نشریه مهندسی زراعی
سال سی و هفتم شماره 1 (تابستان 1393)

Good soil structure is important for crop growth. One of the main characteristics of the soil structure، which affects the plant growth and its yield، is soil aggregate size distribution. There are several ways to characterize the stability of soil aggregates such as the mean weight diameter (MWD). Researchers generally use MWD as the most important criterion to express the degree of soil fragmentation of a loamy sand soil. In this study، the effects of soil moisture content at two levels، tractor forward speed at five levels and working depth at five levels were investigated on soil fragmentation for seedbed preparation using a combination of primary and secondary tillage implements of subsoiler، moldboard plow and disk harrow as conventional tillage combination in the region. Field experiments were carried out in the research field of University of Mohaghegh Ardabili based on a completely randomized design (CRD) with three replications. In this paper، an intelligent model based on Mamdani fuzzy model was developed to predict soil fragmentation during tillage practice. The model included 50 laws. Analysis of variance showed that the main effects of travel speed and working depth were significant on the soil fragmentation (at probability level of 1%). By increasing the forward speed، working depth and soil moisture content، MWD of aggregates significantly increased. Moreover، the interactive effect of speed and working depth was significant (at probability level of 1%). Also، using the fuzzy model، the optimum range of the investigated parameters was achieved 12-16% for moisture content of a loamy sand soil، 5. 92 km/h for travel speed and 15 cm for working depth.

Phytoremediation، a relatively new and an environmentally friendly technology، is the use of plants for the removal of pollutants from contaminated soils. A greenhouse pot experiment was conducted to evaluate the heavy metal (lead، zinc and copper) accumulation of Zea mays، Helianthus annuus، Cannabis sativa and Brassica napus. Plants were grown in two soils; one from Ahangaran Lead-Zinc Mine، and the other from an agricultural soil. The shoot and root dry weight، heavy metal concentrations in shoot and root، translocation factor (TF)، Enrichment factor (EF) and heavy metal fractions were measured. The distribution of different lead and zinc fractions were revealed the following order: residual > carbonate > organic > exchangeable. However، for copper the order was as residual > organic > carbonate > exchangeable. The minimum lead concentration (25. 50 mg kg-1) was observed in Z. mays shoot tissue and the maximum (301. 30 mg kg-1) in C. sativa shoot tissue. Lead TF ranged from 0. 72 to 0. 96 and decreased in the following order: H. annus > C. sativa > B. napus > Z. mays. Zinc TF changed from 0. 70 to 0. 99 and as H. annus > Z. mays> C. sativa > B. napus، and copper TF turned from 0. 49 to 1. 83 and as H. annus > C. sativa > B. napus > Z. mays. The EF value of lead varied from 0. 24 for Z. mays to 0. 48 for C. sativa، from 0. 75 for Z. mays to 1. 01 for H. annus regarding to zinc، and the copper EF value ranged from 0. 39 for C. sativa to 1. 42 in H. annus. Although H. annus and C. sativa accumulated lead more than Z. mays and B. napus، none of the plants was hyperaccumulator for lead، zinc or copper.

In order to determine the effect of plant growth promoting bacteria Pseudomonas fluorescens on yield and nutrient availability in corn some special materials like mesoporous silica nanoparticles، vermicompost، bentonite and a mixture of all were inoculated by the bacteria and preserved for six months. Soil and seeds were treated by the inoculants. The experiment was set up in a randomized complete block design with three replications. The treatments comprised of three inoculants and two fertilizers including diammonium phosphate، single super phosphate and control (without any phosphorus fertilizer). After 60 days of corn emergence، some plant growth indices and the concentration of some elements in plant shoots were measured. The results demonstrated that Pseudomonas fluorescens inoculant significantly increased phosphorus shoot content، total yield and chlorophyll by 74، 46 and 22. 1%، respectively compared to the control treatment (P<0. 05)، but it did not show any significant difference with phosphorus fertilizer treatments (P>0. 05). The vermicompost inoculants could significantly (P<0. 05) increase zinc and iron contents of shoots by 114 and 53. 6%، respectively in comparison to the control treatment. Orthogonal comparisons of the two methods of seed and soil inoculation showed the efficiency of seed inoculation on shoot phosphorus at 5% level، but no significant difference was observed between these two methods for other measured characteristics (P>0. 05).