Reducing NO3 - Leaching and Enhancing N Removal with Perennial Ryegrass in Land Application

In order to provide information for reducing NO3 - leaching and enhance N uptake in land application for treating animal wastewater, an experimental study was carried out in a greenhouse using perennial ryegrass (Lolium perenne L.). The experimental design consisted of two N application rates (300 and 600 kg NH4 + -N /ha) and three irrigation frequencies (2, 4 and 6 days intervals) with three replications in each treatment. The experimental results showed that N application rate had a significant positive effect on both total N uptake and total N content in the ryegrass. The ryegrass fertilized with 300 and 600 kg N /ha had 610 and 780 kg N/ha total N uptake rate and 3.5% and 4.2% total N content, respectively. An increase in N application resulted in elevated ammonification from soil organic N. The 300 and 600 kg N /ha application rates resulted in 337 and 488 kg N/ha net ammonification, consequently rendering a total inorganic N input of 637 and 1088 kg N/ha respectively. Fertilization at 300 kg N /ha decreased the average NO3 - -N concentration over the whole soil profile from 13.4 to 8.57 kg N/ha (by 36%) whereas NH4 + -N concentration increased from 57.5 to 64.7 kg N/ha (by 13%). The average ratio of NH4 + -N to NO3 - -N over the soil profile increased from 4.8 to 12.1. At 600 kg/ha application rate, the NO3 - -N content (69-136 kg N/ha) was much lower than NH4 + -N (193-341 kg N/ha) in the soil immediately after the experiment, and the ratio of NH4 + -N to NO3 - -N was 2.5 –3.0. A significant NO3 - -N concentration increase only appeared within the depth of N application. Below the application depth, there was no significant increase in NO3 - -N and NO3 - -N concentration was as low as 6.0 and 3.3 mg N/kg soil even though the total inorganic N input was 26-57% higher than the total N uptake. Irrigation frequencies had no significant effect on the NO3 - -N concentration at different soil depths.