Deficit irrigation systems have been considered as practical strategies to overcome shortage of irrigation water in arid and semiarid regions. To assess the response of grain sorghum [Sorghum bicolor (L.) Moench] to deficit irrigation and whether arbuscular mycorrhizal fungi (AMF) can moderate drought stress influence on grain yield, a 2-yr field experiment was conducted using split-split lay out on a randomized complete block (RCB) design. Irrigation (full and deficit) was assigned to the main plots. Subplots were allocated to two genotypes (Kimiya and Speedeh) and P sources viz: no fertilizer, sole chemical P fertilizer, seed inoculation with AMF and combined fertilizer (50% of the chemical P fertilizer + AMF) were assigned to the sub-subplots. Results indicated that deficit irrigation reduced grain yield of Kimia and Speedeh by 16 and 26%, respectively, while improving their irrigation water use efficiency (IWUE). Grain yield adjustment by sorghum to water stress was mainly through reducing the number of grains per panicle rather than grain mass. Application of all forms of P fertilizer improved grain yield of sorghum; however, under drought stress, plants were more responsive to combined fertilizer and used irrigation water more efficiently. The root colonization percentage was greater in Kimiya than Speedeh under full and deficit irrigation, however, both genotypes showed a lower degree of root colonization under drought conditions. Application of combined fertilizer could be considered as an alternative to chemical P fertilizer when irrigation water is limited.

According to the results obtained in this study, drought stress can enhance the accumulation of silymarin in milk thistle seeds. Moreover, under drought stress, the share of silybin increased which possess the greatest degree of biological activity among the silymarin components. Silymarin, an isomeric mixture of flavonolignans found in milk thistle (Silybum marianum (L.) Gaertn) seeds, has been used for its hepatoprotective effects for more than 2,000 years. Biosynthesis and accumulation of active substances like silymarin in plant tissues highly interacts with the environmental conditions. Effects of moderate and severe drought stress (based on soil moisture depletion) on silymarin content and composition in milk thistle seeds were evaluated in a field study. Averaged across treatments, milk thistle seeds contained 19.3 g kg(-1) silymarin. Drought stress enhanced silymarin accumulation in milk thistle seeds. Plants grown under moderate and severe drought stress treatments contained 4 and 17 % greater silymarin than those grown in well-watered condition, respectively. Greater content of sylimarin in stressed plants was attributed to more contents of silybin, isosilybin and silychristin, while silydianin content was lower under drought condition. According to the results obtained in this study, drought stress enhanced accumulation of silymarin in milk thistle seeds and improved its quality by increasing the share of silybin, which possess the greatest degree of biological activity among the silymarin components.

Water shortage is the major constraint for biomass production in semiarid regions. Biomass production of milk thistle [Silybum marianum (L.) Gaertn] and energy balance of this crop under different irrigation regimes (full and deficit irrigation) and soil organic amending treatments (poultry manure [PM] and vermicompost [VC]) was evaluated in a two‐year field experiment. Biomass yield reduced by 10 and 22% under moderate (I75) and severe deficit (I50) irrigation, respectively. Under deficit irrigation, the contribution of leaves and heads to the final biomass reduced in favor of the stalk. Regardless of the irrigation regime, application of soil amendments improved biomass yield. Total energy input used for milk thistle production was 9829 MJ ha−1, in which 68% was related to nonrenewable energy sources. Diesel fuel (51%) had the biggest share of energy used for milk thistle production, followed by irrigation water and machinery. Energy input in I75 and I50 was 7 and 15% less than full irrigation (I100). Net energy obtained from milk thistle was 116,688 MJ ha−1 with energy efficiency (energy output/energy input ratio) of 12.8. Taking into account that milk thistle is an annual crop with low energy input requirements, it seems that milk thistle has a considerable potential for biomass production using I75 in regions with limited irrigation water availability.

Pistachio is considered as an important agricultural commodity in Iran and ranks top amongst all exported agricultural products. Conducting an overall energy audit and economic analysis of pistachio production can provide useful information to help implement management strategies for improving energy efficiency. A study was conducted during 2009 and 2010 to evaluate the overall energy inputs and outputs and to perform an economic analysis of pistachio production in the Iranian province of Markazi. The results revealed that the total energy input for pistachio production was 54305 MJ ha -1 . Electricity, followed by diesel fuel and nitrogen fertilizer application were the highest contributors to energy input in pistachio orchards. The contribution of direct energy was higher than indirect energy and share of non-renewable energy was more than renewable energy. Net energy, energy use efficiency, energy productivity and specific energy were 7522 MJ ha -1 , 0.86, 0.08 kg MJ -1 and 13.69 MJ kg -1 , respectively. Econometric model based on Cobb-Douglas function indicated that impacts of electricity, diesel fuel and chemical fertilizer energy inputs on pistachio yield were positive while the impact of machinery was negative. The marginal physical productivity (MPP) value for diesel fuel was the highest among other variables, followed by energy inputs related to the chemicals and irrigation water. The results revealed that production of pistachios in Markazi Province, under current management practices, are not energy efficient and efforts should be made to improve energy use efficiency.Additional key words: econometric model; energy use efficiency; renewable energy; sustainability.