Effects of seeding rates of perennial ryegrass (Lolium perenne L.) on sediment loading and nutrient transport via surface runoff

Abstract

Sediment loading and nutrient losses from construction sites through surface runoff can have detrimental effects on nearby water bodies. Often cool-season grasses such as perennial ryegrass (Lolium perenne L.) are established for temporary coverage until environmental conditions are suitable for warm-season grass establishment. The purpose of this research was to 1) determine if higher seeding rates accelerate establishment thus reducing sediment loading and 2) determine if watering-in fertilizer applications reduces nutrient losses through surface runoff. In the first experiment trays were seeded at 0, 195, 390, or 585 kg ha-1 with 30-min rainfall simulations performed at 16.3 L per minute at 14, 28 and 42 days after seeding (DAS). Increasing seeding rates reduced total sediment loading 48% to 67% and 86% of sediment eroded from bare soil over the 42-day establishment period. Sediment losses were highest during the initial rainfall simulation at 88, 93, 83, and 62% of total sediment lost from 195, 390, or 585 kg ha-1 and bare soil controls, respectively. In the second experiment, established perennial ryegrass was fertilized at 50 kg N ha-1 with grass swards not irrigated or irrigated at 1.25 cm 48 hours prior to rainfall simulation. Thirty-minute rainfall simulations were performed 2 and 7 days after fertilization (DAF). Non-irrigated fertilizer treatments resulted in the highest TKN losses of 12.3 kg N ha-1, moderate dissolved N losses at 3.1 mg N ha-1, and highest TP losses of 2.4 P ha-1 2 DAF compared to 7.0 kg TKN ha-1, 5.2 kg DN ha-1, and 2.0 kg TP ha-1 for irrigated fertilizer treatments. At 7 DAF, iIrrigated fertilizer treatments resulted in higher dissolved N losses of 3.1 kg N ha-1 compared to 0.1 kg N ha-1 for non-irrigated treatments but similar TKN and TP losses of 0.8 kg N ha-1 and 0.4 kg P ha-1 compared to 0.9 kg N ha-1 and 0.2 kg P ha-1 lost from non-irrigated treatments. The two experiments showed increasing perennial ryegrass seeding rates during establishment can significantly reduce sediment losses; while irrigating post N fertilization of established swards may not reduce N losses during surface runoff.