Effect of Fertilizer Management on Some Chemical Properties of Soil and Absorption of Nitrogen and Phosphorus Elements by Purslane (Portulaca oleracea L.)

Legumes are widely used in agricultural systems as green manure due to their ability to stabilize nitrogen in the soil, as well as providing conditions for beneficial soil microorganisms. Organic fertilizers such as vermicompost and manure have high capacity for water absorption and the maintenance of water and nutrients, high porosity, ventilation and appropriate drainage in the soil. Recently, bio-fertilizers have also been used to improve nutrient uptake and root development of plants along with chemical fertilizers. Lack of organic matter in most soils of Iran and its calcite properties will double the need to replace chemical fertilizers with organic fertilizers. Due to the lack of information on nutritional management of medicinal plants, and in order to increase soil fertility and the need to reduce the application of chemical fertilizers, this study was done to investigate the effect of different fertilizers on some soil chemical properties and the absorption of N and P elements in Birjand. This research was carried out in two separate experiments during two growing years from 2014 to 2016 at the research farm of Birjand University with 3 replications. During the first experiment, the effect of four levels of green manures, including control, Eruca sativa, Vicia villosa, mix Eruca sativa + Vicia villosa and three levels of nitrogen (0, 50 and 100 kg.ha-1) on Purslane was studied. Furthermore, during the second experiment, the treatments were combination of four sources of nitrogen supply, including cow manure, vermicompost, chemical fertilizers (NPK) and control, as well as four types of biofertilizers, including Azotobacter and Azospirilum, Glomus intraradices, Thiobacillus with sulfur and control on Purslane was studied. The studied traits were included grain yield and soil chemical properties such as organic carbon, the percentage of nitrogen, absorbable phosphorus, pH, EC and nitrogen and phosphorus content of biomass. The percentage of nitrogen in plant tissue was measured by Kjeldahl method and the percentage of phosphorus was measured by Morphy and Riley method. Furthermore, the organic carbon in soil was determined by Walkley- Black method, total nitrogen and available phosphorus were measured using the Kjeldahl and Olsen methods, respectively. The soil acidity was determined on the saturated water through pH meter and electrical conductivity of the soil saturation extract was determined through EC meter. After collecting data, statistical analysis was performed using Minitab 17 software. LSD test was used at the 5% probability level to compare the averages. The results showed that the application of green manure increased the organic carbon and nitrogen content of soil, the amount of phosphorus absorbed by soil and decreased soil pH. Among green manure treatments, Vicia villosa was superior to the others. Also, using nitrogen fertilizer increased grain yield and the amount of absorbed phosphorus, soil electrical conductivity and reduced soil pH. Among nitrogen supply sources, cow manure had the greatest impact on grain yield and soil chemical properties, but the role of biofertilizer application was limited to increasing the amount of available phosphorus in the soil. Therefore, the role of cow manure in improving the chemical status of soil was superior to the others. Due to the low soil organic matter in most arid and semi-arid regions of Iran, especially South Khorasan, it seems that proper usage of organic resources can improve soil conditions of these areas for the growth and yield of medicinal plants such as Purslane. In this study, in order to reduce the use of chemical fertilizers and to absorb the maximum amount of nitrogen and phosphorus, the Purslane biomass was treated with mix Eruca sativa + Vicia villosa without using nitrogen fertilizer and combined treatment of cow manure and mycorrhiza.  The results recommended that combination of cow manure and mycorrhiza is suitable approach under Birjand condition.