Iranian Journal of Soil Research
Year:2018 | Volume:32 | Issue:2 |Papers Count:14

In order to evaluate the effect of nitrogen (N) and canola residuals on yield and improve the physical and chemical properties of soil in wheat-canola rotation, a split block experiment was carried out in a randomized complete block design (RCBD) with three replications for four years (2010-2014) at Chahartakhte Agricultural Research Station in Shahrekord. The treatments consisted of three rates of N (N1: 0, N2: 25, N3: 50 kg N. ha-1) in the main plots and four rates of canola residues (M1: complete removal of plant residues from plots, M2: Turning and removal of residues with plow, M3: incorporating residues with surface soil by means of discs and M4: first incorporating residues with disks and then turning into the soil with plow) in the subplots. The analysis of variance results revealed that the effect of year was significant on biological and seed yield and weight of 1000 seeds. The maximum of these parameters was obtained in the second year. The effect of N was significant on biological and seed yields, protein percentage, leaf N, and weight of 1000 seeds. The maxima of these parameters were, respectively, 10061 and 3975 kg ha-1, 19%, 2. 9%, and 38. 7 gr and were obtained in N2 treatment. Different managements of residue showed a significant effect on biological and seed yield, harvest index, soil organic carbon, and weight of 1000 seeds. The maximum values of these parameters were, respectively, 10441 and 4186 kg ha-1, 4. 36%, 0. 77%, and 38. 7 gr and obtained in M2. The interaction effect of N and residues was significant on seed yield and weight of 1000 seeds. The maximum of the studied parameters was obtained in the N2M2 treatment. Considering the experimental results, the N2M2 treatment was suggested for wheat in Shahrekord region and regions with the same soil and climate condition.

The range of soil water content where plant growth is least limited by water potential, soil aeration or mechanical resistance is called least limiting water range (LLWR). This study evaluated the values of LLWR determined according to the procedures proposed by da Silva et al. with those calculated on the basis of sunflower plant (Helianthus annuus L) response (LLWRP). In both methods LLWR is taken as the difference between the two soil moisture limits designated as upper (θ UL) and lower (θ LL). In the first method, the two limits are determined basically from the soil moisture and soil resistance characteristic curves, almost overlooking the plant type and its particular needs or behaviors. In the second method, as proposed in this research, the two limits are determined based on the stomatal response in a sandy clay loam soil packed into PVC tubes (called pots hereafter) with 30 cm diameter and 70 cm height at three compaction levels (soil bulk density equal to 1. 75, 1. 55 and 1. 35 Mg. m-3) designated as D1, D2 and D3. Each pot was planted with three pre-soaked sunflower seeds and pots were kept under optimum condition until onset of the flowering stage. At this time two successive drying cycles were imposed and soil moisture and midday stomatal conductance were routinely measured. LLWRP were computed on the basis of relationship between soil matric suction and stomatal conductance. Results showed that on the basis of stomatal conductance behavior water uptake began at the soil matric suctions of 44, 16, 60 and continued up to 17394, 31614, 39983 cm in D1, D2 and D3 treatments, respectively. Appreciable differences were observed between LLWR and LLWRP particularly when the lower limit moisture suction (equivalent to θ UL for LLWR) was set at 330 cm (LLWR330). LLWR330 values of 0. 148, 0. 147 and 0. 080 cm3cm-3 were obtained for D1, D2, D3 treatments, respectively, which were 51, 49 and 63 percent lower than the corresponding LLWRP values. This differences imply that the two moisture limits (θ UL and θ LL) proposed by da Silva et al. may not be applied indiscriminately for all plants and thus need to be modified according to plant needs or responses.

Considering the widespread presence of the date palm groves in the southern provinces of the country, low rainfall, and high evapotranspiration necessitate the need for the pressurized irrigation systems in date palm grove and application of modern fertigation method. This experiment was conducted in a split plot based on randomized complete block design with three levels of irrigation including 60%, 80%, and 100 % of cumulative evaporation from class A pan in the main plots, and three levels of nutrition (without fertilizer use (control), localized placement (Chalkood), and fertigation) in the sub-plots, with 3 replications. The results showed that the nutrition of date palm (Chalkood or fertigation method) increased the yield of date palm by an average of 18%. Also, fresh weight, length, and volume of date fruit and weight of pulp increased by, respectively, 4%, 4%, 7%, while and 4. 4%, the weight of stone and ratio of weight of pulp to stone increased by, respectively, 5% and 4. 5%. Also, increasing the amount of irrigation water increased the yield and the quantitative characteristics of the date fruit, but its effect was not significant. According to the results of this study, proper date palm nutrition by Chalkood or fertigation method along with net irrigation level of 60% cumulative evaporation from class A pan, saved 40% in water use, without significantly reducing the yield.

Nitrogen (N) fertilizer plays an important role in crop yield and its quality. Excess nitrates may cause surface and groundwater pollution, through nitrate leaching and soil erosion. The uptake and distribution of nitrate in crops is important with respect to environmental concerns and the quality of crop products. This study was conducted in a randomized design at harvesting time on some vegetables such as Allium cepa L, Petroselinum crispum, vulgaris subsp, Anethum graveolens, Coriandrum sativum and Mentha Piperita in 7 fields in Zanjan Province. Concentration of nitrogen, nitrate, and activity of nitrate reductase enzyme in the vegetables as well as some physical and chemical properties of soil and water were determined. Results showed that, despite the same climatic conditions and crop management, the highest accumulation of nitrate was observed in samples of irrigation water, soil, and plants in the fields near the municipal sewage sludge outlet that were cultivated with leguminous plants i. e. beans and alfalfa, in previous years; therefore, no nitrogen fertilizer application was required. In all studied field, nitrate concentration in Allium cepa L and Petroselinum crispum was in critical range; however, nitrate concentration in 14. 3% of vulgaris subsp and Mentha Piperita vegetable fields and 28. 6% of Anethum graveolens and Coriandrum sativum vegetable fields were higher than critical range. Concentration of nitrate in vegetables had positive correlation with concentrations of plant nitrogen and water and soil nitrate content and had negative correlation with nitrate reductase activity. Also, significant differences were observed in nitrate reductase activity in various vegetables. Among the studied soil properties, soil nitrate concentration had an important role in nitrate accumulation in vegetables.

The recent study was carried out to evaluate the RUSLE and RUSLE2 models for predicting soil loss in stony rangeland hillslopes of Khamesan watershed using event data obtained from natural rainfall. For this purpose, total runoff and soil loss were measured during three years (2011, 2012 and 2013) in eighteen plots with 24 m long by 1. 8 m wide (six hillslopes with three replicates). The input data for both models were measured and monitored including soil characteristics, plant cover, ground cover etc. Twenty-four rainfall events were examined during the study period. Two models, particularly RUSLE2, estimated average annual soil loss relatively well, despite the overestimation. The results showed that both models, especially RUSLE2, was able to estimate single events soil loss relatively acceptable, especially in rainfalls with lower erosivity index (R2 (RUSLE)=0. 25, R2 (RUSLE2)=0. 53; EF(RUSLE)=0. 23, EF(RUSLE2)=0. 53). Calibration of the erodibility factor in two models led to considerable improvement of model efficiency (R2 (RUSLE)=0. 69, R2 (RUSLE2)=0. 82; EF(RUSLE)=0. 63, EF(RUSLE2)=0. 80). Comparison of estimations of two models showed that in all studied situations, RUSLE2 model had higher efficiency than RUSLE. It seems that with respect to characteristics of studied hillslopes on one hand and improvements of RUSLE2 model relative to RUSLE on the other hand, it has been led better estimates of RUSLE2. Generally, the results showed that in hillslopes with higher rock fragment cover and lime content, efficiency of non-calibrated two models was lower than other hillslopes. This result shows that more research is needed to examine the effect of these parameters on estimation of soil loss in two models, especially for the RUSLE.

Integral water capacity (IWC) is the integral of differential water capacity functions in the range of 0 to infinity soil matric potential multiplied by weighting functions each taking into account the effect of various soil limitations that may develop at a given soil matric potential domain and restrict soil water availability to plant roots. The domains selected for development of weighting functions in most studies have seldom been based on plant response, but rather arbitrary. The purpose of this study was implementing midday green leaf temperature (TL) as a plant-response-based variable to compute integral water capacity. For this purpose, a sandy clay loam soil passed through 4. 76 mm sieve was evenly compacted to three bulk densities of D1=1. 35, D2=1. 55, and D3=1. 75 g cm-3, each replicated thrice, in PVC tubes (called pots hereafter) with 30 cm diameter and 70 cm height. Sunflower (Helianthus Annuus L) seedlings were planted in the pots and, after their full establishment, two periods of wetting and drying cycles were imposed. By monitoring daily soil moisture content at the three depths in the pots and converting them to soil moisture suctions along with the midday TL measurements, a plant-responsebased weighting function was developed and integral water capacity (IWCP) was computed. Integral water capacity (designated as IWCG) was also computed by adopting the weighting functions proposed by Groenevelt et al. IWCP and IWCG in D1 treatment were obtained as 0. 187 and 0. 229 cm3cm-3, respectively. At the highly compacted D3 treatment, the corresponding values diminished to 0. 152 and. 038, respectively, equivalent to 19% and 84% reduction in soil water availability and reflecting the dominant effect of soil compaction on water availability. Averaged over the three compaction levels, IWCP and IWCG were 0. 169 and 0. 14 cm3cm-3, indicating that water availability determined on the plant response basis was 17% greater than that predicted by IWCG. This difference and over-susceptibility (84%) of IWCG to soil compaction imply that the soil suction domains proposed for the various soil limitations and the experimental relations employed in Groenevelt et al. approach to quantify their restricting effects as weighing functions need to be modified according to each particular plant needs or response.

Soil spectroscopy in the visible and near infrared (Vis-NIR) range has widely been used as a rapid, cost-effective, and non-destructive technique to predict soil properties. Since little data is available about soil properties determined by using this technique, the present research was carried out to evaluate the efficiency of Vis-NIR spectroscopy to estimate several soil properties in Bardsir area, Kerman Province. About 150 complex surface soil samples were collected from four different land uses from depth of 0-20 cm. Soil organic carbon, equivalent calcium carbonate, pH, and the amount of silt, clay and sand particles were measured by routine laboratory methods. Reflectance spectra were obtained from air-dried samples under controlled laboratory conditions using an ASD FieldSpec Pro spectroradiometer in 350-2500 nm wavelength range. Partial least squares regression was used for calibration of spectral and laboratory data using cross validation. Coefficient of variation for organic carbon, equivalent calcium carbonate, sand, silt, clay, and pH values were 0. 68, 0. 62, 0. 64, 0. 66, 0. 3, and 0. 01, respectively. Based on RPD values (Ratio of Prediction to Deviation), the precision of the prediction model for sand and silt contents was quite suitable, and for organic carbon and equivalent calcium carbonate it was suitable. However, the predictions of the model for clay content and pH were poor. Furthermore, standard normal variate (SNV) was the best pre-processing method to predict organic carbon, whereas, first derivative with SG smoothing (FD-SG) showed better estimation for carbonate, sand, and silt. Consequently, Vis-NIR spectroscopy is capable of predicting several soil properties at the same time. As the model accuracy is acceptable, it has the potential to substitute conventional laboratory analyses of selected soil properties.

Nowadays, considering the importance of food security, understanding the impact of climate change on land suitability for crop production has become an important issue. The main goal of the present research was to evaluate the climate change impacts on different rainfed crops land suitability under current and future climate change scenario in Miandoab region. For this purpose, Terraza and Almagra models were used in MicroLEIS DSS environment. Almagra model provides evaluation of the suitability of different land units for selected utilization types and Terraza model provides an experimental prediction for bioclimatic deficiency. Morphological and analytical data were obtained from 11 control soil units and saved in the SDBm soil database. Agro ecological data were obtained from Iran Meteorological Organization and saved in the CDBm climate database. Greenhouse gas emission scenarios were selected as future scenarios of climate change from models of Intergovernmental Panel on Climate Change (IPCC). The results revealed that, in the present conditions and in most of the different land units, the suitability order of crops are chickpea >melon> wheat. However, in the future it will be wheat> chickpea> melon. The most important soil limiting factors were salinity, texture, drainage, and lime content. The net effect of climate change on land suitability is negative, except for wheat, and therefore, in climate change conditions, the study area is unsuitable for production of chickpea and melon as rainfed crops. Loss of moisture with increasing drought index in the Terraza model showed that, in future, rainfed cultivation scenario seems to be highly affected by water stress.

Zinc (Zn) is one of the most important nutrient elements for plants, but its availability in calcareous soils is low. The availability of Zn for plants depends on relative distribution of its chemical forms in the soil, which is dependent on soil properties. The present research was conducted to investigate the distribution of chemical forms of Zn in two soils under almond and pomegranate trees using sequential extraction procedure. Results showed that the amount of DTPA extractable Zn in the surface soil under-canopy, surface soil-interspaces, subsurface soil under-canopy, and subsurface soil-interspaces were higher for almond cultivation compared to pomegranate by 12. 10%, 9. 91%, 19. 20%, and 21. 67%, respectively. The amount of available Zn on the surface soil under-canopy was higher compared to the interspaces of pomegranate trees by 9. 71% and in subsoil under-canopy was higher in comparison with interspaces by 10. 18%. The results showed that residual form was the highest chemical fraction of Zn followed by the Zn associated with iron oxides forms which are not available to trees. Generally, the amounts of the chemical forms of Zn were as follows: Soluble+exchangeable > organic-bound >Crystalline Fe-oxide-bound > Carbonate-bound >Mn-oxide-bound > Amorphous Fe-oxide-bound > residual. Overall, it appears that the canopy helps the trees in providing the essential nutrients and thus to have a better establishment in the area. The presence of higher organic matter under trees canopy is one of the most important reasons for the transformation of Zn from stable fractions to more available forms. Such effects were noticeable for almond canopy as compared to that of pomegranate.

One of the most important sources of agricultural water supply in arid areas is groundwater. Moreover, rain water percolation in the soil is the main source of groundwater recharge. Therefore, in this research, the efficiency of various mulches in increasing the percolation depth of rainwater was investigated in Shahrekord Plain. Eight precipitation events from the IDF curves of the study area with 2 and 5 years return periods were selected and the deep percolation of these rainfalls was tested in lysimeters with the same conditions and different mulches including gravel, sand, mixed sand and gravel, and the same soil texture without mulch. A total of 192 data were collected for soil moisture, air temperature and rain percolation. Furthermore, the equations for estimating the depth of rainwater percolation in each rainfall and the estimation of evaporation from soil under each mulch and soil without mulch were derived separately and the efficiency and accuracy of these equations were investigated using the Nash-Sutcliffe index and the coefficient of determination. The results showed that the derived relations had a coefficient of determination in the range of 0. 98-0. 99 and the Nash-Sutcliff index in the range of 0. 98-0. 96. Based on these equations and the water balance equation in soil, a soil moisture model was developed. Then, to evaluate the efficiency of mulches in increasing soil moisture and deep water percolation, this model was performed based on one year rainfall and temperature data of the study area. The results showed that the amount of percolation during this period in all studied mulches increased in comparison with the soil without mulch. The highest percolation amount was 17. 1% in gravel mulch, which shows 21% increase compared to the nonmulched soil. Therefore, mulching of agricultural land can increase aquifer recharging due to increased percolation of rainwater into the soil as one of the sources for supplying agricultural water. However, considering the positive effects of mulching in saving soil moisture, its implementation issues should be considered broadly when selecting this type of mulch.