نشریه پژوهشهای خاک (علوم خاک و آب)
سال بیست و پنجم شماره 4 (زمستان 1390)

The first Iranian chemical fertilizer was produced in1945 in a fertilizer plant in Karaj and the first known research report about the use of chemical fertilizers was published in 1961, one year after the establishment of Soil Fertility Office of Iran by Food and Agriculture Organization (FAO). The primary objectives of the fertilizer research in those early years were to: a) demonstrate the beneficial effects of chemical fertilizer applications, and b) encourage the farmers to use as much chemical fertilizer as they could to obtain the highest amounts of crop yield. However, the harmful effects of over-fertilization on human and animal health and environment soon became apparent and forced the researchers to redefine the objectives and encourage the farmers to, at least partially, substitute chemical fertilizers with animal manures, biosolids, biofertilizers, etc. The latter materials are believed to be friendly to the environment. The present article reviews the reports of Iranian researchers during the last 50 years to highlight the past accomplishments and shortcomings in order to be able to draw a road map for the future research activities in the field of fertilizer production and use in Iran.

The long-term use of heavy-weight agricultural machinery has caused extensive compaction in soils, while information about soil compaction effects on growth and yield of crops in saline soil is scanty. To study the interactive effect of soil compaction and salinity on macronutrient elements uptake by wheat grain, a factorial pot experiment was conducted on loamy soil, arranged in randomized complete block design with three replications. The treatments were two levels of soil salinity (saline and non saline) and five compaction levels (0, 5, 10, 15, 20 percent of compaction). Different compaction levels were achieved at 15% moisture level by dropping 2 kg weight, controlled by tripod stand, from 0.3 m height inside the soil filled pots. Natural saline water was used to provide the desired salinity level of soil (6 dS m-1).The amount of grain nitrogen, phosphorus and potassium were measured and statistically analyzed. The results showed that the soil compaction significantly (p<1%) decreased uptake of N, P, K in grain wheat. Salinity decreased the amount of N, P, and K in grain significantly at %5, %1, and %1 levels, respectively. Also, the interactive effect of soil compaction and salinity on the amounts of nitrogen and potassium was significant at %1 level, i.e. the amount of nitrogen and potassium decreased with the increase in soil compaction in saline treatment, however, this interactive effect on grain P was not significant.

Organic matters have positive effects on soil physical, chemical, and biological properties and its fertility as well. Because of low organic matter content in Bushehr Province soils (in southern Iran), a 5-year study was carried out in randomized block design, using 8 treatments with 7 organic matter sources: M1) control, M2) cow manure, M3) poultry manure, M4) clover as green manure, M5) Palm leaves compost, M6) sesame residues, M7) salicornia residues and M8) urban waste compost, at 2 rates with 3 replications. Clover was planted in the first year followed by onion, faba bean, spinach, and canola, respectively, in the following years. The results showed that the effects of organic matter on plants yield were significant until three years. At the end of the experiment, soil samples were taken from different treatments and their chemical and physical properties were analyzed. The results showed that, with application of organic matter to the soil, E.C and saturation percentage (S.P) increased. On the other hand, soil bulk density declined significantly. Soil organic carbon, phosphorous, organic nitrogen, and potassium did not have significant differences with the control treatment.

Redox potential and pH are two soil conditions that exert major influence on the solubility and bioavailability of metals including copper (Cu). A study was conducted to investigate the effect of waterlogging on fractions of Cu in four soils with different pH values. Alfalfa powder, as an organic material, was also applied to induce more severe reducing conditions in the waterlogged soil samples. Bulk samples were collected from four cultivated areas in Iran: an acid soil from a tobacco field, a neutral soil from a rice paddy around Anzali wetland area, and two calcareous soils from wheat and alfalfa fields. The soil samples were treated with 0 and 2% alfalfa powder and then incubated for 12 weeks under two aerated (60% water holding capacity) and waterlogged (1:2.5, soil: water suspension) conditions at constant temperature (25oC). Subsamples were taken after 1and 12 weeks of incubation and various fractions of Cu were also extracted using a sequential extraction technique. The results in both conditions (aerated and saturated) showed that alfalfa powder application increased soluble and extractable Cu initially, but, during the incubation time, decreased them in almost all soils. However, in waterlogged condition, this treatment, increased Cu concentration in amorphous iron oxides (AFeO) fraction and decreased that in residual (RES) fraction in all soils, except the one taken from the rice fields. The small changes in the Cu fractionation in rice soil may be attributed to the neutral pH as well as the higher organic matter and the initial waterlogged condition as compared to the other soils. This treatment also increased Cu concentration bonded to carbonate (CAR) only in the two calcareous soils. The decrease in redox potential induced by waterlogging increased the mobility factor of Cu, indicating enhanced Cu availability.

The objective of the present study was to investigate the influences of crude oil and various N forms application on C dynamic in a sandy soil. The experiment was conducted as factorial (3×4) arranged in a completely randomized design with three replicates under laboratory conditions during 126 days. Sandy soil samples were first contaminated with 5% and 10% crude oil levels and, then, N salts of KNO3, NH4Cl, and a mixture of them were added. Soil samples were placed at 25±1°C in incubator for 126 days to determine microbial respiration at weekly intervals. Results indicated that N addition to sandy soil would cause soil microbial communities stimulation. The addition of crude oil and N simultaneously, caused the 10% oil level and NH4-treated soils to show the maximum C mineralization. In short, crude oil has positive and negative interactions with soil microorganisms. However, application of N fertilizes in proper form to petroleum-polluted environments may cause the reduction of harmful effects of toxic hydrocarbon compositions on soil microbial communities.

Studying concentration distribution of heavy metals is necessary for soil pollution monitoring and maintaining environmental quality. This study maps the spatial distribution of concentrations of heavy metals, namely, copper, chromium, arsenic, and antimony in an area of ​​19,546 km2, in Hamedan Province. For this purpose, by using a systematic stratified random sampling, 286 samples of surface soil (0-20 cm) were collected and total element concentrations and soil characteristics including pH, organic matter, percent clay, silt, and sand were measured. Zoning map of the concentration of antimony, copper, and chromium were obtained by using ordinary kriging and exponential model, while for arsenic ordinary kriging and spherical model were used. Analysis of zoning map of these heavy metals, land use map, and geological maps showed that arsenic, antimony, copper, and chromium are of geological origin.

Arsenic abundance in calcareous soils of Qorveh watershed, which is the most important agricultural region in Kurdistan Province, has caused arsenic pollution in agricultural products and water resources. In an attempt to investigate the relationships between arsenate (as less soluble fraction of soil arsenic) and the soils physico-chemical characteristics, eight pedons from the most polluted parts across the study area were sampled. Analysis of the results for the 38 soil samples revealed significant relationships between arsenate (considered as major less toxic fraction of soil arsenic) with sand, silt, organic carbon, free iron oxides, nitrate, and phosphate. The most significant relationship found was between arsenate and free iron oxides (r=0.748, α=0.01). Regarding the low quantities of free iron oxides among the studied soils, application of iron fertilizers or iron soluble compounds alongside with efforts to improve soil pH are recommended to reduce arsenic solubility and, consequently, arsenic pollution in the studied soils, while application of nitrate and phosphate fertilizers need to become limited as well.

Measurement of some important soil characteristics may be difficult, time-consuming, and expensive. Thus, it is helpful to predict these properties using easily-available soil properties. These relationships and/or functions are called pedotransfer functions (PTFs). This study was conducted to derive PTFs for estimating field capacity (FC), permanent wilting point (PWP), and cation exchange capacity (CEC) of soils in Kerman Province. Hundred soil samples (0‒30 cm layer) were collected from different locations in Kerman Province including: Kerman, Bardsir, Rafsanjan, Shahre-Babak, Sirjan and Orzoueiyeh of Baft. Then, FC, PWP, CEC, clay, silt, sand, carbonate, organic matter and gypsum contents of the soils were measured. In the regression method, clay, sand, and gypsum contents significantly affected the FC prediction, whereas clay content entered as effective input in the derived model for PWP, and clay and organic matter contents had significant effects on the CEC. Coefficients of determination (i.e. R2) of 0.86, 0.45 and 0.94 were calculated for FC, PWP, and CEC regression models, respectively. The best PTFs were obtained by artificial neural network (ANN) for FC, PWP and CEC with 6 hide layers and including all the input variables (R2 values of 0.98, 0.93 and 0.99, respectively). The accuracy of ANN predictions was greater than that of regression method. Results revealed that regression models can be applied with acceptable accuracy if a few easily-available characteristics are measured. The ANN method presented highly accurate results when the number of known easily-available characteristics increased. The accuracy of ANN decreased with reducing the number of inputs.

Aggregate breakdown and splash particles are the most important results of raindrops impact on soil surface. The study was conducted to investigate the temporal variations of breakdown and splash processes in a virgin marl soil in Zanjan Province. The experiment was carried out as a completely randomized design with eight rainfall duration treatments and three replications, in 2010. Twenty four flat boxes with dimensions of 30 cm× 40 cm were filled with soil aggregates (6-8 mm). The aggregates boxes were placed under a rainfall simulator with a constant intensity of 40 mm h-1.The aggregate breakdown values was obtained based on comparison of the mean weight diameter of the aggregates before and after rainfall events. The splash values were determined from the dry weight of soil particles that had splashed out around the boxes during each rainfall event. Based on the results, there were significant relationships between the rainfall duration and both the aggregate breakdown (R2= 0.99, p<0.01) and the particles splash (R2=0.95, p<0.05). The aggregate breakdown value was low at the beginning of rainfall (7.5 min), but it increased with increasing rainfall duration and, subsequently, soil surface was crusted in 45 min. At this time, aggregate breakdown and particles splash values were almost maximized. After 45 min, aggregate breakdown and particles splash values were negligibly increased due to crust formation at soil surface. There was a significant relationship between the particles splash and the aggregate breakdown (R2=0.98, p<0.05).

In order to evaluate the effects of plant growth promoting rhizobacteria (PGPR) on some quality and quantity traits of button mushroom (Aaricus bisporus) in different industrial and agricultural wastes as growth beds, a factorial experiment was conducted, using a completely randomized design with three replications. Five different beds were used containing wheat straw as the main substance and powdered supplements of fish meal, slaughter-house wastes, olive wastes, and cattle and chicken manures. The beds were inoculated with mixture of Bacillus and pseudomonas, except the uninoculated control. The results indicated that the effects of bed types, PGPR inoculation, and their interactive effects were significant on fresh and dry weight, nutrient elements concentrations, and protein contents of mushroom, but had no significant effects on the number and ash contents of mushrooms. The highest fresh weight (751.5 gr plot-1) of the mushrooms were measured in the bed with cattle manure inoculated with PGPR, whereas the lowest (592.6 gr plot-1) were obtained from the bed containing slaughter-house wastes without PGPR inoculation. Also, the highest (7.1%) and the lowest (4.4%) dry matter of the mushrooms were obtained from the bed containing chicken manure with PGPR inoculation and the bed containing fish meal wastes without PGPR inoculation, respectively. The highest protein contents (29.25%) and concentrations of N, P, Mg, Zn, and Cu were obtained from the bed containing fish meal wastes with PGPR inoculation, while the bed containing cattle manure without any inoculation and the bed containing olive wastes with PGPR inoculation had the lowest protein contents (17.27%) and the highest Fe concentration, respectively. In general, in this experiment the effect of PGPR on fresh and dry weight as well as on protein contents of button mushroom was significant and positive.