Effect of Green Manure and Different Nitrogen levels on Yield and Yield Components of Common Purslane (Portulaca oleracea L.)

Purslane (Portulaca oleracea L.) is an annual C4 plant that belongs to the family of Portulacaceae. The plant is drought and salt tolerant which contains high amounts of beneficial omega-3 fatty acids and antioxidant vitamins. Adaptation to both dry and saline conditions makes it a prime candidate as a vegetable in areas with dry conditions and salty soils, which are often present together where land is irrigated. Purslane seeds provide nutritional value, and have beneficial health effect on the body specially in preventing cardiovascular, cancer and hypertension (high blood pressure) diseases, because it contains omega-3 and omega-6 fatty acids and other nutrients such as antioxidants, tocopherols and dietary fiber.
Nitrogen is the key element in soil fertility and crop production. Attention to the soil quality and health has increased in recent years, especially for sustainable production of medicinal crops. So for production of healthy food in industrialized countries, using natural and on-farm inputs have been considered. One of the practical ways to achieve this goal is planting cover crops and green manure. Given the importance of Purslane as a medicinal plant and due to the fact that there is not detailed information about the nitrogen requirement for this plant, this study was conducted to evaluate the effect of green manure and nitrogen on yield and yield components of common Purslane (Portulaca oleracea L.) in Birjand, Iran.
The effect of four levels of green manure including: control (No plants), Rocket Sativa (Eruca sativa L.), Hairy vetch (Vicia villosa L.), mix rocket sativa and hairy vetch (Eruca sativa Vicia villosa) and three levels of nitrogen (0, 50 and 100 kg ha-1) on Purslane was studied in a split plot design based on randomized complete blocks with 3 replications during growing season 2014-2015 at the Agricultural Research Station, College of Agriculture, University of Birjand, Iran. Each plot was 3m×4m with six planting rows. The space between rows, plots and replications were 0.4, 0.5 and 3 m, respectively. Rocket and hairy vetch were planted on November 11, 2014. Rocket and hairy vetch shoots were returned to the soil by plowing just before flowering. Planting of Purslane was conducted on April 30, 2015. The distance between rows and plants were 40 cm and 15 cm, respectively (plant density was 1,666,666.6 plants per ha). Nitrogen fertilizer as urea was applied, as half of fertilizer at sowing and early spring, half of fertilizer after the first harvest. Measured traits were spad index, plant height, number of capsules per plant, number of seeds per capsule, 1000 seed weight, grain yield, biological yield, harvest index, oil percentage, oil yield, fresh and dry stem yield, fresh and dry leaf yield, fresh and dry forage yield and leaf/stem ratio.
The results showed that the effect of green manure on any one of the traits (except oil percentage) were not significant. The use of green manure compared to the control (no plants) increased seed oil percentage. Due to the gradual releasing of nutrients from green manure and lack of synchronization between the need of the plant and availability of nutrient released by the decomposition, green manure did not affect the next crop. Effects of nitrogen on grain yield, oil percentage and oil yield were not significant. But, effects of nitrogen on all measured forage traits (with the exception of leaf/stem ratio) such as, fresh and dry stem yield, fresh and dry leaf yield, fresh and dry forage yield were significant. Increasing in nitrogen rate enhanced all measured forage traits. Interaction of green manure and nitrogen was not significant on all measured traits.
Green manure and nitrogen had not any significant effect on grain yield and quality. The response of grain and forage yield to nitrogen was different; so that nitrogen application did not change significantly grain yield, oil content and oil yield, but the highest forage yield and its components were achieved in treatments 50 and 100 kg N ha-1, respectively. Considering the cost of production and environmental problems, treatment 50 kg N ha-1 is recommended for forage production of Purslane in Birjand, Iran.