Nitrogen fertilization and row spacing effects on Digitaria eriantha

Abstract

Crude protein (CP, %), yield of protein dry matter (YPDM, kg ha'), nitrogen use efficiency (NUE, kg dry matter kg' N) and nitrogen recovery (NR, %) were evaluated in Digitaria eriantha after exposing this species to various field-treatments during 1998 -1999 and 1999 -2000 in Bahía Blanca (38° 48'S, 62° 13'W), Argentina. Treatments included (1) 3 N fertilization rates (0, 50 or 100 kg ha-'), (2) 2 row spacings (30 or 50 cm), and (3) 2 methods of fertilizer application (either split at the beginning of spring and summer or applied at once in early spring). Plants were cut leaving 5 cm stubble whenever they reached 26-28 cm. Studied parameters were determined on forage harvested in spring, summer or total annual. Crude protein increased (P < 0.05) as N fertilization increased in both seasons. Total annual CP averaged 9.7, 12.0 and 14.0 %, respectively for the 0, 50 and 100 kg ha' fertilization rates, respectively. Crude protein was greater (P < 0.05) on forage which received split rather than bulk N fertilization, and mean values were 13.2 and 11.7 %, respectively. Forage sown at different row spacings had a similar (P > 0.05) CP concentration. In general, YPDM responded positively (P < 0.05) to N fertilization and to a split application of N fertilizer. Although differences were not always significant, there was an inverse relationship between N fertilization rate and NUE and NR. Nitrogen use efficiency was 34.5 and 24.8 kg dry matter kg' N (P < 0.05), and NR was 98 and 79% (P < 0.05) when N fertilization rates were 50 and 100 kg ha', respectively. There was a positive (P < 0.05) relationship between rainfall and NUE or NR. Nitrogen fertilization in D. eriantha should be split with a N fertilization rate close to 50 kg ha', and using 30 rather than 50 cm row spacing.Key Words: N rate and timing, crude protein, N use efficiency, N recovery, semiarid Argentina, perennial grasses Research coming from semiarid environments regarding the effects of N fertilization on forage quality of Digitaria eriantha is scarce. Nitrogen fertilization with 100, 200 or 400 kg ha' did increase crude protein (CP) in this species (Grunow and Rabie 1985). Some studies in Argentina also showed that CP increased in D. eriantha after application of 100 or 127 kg ha' N Terenti 1997, Veneciano et al. 1998). Increases in N or CP percentages as N fertilization rates increase in perennial grasses are common (George et al. 1972, Hanson et al. 1978, Eck et al. 1981, Madakadze et al. 1999).Research was funded by the Universidad Nacional del Sur Manuscript accepted 2 Feb. 2004. ResumenSe efectuaron análisis en el forraje cosechado en un experimento realizado en Bahía Blanca (Argentina) durante los ciclos 1998 -99 y 1999 -00. El ensayo fue en bloques al azar con tres repeticiones. Los tratamientos fueron: 1) dosis de nitrógeno (N): 0, 50 y 100 kg/ha, 2) distancia entre surcos: 30 y 50 cm y 3) sistemas de fertilización: dividida (en mitades al inicio de primavera y de verano) y total (al inicio de primavera). Se efectuaron cortes con fre...