Efficiency of Nitrogen Fertilizer on Rotational Grazing Pastures of Giant Stargrass (Cynodon nlemfuensis Vanderyst) and Transvala Digitgrass (Digitaria eriantha Steud. cv. Transvala) in Subtropical Okinawa, Japan

Abstract

This study was carried out to clarify the efficiency of applied nitrogen fertilizer using ¹⁵N-labelled fertilizer (¹⁵N) on rotational grazing pastures of giant stargrass (GS) and Transvala digitgrass (TR) in subtropical Okinawa, Japan. Dry matter yield, total nitrogen content and ¹⁵N recovery rate of the available herbages to be grazed were not significantly different between GS and TR pastures. The efficiency of nitrogen fertilizer on the available herbages was observed at 33.8 and 31.8% in GS and TR pastures, respectively. The fertilized ¹⁵N in the stubbles and roots, rhizosphere soils and available herbages averaged across the two grass pastures was recovered by 5.1, 10.7 and 32.8％, respectively. ¹⁵N recovery rate in the plant-soil system averaged across both GS and TR pastures was 48.5％, which means that 51.5％ of applied nitrogen fertilizer was lost from the soil-plant system in the present subtropical grazing pastures.