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.
The concept of virtual water in recent years has been proposed with the world's water resource consumption management approach. Hashtgerd study area is one of 609 study areas of the country that is located entirely in Alborz Province. Average annual rainfall in this region was about 200 to 340 mm and the average agricultural production per year was more than one million tons and had more than 16 million cubic meters surplus recovery from underground water resources. The aim of this study is to evaluate resources and amounts of virtual water in the agricultural sector of the study area and its impact on the area water resources balance and ultimately provide solutions to reduce water consumption by the agricultural sector. The most important exported water products in Hashtgerd area in order of importance are peaches and nectarines (33% of water exports), plums (15% of water exports), vegetables (5.14 percent of water exports), cherry (4.7% of water exports) and wheat (6.5 percent of water exports). Virtual water trade balance of agricultural and horticultural products in the digital range is equal to 260+ million cubic meters. Density of agricultural lands can be mentioned as the main reasons for positive balance of virtual water trade in this area.
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