This study examined the effects of different biofertilizers and manure on the absorption and absorption efficiency of macronutrients by wheat in Alborz Province, Iran. The experimental design was factorial in the form of a randomized complete block design with three replications. The four factors of the experiment were Azospirillum (with 600 g/ha and without), mycorrhiza (with 1 kg/ha and without), Streptomyces (with 0.5 kg/ha and without) and manure (with 30 t/ha and without). To measure N, P and K, plants were harvested one time when grains were at dough stage and another time at plant maturity, oven dried, grinded and analyzed. Azospirillum, mycorrhiza and manure had a significant effect (p≤0.01) on most of the measured traits, but the effect of Streptomyces was not significant. The two-fold and three-fold interactions significantly affected the absorption and absorption efficiency of the three macronutrients. In most cases, four-fold interactions yielded the highest values. Overall, the experimental results indicate that biofertilizers and manure can naturally meet most of the plant's nutritional requirements, improve the efficiency of nutrient absorption and replace part of chemical fertilizers in sustainable agricultural production systems.

Intensive agricultural systems have negative impacts on soil and water quality, and on biodiversity conservation. The evolution of intercropping is controlled by a high degree of biodiversity. In sharp contrast intensive agricultural systems uses monocultures associated with high input of chemical fertilisers and pesticides. Intercropping involves two or more crops in the same fi eld at the same time. Intercropping increases biodiversity, improving the ability of an agricultural system to handle changes in growing conditions. Intercropping plays a pivotal role for increasing land use ef fi ciency, weed suppression, enhanced ecological services and greater economic pro fi tability. Bene fi ts of intercropping include improved yields and yield stability, enhanced use of water and nutrients, increased weed suppression, increased pest and disease resistance, reduced soil erosion and improved forage quality.This review reports the relationships between plants in intercropping to understand and design intercropping systems, with special focus on intercropping ef fi ciency. The most common index showing yield advantage of intercropping is the land equivalent ratio (LER). The LER provides a standardized basis so that crops can be added to form 'combined' yields. The LER indicates competitive effects by comparison of individual LER. LER can measure relative yield advantage. We also present new ways to determine and use the LER.

-Two field experiments were conducted to evaluate the effects of multispecies weed competition on wheat grain yield and to determine their economic threshold on the crop. The experiments were conducted in 2002, on two sites in Iran: at the Agricultural Research Station on Ferdowsi University of Mashhad (E1) and on the fields of Shirvan's Agricultural College (E2). A 15 x 50 m area of a 15 ha wheat field in E1 and a 15 x 50 m area of a 28 ha wheat field in E2 were selected as experimental sites. These areas were managed like other parts of the fields, except for the use of herbicides. At the beginning of the shooting stage, 30 points were randomly selected by dropping a 50 x 50 cm square marker on each site. The weeds present in E1 were: Avena ludoviciana, Chenopodium album, Solanum nigrum, Stellaria holostea, Convolvulus spp., Fumaria spp., Sonchus spp., and Polygonum aviculare. In E2 the weeds were A. ludoviciana, Erysimum sp., P. aviculare, Rapistrum rugosum, C. album, Salsola kali, and Sonchus sp. The data obtained within the sampled squares were submitted to regression equations and weeds densities were calculated in terms of TCL (Total Competitive Load). The regression analysis model indicated that only A. ludoviciana, Convolvulus spp. and C. album, in E1; and A. ludoviciana, S. kali, and R. rugosum, in E2 had a significant effect on the wheat yield reduction. Weed economic thresholds were 5.23 TCL in E1 and 6.16 TCL in E2; which were equivalent to 5 plants m -2 of A. ludoviciana or 12 plants m -2 of Convolvulus spp. or 19 plants m -2 of C. album in E1; and 6 plants m -2 A. ludoviciana, 13 plants m -2 S. kali and 27 plants m -2 R. rugosum in E2. Simulations of economic weed thresholds using several wheat grain prices and weed control costs allowed a better comparison of the experiments, suggesting that a more competitive crop at location E1 than at E2 was the cause of a lower weed competitive ability at the first location.Keywords: weed interference, competition, grain yield, mathematical regression.RESUMO -Foram realizados dois experimentos para avaliar os efeitos da interferência de várias espécies daninhas sobre a produtividade e rendimento de trigo e determinar o seu nível de dano econômico (NDE) sobre a cultura. Os experimentos foram conduzidos em 2002, em dois locais no Irã: na Estação de Pesquisa Agrícola (EPA) da Universidade Ferdowsi, Mashhad (E1) e na EPA do Agricultural College, Shirvan (E2). Numa lavoura de trigo de 15 e 28 ha, nas Epa localizadas em E1 e E2, respectivamente, selecionaram-se áreas de 15 x 50 m como local dos experimentos. Estas áreas foram manejadas como outras partes do campo, exceto para o uso de herbicidas. No início do estádio de espigamento foram sorteados 30 pontos de coleta de 50 x 50 cm em cada local. As plantas daninhas presentes em E1 foram: Avena ludoviciana, Chenopodium album, Solanum nigrum, Stellaria holostea, Convolvulus spp., Fumaria spp., Sonchus spp., e Polygonum aviculare. No local E2 as espécies infestantes foram: A. ludoviciana, Erysimum sp., P. av...

In order to study the effect of intercropping on forage yield of Sorghum and yield components of lima bean at different planting proportions and nitrogen fertilizer levels, an experiment was conducted at the research farm of University of Tehran in the year of 2009. Quantitative attributes such as dry weights of sorghum, yield and yield component of lima bean were measured in two sampling during growth season. The highest fresh and dry weight of sorghum fodder belonged to additive proportions of sorghum. Nitrogen application treatments had significant effect on sorghum total dry matter of fodder (160 urea Kgha -1 ) and total yield of lima bean (80 urea Kgha -1 ) seed. Evaluation of Land Equivalent Ratio (LER) indicated that the highest LER obtained in the combination of 100% sorghum and 20% lima bean which indicates the advantage of intercropping (LER=1.26).

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