Effect of Green Manure on pH, Dissolved Organic Carbon and Soil Phosphorous Availability with Distance from Roots of Corn and Canola

Small portion of soil phosphorous (P) is usable by plants. To investigate the effects of alfalfa green manure (2% w/w) and roots of corn and canola in single and intercropping systems on available P concentration in soil, a greenhouse experiment was conducted using rhizobox system. The experiment was arranged as a split factorial design with 3 replications, two levels of green manure (0 and 2%), 4 zones with distance from root (rhizosphere, near rhizosphere, near bulk soil and bulk soil) and 4 culture systems (corn, canola, mixed culture and control (not cultivated)) based on completely randomized design. Canola and corn were cultivated at the middle part of rhizobox in mixed or separate forms. The plants were harvested 85 days after sowing and the soil samples were taken from different parts of the rhizobox. The results showed that the green manure reduced the soil pH more than 0.19 and enhanced the dissolved organic carbon concentration (DOC) and soil available P by 25 mg L-1 and 9.47 mg kg-1, respectively. The soil pH and available-P were increased while the DOC was decreased from rhizosphere toward the bulk soil. The bulk soil (over 16 mm distance from root) was not apparently affected by the root activity. Also the results showed that the green manure addition increased the dry weight in corn and canola and also increased the P concentration and uptake in canola while it decreased the P concentration and uptake in corn. Dry weight of intercropping system was more than that of single culture of corn and canola.