m. bannayan

Cropping history can affect our knowledge about the compositions and diversity of weed communities in the soil. Weed Species composition and density are influenced by farming practices and vary from field to field and among areas within fields. Plants that escape control and produce seeds within the field can be considered as a major source of seed entering the soil. Crop rotation is an effective weed management tool which can change weed distribution pattern by increasing selection pressures. Two types of rotation including corn-winter wheat and fallow-winter wheat are the most common cropping systems in arid and semi-arid areas of Iran. The multiple tillage operations can affect the vertical distribution, germination and emergence of weed seeds in the soil. Weed seed bank density, species composition and diversity will change when crop management practices are altered.

A field experiment was conducted to evaluate the effects of corn-wheat and fallow-wheat crop rotations on weed seed bank dynamics and seedling population during 2016-2018 growing season at Shiraz University. The fields divided into 10 by 10 meter grids. Soil samples were taken from 0-15 and 15-30 cm depths by soil sampler (auger) with 10 cm diameter. These samples collected after seedbed preparation and before crop sowing from 144 points. The samples of each depth were mixed together, placed in black plastic bags, and transferred to the laboratory. Then, 250g of the total soil was weighed and separated. These samples was placed in silk bags and washed with low water pressure. Finally, weed seeds dried, identified and counted to the level of species using a binocular stereomicroscope. Those seeds that were resistant to forceps pressure assumed as healthy seeds. Weed seedling population were calculated using a quadrat before and after application of herbicide at the same points were seed bank was carried out. Geostatistics technique was used to investigate density and spatial distribution of weed seedlings in two different crop rotations.

The highest frequency of weed seed bank belongs to Portalaca oleracea, Amaranthus retroflexus, Chenopodium album and Lamium amplexicaule. Relative density of P. oleracea and A. retroflexus seeds increased in corn-wheat rotation compared with fallow-wheat. The results showed that weed seed frequency was significantly affected by crop rotation and depth of plowing. As corn-wheat rotation had 33% increasing and fallow-wheat 19.44% decreasing of weed seed in 15-30 cm soil depth. The size of the total weed seed bank in corn-wheat caused a greater seed accumulation in the surface layer of the soil (0-15 cm). Weed seed density in corn-wheat rotation increased 89.79% and 62.85% in 0-15 and 15-30 cm, respectively during two years. Shannon diversity index increased by 12% in corn-wheat and decreased by 5.4% in fallow-wheat compared with the first year. Margalf index of corn-wheat rotation at 0-15 and 15-30 cm of soil depths decreased 33.70% and 38.25%, respectively, compared to the fallow-wheat rotation in the first year. Sorenson similarity index of corn-wheat and fallow-wheat at 0-15 and 15-30 soil depths was 0.82% and 0.80% during two years. The slope of linear regression also indicates that fallow-wheat weed seed bank (0.79) decreased more than corn-wheat rotation (0.47). Spatial distribution of weed seedlings showed that there is a large similarity in distribution patterns of total weed population between before and after herbicide application in two different rotations during the second year. However, distribution pattern of seedlings in corn-wheat rotation at the first year herbicide application was different after application of herbicide. Therefore, herbicide application can affect spatial distribution and number of weed seedling species.

Corn-wheat rotation as a high input level cropping system with deep tillage increases the size of the weed seed bank, especially in the soil surface layer (0-15 cm). While fallow-wheat rotation as a low input level cropping system causes a decreasing in weed seed bank dynamics, increasing in the diversity and richness of the seed bank and improving the soil structure by wheat residual on the soil during fallow system. The results of this study will be valuable in aiding the prediction of likely weed infestations in rotation systems. This ability to predict the size of weed seed bank, pouplation, diversity and emergence would also provide valuable input to population dynamics models that can be used in weed management.

The present study was carried out to investigate biochemical, morphological, and physiological processes involved in the adaptive processes of cut roses grown in arching and high-rack culture systems under water deficit condition. Rose plants ‘Club-Nika’ were subjected to three water regimes [control (100% of irrigation needs), moderate water stress (75%), and severe water stress (50%)] factorially combined with two training systems defined as arching and high-rack systems. Water deficit significantly reduced morphological and qualitative traits as well as water relations of cut roses. Water deficit significantly reduced Net CO2 assimilation rate (PN), transpiration rate (E), and stomatal conductance (gs), whereas it did not affect Water Use Efficiency (WUEi) and intercellular CO2 concentration (Ci). Surprisingly, water deficit did not affect chlorophyll content [chl a, chl b and total chl (a + b)] and proline accumulation of leaves. Considering the lack of change in intercellular CO2 concentration, it seems likely that both stomatal closure and metabolic impairment limit photosynthetic CO2 assimilation under water deficit. Regardless of irrigation regimes, rose plants trained with high-rack culture system showed a superiority for most of the qualitative and quantitative attributes compared to those trained with arching system. The high-rack system resulted in 60% higher extra-quality stems (> 60 cm) compared with the plants trained with arching. It can be concluded that cut roses respond to water deficit through adaptive changes in physiological and morphological levels to reduce water loss without any negative impact at biochemical level.

Climate change increases the repetition and frequency of droughts and this event has undergone significant changes. Water resources and agriculture in Iran has not been spared from the harm of these changes. In this study, because of the importance of Kashafrood basin in the North-East of Iran, the meteorological droughts in the region over the next three years (2027-2018), (2037-2028) and (2047-2038) will be discussed. Since the Standardized Precipitation Index (SPI) is one of the most useful indices of drought, this index was calculated in this study. Numerical calculations and dynamic models are the most accurate sources for prediction of meteorological variables. In this research, the precipitation outputs of the EC-EARTH model under the RCP4.5 scenario that has been downscaled with RCA4 dynamic model were used. According to the resolution of the RCA4 dynamical model, the Kashafrood basin was divided into 6 pixels (0.44 at 0.44 degrees) and then assessment values were determined on each pixel. The results showed that the EC-EARTH model is competent in the prediction of precipitation at a confidence level of 99% with a correlation coefficient averaged 64%. The average number of dry and very dry months was calculated on the whole basin. Analysis of the results in the next three years compared to the observation period (2016-1987) showed that the number of droughts will increase, but the severity of future droughts will be reduced

Autumn sowing of sugar beets for harvesting the root yield the following spring is possible in some regions of Iran. Autumnal beets effectively conserve irrigation water because they make use of precipitation during the autumn and winter months and do not grow during the warm summer periodn. The presents study determined the water-use efficiency of autumn-sown sugar beets and investigated the best irrigation scheduling for the Mashhad plain. Testing was carried out during the 2013-2014 growing season at the Agricultural Research Center of KhorasaneRazavi province using a randomized complete block design with a split plot arrangement and four replications. This experiment examined with three irrigation intervals (7, 10 and 14 d) as the main plot and four irrigation levels (50%, 75%, 100%, and 125% of water content of field capacity) as subplots. The results showed that the yields of roots, dry matter, sugar, and white sugar showed no significant difference for irrigation interval, but that irrigation level hadsignificant effect on yield at the 1% level. The best irrigation water-use efficiency for the yield of conversion to white sugar as the final economic product of sugar beet cultivation was achieved at the 75% and 100% irrigation levels using the 14 d irrigation interval. The results of this project for the Mashhad plain under similar climatic conditions indicates that autumn-sown sugar beets should be irrigated every 14 d at 75% to 100% of field capacity. This irrigation schedule decreased irrigation costs (33%), conserved irrigation water (18%), and achieved maximum irrigation water-use efficiency compared with the 7 d irrigation interval.