Evaluation of Sesbania sesban L. (Merr) and Mimosa invisa L. (Fabaceae) as sources of nitrogen in irrigated rice on the Vertisols of the Accra Plains of Ghana

Abstract

Sesbania sesban L. (Merr) and Mimosa invisa L. (Fabaceae) were grown in rotation with lowland rice (var. KRC Baika). The experiments were conducted on three farmers’ fields at the Kpong Irrigation Project (KIP) sites at Akuse (lat 6° 06' N, long 0° 07' E) and Asutsuare (lat 6° 04' N, long 0° 12' E). In Farm 1, S. sesban and M. invisa were incorporated three times, in rotation with rice, over a period of 3 years, and in Farm 2, the green manures were incorporated once and rice planted within the year. The treatments also included a control (no fertilization), recommended inorganic nitrogen (N) that is, 90 kg N ha-1, S. sesban + 50% N and S. sesban + 75% N. Total dry matter and grain (paddy) yield of rice were higher in Farm 1 than Farm 2. Nitrogen contents of the S. sesban and M. invisa plants were 2.5 and 2.4% respectively. Total N of S. sesban ranged from 239 to 259 kg ha-1 and that of M. invisa ranged from 152 to 186 kg ha-1. The single incorporation of the green manures in Farm 2 did not have a significant impact on rice growth and grain yield, while in Farm 1, S.sesban and M. invisa gave comparable yields with those under the recommended inorganic N. Grain yields under S. sesban + 50% N (T2) and mimosa (T4) were comparable to that under the recommended inorganic fertilizer (T5) and both were significantly higher than the control (T6); grain yields were 5.8, 5.8, 6.5 and 3.9 t ha-1, in T2, T4, T5 and T6, respectively. In spite of the good performance of M. invisa it required upland conditions to grow and establish. The application of 50% N requirement, in addition to S. sesban incorporation, enhanced rice growth and yield, and resulted in 20.7% savings on nitrogen fertilizer use. Key words: Green manure, lowland rice, inorganic nitrogen, rotation, incorporation, total dry weight, grain yield.