 millions dollars, respectively, over the total area of Chitgar Park.

Copper (Cu) and manganese (Mn) deficiency have been reported in soils of Iran. These nutrient deficiencies could be due to high soil pH and nutrients imbalance between Cu and Mn and other nutrients including Ca, Mg, Fe, and Zn in calcareous soils. In order to study the effect of Cu, Mn, and Cu × Mn interaction on growth and nutrients imbalance in silage corn (Zea mays L.), a factorial experiment of 4 × 4 was carried out in a completely randomized design with three replicates in a calcareous soil (fine, mixed (calcareous), mesic Typic Calcixerepts) under greenhouse conditions. Treatments consisted of four levels of Cu (0, 5, 10, and 20 mg kg-1 from CuSO4. 5H2O), and four levels of Mn (0, 10, 20, and 40 mg kg-1 from MnSO4. 4H2O) with three replicates. Results indicated that Mn significantly increased corn shoot dry matter yield (SDMY), but application of 20 mg Cu significantly decreased SDMY. Other levels of Cu had no significant effect on plant growth. Reduction of SDMY might be due to the antagonistic effect of Cu on Fe uptake and imbalance of Cu:Mn, Cu:Fe, and Cu:(Mn+Fe+Zn). Application of Cu increased Cu concentration and uptake in plant aerial part but had no effect on concentration and uptake of Mn. Addition of Mn decreased concentration of Cu but increased the plant uptake. Manganese decreased concentration of Fe but increased its uptake. Addition of Cu and Mn had no effect on plant Zn concentration, but Mn increased Zn uptake. Shoot: root ratio was not affected by Mn or Cu addition. The maximum SDMY was obtained by application of 5 or 10 mg Cu kg-1 and 20 or 40 mg Mn kg-1. The sufficiency range for Cu was 6 to 7 µg g-1 and 50 to 55 µg g-1 dry matter for Mn. The results of this study need to be verified under field conditions before making any fertilizer recommendation.

Soil test is necessary to identify optimal concentrations of phosphorus required for plant growth. A greenhouse experiment was conducted using 30 soils with widely different properties. Four extraction methods were used in this stduy including Olsen, Soltanpour, Mehlich-3, and saturation extract. The factorial experiment was arranged into a completely randomized design. Thus, rankings of the extractors studied based on their ability to extract phosphorus were as follows: Mehlich-3 >Olsen> Soltanpour> saturation extract. The results showed that saturation extract is not a suitable method for phosphorus extraction. Among the methods studied, Olsen was the most appropriate one because of having the highest correlation coefficient with plant factors such as dry matter yield and phosphorous uptake. On the other hand, Mehlich-3, as a simultaneous extractor of macro- amd micro-elemnts, is a good alternative for Olsen method in gypsiferous soils.

In order to evaluate organic phosphorus fertilizer and phosphorus biofertilizer Barvar 2, as a substitute for chemical P fertilizers in wheat production, an experiment was conducted during two growing seasons of 2005-06 and 206-07, in a field in Bardsir city, Kerman Province, using a randomized complete block design with 12 treatments and 3 replicates. Treatments were T1=150 kg/ha organic P fertilizer + 100gr Barvar 2, T2=100 kg/ha organic phosphorus fertilizer +100gr Barvar 2, T3=50 kg/ha organic phosphorus fertilizer + 100 gr Barvar 2, T4=50 kg/ha organic phosphorus fertilizer,T5=100 kg/ha organic P fertilizer, T6=150 kg/ha organic phosphorus fertilizer,T7=50 kg/ha triple super phosphate + 100gr Barvar 2, T8=100 kg/ha triple super phosphate + 100gr Barvar 2, T9=150 kg/ha triple super phosphate + 100gr Barvar 2, T10=50 kg/ha triple super phosphate,T11=100 kg/ha triple super phosphate and T12=150 kg/ha triple super phosphate. The measured properties were: grain yield, ears/m2, grains per ear, thousand kernel weight and soil phosphorus after harvest. According to the results, the highest yield (8477 kg/ha) was obtained by application of Barvar 2 together with 150kg/ha organic phosphorus fertilizer, which showed a yield increase of 58.4% in comparison with the control treatment i.e. 50 kg/ha triple super phosphate(T10) (local practice based on soil analysis). The highest yield components measured were 43.3 gr thousand kernel weight, 466ears/m2, and 47.67 grains per ear in treatment T1, which, in comparison with the control, showed an increase of, respectively, 28.3%, 39.2% and 32.9%. The highest phosphorus fixation in soil was 9.78 mg/kg and belonged to the treatment of 150 kg/ha triple super phosphate(T12), which had no significant difference with treatments T11.

Canola planted in rotation with summer crops (e.g. corn) would cause sowing delay, yield reduction, and economic income of farmers. Based on previous research, the most suitable sowing date for canola is about 15-30 November. To investigate effects of late planting on canola yield and nitrogen use efficiency (NUE) a study was conducted in randomized complete blocks design in split plots with three replications. The experiment was carried out for 2 years (2004-2006) in Shavoor agricultural research station of Khuzestan Province. Treatments included four sowing dates, 11th Nov, 21st Nov, 1st Dec and 11thDec in the main plots, and five nitrogen levels (0, 50, 100, 150 and 200 kg N ha-1) in the sub plots. Results showed that sowing date and nitrogen levels had significant effects on yield components and nitrogen use efficiency (α<0.01). Delay in sowing date from Nov (11) to Dec (11) reduced 24.6 pods /plant, 3.1 seed/pod, 0.43gr of thousands seed weights, 1084 kg.ha-1 seed yield, 5.6 % oil seed, and 6.9 % NUE. Increasing nitrogen application rate from 150 to 200 kg N ha-1, increased yield and yield components significantly, but NUE was decreased about 2.2 %. It can be concluded that since normal sowing date (11th Nov- 21st Nov) with 150 kg N ha-1 can produce the highest yield, late planting date is not recommended in Khuzestan Province conditions.

In order to evaluate quality of the statistical methods used in some agricultural research, a total of 100 final research reports, graduate theses, and published papers in Iranian agricultural journals were selected by simple random sampling. Then, using a designed check-list, each sample was reviewed for the factors such as design of the experimental methods, method of treatments randomization, number of investigated treatments, sampling methods, number of measured traits or variables, and the statistical tests and methods applied in the investigation and analyses of the results, methods of mean comparison, frequency distribution of statistical tests and design of experiments, the software used, quality of statistical reference, the way statistical tables and graphs were used in presentation of the results, and whether or not a statistical expert participated or was consulted in the research. After reviewing the Check-Lists, the most common problems and errors in the samples were divided in two groups: first, errors related to design of the experiment and, secondly, errors related to the analysis of the results. Afterwards, the importance of correct decision with respect to each of the abovementioned factors and the impact of negligence in each case were evaluated. Finally, the items whose application in the experimental design or result analyses were not essential, such as describing mathematical model of the design or experimental layout, but could affect experiment implementation and results presentation, were mentioned. According to the results, adequate training in statistical method, design of experiments, and use of the related soft wares would enhance the reliability and efficiency of agricultural research.

In this study, effects of short-term domestic wastewater application on some soil physical properties were analyzed for determining the impacts of four factors including quality of irrigation water (normal water, raw wastewater and treated wastewater), soil texture (two loamy soils), methods of irrigation (surface and subsurface), and presence or absence of plants. The study was carried out in the green house with three replications in 2008. Experimental period was four months and the crop was sorghum. Physical properties of soils, namely, bulk density and basic infiltration rate were measured with completely randomized design in three replications and water retention curves were determined with RETC software and compared with the measurements at the end of the experiments. The analysis of the results on water retention curves for different treatments indicated that the use of wastewater for irrigation resulted in an average increase of the available water capacity of soils by 4% (volumetric) and 24% relative value. Soil water retention on volumetric basis was increased at some tension points in the wastewater irrigated treatments by 9.5 to 10% at 0.1-bar, 4.5 to 5% at 0.33-bar and 1.5 to 2% at 1-bar, on the average. Such results could be related to the improvement of the soil structure. Overall, the basic infiltration rates were somehow increased in soils irrigated with raw and treated wastewater. However, the differences were not statistically significant. Also, soil bulk density was not affected by various treatments because duration of this study was not long enough. Generally, according to the current and previous studies, soil water retention was increased, particularly in the presence of plants, due to addition of organic material to the soil by wastewater and increasing magnesium concentration, in line with the improvement of the soil structure.

Recently, oil total petroleum hydrocarbons (TPHs) are considered important sources of environmental contamination. One of the effective ways to eliminate this contamination from soils is land treatment method i.e. treatment of the contaminated soil by ventilation and provision of better bacterial living condition. Oil substances used for drilling oil wells, have caused soil contamination in Khuzestan Province. Therefore, the objective of this research was to evaluate some remediation methods to decrease soil contamination by oil. A randomized complete design study was conducted with three treatments including control (no ventilation), O1 (daily ventilation), O2 (every four days ventilation). The study was done in pots using soils contaminated by oil drilling base mud for 10 weeks. Carbon dioxide concentration (as an index of microbial activity) and TPHs amounts were measured after 2, 5, and 10 weeks for each treatment. Results showed that ventilation treatment significantly (p<0.05) increased microbial activity compared with the control. Carbon dioxide concentrations in O1 and O2 treatments were, respectively, 16 and 20 percent more than the control Also, TPHs in O1 and O2 were, respectively, 7.7 and 11.7 percent lower than the control. It can be concluded that land treatment (ventilation in this study) can be used as an effective method for remediating soil contaminated by oil drilling bas mud.