*Article* **Combination of Inorganic Nitrogen and Organic Soil Amendment Improves Nitrogen Use Efficiency While Reducing Nitrogen Runoff**

**Ian Phillips 1, Chanyarat Paungfoo-Lonhienne 2,\*, Iman Tahmasbian 1, Benjamin Hunter 1, Brianna Smith 1, David Mayer <sup>1</sup> and Matthew Redding <sup>1</sup>**


**Abstract:** Improved nitrogen fertiliser management and increased nitrogen use efficiency (NUE) can be achieved by synchronising nitrogen (N) availability with plant uptake requirements. Organic materials in conjunction with inorganic fertilisers provide a strategy for supplying plant-available N over the growing season and reducing N loss. This study investigated whether a combined application of inorganic N with an organic soil amendment could improve nitrogen use efficiency by reducing N loss in runoff. Nitrogen runoff from a ryegrass (*Lolium multiflorum*) cover was investigated using a rainfall simulator. Nitrogen was applied at low, medium and high (50, 75 and 100 kg/ha) rates as either (NH4)2SO4 or in combination with a poultry manure-based organic material. We showed that the NUE in the combination (58–75%) was two-fold greater than in (NH4)2SO4 (24–42%). Furthermore, this combination also resulted in a two-fold lower N runoff compared with the inorganic fertiliser alone. This effect was attributed to the slower rate of N release from the organic amendment relative to the inorganic fertiliser. Here, we demonstrated that the combined use of inorganic and organic N substrates can reduce nutrient losses in surface runoff due to a better synchronisation of N availability with plant uptake requirements.

**Keywords:** rainfall simulator; nutrient runoff; ammonium; nitrate; nitrogen use efficiency
